JP7793149B2 - Sound-absorbing wall structure - Google Patents

Description

The present invention relates to a sound-absorbing wall structure.

A known sound-absorbing material is made up of a filling containing at least polyester-based resin fibers and a skin material enclosing the filling, with the skin being made of a nonwoven fabric containing polypropylene-based resin fibers (see, for example, Patent Document 1). The sound absorption coefficient of this sound-absorbing material is resistant to deterioration even in moist environments.

International Publication No. 2021/251279

In recent years, there has been a demand for sound-absorbing wall structures that have low carbon dioxide emissions from crude oil extraction to product disposal (hereinafter also referred to as carbon dioxide emissions during manufacturing, etc. In the present invention, carbon dioxide emissions during manufacturing, etc. refer to the sum of carbon dioxide emissions during manufacturing from crude oil extraction to sound-absorbing material production and carbon dioxide emissions during sound-absorbing material disposal). Reducing the amount of resin used as the sound-absorbing material is effective in reducing carbon dioxide emissions during manufacturing, etc. However, simply reducing the amount of resin used tends to reduce sound-absorbing performance. Furthermore, it has been found that reducing the amount of resin used generally reduces the rigidity of the sound-absorbing material, causing problems such as the sound-absorbing material being crushed by external pressure, or even if the sound-absorbing material is uniformly arranged during manufacturing, this uniform arrangement is not maintained later due to its own weight, resulting in uneven distribution of the resin (filling) in the direction of gravity, which tends to result in a decrease in sound absorption coefficient.
In addition, sound-absorbing panels fixed to sound-absorbing wall structures are replaced due to deterioration of the sound-absorbing material. In order to reduce carbon dioxide emissions from the manufacture of sound-absorbing panels, it is important to not only suppress carbon dioxide emissions during the manufacture of sound-absorbing panels, but also to extend the life cycle of the sound-absorbing material. It has been found that deterioration of sound-absorbing material tends to progress when the air space behind the soundproof wall and sound-absorbing material becomes humid.

The problem that this invention aims to solve is to provide a sound-absorbing wall structure that emits less carbon dioxide during manufacturing, has improved durability for a longer replacement cycle, and is equipped with sound-absorbing material with a high sound absorption rate.

The inventors of the present invention conducted extensive research in light of the above-mentioned problems and discovered that a sound-absorbing material consisting of a filling containing a specific nonwoven fabric containing two or more types of thermoplastic resin fibers and a skin material enclosing the filling emits little carbon dioxide during manufacturing and exhibits high sound absorption properties. This invention was completed based on these findings.

The present invention relates to a sound-absorbing wall structure in which a sound-absorbing panel, which is a frame containing sound-absorbing material, is fixed to a wall surface erected along a railway track or to a support pillar having a pair of flanges facing each other, the sound-absorbing material comprising a filling and a skin material that encases the filling, the filling being a nonwoven fabric containing two or more types of thermoplastic resin fibers, the thermoplastic resin fibers having different fiber diameters, the sum of the surface areas of the outer diameters of the filling fibers per unit area of the filling being 150 to 270 m/m, the skin material being a nonwoven fabric containing polypropylene-based resin fibers, and the clearance between the sound-absorbing panel and the sound- absorbing wall being 5 to 200 mm.
The sum of the surface areas of the outer diameters of the fill fibers per unit area of the fill is preferably 200 to 270 ^{m 2} /m ² .
The filling preferably contains at least one thermoplastic resin fiber selected from the group consisting of fine fibers having a fiber diameter of 10 μm or more and less than 20 μm, medium-thick fibers having a fiber diameter of 20 to 30 μm, and extra-thick fibers having a fiber diameter of 40 to 50 μm.
The filling more preferably includes at least one hollow thermoplastic resin fiber selected from the group consisting of the medium-thick fibers and the extra-thick fibers.
The filling preferably contains thermoplastic resin hollow fibers, and the content of the thermoplastic resin hollow fibers in the filling is preferably 30% by mass or more.
The content of the fine fibers in the filling is preferably 50% by mass or more.
The facing material preferably includes a first spunbond nonwoven fabric, a meltblown nonwoven fabric adjacent to the first spunbond nonwoven fabric, and a second spunbond nonwoven fabric adjacent to the meltblown nonwoven fabric.In another embodiment, the facing material preferably includes a first spunbond nonwoven fabric, a meltblown nonwoven fabric adjacent to the first spunbond nonwoven fabric, a second spunbond nonwoven fabric adjacent to the meltblown nonwoven fabric, and a third spunbond nonwoven fabric adjacent to the second spunbond nonwoven fabric.
At least one selected from the group consisting of the first spunbond nonwoven fabric, the second spunbond nonwoven fabric, and the third spunbond nonwoven fabric preferably contains fibers having an average fiber diameter in the range of 25 to 50 μm.
The meltblown nonwoven preferably comprises fibers with an average fiber diameter in the range of 0.5 to 5 μm.
At least one selected from the group consisting of the first spunbond nonwoven fabric, the second spunbond nonwoven fabric, and the third spunbond nonwoven fabric preferably contains hollow fibers.
The amount of sagging of the padding, as measured by the following test method, is preferably 75 mm or less.
The filling, which is 500 mm wide, 1000 mm long, and 50 mm thick, is placed on the top of a desk that is 500 mm wide or more and 1000 mm long or more and placed on a horizontal floor, so that the length of the filling and the length of the desk are parallel, the filling is contained in the width direction of the desk, and the filling extends 600 mm beyond one side of the length of the desk, and the distance from the floor to the top of the desk and the distance from the floor to the bottom of the tip of the filling sample are measured.
Drooping amount = distance from floor to desk top - distance from floor to bottom of tip of batting sample The carbon dioxide emissions of the skin material and the batting, calculated in accordance with the calculation method for the 3R basic unit reported by the Recycling Society Promotion Office, Planning Division, Waste Management Department, Ministry of the Environment, are preferably 8.0 kg/ ^m2 or less.

The sound-absorbing wall structure of the present invention emits less carbon dioxide during manufacturing, has improved durability for a longer replacement cycle, and is equipped with sound-absorbing material that exhibits high sound absorption properties.

1 is a cross-sectional view of a first embodiment of a sound-absorbing material provided in a sound-absorbing wall structure. FIG. FIG. 4 is a cross-sectional view of a second embodiment of a sound-absorbing material provided in the sound-absorbing wall structure. 1 is a cross-sectional view of one embodiment of an acoustical panel. FIG. 1 is an explanatory diagram showing an example of the configuration of a sound-absorbing wall structure of the present invention. FIG. 10 is an explanatory diagram showing another example of the sound-absorbing wall structure of the present invention. FIG. 10 is an explanatory diagram showing another example of the sound-absorbing wall structure of the present invention.

The present invention will now be described in further detail.
Unless otherwise specified, the "to" in a numerical range means from above to below, and both end values are included. Furthermore, when a numerical range is indicated, the upper and lower limits can be combined as appropriate, and the resulting numerical range is also considered to be disclosed.
Furthermore, in the description of the drawings, the same elements are denoted by the same reference numerals, and duplicate explanations will be omitted. Also, the dimensional proportions of the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

Figure 1 is a cross-sectional view of a first embodiment of a sound-absorbing material provided in a sound-absorbing wall structure of the present invention. The sound-absorbing material 1 of this embodiment consists of a padding 2 and a single skin 3 that is provided on both the front and back sides (upper and lower layers) of the padding 2 and encases the padding 2. The padding 2 is sandwiched between the skin 3 that is folded in half, and the skin 3 has seals 4 on three sides of its periphery. As a result, the padding 2 is surrounded by the folded parts of the skin 3 and the seals 4, and is encased in the skin 3.

Note that the filling 2 only needs to be enclosed within the skin material 3, and the configuration in which the filling 2 is enclosed within the skin material 3 is not limited to the configuration shown in Figure 1.

For example, as shown in Figure 2, the second embodiment of the sound-absorbing material provided in the sound-absorbing wall structure of the present invention may be configured to include padding 2 and two skins 3, 3 provided on both the front and back sides (upper and lower layers) of the padding 2 and enclosing the padding 2, with the skins 3, 3 having a sealing portion 4 on their periphery that surrounds the padding 2.

The basis weight of the sound-absorbing material 1 is preferably in the range of 500 to 3000 g/m2, more preferably in the range of 1000 to 2500 g/m2, and even more preferably in the range of 1300 to 2200 g/ ^m2 , from the viewpoint of further improving the sound absorption coefficient mainly in the range of 100 to 2000 ^Hz in consideration of the rolling noise and aerodynamic noise that are the target noise sources under the Shinkansen, and from the viewpoint of preventing a decrease in workability due to an increase in the weight of the sound-absorbing material. From the viewpoint of reducing carbon dioxide emissions, the basis weight of the sound-absorbing material ¹ is particularly preferably in the range of 1300 to 1800 g/ ^m2 . Furthermore, from the viewpoint of ensuring the strength of the structure that supports the sound-absorbing material, the basis weight of the sound-absorbing material 1 is most preferably in the range of 1300 to 1700 g/ ^m2 .

The thickness of the sound-absorbing material 1 is preferably in the range of 10 to 100 mm, more preferably in the range of 20 to 70 mm, from the perspective of further improving the sound absorption coefficient in the low-frequency range, particularly in the 100 to 1000 Hz range, and from the perspective of ensuring efficient space when installed in a sound-absorbing wall structure.

<Filling>
The sound-absorbing material of the sound-absorbing wall structure of the present invention comprises a padding, which is a nonwoven fabric containing two or more types of thermoplastic resin fibers, the fiber diameters of which are different from each other.

The thermoplastic resin constituting the thermoplastic resin fiber is not limited to a specific thermoplastic resin, and examples of the thermoplastic resin include the following thermoplastic resins.
(1) Biodegradable resins such as polylactic acid, polyhydroxyalkanoate, polybutylene succinate, cellulose acetate, polyvinyl alcohol, polyglycolic acid, polybutylene succinate-co-adipate, polybutylene adipate terephthalate, and polyethylene terephthalate succinate;
(2) Various polyolefin resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high-density polyethylene, polypropylene, polymethylpentene, and copolymers thereof;
(3) chlorine-containing resins such as polyvinyl chloride (PVC) and polyvinylidene chloride (PVdC);
(4) Fluorine-containing resins such as tetrafluoroethylene resins, ethylene-tetrafluoroethylene copolymer resins, perfluoroethylenepropene copolymer resins, polychlorotrifluoroethylene resins, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer resins;
(5) Addition-type thermoplastic resins other than the addition-type thermoplastic resins shown in (1) to (4), such as ethylene vinyl acetate resin, polymethyl methacrylate (PMMA) resin, polystyrene-based resin, ABS resin, and AS resin;
(6) Various polyamide resins such as nylon 6, nylon 66, nylon 12, nylon 11, metaxylylene adipamide (mXD6), hexamethylene terephthalamide (6T), and copolymers thereof;
(7) polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalate (PEN), polybutylene naphthalate (PBN), polyethylene isophthalate (PEI), polybutylene isophthalate (PBI), polyhexamethylene terephthalate (PHT), polyhexamethylene isophthalate (PHI), polyhexamethylene naphthalate (PHN), polymethylene terephthalate (PMT), polypropylene terephthalate (PPT), Polyesters (excluding biodegradable polyesters) copolymerized with polyethylene-p-oxybenzoate (PEOB), poly-1,4-cyclohexylene dimethylene terephthalate (PCT), and copolymerization components such as diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, and dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, and various polyester resins such as liquid crystal polyesters,
(8) Condensation thermoplastic resins other than the condensation thermoplastic resins shown in (6) and (7), such as polyamide-imide resin, thermoplastic polyimide, thermoplastic polyurethane, polycarbonate resin, polyacetal (POM) resin, polyetherimide (PEI) resin, polyphenylene ether (PPE) resin, polyether ether ketone (PEEK) resin, and polyphenylene sulfide (PPS) resin.

The filling may be, for example, a nonwoven fabric containing polyester (polyethylene terephthalate) resin fibers and polypropylene resin fibers.

The basis weight of the fill is preferably in the range of 400 to 2900 g/m², more preferably in the range of 900 to 2400 g/ ^m² , and even more preferably in the range of 1200 to 2100 g/ ^m² , from the viewpoint of further improving the sound absorption coefficient mainly in the 100 to 2000 Hz range and preventing a decrease in workability due to an increase in the weight of the sound-absorbing material. From the viewpoint of reducing carbon dioxide emissions, the basis weight of the fill is particularly preferably in the range of 1200 to 1800 ^g / ^m² . Furthermore, from the viewpoint of ensuring the strength of the fill structure that supports the sound-absorbing material, the basis weight of the fill is most preferably in the range of 1200 to 1400 g/ ^m² . If the basis weight of the fill is small, the fill (resin) tends to be unevenly distributed due to its own weight, so it is particularly important to set the sum of the surface areas of the outer diameters of the fill fibers per unit area, as described below, within a predetermined range.

The polyester (polyethylene terephthalate) resin fibers and the polypropylene resin fibers may be produced by known melt spinning methods, or may be commercially purchased. The polyester (polyethylene terephthalate) resin fibers may have, for example, an average fiber length in the range of 10 to 100 mm and an average fiber diameter in the range of 10 to 70 μm. The polypropylene resin fibers may have, for example, an average fiber length in the range of 10 to 100 mm and an average fiber diameter in the range of 10 to 50 μm. The fiber diameters of the polyester (polyethylene terephthalate) resin fibers and the polypropylene resin fibers may differ.

From the perspective of further improving the sound absorption coefficient, the ratio of polyester-based resin fibers to polypropylene-based resin fibers in the nonwoven fabric molding is preferably in the range of 99:1 to 5:95 by mass (polyester-based resin fibers:polypropylene-based resin fibers), more preferably in the range of 95:5 to 10:90, and even more preferably in the range of 80:20 to 20:80.

The nonwoven fabric molding can be obtained, for example, by mixing 1 to 95% by mass, e.g., 20% by mass, of the polypropylene-based resin fibers, 99 to 5% by mass, e.g., 30% by mass, of polyester (polyethylene terephthalate) binder fibers using a binder resin, and 99 to 5% by mass, e.g., 50% by mass, of polyester fibers using a resin other than the binder resin, forming a web using a fiber opener and then a carding machine, laminating the resulting web in multiple layers using a cross-layer machine, and treating it with a hot air treatment machine set to a predetermined gap distance to fuse the polyester (polyethylene terephthalate) binder fibers and the polypropylene-based resin fibers.

The polypropylene-based resin may be a homopolymer of propylene, or a copolymer with another α-olefin copolymerizable with propylene. Examples of the α-olefin include α-olefins having 2 or more carbon atoms, preferably 2 to 8 carbon atoms, such as ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene. When the polypropylene-based resin is a copolymer of propylene and an α-olefin, it may be a copolymer with one or more α-olefins selected from the above α-olefins. The polypropylene-based resin may have an MFR (melt flow rate) in the range of, for example, 1 to 500 g/min.

The polyester (polyethylene terephthalate) binder fiber can be, for example, one having a polyethylene terephthalate core and a binder component in the sheath. Examples of the binder component include copolymer polyesters consisting of terephthalic acid or its ester-forming derivatives, isophthalic acid or its ester-forming derivatives, lower alcohols, and polyalkylene glycols or their monoethers.

To achieve the effects of the present invention, when combining multiple fibers used in the padding, the sum of the surface areas of the outer diameters of the padding fibers per unit area of the multiple fibers used in the padding is set to a specific range. The sum of the surface areas of the outer diameters of the padding fibers per unit area of the padding is 150 to 270 m ² /m ² , preferably 200 to 270 m ² /m ² . If the sum of the surface areas is less than 150 ^m 2 /m ² , the sound absorption properties of the sound-absorbing material will be reduced. On the other hand, if the sum of the surface areas is greater than 270 m ² /m ² , the amount of carbon dioxide emitted during the production of the sound-absorbing material will increase. It is important to maintain the above numerical range in order to further improve the sound absorption coefficient mainly in the 100 to 2000 Hz range while reducing carbon dioxide emissions.

The total surface area is calculated, for example, as follows: For each fiber constituting the filling, the surface area of the outer diameter of the filling fiber per unit area of the filling is calculated according to the following formula (1), and the total of all fibers is taken as the total surface area. For hollow fibers, the outer diameter of the fiber cross section (n=10) is measured using an electron microscope and the average value is calculated. For the denier, the denier value listed in the fiber product specifications is used.
Surface area of outer diameter of filling fiber per unit area of filling (m ² /m ² )=fiber diameter (outer diameter μm)/10 ⁶ ×3.14×9000 (m)/denier (g)×basis weight (g/m ² )×content (mass %)/100 (1)

For low-carbon dioxide emission padding, combining multiple fibers with specific fiber diameters produces better results. The padding is preferably a nonwoven fabric containing fine fibers with a fiber diameter of 10 μm or more but less than 20 μm, and at least one thermoplastic resin fiber selected from the group consisting of medium-thick fibers with a fiber diameter of 20 to 30 μm and extra-thick fibers with a fiber diameter of 40 to 50 μm. The inventors have discovered that a padding containing the fine fibers and at least one fiber selected from the group consisting of the medium-thick fibers and the extra-thick fibers can better prevent uneven distribution of the padding (resin) than a padding containing only the fine fibers. Combining multiple fibers with specific fiber diameters is useful for achieving good sound absorption performance with a padding with low carbon dioxide emission.
The at least one thermoplastic resin fiber selected from the group consisting of the medium-thick fibers and the extra-thick fibers preferably includes hollow fibers. Hollow fibers tend to have a high degree of fiber orientation and therefore high fiber strength, and therefore contribute to ensuring the strength of the padding structure that supports the sound-absorbing material when reducing the basis weight of the sound-absorbing material or padding. The inventors have found that, among other things, it is preferable that a portion of the medium-thick fibers or the extra-thick fibers be hollow fibers.

The filling preferably contains thermoplastic resin hollow fibers, and the content of the thermoplastic resin hollow fibers in the filling is 30% by mass or more. When the content of the thermoplastic resin hollow fibers in the filling is within this range, the amount of resin used in the sound-absorbing material is reduced. Furthermore, even if the basis weight of the sound-absorbing material or the filling is reduced, the strength of the filling structure that supports the sound-absorbing material can be ensured.

The content (total) of the medium-thick fibers and the extra-thick fibers is preferably 25% by mass or more. This ensures the strength of the padding structure that supports the sound-absorbing material and prevents uneven distribution of the padding. The upper limit can be set appropriately depending on the required performance, but from the perspective of further improving the sound absorption coefficient, it is preferably less than 60% by mass, and more preferably 50% by mass or less.
Furthermore, the content of the fine fibers in the filling is preferably 50% by mass or more and 80% by mass or less. When the content of the fine fibers in the filling is within this range, all of the following are satisfied: further improving the sound absorption coefficient mainly in the 100 to 2000 Hz range; preventing a decrease in workability due to an increase in the weight of the sound-absorbing material; reducing carbon dioxide emissions; and ensuring the strength of the filling structure that supports the sound-absorbing material and the sound-absorbing material. From these perspectives, it is more preferable that the content of the fine fibers in the filling is 55% by mass or more and 75% by mass or less.

The filling may include composite fibers, irregular fibers, crimped fibers, split fibers, etc. The filling may also include heat stabilizers, ultraviolet absorbers, weather stabilizers, flame retardants, water repellents, oils, antistatic agents, colorants, inorganic substances, etc.

<Skin material>
The skin material is made of a nonwoven fabric containing fibers made of a thermoplastic resin. From the viewpoint of further preventing contact between the filling and water, the skin material preferably has a water pressure resistance in the range of 200 to 2000 mmH ₂ O, more preferably a water pressure resistance in the range of 200 to 500 mmH ₂ O, even more preferably a water pressure resistance in the range of 250 to 450 mmH ₂ O, and particularly preferably a water pressure resistance in the range of 280 to 400 mmH ₂ O. The water pressure resistance of the skin material can be further increased by, for example, at least one technique selected from the group consisting of reducing the average fiber diameter of the fibers constituting the skin material, increasing the density of the skin material, using fibers made of a polypropylene resin, and increasing the basis weight of the skin material.
Furthermore, in order to improve the durability of the skin material, the back side of the skin material, which is prone to deterioration, is protected.

The air permeability of the skin material is preferably in the range of 5 to 200 cm 3 /cm 2 /sec, more preferably in the range of 7 to 150 cm ³ /cm ² /sec, and even more preferably in the range of 10 to 50 cm ³ /cm ² /sec, from the viewpoint of further improving the water pressure resistance and further preventing contact between the padding and water, and from the viewpoint of appropriately transmitting sound waves to ^{the padding} side and maintaining a good sound absorption coefficient.

The thickness of the skin material is preferably in the range of 0.1 to 1.5 mm, and more preferably in the range of 0.3 to 1.0 mm, from the viewpoints of further improving water pressure resistance and further preventing contact between the padding and water, maintaining strength such as shot blast resistance, preventing the material from being too thick and hindering the transmission of sound waves to the padding, and preventing the material from being too thick and reducing the workability of ultrasonic sealing, etc.

The average fiber diameter of the fibers located near the surface of the skin material (hereinafter sometimes referred to as the surface fiber diameter) is preferably in the range of 10 to 100 μm from the viewpoint of ensuring the strength of the structure supporting the sound-absorbing material, and is preferably in the range of 20 to 100 μm, and more preferably in the range of 25 to 50 μm, from the viewpoint of further improving shot blast resistance and controlling air permeability within an appropriate range. Furthermore, from the viewpoint of further improving shot blast resistance, it is particularly preferable for the surface fiber diameter to be in the above range for fibers made of polypropylene-based resin.

The polypropylene-based resin used in the nonwoven fabric constituting the skin material, like the polypropylene-based resin used in the filling, may be a propylene homopolymer or a copolymer of propylene with another α-olefin copolymerizable with propylene. As with the polypropylene-based resin used in the filling, one or more α-olefins may be used as the α-olefin.

The fibers that make up the skin material may contain heat stabilizers, UV absorbers, weather stabilizers, flame retardants, water repellents, oils, antistatic agents, colorants, inorganic substances, etc.

The polypropylene resin used in the nonwoven fabric that makes up the skin material can have an MFR (melt flow rate) in the range of 10 to 100 g/min. In the sound-absorbing material 1, the skin material 3 has a water pressure resistance within this range, and the interior is sealed with the sealing section 4, so the padding 2 does not come into contact with water, and the sound absorption rate is less likely to decrease even in humid environments.

The skin material may be a single layer of nonwoven fabric, or a laminated nonwoven fabric in which multiple nonwoven fabrics are laminated. The nonwoven fabric constituting the skin material 3 is not limited to a specific nonwoven fabric, and may be at least one type selected from the group consisting of spunbond nonwoven fabric and meltblown nonwoven fabric. From the viewpoint of further improving strength, such as shot blast resistance, as a sound absorbing material, the skin material preferably contains at least one layer of spunbond nonwoven fabric. Furthermore, from the viewpoint of controlling water pressure resistance and air permeability within preferred ranges, the skin material preferably contains at least one layer of meltblown nonwoven fabric. Spunbond nonwoven fabric and meltblown nonwoven fabric are distinguished by their average fiber diameter. In an embodiment herein, the average fiber diameter of spunbond nonwoven fabric may be in the range of 10 to 100 μm, and the average fiber diameter of meltblown nonwoven fabric may be in the range of 0.5 to 5 μm.

The smaller (thinner) the average fiber diameter of the fibers making up the nonwoven fabric contained in the skin material, the denser the material and the better its water pressure resistance. On the other hand, from the standpoint of abrasion resistance (shot blast resistance) against impacts from solid objects such as hail, sleet, and pebbles, it is desirable for the average fiber diameter of the fibers to be large (thick). Furthermore, the average fiber diameter of fibers contained in spunbond nonwoven fabrics is larger than the average fiber diameter of fibers contained in meltblown nonwoven fabrics.

Therefore, the skin material may have at least a three-layer structure (hereinafter, this three-layer structure may be referred to as an SMS structure or PP-SMS structure) consisting of, for example, a first spunbond nonwoven fabric containing fibers made of polypropylene-based resin with an average fiber diameter in the range of 10 to 50 μm, a meltblown nonwoven fabric containing fibers made of polypropylene-based resin with an average fiber diameter in the range of 0.5 to 5 μm and positioned on the first spunbond nonwoven fabric, and a second spunbond nonwoven fabric containing fibers made of polypropylene-based resin with an average fiber diameter in the range of 10 to 50 μm and positioned on the meltblown nonwoven fabric. The skin material may also further include a third spunbond nonwoven fabric containing fibers made of polypropylene-based resin with an average fiber diameter in the range of 25 to 50 μm. Alternatively, the skin material may consist solely of one of the first, second, or third spunbond nonwoven fabric layers. Here, "consisting only of a spunbond nonwoven fabric layer" means that it does not include nonwoven fabrics manufactured by other manufacturing methods, such as meltblown nonwoven fabrics, and does not exclude the inclusion of multiple layers of the same or different spunbond nonwoven fabrics.

When the skin material 3 has a structure of at least three layers as described above, the meltblown nonwoven fabric forming the inner layer has a small average fiber diameter, making it dense and ensuring the above-mentioned range of water pressure resistance. On the other hand, the meltblown nonwoven fabric contains fibers with a small average fiber diameter, which can easily become fuzzy and have poor shot blast resistance. Therefore, by using the first or second spunbond nonwoven fabric as the outer layer, the meltblown nonwoven fabric can be protected and tends to have better shot blast resistance.

Furthermore, the skin material 3 may have at least a four-layer structure (hereinafter, the four-layer structure may be referred to as an SSMS structure or a PP-SMSS structure) including a third spunbond nonwoven fabric containing fibers with an average fiber diameter in the range of 10 to 100 μm positioned on the second spunbond nonwoven fabric. By providing the third spunbond nonwoven fabric on the outermost surface, the skin material 3 can achieve superior shot blast resistance. The third spunbond nonwoven fabric preferably has an average fiber diameter in the range of 25 to 50 μm and a basis weight in the range of 70 to 150 g/ ^m² . Furthermore, from the viewpoints of further improving the sound absorption coefficient mainly in the 100 to 2000 Hz range, preventing a decrease in workability due to an increase in the weight of the sound-absorbing material, reducing carbon dioxide emissions, and further ensuring the strength of the padding structure that supports the sound-absorbing material, it is preferable to use a third spunbond nonwoven fabric in the above-mentioned range that uses fibers made of polypropylene resin.

Furthermore, when the skin material 3 consists solely of a spunbond nonwoven fabric layer, it can achieve both the water pressure resistance and the sound absorption coefficient within the ranges by including, for example, any one of the first to third spunbond nonwoven fabrics having an average fiber diameter in the range of 10 to 100 μm and a basis weight in the ^range of 70 to 200 g/m2. The spunbond nonwoven fabric layer may consist of a single layer or multiple layers of the third spunbond nonwoven fabric, and another spunbond nonwoven fabric may be laminated on the third spunbond nonwoven fabric.

Furthermore, when the skin material 3 consists solely of a spunbond nonwoven fabric layer, excellent shot blast resistance tends to be achieved by setting the average fiber diameter of the fibers located near the surface (hereinafter sometimes referred to as the surface fiber diameter) in the range of 20 to 100 μm, for example, in the range of more than 30 μm and less than 50 μm. For example, in the case of the spunbond nonwoven fabric layer, the surface fiber diameter can be set within this range by embossing (thermocompression bonding) the embossing roll at a temperature of 140 to 170°C and the mirror roll at a temperature of 140 to 170°C, and achieving a fusion area ratio of 15% or more. This promotes fusion between fibers in non-embossed areas, thereby increasing the apparent fiber diameter. For the same reason, shot blast resistance can be improved by setting the fusion area ratio during embossing to 20% or more, or by using an embossed pattern measuring 0.7 mm square or larger, even with the same fusion area ratio.

The spunbond nonwoven fabric can be produced using a known spunbond nonwoven fabric molding machine. More specifically, the spunbond nonwoven fabric can be produced, for example, by melting the raw material polypropylene resin using an extruder, discharging the molten composition from multiple spinnerets, cooling and stretching the fibrous resin as needed, depositing it on a collection surface, and subjecting it to a heat and pressure treatment using an embossing roll.

The meltblown nonwoven fabric can be produced using a known meltblown nonwoven fabric molding machine. More specifically, meltblown nonwoven fabric can be produced, for example, by melting the raw material polypropylene resin, discharging it from a spinning nozzle, and pulling it with high-temperature, high-pressure gas to form polypropylene meltblown fibers, which are then collected and deposited on a collector such as a perforated belt or perforated drum.

The sealed portions 4 may be formed by thermocompression or ultrasonic sealing. The sealed portions 4 may be formed continuously around the peripheral edges of the skin materials 3, 3 so as to surround the padding 2, or may be formed intermittently. If the sealed portions 4 are formed intermittently, it is preferable that multiple parallel sealed portions 4 are formed so that the discontinuous portions of one sealed portion 4 are complemented by the continuous portions of other sealed portions 4.

The water pressure resistance of the seal portion 4 is not particularly limited as long as the effects of the present invention are achieved, but from the viewpoint of further suppressing water intrusion, it is preferably 100 mmH ₂ O or more, more preferably 150 mmH ₂ O or more, even more preferably 200 mmH ₂ O or more, particularly preferably 250 mmH ₂ O or more, and most preferably 300 mmH ₂ O or more. The upper limit of the water pressure resistance of the seal portion 4 is not particularly limited, but can be, for example, 2000 mmH ₂ O or less, 1000 mmH ₂ O or less, or 500 mmH ₂ O or less.

Sealing conditions are not particularly limited, but in the case of ultrasonic sealing, they can be adjusted as desired by adjusting the sealing pressure, output voltage, sealing time, sealing pattern, etc. If the seal is too strong, the water pressure resistance tends to decrease, so by appropriately adjusting the above factors, it is possible to maintain good water pressure resistance.

The width of the seal portion 4 is not particularly limited, but is preferably in the range of 0.1 to 5.0 mm from the perspective of further improving the water pressure resistance of the seal portion while preventing tearing. The width of the seal portion 4 can be, for example, 0.3 mm.

In the sound-absorbing material, it is preferable that the sagging amount of the filling, measured by the following test method, be 75 mm or less, from the perspective of reducing carbon dioxide emissions while maintaining sound absorption performance. Having a certain degree of rigidity in the filling is useful for preventing deformation of the sound-absorbing material due to external pressure and maintaining sound absorption performance. The sagging amount is more preferably 20 mm or more and 75 mm or less, and even more preferably 40 mm or more and 75 mm or less. The inventors have found that when the sagging amount is within the above range, the filling of the sound-absorbing material can be stored for long periods of time without becoming unevenly distributed due to its own weight.

From the viewpoint of reducing carbon dioxide emissions while maintaining sound absorption performance, it is preferable that the sound-absorbing material has carbon dioxide emissions of the skin and the padding of 5.0 to 8.0 kg/ ^m2 , calculated in accordance with the calculation method for 3R basic units reported by the Recycling-Based Society Promotion Office, Planning Division, Waste Management Department, Ministry of the Environment.

<Sound-absorbing panel>
Next, one embodiment of the sound-absorbing panel of the present invention will be described with reference to FIG.
As shown in Figure 3, the sound-absorbing panel 11 of this embodiment includes a sound-absorbing material 1 and a frame 14 that houses the sound-absorbing material 1. The frame 14 is a box-shaped body that includes a rectangular shielding plate 12 that forms the bottom and side walls 13 that rise from the four sides of the shielding plate 12, and has an open end at the top, and is equipped with a protective panel 15 that is placed at the open end of the frame 14 when the sound-absorbing material 1 is housed in the frame 14, and a support part 16 that is placed on the back surface of the frame 14 and supports the sound-absorbing panel 11 when the sound-absorbing panel 11 is attached to a building or the like.

The frame 14 may be formed by integrally forming the shielding plate 12, side wall 13, and support portion 16, or by connecting separate components. The material of the frame 14 is not particularly limited as long as it is durable against weather, moisture, etc., and can be made of metal or resin. Lightweight metals such as aluminum and stainless steel are preferably used.

The protective panel 15 preferably protects the sound-absorbing material 1 from solid objects such as hail, sleet, and pebbles while allowing sound waves to penetrate easily. For this reason, in this embodiment, a perforated plate with numerous through-holes 15a arranged on its surface is preferably used as the protective panel 15, but it is not limited to a perforated plate as long as it protects the sound-absorbing material 1 while allowing sound waves to penetrate easily. The total area of the through-holes 15a relative to the total surface area of the protective panel 15 is not particularly limited, but is, for example, in the range of 20% to 80%.

The material of the protective panel 15 is not particularly limited as long as it can protect the sound-absorbing material 1 and be durable against sound wave penetration, weather, moisture, etc., and can be made of metal or resin. Lightweight metals such as aluminum and stainless steel are preferably used.

<Method of manufacturing sound-absorbing material>
Next, a method for manufacturing the sound-absorbing material 1 of this embodiment shown in FIG. 1 or 2 will be described.
Examples of methods for fusing the ends include a method in which a heat source such as an iron is applied to heat the end pieces to melt the resin and then pressure bond the end pieces, an ultrasonic sealing method in which ultrasonic waves are applied to melt the resin while pressure bonding the end pieces, a laser welding method, a vibration welding method, a high-frequency welding method, and a hot plate welding method. Of these, the ultrasonic sealing method is preferred for fusing the end pieces.

There are no particular restrictions on the fusion temperature, as long as it is a temperature at which the resin of the skin material 3 can be fused. However, from the perspective of further improving water pressure resistance and preventing peeling at the fused portion, a temperature in the range of 130 to 160°C is preferred, and a temperature in the range of 140 to 155°C is even more preferred.

When the fusion process is performed using an ultrasonic sealing method, the output of the ultrasonic sealing device is not particularly limited as long as it can fuse the resin of the skin material 3, but it is preferably in the range of 1 to 5 V from the perspective of further improving water pressure resistance and preventing peeling of the fused portion (sealed portion 4). Furthermore, the pressure used for crimping is not particularly limited as long as it can fuse the resin of the skin material 3, but it is preferably in the range of 0.1 to 5 MPa from the perspective of further improving water pressure resistance and preventing peeling of the fused portion. Furthermore, the speed at which the fused portion is formed is preferably 1 to 30 m/min from the perspective of improving work efficiency while preventing peeling of the fused portion.

<Sound-absorbing wall structure>
The sound absorbing wall structure of this embodiment will be described with reference to Figures 4 to 6. The sound absorbing wall structure is preferably for use in railways.

First, as shown in Figure 4, as an example of a sound-absorbing wall structure of this embodiment, a structure in which sound-absorbing panels 11 are fixed to a wall surface 20 erected along railway tracks will be described. Note that erecting along railway tracks refers to erecting along railway tracks within railway premises.

When fixing a sound-absorbing panel 11 to a wall surface 20 made of concrete or other material, an L-shaped joint plate 21 made by bending a metal plate into an L shape is usually used.

The L-shaped joint plate 21 has a flat portion 21a that extends from the upper surface of the upper wall 13 or the lower surface of the lower wall 13 of the frame 14 of the sound-absorbing panel 11 to the wall surface 20, and a rising portion 21b that rises vertically at a position where it abuts against the wall surface 20.

The flat plate portion 21a is formed with a width greater than the width of the upper surface of the upper wall 13 or the lower surface of the lower wall 13 of the frame 14, so as to form a gap between the shielding plate 12 on the rear side of the sound-absorbing panel 11 and the wall surface 20. The gap on the rear side of the panel 11 may be covered with a reinforcing material or the like.

The flat plate portion 21a also has frame connecting holes 22, 22 at positions where it abuts against the upper surface of the upper wall 13 or the lower surface of the lower wall 13 of the frame 14 of the sound-absorbing panel 11. Fixing screws 23, 23 that are screwed into the upper surface of the upper wall 13 or the lower surface of the lower wall 13 of the frame 14 are inserted into the frame connecting holes 22, 22, and the L-shaped joint plate 21 and the sound-absorbing panel 11 are fastened together by the fixing screws 23, 23.

The rising portion 21b has a wall connection hole 24, for example, at its center, through which an anchor bolt 25 is inserted and driven into the wall 20, thereby fastening the L-shaped joint plate 21 to the wall 20.

The anchor bolts 25 may be driven into the wall surface 20 by embedding an anchor in the wall surface 20 in advance and then fastening the anchor bolts 25 to the anchor, or by fastening a no-plug anchor bolt 25, which does not require an anchor, directly into the wall surface 20.

Furthermore, when the sound-absorbing panels 11 are divided vertically into multiple tiers, L-shaped joint plates 21 may be provided on the upper surface of the upper wall 13 of the topmost sound-absorbing panel 11 and on the lower surface of the lower wall 13 of the bottommost sound-absorbing panel 11, and the sound-absorbing panels 11 in the middle tier may be connected to each other by connecting members that connect the upper and lower sound-absorbing panels.

Furthermore, the fastening position between the sound-absorbing panel 11 and the wall surface 20 by the L-shaped joint plate 21 may be at the left and right sides of the left and right side walls 13 of the sound-absorbing panel 11 in addition to or instead of the upper surface of the upper wall 13 or the lower surface of the lower wall 13 of the sound-absorbing panel 11.
The clearance between the sound absorbing panel 11 and the wall surface 20 is preferably 5 to 200 mm, more preferably 30 to 150 mm, and even more preferably 50 to 100 mm.

Next, we will explain another example of the sound-absorbing wall structure of this embodiment, shown in Figure 5.

When fixing the sound-absorbing panel 11 to a support 30 erected along a railway track, an S-shaped joint plate 31 (corresponding to the interposing member of the present invention) made by bending a metal plate into an S shape is used. Note that the support 30 is not limited to an H-beam having two pairs of flanges 30a, 30a, but may have at least one pair of flanges 30a, 30a.

The S-shaped joint plate 31 comprises a first flat portion 31a that is parallel to and abuts the front surface 15 of the sound-absorbing panel 11, a second flat portion 31b that is parallel to and abuts the flange a, and a vertical surface portion 31c that connects the first flat portion 31a and the second flat portion 31b with a plane perpendicular to each other.

A through-hole (not shown) is formed in the first flat portion 31a, passing through both the first flat portion 31a and the side wall 13 (more precisely, the front surface of the upper wall 13) of the sound-absorbing panel 11 at the same time, and the S-shaped joint plate 31 and the sound-absorbing panel 11 are fastened together by threading a bolt 32 inserted through the through-hole into a nut (not shown) provided on the side wall 13.

A through-hole (not shown) is formed in the second flat portion 31b, passing through both the second flat portion 31b and the flange 30a of the support 30 at the same time, and a bolt (not shown) provided on the flange 30a side is inserted into the through-hole and a nut 33 is screwed into place, thereby fastening the S-type joint plate 31 to the support 30.

The S-shaped joint plate 31 may be fastened to the side walls 13 of the sound-absorbing panel 11 in addition to or instead of the upper side wall 13 of the sound-absorbing panel 11.

Next, another example of the sound absorbing wall structure of this embodiment shown in FIG. 6 will be described.
The fixing structure between the flange 30a of the support 30 and the sound-absorbing panel 11 may be configured by interposing a leaf spring 40 (corresponding to the interposing member of the present invention) formed by bending a steel plate between the flange 30a and the sound-absorbing panel 11. In this case, the leaf spring 40 is provided on the outside of the support 2 (the side opposite the railway tracks).

The leaf spring 40 has a U-shaped clamping portion 41 that clamps both the inner and outer surfaces of one end of a metal plate member 50 from which the flange 30a extends. The clamping portion 41 is composed of an outer piece 41a and an inner piece 41b that face each other.

The clamping portion 41 has an insertion hole (not shown) formed in each of the outer piece 41a and inner piece 41b, through which the retractable bolt 42 passes when the retractable bolt 42 is threaded into the threaded hole 43 of the plate member 50.

An abutment piece 44 that abuts against the frame 12 of the sound-absorbing panel 11 is attached to the inner piece 41b of the clamping portion 41. The abutment piece 44 folds back and extends to the side opposite the inner piece 41b.

Furthermore, an input portion 45 is connected to the abutment piece 44 and bent back toward the space between the inner piece 41b and the abutment piece 44. The tip of the advance/retract bolt 42 that screws into the plate member 50 abuts against the input portion 45.

A tapered protrusion 42a is formed at the tip of the retractable bolt 42. A receiving hole (not shown) into which the protrusion 42a at the tip of the retractable bolt 42 fits is formed in the input portion 45 of the leaf spring 40, which serves as an intervening member.

In this configuration, the retractable bolt 42 is threaded into the plate member 50, and simply by rotating the head 42b of the retractable bolt 42, the retractable bolt 42 advances and retreats, allowing the tip of the retractable bolt 42 to press against the input portion 45 at a fixed position, ensuring that the pressing force of the retractable bolt 42 is reliably transmitted to the contact piece portion 44.

In this embodiment, the flange 30a is extended by the plate member 50, i.e., the flange 30a and the plate member 50 are fastened together by fastening bolts 51 and nuts 52. However, this is not limited to this, and the plate member 50 may be omitted and the leaf spring 40 may be attached directly to the flange 30a.

The present invention will be explained in more detail below based on examples, but the present invention is not limited to these.

In the examples and comparative examples, various physical properties were measured or calculated as follows.
(1) Basis Weight Five 10 cm square samples were taken from the sound-absorbing material, excluding the side peripheral surface. The mass of each sample (sound-absorbing material, padding) was measured, and the total mass was divided by the total area to calculate the basis weight (g/m ² ).

(2) Average Fiber Diameter For spunbond nonwoven fabrics, ten 10 mm x 10 mm test pieces were taken, and the diameters of 20 randomly selected points on each test piece were read in μm units to the first decimal place at a magnification of 50x using a microscope (Nikon Corporation, product name: ECLIPSE E400), and the average value was taken as the average fiber diameter. For meltblown nonwoven fabrics, the fiber diameters (μm) of 30 constituent fibers of the taken sample pieces were measured at a magnification of 500x or 1000x using a scanning electron microscope (Hitachi, Ltd., model name: SU3500), and the average value was taken as the average fiber diameter.

(3) Sum of surface areas of outer diameters of filling fibers per unit area of filling For each fiber constituting the filling, the surface area of the outer diameter of the filling fiber per unit area of the filling was calculated according to the following formula (1), and the sum of all fibers was taken as the sum of the surface areas. For hollow fibers, the outer diameters of the fiber cross sections (n=10) were measured using an electron microscope and the average value was calculated. For the denier, the denier value listed in the fiber product specifications was used.
Surface area of outer diameter of filling fiber per unit area of filling (m ² /m ² )=fiber diameter (outer diameter μm)/10 ⁶ ×3.14×9000 (m)/denier (g)×basis weight (g/m ² )×content (mass %)/100 (1)

(4) Sound Absorption Coefficient According to JIS A 1405-2 (Transfer Function Method), a normal incidence sound absorption coefficient was measured using a thick tube with an inner diameter of 100 mm and a thin tube with an inner diameter of 29 mm. The measurement was performed by placing an SMS structure nonwoven fabric or an SSMS structure nonwoven fabric (in this case, an SSMS structure nonwoven fabric laminated with the third spunbond nonwoven fabric facing outward) on both the front and back sides of the padding cut to the specified size. The sound absorption coefficient in the 1/3 octave band center frequency range of 125 to 1000 Hz was measured using a thick tube, and the sound absorption coefficient in the 1250 to 6300 Hz range was measured using a thin tube.

(5) Carbon dioxide emissions were calculated in accordance with the 3R basic unit calculation method reported by the Recycling Society Promotion Office, Planning Division, Waste Management and Recycling Department, Ministry of the Environment (see https://www.env.go.jp/press/files/jp/19747.pdf). Here, recycled fibers in this context are treated as a concept encompassing reused fibers, and the carbon dioxide emissions from the process of recycled fibers from crude oil extraction to resin production were calculated as zero. Furthermore, to precisely evaluate the carbon dioxide emission reduction rate, the carbon dioxide emissions from resin to sound-absorbing material production were calculated using data for nonwoven fabrics containing polypropylene resin fibers, polyolefin fibers, and polyester (polyethylene terephthalate) fibers, respectively, from the "Carbon Footprint System Pilot Project _CO2 Equivalent Common Basic Unit Database ver. 4.01 (Domestic Data)" (public reference numbers JP212022 and JP212024). Furthermore, carbon dioxide emissions that may occur during the sound-absorbing material production process were ignored and assumed to be zero.
The carbon dioxide emissions from crude oil extraction to resin production per 1 kg of nonwoven fabric and polyolefin fiber containing polypropylene-based resin fiber were calculated as 1.49 kg, and the carbon dioxide emissions from crude oil extraction to resin production per 1 kg of polyester (polyethylene terephthalate)-based fiber were calculated as 1.59 kg. Furthermore, sound-absorbing material was disposed of by incineration, and the carbon dioxide emissions during incineration per 1 kg of nonwoven fabric and polyolefin fiber containing polypropylene-based resin fiber were calculated as 3.14 kg, and the carbon dioxide emissions during incineration per 1 kg of polyester (polyethylene terephthalate)-based fiber were calculated as 2.29 kg.
The GHG (Greenhouse Gas) emissions were calculated as carbon dioxide emissions.
"Calculated in accordance with the calculation method for the 3R intensity reported by the Recycling Society Promotion Office, Planning Division, Waste Management Department, Ministry of the Environment" means that the calculation includes these prerequisites. An example of calculating carbon dioxide emissions is given below.

(6) Amount of sagging of the filling A piece of filling measuring 500 mm wide x 1000 mm long x 50 mm thick was placed on the top of a desk measuring 500 mm or wider x 1000 mm or longer, which was placed on a horizontal floor, with the length of the filling parallel to the length of the desk, the filling contained within the width of the desk, and the filling protruding 600 mm from one side of the length of the desk. The distance from the floor to the top of the desk and the distance from the floor to the bottom of the tip of the filling sample were measured, and the amount of sagging of the filling was calculated using the following formula (2).
Amount of sagging =
Distance from the floor to the desk top - Distance from the floor to the bottom of the tip of the batting sample... (2)

(7) Uneven distribution of filling A sound-absorbing material measuring 250 mm wide x 250 mm long x 50 mm thick was prepared and placed vertically between wall surfaces spaced 60 mm apart. When visually inspecting the top surface, if it was found to be not a square but a mountain-shaped surface, it was determined that the filling was unevenly distributed.

(8) Hollow ratio of hollow fibers in spunbonded nonwoven fabric: The hollow fibers in a spunbonded nonwoven fabric were embedded in epoxy resin and then cut with a microtome to obtain a sample piece. This was observed under an electron microscope (manufactured by Hitachi, Ltd., model name: SU3500), and the cross-sectional area of the entire fiber and the cross-sectional area of the central portion in the obtained cross-sectional image of the fiber were determined and calculated using the following formula.
Hollow ratio [%] = (cross-sectional area of hollow portion/cross-sectional area of entire fiber) × 100 (2)
The hollowness ratio was calculated as an average value obtained by measuring 100 fibers.

The fibers that make up the filling are as follows:
Fiber 1: Solid short fiber of propylene polymer (manufactured by Ube Exsymo Co., Ltd., product name: UC Fiber, average fiber diameter 21 μm, 2 denier, average fiber length 51 mm)
Fiber 2: Solid short fiber of polyethylene terephthalate resin as a binder fiber (manufactured by Unitika Ltd., product name: Melty 4080, 2 denier, average fiber diameter 14 μm, average fiber length 51 mm)
Fiber 3: Solid short fiber of polyethylene terephthalate resin (average fiber diameter 14 μm, 2 denier, average fiber length 51 mm)
Fiber 4-1: Solid short fiber of polyethylene terephthalate resin (average fiber diameter 14 μm, 2 denier, average fiber length 51 mm)
Fiber 4-2: Solid short fiber of polyethylene terephthalate resin (average fiber diameter 14 μm, 2 denier, recycled fiber, average fiber length 51 mm)
Fiber 5: Solid short fiber of polyethylene terephthalate resin (average fiber diameter 25 μm, 6 denier, average fiber length 51 mm)
Fiber 6: Hollow short fiber of polyethylene terephthalate resin (average fiber diameter 21 μm, 6 denier, hollow ratio 28%, average fiber length 51 mm)
Fiber 7: Hollow short fiber of polyethylene terephthalate resin (average fiber diameter 45 μm, 14 denier, hollow ratio 28%, recycled fiber, average fiber length 51 mm)
Fiber 8: Recycled solid short fiber of polyethylene terephthalate resin (average fiber diameter 45 μm, 20 denier, average fiber length 51 mm)

[Example 1]
<Preparation of skin material>
A propylene homopolymer having an MFR of 60 g/10 min was used to perform melt spinning at 230°C by a conventional spunbonding method in a spunbond nonwoven fabric molding machine having a spinneret with a diameter of 0.6 mm, and the fibers obtained by spinning were deposited on a collection surface to obtain a first spunbond nonwoven fabric having an average fiber diameter of 13 μm and a basis weight of 10 g/ ^m2 .
Next, a propylene homopolymer having an MFR of 400 g/10 min was melted at 280°C using an extruder, and the resulting melt was extruded from a spinneret and simultaneously blown with heated air at 280°C using a conventional meltblown method to deposit fibers having an average fiber diameter of 3 μm onto the first spunbond nonwoven fabric, thereby forming a meltblown nonwoven fabric having a basis weight of 5 g/ ^m2 .
Next, fibers were deposited on the meltblown nonwoven fabric in the same manner as for the spunbond nonwoven fabric to form a second spunbond nonwoven fabric having an average fiber diameter of 13 μm and a basis weight of 10 g/m ² .
Next, the laminate consisting of the first spunbond nonwoven fabric, meltblown nonwoven fabric, and second spunbond nonwoven fabric stacked in this order was integrated using a hot embossing roll with an imprint area ratio of 18%, with the embossing roll temperature set at 145°C and the mirror roll at 150°C, to obtain a three-layer (SMS) nonwoven fabric in which the first spunbond nonwoven fabric and the second spunbond nonwoven fabric were stacked on both the front and back sides of the meltblown nonwoven fabric. The resulting SMS nonwoven fabric had a basis weight of 25 g/ ^m² .
Next, a propylene homopolymer having an MFR of 60 g/10 min was used to perform melt spinning at 230°C by a conventional spunbonding method in a spunbond nonwoven fabric molding machine having a spinneret with a diameter of 1.3 mm, and the fibers obtained by spinning were deposited on the SMS structure nonwoven fabric to form a third spunbond nonwoven fabric having an average fiber diameter of 35 μm and a basis weight of 100 g/ ^m2 .
Next, the laminate of the SMS nonwoven fabric and the spunbond nonwoven fabric in contact with the second spunbond nonwoven fabric side of the SMS nonwoven fabric was integrated using a hot embossing roll (embossing pattern 0.9 mm square) with an imprint area ratio of 18%, with the embossing roll temperature set at 155°C and the mirror roll temperature set at 160°C, to obtain a four-layer (SSMS) nonwoven fabric in which the spunbond nonwoven fabric was laminated on the SMS nonwoven fabric as a skin material. The SSMS nonwoven fabric had a basis weight of 125 g/ ^m2 and a carbon dioxide emission of 0.7 kg/ ^m2 . The carbon dioxide emissions from the SSMS structure nonwoven fabric were calculated as follows based on the carbon dioxide emissions from crude oil extraction to resin production per 1 kg of nonwoven fabric containing polypropylene-based resin fibers and polyolefin fibers, the carbon dioxide emissions per kg of nonwoven fabric containing polypropylene-based resin fibers upon incineration, and the public reference number JP212022 of the "Carbon Footprint System Pilot Project _CO2 Equivalent Common Basic Unit Database ver. 4.01 (Domestic Data)."

<Calculating carbon dioxide emissions from covering materials using polypropylene-based fibers>
The carbon dioxide emissions from the covering material using polypropylene fiber were calculated as follows.
(Carbon dioxide emissions from a skin material using polypropylene-based fibers) = [(Carbon dioxide emissions from crude oil extraction to resin production per 1 kg of nonwoven fabric containing the polypropylene-based resin fibers) + (Carbon dioxide emissions at incineration per 1 kg of nonwoven fabric containing the polypropylene-based resin fibers) + (Carbon dioxide emissions based on the public reference number JP212022 of the "Carbon Footprint System Pilot Project _CO2 Equivalent Common Basic Unit Database ver. 4.01 (Domestic Data)")] × Basis Weight / 1,000 ... (3)

<Making the filling>
5 parts by mass of Fiber 1, 30 parts by mass of Fiber 6, 30 parts by mass of Fiber 8, and 35 parts by mass of Fiber 3 were mixed, and a web was formed using a fiber opener and then a carding machine. The web was then multi-layered using a cross-layer machine and treated using a hot air treatment machine set to a gap distance of approximately 50 mm, to obtain a sheet-like nonwoven fabric molding having a thickness of approximately 50 mm, which contained short fibers of a propylene-based polymer and short fibers of a polyethylene terephthalate-based resin.

<Production of sound-absorbing material>
The batting was cut into a size of 250 mm (length) × 250 mm (width) × 49 mm (thickness). Next, the SSMS nonwoven fabric was placed on both sides of the cut batting, with the third spunbond nonwoven fabric side facing outward. The peripheral edge of the SSMS nonwoven fabric around the batting was fused using an ultrasonic sealing machine (manufactured by Seidensha Electronics Co., Ltd., product name: JII430SA) under conditions of an output of 2.0 V, a pressure of 0.3 MPa, and a speed of 5 m/min to form a continuous sealed portion 0.3 mm wide, thereby obtaining a sound-absorbing material in which the batting was encapsulated in the SSMS nonwoven fabric. The excess portion around the periphery of the sealed portion was cut away.

The physical properties and performance of the sound-absorbing material were measured or calculated. The results are shown in Table 1. The " _CO2 emissions from the filling" in Table 1 are the carbon dioxide emissions per 1 kg of the polypropylene-based resin fiber from crude oil extraction to resin production, the carbon dioxide emissions per 1 kg of the polyester (polyethylene terephthalate)-based resin fiber from crude oil extraction to resin production, the carbon dioxide emissions per 1 kg of the polypropylene-based resin fiber during incineration, and the carbon dioxide emissions per 1 kg of the polyester (polyethylene terephthalate)-based resin fiber from crude oil extraction to resin production, calculated as follows based on the public reference numbers JP212022 and JP212024 of the "Carbon Footprint System Pilot Project _CO2 Equivalent Common Basic Unit Database ver. 4.01 (Domestic Data)."

<Calculating carbon dioxide emissions from filling made with polypropylene fiber and polyester (polyethylene terephthalate) resin fiber>
The carbon dioxide emissions from filling made from polypropylene-based fibers and polyester (polyethylene terephthalate)-based resin fibers were calculated as follows.
(Carbon dioxide emissions from batting using polypropylene fiber and polyester (polyethylene terephthalate) resin fiber) = [(Carbon dioxide emissions from crude oil extraction to resin production per 1 kg of the polypropylene resin fiber) + (Carbon dioxide emissions at incineration per 1 kg of the polypropylene resin fiber) + (Carbon dioxide emissions based on public reference number JP212022 of the "Carbon Footprint System Pilot Project _CO2 Equivalent Common Basic Unit Database ver. 4.01 (Domestic Data)")] × Basis weight of batting × [Content (mass%) of polypropylene resin fiber in batting] / 1000 + [(Carbon dioxide emissions from crude oil extraction to resin production per 1 kg of the polyester (polyethylene terephthalate) resin fiber) + (Carbon dioxide emissions at incineration per 1 kg of the polyester (polyethylene terephthalate) resin fiber) + (Carbon dioxide emissions based on the "Carbon Footprint System Pilot Project CO2 Equivalent Common Basic Unit Database ver. 4.01 (Domestic Data)" (carbon dioxide emissions based on the public reference number JP212024 of the "Japan Domestic Data Common Basic Unit Database for Energy Conversion ver. _4.01 ") × basis weight of batting × [content of polyester (polyethylene terephthalate) resin fiber in batting (mass%)] / 1000... (4)

[Examples 2 to 12] and [Comparative Examples 1 to 5]
Sound-absorbing materials were prepared in the same manner as in Example 1, except that the fibers used in preparing the padding were changed as shown in Tables 1 to 3, and the physical properties and performance of the sound-absorbing materials were measured or calculated. The results are shown in Tables 1 to 3.

[Example 13]
<Preparation of skin material>
A propylene homopolymer having an MFR of 60 g/10 min was used to perform melt spinning at 230°C by a conventional spunbonding method in a spunbond nonwoven fabric molding machine having a spinneret with a diameter of 0.6 mm, and the fibers obtained by spinning were deposited on a collection surface to obtain a first spunbond nonwoven fabric having an average fiber diameter of 13 μm and a basis weight of 10 g/ ^m2 .
Next, a propylene homopolymer having an MFR of 400 g/10 min was melted at 280°C using an extruder, and the resulting melt was extruded from a spinneret and simultaneously blown with heated air at 280°C using a conventional meltblown method to deposit fibers having an average fiber diameter of 3 μm onto the first spunbond nonwoven fabric, thereby forming a meltblown nonwoven fabric having a basis weight of 5 g/ ^m2 .
Next, fibers were deposited on the meltblown nonwoven fabric in the same manner as for the spunbond nonwoven fabric to form a second spunbond nonwoven fabric having an average fiber diameter of 13 μm and a basis weight of 10 g/m ² .
Next, the laminate consisting of the first spunbond nonwoven fabric, meltblown nonwoven fabric, and second spunbond nonwoven fabric stacked in this order was integrated using a hot embossing roll with an imprint area ratio of 18%, with the embossing roll temperature set at 145°C and the mirror roll at 150°C, to obtain a three-layer (SMS) nonwoven fabric in which the first spunbond nonwoven fabric and the second spunbond nonwoven fabric were stacked on both the front and back sides of the meltblown nonwoven fabric. The resulting SMS nonwoven fabric had a basis weight of 25 g/ ^m² .
Next, a propylene homopolymer having an MFR of 60 g/10 min was used to perform melt spinning at 230°C by a conventional spunbonding method in a spunbond nonwoven fabric molding machine having a spinneret with a hole shape as shown in Figure 4 and a cross section of a substantially circular hollow shape, and the fibers obtained by spinning were deposited on the SMS structure nonwoven fabric to form a third spunbond nonwoven fabric having an average fiber diameter of 40 µm, a hollowness of 16%, and a basis weight of 100 g/ ^m2 .
Next, the laminate of the SMS nonwoven fabric and the spunbond nonwoven fabric in contact with the second spunbond nonwoven fabric side of the SMS nonwoven fabric was integrated using a hot embossing roll (embossing pattern 0.9 mm square) with an imprint area ratio of 18%, with the embossing roll temperature set at 155°C and the mirror roll temperature set at 160°C, to obtain a four-layer (SSMS) nonwoven fabric in which the spunbond nonwoven fabric was laminated on the SMS nonwoven fabric as a skin material. The SSMS nonwoven fabric had a basis weight of 125 g/ ^m2 and a carbon dioxide emission of 0.7 kg/ ^m2 . The carbon dioxide emissions from the SSMS structure nonwoven fabric were calculated as follows based on the carbon dioxide emissions from crude oil extraction to resin production per 1 kg of nonwoven fabric containing polypropylene-based resin fibers and polyolefin fibers, the carbon dioxide emissions per kg of nonwoven fabric containing polypropylene-based resin fibers upon incineration, and the public reference number JP212022 of the "Carbon Footprint System Pilot Project _CO2 Equivalent Common Basic Unit Database ver. 4.01 (Domestic Data)."
Sound-absorbing materials were prepared in the same manner as in Example 1, except that the fibers used in preparing the skin and padding were changed as shown in Table 2, and the physical properties and performance of the sound-absorbing materials were measured or calculated. The results are shown in Table 2.

[Example 14]
Sound-absorbing materials were prepared in the same manner as in Example 13, except that the fibers used in preparing the padding were changed as shown in Table 2, and the physical properties and performance of the sound-absorbing materials were measured or calculated. The results are shown in Table 2.

[Example 15]
A sound-absorbing material was prepared in the same manner as in Example 13, except that the basis weight of the third spunbond nonwoven fabric in Example 13 was changed to 80 g/m ² and the fibers used in preparing the padding were changed as shown in Table 3, and the physical properties and performance of the sound-absorbing material were measured or calculated. The results are shown in Table 3.

The sound-absorbing panels of Comparative Examples 1 to 3, in which the sum of the surface areas of the outer diameters of the batting fibers per unit area of the batting was too small, had low sound absorption coefficients. Furthermore, the sound-absorbing panels of Comparative Examples 4 and 5, in which the sum of the surface areas of the outer diameters of the batting fibers per unit area of the batting was too large, had very low sound absorption coefficients, the batting was unevenly distributed, and the carbon dioxide emissions were high. On the other hand, the sound-absorbing panels of Examples 1 to 15 had high sound absorption coefficients, the carbon dioxide emissions of the resins that make up these sound-absorbing panels were low, and the batting they contained was not unevenly distributed.

1...sound-absorbing material, 2...filling, 3...surface material, 4...sealing portion, 11...sound-absorbing panel, 12...shielding plate
13...Side wall, 14...Frame, 15...Protective panel, 16...Support portion, 20...Wall surface (concrete wall), 21...L-shaped joint plate, 21a...Flat plate portion, 21b...Rising portion, 30...Support, 30a...Flange, 31...S-shaped joint plate, 31a...First flat portion, 31b...Second flat portion, 31c...Vertical surface portion, 40...Leaf spring, 41...Clamping portion, 42...Advance/retreat bolt, 44...Abutment piece portion, 45...Input portion, 50...Plate member.

Claims (12)

A sound-absorbing wall structure in which sound-absorbing panels, each containing a frame of sound-absorbing material, are fixed to a wall surface erected along a railway track or to a support pillar having a pair of flanges facing each other,
The sound-absorbing material is made of a padding and a skin material that contains the padding,
The filling is a nonwoven fabric containing two or more types of thermoplastic resin fibers,
The thermoplastic resin fibers have different fiber diameters,
The sum of the surface areas of the outer diameters of the filling fibers per unit area of the filling is 150 to 270 m ² /m ² ;
the skin material is a nonwoven fabric containing polypropylene-based resin fibers,
The sound-absorbing wall structure has a clearance of 5 to 200 mm between the sound-absorbing panel and the sound-absorbing wall. 2. The sound-absorbing wall structure according to claim 1, wherein the sum of the surface areas of the outer diameters of the fill fibers per unit area of the fill is 200 to 270 m ² /m ² . The sound-absorbing wall structure described in claim 1, wherein the padding is a nonwoven fabric containing at least one thermoplastic resin fiber selected from the group consisting of fine fibers having a fiber diameter of 10 μm or more but less than 20 μm, medium-thick fibers having a fiber diameter of 20 to 30 μm, and extra-thick fibers having a fiber diameter of 40 to 50 μm. The sound-absorbing wall structure according to claim 3, wherein the padding contains at least one thermoplastic resin fiber selected from the group consisting of the medium-thick fibers and the extra-thick fibers, and the thermoplastic resin fiber contains hollow fibers. The sound-absorbing wall structure described in claim 1, wherein the padding contains thermoplastic resin hollow fibers, and the content of the thermoplastic resin hollow fibers in the padding is 30% by mass or more. The sound-absorbing wall structure described in claim 3, wherein the content of the fine fibers in the padding is 50% by mass or more. The sound-absorbing wall structure described in claim 1, wherein the skin material is a skin material including a first spunbond nonwoven fabric, a meltblown nonwoven fabric adjacent to the first spunbond nonwoven fabric, and a second spunbond nonwoven fabric adjacent to the meltblown nonwoven fabric, or a skin material including a first spunbond nonwoven fabric, a meltblown nonwoven fabric adjacent to the first spunbond nonwoven fabric, a second spunbond nonwoven fabric adjacent to the meltblown nonwoven fabric, and a third spunbond nonwoven fabric adjacent to the second spunbond nonwoven fabric. The sound-absorbing wall structure described in claim 7, wherein at least one selected from the group consisting of the first spunbond nonwoven fabric, the second spunbond nonwoven fabric, and the third spunbond nonwoven fabric contains fibers with an average fiber diameter in the range of 25 to 50 μm. The sound-absorbing wall structure described in claim 7, wherein the meltblown nonwoven fabric contains fibers with an average fiber diameter in the range of 0.5 to 5 μm. The sound-absorbing wall structure described in claim 7, wherein at least one selected from the group consisting of the first spunbond nonwoven fabric, the second spunbond nonwoven fabric, and the third spunbond nonwoven fabric contains hollow fibers. 2. The sound-absorbing wall structure according to claim 1, wherein the amount of sagging of the padding measured by the following test method is 75 mm or less.
The filling, which is 500 mm wide, 1000 mm long, and 50 mm thick, is placed on the top of a desk that is 500 mm wide or more and 1000 mm long or more and placed on a horizontal floor, so that the length of the filling and the length of the desk are parallel, the filling is contained in the width direction of the desk, and the filling extends 600 mm beyond one side of the length of the desk, and the distance from the floor to the top of the desk and the distance from the floor to the bottom of the tip of the filling sample are measured.
Drooping amount = distance from floor to desk top - distance from floor to bottom of tip of batting sample 2. The sound-absorbing wall structure according to claim 1, wherein the carbon dioxide emissions of the skin material and the padding are 8.0 kg/ ^m2 or less, calculated in accordance with the 3R basic unit calculation method reported by the Recycling-Based Society Promotion Office, Planning Division, Waste Management and Recycling Department, Ministry of the Environment.