Sound absorbing structure

Abstract

To provide a sound absorbing structure which can be efficiently produced.SOLUTION: In this sound absorbing structure 10, skin layers 30, 40 are laminated on a main surface of a hollow plate material 20 in which a plurality of cells S are juxtaposed, the hollow plate material 20 includes a side wall part 23 erected in the thickness direction and partitioning the cells S, and a plurality of holes 15 are formed in the skin layers 30, 40. The hole 15 includes a hole 15 formed at a position overlapping the end portion of the side wall portion 23 in the thickness direction, and a hole 15 formed at a position not overlapping the end portion of the side wall portion 23 in the thickness direction and communicating the inside and the outside of the hollow plate material 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sound absorbing structure having a hollow plate member with communication holes formed therein that connect the inside and outside of the hollow plate member. [Background technology]

[0002] Hollow plate-like hollow structures with multiple cells arranged side by side inside are lightweight yet have appropriate strength, and are therefore sometimes used for containers, boxes, etc. Attempts have also been made to improve the versatility of such hollow structures by adding some kind of function to them. Patent Document 1 describes an invention relating to a sound-absorbing structure, which is a hollow structure with multiple cells arranged upright inside and multiple communicating holes formed on the top surface thereof, thereby improving sound absorption performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-65026 Summary of the Invention [Problem to be solved by the invention]

[0004] The sound-absorbing structure described in Patent Document 1 has a hollow structure in which sheet-like skin layers are bonded to the upper and lower surfaces of a hollow plate-like core layer in which a plurality of cells are arranged side by side, and a plurality of through holes that connect the inside and outside of the cells are formed in one of the main surfaces of the hollow structure. These through holes are formed by manufacturing a hollow structure in which a skin layer is bonded to a hollow plate material, and then, as a post-processing step, passing a needle-shaped connecting jig through one of the main surfaces of the hollow structure. Therefore, the process for manufacturing the hollow structure and the process for forming the through holes are separate processes, which increases the number of manufacturing steps and makes it unsuitable for mass production.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sound-absorbing structure that can be produced efficiently. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a sound-absorbing structure in which a skin layer is laminated on the main surface of a hollow board in which a plurality of cells are arranged side by side, the hollow board having side wall portions that are erected in the thickness direction and that divide the cells, and a plurality of holes are formed in the skin layer, the holes including holes formed at positions that overlap with the ends of the side wall portions in the thickness direction and holes formed at positions that do not overlap with the ends of the side wall portions in the thickness direction and that connect the inside and outside of the hollow board.

[0007] According to the above configuration, the skin layer laminated on the main surface of the hollow plate has holes formed in positions that overlap the thickness-wise ends of the side walls of the hollow plate, and holes formed in positions that do not overlap the thickness-wise ends of the side walls of the hollow plate, thereby providing communication between the inside and outside of the hollow plate. For example, if there are closed and open hollow portions on at least one of the front and back surfaces of the hollow plate, laminating a skin layer with holes formed therein will result in holes that communicate between the inside and outside of the hollow plate if the holes are located in positions that do not overlap the thickness-wise ends of the side walls of the hollow plate. A sound-absorbing structure having a mixture of holes formed in positions that overlap the thickness-wise ends of the side walls of the hollow plate and holes formed in positions that do not overlap the thickness-wise ends of the side walls of the hollow plate can be produced efficiently by simply laminating a skin layer with holes formed in advance on the hollow plate.

[0008] In the above configuration, it is preferable that the holes include holes formed at positions overlapping with the ends of the side walls in the thickness direction and communicating between the inside and outside of the hollow plate material. In the above configuration, it is preferable that the cells are formed in a polygonal columnar shape, and the holes formed at positions overlapping with the ends of the side wall portions in the thickness direction are formed so as to share one corner and span multiple adjacent cells.

[0009] In the above configuration, it is preferable that a portion of the side wall portion is formed as a two-layer structure, and the hole formed at a position overlapping with the end of the side wall portion in the thickness direction is formed at a position overlapping with the end of the side wall portion of the two-layer structure so as to span multiple adjacent cells. [Effects of the Invention]

[0010] According to the present invention, a sound absorbing structure that can be produced efficiently can be obtained. [Brief explanation of the drawings]

[0011] [Figure 1] 1A is a perspective view of a sound absorbing structure according to a first embodiment, FIG. 1B is a cross-sectional view taken along line α-α in FIG. 1A, and FIG. 1C is a cross-sectional view taken along line β-β in FIG. [Figure 2] FIG. 1A is a perspective view of a sheet material that constitutes a core layer of the sound-absorbing structure of the first embodiment, FIG. 1B is a perspective view showing the sheet material in the middle of being folded, and FIG. 1C is a perspective view showing the sheet material in the folded state. [Figure 3] FIG. 2 is a perspective view of a core layer according to the first embodiment. [Figure 4] 5A to 5C are diagrams illustrating a manufacturing process of the sound absorbing structure. [Figure 5] 1A is a perspective view of a sound absorbing structure according to a second embodiment, FIG. 1B is a cross-sectional view taken along the line γ-γ in FIG. 1A, and FIG. 1C is a cross-sectional view taken along the line σ-σ in FIG. [Figure 6] 10A is a perspective view of a sheet material that constitutes a core layer of a sound-absorbing structure of a second embodiment, FIG. 10B is a perspective view showing the sheet material in the middle of being folded, and FIG. 10C is a perspective view showing the sheet material in the folded state. [Figure 7] 1A is a perspective view of a modified example of the sound absorbing structure, and FIG. 1B is a cross-sectional view thereof. DETAILED DESCRIPTION OF THE INVENTION

[0012] (First embodiment) A sound absorbing structure according to a first embodiment of the present invention will now be described with reference to FIG. 1(a), the sound absorbing structure of this embodiment is composed of a core layer 20 having a plurality of cells S arranged side by side therein, a sheet-like skin layer 30 joined to the upper surface of the core layer 20, and a sheet-like skin layer 40 joined to the lower surface of the core layer 20. The core layer 20 and the skin layers 30 and 40 of this embodiment are made of a thermoplastic resin.

[0013] The thermoplastic resin constituting the core layer 20 may be any conventionally known thermoplastic resin, such as polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, polybutylene terephthalate resin, etc. In this embodiment, the core layer 20 is made of polypropylene resin. In addition, the thermoplastic resin constituting the skin layers 30, 40 may also be any conventionally known thermoplastic resin. The thermoplastic resin constituting the skin layers 30, 40 is preferably the same thermoplastic resin as that of the core layer 20, and in this embodiment, the skin layers 30, 40 are made of polypropylene resin.

[0014] As shown in Figures 1(b) and 1(c), the core layer 20 is formed by folding a single sheet of thermoplastic resin formed into a predetermined shape. The core layer 20 is composed of an upper wall portion 21, a lower wall portion 22, and side wall portions 23 that are erected between the upper wall portion 21 and the lower wall portion 22 and define cells S in the shape of hexagonal columns. The size of the cells S is not particularly limited, but it is preferable that the distance between opposing sides of the regular hexagon that is the cross-sectional shape of the cells S is approximately 5 to 20 mm. The height of the cells S in the thickness direction of the sound absorbing structure 10 is preferably approximately 5 to 40 mm, and more preferably approximately 10 to 30 mm.

[0015] As shown in FIGS. 1(b) and 1(c), the cells S formed within the core layer 20 include a first cell S1 and a second cell S2, each having a different structure. As shown in FIG. 1(b), the first cell S1 has a two-layer upper wall portion 21 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. The first cell S1 also has a single-layer lower wall portion 22 provided on the lower part of the side wall portion 23. On the other hand, as shown in FIG. 1(c), the second cell S2 has a single-layer upper wall portion 21 provided on the upper part of the side wall portion 23. The second cell S2 also has a two-layer lower wall portion 22 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. As shown in FIGS. 1(b) and 1(c), adjacent first cells S1 and adjacent second cells S2 are each separated by a two-layer side wall portion 23. In addition, in FIG. 1(a) and FIG. 3, the upper wall portion 21 and the lower wall portion 22 of the core layer 20 are shown as having a single-layer structure.

[0016] 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.

[0017] 1(a) and 3, in the upper wall portion 21 and the lower wall portion 22 of the core layer 20, a substantially spindle-shaped opening 24 is formed at the position of the longest diagonal of the regular hexagon, which is the cross-sectional shape of the cell S, so as to bisect the upper wall portion 21 and the lower wall portion 22. The opening 24 is formed only in the upper wall portion 21 in the first cell S1, and only in the lower wall portion 22 in the second cell S2. That is, in each cell S, the opening 24 is formed only in the upper wall portion 21 and the lower wall portion 22 of the two-layer structure.

[0018] 1(a) to 1(c), a skin layer 30 is bonded to the upper surface of the core layer 20, and a skin layer 40 is bonded to the lower surface of the core layer 20. Therefore, the upper wall portion 21 of the core layer 20 and the skin layer 30 are provided at the upper edge of the side wall portion 23 of the core layer 20, thereby closing the cells S. Similarly, the lower wall portion 22 of the core layer 20 and the skin layer 40 are provided at the lower edge of the side wall portion 23 of the core layer 20, thereby closing the cells S.

[0019] As shown in FIGS. 1(a) to 1(c), a plurality of holes 15 are formed in the skin layers 30, 40 to connect the skin layers 30, 40. The plurality of holes 15 are formed so as to be aligned in the vertical and horizontal directions of the skin layers 30, 40 (the X and Y directions in FIG. 1(a)). The holes 15 are regularly formed at equal intervals in both the vertical and horizontal directions. The formation pitch of the holes 15 is smaller than the formation pitch of the cells S, and is preferably about 1 / 5 to 5 / 5 of the formation pitch of the cells S, and more preferably about 1 / 5 to 3 / 5 of the formation pitch of the cells S. Therefore, a plurality of holes 15 are formed for each cell S in the core layer 20. The formation pitch of the cells S refers to the distance between the centers of adjacent cells S that share one side of a hexagon.

[0020] The shape of the holes 15 is not particularly limited, but may be round or rectangular in top view, or may be irregular. The size of the holes 15 is also not particularly limited, but from the perspective of the sound absorbing properties of the sound absorbing structure 10, the holes 15 preferably have a diameter that is approximately 1 / 20 to 1 / 5 of the distance between opposing sides of the regular hexagon that is the cross-sectional shape of the cells S. For example, the diameter of the holes 15 is preferably approximately 0.25 to 4.0 mm, and more preferably approximately 0.5 to 1.5 mm.

[0021] As shown in FIG. 1(b), in a first cell S1 having an opening 24 formed in the upper wall portion 21, some of the multiple holes 15 formed in the skin layer 30 are formed in positions overlapping the opening 24. As a result, the inside and outside of the first cell S1 are in communication with each other via the holes 15 and the opening 24. In addition, in the first cell S1, some of the multiple holes 15 formed in the skin layer 30 are formed in positions not overlapping the opening 24, so that the inside and outside of the first cell S1 are not in communication with each other. Here, the holes 15 formed in positions overlapping the opening 24 are referred to as first holes 15a, and the holes 15 formed in positions not overlapping the opening 24 are referred to as second holes 15b. The first holes 15a are holes 15 that are at least partially formed in positions overlapping the opening 24 and that are in communication with each other via the opening 24, and the holes 15 that are not in communication with each other via the opening 24 and that are not in communication with each other via the opening 24 are referred to as second holes 15b. On the other hand, in the first cell S1 in which the opening 24 is not formed in the lower wall portion 22, the plurality of holes 15 formed in the skin layer 40 all become second holes 15b.

[0022] As shown in FIG. 1(c), in a second cell S2 having an opening 24 formed in the lower wall portion 22, some of the multiple holes 15 formed in the skin layer 40 become first holes 15a formed in positions overlapping with the opening 24. As a result, the holes 15 and the opening 24 communicate with the inside and outside of the second cell S2. In addition, in the second cell S2, some of the multiple holes 15 formed in the skin layer 40 become second holes 15b formed in positions not overlapping with the opening 24. On the other hand, in a second cell S2 having no opening 24 formed in the upper wall portion 21, all of the multiple holes 15 formed in the skin layer 30 become second holes 15b.

[0023] Next, a method for manufacturing the sound absorbing structure 10 will be described with reference to FIGS. The method for manufacturing the sound-absorbing structure 10 comprises a folding step, a heating step, a hole-forming step, and a lamination step. The folding step is a step of folding and shaping a sheet material 100 that has been vacuum-formed into a predetermined uneven shape to form a core layer 20 as a hollow plate material. The heating step is a step of heating the upper and lower sides of the core layer 20 to bond the upper wall portion 21 and the lower wall portion 22 of the two-layer structure to each other and form openings 24. The hole-forming step is a step of drilling a plurality of holes 15 through sheets that will become the skin layers 30 and 40 to form perforated sheets 70 and 80. The lamination step is a step of laminating the perforated sheets 70 and 80 onto the main surface of the core layer 20 as a hollow plate material to obtain the sound-absorbing structure 10.

[0024] In this embodiment, these steps are performed in a series by the apparatus T shown in Figure 4. Figure 4 is a schematic diagram of the apparatus T, with the left side being the upstream side and the right side being the downstream side. The apparatus T includes, from upstream to downstream, a sheet roll 61 on which a thermoplastic resin sheet is wound, a vacuum forming drum 62 for forming the sheet material 100 with the concave and convex shape, a transport roll 63 and a first conveyor 64 for folding the core layer 20, a second conveyor 65 for heating the core layer 20, a sheet roll 66 on which a sheet to become the skin layers 30 and 40 is wound, a perforation forming roll 67 for forming the perforated sheets 70 and 80 by drilling a plurality of holes in the sheet to become the skin layers 30 and 40, and a third conveyor 68 for joining the perforated sheets 70 and 80 to form the skin layers 30 and 40. The holes formed in the perforated sheets 70 and 80 are referred to as "holes 16" here to distinguish them from the holes 15 formed in the sound-absorbing structure 10.

[0025] As shown in Figure 4, in the folding process, a thermoplastic resin sheet wound around a sheet roll 61 is supplied to a vacuum forming drum 62, and a sheet material 100 having a predetermined uneven shape formed on the sheet is formed, and the sheet material 100 is supplied to a transport roll 63 and a first conveyor 64 and folded to form a core layer 20.

[0026] As shown in FIG. 2(a), the sheet material 100 formed by the vacuum forming drum 62 has a predetermined uneven shape. The sheet material 100 has band-shaped flat regions 110 and bulged regions 120 alternately arranged in the longitudinal direction (X direction) of the sheet material 100. In the bulged region 120, a first bulge 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 bulged region 120. Note that the angle between the upper surface and the side surface of the first bulge portion 121 is preferably 90 degrees, so that the cross section of the first bulge portion 121 has a downward U-shape. The width of the first bulge 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 to be twice the bulge height of the first bulge portion 121 (the length in the short direction of the side surfaces).

[0027] 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.

[0028] The first bulging portion 121 and the second bulging portion 122 are formed by partially bulging the sheet upwards by utilizing the plasticity of the sheet. As shown in FIG. 4, the sheet material 100 moves toward the transport roll 63 and the first conveyor 64. The transport speed of the first conveyor 64 is set to be slower than the rotation speed of the transport roll 63. As a result, as shown in FIGS. 2(a) to 2(c), the sheet material 100 is sequentially folded along the boundary lines P and Q to form the core layer 20. Specifically, the sheet material 100 is folded in the X direction by being 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. Then, as shown in FIGS. 2(b) and 2(c), the top surface and side surface of the first bulging portion 121 are folded over each other, and the end surface of the second bulging portion 122 is folded over the flat region 110, thereby forming a rectangular column-shaped partition 130 extending in the Y direction for each bulging region 120. The partitions 130 are formed successively in the X direction to form the hollow plate-shaped core layer 20.

[0029] When the sheet material 100 is folded 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 Fig. 2(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, respectively, become overlapping portions 131.

[0030] Furthermore, a hexagonal columnar region formed by folding the second bulging portion 122 becomes the second cell S2, and a hexagonal columnar region formed between a pair of adjacent partitions 130 becomes the first cell S1. In this embodiment, the upper and side surfaces of the second bulging portion 122 form the side wall portion 23 of the second cell S2, and the side surfaces of the second bulging portion 122 and flat portions located between the second bulging portions 122 in the bulging region 120 form the side wall portion 23 of the first cell S1. The contact areas between the upper surfaces of the second bulging portions 122 and the contact areas between the flat portions in the bulging region 120 form the side wall portion 23 having a two-layer structure.

[0031] Next, in the heating process, the core layer 20 formed by folding the sheet material 100 moves toward the second conveyor 65. The conveying speed of the second conveyor 65 is set to be equal to the conveying speed of the first conveyor 64. A heating device 65a is provided within the second conveyor 65. The heating temperature of the heating device 65a is set to a temperature at which the thermoplastic resin constituting the core layer 20 melts. Therefore, in the core layer 20 that has passed through the second conveyor 65, the thermoplastic resin constituting the core layer 20 melts and thermally shrinks due to the heating by the heating device 65a, and openings 24 are formed in the two-layer upper wall portion 21 of the first cell S1 and the two-layer lower wall portion 22 of the second cell S2.

[0032] 3, the upper wall 21 of the first cell S1 has a two-layer structure with an overlapping portion 131 formed by folding the top surface and side surface of the first bulge portion 121 over, and the two-layer upper wall portions 21 of adjacent compartments 130 are abutted together to form the upper wall portion 21 of one first cell S1. Therefore, the opening 24 formed in the two-layer upper wall portion 21 of the first cell S1 is formed by thermal shrinkage of the abutted portion, and is formed into a generally spindle shape that divides the hexagonal upper wall portion 21 of the first cell S1 in half. On the other hand, the upper wall 21 of the second cell S2, which is formed by folding the second bulge portion 122, has a single-layer structure formed by the first bulge portion 121, and no opening 24 is formed therein.

[0033] The bottom wall 22 of the second cell S2 has a two-layer structure with an overlapping portion 131 formed by folding the end face of the second bulge portion 122 and the flat region 110, and this overlapping portion 131 is butted together to form the bottom wall 22 of one second cell S2. Therefore, the opening 24 formed in the two-layer bottom wall 22 of the second cell S2 is formed by thermal contraction of the butted overlapping portion 131, and is formed into a roughly spindle shape that divides the hexagonal bottom wall 22 of the second cell S2 in half. On the other hand, the bottom wall 22 of the first cell S1 has a single-layer structure formed by the flat region 110, and no opening 24 is formed therein.

[0034] 4, the core layer 20 heated by the second conveyor 65 moves toward the third conveyor 68. The conveying speed of the third conveyor 68 is set to be equal to the conveying speed of the second conveyor 65.

[0035] Various rolls and the like for the hole forming process are arranged near the entrance of the third conveyor 68. Specifically, a sheet roll 66 on which a thermoplastic resin sheet that will become the skin layers 30, 40 is wound, and a hole forming roll 67 for forming a plurality of holes 16 in the sheet that will become the skin layers 30, 40 to form perforated sheets 70, 80 are arranged above and below the core layer 20. The conveying speeds of the sheet roll 66 and the hole forming roll 67 are set to be equal to the conveying speeds of the second conveyor 65 and the third conveyor 68. An adhesive layer is laminated on the sheet wound around the sheet roll 66.

[0036] A large number of needle-like members protrude from the surface of the perforation roll 67 for forming holes 16 in the sheet that will become the skin layers 30 and 40. Therefore, when the sheet passes through the perforation roll 67 located on the upper side of the device T, a perforated sheet 70 with a large number of holes 16 formed therein is formed, and when the sheet passes through the perforation roll 67 located on the lower side, a perforated sheet 80 with a large number of holes 16 formed therein is formed.

[0037] As shown in Fig. 4, the hole-forming roll 67 is disposed on the side that will become the surface of the skin layers 30, 40. When the needle-shaped members penetrate the sheet, the tips of the needle-shaped members pierce the sheet and push the sheet apart to form holes 16, and therefore, at the periphery of the holes 16 that are formed in the sheet, turned-over pieces of the sheet are formed. In this embodiment, because the hole-forming roll 67 is disposed on the side that will become the surface of the skin layers 30, 40, the turned-over pieces at the periphery of the holes 16 are formed on the side that will become the back surface of the skin layers 30, 40. As a result, the surfaces of the skin layers 30, 40 are smooth.

[0038] The upper and lower perforation forming rolls 67 have the same configuration, and the shape and number of the protruding needle-like members are the same. The needle-like members are protruding so that their formation pitch is smaller than the formation pitch of the openings 24 formed in the core layer 20. The diameter of the needle-like members is larger than the diameter of the actual holes 15. This is because the diameter of the holes 16 becomes smaller when the perforated sheets 70, 80 are heat-bonded by heating with the heating device 68a of the third conveyor 68 in the lamination process described later.

[0039] Next, in the lamination process, the perforated sheet 70 is supplied to the upper surface of the core layer 20 upstream of the third conveyor 68, and the perforated sheet 80 is supplied to the lower surface of the core layer 20 upstream of the third conveyor 68. As the core layer 20 passes between the third conveyors 68, the perforated sheets 70, 80 are sequentially bonded to the upper and lower surfaces of the core layer 20. The third conveyor 68 is provided with a heating device 68a, and the adhesive layers of the perforated sheets 70, 80 supplied to the core layer 20 are melted as the core layer 20 passes through the third conveyor 68. Therefore, when the core layer 20 with the perforated sheets 70, 80 laminated thereon passes through the third conveyor 68, the adhesive layers are cooled and solidified. As a result, the perforated sheet 70 is bonded to the core layer 20 as the skin layer 30, and the perforated sheet 80 is bonded to the core layer 20 as the skin layer 40. At this time, the diameter of the holes 16 formed in the perforated sheets 70, 80 becomes smaller, and holes 15 are formed. In this way, the skin layers 30, 40 are joined to the upper and lower surfaces of the core layer 20 via adhesive layers, and the sound-absorbing structure 10 is obtained, in which first holes 15a that communicate between the inside and outside of the cells S and second holes 15b that do not communicate between the inside and outside of the cells S are formed.

[0040] In addition, the two-layered upper wall portions 21 and the two-layered lower wall portions 22 are joined together in the heating process when forming the core layer 20. In addition, the thermoplastic resin is melted and heat-welded at the upper and lower edges of the two-layered side wall portions 23, while a portion is formed in the center of the core layer 20 in the thickness direction where the side wall portions 23 are not heat-welded to each other.

[0041] Next, the operation and effects of the sound absorbing structure 10 of the first embodiment will be described. (1) In the sound absorbing structure 10 of the above embodiment, a plurality of holes 15 are formed in the skin layers 30, 40 laminated on the main surfaces of the core layer 20, and the plurality of holes 15 include first holes 15a that communicate between the inside and outside of the core layer 20 and second holes 15b that do not communicate between the inside and outside of the core layer 20. These holes 15a, 15b are formed by laminating perforated sheets 70, 80, in which a plurality of holes 16 have been formed beforehand, onto the core layer 20. This allows for more efficient production than a sound absorbing structure in which holes that communicate between the inside and outside of the cells S are formed after the skin layers 30, 40 have been laminated on the core layer 20.

[0042] (2) In the sound-absorbing structure 10 of the above embodiment, a plurality of openings 24 are formed in the upper wall portion 21 and the lower wall portion 22 of the core layer 20 in which a plurality of cells S are arranged side by side. Some of the plurality of holes 15 formed in the skin layers 30, 40 are located in the portions where the openings 24 are formed and form first holes 15a that communicate between the inside and outside of the cells S, and some of the remaining holes are located in the portions where the openings 24 are not formed and form second holes 15b that do not communicate between the inside and outside of the cells S. Therefore, the first holes 15a and the second holes 15b are formed by laminating the perforated sheets 70, 80, in which a plurality of holes 16 have been formed in advance, onto the core layer 20. The first holes 15a that communicate between the inside and outside of the cells S are easily formed.

[0043] (3) The pitch at which the holes 15 formed in the skin layers 30, 40 are formed is smaller than the pitch at which the openings 24 are formed in the upper wall portion 21 and the lower wall portion 22. Therefore, any of the holes 15 formed in the skin layers 30, 40 is likely to overlap with the position at which the openings 24 are formed.

[0044] (4) The method for manufacturing the sound absorbing structure 10 of the above embodiment includes a hole forming step in which perforated sheets 70, 80 are formed by drilling a plurality of holes 16 through the sheets before joining the skin layers 30, 40 to the core layer 20, and the perforated sheets 70, 80 are laminated on the main surfaces of the core layer 20. Therefore, the productivity of the sound absorbing structure 10 can be improved compared to when communicating holes connecting the inside and outside of the cells S are formed after joining the skin layers 30, 40 to the core layer 20.

[0045] (5) When forming communication holes that connect the inside and outside of the cells S after joining the skin layers 30, 40 to the core layer 20, foreign matter such as tiny pieces of thermoplastic resin that are generated when forming the communication holes may get into the cells S. Once such foreign matter gets into the cells S, it is difficult to remove it. In this regard, in the manufacturing method of the sound-absorbing structure 10 of the above embodiment, the perforated sheets 70, 80 are laminated on the main surface of the core layer 20, and therefore, the entry of foreign matter such as tiny pieces into the cells S is suppressed.

[0046] (6) In the manufacturing method of the sound absorbing structure 10 of the above embodiment, each step is performed in a continuous flow using the device T. Therefore, the steps of forming the core layer 20, heating the core layer 20 to form the openings 24, forming the perforated sheets 70, 80, and supplying the perforated sheets 70, 80 to the core layer 20 can be performed continuously. This allows the sound absorbing structure 10 to be manufactured efficiently, improving productivity.

[0047] (7) In the hole-forming step, the holes 16 are formed by passing the sheet through a hole-forming roll 67 having a large number of needle-like members protruding therefrom. This allows the perforated sheets 70, 80 to be continuously produced and continuously supplied to the core layer 20. This allows the sound-absorbing structure 10 to be produced efficiently.

[0048] (8) The perforated sheets 70, 80 are formed by the sheet roll 66, the perforation roll 67, etc., which are provided near the upstream side of the third conveyor 68. The sheet roll 66, the perforation roll 67, etc. are synchronized with the second conveyor 65 and the third conveyor 68. This makes it easy to supply the perforated sheets 70, 80 to the core layer 20, improving the productivity of the sound-absorbing structure 10.

[0049] (9) In the sound absorbing structure 10 of the above embodiment, the openings 24 are formed in the upper wall portion 21 and the lower wall portion 22 of the core layer 20 formed by the folding process and the heating process. Therefore, by laminating the perforated sheets 70, 80, the first holes 15a that communicate between the inside and outside of the cells S can be easily formed.

[0050] (10) In the manufacturing method of the sound absorbing structure 10 of the above embodiment, the pitch of the holes 16 formed in the hole forming step is set smaller than the pitch of the openings 24. Therefore, the first holes 15a that communicate between the inside and outside of the cells S can be easily formed without strict alignment between the holes 16 and the openings 24.

[0051] (11) In the hole forming step, the hole forming roll 67 is positioned on the side that will become the front surface of the skin layers 30, 40. Therefore, the return pieces around the edges of the holes 16 drilled through the sheet are formed on the side that will become the back surface of the skin layers 30, 40. The surfaces of the skin layers 30, 40 become smooth, and the surface of the sound absorbing structure 10 can be made smooth.

[0052] (12) The diameter of the needle-like members of the hole-forming roll 67 in the hole-forming step is larger than the diameter of the actual holes 15. Therefore, even if the opening diameter of the holes 16 in the perforated sheets 70, 80 becomes smaller due to heating by the heating device 68a of the third conveyor 68 in the laminating step, the opening diameter required for the holes 15 in the sound-absorbing structure 10 can be ensured.

[0053] (13) In the hole forming step, ring-shaped return pieces are formed around the periphery of the hole 16 drilled through the sheet. Therefore, when heated in the lamination step, the return pieces around the periphery of the hole 16 become pockets of material, making the periphery of the hole 16 in the perforated sheets 70, 80 less likely to tear.

[0054] (Second embodiment) Next, a sound absorbing structure according to a second embodiment of the present invention will be described with reference to FIGS.

[0055] The sound absorbing structure 10a of the second embodiment differs from the core layer 20 of the first embodiment in the structure of the core layer 20a. Other than the structure of the core layer 20a, the sound absorbing structure 10a is the same as the sound absorbing structure 10 of the first embodiment, and its manufacturing method is also basically the same as that of the sound absorbing structure 10 of the first embodiment, so the following description will mainly focus on the differences.

[0056] The core layer 20a is formed by folding and molding a sheet material 200 shaped into the shape shown in FIG. 6(a). Cells S defined within the core layer 20a include a first cell S1a and a second cell S2a, each having a different configuration. As shown in FIG. 5(b), the upper end of the first cell S1 is closed by a single-layer upper wall portion 21a, and its lower end is open downward without being closed. That is, the upper surface of the first cell S1a of the core layer 20a is formed by the single-layer upper wall portion 21a, and its lower surface is formed by the lower edge of the side wall portion 23a. The unclosed lower end of the first cell S1a functions as an opening 24a formed in the lower wall portion 22a.

[0057] 5(c), the second cell S2a has its lower end blocked by a single-layered lower wall 22, and its upper end is open and not blocked. That is, in the second cell S2a, the lower surface of the core layer 20a is formed by a single-layered lower wall 22a, and the upper surface is formed by the upper edge of the side wall 23a. The unblocked upper end of the second cell S2a functions as an opening 24a formed in the upper wall 21a.

[0058] 5(a), the first cells S1a and the second cells S2a are arranged in a row in the X direction, with the first cells S1a or the second cells S2a adjacent to each other. In the Y direction perpendicular to the X direction, the rows of the first cells S1a and the rows of the second cells S2a are arranged alternately.

[0059] 5(b) and 5(c), adjacent first cells S1a and adjacent second cells S2a are separated by sidewalls 23a having a two-layer structure formed perpendicular to the upper wall 21a and the lower wall 22a. On the other hand, adjacent first cells S1a and second cells S2a are separated by sidewalls 23 having a single layer structure formed perpendicular to the upper wall 21a and the lower wall 22.

[0060] As shown in Fig. 5(a), the skin layers 30, 40 are bonded to the upper surface of the upper wall portion 21a and the lower surface of the lower wall portion 22a of the core layer 20a via adhesive layers (not shown). The skin layer 30 is bonded to the upper surface of the core layer 20a, the upper wall portion 21a of the first cell S1a, and the upper ends of the side wall portions 23a of the second cell S2a. The skin layer 40 is bonded to the lower surface of the core layer 20a, the lower ends of the side wall portions 23a of the first cell S1a, and the lower wall portions 22a of the second cell S2a. Therefore, the upper surface of the sound absorbing structure 10a of the second embodiment has a two-layer structure consisting of the upper wall portion 21a of the core layer 20a and the skin layer 30 in the first cell S1a, and a single-layer structure consisting of only the skin layer 30 in the second cell S2a, with the openings 24a being closed by the skin layer 30. In addition, the underside of the sound-absorbing structure 10a has a single-layer structure in the first cell S1a, with the opening 24a blocked by the skin layer 40, and a two-layer structure in the second cell S2a, consisting of the lower wall portion 22a of the core layer 20a and the skin layer 40.

[0061] Next, a method for manufacturing the sound absorbing structure 10a of the second embodiment will be described with reference to FIG. The method for manufacturing the sound absorbing structure 10a of the second embodiment is similar to the method for manufacturing the sound absorbing structure 10 of the first embodiment, and comprises a folding step, a heating step, a hole forming step, and a lamination step, with only the folding step being different from that of the first embodiment. Each step is performed in a series of steps using an apparatus similar to apparatus T shown in Figure 4. The only difference from apparatus T is the surface shape of the vacuum forming drum 62.

[0062] The core layer 20a is obtained by folding and molding a sheet material 200 that has been vacuum-formed into a predetermined uneven shape as shown in FIG. 6(a). The sheet material 200 has strip-shaped first bulging portions 210 and second bulging portions 220 that are alternately arranged in the width direction (Y direction) of the sheet material 200. The first bulging portions 210 are formed in a shape that protrudes upward, and the second bulging portions 220 are formed in a shape that protrudes downward. The first bulging portions 210 and the second bulging portions 220 are alternately arranged to extend in the X direction. The first bulging portions 210 when the sheet material 200 is viewed from above and the second bulging portions 220 when the sheet material 200 is viewed from below have the same shape and are formed at positions that are shifted by 1 / 2 pitch in the X direction.

[0063] The first bulge 210 is composed of an upper surface 210a, a pair of side surfaces 210b, and a pair of end surfaces 210c, and its cross section in the Y direction is a trapezoid obtained by bisecting a regular hexagon along its longest diagonal. The pair of end surfaces 210c are formed at the position of the boundary line P' shown in Figure 6(a). The angle between the end surfaces 210c and the upper surface 210a is approximately 90°.

[0064] On the other hand, the second bulge portion 220 comprises a lower surface 220a, a pair of side surfaces 220b, and a pair of end surfaces 220c, and its cross-sectional shape in the Y direction is a trapezoid obtained by bisecting a regular hexagon along its longest diagonal. The pair of end surfaces 220c are formed at the boundary line Q' shown in FIG. 6(a). The angle between the end surfaces 220c and the lower surface 220a is approximately 90°. The length of the second bulge portion 220 in the X direction, i.e., the length between the pair of end surfaces 220c, is the same as the length of the first bulge portion 210 in the X direction, i.e., the length between the pair of end surfaces 210c. The end surfaces 220c of the second bulge portion 220 are located at the center of the first bulge portion 210 in the X direction. Note that the side surfaces 210b of the first bulge portion 210 and the side surfaces 220b of the second bulge portion 220 are separated for ease of explanation, but they have the same configuration.

[0065] The core layer 20a is formed by sequentially folding the sheet material 200 along boundary lines P' and Q'. Specifically, as shown in FIG. 6(b), the sheet material 200 is mountain-folded along boundary line P' and valley-folded along boundary line Q'. As shown in FIG. 6(c), one first bulging portion 210 is valley-folded at boundary line Q' 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 bulging 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 the side wall portion 23a of the core layer 20a having a two-layer structure, and the side surface 210b forms the side wall portion 23a of the core layer 20a having a single-layer structure. An upper wall portion 21a having a single-layer structure made up of end faces 210c of adjacent first bulging portions 210 is formed at the upper end of the side wall portion 23a, while an opening 24a is formed at the lower end of the side wall portion 23a.

[0066] Furthermore, each second bulge portion 220 is mountain-folded at boundary line P' located in the center in the X direction between adjacent boundary lines Q', 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 bulge 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 two-layered side wall portion 23a of the core layer 20a, and the side surface 220b forms a single-layered side wall portion 23a of the core layer 20a. A single-layered bottom wall portion 22a made up of end surfaces 220c of adjacent second bulge portions 220 is formed at the lower end of the side wall portion 23a, while an opening 24a is formed at the upper end of the side wall portion 23a.

[0067] Because the second conveyor 65 is heated by a heating device 65a, the folded core layer 20a is heated and pressed by the second conveyor 65. As a result, the upper and lower edges of the two-layered side wall portion 23a of the folded core layer 20a are heat-welded, while the portions other than the upper and lower edges are not heat-welded. In addition, the upper wall portion 21a and the lower wall portion 22a are partially melted by heating, forming burr-like protrusions toward the inside of the cells S. This increases the bonding area between the core layer 20a and the skin layers 30, 40 in the bonding process.

[0068] The perforated sheets 70, 80 are joined to the core layer 20a in the same manner as in the sound absorbing structure 10 of the first embodiment. Therefore, by joining the perforated sheets 70, 80 in which holes 15 have been formed, the holes 15 located at the openings 24a become first holes 15a, and the holes 15 not located at the openings 24a become second holes 15b.

[0069] Next, according to the sound absorbing structure 10a of the second embodiment, the following effects can be obtained in addition to the effects (1) to (10) of the sound absorbing structure 10 of the first embodiment. (11) In the sound-absorbing structure 10a, the openings 24a are formed along the entire lower edges of the first cells S1a, and the openings 24a are formed along the entire upper edges of the second cells S2a. Therefore, when joining the perforated sheets 70, 80, it is easy to form the first holes 15a that communicate between the inside and outside of the cells S. The first holes 15a can be easily formed without strict alignment of the holes 15 and the openings 24.

[0070] The above-described embodiments can be modified as follows: The above-described embodiments and the following modifications can be applied in combination with each other within the scope of technical compatibility. The multiple holes 15 may be formed only in the skin layer 30, or may be formed only in the skin layer 40. In this case, in the device T, a hole-forming roll 67 without protruding needle-like members may be installed on the side of the skin layer 30, 40 where the holes 15 are not formed.

[0071] The holes 15 are regularly formed so that the formation pitch in the vertical and horizontal directions is equal, but this is not limited to this. The formation pitch of all the holes 15 does not have to be equal, and they may be formed irregularly. Furthermore, at least one of the formation pitch in the vertical and horizontal directions does not have to be equal. Furthermore, the formation pitch may be different between the skin layer 30 and the skin layer 40.

[0072] The plurality of holes 15 do not all have to have the same shape. Holes 15 of different shapes may be mixed. The pitch at which the holes 15 are formed may be the same as the pitch at which the openings 24 are formed. In this case, in the lamination process, the holes 16 formed in the perforated sheets 70, 80 may be adjusted to match the positions of the openings 24 in the core layer 20. In the perforated sheet 70 laminated on the upper surface of the core layer 20, the holes 16 formed at the positions of the openings 24 in the upper wall 21 of the first cell S1 become first holes 15a, and the holes 16 formed at the positions of the upper wall 21 of the second cell S2 become second holes 15b. In the perforated sheet 80, the holes 16 formed at the positions of the openings 24 in the lower wall 22 of the second cell S2 become first holes 15a, and the holes 16 formed at the positions of the lower wall 22 of the first cell S1 become second holes 15b.

[0073] The openings 24 do not have to be formed in all the upper wall portions 21 of the first cell S1, and do not have to be formed in all the lower wall portions 22 of the second cell S2. The first cell S1 may have a mixture of upper wall portions 21 with and without openings 24, and the second cell S2 may have a mixture of lower wall portions 22 with and without openings 24.

[0074] The shape of the opening 24 does not have to be substantially spindle-shaped. There are no particular limitations on the shape as long as the two-layer structure of the upper wall portion 21 and the lower wall portion 22 is formed by thermal shrinkage. The opening 24 does not have to be formed by thermal shrinkage of the two-layer structure of the upper wall portion 21 and the lower wall portion 22. After the core layer 20 is formed, the opening 24 may be formed in the core layer 20 using a communication jig or the like.

[0075] The shape of the cells formed in the hollow plate is not limited to a hexagonal prism. For example, it may be a cylinder, or a polygonal prism such as a square prism or an octagonal prism. The shape of the cells S may be, for example, a frustum shape or a shape in which the top surfaces of two frustums are butted together. That is, any shape may be used as long as it forms a columnar shape as a whole. Furthermore, cells of different shapes may be mixed within the core layer 20, and spaces (gaps) may be formed between the cells. If a communicating portion that connects the inside and outside of the hollow portion formed in the hollow plate is formed, the first holes 15a can be formed when the perforated sheets 70, 80 are laminated.

[0076] The hollow plate does not have to be formed by folding a sheet. For example, as shown in FIG. 7(a), a hollow plate 90 may be used in which a plurality of columnar hollow protrusions are formed by expanding a thermoplastic resin sheet 101. The internal spaces of the hollow protrusions form cells C. One main surface 90a of the hollow plate 90 is formed by the portion of the sheet 101 in which the hollow protrusions are not expanded, and the other main surface 90b is formed by the top surfaces 91 of the hollow protrusions (cells C). Furthermore, openings 92 of the hollow protrusions (cells C) are formed on the main surface 90a. As shown in FIG. 7(b), when a perforated sheet 70 is bonded to the main surface 90a of such a hollow plate material 90 to form the skin layer 30 and a perforated sheet 80 is bonded to the main surface 90b to form the skin layer 40, among the holes 15 formed in the skin layer 30, the holes 15 located in the portions where the openings 92 of the cells C are formed become first holes 15a, and the holes 15 located in the portions where the cells C are not formed (the portions of the sheet material 101) become second holes 15b. Among the holes 15 formed in the skin layer 40, the holes 15 located in the portions where the cells C are not formed become first holes 15a, and the holes 15 located in the portions where the top surfaces 91 of the cells C are formed become second holes 15b. Furthermore, the holes 15 that straddle the portions where the top surfaces 91 of the cells C are formed and the portions where the cells C are not formed also become first holes 15a. Note that FIG. 7(b) is a cross-sectional view in which the top and bottom surfaces in FIG. 7(a) are reversed.

[0077] The sound absorbing structure 10 does not have to be manufactured in a single process using the device T. As long as it includes a step of joining the perforated sheets 70, 80 to the hollow plate material, it may be manufactured using a combination of different devices.

[0078] In the perforation forming step in each of the above embodiments, the perforated sheets 70, 80 that have passed through the sheet roll 66 and the perforation forming roll 67 are supplied to the upper and lower surfaces of the core layer 20. However, this is not limiting. For example, the perforated sheets 70, 80 that have passed through the sheet roll 66 and the perforation forming roll 67 may be temporarily wound onto a separate sheet roll, and the perforated sheets 70, 80 may then be supplied to the upper and lower surfaces of the core layer 20 from the wound sheet roll. In this case, the step of temporarily winding the perforated sheets 70, 80 that have passed through the sheet roll 66 and the perforation forming roll 67 onto a separate sheet roll may be performed in a separate device. The device T may also be provided with a sheet roll around which the perforated sheets 70, 80 are wound. Furthermore, the perforated sheets 70, 80 may be obtained by extruding a sheet and then performing the perforation forming step, and the perforated sheets 70, 80 may be wound onto a sheet roll, which may then be placed in the device. In this case, the sheet roll may be directly transported to the device T in the above embodiments.

[0079] The holes 16 in the perforated sheets 70, 80 do not have to be formed by the hole-forming roll 67. A plurality of holes 16 may be formed by moving a communication jig, to which many needle-like members are attached, up and down relative to the sheet.

[0080] In the bonding step, the adhesive layers of the perforated sheets 70, 80 supplied to the core layer 20 are melted by the heating device 68a provided on the third conveyor 68, but the heating device 68a may be omitted. In this case, if the adhesive layers of the perforated sheets 70, 80 are in a molten state before being supplied to the third conveyor 68, the adhesive layers will cool and solidify as they pass through the third conveyor 68, bonding the skin layers 30, 40 to the core layer 20.

[0081] The holes 16 formed in the perforated sheets 70, 80 may be the same size as the holes 15. Functional resins may be added to the thermoplastic resins that make up the core layer 20 and the skin layers 30, 40, for example, by adding a flame-retardant resin to increase flame retardancy. Furthermore, inorganic substances such as wood flour or talc may be added to improve bending strength. This allows the sound-absorbing structure 10 to have different functions, thereby improving its versatility.

[0082] The core layer 20 is not limited to being formed by folding a single sheet material 100, but may be formed using multiple sheets. For example, the core layer may be formed by bending strip-shaped sheet material at predetermined intervals and arranging multiple sheets side by side. In this modified example, the bent portions of each sheet material form the side walls of the cells.

[0083] The skin layers 30, 40 may not necessarily have adhesive layers laminated thereon. The skin layers 30, 40 may be thermally melted and fused to the core layer 20 by the heating device 65a. Another sheet material may be bonded to the outer surface of at least one of the skin layers 30 and 40. The other sheet material does not have to be made of synthetic resin and may be, for example, a metal sheet (metal foil, steel plate), paper, cloth, or the like, or may be a nonwoven fabric sheet, woven fabric sheet, or knitted fabric sheet. It may also be a printed resin sheet or a resin sheet such as melamine. Furthermore, the skin layer 30 or the skin layer 40 itself may be made of a metal sheet (metal foil, steel plate), paper, cloth, or the like. In this case, it is preferable to similarly form multiple holes in the other sheet material before bonding. If the other sheet material is a nonwoven fabric sheet, woven fabric sheet, or knitted fabric sheet, since multiple holes are formed in the sheet itself, the communication state of the first holes 15a can be maintained even without forming multiple holes in advance.

[0084] A plurality of holes 15 may be formed in a sheet with nonwoven fabric obtained by laminating a resin sheet and a nonwoven fabric. In this case, the sheet with nonwoven fabric may be placed in apparatus T and holes may be formed with a hole-forming roll before being bonded to the core layer 20, or the perforated sheet with nonwoven fabric may be formed in a separate apparatus, and then the sheet roll around which the perforated sheet with nonwoven fabric is wound may be placed in apparatus T and bonded to the core layer 20.

[0085] The hole 15 may be formed so as to span three adjacent cells S with one common corner, or may be formed so as to span multiple cells S that share a common side wall and extend continuously. [Explanation of symbols]

[0086] S...cell, S1, S1a...first cell, S2, S2a...second cell, 10, 10a...sound-absorbing structure, 15...hole, 15a...first hole, 15b...second hole, 20, 20a...core layer (hollow plate material), 21, 21a...upper wall portion, 22, 22a...lower wall portion, 23, 23a...side wall portion, 24, 24a, 92...opening, 30...skin layer, 40...skin layer, 70, 80...perforated sheet, 100, 200...sheet material.

Claims

1. A sound-absorbing structure in which a skin layer is laminated on a main surface of a hollow plate material in which a plurality of cells are arranged side by side, The hollow plate material has sidewall portions that are erected in a thickness direction and that divide the cells, a plurality of holes are formed in the skin layer; The sound-absorbing structure is characterized in that the holes include holes formed at positions overlapping the ends of the side wall portions in the thickness direction, and holes formed at positions not overlapping the ends of the side wall portions in the thickness direction, connecting the inside and outside of the hollow plate material.

2. The sound absorbing structure according to claim 1 , wherein the holes include holes formed at positions overlapping with the ends of the side walls in the thickness direction and communicating the inside and outside of the hollow plate material.

3. The cells are formed in a polygonal columnar shape, The sound absorbing structure according to claim 1 , wherein the holes formed at positions overlapping the ends of the side wall portions in the thickness direction are formed so as to straddle a plurality of adjacent cells with one common corner.

4. A portion of the side wall portion is formed as a two-layer structure. The sound-absorbing structure according to claim 1, wherein the holes formed at positions overlapping with the ends of the side wall portions in the thickness direction are formed at positions overlapping with the ends of the side wall portions of the two-layer structure so as to span a plurality of adjacent cells.

Images