JP2024065446A - Composite sound absorbing material - Google Patents

Abstract

[Problem] To provide a composite sound absorbing material with high sound absorbing performance in the low to high frequency range of 300 to 2000 Hz. [Solution] A composite sound absorbing material 8 includes a synthetic resin film layer 4, a nonwoven fabric layer 1 having projections and recesses, and dry nonwoven fabric layers 7a-7d, the nonwoven fabric layer 1 having projections and recesses has a fiber density of 50 kg/m3 to 500 kg/m3, and is arranged in front of the dry nonwoven fabric layers 7a-7d when viewed from the direction of sound incidence, and both main surfaces of the dry nonwoven fabric layers 7a-7d are flat, and there are one or more layers. This results in a composite sound absorbing material with a normal incidence sound absorption coefficient of 47% or more at 300 Hz, and normal incidence sound absorption coefficients of 55% or more at 500 Hz, 1000 Hz, and 2000 Hz, respectively, which can deal with road noise from electric vehicles, etc. [Selected Figure] Figure 3

Description

The present invention relates to a composite sound-absorbing material. More specifically, the present invention relates to a composite sound-absorbing material that has a high normal incidence sound absorption coefficient from the low frequency region to the high frequency region.

Sound absorbing materials (also called soundproofing materials) are used in various fields such as automobiles, railroad vehicles, aircraft, buildings, and acoustic facilities. Conventionally, sound absorbing materials in which a fiber layer and a porous layer are laminated have been known. For example, Patent Document 1 proposes a sound absorbing material in which a fiber layer with an air permeability of 30 to 220 cc/ ^cm2 ·sec is arranged on the incident side and a porous layer is arranged on the non-incident side. Patent Document 2 proposes a sound absorbing material in which a porous sound absorber and two or more sheets of nonwoven fabric are laminated, and the nonwoven fabric is a long fiber nonwoven fabric that is stretched and arranged. Patent Document 3 proposes a laminated sound absorbing material having a low density layer and a high density layer, and the low density layer is an ethylene propylene diene rubber foam having an open cell structure. Patent Document 4 proposes a construction sound absorbing material in which a first layer is made of silicone rubber and a second layer is made of glass wool or rock wool. Patent Document 5 proposes a sound absorbing material in which a hard fiber layer and a soft fiber layer are laminated.

Japanese Patent No. 6646267 JP2019-005939A Patent No. 6577720 Patent No. 4891897 JP 2010-085873 A

However, the composite sound-absorbing materials of the conventional technology described above have a problem in that they have low sound-absorbing performance in the low-frequency range. Electric vehicles (EVs), which have been increasingly developed and produced in recent years, use electricity as their energy source and are powered by an electric motor, so they run quietly without generating the noise of an internal combustion engine. However, there is a problem in that road noise, which is the friction sound between the tires and the ground that was previously hidden by the noise and went unnoticed, becomes apparent. The frequency of this road noise is said to be 500 Hz or less. There is also a demand for sound-absorbing materials with high sound-absorbing performance in the low to high frequency range of 300 to 2000 Hz.

To solve the above-mentioned problems, the present invention provides a composite sound-absorbing material with high sound-absorbing performance at low to high frequencies of 300 to 2000 Hz.

The present invention provides a composite sound-absorbing material including a synthetic resin film layer, a nonwoven fabric layer having projections and recesses, and a dry nonwoven fabric layer, wherein the nonwoven fabric layer having projections and recesses has a fiber density of 50 kg/ ^m3 or more and 500 kg/ ^m3 or less, is disposed in front of the dry nonwoven fabric layer when viewed from the direction of sound incidence, and both main surfaces of the dry nonwoven fabric layer are flat, providing a composite sound-absorbing material having one or more layers.

The composite sound-absorbing material of the present invention comprises a synthetic resin film layer, a nonwoven fabric layer having projections and recesses, and a dry nonwoven fabric layer, the nonwoven fabric layer having projections and recesses has a fiber density of 50 kg/ ^m3 or more and 500 kg/ ^m3 or less, is disposed in front of the dry nonwoven fabric layer when viewed from the direction of sound incidence, and both main surfaces of the dry nonwoven fabric layer are flat, and by having one or more layers, a composite sound-absorbing material with high sound-absorbing performance in the low to high frequency range of 300 to 2000 Hz can be provided, which can deal with road noise from electric vehicles and the like.

FIG. 1A is a schematic perspective view of a nonwoven fabric layer having projections and recesses according to one embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view taken along line II of FIG. 1A. FIG. 2 is a schematic cross-sectional view of a synthetic resin film layer according to one embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a composite sound-absorbing material according to one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a composite sound-absorbing material according to another embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of a composite sound-absorbing material according to still another embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of a composite sound-absorbing material according to still another embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a composite sound-absorbing material according to still another embodiment of the present invention. FIG. 8 is a schematic cross-sectional view of the composite sound-absorbing material of Comparative Example 1. FIG. 9 is a schematic cross-sectional view of the composite sound-absorbing material of Comparative Example 2. FIG. 10 is a schematic cross-sectional view of the composite sound-absorbing material of Comparative Example 3. FIG. 11 is a schematic cross-sectional view of the composite sound-absorbing material of Comparative Example 4. FIG. 12 is a schematic explanatory diagram showing a location where the composite sound-absorbing material of the present invention is mounted in an automobile. FIG. 13 is a graph showing normal incidence sound absorption coefficients of Examples 1 to 3 of the present invention. FIG. 14 is a graph showing normal incidence sound absorption coefficients of Examples 4 and 5 of the present invention. FIG. 15 is a graph showing normal incidence sound absorption coefficients of Comparative Examples 1 and 2. FIG. 16 is a graph showing normal incidence sound absorption coefficients of Comparative Examples 4 and 5. FIG. 17 is a schematic cross-sectional view of a composite sound-absorbing material according to a seventh embodiment of the present invention. FIG. 18 is a schematic cross-sectional view of the composite sound-absorbing materials of Examples 8 and 9 of the present invention. FIG. 19 is a schematic cross-sectional view of a composite sound-absorbing material according to an eleventh embodiment of the present invention. FIG. 20 is a graph showing normal incidence sound absorption coefficients of Examples 6 to 9 of the present invention. FIG. 21 is a graph showing normal incidence sound absorption coefficients of Examples 10 to 12 of the present invention. FIG. 22 is a schematic cross-sectional view of a composite sound-absorbing material according to a thirteenth embodiment of the present invention. FIG. 23 is a schematic cross-sectional view of a composite sound-absorbing material according to a fourteenth embodiment of the present invention. FIG. 24 is a schematic cross-sectional view of the composite sound-absorbing material of Comparative Example 5. FIG. 25 is a graph showing the normal incidence sound absorption coefficient of Example 13 of the present invention. FIG. 26 is a graph showing the normal incidence sound absorption coefficient of Example 14 of the present invention. FIG. 27 is a graph showing the normal incidence sound absorption coefficient of Comparative Example 5.

The present invention is a composite sound absorbing material including a synthetic resin film layer, a nonwoven fabric layer having projections and recesses, and a dry nonwoven fabric layer. The nonwoven fabric layer having projections and recesses is formed by compression molding. Since it is compression molded, it is a high density layer. The fiber density of the nonwoven fabric layer having projections and recesses is 50 kg/m ³ or more and 500 kg/m ³ or less, preferably 60 kg/m ³ or more and 450 kg/m ³ or less, and more preferably 70 kg/m ³ or more and 410 kg/m ³ or less. Within this range, when sound comes into contact with the nonwoven fabric layer having projections and recesses, there is little reflection of the sound on the material surface, and the sound energy is effectively attenuated by friction with the fibers, so that the sound absorbing performance in the low to high frequency range is good. In addition, the nonwoven fabric layer having projections and recesses of the present invention is disposed in front of the dry nonwoven fabric layer when viewed from the direction of sound incidence. As a result, there is little reflection of sound on the projections and recesses surface, and sound can be effectively absorbed from the nonwoven fabric layer having projections and recesses to the dry nonwoven fabric layer. As a result, the effect of the uneven nonwoven fabric layer providing good sound absorption in the low frequency range and the effect of the dry nonwoven fabric layer providing good sound absorption in the high frequency range combine to provide a composite sound-absorbing material with high sound absorption performance in the low to high frequency range of 300 to 2000 Hz.

The dry nonwoven fabric layer of the present invention has both flat main surfaces (front and back) and exists in one or multiple layers. If both main surfaces (front and back) are flat, it is convenient for interfacial adhesion when multiple layers are laminated. In addition, there is an effect that a thin uniform layer can be formed compared to making a single thick layer. Of course, it is also possible to make a single thick layer.

It is preferable that the normal incidence sound absorption rate of the composite sound absorbing material at 300 Hz is 47% or more, and that at 500 Hz, 1000 Hz, and 2000 Hz is 55% or more. More preferably, the normal incidence sound absorption rate at 300 Hz is 50% or more, and that at 500 Hz, 1000 Hz, and 2000 Hz is 56% or more. This makes it possible to deal with not only road noise, but also engine noise, braking noise, etc.

The thickness of the composite sound-absorbing material is preferably 30 mm to 100 mm, more preferably 35 mm to 80 mm, and even more preferably 40 mm to 60 mm. This results in good sound-absorbing performance in the low to high frequency range, and makes the sound-absorbing material excellent in space-saving.

The nonwoven fabric layer having the unevenness preferably has an average height from the bottom to the top of 1 mm to 10 mm, an average pitch between the peaks of 1 to 30 mm, and an average thickness of 0.2 to 5 mm. The mass per unit area (basis weight) is preferably 150 to 1500 g/ ^m2 , more preferably 180 to 1350 g/ ^m2 , and even more preferably 210 to 1230 g/ ^m2 . The average fiber diameter constituting the nonwoven fabric layer having the unevenness is preferably 0.1 to 100 μm, more preferably 0.7 to 70 μm, and even more preferably 0.8 to 60 μm. In addition, the fibers constituting the nonwoven fabric layer having the unevenness are preferably polyester such as polyethylene terephthalate (PET), acrylic, polypropylene, nylon, rayon, aramid, and the like, and these may be mixed. This results in a composite sound absorbing material with high sound absorbing performance in the low to high frequency range of 300 to 2000 Hz. The airflow resistance of the nonwoven fabric layer having the unevenness is preferably 0 to 150 mTorr, more preferably 1 to 140 mTorr, and even more preferably 2 to 135 mTorr. The airflow resistance can be measured using a flow resistance measuring device (manufactured by Mecanum, device name SIGMA) in accordance with ASTM C522-03:2016.

The composite sound-absorbing material of the present invention may include multiple nonwoven fabric layers having irregularities, at least one of which is disposed in front of the dry nonwoven fabric layer, and the remaining at least one may be disposed between the dry nonwoven fabric layers. For example, two uneven nonwoven fabrics may be used, and the uneven nonwoven fabric layer and the dry nonwoven fabric layer may be alternately laminated from the sound incident side. This prevents a decrease in sound absorption performance in the high frequency range, and maintains sound absorption performance in the low to high frequency range.
The fibers constituting the uneven nonwoven fabric layer may be short fibers or long fibers. The uneven nonwoven fabric may be produced by combining spunbond, meltblown, or SMS (spunbond/meltblown/spunbond) made of long fibers with a nonwoven fabric made of short fibers. The uneven nonwoven fabric layer may have a density difference inside the uneven structure. The density difference inside the uneven structure may be formed in the peaks, valleys, and intermediate portions of the uneven nonwoven fabric when the uneven nonwoven fabric passes between the rollers of the unevenness imparting device in the uneven nonwoven fabric production process.

The synthetic resin film layer is preferably placed in at least one position selected from the group consisting of the front and back of the nonwoven fabric layer having the unevenness as viewed from the direction of sound incidence, and between the dry nonwoven fabric layer, and more preferably placed in front of the nonwoven fabric layer having the unevenness. This improves the sound absorption performance in the low to high frequency range, resulting in a sound absorbing material with excellent space saving. In particular, when the synthetic resin film layer is placed in front of the nonwoven fabric layer having the unevenness and the dry nonwoven fabric layer is placed after the nonwoven fabric layer having the unevenness, there is an air layer on both sides of the nonwoven fabric layer having the unevenness, so there is little sound reflection on the uneven surface, and sound can be effectively absorbed from the nonwoven fabric layer having the unevenness to the dry nonwoven fabric layer, and the presence of an air layer on the back side of the unevenness improves sound absorption in the low frequency range. In addition, the synthetic resin film layer and the nonwoven fabric layer having the unevenness come into contact with each other, improving the efficiency of attenuation of sound energy due to the membrane vibration of the synthetic resin film layer. Furthermore, the vibrations of the film are transmitted to the uneven nonwoven fabric layer and the dry nonwoven fabric layer, increasing the vibrations of those fibers and improving the efficiency of sound energy attenuation, resulting in good sound absorption performance in the low to high frequency range.

The synthetic resin film layer is preferably a multi-layer hot melt film in which both surface layers are resin layers with a lower melting point than the inner layer, and the inner layer is a resin layer with a higher melting point than the surface layer. One example is a multi-layer hot melt film in which both surface layers are polyethylene layers, and the inner layer is a nylon layer, polypropylene layer, or polyester layer. This multi-layer hot melt film can be hot melt bonded, and is useful for laminating and integrating. The thickness of the synthetic resin film layer is preferably 1 to 100 μm.

The density of the dry nonwoven fabric is preferably 10 to 75 kg/m ³ , more preferably 13 kg/m ³ to 70 kg/m ³ , and even more preferably 16 kg/m ³ to 60 kg/m ^3. Within this range, when the sound comes into contact with the sound absorbing material as a low-density layer, the sound energy is effectively attenuated by friction with the fibers, resulting in good sound absorption in the low to high frequency range. The dry nonwoven fabric layer is preferably a needle-punched nonwoven fabric layer in which high-melting point fibers and heat-sealing fibers are mixed. The needle-punched nonwoven fabric layer has good integrity and is easy to handle. The high-melting point fiber is, for example, polyethylene terephthalate (PET) fiber. The heat-sealing fiber can be, for example, a core-sheath composite heat-sealing polyester fiber in which the core is polyethylene terephthalate (PET) and the sheath is a copolymer polyester with a melting point lower than that of PET. By forming a needle-punched nonwoven fabric layer containing heat-sealing fibers in this way, the composite sound absorbing material can be molded into a desired shape by hot pressing when it is attached to a car. The heat-fusible fibers can be of the full melt type, split type, sheath-core type, or side-by-side type, but the sheath-core type is preferred. The core and sheath materials of the sheath-core type can be PET/PET, PET/PE (polyethylene), PET/PP (polypropylene), PP/PE, PE/PE, PP/PP, etc., but from the viewpoint of strength, the same material is preferred, and PET/PET is more preferred.

In addition to the needle-punched nonwoven fabric layer, the dry nonwoven fabric may be laminated with a thermal bond nonwoven fabric layer having a density of 1 to 20 kg/ ^m3 . This allows for weight reduction while maintaining sound absorbing performance.

The mass per unit area of the composite sound-absorbing material of the present invention is preferably 2800 g/ ^m2 or less, more preferably 700 to 2800 g/ ^m2 , and even more preferably 800 to 2600 g/ ^m2 . This results in a sound-absorbing material with a moderate mass and high sound-absorbing properties in the low to high frequency range.

The synthetic resin film layer, the uneven nonwoven fabric layer, and the dry nonwoven fabric layer may or may not be laminated together using hot melt, adhesive, or double-sided tape. As for the method of bonding each layer, the hot melt, adhesive, or double-sided tape may be applied or stuck to the entire bonding surface, or may be applied or stuck in a dotted, linear, or lattice pattern. In the manufacturing process of the nonwoven fabric, heat-sealing fibers may be mixed and the layers may be bonded by heating in a later process. Alternatively, in the manufacturing process of the nonwoven fabric, a heat-sealing sheet may be sandwiched between each layer and the layers may be bonded by heating in a later process. As a preferred example, the method of bonding the film layer and the uneven layer, and the film layer and the dry nonwoven fabric layer is hot melt bonding using a film layer (multilayer hot melt film layer) rather than using a separate adhesive material.

The composite sound-absorbing material is useful as a sound-absorbing material for absorbing road noise in automobiles, particularly in electric vehicles (EVs). It can be incorporated in locations around the tires, on the dashboard, or on the interior surfaces of automobiles.
The composite sound-absorbing material of the present invention is preferably manufactured in a long sheet and wound in a roll. When it is a long sheet, it can be cut to a size and shape according to the purpose. Furthermore, when it is in a roll form, it is convenient to transport, move, and supply.
In addition, when flame retardancy is required, the nonwoven fabric layer having irregularities, the dry nonwoven fabric layer, and other fiber materials can be made of fibers such as flame retardant acrylic, modacrylic, flame retardant polyester, flame retardant rayon, flame retardant wool (zapro processing), flame retardant vinylon, aromatic polyamide (aramid), novolac, polyarylate, polyamideimide, polybenzimidazole (PBI), etc. Alternatively, non-flame retardant fibers can be made flame retardant by coating, spraying, or impregnating them with a flame retardant (liquid or powder).

Next, the drawings will be used for explanation. In the following description of the drawings, the same reference numerals indicate the same objects. FIG. 1A is a schematic perspective view of a nonwoven fabric layer 1 having projections and recesses according to one embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view of line I-I in FIG. 1A. The nonwoven fabric layer 1 having projections and recesses is formed with projections and recesses 2 and has, for example, an average height H from the bottom to the top of 3 mm, an average pitch P between the peaks of 10 mm, an average thickness t of 2 mm, a density of 180 kg/m ³ , and an air resistance of 26 mTorr. The nonwoven fabric layer 1 having projections and recesses is obtained by processing the nonwoven fabric layer 1 having projections and recesses by using a projection and recess imparting device with a pair of projection and recess rollers, an embossing device such as a pair of metal engraved rolls or a combination of a metal engraved roll and a paper roll on one side, a flat plate press device with a metal engraved plate, a cylindrical press device having projections and recesses, etc. The projections and recesses may be continuous, such as a typical wave type, gear type, or lattice type, or may be discontinuous, staggered, or arranged at regular intervals with hemispherical or polygonal recesses. The number of recesses, protrusions, or uneven portions per unit area is preferably 10 to 5,000/100 cm ² , and more preferably 50 to 1,500/100 cm ² .

Figure 2 is a schematic cross-sectional view of a synthetic resin film layer 4 according to one embodiment of the present invention. This synthetic resin film layer 4 is a multi-layer hot melt film in which both surface layers 5a, 5a are polyethylene (PE) layers, and the inner layer 5b is a nylon (Ny) layer. Various nylons can be used, such as nylon 6, nylon 6,6, nylon 10, nylon 12, or any blend of these nylons.

3 is a schematic cross-sectional view of a composite sound-absorbing material 8 according to one embodiment of the present invention. This composite sound-absorbing material 8 is a composite sound-absorbing material in which a synthetic resin film layer 4, a nonwoven fabric layer 1 having projections and recesses, and dry nonwoven fabric layers 7a-7d are laminated in this order.
4 is a schematic cross-sectional view of a composite sound-absorbing material 9 according to another embodiment of the present invention. The composite sound-absorbing material 9 is a composite sound-absorbing material formed by laminating a synthetic resin film layer 4a, a nonwoven fabric layer 1 having irregularities, a dry nonwoven fabric layer 7a, a synthetic resin film layer 4b, and dry nonwoven fabric layers 7b-7d in this order.
5 is a schematic cross-sectional view of a composite sound-absorbing material 10 according to yet another embodiment of the present invention. The composite sound-absorbing material 10 is a composite sound-absorbing material formed by laminating a synthetic resin film layer 4a, a nonwoven fabric layer 1 having projections and recesses, a synthetic resin film layer 4b, and dry nonwoven fabric layers 7a-7d in this order.
6 is a schematic cross-sectional view of a composite sound-absorbing material 11 according to yet another embodiment of the present invention. The composite sound-absorbing material 11 is a composite sound-absorbing material in which a synthetic resin film layer 4a, a nonwoven fabric layer 1 having irregularities, a synthetic resin film layer 4b, a dry nonwoven fabric layer 7a, a synthetic resin film layer 4c, a dry nonwoven fabric layer 7b, and a thermal bond nonwoven fabric layer 12 are laminated in this order.
7 is a schematic cross-sectional view of a composite sound-absorbing material 29 according to yet another embodiment of the present invention. The composite sound-absorbing material 29 is a composite sound-absorbing material formed by laminating a synthetic resin film layer 4a, a nonwoven fabric layer 1 having irregularities, a synthetic resin film layer 4b, a dry nonwoven fabric layer 7a, a synthetic resin film layer 4c, and dry nonwoven fabric layers 7b-7d in this order.

Figure 12 is a schematic explanatory diagram showing where the composite sound-absorbing material of the present invention is mounted on an automobile 20. A fender liner 21 is attached to the fender above the front wheels of the automobile 20, a rear wheel house liner 22 is attached to the rear wheel above the rear wheels, a dash silencer 23 is attached to the dash panel, a floor silencer 24 is attached to the floor panel, a hood silencer 25 is attached to the back of the bonnet, a roof lining insulator 26 is attached to the ceiling, and a luggage mat and a luggage front silencer 27 are attached to the trunk room. These are examples, but they may be used at least in part or in the entirety. This makes it possible to absorb or insulate sounds from outside the automobile 20. In particular, the liner material can prevent road noise, which is the friction sound between the tires and the ground, as well as the sound of gravel, pebbles, and rainwater caught by the tires hitting the body from being transmitted inside the vehicle. These liner materials or silencer materials are obtained by thermoforming the composite sound-absorbing material of the present invention.

The sound-absorbing material of the present invention can be installed in various locations in an automobile and is designed to have sound-absorbing properties not only in the low frequency range (road noise countermeasures) but also in the high frequency range. It can also be used in dash silencers and floor silencers, which are locations that require sound-absorbing properties in the low frequency range.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.
The measurement methods in the following Examples and Comparative Examples are as follows.
<Normal incident sound absorption coefficient>
Each sample was taken and laminated under each condition, and then the normal incidence sound absorption coefficient of the sample was measured in the frequency range of 117 to 5000 Hz using a normal incidence sound absorption coefficient measuring device "WinZacMTX manufactured by Nippon Acoustic Engineering Co., Ltd." in accordance with ASTM E 1050:2019.
<Air flow resistance>
The airflow resistance of the nonwoven fabric layer having unevenness was measured using a flow resistance measuring device (manufactured by Mecanum, device name SIGMA) in accordance with ASTM C522-03:2016, with an air hole diameter of 29 mm and an air flow rate of 100 SCCM.
<Thickness>
The thickness was measured using a thickness gauge.
＜Other＞
The measurement was performed according to JIS or an industry-specified measurement method.

(Creating materials)
(1) Synthetic resin film layer The synthetic resin film layer shown in Fig. 2 was used. This synthetic resin film layer 4 is a multi-layer hot melt film with both surface layers 5a and 5b being polyethylene (PE) layers and an inner layer 6 being a nylon (Ny) layer. The thicknesses of the layers are PE12μm/Ny10μm/PE12μm and PE14μm/Ny10μm/PE14μm.
(2) Nonwoven fabric layer having projections and recesses. Described in each example.
(3) Dry nonwoven fabric layer (needle-punched nonwoven fabric layer)
80% by mass of polyethylene terephthalate fiber having a fineness of 2.2 decitex and a fiber length of 51 mm was mixed with 20% by mass of core-sheath composite heat-bonded polyester fiber having a fineness of 4.4 decitex and a fiber length of 51 mm (core: polyethylene terephthalate, sheath: copolymer polyester having a melting point or softening point of 110°C), and the resulting web was needle-punched. It was further heat-treated at 150°C for 10 minutes to obtain a needle-punched nonwoven layer having a density of 32 kg/ ^m3 , a mass of 318 g/ ^m2 , and a thickness of 10 mm.
(4) Dry nonwoven fabric layer (thermal bond nonwoven fabric layer)
A blend of 35% by mass of ultrafine polyester (PET) fibers having a fineness of 1.0 decitex and a fiber length of 51 mm, 35% by mass of hollow polyester (PET) fibers having a fineness of 7.8 decitex and a fiber length of 51 mm, 20% by mass of core-sheath composite heat-fused polyester fibers having a fineness of 4.4 decitex and a fiber length of 51 mm (core made of polyethylene terephthalate, sheath made of copolymer polyester having a melting point or softening point of 110°C), and 10% by mass of core-sheath composite heat-fused polyester fibers having a fineness of 2.2 decitex and a fiber length of 51 mm (core made of polyethylene terephthalate, sheath made of copolymer polyester having a melting point or softening point of 110°C), was obtained, and the resulting web was heat-treated at 170°C for 2 minutes to obtain a thermal bonded nonwoven fabric layer having a thickness of 20 mm, a mass of 183 g/ ^m2 , and a density of 9 kg/ ^m3 .

Example 1
The uneven nonwoven fabric was made by opening acrylic fibers (fineness 3.3 decitex, fiber length 76 mm) and passing the resulting web between uneven rollers after needle punching to produce a nonwoven fabric layer with unevenness as shown in Figures 1A-B, average height H = 3 mm, average peak-to-peak pitch P = 10 mm, average thickness t = 2 mm, density 180 kg/ ^m3 , and air resistance 26 mTorr.
As shown in Figure 4, two synthetic resin film layers (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/ ^m2 ) described in the description of the preparation of the material, one nonwoven fabric layer having irregularities, and four dry nonwoven fabric layers (needle-punched nonwoven fabrics) were arranged.

Example 2
The uneven nonwoven fabric was prepared by spreading polyethylene terephthalate having a fineness of 3.3 decitex and a fiber length of 64 mm, and the resulting web was needle-punched and passed between uneven rollers to produce a nonwoven fabric layer having unevenness with an average height H of 3 mm, an average peak-to-peak pitch P of 10 mm, an average thickness t of 2 mm, a density of 80 kg/ ^m3 , and an air resistance of 3 mTorr, as shown in Figures 1A-B.
As shown in Figure 4, two synthetic resin film layers (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/ ^m2 ) were used, with the first one placed at the tip in the direction of sound incidence and the second one placed between the first and second dry nonwoven fabric layers (needle-punched nonwoven fabric).

Example 3
The same uneven nonwoven fabric as in Example 1 was used.
As shown in Figure 5, two synthetic resin film layers (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/m ² ) were used, with the first one placed at the tip in the direction of sound incidence and the second one placed behind the nonwoven fabric layer with irregularities.

Example 4
The same uneven nonwoven fabric as in Example 2 was used.
As shown in Figure 6, three synthetic resin film layers (PE 14 μm/Ny 10 μm/PE 14 μm, mass 37 g/ ^m2 ) were used, with the first one placed at the tip in the direction of sound incidence, the second one placed behind the nonwoven fabric layer with irregularities, the third one placed between the first and second dry nonwoven fabric layers (needle-punched nonwoven fabric layers), and a dry nonwoven fabric layer (thermal bonded nonwoven fabric layer) placed behind the second dry nonwoven fabric layer (needle-punched nonwoven fabric layer).

Example 5
The same operations as in Example 4 were carried out except that a synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/m ² ) was used.

(Comparative Example 1)
8 is a schematic cross-sectional view of a composite sound-absorbing material 13 of Comparative Example 1. This composite sound-absorbing material 13 is a composite sound-absorbing material in which a synthetic resin film layer 4a, dry nonwoven fabric layers 7a-7b, a synthetic resin film layer 4b, and dry nonwoven fabric layers 7c-7d are laminated in this order. This is a comparative example in that no nonwoven fabric layer having irregularities is used.
As shown in FIG. 8 , a synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm), two dry nonwoven fabric layers (needle-punched nonwoven fabric layers), a synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm), and two dry nonwoven fabric layers (needle-punched nonwoven fabric layers) were arranged from the direction of sound incidence.

(Comparative Example 2)
9 is a schematic cross-sectional view of a composite sound-absorbing material 14 of Comparative Example 2. This composite sound-absorbing material 14 is a composite sound-absorbing material in which a synthetic resin film layer 4a, a dry nonwoven fabric layer 7a, a synthetic resin film layer 4b, a dry nonwoven fabric layer 7b, a synthetic resin film layer 4c, and dry nonwoven fabric layers 7c-7d are laminated in this order. This is a comparative example in that no nonwoven fabric layer having irregularities is used.
As shown in FIG. 9 , three synthetic resin film layers (PE 12 μm/Ny 10 μm/PE 12 μm) and three dry nonwoven fabric layers (needle-punched nonwoven fabric layers) were arranged from the direction of sound incidence, followed by one dry nonwoven fabric layer (needle-punched nonwoven fabric layer).

(Comparative Example 3)
As shown in Fig. 10, a flat nonwoven fabric layer 6 was used instead of the uneven nonwoven fabric. The flat nonwoven fabric was made by spreading acrylic fibers (fineness 3.3 decitex, fiber length 76 mm) and needle punching the obtained web, which had an average thickness t of 2 mm, density of 262 kg/ ^m3 , and air resistance of 18 mTorr. 15 in Fig. 10 is a composite sound absorbing material.
Arranged from the direction of sound incidence were four layers: a synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm), a flat nonwoven fabric layer, a synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm), and a dry nonwoven fabric layer (needle-punched nonwoven fabric layer).

(Comparative Example 4)
11, a flat nonwoven fabric layer 6 was used instead of the uneven nonwoven fabric. The flat nonwoven fabric layer was the same as that of Comparative Example 4.
From the sound incidence direction, three layers were arranged: a synthetic resin film layer (PE12μm/Ny10μm/PE12μm), a flat nonwoven fabric layer, a dry nonwoven fabric layer (needle-punched nonwoven fabric layer), a synthetic resin film layer (PE12μm/Ny10μm/PE12μm), and a dry nonwoven fabric layer (needle-punched nonwoven fabric layer). 16 in Figure 11 is a composite sound-absorbing material.

The above conditions and results are summarized in Tables 1 and 2. In addition, Fig. 13 shows normal incidence sound absorption coefficient graphs for Examples 1 to 3, Fig. 14 shows Examples 4 and 5, Fig. 15 shows Comparative Examples 1 to 3, and Fig. 16 shows Comparative Examples 4 and 5.

As is clear from Tables 1 and 2 and the normal incidence sound absorption coefficient graphs of Figures 13 to 16, it was confirmed that the composite sound-absorbing materials of Examples 1 to 5 have high sound absorption performance in the low to high frequency range of 300 to 2000 Hz.
In contrast, Comparative Examples 1 and 2 did not have a concave-convex nonwoven fabric layer, and therefore had poor sound absorption performance in the high frequency range. Comparative Examples 3 and 4 used a flat nonwoven fabric layer 6 instead of a concave-convex nonwoven fabric layer, and therefore had poor sound absorption performance in the low frequency range.

Example 6
The same uneven nonwoven fabric as in Example 1 was used.
As shown in FIG. 3, one synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/m ² ) was used and placed at the tip in the sound incidence direction.

(Example 7)
The uneven nonwoven fabric was prepared by opening polypropylene fibers (fineness 7.8 decitex, fiber length 64 mm) and passing the resulting web between uneven rollers after needle punching to produce a nonwoven fabric layer having unevenness with average height H = 3 mm, average peak-to-peak pitch P = 10 mm, average thickness t = 2 mm, density 184 kg/ ^m3 and air resistance 15 mTorr, as shown in Figures 1A-B.
As shown in FIG. 17, one synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/m ² ) was used and placed behind the nonwoven fabric layer having projections and recesses.

(Example 8)
The same uneven nonwoven fabric as in Example 1 was used.
As shown in FIG. 18, one synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/m ² ) was used and placed between the first and second dry nonwoven fabric layers (needle-punched nonwoven fabric layers).

Example 9
The uneven nonwoven fabric was prepared by spreading polyethylene terephthalate having a fineness of 1.3 decitex and a fiber length of 38 mm, and the resulting web was needle-punched and passed between uneven rollers to produce a nonwoven fabric layer having unevenness with an average height H of 3 mm, an average peak-to-peak pitch P of 10 mm, an average thickness t of 2 mm, a density of 186 kg/ ^m3 , and an air resistance of 33 mTorr, as shown in Figures 1A-B.
Other than the above, the same procedure as in Example 8 was carried out.

Example 10
The same procedure was carried out as in Example 3, except that the same uneven nonwoven fabric as in Example 2 was used.

(Example 11)
The same uneven nonwoven fabric as in Example 1 was used.
As shown in Figure 19, two synthetic resin film layers (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/ ^m2 ) were used, with the first layer being placed behind the nonwoven fabric layer having irregularities, and the second layer being placed between the first and second dry nonwoven fabric layers (needle-punched nonwoven fabric layers).

Example 12
The same uneven nonwoven fabric as in Example 1 was used.
As shown in Figure 7, three synthetic resin film layers (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/ ^m2 ) were used, with the first one placed at the tip in the direction of sound incidence, the second one placed behind the nonwoven fabric layer with irregularities, and the third one placed between the first and second dry nonwoven fabric layers (needle-punched nonwoven fabric layers).

The above conditions and results are summarized in Tables 3 and 4. Figures 20 and 21 show normal incidence sound absorption coefficient graphs.

As is clear from Tables 3-4 and the normal incidence sound absorption coefficient graphs in Figures 20-21, it was confirmed that the composite sound-absorbing materials of Examples 6-12 have high sound absorption performance in the low to high frequency range of 300 to 2000 Hz.

(Example 13)
The same uneven nonwoven fabric as in Example 2 was used.
As shown in Figure 22, a composite sound-absorbing material 30 is formed by arranging three layers from the direction of sound incidence: a nonwoven fabric layer 1a with irregularities, a synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/ ^m2 ) 4, a dry nonwoven fabric layer (needle-punched nonwoven fabric layer) 7a, a nonwoven fabric layer 1b with irregularities, and dry nonwoven fabric layers (needle-punched nonwoven fabric layers) 7b-7d.

(Example 14)
The same uneven nonwoven fabric as in Example 2 was used.
As shown in Figure 23, a composite sound-absorbing material 31 is formed by arranging, from the direction of sound incidence, a nonwoven fabric layer 1a having irregularities, a synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/ ^m2 ) 4, a dry nonwoven fabric layer (needle-punched nonwoven fabric layer) 7a, a nonwoven fabric layer 1b having irregularities, a dry nonwoven fabric layer (needle-punched nonwoven fabric layer) 7b, and a dry nonwoven fabric layer (thermal bonded nonwoven fabric layer) 12.

(Comparative Example 5)
The flat nonwoven fabric was prepared by spreading polyethylene terephthalate having a fineness of 1.3 decitex and a fiber length of 38 mm, and needle-punching the resulting web to obtain a nonwoven fabric layer having an average thickness t of 2 mm, a density of 283 kg/m ³ and an air resistance of 34 mTorr.
As shown in Figure 24, a composite sound-absorbing material 32 is formed by arranging three layers from the direction of sound incidence: a flat nonwoven fabric layer 6a, a synthetic resin film layer (PE 12 μm/Ny 10 μm/PE 12 μm, mass 33 g/ ^m2 ) 4, a dry nonwoven fabric layer (needle-punched nonwoven fabric layer) 7a, a flat nonwoven fabric layer 6b, and dry nonwoven fabric layers (needle-punched nonwoven fabric layers) 7b-7d.

The above conditions and results are summarized in Table 5. Figures 25 to 27 show normal incidence sound absorption coefficient graphs.

As is clear from Table 5 and the normal incidence sound absorption coefficient graphs in Figures 25 to 26, the composite sound-absorbing materials of Examples 13 and 14, which use two uneven nonwoven fabric layers, have high sound absorption performance in the low to high frequency range of 300 to 2000 Hz.
In contrast, in Comparative Example 5, two flat nonwoven fabrics were used instead of the uneven nonwoven fabric layer, but the sound absorbing performance in the low to high frequency range of 300 to 2000 Hz was poor.

The preferred aspects of the present invention are as follows.
[1] A composite sound-absorbing material including a synthetic resin film layer, a nonwoven fabric layer having projections and recesses, and a dry nonwoven fabric layer, wherein the nonwoven fabric layer having projections and recesses has a density of 50 kg/ ^m3 or more and 500 kg/ ^m3 or more, and is disposed in front of the dry nonwoven fabric layer when viewed from the direction of sound incidence, and both main surfaces of the dry nonwoven fabric layer are flat, and the composite sound-absorbing material may include one or more layers.
[2] The composite sound-absorbing material according to 1, wherein the normal incident sound absorption coefficient at 300 Hz is 47% or more, and the normal incident sound absorption coefficients at 500 Hz, 1000 Hz and 2000 Hz are each 55% or more.
[3] The composite sound-absorbing material according to 1 or 2, wherein the thickness of the composite sound-absorbing material is 30 mm or more and 100 mm or less.
[4] The composite sound-absorbing material according to any one of claims 1 to 3, wherein the nonwoven fabric layer having the unevenness has an average height from the bottom to the top of 1 mm to 10 mm, an average pitch between peaks of 1 to 30 mm, and an average thickness of 0.2 to 5 mm.
[5] The composite sound-absorbing material according to any one of claims 1 to 4, wherein the nonwoven fabric layer having the unevenness has an air resistance of 0 to 150 mTorr.
[6] The composite sound-absorbing material according to any one of claims 1 to 5, wherein the mass per unit area of the nonwoven fabric layer having the unevenness is 150 to 1500 g/ ^m2 .
[7] The composite sound-absorbing material described in any one of 1 to 6, wherein the synthetic resin film layer is arranged at at least one position selected from the group consisting of the front and rear of the nonwoven fabric layer having projections and recesses when viewed from the direction of sound incidence, and between the dry nonwoven fabric layers.
[8] A composite sound-absorbing material described in any one of items 1 to 7, wherein the synthetic resin film layer is a multi-layer hot melt film in which both surface layers are resin layers having a lower melting point than the inner layer, and the inner layer is a resin layer having a higher melting point than the surface layer.
[9] The composite sound-absorbing material according to any one of claims 1 to 8, wherein the synthetic resin film layer has a thickness of 1 to 100 μm.
[10] The composite sound-absorbing material according to any one of claims 1 to 9, wherein the density of the drylaid nonwoven fabric is 10 to 75 kg/ ^m3 .
[11] The composite sound-absorbing material according to any one of claims 1 to 10, wherein the dry nonwoven fabric layer is a needle-punched nonwoven fabric layer made of a blend of high melting point fibers and heat-fusible fibers.
[12] The composite sound-absorbing material according to 11, wherein the dry nonwoven fabric has a layer of thermally bonded nonwoven fabric having a density of 1 to 20 kg/ ^m3 laminated thereon in addition to the layer of needle-punched nonwoven fabric.
[13] The composite sound-absorbing material according to any one of claims 1 to 12, wherein the mass per unit area of the composite sound-absorbing material is 2800 g/ ^m2 or less.
[14] The composite sound-absorbing material according to any one of claims 1 to 13, wherein the composite sound-absorbing material is thermoformable.
[15] The composite sound-absorbing material according to any one of claims 1 to 14, which includes a plurality of nonwoven fabric layers having irregularities, at least one of which is disposed in front of the dry nonwoven fabric layer, and at least one of which is disposed between the dry nonwoven fabric layers.
[16] The composite sound-absorbing material according to any one of claims 1 to 15, which is a sound-absorbing material for automobile road noise.

The composite sound-absorbing material of the present invention is useful as a sound-absorbing material for road noise in automobiles, and can be incorporated in the areas around the tires, dashboards, or interior surfaces of automobiles. Specific examples include fender liners, rear wheel house liners, dash silencers, floor silencers, hood silencers, roof lining insulators, luggage mats, and luggage front silencers. It can also be suitably used in air conditioning equipment such as air conditioners, freezers, heat pumps, and other parts that form air passages such as ducts, where noise reduction is required, electrical appliances such as washing machines, dryers, refrigerators, and vacuum cleaners, office equipment such as printers, copiers, and fax machines, and building materials such as wall core materials, floor materials, sound-absorbing boards, and sound-adjusting boards.

Reference Signs List 1, 1a, 1b Nonwoven fabric layer having irregularities 2 Convex portion 3 Concave portion 4, 4a-4c Synthetic resin film layer 5a Surface layer 5b Inner layer 6, 6a, 6b Flat nonwoven fabric layer 7, 7a-7d Dry nonwoven fabric layer 8-11, 13-19, 29-32 Composite sound absorbing material 12 Thermal bond nonwoven fabric layer 20 Automobile 21 Fender liner 22 Rear wheel house liner 23 Dash silencer 24 Floor silencer 25 Hood silencer 26 Roof lining insulator 27 Luggage mat and luggage front silencer

Claims (16)

A composite sound-absorbing material including a synthetic resin film layer, a nonwoven fabric layer having irregularities, and a dry nonwoven fabric layer,
The nonwoven fabric layer having projections and recesses has a fiber density of 50 kg/ ^m3 or more and 500 kg/ ^m3 or less, and is disposed in front of the dry nonwoven fabric layer as viewed from the direction in which sound is incident,
The dry nonwoven fabric layer has both flat main surfaces and is present in one or more layers. The composite sound-absorbing material according to claim 1 or 2, wherein the normal incidence sound absorption coefficient of the composite sound-absorbing material at 300 Hz is 47% or more, and the normal incidence sound absorption coefficients at 500 Hz, 1000 Hz, and 2000 Hz are each 55% or more. The composite sound-absorbing material according to claim 1 or 2, wherein the thickness of the composite sound-absorbing material is 30 mm or more and 100 mm or less. The composite sound-absorbing material according to claim 1 or 2, wherein the nonwoven fabric layer having the irregularities has an average height from the bottom to the top of 1 mm to 10 mm, an average pitch between the peaks of 1 to 30 mm, and an average thickness of 0.2 to 5 mm. The composite sound-absorbing material according to claim 1 or 2, wherein the airflow resistance of the nonwoven fabric layer having the irregularities is 0 to 150 mTorr. 3. The composite sound-absorbing material according to claim 1 or 2, wherein the mass per unit area of the nonwoven fabric layer having the irregularities is 150 to 1500 g/ ^m2 . The composite sound-absorbing material according to claim 1 or 2, wherein the synthetic resin film layer is disposed in at least one position selected from the group consisting of in front of and behind the nonwoven fabric layer having irregularities as viewed from the direction of sound incidence, and between the dry nonwoven fabric layers. The composite sound-absorbing material according to claim 1 or 2, wherein the synthetic resin film layer is a multi-layer hot melt film in which both surface layers are resin layers having a lower melting point than the inner layer, and the inner layer is a resin layer having a higher melting point than the surface layer. The composite sound-absorbing material according to claim 1 or 2, wherein the thickness of the synthetic resin film layer is 1 to 100 μm. 3. The composite sound-absorbing material according to claim 1 or 2, wherein the density of the dry nonwoven fabric is 10 to 75 kg/ ^m3 . The composite sound-absorbing material according to claim 1 or 2, wherein the dry nonwoven fabric layer is a needle-punched nonwoven fabric layer made of a blend of high melting point fibers and heat-sealing fibers. The composite sound-absorbing material according to claim 10, wherein the dry nonwoven fabric is a layer of a thermal bonded nonwoven fabric having a density of 1 to 20 kg/ ^m3 laminated thereon in addition to the needle punched nonwoven fabric layer. 3. The composite sound-absorbing material according to claim 1 or 2, wherein the mass per unit area of the composite sound-absorbing material is 2800 g/ ^m2 or less. The composite sound-absorbing material according to claim 1 or 2, which is capable of being thermoformed. The composite sound-absorbing material according to claim 1 or 2, which includes multiple nonwoven fabric layers having irregularities, at least one of which is placed in front of the dry nonwoven fabric layer, and at least one of which is placed between the dry nonwoven fabric layers. The composite sound-absorbing material according to claim 1 or 2 is a sound-absorbing material for absorbing road noise in automobiles.

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