Patent Description:
Single-layered sound-absorbing structures formed from melt-blown nonwoven fabrics are known (for example, Patent Literature <NUM>).

In the case of a single-layered sound-absorbing structure formed from a nonwoven fabric, the sound-absorbing characteristics particularly in a low-frequency region are insufficient.

One example of sound-absorbing material is disclosed in <CIT>, which describes a system and method for temporarily sealing holes in a perforated material layer of composite acoustic panel during processing and testing processes. In another example <CIT>, a process and an apparatus are described to produce perforations, especially for perforated acoustic skins. In addition, <CIT> discusses a sound absorbing material which is thin and lightweight with sound absorbing properties in low frequency.

The present invention has been achieved in view of such circumstances as described above, and it is an object of the present invention to provide a sound-absorbing material having excellent sound-absorbing characteristics in a low-frequency region.

The present invention provides a sound-absorbing material according to claim <NUM>.

According to an embodiment, the resin film may be formed from a polyolefin, a polyester, or a polyamide.

According to an embodiment, the thickness of the sound-absorbing material may be <NUM> to <NUM>.

According to an embodiment, the sound-absorbing material may have a normal incidence sound absorption coefficient of <NUM> or higher at a certain frequency of <NUM> or less as measured according to JIS A <NUM>-<NUM>.

According to the present invention, a sound-absorbing material having excellent sound-absorbing characteristics in a low-frequency region can be provided.

<FIG> is a schematic cross-sectional view of a sound-absorbing material. A sound-absorbing material <NUM> comprises a resin film <NUM>; a first substrate layer <NUM> having communication holes; and a second substrate layer <NUM> having communication holes, in this order. Sound (acoustic energy) incident from the resin film side is dissipated as thermal energy when it passes through the sound-absorbing material. As a result, attenuation of sound is observed.

Examples of the substrate layer having communication holes include a resin foam, a nonwoven fabric, a polymer porous body, and a porous ceramic. Among these, from the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the substrate layer may be a resin foam or a nonwoven fabric. The first substrate layer and the second substrate layer may be formed from the same material or may be formed from different materials.

Examples of the material for the resin foam include a polyethylene resin, a polypropylene resin, a polyurethane resin, a polyester resin, an acrylic resin, a polystyrene resin, a melamine resin, a silicone resin, natural rubber, and a synthetic rubber. From the viewpoints of heat resistance, flame retardancy, and the like, the material for the resin foam may be a melamine resin.

Examples of the fiber forming the nonwoven fabric include organic fibers and inorganic fibers. Examples of the organic fibers include fibers of polyolefins such as polyethylene (low-density or high-density), polypropylene, copolymerized polyethylene, and copolymerized polypropylene; fibers of polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate; acrylic fibers, polyamide fibers, nylon fibers, rayon fibers; and natural fibers such as wool. Furthermore, examples of the inorganic fibers include glass fibers, metal fibers, ceramic fibers, and carbon fibers. The fibers forming the nonwoven fabric can comprise one kind or two or more kinds of these.

From the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the thickness of the substrate layer can be set to <NUM> to <NUM> and may be <NUM> to <NUM>, may be <NUM> to <NUM>, or may be <NUM> or <NUM>. The first substrate layer and the second substrate layer may have the same thickness or may have different thicknesses. From the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the thickness of the first substrate layer (substrate layer on the incident side of sound) is thinner than the thickness of the second substrate layer.

From the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the areal weight of the substrate layer can be set to <NUM> to <NUM>/m<NUM> and may be <NUM> to <NUM>/m<NUM>, may be <NUM> to <NUM>/m<NUM>, may be <NUM> to <NUM>/m<NUM>, or may be <NUM> to <NUM>/m<NUM>. The first substrate layer and the second substrate layer may have the same areal weight or may have different areal weights.

From the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the density of the substrate layer is set to <NUM> to <NUM>/cm<NUM> according to the claimed invention. The first substrate layer and the second substrate layer may have the same density or may have different densities.

From the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the sound-absorbing material may further comprise another substrate layer having communication holes. That is, the sound-absorbing material may further comprise a third substrate layer having communication holes, a fourth substrate layer having communication holes, and the like in addition to the first substrate layer having communication holes and the second substrate layer having communication holes. Each of the substrate layers may be formed from the same material or may be formed from different materials.

Examples of the resin forming the resin film include polyolefin-based resins such as polyethylene (low-density or high-density), polypropylene, copolymerized polyethylene, and copolymerized polypropylene; polyester-based resins such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate; fluorine-based resins such as PTFE, FEP, and PFA; polyimide-based resins, polyamide-based resins, aramid-based resins, vinyl chloride-based resins, acrylic resins, polycarbonate-based resins, polyphenylene sulfide-based resins, polyvinyl alcohol-based resins, polystyrene-based resin, polyacrylonitrile-based resins, and ethylene-vinyl acetate-based resins.

From the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the thickness of the resin film can be set to <NUM> to <NUM> and may be <NUM> to <NUM> or may be <NUM> to <NUM>. The first resin film and the second resin film may have the same thickness or may have different thicknesses. Furthermore, from the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the ratio of the thickness of the resin film to the thickness of the substrate layers (thickness of substrate layers/thickness of resin film) can be set to <NUM> to <NUM> and may be <NUM> to <NUM> or may be <NUM> to <NUM>.

From the viewpoint of imparting a function of enhancing the sound absorbing effect by adjustment of the film characteristics and a heat-ray reflecting function, the resin film comprises a metal vapor deposition layer on the surface. That is, the sound-absorbing material further comprises a metal vapor deposition layer on at least one surface of the first resin film and the second resin film. The metal vapor deposition layer can be formed by physical vapor deposition such as vacuum vapor deposition or chemical vapor deposition of a metal such as aluminum, copper, zinc, a zinc alloy, or silver. The metal vapor deposition layer may be provided on both surfaces of a resin film or may be provided on one surface.

From the viewpoint of enhancing the sound absorbing effect in a low-frequency region and adjusting the sound absorption frequency peak, the resin film may be a perforated film. The perforated film may have holes arranged in a grid pattern or in a diamond pattern. From the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, these holes may have a circular shape with a diameter of <NUM> to <NUM>, may have a circular shape with a diameter of <NUM> to <NUM>, or may have a circular shape with a diameter of <NUM> to <NUM>. The shape of the holes may be a circular shape, an elliptical shape, a rectangular shape, a polygonal shape, or the like.

From the viewpoint of having excellent sound-absorbing characteristics in a low-frequency region, the resin film may be further provided between the first substrate layer having communication holes and the second substrate layer having communication holes. Furthermore, in a case where the sound-absorbing material further comprises a third substrate layer, a fourth substrate layer, and the like, the resin film may be further provided between those substrate layers. Each of the resin films may be formed from the same material or may be formed from different materials.

The sound-absorbing material further comprises an adhesive layer between the respective above-described layers. The sound-absorbing material comprises an adhesive layer between the resin film and the first substrate layer and between the first substrate layer and the second substrate layer. Examples of the adhesive layer include, a layer including an adhesive component such as a polyester resin, a vinyl acetate resin, an ethylene-vinyl acetate copolymerized resin, an isobutene-maleic anhydride copolymerized resin, an acrylic copolymerized resin, an acrylic monomer, an acrylic oligomer, a vinyl chloride resin, a urethane resin (including a moisture-curable resin), a silylated urethane resin, an epoxy resin, a modified epoxy resin, a polyolefin resin such as a polyethylene resin, an ionomer resin, a silicone resin, a modified silicone resin, a synthetic rubber such as a styrene-butadiene rubber, a chloroprene rubber, or a nitrile rubber, natural rubber such as isoprene rubber, water glass, or silicate; and a layer formed from a laminate comprising layers containing these adhesive components on both surfaces of a support formed from paper, cloth, a resin tape, a metal tape, or the like. Furthermore, the adhesive layer may also be a product (adhesive sheet) comprising the above-described layer containing an adhesive component or the above-described laminate on both surfaces of a resin film. In this case, as the resin film, the above-described resin films can be used. The respective adhesive layers may be formed from the same material or may be formed from different materials.

The thickness of the adhesive layer is not particularly limited; however, the thickness can be set to <NUM> to <NUM> or may be <NUM> to <NUM>. The respective adhesive layers may have the same thickness or may have different thicknesses.

From the viewpoints of exhibiting sound-absorbing characteristics, workability of the materials, space saving, and the like, the thickness of the sound-absorbing material can be set to <NUM> to <NUM> and may be <NUM> to <NUM> or may be <NUM> to <NUM>.

The sound-absorbing material can have a normal incidence sound absorption coefficient of <NUM> or higher, or <NUM> or higher, as measured according to JIS A <NUM>-<NUM> at a certain frequency of <NUM> or less, specifically at least at any one frequency of <NUM>, <NUM>, and <NUM>. This normal incidence sound absorption coefficient can be set to <NUM> or higher and may also be <NUM> or higher, at <NUM>. This normal incidence sound absorption coefficient can be set to <NUM> or higher and may be <NUM> or higher, at <NUM>. This sound absorption coefficient can be set to <NUM> or higher and may be <NUM> or higher, at <NUM>.

The sound-absorbing material is produced by laminating each of the layers. The sound-absorbing material is used in a state in which the respective layers are adhered by providing the adhesive layers as described above;
Furthermore, the adhesive layer may be provided between some layers only. The laminate constituting the sound-absorbing material may be used in a state of being housed in a case.

The sound-absorbing material has excellent sound-absorbing characteristics in a low-frequency region. Therefore, the sound-absorbing material can be suitably used for use applications such as automobiles, railroad vehicles, aircrafts, ships, buildings such as houses, electronic devices, and precision machines. The low-frequency region as used herein can be set to a region with a frequency of <NUM> or less and may be a region with a frequency of <NUM> or less, may be a region with a frequency of <NUM> or less, or may be a region with a frequency of <NUM> or less.

Hereinafter, the present invention will be described in more detail by way of Examples; however, the present invention is not intended to be limited to these Examples.

The substrate layers indicated in Table <NUM> were prepared.

The following resin films were prepared.

The following adhesive layers were prepared.

Sound-absorbing materials having the configurations shown in Table <NUM> and Table <NUM> were produced. For the adhesion of each layer, a double-sided tape, an adhesive, or an adhesive sheet was used. Regarding *<NUM> in the tables, the adhesion between a resin film and a first substrate layer was conducted using the double-sided tape A or the adhesive A, and the adhesion between a first substrate layer and a second substrate layer was conducted using the adhesive sheet A, the adhesive sheet B, or the double-sided tape B.

The normal incidence sound absorption coefficient of each of the produced sound-absorbing materials was measured as follows. Sound was made incident from the layer described on the left-hand side in Table <NUM>. The measurement results are shown in Table <NUM> and Table <NUM>.

<FIG> are diagrams showing the respective normal incidence sound absorption coefficients of Examples and Comparative Examples. As shown in the same diagrams, it is understood that the sound-absorbing materials of Examples have excellent sound-absorbing characteristics in a low-frequency region.

Claim 1:
A sound-absorbing material (<NUM>) comprising a resin film (<NUM>); a first adhesive layer; a first substrate layer (<NUM>) having communication holes; a second adhesive layer; and a second substrate layer (<NUM>) having communication holes, in this order, wherein the first substrate layer (<NUM>) is laminated to the resin film (<NUM>) via the first adhesive layer and the second substrate layer (<NUM>) is laminated to the first substrate layer (<NUM>) via the second adhesive layer, wherein each of the first substrate layer (<NUM>) and the second substrate layer (<NUM>) is a resin foam or a nonwoven fabric and the density of each of the first substrate layer (<NUM>) and the second substrate layer (<NUM>) is <NUM> to <NUM>/cm<NUM>, characterized in that a thickness of the first substrate layer (<NUM>) is thinner than a thickness of the second substrate layer (<NUM>), and that the sound-absorbing material (<NUM>) further comprises a metal vapor deposition layer on at least one surface of the resin film (<NUM>).