Patent Description:
A sound absorbing material is a product having a function of absorbing sound and is widely used in the fields of construction and automobiles. Use of a nonwoven fabric as a material constituting a sound absorbing material is known. For example, <CIT> discloses that a support body layer and a submicron fiber layer laminated on the support body layer are included as a multilayer article having a sound absorbing property, in which the submicron fiber layer has a central fiber diameter of less than <NUM> and an average fiber diameter in a range of <NUM> to <NUM> and is formed by a molten film fibrillation method or an electrospinning method. An example of <CIT> discloses a laminated article in which a polypropylene spunbonded nonwoven fabric having a basis weight (basis weight) of <NUM>/m<NUM> and a diameter of about <NUM> is used as a support body layer, and a submicron polypropylene fiber having a basis weight of <NUM> to <NUM>/m<NUM> and an average fiber diameter of about <NUM> is laminated thereon. Also, another example discloses a multilayer article in which electrospun polycaprolactone fibers having a basis weight of <NUM> to <NUM>/m<NUM> and an average fiber diameter of <NUM> are laminated on a polyester card-treated web having a basis weight of <NUM>/m<NUM>. The multilayer articles produced in the examples have been measured for sound absorption characteristics, and this has shown that the sound absorption characteristics are superior to sound absorption characteristics of the support body alone.

Use of a foamed body as a sound absorbing material is also known. For example, <CIT> discloses a laminated structure for improving acoustic comfort (reducing and optimizing sound reflection components) and thermal comfort including an organic polymer foamed body having an open porosity in a specific range as a support layer, a glass fabric having specific permeability resistance as a surface layer, and a discontinuous adhesive layer between the support layer and the surface layer. It is disclosed that examples of the organic polymer foamed body include polyurethane, particularly polyester urethane, neoprene (registered trademark), and those using silicone or melamine as a basic material, and a density thereof is preferably <NUM> to <NUM>/m<NUM> and a thickness is preferably <NUM> to <NUM>.

<CIT> discloses a multilayer sheet used as an insulator for automobiles. The multilayer sheet of <CIT> is one in which a first porous sheet and a second porous sheet are fused and integrated by polypropylene melt-blown nonwoven fabrics inserted therebetween. Short-fiber adhesive entangled nonwoven fabric sheets, glass wool mat sheets, and the like are exemplified as the first porous sheet and the second porous sheet, dense polypropylene melt-blown nonwoven fabrics with low air permeability are inserted therebetween, and when the melt-blown nonwoven fabrics with an average fiber diameter of <NUM> or less are used, it is thought that the fibers can be uniformly dispersed and a physical property of the low air permeability of the melt-blown nonwoven fabrics can be inherited even when they are melted during molding.

<CIT> relates to nonwoven structures and composites comprising such nonwoven structures, particularly structures incorporating foam, and methods of making and use thereof. One aspect of the document is directed to composites comprising a nonwoven structure immobilized to foam, e.g., using adhesive, needling, or other techniques. The nonwoven structure may comprise any of a variety of fibers. Other aspects of the document are generally directed to systems and methods for making such composites, methods of use of such composites, and kits comprising such composites Patent document <CIT> discloses a sound absorbing material comprising a fiber layer and a porous layer, and suggests that the air permeability of the fiber layer should not exceed <NUM> cc/cm<NUM>. s (100ft<NUM>/min·ft<NUM>).

As described above, laminates with various configurations have been studied as sound absorbing materials, and combining a plurality of layers having different fiber diameters and air permeabilities (densities) is also known. On the other hand, particularly in a sound absorbing material for automobiles, there is a demand for a sound absorbing material having better sound absorption characteristics, particularly a sound absorbing material that exhibits excellent sound absorbing performance in a low-frequency range of <NUM> or less, an intermediate-frequency range of <NUM> to <NUM>, and a high-frequency range of <NUM> to <NUM> and has an excellent space-saving property. In view of this situation, an objective of the present invention is to provide a sound absorbing material having an excellent sound absorbing property in a low-frequency range, an intermediate-frequency range, and preferably a higher frequency range.

The inventors conducted intensive research to solve the above-described problems. As a result, they found that the above-described problems can be solved when a laminated sound absorbing material including a porous layer and a fiber layer is made to have a structure including a dense fiber layer having a mean flow pore size in a specific range and an air permeability in a specific range, and a sparse porous layer having a constant thickness and density and formed of at least one selected from the group consisting of a foamed resin, a nonwoven fabric, and a woven fabric, and thus completed the present invention.

The present invention refers to a laminated sound absorbing material according to claim <NUM>.

Other advantageous embodiments are defined in the dependent claims.

According to the present invention having the above-described configurations, when a fiber layer and a porous layer having a specific configuration are included in the laminated sound absorbing material, a high sound absorbing property can be realized with a small number of layers, and a thickness of a sound absorbing material can be reduced. Also, according to the present invention having the above-described configurations, a sound absorbing material having excellent sound absorbing characteristics can be obtained in a low-frequency range, an intermediate-frequency range, and preferably a higher frequency range. The laminated sound absorbing material of the present invention is excellent in sound absorbing performance in a range in which a peak of sound absorbing characteristics is lower than that of a conventional sound absorbing material, that is, in a range of <NUM> or less and particularly in a range of <NUM> or less. In the field of construction, it is reported that most of daily life noise is about <NUM> to <NUM>, and in the field of automobiles, it is reported that road noise is about <NUM> to <NUM>, noise during acceleration or a transmission change is about <NUM> to <NUM>, and wind noise during vehicle traveling is about <NUM> to <NUM>. The laminated sound absorbing material of the present invention is useful for a countermeasure against such noise. Also, since the laminated sound absorbing material of the present invention is lighter than a sound absorbing material made of a porous material, a glass fiber, or the like, weight reduction and space saving of the member is possible, and it is particularly useful as a sound absorbing material for the field of automobiles in this respect.

A laminated sound absorbing material of the present invention is a laminated sound absorbing material including at least a fiber layer and a porous layer, in which the fiber layer has a mean flow pore size of <NUM> to <NUM> and an air permeability of <NUM> to <NUM> cc/cm<NUM>·s by the Frazier method, the porous layer is a layer formed of at least one selected from the group consisting of a foamed resin, a nonwoven fabric, and a woven fabric and has a thickness of <NUM> to <NUM> and a density which is lower than that of the fiber layer and is <NUM> to <NUM>/m<NUM>, and the fiber layer is disposed on a sound incidence side.

In the laminated sound absorbing material, at least one fiber layer is included, and specifically, one or two layers can be included, but one layer is more preferable from the perspective of reducing a thickness of the sound absorbing material. Each fiber layer may be formed of one fiber aggregate or may have a form in which a plurality of fiber aggregates is overlapped in one fiber layer. Also, in the laminated sound absorbing material, at least one fiber layer is disposed on a sound incidence side.

The fiber layer and the porous layer included in the laminated sound absorbing material may be one type each but may be two or more different types of fiber layers or porous layers. Also, as long as the effects of the present invention are not impaired, a constituent other than the fiber layer and the porous layer may be included, and for example, an additional fiber layer (one layer or two or more layers), a printing layer, a foamed body, a foil, a mesh, a woven fabric, or the like outside the range specified in the present invention may be included. Also, an adhesive layer, a clip, a suture thread, or the like for connecting each layer may be included.

The laminated sound absorbing material of the present invention may be a two-layer laminate in which a fiber layer is disposed on a sound incidence side and a porous layer is disposed on a sound transmission side, may be a three-layer laminate in which a porous layer is sandwiched between a first fiber layer and a second fiber layer, or may be a four-layer laminate in which a first fiber layer/a first porous layer/a second fiber layer/a second porous layer are laminated in that order. When two fiber layers are included, a first fiber layer and a second fiber layer may have densities that are the same as or different from each other. When the densities are different from each other, the second fiber layer positioned on the sound transmission side preferably has a higher density than the first fiber layer. When two porous layers are included, a first porous layer and a second porous layer may have densities that are the same as or different from each other. When the densities are different from each other, the second porous layer positioned on a sound transmission side preferably has a higher density than the first porous layer.

Spaces between layers of the laminated sound absorbing material may or may not be physically and/or chemically adhered. The laminated sound absorbing material may have a form in which a part between the plurality of layers is adhered and a part therebetween is not adhered. In regard to adhesion, the fiber layer and the porous layer may be adhered by performing heating to melt some of the fibers constituting the fiber layer and fusing the fiber layer to the porous layer, for example, in a step of forming the fiber layer or as a post-step. It is also preferable to adhere the layers by applying an adhesive to a surface of the porous layer or the fiber layer and then overlapping the porous layer or the fiber layer thereon.

A thickness of the laminated sound absorbing material is not particularly limited as long as the effects of the present invention can be obtained, but can be, for example, <NUM> to <NUM>, preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM> from the perspective of a space-saving property. Further, the thickness of the laminated sound absorbing material is typically a total thickness of the fiber layer and the porous layer, and when an exterior body such as a cartridge or a lid is attached, a thickness of that portion is not included therein.

An air permeability of the laminated sound absorbing material is not particularly limited as long as desired sound absorbing performance can be obtained, the air permeability of the fiber layer is <NUM> to <NUM> cc/cm<NUM>·s. When the air permeability is <NUM> cc/cm<NUM>·s or more, there is no decrease in sound absorption coefficient due to sound reflection on a surface of the sound absorbing material, and when the air permeability is <NUM> cc/cm<NUM>·s or less, tortuosity inside the sound absorbing material decreases and there is no decrease in energy loss inside the sound absorbing material. Also, a density of the fiber layer is higher than a density of the porous layer, in other words, a structure is obtained of in which a layer having a relatively low density (porous layer) is positioned on a sound transmission side with respect to a layer having a high density (fiber layer) or is sandwiched between the fiber layers. Conventionally, in a sound absorbing material that is expected to have sound insulating performance as well as sound absorbing performance, it has been thought that a higher density would make it more difficult for a sound to pass through, that is, more effective for a sound insulating property, but the laminated sound absorbing material of the present invention reduces sound reflection by having high air permeability, and furthermore, can obtain a high sound absorbing property by employing a porous layer having an excellent sound absorbing property. To adjust the air permeability, a fiber layer having a high density and low air permeability can be obtained by, for example, making fibers constituting the fiber layer small in diameter. The air permeability can also be adjusted by a method such as embossing or heating and pressurizing. Further, the air permeability can be measured by a known method, for example, by the Frazier method.

The laminated sound absorbing material has a laminated structure in which the porous layer is positioned downstream (sound transmission side) of the fiber layer, or the porous layer is sandwiched between the fiber layers. When the porous layer is sandwiched between the fiber layers, a distance between the fiber layers (also referred to as a thickness of the porous layer or an interlayer distance) is <NUM> to <NUM>. When the interlayer distance is <NUM> or more, sound absorbing performance in a low-frequency range is satisfactory, and when the interlayer distance is <NUM> or less, a thickness of the sound absorbing material does not become too large and a sound absorbing material having an excellent space-saving property can be obtained. Typically, the sound absorbing material of the present invention preferably has a structure in which a thick porous layer is sandwiched between thin fiber layers, and a thickness of the porous layer preferably occupies most of the thickness of the laminated sound absorbing material.

The fiber layer included in the laminated sound absorbing material of the present invention is a layer formed of fibers having an average fiber diameter of <NUM> to <NUM>. The layer is preferably formed of fibers having an average fiber diameter of <NUM> to <NUM>. The average fiber diameter of <NUM> to <NUM> means that the average fiber diameter is within this numerical range. When the fiber diameter is in the range of <NUM> to <NUM>, this is preferable because a high sound absorbing property can be obtained. The fiber diameter can be measured by a known method. For example, the fiber diameter is a value obtained by measuring or calculating from an enlarged image of a surface of the fiber layer, and a detailed measurement method is described in detail in examples.

In the fiber layer included in the laminated sound absorbing material of the present invention, one fiber layer may be formed of one fiber aggregate, and one in which a plurality of fiber aggregates is included in one fiber layer and layers of the fiber aggregates are overlapped may form one fiber layer. Further, in the present specification, the fiber aggregate is a fiber aggregate which is configured as one continuum. A basis weight of the fiber layer is preferably <NUM> to <NUM>/m<NUM>, and more preferably <NUM> to <NUM>/m<NUM>. When the basis weight is <NUM>/m<NUM> or more, control of flow resistance due to a density difference between the fiber layer and the porous layer is satisfactory, and when the basis weight is less than <NUM>/m<NUM>, the productivity as a sound absorbing material is excellent. From the perspective of reducing a thickness of the sound absorbing material, a thickness of the fiber layer is preferably thin, specifically, preferably less than <NUM>, more preferably less than <NUM>, still more preferably less than <NUM>, and particularly preferably less than <NUM>.

An air permeability of the fiber layer is <NUM> to <NUM> cc/cm<NUM>·s. It is thought that, when the air permeability is <NUM> cc/cm<NUM>·s or more, sound generated from a sound source can be introduced into the sound absorbing material, and thus the sound can be efficiently absorbed, and when the air permeability is <NUM> cc/cm<NUM>·s or less, a flow of sound waves with respect to the porous layer inside can be adjusted, and thus this is preferable. Also, a mean flow pore size of the fiber layer is <NUM> to <NUM>. When the mean flow pore size is <NUM> or more, a reflected wave to be able to be suppressed and the sound to be able to be taken into the sound absorbing material, and when the mean flow pore size is <NUM> or less, the sound can be efficiently eliminated inside the sound absorbing material by confining the sound inside the sound absorbing material in the fiber layer and the porous layer controlled by the density.

The fiber aggregate constituting the fiber layer is preferably a nonwoven fabric and is not particularly limited as long as a fiber diameter and a basis weight thereof are in the range described above, but is preferably a spunbonded nonwoven fabric, a melt-blown nonwoven fabric, a nonwoven fabric formed by an electrospinning method, or the like. According to the melt-blown nonwoven fabric, fibers having a small diameter can be efficiently laminated on another member such as a base material. Details of the melt-blown nonwoven fabric will be described in description of the manufacturing method.

A resin constituting the fiber layer is not particularly limited as long as the effects of the invention can be obtained, and examples thereof include a polyolefin-based resin, polyurethane, polylactic acid, an acrylic resin, polyesters such as polyethylene terephthalate and polybutylene terephthalate, nylons (amide resins) such as nylon <NUM>, nylon <NUM>,<NUM>, and nylon <NUM>,<NUM>, polyphenylene sulfide, polyvinyl alcohol, polystyrene, polysulfone, liquid crystal polymers, a polyethylene-vinyl acetate copolymer, polyacrylonitrile, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and the like. As the polyolefin-based resin, a polyethylene resin and a polypropylene resin can be exemplified. As the polyethylene resin, low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and the like can be exemplified, and as the polypropylene resin, a propylene homopolymer, a polypropylene copolymer in which propylene and other monomers and ethylene, butene, or the like are polymerized, and the like can be exemplified. The fiber aggregate preferably contains one type of the above-described resins and may also include two or more types.

Also, the fiber layer is preferably a spunbonded nonwoven fabric using flat yarn in which a cross-sectional shape of the fiber is flat. Specifically, for example, a spunbonded nonwoven fabric using flat yarn having a denier of <NUM> to <NUM> dtex such as a polyolefin-based resin (polypropylene, polyethylene), polyethylene terephthalate, and nylon may be prepared and used as the flat yarn, and a product available on the market can also be used. When a product available on the market is used, for example, Eltas FLAT, Eltas Emboss (trade name, manufactured by Asahi Kasei Corporation), or the like can be preferably used. It is thought that the spunbonded nonwoven fabric using flat yarn can be preferably used for the laminated sound absorbing material of the present invention due to its low basis weight, small thickness, and high density.

Also, the above-described fiber may contain additives of various types other than a resin. As additives that can be added to a resin, for example, a filler, a stabilizer, a plasticizer, a pressure-sensitive adhesive, an adhesion promoter (for example, silane and titanate), silica, glass, clay, talc, a pigment, a colorant, an antioxidant, a fluorescent whitening agent, an antibacterial agent, a surfactant, a flame retardant, and a fluoropolymer can be exemplified. Using one or more of the above-described additives, a weight and/or costs of the fibers and layers to be obtained may be reduced, viscosity may be adjusted, thermal properties of the fibers may be modified, or activation of various physical properties derived from properties of the additives including electrical properties, optical properties, properties related to a density, or properties related to a liquid barrier or adhesiveness may be imparted.

The porous layer in the laminated sound absorbing material of the present invention has a sound absorbing property and a function of keeping a shape of the entire sound absorbing material by supporting the fiber layer. The porous layer may be formed of one porous layer or may be in a form in which a plurality of porous layers is overlapped. The porous layer has a density lower than that of the fiber layer by the Frazier method, is a layer formed of at least one selected from the group consisting of a foamed resin, a nonwoven fabric, and a woven fabric, and has a thickness of <NUM> to <NUM> and a density of <NUM> to <NUM>/m<NUM>.

When a member constituting the porous layer is a nonwoven fabric or a woven fabric, the nonwoven fabric or the woven fabric is preferably formed of at least a fiber of one type selected from the group consisting of a polyethylene phthalate fiber, a polybutylene terephthalate fiber, a polyethylene fiber, a polypropylene fiber, and a glass fiber, or formed of a composite fiber in which two or more types thereof are composited.

When the member constituting the porous layer is a foamed resin, the porous layer is particularly preferably a layer formed of a urethane foam resin or a melamine foam resin. The laminated sound absorbing material may include a member of one type and preferably includes members of two or more types. Since it is particularly preferable that these have air permeability, it is preferable to have open pores when the air permeability is low. The foamed resin is preferably a foamed resin having open cells (communicating pores).

As a resin constituting the above-described foamed resin, for example, a polyolefin-based resin, a polyurethane-based resin, and a melamine-based resin can be exemplified. As the polyolefin-based resin, a homopolymer such as ethylene, propylene, butene-<NUM>, <NUM>-methylpentene-<NUM>, or the like, a random or block copolymer of these with other α-olefins, that is, with one or more of ethylene, propylene, butene-<NUM>, pentene-<NUM>, hexene-<NUM>, <NUM>-methylpentene-<NUM>, and the like, a copolymer obtained by combining them, or a mixture thereof can be exemplified.

In the laminated sound absorbing material of the present invention, the porous layer is positioned downstream of the fiber layer (sound transmission side) or is positioned between the fiber layers. In addition to being positioned between the fiber layers, the porous layer may also be included as a layer positioned on an outermost surface of the laminated sound absorbing material. The member may form the porous layer with only one layer, and it is also preferable that two or more layers be continuously disposed to form one porous layer. When two or more layers of the member are continuously disposed, there is an advantage that an interlayer distance of the layer can be controlled by a thickness of the porous layer.

A density of the porous layer is <NUM> to <NUM>/m<NUM> and preferably <NUM> to <NUM>/m<NUM>. As the foamed resin layer, a foamed resin layer having open cells (communicating pores) is preferable, and examples thereof include a urethane foam resin, an acrylic-based foam resin, a melamine foam resin, and the like. When the density is <NUM>/m<NUM> or more, it is preferable in terms of good moldability and being easily obtainable due to being available on the market generally, and when the density is <NUM>/m<NUM> or less, it is preferable because it is lightweight as the sound absorbing material and has high workability during installation or the like.

In the present invention, the porous layer has a thickness of <NUM> or more. An upper limit of the thickness of the porous layer is <NUM> to <NUM>. When the porous layer is constituted by a plurality of members, a thickness of each member constituting the porous layer can be, <NUM> to <NUM>. When a thickness of the member is <NUM> or more, wrinkles do not occur, handling is easy, and the productivity is satisfactory, and when the thickness of the member is <NUM> or less, there is no likelihood of hindering the space-saving property.

The porous layer is a thicker layer having a lower density than the fiber layer, and it is thought that such a structure reduces sound reflection and contributes to a sound absorbing property. An air permeability of the porous layer can be, for example, <NUM> cc/cm<NUM>·s or more.

Additives of various types such as, for example, a colorant, an antioxidant, a light stabilizer, an ultraviolet absorbing agent, a neutralizer, a nucleating agent, a lubricant, an antibacterial agent, a flame retardant, a plasticizer, other thermoplastic resins, and the like may be added to the porous layer within a range not hindering the effects of the present invention. Also, a surface thereof may be treated with finishing agents of various types, and thereby functions such as water repellency, an antistatic property, surface smoothness, wear resistance, and the like may be imparted.

The laminated sound absorbing material of the present invention has a feature of having an excellent sound absorbing property particularly in a low-frequency range (frequency range of <NUM> to <NUM> or less), an intermediate-frequency range (frequency range of <NUM> to <NUM>), and preferably a higher frequency range (frequency range of <NUM> to <NUM>). The laminated sound absorbing material of the present invention exhibits sound absorbing characteristics different from those of conventional sound absorbing materials in that the sound absorbing property is excellent particularly in the range of <NUM> to <NUM>. Although not bound by a particular theory, it is thought that the laminated sound absorbing material of the present invention can obtain a small thickness and a performance of having excellent absorbency in the low-frequency range, the intermediate-frequency range, and the high-frequency range as a result of utilizing a density difference between the fiber layer and the porous layer to control flow resistance of sound waves and utilizing transmission, reflection, and interference of the sound waves.

A method for evaluating the sound absorption property will be described in detail in examples.

In the laminated sound absorbing material of the present invention, it is preferable that a sound absorption coefficient by a vertical incidence sound absorption coefficient measuring method at the frequency of <NUM> to <NUM> be improved by <NUM> or more compared to a sound absorption coefficient of a case in which only one porous layer is included in the laminated sound absorbing material. Also, in the laminated sound absorbing material of the present invention, it is preferable that a sound absorption coefficient by the vertical incidence sound absorption coefficient measuring method at the frequency of <NUM> to <NUM> be improved by <NUM> or more compared to the sound absorption coefficient of the case in which only one porous layer is included in the laminated sound absorbing material. Further, in the laminated sound absorbing material of the present invention, it is preferable that a sound absorption coefficient by the vertical incidence sound absorption coefficient measuring method at the frequency of <NUM> to <NUM> be improved by <NUM> or more compared to the sound absorption coefficient of the case in which only one porous layer is included in the laminated sound absorbing material.

A method of manufacturing the laminated sound absorbing material is not particularly limited, but can be obtained by a manufacturing method including, for example, a step of preparing a fiber layer that forms a fiber aggregate of one layer on one porous layer, and a step of overlapping and integrating a predetermined number of a plurality of fiber layers in a predetermined order. In the step of overlapping the fiber layers, an additional layer (for example, an additional protective layer) other than the fiber layers can be further added and laminated.

A foamed resin, a nonwoven fabric, and/or a woven fabric used as the porous layer may be manufactured by a known method and used, or a product available on the market may be selected and used.

A method of overlapping and integrating a plurality of laminates formed of two layers of the porous layer/the fiber layer obtained as described above is not particularly limited and may be simple overlapping without performing adhesion, and adhesion methods of various types, that is, thermo-compression bonding with a heated flat roll or embossed roll, adhesion with a hot melt agent or a chemical adhesive, thermal adhesion with circulating hot air or radiant heat, and the like can also be employed. Of these, a heat treatment with circulating hot air or radiant heat is particularly preferable from the perspective of suppressing deterioration of physical properties of the fiber layer. In a case of the thermo-compression bonding with a flat roll or embossed roll, deterioration in performance such as deterioration of sound absorption characteristics is likely to occur and stable manufacture is likely to be difficult because of damage such as the fiber layer being melted to form a film and tearing occurring at a portion near an embossed point. Also, in a case of the adhesion with a hot melt agent or a chemical adhesive, spaces between fibers of the fiber layer may be filled with components thereof, and deterioration in performance is likely to occur. On the other hand, integration by the heat treatment with circulating hot air or radiant heat is preferable because damage to the fiber layer is small and integration can be performed with a sufficient delamination strength. In the case of integration by the heat treatment with circulating hot air or radiant heat, although not particularly limited, it is preferable to use a nonwoven fabric and a foamed resin made of heat-fusible composite fibers.

Hereinafter, the present invention will be described in more detail using examples, but the following examples are merely for the purpose of exemplification. The scope of the present invention is not limited to the present examples.

Measurement methods and definitions of physical property values used in the examples are described below.

Fibers were observed using a scanning electron microscope SU8020 manufactured by Hitachi High-Technologies Corporation, and diameters of <NUM> fibers were measured using image analysis software. An average value of the fiber diameters of the <NUM> fibers was taken as an average fiber diameter.

After taking a sample with a diameter of <NUM> from each fiber layer and porous layer and laminating them under each condition, a vertical incidence sound absorption coefficient measurement when a plane sound wave was vertically incident on a test piece at a frequency of <NUM> to <NUM> was performed in accordance with ASTM E <NUM> using a vertical incidence sound absorption coefficient measuring device "WinZac MTX manufactured by Nihon Onkyo Engineering Co.

A sound absorption coefficient was measured in one-third octave band of sound absorption of the obtained sample, and an improvement range was evaluated by a comparative evaluation with a sample without the fiber layer. The vertical incidence sound absorption coefficient of each sample was measured in the <NUM>/<NUM> octave band, and an evaluation was performed by calculating a difference. When an improvement range of the sound absorbing performance in the frequency range of <NUM> to <NUM> is shown, it is determined that the improvement range of the sound absorbing property is high when the numerical value is high. When the values were <NUM> or more at all measurement points (specifically, <NUM>, <NUM>, <NUM>, <NUM>), the improvement of the sound absorbing property in the low-frequency range was evaluated as satisfactory (O), and when there was a measurement point less than <NUM>, the improvement of the sound absorbing property was evaluated as poor (x).

An evaluation was performed in the same manner as the sound absorbing property in the low-frequency range except that the frequency range evaluated in the low-frequency range was changed to <NUM> to <NUM>, and calculation of the improvement range was performed at <NUM>, <NUM>, and <NUM>.

An evaluation was performed in the same manner as the sound absorbing property in the low-frequency range except that the frequency range evaluated in the low-frequency range was changed to <NUM> to <NUM>, and calculation of the improvement range was performed at <NUM>, <NUM>, <NUM>, and <NUM>.

An air permeability was measured by a woven fabric air permeability tester (Frazier method) manufactured by Toyo Seiki Seisaku-sho Ltd. in accordance with JIS L1913.

A thickness was measured by DIGI THICKNESS TESTER manufactured by Toyo Seiki Seisaku-sho Ltd. in accordance with JIS K6767 at a pressure of <NUM>/cm<NUM> of <NUM>.

An MFR of a polypropylene resin is a value measured at <NUM> under a load condition of <NUM> in accordance with JIS K <NUM> (<NUM>).

An MFR of a polyethylene resin is a value measured at <NUM> under a load condition of <NUM> in accordance with JIS K <NUM> (<NUM>).

As a protective layer, a commercially available card method through-air nonwoven fabric (with a basis weight of <NUM>/m<NUM> and a thickness of <NUM>) made of polyethylene terephthalate was prepared.

Kynar (trade name) <NUM>, which was polyvinylidene fluoride-hexafluoropropylene (hereinafter abbreviated as "PVDF-HFP"), manufactured by Arkema was dissolved in a co-solvent of N, N-dimethylacetamide and acetone (<NUM>/<NUM> (w/w)) at a concentration of <NUM>% by mass to prepare an electrospinning solution, and <NUM>% by mass of a conductive auxiliary agent was added. The PVDF-HFP solution was electrospun on the protective layer to prepare a fiber laminate formed of two layers of the protective layer and PVDF-HFP ultrafine fibers. Conditions for the electrospinning were that a <NUM> needle was used, a single-hole solution supply amount was <NUM>/h, an applied voltage was <NUM> kV, and a spinning distance was <NUM>.

For the PVDF ultrafine fibers in the fiber laminate, a basis weight of the layer was <NUM>/m<NUM>, an average fiber diameter was <NUM>, and a melting temperature was <NUM>. This was defined as a fiber layer A. A mean flow pore size thereof was evaluated to be <NUM>, and an air permeability by the Frazier method was <NUM> cc/cm<NUM>·s.

Also, a transfer speed of the protective layer was changed so that the basis weight was adjusted to <NUM>/m<NUM>. An average fiber diameter of the obtained fiber layer was <NUM>, and the melting temperature was <NUM>. This was defined as a fiber layer B. A mean flow pore size was evaluated to be <NUM>, and an air permeability by the Frazier method was <NUM> cc/cm<NUM>·s.

Further, the basis weight was adjusted to <NUM>/m<NUM>. At this time, the average fiber diameter was <NUM> and the melting temperature was <NUM>. This was defined as a fiber layer C. A mean flow pore size was evaluated to be <NUM>, and an air permeability by the Frazier method was <NUM> cc/cm<NUM>·s.

As nonwoven fabric materials available on the market, Asahi Kasei ELTAS (registered trademark) FLAT EH5025 (thickness <NUM>) was used as a fiber layer D, EH5035 (thickness <NUM>) was used as a fiber layer E, EH5035C (thickness <NUM>) was used as a fiber F, ELTAS E01100 (thickness <NUM>) was used as a fiber layer G, E05030 (thickness <NUM>) was used as a fiber layer H, E01030 (thickness <NUM>) was used as a fiber layer I, E01025 (thickness <NUM>) was used as a fiber layer J, and EH5045C (thickness <NUM>) was used as a fiber layer K. Further, the fiber layers D, E, and F were spunbonded nonwoven fabrics using flat yarn, a fiber diameter of the fibers had a major axis diameter of <NUM> and a minor axis diameter of <NUM> of an ellipse, and the fiber layer D had a mean flow pore size of <NUM> and an air permeability of <NUM> cc/cm<NUM>·s by the Frazier method. The fiber layer E had a mean flow pore size of <NUM> and an air permeability of <NUM> cc/cm<NUM>·s by the Frazier method. The fiber layer F had a mean flow pore size of <NUM> and an air permeability of <NUM> cc/cm<NUM>·s by the Frazier method.

A polypropylene homopolymer <NUM> (MFR = <NUM>/<NUM> minutes) was used for a polypropylene resin as a raw material of the fiber layer, the polypropylene resin was put into two extruders of a nonwoven fabric manufacturing apparatus, the polypropylene resin was heat-melted at <NUM> by the extruders with a mass ratio of gear pumps set to <NUM>/<NUM>, and the molten resin was ejected from a spinneret at a spinning speed of <NUM>/min per single hole. The ejected fibers were sprayed onto a collecting conveyor at a distance of <NUM> from the spinneret by a compressed air of <NUM> kPa (gauge pressure) heated to <NUM> to form a fiber layer. A basis weight thereof was arbitrarily set by adjusting a speed of the collecting conveyor. An average fiber diameter was <NUM>, and a basis weight of the fiber layer was <NUM>/m<NUM> and a thickness thereof was <NUM>. A mean flow pore size of the fiber layer M was <NUM>, and an air permeability by the Frazier method was <NUM> cc/cm<NUM>·s.

A nonwoven fabric manufacturing apparatus including two extruders each having a screw (<NUM> diameter), a heating body, and a gear pump, a spinneret for mixed fibers (a hole diameter of <NUM>, and an effective width of <NUM> in which <NUM> holes through which resins from the two extruders were alternately ejected were aligned in a line), a compressed air generator, an air heater, a collecting conveyor having a polyester net, and a winder was used to form a fiber layer.

A polypropylene homopolymer <NUM> (MFR = <NUM>/<NUM> minutes) and a polypropylene homopolymer <NUM> ("<CIT>" (MFR = <NUM>/<NUM> minutes) manufactured by LOTTE Chemical Corporation) were used for polypropylene as a raw material, the polypropylenes of the two types were put into the two extruders of the nonwoven fabric manufacturing apparatus, the polypropylenes were heat-melted at <NUM> by the extruders with a mass ratio of gear pumps set to <NUM>/<NUM>, and the molten resin was ejected from the spinneret at a spinning speed of <NUM>/min per single hole. The ejected fibers were sprayed onto a collecting conveyor at a distance of <NUM> from the spinneret by a compressed air of <NUM> kPa (gauge pressure) heated to <NUM> to form a fiber layer. A basis weight thereof was set to <NUM>/m<NUM> by adjusting a speed of the collecting conveyor. An average fiber diameter was <NUM>, and this was defined as a fiber layer N. A mean flow pore size thereof was evaluated to be <NUM>, and an air permeability by the Frazier method was <NUM> cc/cm<NUM>·s.

From urethane foam resin materials available on the market, Calmflex F-<NUM> (density <NUM>/m<NUM>) manufactured by Inoac Corporation with a thickness of <NUM> was used as a porous layer α, that with a thickness of <NUM> was used as a porous layer β, and that with a thickness of <NUM> was used as a porous layer γ. An air permeability by the Frazier method was <NUM> cc/cm<NUM>·s for the porous layer α, <NUM> cc/cm<NUM>·s for the porous layer β, and <NUM> cc/cm<NUM>·s for the porous layer γ.

A sheath-core type thermally fusible composite fiber in which a sheath component with a fiber diameter of <NUM> was made of a high-density polyethylene resin and a core component was made of a polypropylene resin was prepared by a heat-melt spinning method using high-density polyethylene "M6900" (MFR <NUM>/<NUM> minutes) manufactured by KEIYO Polyethylene Co. as the high-density polyethylene resin, and a polypropylene homopolymer "SA3A" (MFR = <NUM>/<NUM> minutes) manufactured by Japan Polypropylene Corporation as the polypropylene resin. Using the obtained sheath-core type thermally fusible composite fiber, a card method through-air nonwoven fabric having a basis weight of <NUM>/m<NUM>, a thickness of <NUM>, and a width of <NUM> was prepared. The card method through-air nonwoven fabric was crushed to about <NUM> using a uniaxial crusher (ES3280) manufactured by Shoken Co. This crushed nonwoven fabric was heated at a set temperature of <NUM> by an air-laid tester to obtain a porous layer δ having a basis weight of <NUM>/m<NUM> and a thickness of <NUM>, a porous layer ζ having a basis weight of <NUM>/m<NUM> and a thickness of <NUM>, and a porous layer θ having a basis weight of <NUM>/m<NUM> and a thickness of <NUM>. The porous layer δ had a density of <NUM>/m<NUM> and an air permeability of <NUM> cc/cm<NUM>·s. The porous layer ζ had a density of <NUM>/m<NUM> and an air permeability of <NUM> cc/cm<NUM>·s. The porous layer θ had a density of <NUM>/m<NUM> and an air permeability of <NUM> cc/cm<NUM>·s.

As a glass fiber material available on the market, an Aclear mat (trade name) having a thickness of <NUM> manufactured by Asahi Fiber Glass Co. was processed to have a basis weight of <NUM>/m<NUM> and a thickness of <NUM> and was used as a porous layer ε. Also, it was processed to have a basis weight of <NUM>/m<NUM> and a thickness of <NUM> and was used as a porous layer η. Further, it was processed to have a basis weight of <NUM>/m<NUM> and a thickness of <NUM> and was used as a porous layer κ. The porous layer ε had a density of <NUM>/m<NUM> and an air permeability of <NUM> cc/cm<NUM>·s. The porous layer η had a density of <NUM>/m<NUM> and an air permeability of <NUM> cc/cm<NUM>·s. The porous layer κ had a density of <NUM>/m<NUM> and an air permeability of <NUM> cc/cm<NUM>·s.

The fiber layer A as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer A/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. A difference of the sound absorption coefficient compared to that of a sample in which the fiber layer A was not present (comparative example <NUM>) was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory. Further, when a difference of the sound absorption coefficient in the high-frequency range from that of comparative example <NUM> was taken in the same manner and an improvement range was calculated, the improvement range was <NUM> or more and was satisfactory.

The fiber layer D as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer D/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. A difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer E as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer E/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. A difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer G as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer G/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. A difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer M as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer M/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. A difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer A as the first fiber layer and the porous layer δ were used and overlapped to form the fiber layer A/the porous layer δ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. A difference of the sound absorption coefficient compared to that of comparative example <NUM> (only the porous layer δ) was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer G as the first fiber layer and the porous layer δ were used and overlapped to form the fiber layer G/the porous layer δ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. A difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer A as the first fiber layer and the porous layer ε were used and overlapped to form the fiber layer A/the porous layer ε, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, and a difference of the sound absorption coefficient from that of a sample of comparative example <NUM> in which the fiber layer is not present was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer H as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer H/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. A difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated. The improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

Only the porous layer α (thickness <NUM>) was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement, and a sound absorption coefficient was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. Since the sample was an object itself to be compared, a difference in sound absorption coefficient of the sample was <NUM> in the low-frequency range, the intermediate-frequency range, and the high-frequency range, and improvement of the sound absorbing property was poor.

Only the porous layer δ (thickness <NUM>) was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement, and a sound absorption coefficient was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. Since the sample was an object itself to be compared, a difference in sound absorption coefficient of the sample was <NUM> in the low-frequency range, the intermediate-frequency range, and the high-frequency range, and improvement of the sound absorbing property was poor.

Only the porous layer ε (thickness <NUM>) was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement, and a sound absorption coefficient was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. Since the sample was an object itself to be compared, a difference in sound absorption coefficient of the sample was <NUM> in the low-frequency range, the intermediate-frequency range, and the high-frequency range, and improvement of the sound absorbing property was poor.

The fiber layer J as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer J/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were poor.

The fiber layer C as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer C/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the result was that no improvement tendency was observed in both the low-frequency range and the intermediate-frequency range.

The fiber layer F as the first fiber layer and the porous layer α were used and overlapped to form the fiber layer F/the porous layer α, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, although the improvement range was <NUM> or more in the low-frequency range and was satisfactory, it was <NUM> or more in the intermediate-frequency range and was poor.

The configurations of examples <NUM> to <NUM> are summarized in Table <NUM>, and the configurations of comparative examples <NUM> to <NUM> are summarized in Table <NUM>. The sound absorption coefficients of examples <NUM> to <NUM> are summarized in Table <NUM>, the sound absorption coefficients of comparative examples <NUM> to <NUM> are summarized in Table <NUM>, and the improvement ranges of the sound absorption coefficient are summarized in Tables <NUM> and <NUM>.

The fiber layer A as the first fiber layer and the porous layer β were used and overlapped to form the fiber layer A/the porous layer β, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> (only the porous layer β) was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer E as the first fiber layer and the porous layer β were used and overlapped to form the fiber layer E/the porous layer β, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer G as the first fiber layer and the porous layer β were used and overlapped to form the fiber layer G/the porous layer β, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer M as the first fiber layer and the porous layer β were used and overlapped to form the fiber layer M/the porous layer β, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer A as the first fiber layer and the porous layer ζ were used and overlapped to form the fiber layer A/the porous layer ζ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> (only the porous layer ζ) was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer G as the first fiber layer and the porous layer ζ were used and overlapped to form the fiber layer G/the porous layer ζ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer A as the first fiber layer and the porous layer η were used and overlapped to form the fiber layer A/the porous layer η, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> (only the porous layer η) was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

Only the porous layer β (thickness <NUM>) was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. Since the sample is an object itself to be compared, a difference in sound absorption coefficient of the sample is <NUM> in the low-frequency range, the intermediate-frequency range, and the high-frequency range, and no improvement effect is observed.

Only the porous layer ζ (thickness <NUM>) was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. Since the sample is an object itself to be compared, a difference in sound absorption coefficient of the sample is <NUM> in the low-frequency range, the intermediate-frequency range, and the high-frequency range, and no improvement effect is observed.

Only the porous layer η (thickness <NUM>) was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. Since the sample is an object itself to be compared, a difference in sound absorption coefficient of the sample is <NUM> in the low-frequency range, the intermediate-frequency range, and the high-frequency range, and no improvement effect is observed.

The fiber layer J as the first fiber layer and the porous layer β were used and overlapped to form the fiber layer J/the porous layer β, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measure in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and the improvement range was small and poor.

The fiber layer F as the first fiber layer and the porous layer β were used and overlapped to form the fiber layer F/the porous layer β, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the result was that no improvement tendency was observed in the intermediate-frequency range, although the improvement range was <NUM> or more in the low-frequency range.

The configurations of examples <NUM> to <NUM> and comparative examples <NUM> to <NUM> are summarized in Table <NUM>, the vertical incidence sound absorption coefficients are summarized in Table <NUM>, and the improvement ranges of the sound absorption coefficient are summarized in Table <NUM>.

The fiber layer A as the first fiber layer and the porous layer β as the porous layer were used and overlapped to form the fiber layer A/the porous layer β/the fiber layer B, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient with respect to that of comparative example <NUM> (only the porous layer β) was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer D as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β as the porous layer were used and overlapped to form the fiber layer D/the porous layer β/the fiber layer K, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer E as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β as the porous layer were used and overlapped to form the fiber layer E/the porous layer β/the fiber layer K, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measure in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer G as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β as the porous layer were used and overlapped to form the fiber layer G/the porous layer β/the fiber layer K, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer M as the first fiber layer, the fiber layer N as the second fiber layer, and the porous layer β as the porous layer were used and overlapped to form the fiber layer M/the porous layer β/the fiber layer N, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient from that of a sample of comparative example <NUM> in which the fiber layer is not present was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer A as the first fiber layer, the fiber layer B as the second fiber layer, and the porous layer ζ as the porous layer were used and overlapped to form the fiber layer A/the porous layer ζ/the fiber layer B, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer G as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer ζ were used and overlapped to form the fiber layer G/the porous layer ζ/the fiber layer K, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer A as the first fiber layer, the fiber layer B as the second fiber layer, and the porous layer η were used and overlapped to form the fiber layer A/the porous layer η/the fiber layer B, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range and <NUM> or more in the intermediate-frequency range, and these were satisfactory.

The fiber layer J as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β were used and overlapped to form the fiber layer J/the porous layer β/the fiber layer K, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the result was that the improvement range was <NUM> or more in the low-frequency range and no improvement tendency was observed in the intermediate-frequency range.

The fiber layer F as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β were used and overlapped to form the fiber layer F/the porous layer β/the fiber layer K, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. A sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range. When a difference of the sound absorption coefficient with respect to that of comparative example <NUM> was taken and an improvement range was calculated, the result was that no improvement tendency was observed in both the low-frequency range and the intermediate-frequency range, although the improvement range in the low-frequency range was <NUM> or more and was satisfactory.

The configurations of examples <NUM> to <NUM> and comparative examples <NUM> and <NUM> are summarized in Table <NUM>, the vertical incidence sound absorption coefficients are summarized in Table <NUM>, and the improvement ranges of the sound absorption coefficient are summarized in Table <NUM>.

The fiber layer A as the first fiber layer, the fiber layer B as the second fiber layer, and the porous layer β and the porous layer γ as the porous layers were used and overlapped to form the fiber layer A/the porous layer β/the fiber layer B/the porous layer γ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range, <NUM> or more in the intermediate-frequency range, and <NUM> or more in the high-frequency range, and these were satisfactory.

The fiber layer D as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β and the porous layer γ as the porous layers were used and overlapped to form the fiber layer D/the porous layer β/the fiber layer K/the porous layer γ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range, <NUM> or more in the intermediate-frequency range, and <NUM> or more in the high-frequency range, and these were satisfactory.

The fiber layer E as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β and the porous layer γ as the porous layers were used and overlapped to form the fiber layer E/the porous layer β/the fiber layer K/the porous layer γ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range, <NUM> or more in the intermediate-frequency range, and <NUM> or more in the high-frequency range, and these were satisfactory.

The fiber layer G as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β and the porous layer γ as the porous layers were used and overlapped to form the fiber layer G/the porous layer β/the fiber layer K/the porous layer γ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range, <NUM> or more in the intermediate-frequency range, and <NUM> or more in the high-frequency range, and these were satisfactory.

The fiber layer A as the first fiber layer, the fiber layer B as the second fiber layer, and the porous layer ζ and the porous layer θ as the porous layers were used and overlapped to form the fiber layer A/the porous layer ζ/the fiber layer B/the porous layer θ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range, <NUM> or more in the intermediate-frequency range, and <NUM> or more in the high-frequency range, and these were satisfactory.

The fiber layer G as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer ζ and the porous layer θ as the porous layers were used and overlapped to form the fiber layer G/the porous layer ζ/the fiber layer K/the porous layer θ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range, <NUM> or more in the intermediate-frequency range, and <NUM> or more in the high-frequency range, and these were satisfactory.

The fiber layer A as the first fiber layer, the fiber layer B as the second fiber layer, and the porous layer η and the porous layer κ as the porous layers were used and overlapped to form the fiber layer A/the porous layer η/the fiber layer B/the porous layer κ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated, the improvement range was <NUM> or more in the low-frequency range, <NUM> or more in the intermediate-frequency range, and <NUM> or more in the high-frequency range, and these were satisfactory.

The fiber layer J as the first fiber layer, the fiber layer K as the second fiber layer, and the porous layer β and the porous layer γ as the porous layers were used and overlapped to form the fiber layer J/the porous layer β/the fiber layer K/the porous layer γ, which was cut out into a circle having a diameter of <NUM> to prepare a sample for sound absorption coefficient measurement. When a sound absorption coefficient thereof was measured in the low-frequency range, the intermediate-frequency range, and the high-frequency range, a difference of the sound absorption coefficient compared to that of comparative example <NUM> was taken, and an improvement range was calculated, although the improvement range was <NUM> or more in the intermediate-frequency range and <NUM> or more in the high-frequency range and these were satisfactory, the improvement range in the low-frequency range was <NUM> or more and was poor.

The configurations of examples <NUM> to <NUM> and comparative example <NUM> are summarized in Table <NUM>, the vertical incidence sound absorption coefficients are summarized in Table <NUM>, and the improvement ranges of the sound absorption coefficient are summarized in Table <NUM>.

Claim 1:
A laminated sound absorbing material comprising at least a fiber layer and a porous layer, wherein
the fiber layer has a mean flow pore size of <NUM> to <NUM>,
the porous layer is a layer formed of at least one selected from the group consisting of a foamed resin, a nonwoven fabric, and a woven fabric, has a thickness of <NUM> to <NUM>, and a density of the porous layer is lower than a density of the fiber layer, and the density of the porous layer is <NUM> to <NUM>/m<NUM>
the fiber layer is disposed on a sound incidence side, and
the laminated sound absorbing material is characterized in:
an air permeability of the fiber layer is <NUM> to <NUM> cc/cm<NUM>·s by the Frazier method.