Soundproofing material

Abstract

The present invention provides a soundproofing material that improves sound insulation performance against specific frequencies in the low-frequency range below 2000 Hz. [Solution] The soundproofing material comprises an elastic sheet 2 and two grid structures 1 formed by filling a plane with cylindrical cells 11 of uniform height, and has a surface density of 3.24 kg / m². 2 The following describes the two lattice structures, in which their cylindrical cells are arranged opposite each other, and the opposing cylindrical cells sandwich an elastic sheet to form a compartment. The elastic sheet has a resonant frequency (f0) of the compartment that satisfies the formula (resonant frequency (f0) = (1 / 2π)√(K / M) ≥ 1473 [Hz], where K is surface stiffness and M is surface density). Since the cylindrical cells are not adhesive to the elastic sheet and compress the elastic sheet by 10% or more, it is possible to provide a soundproofing material that can improve sound insulation performance against a specific target frequency in the low frequency range below 2000 Hz.

Description

[Technical Field]

[0001] The present invention relates to soundproofing materials, and more particularly to soundproofing materials that have been incorporated into acoustic metamaterials. [Background technology]

[0002] Generally, soundproofing materials tend to show improved sound insulation performance (transmission loss) as the density of their constituent materials increases (mass law). However, acoustic metamaterials are known as lightweight materials that also offer excellent sound insulation performance.

[0003] Acoustic metamaterials have a lattice structure with periodically arranged elements at intervals smaller than the wavelength of sound, to which a membrane is attached. Sound is blocked by the membrane resonating and vibrating in response to the vibrations of the air when sound is transmitted. Furthermore, since the above-described lattice structure can be used to add specific acoustic characteristics of resonance systems, it is possible to soundproof sounds of specific frequencies.

[0004] In Patent Document 1, the present inventors disclosed that an acoustic metamaterial in which an elastic sheet is partitioned and supported by a lattice structure having a plurality of continuously formed cylindrical cells exhibits high sound insulation performance in the low frequency range of 2000 Hz or less by setting the resonant frequency (f0) of the partitioned elastic sheet to 1473 Hz or higher. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6879369 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the case described in Patent Document 1, the acoustic characteristics of the resonance system are controlled by bonding a cylindrical cell forming a lattice structure to an elastic sheet and partitioning the elastic sheet. As a result, variations in adhesive application and uneven bonding can cause the size of the partitions to deviate from the target size, causing the wavelength of the resonance system to vary and broadening the frequency range in which sound can be blocked, thus reducing the soundproofing effect against sounds of a specific target frequency.

[0007] This invention has been made in view of the problems of the prior art, and its objective is to provide a soundproofing material that allows for precise control of the size of the above-mentioned compartments and can improve soundproofing performance against sounds of a specific frequency targeted in the low-frequency range of 2000 Hz or less. [Means for solving the problem]

[0008] The inventors of this invention conducted extensive research to achieve the above objectives and discovered that the objectives can be achieved by sandwiching an elastic sheet between two opposing cylindrical cells without adhesive, and by compressing and partitioning the elastic sheet with the cylindrical cells. This led to the completion of the present invention.

[0009] In other words, the soundproofing material of the present invention comprises an elastic sheet and two grid structures formed by filling a plane with cylindrical cells of uniform height. Furthermore, the surface density is 3.24 kg / m³. 2 The following: The two grid structures described above have their cylindrical cells arranged opposite each other. The opposing cylindrical cells described above sandwich the elastic sheet to form a partitioned section. The above elastic sheet satisfies the following equation (1) in which the resonant frequency (f0) of the above-mentioned section is: A soundproofing material characterized in that the above-mentioned cylindrical cells are not adhered to the above-mentioned elastic sheet and compress the above-mentioned elastic sheet by 10% or more; Resonant frequency (f0)=(1 / 2π)√(K / M)≧1473[Hz]····Formula (1) However, in equation (1), K represents surface stiffness and M represents surface density.

Advantages of the Invention

[0010] According to the present invention, an acoustic metamaterial soundproofing material is formed by sandwiching an elastic sheet between two opposing cylindrical cells without adhesion and compressing the elastic sheet with the cylindrical cells, so that a soundproofing material capable of improving the soundproofing performance of sound at a targeted specific frequency can be provided in a low frequency range of 2000 Hz or less.

Brief Description of the Drawings

[0011] [Figure 1] It is a perspective view showing an example of the appearance of the soundproofing material of the present invention. [Figure 2] It is a cross-sectional view showing an example of a soundproofing material in which a lattice structure sandwiching an elastic sheet is housed in a housing. [Figure 3] It is a graph showing the soundproofing characteristics of the soundproofing materials of Example 1 and Comparative Example 1.

Modes for Carrying Out the Invention

[0012] The soundproofing material of the present invention will be described in detail. As shown in FIG. 1, the soundproofing material includes an elastic sheet 2 and two lattice structures 1 formed by planar filling of cylindrical cells 11 having a uniform height. The elastic sheet is inserted between the two lattice structures, and the elastic sheet is sandwiched between the two lattice structures.

[0013] The two lattice structures 1 are arranged such that their cylindrical cells 11 face each other. That is, when the cylindrical cells are viewed from their height direction, they are arranged at positions where the walls constituting the cylindrical cells of one lattice structure overlap with the walls constituting the cylindrical cells of the other lattice structure.

[0014] The opposing cylindrical cells sandwich the elastic sheet and compress it by 10% or more, partitioning the elastic sheet to form partition portions.

[0015] In the soundproofing material of the present invention, the elastic sheet is compressed by 10% or more and sandwiched between the cells, so even if the tubular cells constituting the lattice structure and the elastic sheet are not adhered, the elastic sheet is firmly partitioned, and no displacement of the elastic sheet occurs between adjacent partitions.

[0016] Therefore, the resonance frequency of the elastic sheet can be controlled by the arrangement period of the tubular cells that constitute the lattice structure. Since it is not necessary to precisely match the width of the adhesive application with the thickness of the tubular cell walls, and strict control of the adhesive bonding area is unnecessary, the elastic sheet can be made to resonate with a specific frequency of sound, thereby improving the sound insulation performance against that specific frequency.

[0017] The compression ratio of the elastic sheet is preferably 15% or more, and more preferably 20% or more, from the viewpoint of the tubular cells further preventing the elastic sheet from shifting. There is no particular upper limit to the above compression ratio, however, for example, if the compression ratio exceeds 50%, the walls of the tubular cells may bite into the elastic sheet and become easily cut, depending on the thickness of the walls of the tubular cells and the material of the elastic sheet.

[0018] Furthermore, the elastic sheet in the partitioned area separated by the cylindrical cell satisfies the following equation (1) at its resonant frequency (f0). Resonant frequency (f0)=(1 / 2π)√(K / M)≧1473[Hz]····Formula (1) However, in equation (1), K represents surface stiffness and M represents surface density.

[0019] The soundproofing material of the present invention can exhibit soundproofing performance exceeding that of the "mass law" for low-frequency sounds. The mechanism is already disclosed in the above-mentioned Patent Document 1, so the details will be omitted here, but the theoretical value of the transmission loss (TL) of the soundproofing material that follows the rigidity law shows that, with the above-mentioned resonance frequency (f0) as the frequency of the sound to be soundproofed decreases, the soundproofing performance according to the rigidity law improves.

[0020] By fulfilling the relationship in equation (1) above, the sound insulation effect according to the "rigidity law" for sound insulation performance (transmission loss) is increased, and sound insulation performance exceeding that of the "mass law" can be obtained for low-frequency sounds below 2000 Hz.

[0021] Shifting the resonant frequency (f0) towards higher frequencies improves sound insulation performance according to the "rigidity law" for low-frequency sounds below 2000 Hz. Therefore, it is preferable that the resonant frequency (f0) is 2000 Hz or higher, more preferably 3000 Hz or higher, and even more preferably 4000 Hz or higher. There is no particular upper limit, but for example, it should be 1,000,000 Hz or lower.

[0022] In equation (1) above, the surface stiffness (K) is the spring constant when one of the compartments of the elastic sheet partitioned by the grid structure is approximated as a mass spring model having mass m and vibrating in response to incident sound waves. Note that the larger the surface stiffness (K), the less easily it deforms under input.

[0023] In this invention, each section of the elastic sheet is approximated by a disk of equal area, and the surface stiffness of the section when a load p is applied is given by the average deflection (w) when the disk vibrates in a peripherally fixed, uniformly distributed load mode. ave The calculation was performed using the following formula (2). K = p / w ave = 16E·h 3 ·(1-v 2 )a 4 ...Equation (2) However, in equation (2), v is the Poisson's ratio of the sheet in the partitioned area, E is the Young's modulus of the elastic sheet in the partitioned area [Pa], h is the thickness of the sheet in the partitioned area [m], and a is the area equivalent radius of a circle with the same area as the area of ​​the partitioned area [m].

[0024] Furthermore, in the above formula (1), the surface density (M) is expressed as m = ρ·h, where ρ is the density of the elastic sheet in the partitioned area [kg / m³]. 3 ], where h is the film thickness [m] of the sheet in the above-mentioned section.

[0025] The resonance frequency (f0) in the partition portion can be adjusted by the size and shape of the partition portion, the material and film thickness of the elastic sheet of the partition portion.

[0026] Specifically, by reducing the size of the partition portion to increase the surface rigidity (K), making the elastic sheet of a material with a low density, or reducing the surface density (M) by reducing its thickness, the resonance frequency (f0) can be shifted to the high-frequency side.

[0027] The surface density of the soundproof material of the present invention is less than 3.24 kg / m 2 and preferably less than 2.0 kg / m from the viewpoint of weight reduction, 2 more preferably less than 1.5 kg / m, 2 even more preferably less than 1.0 kg / m. 2 It is preferable that it is as follows.

[0028] Since the surface density of the soundproof material is less than 3.24 kg / m 2 it is possible to obtain an advantageous soundproof effect according to the "rigidity rule", and for sounds in the low-frequency range of 2000 Hz or less, which is the soundproof target, a soundproof performance exceeding that of a flat soundproof material of the same weight according to the "mass rule" can be obtained.

[0029] As a method of non-adhesively compressing and sandwiching the opposing cylindrical cells of the lattice structure with the elastic sheet, it is sufficient that the walls of the opposing cylindrical cells can be brought close to each other and fixed in a state where the elastic sheet is compressed.

[0030] For example, a method of mechanically fixing the lattice structures to each other by mechanical fixing means such as screws, wires, and snap fits that penetrate the elastic sheet can be mentioned.

[0031] Also, as shown in FIG. 2, the lattice structure 1 sandwiching the elastic sheet 2 may be housed in the housing 3, and the housing 3 may press the lattice structure 1 from the out-of-plane direction of the elastic sheet 2.

[0032] Furthermore, in order to prevent in-plane misalignment between the housing 3 and the lattice structure 1, the structure of the housing 3 may be such that projections 31 are provided at the points where the housing contacts the outer edge of the lattice structure, or the housing 3 and the lattice structure 1 may be integrated into a single structure.

[0033] Furthermore, the housing itself, which contains the elastic sheet and the grid structure, can maintain its structure against the reaction force from the elastic sheet by being fixed with mechanical fastening means 32 such as screws or snap-fit ​​fasteners.

[0034] As described above, by housing the lattice structure with the elastic sheet sandwiched inside the enclosure, there is no need for mechanical fastening means such as screws to penetrate vertically through the walls of the cylindrical cell, thus making it possible to thin the walls of the cylindrical cell and reduce its weight, as well as making it easy to manufacture.

[0035] (Elastic sheet) As the elastic sheet mentioned above, a sheet made from a material having a Young's modulus in the range of 0.001 to 70 [GPa] can be used.

[0036] As constituent materials for elastic sheets, for example, rubber materials such as latex rubber, chloroprene rubber (CR), styrene-butadiene rubber (SBR), ethylene-propylene-diene rubber (EPDM), and acrylonitrile-butadiene rubber (NBR), as well as resin materials, metal materials, and paper materials can be used.

[0037] In particular, latex rubber or EPDM rubber are preferred for use in vehicles because their lightweight nature contributes significantly to improving fuel efficiency.

[0038] From the viewpoint of the sound-insulating effect of the sound-insulating material, the thickness of the elastic sheet described above is preferably 10 to 1000 μm, and more preferably 100 to 500 μm.

[0039] (lattice structure) There are no particular restrictions on the constituent materials of the lattice structure, but thermoplastic resins and thermosetting resins can be suitably used. In particular, polyvinyl chloride resin and polyolefin resin are preferred because they are lightweight and highly durable.

[0040] Examples of base shapes for cylindrical cells used to tile a plane include regular hexagons, as well as regular squares and equilateral triangles. The above lattice structure does not necessarily have to be filled with only cylindrical cells having a single base shape; it may also be a pattern in which multiple types of cylindrical cells, each with a different base shape (regular polygon), are regularly arranged, as in Archimedes' tessellation method.

[0041] The size of the base shape described above can be set according to the frequency range to be soundproofed.

[0042] The wall thickness of the cylindrical cell is more preferably 1 to 2 mm.

[0043] The height of the cylindrical cells, i.e., the thickness of one lattice structure, is preferably 3 mm or more. Having sufficient height in the cylindrical cells improves the rigidity of the lattice structure itself, making it less prone to bending, and thus improving the sound insulation performance against low-frequency sounds not only for the elastic sheet in the partitioned area but also for the sound insulation material as a whole.

[0044] The soundproofing material of the present invention can be suitably used for applications that block noise originating from various sound sources. In particular, using it on vehicle floor panels and fender protectors can reduce road noise entering the vehicle's interior. [Examples]

[0045] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0046] [Example 1] Using the elastic sheet and lattice structure described below, a soundproofing material was fabricated by sandwiching the elastic sheet between the lattice structure and compressing the elastic sheet by 15%. Furthermore, each cylindrical cell constituting the lattice structure was fixed by wires that penetrated the walls of the cylindrical cells vertically, so that on average, each cylindrical cell had three fixing points.

[0047] Elastic sheet: Polyester elastomer sheet, film thickness 0.40 (mm), surface density 0.43 (kg / m²) 2 ), surface rigidity 31122 (N / mm) Grid structure: PP honeycomb structure (cylindrical cell height 3 mm, distance between opposite parallel sides in the regular hexagon at the base 10 mm, wall thickness of cylindrical cell 1.5 mm)

[0048] The overall surface density of this soundproofing material is 2.23 kg / m³. 2 The resonant frequency (f0) of the compartment was 1357 Hz.

[0049] [Example 2] A soundproofing material was fabricated using the elastic sheet and lattice structure described below. The elastic sheet was sandwiched between the lattice structure, and the structure was further sandwiched between the enclosure described below.

[0050] Enclosure: Acrylic sheet, 1.5mm thick Elastic sheet: Polyester elastomer sheet, film thickness 0.40 (mm), surface density 0.43 (kg / m²) 2 ), surface rigidity 31122 (N / mm) Grid structure: PP honeycomb structure (cylindrical cell height 3 mm, distance between opposite parallel sides in the regular hexagon at the base 10 mm, wall thickness of cylindrical cell 1.5 mm)

[0051] The overall surface density of this soundproofing material is 3.84 kg / m³. 2 ) was.

[0052] [Comparative Example 1] A soundproofing material was manufactured in the same manner as in Example 1, except that the elastic sheet was not compressed but was simply sandwiched between the elastic sheet and the lattice structure.

[0053] [Comparative Example 2] The soundproofing material was manufactured in the same manner as in Example 2, except that the lattice structure was a frame-like structure made of PP (frame height 3 mm, frame wall thickness 15 mm).

[0054] <Evaluation of soundproofing performance> The soundproofing performance of the fabricated soundproofing material against sound waves of various frequencies was measured. The sound insulation performance was evaluated by measuring the insertion loss [unit: dB] compared to a control case (without sound insulation material) when sound was generated from the speaker inside the sound insulation box, with the measurement performed by placing a speaker inside the sound insulation box and placing sound-insulating material at the opening of the box. Furthermore, the conditions for generating the sound source were as follows: Spectral level: White noise (100~8192Hz) F max :8192Hz Average value: Average of 300 measurements (300 measurements were taken with slight time delays between each measurement, and the average of these measurements was used as the measured value). Overlap: 75%

[0055] The evaluation results for Example 1 and Comparative Example 1 are shown in Figure 3, and the evaluation results for Example 2 and Comparative Example 2 are shown in Figure 4. In the graphs in Figures 3 and 4, the dotted lines represent the sound insulation characteristics of a flat plate with the same surface density as the sound insulation material of the example or comparative example.

[0056] The graphs in Figures 3 and 4 show that the soundproofing materials of Examples 1 and 2 exhibit a transmission loss of sound in the low-frequency range of 800-1200 Hz that far exceeds the mass law, demonstrating that they can effectively block sound in the target low-frequency range. Furthermore, while the target frequency ranges of the soundproofing materials in Comparative Examples 1 and 2 were the same as those of the soundproofing materials in Examples 1 and 2, the lack of compression of the elastic sheet resulted in variations in the resonant frequency (f0), broadening the soundproofing characteristics and preventing sound from being blocked in the target low-frequency range. [Explanation of symbols]

[0057] 1 Lattice structure 11. Cylindrical cell 2 Elastic Sheets 3 cabinets 31 Protrusion 32 Mechanical fastening means (snap fit)

Claims

1. A soundproofing material comprising an elastic sheet and two grid structures formed by filling a plane with cylindrical cells of uniform height, Surface density is 3.24 kg / m³ ２ The following: The two grid structures described above have their cylindrical cells arranged opposite each other. The opposing cylindrical cells described above sandwich the elastic sheet to form a partitioned section. The elastic sheet described above has a resonant frequency (f) of the partitioned portion. ０ ) satisfies the following equation (1), A soundproofing material characterized in that the tubular cell is not adhered to the elastic sheet and compresses the elastic sheet by 10% or more. Resonance frequency (f) ０ = (1 / 2π)√(K / M)≧1473[Hz]···Equation (1) However, in equation (1), K represents surface stiffness and M represents surface density.

2. Furthermore, it has a casing, The soundproofing material according to claim 1, characterized in that the housing presses the grid structure from the out-of-plane direction of the elastic sheet.

3. The soundproofing material according to claim 2, characterized in that the housing and the grid structure are integrated.

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