Sound absorbing structure and manufacturing method thereof

Abstract

To provide a sound absorbing structure which can improve sound absorption performance in a low frequency range.SOLUTION: A sound absorbing structure 1 is made of hollow plates in which a plurality of columnar cells S are arranged side by side inside. The hollow plate has a side wall part 23 which extends in a thickness direction to divide the cell S, and a pair of closing walls 11, 12 which close the cell in both end parts of the side wall part 23. The hollow plate has communicating cell groups which adjoin each other via spaces, and are configured by the plurality of cells S in which internal spaces of the cells communicate each other via a communicating cylinder 14. In at least one of the cells S configuring the communicating cell group, a through hole 13 which allows communication between the interior and the exterior of the sell S is formed in one of the closing walls 11. In other cells S of the cells S configuring the communicating cell group, the through hole 13 is not formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sound absorbing structure and a method for manufacturing the same. [Background technology]

[0002] Conventionally, hollow plate-shaped sound-absorbing structures have been known, each having a plurality of polygonal or cylindrical cells arranged side by side inside. Patent Document 1 describes an invention relating to a sound-absorbing structure made of a hollow plate material having a plurality of hexagonal pillar-shaped cells arranged side by side inside. The hollow plate material has side walls extending in the thickness direction to separate the cells, and a pair of closing walls at both ends of the side walls to close the cells, with through holes formed in the closing walls that close the cells to connect the inside and outside of the cells. The through holes allow each cell to function as a so-called Helmholtz resonator, and sound pressure enters the internal space of the cell through the through holes, thereby reducing sound pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-66914 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the sound absorption characteristics of a Helmholtz resonator depend on the opening area of ​​the opening, the length of the tubular portion that guides sound waves from the outside to the inside of the container, and the internal volume of the container. Therefore, in the sound-absorbing structure described in Patent Document 1, the opening edge of the through-hole is positioned in the internal space of the cell, thereby lengthening the portion that functions as the "length of the tubular portion" of the Helmholtz resonator. This makes it easier to shift the region with high sound absorption performance to the low-frequency region, and it is possible to maintain high sound absorption performance even in a relatively low-frequency region.

[0005] However, the sound absorbing structure described in Patent Document 1 still has room for improvement in terms of improving sound absorbing performance in the low frequency range. [Means for solving the problem]

[0006] In order to solve the above problems, the sound-absorbing structure of the present invention is a sound-absorbing structure made of a hollow plate material having a plurality of columnar cells arranged side by side inside, the hollow plate material having side wall portions extending in the thickness direction to divide the cells, and a pair of blocking walls that close the cells at both ends of the side wall portions, and a communicating cell group made up of a plurality of cells that are adjacent to each other through a space and whose internal spaces are communicated via communicating tubes, at least one of the cells that make up the communicating cell group has a through hole formed in one of the blocking walls that connects the inside and outside of the cell, and the other cells of the communicating cell group do not have such a through hole formed.

[0007] According to the above configuration, the sound-absorbing structure has a group of communicating cells in which the internal spaces of multiple cells are connected via communicating tubes, and some of the multiple cells constituting the communicating cell group have through-holes formed in one of the blocking walls that close the cells, connecting the inside and outside of the cells. Therefore, the internal volume of the internal space of the communicating part can be made larger than that of a sound-absorbing structure that has through-holes formed in the cells but does not have a group of communicating cells. As described above, the sound-absorbing characteristics of a Helmholtz resonator are influenced by the internal volume of the container. By forming a group of communicating cells from multiple cells, the part that functions as the "internal volume of the container" of the Helmholtz resonator is enlarged. This makes it easier to shift the region with high sound absorption performance to the low-frequency region, and improves sound absorption performance in the low-frequency region.

[0008] In the above configuration, it is preferable that the equivalent diameter of the communication tube is larger than the equivalent diameter of the through hole. With this configuration, the air flow resistance in the communicating tube is small, and sound pressure that enters the internal space of a cell through the through-holes can easily enter the internal space of cells that do not have through-holes through the communicating holes. This allows the internal spaces of all of the cells that make up the communicating cell group to function as the "internal volume of the container" of the Helmholtz resonator. This allows high sound absorption performance in the low-frequency range.

[0009] In order to solve the above problems, the method for manufacturing a sound-absorbing structure of the present invention is a method for manufacturing a sound-absorbing structure composed of a hollow plate material having side walls extending in the thickness direction to separate a plurality of column-shaped cells, and a pair of blocking walls that block the cells at both ends of the side walls, and comprises a hollow plate material forming process in which an uneven sheet material having a predetermined uneven shape is formed from a single flat sheet material made of synthetic resin to form the hollow plate material, and a through hole forming process in which a through hole that connects the inside and outside of the cell is formed in one of the blocking walls, in which in the hollow plate material forming process, grooves are formed in the uneven sheet material to form communicating tubes that connect the internal spaces of a plurality of the cells in the hollow plate material, and in the through hole forming process, the through hole is formed in at least one of a plurality of cells that are connected by the communicating tube in the hollow plate material.

[0010] According to the above configuration, grooves that will become the communicating tubes in the hollow plate are formed in the concave-convex sheet material during the hollow plate forming process. Therefore, the grooves can be formed simultaneously when the concave-convex sheet material is formed, and there is no need to form the communicating tubes in the hollow plate material as a post-process. The communicating tubes can be easily formed, simplifying the manufacturing process of the sound-absorbing structure.

[0011] In the above configuration, the hollow plate forming process includes a molding process for molding the uneven sheet material and a folding process for forming the hollow plate material by folding the uneven sheet material, and in the molding process, it is preferable that the groove extending in the width direction of the side wall portion is molded in the part of the uneven sheet material that will become the side wall portion, and in the folding process, the groove forms the communicating tube in the side wall portion.

[0012] According to the above configuration, grooves can be formed simultaneously with the formation of the textured sheet material, and the grooved textured sheet material can be folded to form a communicating tube in the side wall of the hollow plate material. Not only can the communicating tube be easily formed, but the shape, size, number, and forming position of the grooves can also be easily adjusted as needed. This allows the production of a sound-absorbing structure with excellent sound-absorbing performance in the low frequency range. [Effects of the Invention]

[0013] According to the present invention, a sound absorbing structure capable of improving sound absorbing performance in the low frequency range can be obtained. [Brief explanation of the drawings]

[0014] [Figure 1] 1A is a partial perspective view of the sound absorbing structure of this embodiment as seen from above, FIG. 1B is a cross-sectional view taken along the β-β line in FIG. 1A, and FIG. 1C is a cross-sectional view taken along the γ-γ line in FIG. [Figure 2] (a) is a schematic diagram for explaining the interconnected cell group, and (b) is a top view of the sound-absorbing structure. [Figure 3] 1A and 1B are diagrams illustrating a method for manufacturing a sound-absorbing structure, in which (a) is a diagram illustrating a molding process for molding a textured sheet material, (b) and (c) are diagrams illustrating a folding process for folding the textured sheet material to form a hollow plate material, and (d) is a diagram illustrating a through-hole forming process for forming a through-hole in the hollow plate material. [Figure 4] 10A and 10B are diagrams illustrating a manufacturing method for a modified sound-absorbing structure, in which (a) is a diagram illustrating a molding process for molding a textured sheet material, and (b) and (c) are diagrams illustrating a folding process for folding the textured sheet material to form a hollow plate material. [Figure 5] 1A is a top view of a modified sound-absorbing structure, FIG. 1B is a cross-sectional view taken along the σ-σ line in FIG. 1A, and FIG. 1C is a diagram illustrating a modified sound-absorbing structure in which the groove formation position is changed. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of a sound absorbing structure embodying the present invention will now be described with reference to FIGS. As shown in Figure 1(a), the sound-absorbing structure 1 of this embodiment consists of a hollow plate material 10 with a plurality of hexagonal column-shaped cells S arranged side by side inside, and has a shape in which a plurality of through holes 13 are formed in one main surface (top surface 10a) of the hollow plate material 10.

[0016] The hollow plate 10 is made of a conventionally known thermoplastic resin material, and the material is not particularly limited. Examples of the material include polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyvinyl acetate, polyurethane, and acrylonitrile-butadiene-styrene.

[0017] First, the structure of the hollow plate material 10 will be described. As shown in Figure 1(a), the hollow board 10 is composed of a core layer 20 having a plurality of cells S arranged side by side therein, and sheet-like skin layers 30, 40 bonded to both sides of the core layer 20 in the thickness direction. Hereinafter, in Figure 1, the main surface shown on the upper side of the hollow board 10 will be referred to as the upper surface 10a, and the main surface shown on the lower side will be referred to as the lower surface 10b. The skin layer 30 is bonded to the upper surface 10a of the hollow board 10, and the skin layer 40 is bonded to the lower surface 10b of the hollow board 10.

[0018] 1(b) and 1(c), the core layer 20 is formed by folding a single thermoplastic resin sheet formed into a predetermined shape. The core layer 20 is composed of an upper wall portion 21, a lower wall portion 22, and a side wall portion 23 that is erected between the upper wall portion 21 and the lower wall portion 22 and divides the cells S into a hexagonal columnar shape.

[0019] As shown in FIG. 1(a), the cells S formed within the core layer 20 include a first cell S1 and a second cell S2 having different configurations. As shown in FIG. 1(b), in the first cell S1, a two-layer upper wall portion 21 is provided on the upper part of the side wall portion 23. The layers of this two-layer upper wall portion 21 are bonded to each other. In addition, in the first cell S1, a one-layer lower wall portion 22 is provided on the lower part of the side wall portion 23. On the other hand, as shown in FIG. 1(c), in the second cell S2, a one-layer upper wall portion 21 is provided on the upper part of the side wall portion 23. In addition, in the second cell S2, a two-layer lower wall portion 22 is provided on the lower part of the side wall portion 23. The layers of this two-layer lower wall portion 22 are bonded to each other. In addition, as shown in FIGS. 1(b) and 1(c), adjacent first cells S1 and adjacent second cells S2 are each partitioned by a two-layer side wall portion 23.

[0020] As shown in FIG. 1(a), the first cells S1 are arranged in a row along the X direction, and when viewed from above, two adjacent first cells S1 share one side of a hexagon. Similarly, the second cells S2 are arranged in a row along the X direction, and when viewed from above, two adjacent second cells S2 share one side of a hexagon. The rows of first cells S1 and the rows of second cells S2 are alternately arranged in the Y direction, which is perpendicular to the X direction. The first cells S1 and second cells S2 form a honeycomb structure as a whole in the core layer 20.

[0021] 1(a) to 1(c), the skin layer 30 is bonded to the upper surface of the core layer 20, so that the upper portions of the side wall portions 23 of the core layer 20 are blocked by the upper wall portions 21 of the core layer 20 and the skin layer 30. That is, the upper wall portions 21 and the skin layer 30 form an upper blocking wall 11 that separates the cells S from above. Similarly, the skin layer 40 is bonded to the lower surface of the core layer 20, so that the lower portions of the side wall portions 23 of the core layer 20 are blocked by the lower wall portions 22 of the core layer 20 and the skin layer 40. That is, the lower wall portions 22 and the skin layer 40 form a lower blocking wall 12 that separates the cells S from below.

[0022] The hollow plate material 10 has a shape in which multiple cells S are arranged side by side inside, with the core layer 20 and skin layers 30 and 40, and the upper blocking wall 11 side of the hollow plate material 10 forms the upper surface 10a of the hollow plate material 10, and the lower blocking wall 12 side forms the lower surface 10b of the hollow plate material 10.

[0023] As shown in FIGS. 1(b) and 1(c), the sound-absorbing structure 1 is formed by providing a plurality of through holes 13 in the upper surface 10a of the hollow board material 10. The through holes 13 are formed to penetrate an upper blocking wall 11 that blocks the upper side of the hollow board material 10. The internal space of the cell S and the external space of the sound-absorbing structure 1 are connected via the through holes 13. Specifically, as shown in FIG. 1(b), in the first cell S1, the through holes 13 penetrate the upper wall portion 21 and skin layer 30, which have a two-layer structure. Furthermore, as shown in FIG. 1(c), in the second cell S2, the through holes 13 penetrate the upper wall portion 21 and skin layer 30, which have a single-layer structure. This allows the sound-absorbing structure 1 to function as a sound-absorbing material.

[0024] As shown in FIGS. 1(b) and 1(c), the peripheral portion of the opening edge 13a of each through hole 13 is recessed relative to the upper surface of the skin layer 30 in the portion where the through hole 13 is not formed. As a result, the opening edge 13a of the through hole 13 is located in the internal space of the cell S, which is the space below the inner surface of the upper wall portion 21 of the core layer 20. The diameter of the opening edge 13a of each through hole 13 is set to be equal to or less than the length of one side of the hexagon when the cell S is viewed from above. Specifically, when the average value of the distances between the centers of adjacent cells S in the X direction is defined as the "average pitch P1," the diameter of the opening edge 13a of each through hole 13 is preferably set to be a fraction of the average pitch P1. The diameter of the opening edge 13a is preferably approximately 0.5 to 3 mm, and more preferably approximately 1.0 to 1.5 mm. When the diameter of the opening edge 13a is within this range, the sound absorption coefficient of the sound-absorbing structure 1 can be increased.

[0025] 1(a), in the sound absorbing structure 1 of this embodiment, in the second cells S2, one through hole 13 is provided in each of the second cells S2 at a central position in a top view. Meanwhile, in the first cells S1, among the multiple rows of the first cells S1 arranged side by side in the Y direction, rows of the first cells S1 with the through hole 13 formed therein and rows of the first cells S1 without the through hole 13 formed therein are arranged alternately. In the first cells S1 in which the through hole 13 is formed, one through hole 13 is provided in each of the first cells S1 at a central position in a top view.

[0026] 1(c), 2(a) and 2(b), a communication tube 14 that connects the internal spaces of adjacent first cells S1 in the Y direction is formed on the side wall 23 of the second cell S2 so as to extend in the Y direction. The communication tube 14 is formed in the approximate center in the up-down direction of the two-layered side wall 23 of the second cells S2 adjacent in the X direction.

[0027] As shown in Fig. 2(a), the communicating tube 14 has openings at both ends in the Y direction in the side wall portions 23 of the first cells S1 adjacent in the Y direction, thereby communicating the internal spaces of two first cells S1 adjacent in the Y direction. Two first cells S1 whose internal spaces communicate via the communicating tube 14 constitute a communicating cell group as defined in the claims. Note that in Fig. 2(a), to make it easier to understand the shape, formation position, and formation mode of the communicating tube 14, of the cells S that make up the sound absorbing structure 1, four adjacent first cells S1 and four adjacent second cells S2 are shown, and only the core layers 20 of these first cells S1 and second cells S2 are shown in a perspective view.

[0028] 1(c), 2(a) and 2(b), the side wall portion 23 of the first cell S1 does not have a communicating cylinder 14, and none of the second cells S2 communicates with the internal space of the other second cells S2. In other words, the second cells S2 do not constitute a communicating cell group.

[0029] As described above, in the second cells S2, one through hole 13 is formed for each of the second cells S2, whereas in the first cells S1, rows with through holes 13 formed and rows without through holes 13 are arranged alternately. The internal spaces of two first cells S1 adjacent in the Y direction form a communicating cell group that is connected via a communicating tube 14. In other words, the communicating cell group forms an internal space with an internal volume twice that of the second cells S2. As shown in FIG. 2(b), one through hole 13 is formed for each portion where the internal spaces are connected to each other.

[0030] As shown in FIG. 1(c), the communicating tube 14 is formed in the vertical center of the side wall portion 23. In addition, the communicating tube 14 in this embodiment is formed to have a circular cross section. The diameter of the communicating tube 14 is larger than the diameter of the through hole 13, which is formed to have a circular shape when viewed from above. Because the diameter of the communicating tube 14 is larger than the diameter of the through hole 13, sound pressure that enters one of the first cells S1 constituting the communicating cell group via the through hole 13 can easily enter the other first cell S1 via the communicating tube 14, making it easier to improve sound absorption performance in the low frequency range. The diameter of the communicating tube 14 is preferably approximately 0.5 to 3.0 mm, and more preferably approximately 1.5 to 3.0 mm.

[0031] Next, a method for manufacturing the sound absorbing structure 1 will be described with reference to FIG. The manufacturing method of the sound-absorbing structure 1 includes a molding process of molding a textured sheet material 100 having a predetermined textured shape from a single flat sheet material made of thermoplastic resin, a folding process of folding the textured sheet material 100 to form a core layer 20, a joining process of joining skin layers 30, 40 to both main surfaces of the core layer 20 to form a hollow plate material 10, and a through-hole forming process of forming through holes 13 in the hollow plate material 10.

[0032] As shown in FIG. 3(a), in the molding process, a single flat sheet material made of thermoplastic resin is molded into a predetermined shape to form a textured sheet material 100. The textured sheet material 100 has band-shaped flat regions 110 and bulging regions 120 alternately arranged in the longitudinal direction (X direction) of the textured sheet material 100. In the bulging region 120, a first bulging portion 121 having a downward groove-like cross section and consisting of an upper surface and a pair of side surfaces is formed over the entire extension direction (Y direction) of the bulging region 120. Note that the angle between the upper surface and the side surface of the first bulging portion 121 is preferably 90 degrees, so that the cross section of the first bulging portion 121 has a downward U-shape. The width of the first bulging portion 121 (the length in the short direction of the upper surface) is set to be equal to the width of the flat region 110 and twice the bulging height of the first bulging portion 121 (the length in the short direction of the side surfaces).

[0033] In addition, in the bulging region 120, a plurality of second bulging portions 122, each of which has a cross-sectional shape that is a trapezoid obtained by bisecting a regular hexagon along its longest diagonal, are formed so as to be perpendicular to the first bulging portions 121. The bulging height of the second bulging portions 122 is set to be equal to the bulging height of the first bulging portions 121. The interval between adjacent second bulging portions 122 is equal to the width of the upper surface of the second bulging portions 122.

[0034] Furthermore, a groove 123 extending in the Y direction is formed in the center in the X direction on the upper surface of the second bulge portion 122. The groove 123 has a semicircular cross section in a side view, and is formed in a part of the second bulge portion 122. The second bulge portions 122 with the groove 123 formed therein and the second bulge portions 122 without the groove 123 formed therein are alternately arranged in every other row in the Y direction of the textured sheet material 100. The second bulge portions 122 with the groove 123 formed therein are arranged in the X direction of the textured sheet material 100, and the second bulge portions 122 without the groove 123 formed therein are also arranged in the X direction of the textured sheet material 100. The second bulge portions 122 with the groove 123 formed therein are formed at the same position in the X direction of the second bulge portions 122.

[0035] The textured sheet material 100 is formed by partially expanding a flat sheet material made of thermoplastic resin by utilizing its plasticity. The textured sheet material 100 can be formed from a single flat sheet material by a well-known forming method such as vacuum forming or compression forming.

[0036] As shown in FIGS. 3(a) and 3(b), in the folding process, the core layer 20 is formed by folding the textured sheet material 100 configured as described above along the boundary lines P and Q. Specifically, the textured sheet material 100 is valley-folded at the boundary line P between the flat region 110 and the bulging region 120, and mountain-folded at the boundary line Q between the top surface and side surface of the first bulging portion 121, thereby compressing in the X direction. Then, as shown in FIGS. 3(b) and 3(c), the top surface and side surface of the first bulging portion 121 are folded over, and the end surface of the second bulging portion 122 is folded over with the flat region 110, thereby forming a rectangular columnar partition 130 extending in the Y direction for each bulging region 120. These partitions 130 are continuously formed in the X direction, thereby forming the hollow plate-like core layer 20. Note that in this embodiment, the direction in which the textured sheet material 100 is compressed for folding is the direction in which the cells S are arranged side by side (the X direction).

[0037] When the textured sheet material 100 is compressed as described above, the upper wall portion 21 of the core layer 20 is formed by the upper surface and side surface of the first bulge portion 121, and the lower wall portion 22 of the core layer 20 is formed by the end surface of the second bulge portion 122 and the flat region 110. As shown in Figure 3(c), the portion of the upper wall portion 21 where the upper surface and side surface of the first bulge portion 121 are folded over to form a two-layer structure, and the portion of the lower wall portion 22 where the end surface of the second bulge portion 122 and the flat region 110 are folded over to form a two-layer structure are overlapping portions 131.

[0038] Furthermore, the hexagonal columnar region formed by folding the second bulge portion 122 becomes the second cell S2, and the hexagonal columnar region formed between a pair of adjacent partitions 130 becomes the first cell S1. In this embodiment, the upper surface and side surface of the second bulge portion 122 form the side wall portion 23 of the second cell S2, and the side surface of the second bulge portion 122 and the flat portion located between the second bulge portions 122 in the bulge region 120 form the side wall portion 23 of the first cell S1.

[0039] The abutting area between the flat surfaces in the bulging region 120 forms the side wall 23 of the two-layer structure of the first cell S1, and the abutting area between the upper surfaces of the second bulging portions 122 forms the side wall 23 of the two-layer structure of the second cell S2. A groove 123 having a semicircular cross section is formed in a part of the second bulging portion 122, so that when the upper surfaces of the second bulging portions 122 abut against each other, the groove 123 formed in the abutting area forms a communicating tube 14 having a circular cross section in the side wall 23 of the second cell S2. By forming the communicating tube 14, adjacent first cells S1 are communicated with each other via the communicating tube 14 in the second bulging portions 122 in which the groove 123 is formed.

[0040] 3(c), the first cell S1 has an upper portion defined by a pair of overlapping portions 131, and the second cell S2 has a lower portion defined by a pair of overlapping portions 131. When carrying out this folding process, it is preferable to heat-treat the textured sheet material 100 to soften it.

[0041] In the joining process, thermoplastic resin sheet materials are joined by heat welding to the upper and lower surfaces of the core layer 20 obtained in the folding process. The sheet material joined to the upper surface of the core layer 20 becomes the skin layer 30, and together with the upper wall portion 21 of the core layer 20, constitutes the upper closing wall 11 that closes the upper part of the side wall portion 23. The sheet material joined to the lower surface of the core layer 20 becomes the skin layer 40, and together with the lower wall portion 22 of the core layer 20, constitutes the lower closing wall 12 that closes the lower part of the side wall portion 23.

[0042] When the sheet material (skin layers 30, 40) is heat-sealed to the core layer 20, the two-layered upper wall portions 21 (overlapped portions 131) of the first cells S1 are heat-sealed to each other. Similarly, the two-layered lower wall portions 22 (overlapped portions 131) of the second cells S2 are heat-sealed to each other.

[0043] The joining step results in a hollow plate material 10 in which a large number of first cells S1 or second cells S2 are arranged in rows in the X direction and a large number of first cells S1 and second cells S2 are arranged alternately in the Y direction.

[0044] In the through-hole forming process, a large number of through-holes 13 are formed in the upper blocking wall 11 of the hollow plate 10. The through-holes 13 are formed by penetrating the upper blocking wall 11 of the hollow plate 10 with a penetrating member 50 such as a drill, needle, or punch. As shown in FIG. 3(d), a plurality of the penetrating members 50 are arranged in a row at intervals substantially equal to the distance between the centers of adjacent cells S. The penetrating members 50 are arranged and fixed below the hollow plate 10 so that the X direction of the hollow plate 10 coincides with the arrangement direction of the penetrating members 50. The penetrating members 50 are moved downward to form the through-holes 13 in the upper blocking wall 11 of the hollow plate 10. Each time the penetrating member 50 is lowered, it is moved in the Y direction of the hollow plate 10 by the formation pitch of the cells S. Furthermore, every three times it is lowered, it is moved in the Y direction of the hollow plate 10 by twice the formation pitch of the cells S. In this way, one through hole 13 is formed in the upper blocking wall 11 of the hollow plate material 10 at approximately the center of each of the second cells S2, and in the first cells S1 arranged side by side in the Y direction, one through hole 13 is formed in the approximately center of each of the alternatingly arranged first cells S1.

[0045] Through the above steps, a plurality of through holes 13 are formed, and the sound absorbing structure 1 in which the internal spaces of the first cells S1 are communicated with each other via the communication tubes 14 is manufactured. Next, the operation and effects of the sound absorbing structure 1 of this embodiment will be described.

[0046] (1) In the sound absorbing structure 1 of this embodiment, of two first cells S1 that are connected via a connecting tube 14 to form a connected cell group, one of the first cells S1 has a through hole 13 formed in the upper blocking wall 11, while the other first cell S1 has no through hole 13 formed in the upper blocking wall 11. Furthermore, all of the second cells S2 are not connected via the connecting tube 14, and have through holes 13 formed in their upper blocking walls 11.

[0047] Therefore, in the sound absorbing structure 1, the communicating cell group consisting of two first cells S1 and the second cell S2 each function as a Helmholtz resonator. Here, the sound absorption characteristics of a Helmholtz resonator depend on the internal volume of the container, and the larger the "internal volume of the container," the better the sound absorption performance in the low frequency range. Since the two first cells S1 are connected via the communicating tube 14, the communicating cell group has an "internal volume of the container" that is twice that of the second cell S2, and has better sound absorption performance in the low frequency range than the second cell S2. As a result, in the sound absorbing structure 1, the region with high sound absorption performance tends to shift to the low frequency range, improving sound absorption performance in the low frequency range.

[0048] (2) The diameter of the communication tube 14 is larger than the diameter of the through-hole 13 . Therefore, the flow resistance of air flowing into the communicating cell group via the communicating tube 14 is smaller than the flow resistance of air entering the communicating cell group via the through holes 13. This makes it easier for sound pressure that enters one of the first cells S1 constituting the communicating cell group via the through holes 13 to enter the other first cell S1 via the communicating tube 14. This improves the sound absorption performance of the sound absorbing structure 1 in the low frequency range.

[0049] (3) The opening edge 13 a of the through-hole 13 is located in the internal space of the cell S, which is the space below the inner surface of the upper wall portion 21 of the core layer 20 . This increases the length of the tube portion of the Helmholtz resonator, making it easier to shift the region with high sound absorption performance to the low frequency range. Sound absorption performance in the low frequency range is also improved.

[0050] (4) In the manufacturing method of the sound absorbing structure 1 of this embodiment, in the molding process of molding the uneven sheet material 100 from a flat sheet material, the grooves 123 are formed simultaneously with the molding of the uneven sheet material 100. Then, in the folding process, the uneven sheet material 100 is folded so that the communicating tubes 14 are formed in the side wall portions 23 of the core layer 20.

[0051] Therefore, the communicating tube 14 can be easily formed in the hollow plate material 10. Here, one possible method for connecting the internal spaces of multiple cells S to form a connected cell group is to join skin layers 30 and 40 to the core layer 20 to form a hollow plate 10, and then penetrate the hollow plate 10 from the side with a penetrating tool to connect the internal spaces of multiple cells S. However, this method is prone to problems such as uneven shapes of the connecting tubes 14, difficulty in forming the connecting tubes 14 in the desired locations, and damage to the sidewalls 23. In this regard, in this embodiment, the grooves 123 are formed during the molding of the textured sheet material 100, making it easy to form grooves 123 of the desired shape only in the necessary locations. This makes it easy to manufacture a sound-absorbing structure 1 with excellent sound-absorbing properties in the low-frequency range.

[0052] (5) Since the grooves 123 are formed when the textured sheet material 100 is formed, the shape, size, number, forming position, etc. of the grooves 123 can be easily adjusted as needed. The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0053] In the sound absorbing structure 1 of the above embodiment, the communicating tube 14 is formed in the vertical center of the side wall portion 23, but the position where the communicating tube 14 is formed is not limited to this. The communicating tube 14 may be formed closer to the lower or upper part of the vertical center of the side wall portion 23.

[0054] In the above embodiment, the communication tube 14 extends in a direction along the upper wall portion 21 and the lower wall portion 22 at the vertical center of the side wall portion 23, but is not limited to this. The communication tube 14 may extend at an angle relative to the upper wall portion 21 and the lower wall portion 22.

[0055] In the above embodiment, the communication tube 14 is formed in the center portion, which is a part of the side wall portion 23 in the vertical direction. However, the communication tube 14 may be formed in the entire side wall portion 23 . In the above embodiment, the communicating tube 14 extends straight along the upper wall portion 21 and the lower wall portion 22 at the vertical center of the side wall portion 23, but the shape is not limited to this. The communicating tube 14 may be bent or curved along the middle.

[0056] The communicating tube 14 is formed with approximately the same diameter from one side wall portion 23 to the other side wall portion 23 of adjacent first cells S1 in the Y direction, but the diameter may vary along the way. For example, the opening diameter of the communicating tube 14 may be larger on the side of the first cell S1 where the through hole 13 is formed. This can further improve the sound absorption effect.

[0057] In the sound-absorbing structure 1 of the above embodiment, the communicating tube 14 is formed in one location in the vertical direction of the side wall portion 23, but two or more locations are also acceptable. From the perspective of improving sound absorption performance in the low frequency range, it is preferable that the equivalent diameter of one communicating tube 14 is larger than the equivalent diameter of the through hole 13. From the perspective of improving sound absorption performance, it is preferable that the equivalent diameter of one communicating tube 14 is larger than the equivalent diameter of the through hole 13 and that the number of locations where the communicating tubes 14 are formed is smaller.

[0058] In the sound-absorbing structure 1 of the above embodiment, the communicating tube 14 has a circular cross section, but is not limited to this. The cross section may be semicircular, elliptical, triangular, rectangular, or other polygonal, or may be irregular. From the viewpoint of efficiently shifting the sound absorption characteristics of the communicating cell group to the low-frequency range, it is preferable that the equivalent diameter of the communicating tube 14, when the cross section is not circular, be larger than the diameter of the through hole 13.

[0059] In the sound absorbing structure 1 of the above embodiment, the through holes 13 are provided in the second cells S2 at a central position for each of the second cells S2 in a top view. Furthermore, in the first cells S1, one through hole 13 is provided in each of the first cells S1 constituting the communicating cell group at a central position in a top view. However, the positions and number of the through holes 13 in the first cells S1 and second cells S2 in which the through holes 13 are formed are not limited to this. The through holes 13 may be provided in positions shifted from the centers of the first cells S1 and second cells S2. Furthermore, the through holes 13 may be formed in multiple positions in one first cell S1 or one second cell S2.

[0060] In the hollow plate material 10 of the above embodiment, the core layer 20 is formed by folding and molding the textured sheet material 100 to form a honeycomb structure in which hexagonal cells S are partitioned inside the core layer 20, but the shape of the textured sheet material that forms the core layer 20 is not limited to this. A core layer 24 as a honeycomb structure may also be formed by sequentially folding a textured sheet material 200 as a three-dimensional structure in which multiple rows of convex portions with trapezoidal cross sections are arranged, as shown in Figure 4.

[0061] 4(a), the textured sheet material 200 is formed from a single flat sheet material made of thermoplastic resin, and strip-shaped first bulge portions 210 extending in the X direction are formed on the textured sheet material 200. The first bulge portions 210 are alternately formed in the Y direction, and therefore second bulge portions 220 that are relatively recessed compared to the first bulge portions 210 are formed between the first bulge portions 210 and extend in the X direction.

[0062] A groove 223 extending in the Y direction is formed in the center of the X direction in the region sandwiched between the boundary lines R and T on the upper surface 210a of the first bulging portion 210. The groove 223 has a semicircular cross section in a side view, and is formed in a part of the first bulging portion 210. The first bulging portions 210 with the groove 223 formed therein and the first bulging portions 210 without the groove 223 formed therein are alternately arranged in every other row in the Y direction of the textured sheet material 200. Furthermore, the grooves 223 are formed at the same position in the X direction in the region sandwiched between the boundary lines R and T on the upper surface 210a of the first bulging portion 210.

[0063] The core layer 24 is formed by sequentially folding the textured sheet material 200 along the boundary lines R and T. Specifically, as shown in FIG. 4(b), the textured sheet material 200 is mountain-folded along the boundary line R and valley-folded along the boundary line T. As shown in FIG. 4(c), one first bulge portion 210 is valley-folded at the boundary line T provided in the center portion in the X direction, so that the upper surface 210a on the right side in the X direction and the upper surface 210a on the left side in the X direction abut in an upright state. In the folded first bulge portion 210, the upper surface 210a on the right side in the X direction and the upper surface 210a on the left side in the X direction abut in an upright state to form a two-layered side wall portion 27 of the core layer 24, and the side surface 210b forms a single-layered side wall portion 27 of the core layer 24. An upper wall portion 25 consisting of the end surfaces 210c of adjacent first bulge portions 210 is formed at the upper end of the side wall portion 27. In addition, the upper surface 210a on the right side in the X direction and the upper surface 210a on the left side in the X direction abut against each other in an upright state, and thus a communicating tube (not shown) is formed as an internal space of the two grooves 223 in the vertical center of the two-layered side wall portion 27.

[0064] Furthermore, each second bulging portion 220 is mountain-folded at boundary line R located in the center in the X direction between adjacent boundary lines T, so that the lower surface 220a on the right side in the X direction and the lower surface 220a on the left side in the X direction abut in an upright state. In the folded second bulging portion 220, the lower surface 220a on the right side in the X direction and the lower surface 220a on the left side in the X direction abut in an upright state to form a side wall portion 27 of the core layer 24 having a two-layer structure, and the side surface 220b forms a side wall portion 27 of the core layer 24 having a single-layer structure. At the lower end of the side wall portion 27, a lower wall portion 26 consisting of the end surfaces 220c of adjacent second bulging portions 220 is formed.

[0065] The core layer 24 thus obtained, with the skin layers 30 and 40 bonded to both the upper and lower surfaces thereof, may be used as the hollow plate material 10. In the core layer 24 shown in FIG. 4(c), grooves 223 extending in the Y direction are formed on the upper surface 210a of the first bulge 210 during molding of the corrugated sheet material 200, thereby forming a communicating tube that connects the communicating cell groups. However, the structure that connects the communicating cell groups is not limited to grooves 223. For example, as shown in FIG. 4(b), recesses 224 are formed in the side wall portions of the core layer 24 when the corrugated sheet material 200 is folded. Because the corrugated sheet material 200 is softened by heat treatment during folding, recesses are likely to form in the mountain fold portion at the boundary line R, which becomes the groove-shaped recesses 224. In the state shown in FIG. 4(c), the recesses 224 form a communicating tube 225 that connects adjacent cells in the X direction. The communicating tube 225 is formed to penetrate the side wall portion of the two-layer structure and has a length equivalent to the thickness of the side wall portion of the two-layer structure. The communicating cylinder 225 allows adjacent cells in the X direction to form a communicating cell group.

[0066] In the hollow plate 10 of the above embodiment, the core layer 20 is partitioned and formed with hexagonal prism-shaped cells S. However, the shape of the cells S is not particularly limited. For example, the cells S may be polygonal, such as a square prism or an octagonal prism, or cylindrical. The cells S may also be frustoconical. In this case, cells of different shapes may be mixed. Furthermore, the cells do not have to be adjacent to each other, and gaps (spaces) may exist between the cells. In this case, a communicating tube is formed between adjacent cells via the space, connecting the internal spaces of the cells. An example of a core layer with such a configuration is described in Japanese Patent Laid-Open Publication No. 10-156985. Alternatively, the core layer may be made of plastic cardboard with a harmonica-shaped cross section.

[0067] Japanese Patent Laid-Open Publication No. 10-156985 discloses an invention relating to a sound-absorbing structure in which a plurality of cylindrical cells S' are arranged side by side with spaces between them. As shown in FIG. 5(b), this is a hollow plate material formed by bonding a pair of thermoplastic resin sheets 400 and 500 to a textured thermoplastic resin textured sheet material 300. The textured sheet material 300 is formed by molding one surface of a flat sheet material so that multiple cylindrical protrusions 301 are formed on the one surface, and the portions other than the protrusions 301 are formed as relatively recessed recesses 302. In the textured sheet material 300, the protrusions 301 are arranged side by side with the recesses 302 as spaces. When the textured sheet material 300 has such a shape, grooves 303 that connect the internal spaces of the protrusions 301 can be simultaneously formed during molding of the textured sheet material 300, as shown in FIG. 5(a). The grooves 303 can be formed by protruding the bottom surfaces of the recesses 302 upward in a groove shape so as to connect the protrusions 301. By forming the grooves 303, when the thermoplastic resin sheets 400 and 500 are joined, the grooves 303 function as a communicating tube that communicates with the internal spaces of the protrusions 301 as cells S'.

[0068] In the above embodiment, the hollow plate 10 is formed by bonding the skin layers 30, 40 to both sides of the core layer 20, but at least one of the skin layers 30, 40 may be omitted. When the skin layer 30 is omitted, the upper blocking wall 11 is formed only by the upper wall portion 21 of the core layer 20. When the skin layer 40 is omitted, the lower blocking wall 12 is formed only by the lower wall portion 22 of the core layer 20.

[0069] In the cells S in which the through-hole 13 is formed, one through-hole 13 is formed in approximately the center of each cell S, but the formation location and number of the through-holes 13 are not limited to this. For example, the through-holes 13 may be formed in different positions in each cell S. Furthermore, the through-holes 13 may be formed in one or more places in each cell S.

[0070] Although the through-holes 13 are formed in all the second cells S2, the second cells S2 with the through-holes 13 formed therein and the second cells S2 without the through-holes 13 formed therein may be mixed. In the sound absorbing structure 1 of the above embodiment, all of the first cells S1 are connected in pairs via the connecting tubes 14 to form a connected cell group, and all of the second cells S2 are not connected to one another. This is not limited to this, and some of the first cells S1 may be connected in pairs via the connecting tubes 14 to form a connected cell group, and the remaining first cells S1 may not be connected to one another. Alternatively, the second cells S2 may form a connected cell group, and the first cells S1 may not be connected to one another. Furthermore, some of the first cells S1 and some of the second cells S2 may form a connected cell group.

[0071] In the sound absorbing structure 1 of the above embodiment, the communicating cell group is composed of two first cells S1, but it may also be composed of three or more first cells S1. It may also be composed of three or more second cells S2. When the communicating cell group is composed of three or more cells S, it is sufficient that the through-hole 13 is not formed in at least one cell S of the three or more cells S that make up the communicating cell group. This allows the size of the "internal volume of the container" as a Helmholtz resonator to be larger than that of cells S that are not communicating, and improves sound absorption performance in the low frequency range.

[0072] When the interconnected cell group is composed of three or more cells S, the cells S may be arranged in a linear fashion or in an arc. For example, as shown in FIG. 3(a), when grooves 123 are formed on the upper surface of the second bulge 122 of the textured sheet material 100, the three or more first cells S1 that constitute the interconnected cell group are arranged in a linear fashion in the Y direction. Alternatively, if holes penetrating the side surfaces of the second bulge 122 are formed on the upper surface of the second bulge 122 along with the grooves 123, a communicating hole is formed between the first cell S1 and the second cell S2 when the textured sheet material 100 is folded. This allows adjacent first cells S1 in the Y direction to communicate with each other via the communicating tube 14, and also allows the second cell S2 adjacent to the first cell S1 that constitutes the interconnected cell group to communicate with the interconnected cell group. In this way, four adjacent cells S, as shown in FIG. 2(a), can be configured as an interconnected cell group. Furthermore, since the multiple cells S that make up the adjacent cell group are formed in a shape that is closer to an arc rather than in a straight line, when they function as a Helmholtz resonator, loss of sound absorption performance is suppressed and sound absorption characteristics are improved.

[0073] As an example of a group of interconnected cells composed of three or more cells S arranged in a circular shape, the core layer described in JP-A-10-156985 will be described. As shown in Fig. 5(c), when a through hole 13 is formed in one cell S', the cells S' arranged in a circle around the cell S' with the through hole 13 formed therein are connected by grooves 303. This reduces loss of sound absorption performance and improves the sound absorption characteristics of the group of interconnected cells.

[0074] Another sheet material may be bonded to the outer surface of the hollow plate 10 on the skin layer 40 side. This sheet material is not limited to synthetic resin, but may be, for example, a metal sheet (metal foil), steel plate, paper, cloth, etc. Furthermore, the skin layer 40 itself may be made of a metal sheet (metal foil), paper, cloth, etc.

[0075] Resins or additives that impart functionality may be added to the thermoplastic resin that constitutes the hollow plate material 10. For example, flame-retardant resins or additives, or deodorizers or fragrances may be added.

[0076] In the manufacturing method of the sound absorbing structure 1 of the above embodiment, grooves 123 are formed on both of the portions of the upper surface of the second bulge 122 of the textured sheet material 100 that come into contact during the folding process. However, grooves 123 may be formed on only one of the portions that come into contact. In this case, for example, if grooves 123 with a semicircular cross section are formed on only one of the portions that come into contact, the communicating tube 14 will have a semicircular cross section. If the communicating tube 14 is formed on only one of the two-layer side wall portions 23 of the folded core layer 20, the side wall portion 23 is less likely to buckle when a load is applied from one side of the sound absorbing structure 1. This increases the strength of the sound absorbing structure 1.

[0077] In the manufacturing method of the sound absorbing structure 1 of the above embodiment, grooves 123 of the same shape are formed on both of the portions of the upper surface of the second bulge 122 of the textured sheet material 100 that come into contact during the folding process, but grooves 123 of different shapes may also be formed. For example, a groove 123 with a semicircular cross section may be formed on one of the contacting portions, and a groove 123 with a triangular cross section may be formed on the other.

[0078] In the manufacturing method of the sound absorbing structure 1 of the above embodiment, the skin layers 30, 40 are joined to the core layer 20 by thermal welding, but the method of joining the skin layers 30, 40 is not limited to this. For example, the skin layers 30, 40 may be joined to the core layer 20 by attaching them with an adhesive or the like. Alternatively, an adhesive layer made of, for example, a thermoplastic resin may be interposed between the core layer 20 and the skin layers 30, 40, and the skin layers 30, 40 may be joined to the core layer 20 by the adhesive strength of this adhesive layer.

[0079] The technical ideas that can be understood from the above-described embodiment and modified examples will be described. (i) A sound-absorbing structure made of a hollow board having a plurality of columnar cells arranged side by side inside, the hollow board having a side wall portion extending in the thickness direction to divide the cells, and a pair of blocking walls at both ends of the side wall portion to block the cells, and a communicating cell group made up of a plurality of cells that are adjacent to each other through a space and whose internal spaces are connected via a communicating tube, the communicating tube being formed into a circular cross section, at least one of the cells that make up the communicating cell group has a through hole formed in one of the blocking walls that connects the inside and outside of the cell, and the other cells that make up the communicating cell group do not have such a through hole formed.

[0080] (b) A sound-absorbing structure made of a hollow board having a plurality of columnar cells arranged side by side inside, the hollow board having side walls extending in the thickness direction to divide the cells, and a pair of blocking walls closing the cells at both ends of the side walls, and a communicating cell group made up of a plurality of cells adjacent to each other through a space and whose internal spaces are connected via communicating tubes, at least one of the cells making up the communicating cell group has a through hole formed in one of the blocking walls that connects the inside and outside of the cell, and the other cells making up the communicating cell group do not have a through hole formed therein, and the opening edge of the through hole is located in the internal space of the cell. [Explanation of symbols]

[0081] S...cell 1...Sound-absorbing structure 10...Hollow plate material 11...Upper closing wall 12…Lower blocking wall 13...Through hole 14...Communication tube 23, 27...Side wall 100, 200, 300...Concave and convex sheet material 123, 223,303…Groove

Claims

1. A sound absorbing structure made of a hollow plate material having a plurality of column-shaped cells arranged side by side therein, The hollow plate material has a side wall portion extending in a thickness direction to partition the cell, and a pair of closing walls at both ends of the side wall portion to close the cell, The cells include first cells arranged in a row along a first direction perpendicular to the thickness direction, and second cells arranged in a row along the first direction, the first cells and the second cells being alternately arranged in a second direction perpendicular to the first direction, the second cell has a communicating tube between layers of a side wall portion having a two-layer structure, and the first cell constitutes a communicating cell group in which internal spaces of the first cells adjacent to each other in the second direction are communicated with each other via the communicating tube, A sound-absorbing structure characterized in that at least one of the first cells constituting the communicating cell group has a through hole formed in one of the blocking walls connecting the inside and outside of the first cell, and the other first cells of the first cells constituting the communicating cell group do not have a through hole formed therein.

2. 2. The sound absorbing structure according to claim 1, wherein the equivalent diameter of the communicating tube is larger than the equivalent diameter of the through hole.

3. An sound-absorbing structure as described in claim 1 or claim 2, characterized in that the hollow plate material is made of a resin in which a flame-retardant resin has been added to a thermoplastic resin.

4. A sheet material is provided which is joined to an outer surface of the hollow plate material, 4. The sound absorbing structure according to claim 1, wherein the sheet material is a metal foil or a steel plate.

5. A method for manufacturing a sound absorbing structure made of a hollow plate material having a side wall portion that extends in a thickness direction and divides a plurality of columnar cells, and a pair of closing walls that close the cells at both ends of the side wall portion, comprising: a hollow plate forming step of forming a hollow plate by forming a concave-convex sheet material having a predetermined concave-convex shape from a single flat sheet material made of synthetic resin; a through-hole forming step of forming a through-hole in one of the blocking walls, the through-hole communicating the inside and the outside of the cell; Equipped with In the hollow plate forming step, a groove is formed in the concave-convex sheet material to serve as a communicating tube that communicates between internal spaces of the plurality of cells in the hollow plate material, A method for manufacturing a sound-absorbing structure, characterized in that in the through hole forming step, the through hole is formed in at least one of a plurality of cells in the hollow plate material that are connected by the connecting tube.

6. The hollow plate forming step includes a forming step of forming the concave-convex sheet material, and a folding step of forming the hollow plate material by folding the concave-convex sheet material, In the forming step, the groove is formed in a portion of the concave-convex sheet material that will become the side wall portion, the groove extending in a width direction of the side wall portion, 6. The method for manufacturing a sound absorbing structure according to claim 5, wherein in the folding step, the communicating tube is formed in the side wall portion by the groove.

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