Sound absorption sheet

Abstract

To provide a sound absorption sheet that absorbs sounds in frequency bands of human speech voice.SOLUTION: A sound absorption sheet includes a back air layer forming sheet with numerous protrusions formed in a hollow shape, and a sound absorption surface layer forming sheet laminated on the opening side of the protrusions to seal air within the protrusions. The protrusions are arranged at intervals, and the height h of the protrusions is 8 to 15 mm, the height h of the protrusions and the diameter d of the protrusions satisfy a relationship h>d / 3, and center-to-center distance between adjacent protrusions is 35 to 45 mm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sound-absorbing sheet.

Background Art

[0002] In recent years, so-called telework, which involves working outside the workplace, has become widespread. Along with the establishment of such a work style, online meetings (also referred to as Web meetings) using telephone conferences or Internet lines are frequently held to communicate with counterparts in remote locations. With the recent changes in the working environment, the demand for indoor sound insulation, particularly sound absorption during meetings, has been increasing. However, in general residential living spaces, there are few inner walls equipped with sound insulation means, and there is a need for means that can be installed retroactively.

[0003] As a type of sound insulation means that can be temporarily installed at a desired location, a sound insulation sheet is known. For example, Patent Document 1 discloses a resin sheet having a sandwich structure in which a sheet having protrusions that enclose air is used as a sound absorption material layer, and the sound absorption material layer is sandwiched between another sheet that becomes a sound insulation material layer and laminated and integrated, as a sound insulation sheet having a sound insulation effect of blocking noise generated from a construction work site and a sound absorption effect of reducing sound reflection.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The human voice has a different frequency band from the noise generated in factories or construction sites. Therefore, it is difficult to obtain a sufficient sound absorption effect for the sound in the frequency band to which the human voice belongs by using the sound insulation sheets used in factories or construction sites. In addition, when installing means having a sound absorption effect in a general residential room or office, it is required to be easily handled and installed simply in a form that does not interfere with the use of the room without taking the trouble of moving furniture or objects such as shelves that are already installed.

[0006] An object of the present invention is to provide a sound absorption sheet that absorbs sound in the frequency band to which the human voice belongs and is easy to handle and can be installed simply.

Means for Solving the Problems

[0007] In order to solve the above problems, one embodiment of the present invention includes a back air layer forming sheet in which a large number of protrusions bulging in a hollow shape are formed, and a sound absorption side surface layer forming sheet laminated on the opening side of the protrusions to enclose air in the protrusions. The protrusions are arranged at intervals from each other, the height h of the protrusions is 8 to 15 mm, the height h of the protrusions and the diameter d of the protrusions are in a relationship of h > d / 3, and the center-to-center distance between adjacent protrusions is 35 to 45 mm.

Effects of the Invention

[0008] According to the present invention, a sound absorption sheet that absorbs sound in the frequency band to which the human voice belongs can be provided. Further, according to the sound absorption sheet of the present invention, it is easy to handle and can be installed simply.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] There are three known mechanisms by which a sound-absorbing material absorbs sound: the porous type, the plate / membrane vibration type, and the resonator type. In the present embodiment, a resin sound-absorbing sheet is provided that is considered to absorb sound based on the membrane vibration type sound absorption principle, which exhibits a sound absorption effect through resonance between an airtight sound-absorbing side surface layer that serves as the surface where sound is incident and a back air layer formed on the back surface thereof.

[0011] In principle, for example, by attaching a bubble cushioning material used as a cushioning packaging material to an indoor wall, a sound absorption effect based on the membrane vibration type sound absorption principle is expected. This is presumably because the flat film forming the bubble cushioning material serves as the sound-absorbing side surface layer, and the back air layer is formed by the bubbles and the space other than the bubbles due to the arrangement of the bubbles between the flat film and the wall. However, human speech belongs to the frequency band of 500 to 2000 Hz, and in the case of a bubble cushioning material, there is a risk that a sufficient sound absorption effect cannot be obtained in the frequency band of 1000 Hz or less, particularly in the region of male voices among human voices.

[0012] Therefore, the frequency band of sound absorption targeted in the present embodiment is the frequency band to which human speech that is likely to be a problem during a meeting belongs. In particular, in the present embodiment, a sufficient sound absorption effect is to be obtained even in the frequency band to which male voices belong. Specifically, it is configured such that the peak of the sound absorption rate is included in the frequency band of 750 to 1200 Hz, preferably 800 to 1100 Hz, and more preferably 800 to 1000 Hz. Also, in order to obtain a sufficient sound absorption effect, it is preferable that the sound absorption rate achieves 0.7 or more, preferably 0.8 or more, and more preferably 0.9 or more at the peak frequency. Note that the sound absorption rate is measured by a measurement method compliant with ISO10534-2, ASTM E1050-19, and ASTM E2611-09.

[0013] [First Embodiment] Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing a perspective view of a main part of a first embodiment of the sound absorption sheet 1. FIG. 2 is an explanatory view schematically showing a cross section of a first embodiment of the sound absorption sheet 1. FIG. 3 is an explanatory view showing a plan view of a part of a first embodiment of the sound absorption sheet 1.

[0014] The sound absorption sheet 1 of the present embodiment includes a back air layer forming sheet 2 in which a large number of protrusions 20 bulging in a hollow shape are formed, and a sound absorption side surface layer forming sheet 3 laminated on the opening side of the protrusions 20 to enclose air in the protrusions 20. By attaching the top 20a side of the protrusions 20 of the back air layer forming sheet 2 of such a sound absorption sheet 1 to a wall or a window, a sound absorption side surface layer that becomes a surface on which sound is incident is formed by the sound absorption side surface layer forming sheet 3. Then, the protrusions 20 of the back air layer forming sheet 2 are supported so as to have a predetermined space between the wall and the surface layer as hollow columnar bodies, and an air layer is formed between the sound absorption side surface layer and the wall. At the same time, each of the protrusions 20 also contains air as bubbles and forms an air layer independently, so that a sound absorption effect is considered to be obtained.

[0015] In the illustrated example, the protrusions 20 are formed in a cylindrical shape and are arranged in a staggered grid pattern with substantially equal spacing from each other.

[0016] In the sound absorption sheet 1 of the present embodiment, the height h of the protrusions 20 of the back air layer forming sheet 2 is preferably 8 to 15 mm, and more preferably 8 to 10 mm (see FIG. 2).

[0017] Here, according to the sound absorption principle of the membrane vibration type, for the resonance frequency f0, the following equation holds for the structure of the membrane (sound absorption side surface layer) and the air layer (back air layer). [Equation] According to such an equation (1), it is known that the thicker the air layer, the lower the frequency band of the sound to be absorbed. Therefore, it is considered that the higher the height h of the protrusion 20 of the rear air layer forming sheet 2, the lower the frequency band of the sound to be absorbed. However, in the present embodiment, from the viewpoint of moldability, it is preferably 15 mm or less. Further, considering the handleability of the sound absorption sheet 1 and that it does not interfere with the opening and closing of a window when, for example, attached to the window, it is more preferable that the height h of the protrusion 20 of the rear air layer forming sheet 2 is 10 mm or less.

[0018] Further, in the present embodiment, in order to make the peak of the sound absorption rate belong to the frequency band of 750 to 1200 Hz, the planar shape size of the protrusion 20 of the rear air layer forming sheet 2 is defined in relation to its height h. Specifically, it is preferable that the height h of the protrusion 20 and the diameter d of the protrusion 20 are in the relationship of h > d / 3, and it is more preferable that they are in the relationship of h > d / 2 (see FIGS. 2 and 3). When the protrusion 20 is not cylindrical but is formed, for example, in a polygonal cylindrical shape or in a cylindrical shape of another shape, it is only necessary that the planar shape (the shape of the top 20a) of the protrusion 20 fits inside the circle drawn by the aforementioned diameter d in relation to the height h.

[0019] Further, in the present embodiment, in order to make the peak of the sound absorption rate belong to the frequency band of 750 to 1200 Hz, the protrusion 20 and the adjacent protrusion 20 are arranged while maintaining a predetermined distance. Specifically, when the height h and the diameter d of the protrusion 20 of the rear air layer forming sheet 2 are within the aforementioned ranges, the center-to-center distance i between the protrusion 20 and the adjacent protrusion 20, that is, the center of the planar shape of the protrusion 20, in the illustrated example, since the protrusion 20 is cylindrical, the distance between the center of the circle indicated by the top 20a and the center of the planar shape of the adjacent protrusion 20, the protrusion 20 is preferably arranged so as to be 35 to 45 mm, and more preferably arranged so as to be 38 to 40 mm (see FIG. 3). In addition, when the protrusion 20 is not cylindrical but is formed, for example, in a polygonal cylindrical shape or in a cylindrical shape with another shape, the adjacent protrusions 20 may be arranged with the same center-to-center distance i as described above around the center of the planar shape of the protrusion 20.

[0020] As the resin material for forming the sound-absorbing side surface layer forming sheet 3, any thermoplastic resin that can be laminated and molded by heat fusion with other sheets used in manufacturing the sound-absorbing sheet 1 can be used without particular limitation. However, in this embodiment, it is preferable to use a resin with a high density. The specific density of the resin material is preferably 0.900 to 1.400 g / cm 2 and more preferably 0.930 to 1.300 g / cm 2 As shown in the above formula (1), by using a resin material with a high density for the sound-absorbing side surface layer forming sheet 3 to increase the surface density of the sound-absorbing side surface layer, the frequency of the sound absorbed by the sound-absorbing sheet 1 can be made lower.

[0021] Specific examples of the resin material for forming the sound-absorbing side surface layer forming sheet 3 include, for example, polyvinyl chloride (PVC), ethylene-methyl methacrylate copolymer resin (EMMA), and ethylene-vinyl acetate copolymer resin (EVA). By selecting such a resin with a high density and elasticity, the frequency of the sound absorbed by the sound-absorbing sheet 1 can be made lower.

[0022] A more preferable resin material for forming the sound-absorbing side surface layer forming sheet 3 is an ethylene-vinyl acetate copolymer resin with a vinyl acetate ratio of 10 to 40%, and more preferably, an ethylene-vinyl acetate copolymer resin with a vinyl acetate ratio of 14 to 19%. Among commercially available products, for example, Evaflex (EV460) manufactured by Mitsui Dow Chemical Co., Ltd. can be preferably used. It has been confirmed that by increasing the ratio of vinyl acetate, the frequency of the sound absorbed by the sound-absorbing sheet 1 can be made lower. On the other hand, when the ratio of vinyl acetate exceeds 40%, the mold release becomes poor and the moldability deteriorates during sheet forming, which is not preferable.

[0023] Also, as the resin material for forming the sound-absorbing side surface layer forming sheet 3, it is preferable to use a resin material having transparency or translucency. The same applies to the resin material for forming the rear air layer forming sheet 2 described later. Specifically, natural light or fluorescent light is incident from the side of the rear air layer forming sheet 2, and the visible light transmittance transmitted to the surface side of the sound-absorbing side surface layer forming sheet 3 is preferably 40% or more. By forming the sound-absorbing sheet 1 with a resin material having transparency or translucency in this way, even when the sound-absorbing sheet 1 is pasted on a window for use, it does not interfere with the daylighting from the window, and it becomes possible to secure a certain area when pasting the sound-absorbing sheet 1 indoors. By pasting it on a window, even if furniture is placed on the wall side of the room where the sound-absorbing sheet 1 is used, the sound-absorbing sheet 1 can be installed over a relatively large area.

[0024] Note that as the sound-absorbing side surface layer forming sheet 3, a sheet or film having a structure in which a plurality of layers are laminated instead of a single layer can be used. For example, a structure in which an ethylene-vinyl acetate copolymer resin is used as an intermediate layer, and the upper and lower layers sandwiching the intermediate layer are formed of polyethylene can be preferably used.

[0025] In addition, as the raw material of the sound-absorbing side surface layer forming sheet 3, various additives can be blended as needed with the resin described above as the base material. Examples of the additives include antioxidants, antistatic agents, ultraviolet absorbers, pigments, light stabilizers, weathering agents, flame retardants, antioxidants, fillers, talc, silica, silica balloons, glass balloons, blocking preventives such as polymer microspheres, organic antibacterial agents, inorganic antibacterial agents, lubricants, antifogging agents, colorants, tackifiers, adhesion promotion control agents, inorganic fillers (talc, silica, calcium carbonate), organic fillers (carbon fiber, amide transition), etc.

[0026] From the viewpoint of increasing the surface density of the sound-absorbing side surface layer and from the viewpoints of the handleability, moldability, and productivity of the sound-absorbing sheet 1, the thickness of the sound-absorbing side surface layer forming sheet 3 is preferably 200 to 400 μm, and more preferably 290 to 310 μm.

[0027] The resin material for forming the back air layer forming sheet 2 is not particularly limited as long as it is a thermoplastic resin that can be laminated and molded by heat fusion with other sheets used in manufacturing the sound-absorbing sheet 1. For example, it may be the same as the resin specifically mentioned for the sound-absorbing side surface layer forming sheet 3, or it may be different. However, from the viewpoint of increasing the surface density of the sound-absorbing side surface layer, it is preferable to use a resin material with a high density for the back air layer forming sheet 2 as well as for the sound-absorbing side surface layer forming sheet 3. As described above, when sound absorption is performed by the membrane vibration type sound absorption principle, the higher the surface density of the sound-absorbing side surface layer, the lower the frequency of the sound to be absorbed. As shown in FIGS. 1 and 2, the portion of the back air layer forming sheet 2 other than the protrusion 20 is laminated and integrated with the sound-absorbing side surface layer forming sheet 3, and substantially forms a part of the sound-absorbing side surface layer. This is because the surface density of a part of the sound-absorbing side surface layer is the sum of the back air layer forming sheet 2 and the sound-absorbing side surface layer forming sheet 3. Similarly, the thickness of the rear air layer forming sheet 2 is not particularly limited as long as it has a strength that can support the formation of an air layer between the installation surface of the sound absorption sheet 1 and the surface layer of the sound absorption side surface layer at the protrusion 20. However, from the viewpoint of increasing the surface density of the sound absorption side surface layer, it is preferably 250 to 400 μm, and more preferably 290 to 310 μm.

[0028] Also, as described above, as the resin material for forming the rear air layer forming sheet 2, from the viewpoint of light transmissibility when the sound absorption sheet 1 is attached to the window, it is preferable to use a resin material having transparency or translucency similar to that of the sound absorption side surface layer forming sheet 3.

[0029] The means for installing the sound absorption sheet 1 on a structure such as a wall or a window is not particularly limited as long as it can be installed and attached so that the top 20a side of the protrusion 20 of the rear air layer forming sheet 2 contacts the wall or the window. For example, an adhesive seal may be used, or it may be attached by applying an adhesive.

[0030] Such a sound absorption sheet 1 is lightweight and flexible, and easy to handle. It can be easily attached / detached so as to cover indoor walls, windows, and even furniture. When installed on a wall, it does not damage the decorations provided on the wall. Also, it is easy to cut and process with scissors or a cutter, and can be easily cut and arranged according to the shape, size, space, etc. of the indoor wall surface or window where the sound absorption sheet 1 is to be installed and attached. Also, when not in use, it can be stored in a rolled or folded state. Also, in the case of the sound absorption sheet 1 using a film formed of a resin material having transparency or translucency, even if the sound absorption sheet 1 is attached to a window, it is possible to let light into the room. It is preferable because attaching the sound absorption sheet 1 to a window can secure a flat surface having a predetermined area where no furniture or the like is installed indoors. Also, by attaching the sound absorption sheet 1 to a window or the like, it can be expected to function as a heat insulation sheet and improve the heating and cooling efficiency.

[0031] [Second Embodiment] Another preferred embodiment of the present invention will be described with reference to the drawings. FIG. 4 is an explanatory view showing a perspective view of the main part of the second embodiment of the sound absorption sheet 1. FIG. 5 is an explanatory view schematically showing a cross section of the second embodiment of the sound absorption sheet 1.

[0032] In the first embodiment, the sound absorption sheet 1 has a two-layer structure composed of a rear air layer forming sheet 2 in which a large number of protrusions 20 bulging in a hollow shape are formed, and a planar sound absorption side surface layer forming sheet 3 laminated on the opening side of the protrusions 20 to enclose air in the protrusions 20. However, in the second embodiment, it is different from the first embodiment in that an adhesive surface forming sheet 4 is further laminated on the top 20a side of the protrusions 20 of the rear air layer forming sheet 2 to form a three-layer structure.

[0033] When using the sound absorption sheet 1 having a three-layer structure including the adhesive surface forming sheet 4, instead of installing and attaching the sound absorption sheet 1 to a wall or the like, for example, even if it is simply suspended from the ceiling, a sound absorption effect can be expected. This is because the adhesive surface forming sheet 4 is provided on the opposite side of the sound absorption side surface layer forming sheet 3 with the rear air layer forming sheet 2 interposed therebetween, so that the sound absorption side surface layer and the rear air layer behind it are formed without installing and attaching to a wall or the like.

[0034] The resin material for forming the attachment surface forming sheet 4 is not particularly limited as long as it can be laminated and formed by heat fusion with other sheets used in manufacturing the sound absorption sheet 1. It may be the same as or different from the resin specifically mentioned in the sound absorption side surface layer forming sheet 3. In addition to the resins specifically mentioned above, for example, polyolefin resins such as branched low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-propylene block copolymer, ethylene-propylene random copolymer, ethylene-butene block copolymer, ethylene-butene random copolymer, propylene homopolymer, propylene-butene random copolymer, polybutene, polypentene, propylene-ethylene-butene terpolymer, propylene-acrylic acid copolymer, and propylene-maleic anhydride copolymer can be used. These polyolefin resins may be used alone or in combination of two or more. Further, a recycled raw material may be mixed with a virgin raw material and used, or only a recycled raw material may be used. However, as the resin material for forming the attachment surface forming sheet 4, from the viewpoint of light transmittance when the sound absorption sheet 1 is attached to the window, it is preferable to use a resin material having transparency or translucency similar to the sound absorption side surface layer forming sheet 3 and the back air layer forming sheet 2.

[0035] The attachment surface forming sheet 4 may be a water-applicable film. By forming the attachment surface forming sheet 4 into a water-applicable film, the sound absorption sheet 1 can be easily attached to the window glass. A water-applicable film can be attached to a planar attachment surface such as glass by applying water to the attachment surface, placing the film thereon, and closely adhering the film so that no air remains between the attachment surface and the film.

[0036] This type of water-applicable film can be formed of a film obtained by kneading a predetermined hydrophilic substance into a base resin that serves as the material of the attachment surface forming sheet 4 and then forming a film. Examples of the predetermined hydrophilic substance include a polymer obtained by graft-polymerizing acrylic acid and / or maleic anhydride onto polyethylene, and one or two substances selected from mono- or diglycerin fatty acid esters. More specifically, for example, a water-applicable film can be constituted by blending 25% by weight or more of an ethylene-polyester copolymer (for example, "Modic L513" manufactured by Mitsubishi Chemical Corporation) with the base resin.

[0037] Since the water-applicable film contains a hydrophilic substance in this way, for example, by placing the water-applicable film on an object such as a glass plate coated with water and bringing them into close contact so that no air remains between the glass plate and the water-applicable film, the water-applicable film adheres to the glass plate, and the adhered state is maintained even when the water has dried in terms of appearance. Therefore, if the sound absorption sheet 1 using the water-applicable film is attached to, for example, a window glass, the attached state is maintained. Furthermore, the water-applicable film does not naturally fall off, but can be easily peeled off with a little force. For this reason, for example, when it is desired to sound-absorb the interior for a certain period such as during a meeting, after use, the sound absorption sheet 1 attached to the window glass by the water-applicable film can be easily peeled off, and there will be no "trace remaining" on the glass surface where the sound absorption sheet 1 was attached.

[0038] The thickness of the attachment surface forming sheet 4 is not particularly limited, but can be set to 20 to 50 μm in consideration of the handleability of the sound absorption sheet 1.

[0039] This embodiment is different from the first embodiment in the above points, but since other configurations are the same as those of the first embodiment, duplicate explanations are omitted.

[0040] The sound-absorbing sheet 1 described above, although the thickness of each sheet (film) constituting the sound-absorbing sheet 1, the shape, size, number, pitch, etc. of the protrusions 20 formed on the back air layer forming sheet 2 are different from those of the bubble sheet used as a cushioning packaging material, it can be produced in the same manner as producing a bubble sheet used as a cushioning packaging material by changing the settings of the production apparatus or the like.

[0041] [Third Embodiment] In the first embodiment, the sound-absorbing sheet 1 is composed of a back air layer forming sheet 2 in which a large number of protrusions 20 bulging in a hollow shape are formed, and a planar sound-absorbing side surface layer forming sheet 3 laminated on the opening side of the protrusions 20 to enclose air in the protrusions 20. However, in the third embodiment, it is different from the first embodiment in that a filler is enclosed in the protrusions 20. That is, in the first and second embodiments, air was enclosed in the protrusions 20, but in the third embodiment, the filler is contained in the protrusions 20 so that the air is replaced by the filler, and the protrusions 20 are no longer hollow.

[0042] The filler may be any material as long as it can be easily enclosed in the protrusions 20 and there is no risk of problems such as leakage from the protrusions 20 when the sound-absorbing sheet 1 is used. For example, after injecting the filler into the protrusions 20, mortar that solidifies, silicone such as silicone resin or silicone rubber is preferably mentioned.

[0043] By attaching the top 20a side of the protrusion 20 of the rear air layer forming sheet 2 of such a sound-absorbing sheet 1 to a wall or a window, a sound-absorbing side surface layer, which is the surface on which sound is incident, is formed by the sound-absorbing side surface layer forming sheet 3. Then, the protrusion 20 of the rear air layer forming sheet 2 is supported as a solid columnar body so as to have a predetermined space between the wall or the like and the surface layer, and an air layer is formed between the sound-absorbing side surface layer and the wall or the like, and it is considered that a sound-absorbing effect can be obtained. The sound-absorbing sheet 1 of the third embodiment in which a filler is enclosed in the protrusion 20 and the protrusion 20 supports the sound-absorbing side surface layer forming sheet 3 as a solid columnar body has a tendency that the peak of the sound absorption rate is included in a frequency band with a lower frequency than that of the sound-absorbing sheet 1 of the first embodiment in which the protrusion 20 is formed as a hollow columnar body.

[0044] The sound-absorbing sheet 1 described in the third embodiment is produced by laminating the sound-absorbing side surface layer forming sheet 3 on the opening side of the protrusion 20 formed in the rear air layer forming sheet 2, enclosing air in the protrusion 20, and making fine holes in the rear air layer forming sheet 2 forming the protrusion 20 or the sound-absorbing side surface layer forming sheet 3 closing the opening of the protrusion 20, and injecting a filler into the protrusion 20.

[0045] This embodiment is different from the first embodiment in the above points, but since other configurations are the same as those of the first embodiment, duplicate explanations are omitted.

[0046] Even in the sound-absorbing sheet 1 in which a filler is enclosed in the protrusion 20 as in the third embodiment, according to the shape of the protrusion 20 of the present invention and the arrangement on the sound-absorbing sheet 1, even when the sound-absorbing sheet 1 is attached to a window and used, there is little possibility of affecting the daylighting property from the window. Also, there is little possibility of affecting the handleability of the sound-absorbing sheet 1.

Example

[0047] Hereinafter, the present invention will be described in more detail with specific examples.

[0048] [Example 1] A 300-μm-thick ethylene-methyl methacrylate copolymer resin (density: 0.937 g / cm 2 ) was used for the sound-absorbing side surface layer forming sheet, and a 300-μm-thick ethylene-methyl methacrylate copolymer resin (density: 0.937 g / cm 2 ) was used for the back air layer forming sheet to form a sound-absorbing sheet with a two-layer structure. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, being spaced apart from each other approximately evenly. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet thus obtained, two test pieces were punched out at arbitrary positions, and in a state where they were arranged such that sound waves were perpendicularly incident on the sound-absorbing side surface layer forming sheet side by the perpendicular incidence method conforming to ISO10534-2, the sound absorption rate was measured. The results are shown in Fig. 6. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 890 Hz.

[0049] [Example 2] A 275-μm-thick polyvinyl chloride (density: 1.266 g / cm 2 ) was used for the sound-absorbing side surface layer forming sheet, and a 275-μm-thick polyvinyl chloride (density: 1.266 g / cm 2 ) was used for the back air layer forming sheet to form a sound-absorbing sheet composed of a two-layer structure bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, being spaced apart from each other approximately evenly. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet thus obtained, two test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 7. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 950 Hz.

[0050] [Example 3] A film with a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.960 g / cm 2, containing 33% vinyl acetate), a film having a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.960 g / cm 2 , containing 33% vinyl acetate) was used to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the rear air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, being spaced apart from each other approximately evenly. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet obtained in this way, two test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in FIG. 8. It was confirmed that the average value of the peaks of the sound absorption rate of each test piece was around 950 Hz.

[0051] [Example 4] A film having a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.967 g / cm 2 , containing 40% vinyl acetate) was used for the sound-absorbing side surface layer forming sheet, and a film having a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.967 g / cm 2 , containing 40% vinyl acetate) was used for the rear air layer forming sheet to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the rear air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, being spaced apart from each other approximately evenly. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet obtained in this way, two test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in FIG. 9. It was confirmed that the average value of the peaks of the sound absorption rate of each test piece was around 890 Hz.

[0052] [Example 5] A film with a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.940 g / cm 2 , containing 19% vinyl acetate) was used for the sound-absorbing side surface layer forming sheet, and a film with a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.940 g / cm 2 , containing 19% vinyl acetate) was used for the back air layer forming sheet to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered grid pattern with substantially equal spacing from each other. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet obtained in this way, six test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 10. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 890 Hz.

[0053] [Example 6] A film with a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.932 g / cm 2 , containing 14% vinyl acetate) was used for the sound-absorbing side surface layer forming sheet, and a film with a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.932 g / cm 2 , containing 14% vinyl acetate) was used for the back air layer forming sheet to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered grid pattern with substantially equal spacing from each other. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet obtained in this way, six test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 11. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 1020 Hz.

[0054] [Example 7] A film with a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.931 g / cm 2 , containing 10% vinyl acetate) was used for the sound-absorbing side surface layer forming sheet, and a film with a three-layer laminated structure of polyethylene / ethylene-vinyl acetate copolymer resin / polyethylene with a thickness of 300 μm (density: 0.931 g / cm 2 , containing 10% vinyl acetate) was used to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, being spaced approximately evenly from each other. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet thus obtained, six test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 12. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 1080 Hz.

[0055] [Example 8] An ethylene-vinyl acetate copolymer resin with a thickness of 300 μm (density: 0.932 g / cm 2 , containing 14% vinyl acetate) was used for the sound-absorbing side surface layer forming sheet, and an ethylene-vinyl acetate copolymer resin with a thickness of 300 μm (density: 0.932 g / cm 2 , containing 14% vinyl acetate) was used to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, being spaced approximately evenly from each other. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 8 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet thus obtained, four test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 13. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 1010 Hz.

[0056] [Example 9] A 300-μm-thick ethylene-vinyl acetate copolymer resin (density: 0.940 g / cm 2 and containing 19% vinyl acetate) was used for the sound-absorbing side surface layer forming sheet, and a 300-μm-thick ethylene-vinyl acetate copolymer resin (density: 0.940 g / cm 2 and containing 19% vinyl acetate) was used for the back air layer forming sheet to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, being spaced approximately evenly from each other. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 8 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet thus obtained, four test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 14. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 1010 Hz.

[0057] [Example 10] A 300-μm-thick ethylene-vinyl acetate copolymer resin (density: 0.940 g / cm 2 and containing 19% vinyl acetate) was used for the sound-absorbing side surface layer forming sheet, and a 300-μm-thick ethylene-vinyl acetate copolymer resin (density: 0.940 g / cm 2 and containing 19% vinyl acetate) was used for the back air layer forming sheet to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, being spaced approximately evenly from each other. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 8 mm, and the diameter of the protrusions was 15 mm. Regarding the sound-absorbing sheet thus obtained, four test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 15. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 950 Hz.

[0058] [Example 11] A 300-μm-thick ethylene-vinyl acetate copolymer resin (density: 0.932 g / cm 2, containing 14% vinyl acetate), a 300 μm thick ethylene-vinyl acetate copolymer resin (density: 0.932 g / cm 2 , containing 14% vinyl acetate) was used to form a sound-absorbing sheet composed of a two-layer bubble sheet. The protrusions of the rear air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, spaced approximately evenly from each other. The center-to-center distance between adjacent protrusions was 38 - 39 mm. The height of the protrusions was 8 mm, and the diameter of the protrusions was 15 mm. Regarding the sound-absorbing sheet thus obtained, four test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 16. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 970 Hz.

[0059] [Example 12] A 300 μm thick ethylene-vinyl acetate copolymer resin (density: 0.940 g / cm 2 , containing 19% vinyl acetate) was used for the sound-absorbing side surface layer forming sheet, and a 300 μm thick ethylene-vinyl acetate copolymer resin (density: 0.940 g / cm 2 , containing 19% vinyl acetate) was used to form a sound-absorbing sheet composed of a two-layer bubble sheet, and mortar (Asahi Pen Co., Ltd.'s "Concrete Crack Repair Material for Walls") was injected as a filler into the protrusions. No air remained in the protrusions. The protrusions of the rear air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, spaced approximately evenly from each other. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 8 mm, and the diameter of the protrusions was 15 mm. Regarding the sound-absorbing sheet thus obtained, two test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 17. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 780 Hz.

[0060] [Example 13] A 300 μm thick ethylene-vinyl acetate copolymer resin (density: 0.940 g / cm 2, containing 19% vinyl acetate), a 300-μm-thick ethylene-vinyl acetate copolymer resin (density: 0.940 g / cm 2 , containing 19% vinyl acetate) was used to form a sound-absorbing sheet composed of a two-layer bubble sheet, and silicone (Konishi Co., Ltd.'s "Bond Silicon Sealant") was injected as a filler into the protrusions. No air remained in the protrusions. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, spaced approximately evenly from each other. The center-to-center distance between adjacent protrusions was 38 - 40 mm. The height of the protrusions was 8 mm, and the diameter of the protrusions was 15 mm. Regarding the sound-absorbing sheet thus obtained, two test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 18. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 820 Hz.

[0061] [Comparative Example 1] A 30-μm-thick polyethylene (density: 0.920 g / cm 2 ) was used for the sound-absorbing side surface layer forming sheet, and a 30-μm-thick polyethylene (density: 0.920 g / cm 2 ) was used for the back air layer forming sheet to prepare a commercially available two-layer bubble sheet as a packaging cushioning material. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered lattice pattern, spaced approximately evenly from each other. The center-to-center distance between adjacent protrusions was 20 - 22 mm. The height of the protrusions was 8 mm, and the diameter of the protrusions was 20 mm. Regarding such a sound-absorbing sheet, one test piece was punched out at an arbitrary position, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 19. No peak of the sound absorption rate could be confirmed in the frequency band below 1550 Hz.

[0062] [Comparative Example 2] A 300-μm-thick polyethylene (density: 0.917 g / cm 2 ) was used for the sound-absorbing side surface layer forming sheet, and a 300-μm-thick polyethylene (density: 0.917 g / cm 2) was used to form a two-layer bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered grid pattern, being spaced apart from each other approximately evenly. The center-to-center distance between adjacent protrusions was 20 to 22 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet thus obtained, six test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 20. It was confirmed that the average value of the peaks of the sound absorption rates of each test piece was around 1300 Hz.

[0063] [Reference Example 1] Polyethylene with a thickness of 300 μm (density: 0.917 g / cm 2 ) was used for the sound-absorbing side surface layer forming sheet, and polyethylene with a thickness of 300 μm (density: 0.917 g / cm 2 ) was used to form a two-layer bubble sheet. The protrusions of the back air layer forming sheet were cylindrical, and the protrusions were arranged in a staggered grid pattern, being spaced apart from each other approximately evenly. The center-to-center distance between adjacent protrusions was 38 to 40 mm. The height of the protrusions was 10 mm, and the diameter of the protrusions was 20 mm. Regarding the sound-absorbing sheet thus obtained, six test pieces were punched out at arbitrary positions, and the sound absorption rate was measured in the same manner as in Example 1. The results are shown in Fig. 21. The average value of the peaks of the sound absorption rates of each test piece was around 1150 Hz, but there were test pieces exceeding 1250 Hz, showing variations.

[0064] As described above, the present invention has been described by showing preferred embodiments, but it goes without saying that the present invention is not limited only to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0065] For example, a sound-absorbing sheet 1 having a three-layer structure composed of a back air layer forming sheet 2, a sound-absorbing side surface layer forming sheet 3, and an adhesive surface forming sheet 4, in which a filler is encapsulated in the protrusions 20, may be formed by combining the above-described second embodiment and third embodiment.

Explanation of Reference Numerals

[0066] 1 Sound-absorbing sheet 2 Back air layer forming sheet 20 Protrusion 3 Sound-absorbing side surface layer forming sheet 4 Attachment surface forming sheet

Claims

1. A back air layer forming sheet having a number of protrusions that bulge in a hollow shape, a sound absorption side surface layer forming sheet laminated on the opening side of the protrusion and enclosing air in the protrusion, and including, the protrusions are arranged spaced apart from each other, the height h of the protrusion is 8 to 15 mm, the height h of the protrusion and the diameter d of the protrusion are in a relationship of h > d / 3, A sound absorption sheet, wherein the center-to-center distance between adjacent protrusions is 35 to 45 mm.

2. The sound absorption side surface layer forming sheet is formed of a base resin having a density of 0.900 to 1.400 g / cm ２ The sound absorption sheet according to claim 1.

3. The base resin forming the sound absorption side surface layer forming sheet is at least one of polyvinyl chloride, ethylene-methyl methacrylate copolymer resin, or ethylene-vinyl acetate copolymer resin. The sound absorption sheet according to claim 1 or 2.

4. The base resin forming the sound absorption side surface layer forming sheet is an ethylene-vinyl acetate copolymer resin containing vinyl acetate in a ratio of 10 to 40%. The sound absorption sheet according to claim 1 or 2.

5. The thickness of the sound absorption side surface layer forming sheet is 200 to 400 μm. The sound absorption sheet according to claim 1 or 2.

6. The sound absorption sheet further includes an attachment surface forming sheet laminated on the top surface side of the protrusion of the back air layer forming sheet, The attachment surface forming sheet is formed of a water-pasting film. The sound absorption sheet according to claim 1 or 2.

7. The sound absorption sheet according to claim 1 or 2, wherein a filler is enclosed in the protrusion.

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