Hollow structure

Abstract

To improve strength of a hollow structure.SOLUTION: A hollow structure 10 made of a thermoplastic resin includes hollow plate-like core layers 20 formed by providing cells S partitioned by side wall parts 23 in parallel, and skin layers 30 and 40 which are joined to at least one main surfaces 20a and 20b of the core layer 20. The cell S has one end in a thickness direction blocked by a wall part and has the other end opened, and projection parts 24 to 27 projecting to the inner side of the cell S are formed on the side wall part 23 of the core layer 20. The projection parts 24 to 27 include first projection parts 26 and 27 which are formed of the side wall parts 23 compressed in the thickness direction, and are formed on the end edges of the side wall parts 23 on the one ends of the cells S, and second projection parts 24 and 25 which are formed on the end edges of the side wall parts 23 on the other ends of the cells S and are joined to the skin layers 30 and 40. The projection amounts of the second projection parts 24 and 25 are larger than the projection amounts of the first projection parts 26 and 27.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a hollow structure. [Background technology]

[0002] A hollow structure with a plurality of cells arranged side by side inside is lightweight yet has an appropriate strength, and may be used as a component part of various vehicles, a building material, etc. The hollow structure described in Patent Document 1 has a sandwich panel structure in which a pair of coating layers are bonded to both main surfaces of a honeycomb structure, and a plurality of hexagonal cells are arranged side by side inside the honeycomb structure, partitioned by side walls extending in the thickness direction of the hollow structure. The honeycomb structure here is formed by vacuum forming a flat sheet material to form a corrugated sheet material with convex bulges formed therein, and folding the corrugated sheet material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2008-520456 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in a rugged sheet material in which a bulge is formed by vacuum forming, the wall thickness of the rugged sheet material on the bulging side tends to be thinner than the wall thickness of the rugged sheet material on the non-bulging side. Therefore, in a honeycomb structure formed by folding a rugged sheet material in which a bulge is formed by vacuum forming as described in Patent Document 1, the wall thickness of the side wall portion is likely to be thin in the portion where the rugged sheet material on the bulging side is located, and the strength of the side wall portion may not be sufficiently maintained. In addition, the bonding strength with the coating layer may not be sufficiently secured on the side where the rugged sheet material on the bulging side is located. The issue of further improving the strength is also common to hollow structures formed by methods other than vacuum forming.

[0005] The present invention has been made to solve these problems in the past, and an object of the present invention is to provide a hollow structure having excellent strength. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a hollow structure made of thermoplastic resin, comprising a hollow plate-shaped core layer in which a plurality of cells are arranged side by side and partitioned by side wall portions extending in the thickness direction, and a skin layer bonded to at least one main surface of the core layer, wherein one end of the cells in the thickness direction is closed by a wall portion and the other end is open, and a protrusion protruding toward the inward side of the cell is formed on the side wall portion of the core layer, the protrusion being formed by the side wall portion compressed in the thickness direction, the protrusion comprising a first protrusion formed on an edge of the side wall portion at the one end of the cell, and a second protrusion formed on the edge of the side wall portion at the other end of the cell and bonded to the skin layer, and the protrusion amount of the second protrusion is greater than the protrusion amount of the first protrusion.

[0007] According to the above-mentioned configuration, the strength of the side wall portion is improved in the portion where the protrusion is formed, and a hollow structure having excellent strength is obtained. The protrusion is formed integrally with the side wall portion made of thermoplastic resin by compressing the side wall portion in the thickness direction, which makes it easier to improve the strength of the side wall portion compared to when other members are used for reinforcement.

[0008] On the side of the skin layer bonded to at least one of the main surfaces of the core layer, a protrusion is formed on the edge of the sidewall of the core layer so as to protrude along the main surface of the core layer. Therefore, the protrusion increases the bonding area of ​​the core layer to the skin layer. This can improve the bonding strength of the skin layer to the core layer. Also, the bending strength of the hollow structure can be improved. Effect of the Invention

[0009] According to the present invention, a hollow structure having excellent strength can be obtained. [Brief description of the drawings]

[0010] [Figure 1] 1A is a perspective view of a hollow structure according to a first embodiment, FIG. 1B is a cross-sectional view taken along line 1B-1B in FIG. 1A, and FIG. 1C is a cross-sectional view taken along line 1C-1C in FIG. [Diagram 2] FIG. 2A is a perspective view of the embossed sheet material of the first embodiment, FIG. 2B is a perspective view showing the embossed sheet material in the middle of being folded, and FIG. 2C is a perspective view showing the embossed sheet material in the folded state. [Diagram 3] FIG. 1 is a schematic diagram showing an example of a production apparatus. [Figure 4] 4A is a perspective view of a hollow structure according to a second embodiment, FIG. 4B is a cross-sectional view taken along line 4B-4B in FIG. 4A, and FIG. 4C is a cross-sectional view taken along line 4C-4C in FIG. [Diagram 5] 10A is a perspective view of a rugged sheet material according to a second embodiment, FIG. 10B is a perspective view showing the rugged sheet material in the middle of being folded, and FIG. 10C is a perspective view showing the rugged sheet material in a folded state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (First embodiment) A hollow structural body 10 according to a first embodiment of the present invention will be described below. First, the structure of the hollow structural body 10 according to the present embodiment will be described with reference to FIG.

[0012] 1(a), the hollow structure 10 of this embodiment includes a core layer 20 having a plurality of cells S arranged side by side therein, a skin layer 30 joined to an upper surface 20a of the core layer 20, and a skin layer 40 joined to a lower surface 20b of the core layer 20. In the following description, the hollow structure 10 and the core layer 20 will be described with the side to which the skin layer 30 is joined as the upper side and the side to which the skin layer 40 is joined as the lower side.

[0013] The core layer 20 and the skin layers 30, 40 are made of a conventionally known thermoplastic resin. Examples of the thermoplastic resin that constitutes the core layer 20 and the skin layers 30, 40 include polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, polybutylene terephthalate resin, etc. The core layer 20 and the skin layers 30, 40 are preferably made of the same thermoplastic resin, and in this embodiment, they are made of polypropylene resin.

[0014] 1(b) and 1(c), the core layer 20 is formed by folding a single uneven sheet material that is made by vacuum forming a flat sheet material made of polypropylene resin 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 forms a hexagonal cylindrical wall portion. The upper wall portion 21, the lower wall portion 22, and the side wall portion 23 define hexagonal columnar cells S inside the core layer 20.

[0015] As shown in FIG. 1(a), the cells S defined within the core layer 20 include a first cell S1 and a second cell S2 having different configurations. 1(b), the first cell S1 has an upper end closed by an upper wall portion 21, and a lower end open downward without being closed. A protrusion 24 that protrudes toward the inside of the first cell S1 so as to extend along the lower surface 20b of the core layer 20 is formed on the lower edge of the side wall portion 23 of the first cell S1, which is the opening end of the first cell S1. That is, in the first cell S1, the upper surface 20a of the core layer 20 is formed by the upper wall portion 21, and the lower surface 20b is formed by the lower edge of the side wall portion 23 and the protrusion 24.

[0016] 1(c), the second cell S2 has a lower end closed by a lower wall portion 22 and an upper end open upward without being closed. A protrusion 25 that protrudes toward the inside of the second cell S2 so as to extend along the upper surface 20a of the core layer 20 is formed on the upper edge of the side wall portion 23 of the second cell S2, which is the opening end of the second cell S2. That is, in the second cell S2, the lower surface 20b of the core layer 20 is formed by the lower wall portion 22, and the upper surface 20a is formed by the upper edge of the side wall portion 23 and the protrusion 25.

[0017] The thickness of the upper wall 21 of the first cell S1 and the thickness of the lower wall 22 of the second cell S2 are approximately the same. In addition, the size of the protrusion 24 formed on the lower edge of the side wall 23 of the first cell S1 is relatively larger than the size of the protrusion 25 formed on the upper edge of the side wall 23 of the second cell S2.

[0018] Further, a protrusion 26 is formed on the upper edge of the side wall 23 opposite the open end of the first cell S1 so as to extend along the lower surface of the upper wall 21. The protrusion amount of the protrusion 26 is less than that of the protrusion 24, and the size of the protrusion 26 is smaller than that of the protrusion 24. A protrusion 27 is formed on the lower edge of the side wall 23 of the second cell S2 opposite the open end of the second cell S2 so as to extend along the upper surface of the lower wall 22. The protrusion amount of the protrusion 27 is less than that of the protrusion 25, and the size of the protrusion 27 is smaller than that of the protrusion 25.

[0019] 1(a), the first cells S1 and the second cells S2 are arranged in a row in the X direction, with the first cells S1 adjacent to each other or the second cells S2 adjacent to each other. In the Y direction perpendicular to the X direction, the rows of the first cells S1 and the rows of the second cells S2 are arranged alternately.

[0020] As shown in FIG. 1(b) and FIG. 1(c), the adjacent first cells S1 and the adjacent second cells S2 are partitioned by the side wall portion 23 having a two-layer structure formed perpendicular to the upper wall portion 21 and the lower wall portion 22 and including the first side wall portion 23a and the second side wall portion 23b. In the two-layer side wall portion 23, the first side wall portion 23a and the second side wall portion 23b each have a curved shape when viewed from above, in which the widthwise center is slightly curved so as to bulge toward the inner side of the cell S. The first side wall portion 23a and the second side wall portion 23b are heat-welded to each other at their upper and lower edges, and are not heat-welded to each other at the vertical intermediate portions excluding the upper and lower edges. The adjacent first cell S1 and the second cell S2 are partitioned by the side wall portion 23 having a single layer structure formed perpendicular to the upper wall portion 21 and the lower wall portion 22.

[0021] At the upper end edge of the side wall portion 23 having a two-layer structure in the first cell S1, a protruding portion (not shown) protruding from the side wall portion 23 is formed in the heat-welded portion. The protruding portion is formed along the curved shape of the first side wall portion 23a and the second side wall portion 23b. As a result, the first side wall portion 23a and the second side wall portion 23b are connected to each other, and the first side wall portion 23a and the second side wall portion 23b are not joined to each other in the non-heat-welded portion in the vertical middle portion except for the upper end edge and the lower end edge. Also, at the lower end edge of the side wall portion 23 having a two-layer structure in the second cell S2, a protruding portion (not shown) protruding from the side wall portion 23 is formed in the heat-welded portion. The protruding portion is formed along the curved shape of the first side wall portion 23a and the second side wall portion 23b. As a result, the first side wall 23a and the second side wall 23b are connected to each other, and the first side wall 23a and the second side wall 23b are not joined to each other in the non-thermally welded portion in the vertical middle part excluding the upper and lower edges. The protrusion length of the protrusion formed between the two-layered side wall 23 of the first cell S1 and the protrusion length of the protrusion formed between the two-layered side wall 23 of the second cell S2 are approximately the same width and size. Moreover, these protrusions have shorter protrusion lengths and smaller sizes than the protrusions 24, 25, 26, and 27.

[0022] The thickness of the first side wall portion 23a and the thickness of the second side wall portion 23b formed between adjacent first cells S1 are approximately the same. Also, the thickness of the first side wall portion 23a and the thickness of the second side wall portion 23b formed between adjacent second cells S2 are approximately the same. On the other hand, the thickness of the first side wall portion 23a and the second side wall portion 23b formed between adjacent first cells S1 is relatively thinner than the thickness of the first side wall portion 23a and the second side wall portion 23b formed between adjacent second cells S2.

[0023] In addition, the thickness of the side wall portion 23 having a single layer structure is relatively thicker than the thickness of the first side wall portion 23a or the second side wall portion 23b formed between the first cells S1, and is relatively thinner than the thickness of the first side wall portion 23a or the second side wall portion 23b formed between the second cells S2.

[0024] As shown in FIG. 1(a), the skin layers 30, 40 are bonded to the upper surface 20a and the lower surface 20b of the core layer 20, respectively, via adhesive layers (not shown). The skin layer 30 is bonded to the upper wall portion 21 on the upper surface of the first cell S1, and is bonded to the upper end and protruding portion 25 of the side wall portion 23 on the upper surface of the second cell S2. The skin layer 40 is bonded to the lower end and protruding portion 24 of the side wall portion 23 on the lower surface of the first cell S1, and is bonded to the lower wall portion 22 on the lower surface of the second cell S2. Therefore, the upper surface of the hollow structure 10 has a two-layer structure consisting of the upper wall portion 21 of the core layer 20 and the skin layer 30 in the first cell S1, and a two-layer structure consisting of only the skin layer 30 and the protruding portion 25 partially bonded to the skin layer 30 in the second cell S2. In addition, the underside of the hollow structure 10 in the second cell S2 has a two-layer structure consisting of the lower wall portion 22 of the core layer 20 and the skin layer 40, while in the first cell S1, it has a one-layer structure consisting of only the skin layer 40 and a two-layer structure in which the protrusion 24 is partially joined to the skin layer 30.

[0025] Next, a method for manufacturing the hollow structural body 10 of this embodiment will be described with reference to FIGS. The manufacturing method of the hollow structure 10 includes a vacuum forming step, a core layer forming step, and a skin layer joining step. The vacuum forming step is a step of vacuum forming a concave-convex sheet material 100 having bulging portions of convex stripes from a single flat sheet material made of thermoplastic resin. The core layer forming step is a step of forming the core layer 20 by folding and heating the concave-convex sheet material 100. The skin layer joining step is a step of joining the skin layers 30, 40 to the upper surface 20a and the lower surface 20b of the core layer 20 to form the hollow structure 10. Each of these steps for manufacturing the hollow structure 10 is performed in a series of flows by an apparatus T shown in FIG. 3.

[0026] First, the apparatus shown in Fig. 3 will be described. Fig. 3 shows the apparatus T as a schematic diagram, with the left side being the upstream side and the right side being the downstream side. In the apparatus T, in order from the upstream side, a sheet roll 61 on which a flat sheet material made of a thermoplastic resin is wound, a vacuum forming drum 62 for the vacuum forming process, a first conveyor 63 for the core layer forming process, sheet rolls 64 and 65 on which sheets serving as the raw materials for the skin layers 30 and 40 are wound, and a second conveyor 66 for the skin layer joining process are arranged.

[0027] As shown in FIG. 3, in the vacuum forming process, a flat sheet material made of thermoplastic resin wound around a sheet roll 61 is supplied to a vacuum forming drum 62. By passing through the vacuum forming drum 62, a bulging portion of a convex stripe is formed on the flat sheet material, and a corrugated sheet material 100 having a predetermined corrugated shape is formed. The vacuum forming drum 62 is supported on a shaft so as to be rotatable and is configured so as to be heated to a predetermined temperature. The rotation speed of the vacuum forming drum 62 is set to be equal to the rotation speed of the sheet roll 61. Furthermore, a cylindrical forming die is attached to the vacuum forming drum 62, and a vacuum can be drawn through a through hole formed on the outer circumferential surface of the forming die (not shown). On the outer circumferential surface of the forming die, a corrugated shape similar to the corrugated shape formed on the corrugated sheet material 100 (a first bulging portion 110 and a second bulging portion 120 described later) is formed so that the X direction of the corrugated sheet material 100 is aligned with the circumferential direction of the outer circumferential surface of the forming die. As a result, the flat sheet material conveyed along the vacuum forming drum 62 is vacuumed toward the outer circumferential surface of the vacuum forming drum 62, and a bulge is formed.

[0028] As shown in FIG. 2(a), the corrugated sheet material 100 formed by the vacuum forming process has band-shaped first bulges 110 formed in a shape that protrudes upward. As a result of the first bulges 110 being formed to bulge from the flat sheet material, second bulges 120 that protrude downward relative to the first bulges 110 are formed between the first bulges 110. The first bulges 110 and the second bulges 120 are alternately arranged in the width direction (Y direction). The first bulges 110 and the second bulges 120 are arranged to extend in the X direction. The first bulges 110 when the corrugated sheet material 100 is viewed from above and the second bulges 120 when the corrugated sheet material 100 is viewed from below have the same shape and are formed at positions shifted by 1 / 2 pitch in the X direction.

[0029] The first bulging portion 110 is composed of an upper surface 110a, a pair of side surfaces 110b, and a pair of end surfaces 110c, and its cross-sectional shape in the Y direction is a trapezoid obtained by bisecting a regular hexagon by its longest diagonal. The pair of end surfaces 110c are formed at the position of the folding line P shown in Fig. 2(a). The angle between the end surfaces 110c and the upper surface 110a is approximately 90°.

[0030] On the other hand, the second bulging portion 120 is composed of a lower surface 120a, a pair of side surfaces 120b, and a pair of end surfaces 120c, and its Y-direction cross-sectional shape is a trapezoid obtained by bisecting a regular hexagon by the longest diagonal. The pair of end surfaces 120c are formed at the position of the folding line Q shown in FIG. 2(a). The angle between the end surface 120c and the lower surface 120a is about 90°. The length in the X-direction of the second bulging portion 120, that is, the length between the pair of end surfaces 120c, is the same as the length in the X-direction of the first bulging portion 110, that is, the length between the pair of end surfaces 110c. The end surface 120c of the second bulging portion 120 is located at the center of the first bulging portion 110 in the X-direction. Note that the side surface 110b of the first bulging portion 110 and the side surface 120b of the second bulging portion 120 are separated for convenience of explanation, but have the same configuration.

[0031] In the vacuum forming process, the first bulging portion 110 is formed to bulge relative to the flat sheet material, so that the thickness of the upper surface 110a of the first bulging portion 110 is thinner than the thickness of the flat sheet material. The thicknesses of the pair of side surfaces 110b are thicker than the thickness of the upper surface 110a and thinner than the thickness of the flat sheet material. Furthermore, the thicknesses of the pair of end surfaces 110c are also thicker than the thickness of the upper surface 110a and thinner than the thickness of the flat sheet material.

[0032] On the other hand, the thickness of the lower surface 120a of the second bulging portion 120 is equal to the thickness of the flat sheet material. The thickness of the pair of side surfaces 120b is thinner than the thickness of the lower surface 120a, i.e., the thickness of the flat sheet material. Furthermore, the thickness of the pair of end surfaces 120c is also thinner than the thickness of the lower surface 120a, i.e., the thickness of the flat sheet material.

[0033] In this manner, in the vacuum forming process, a vacuum forming method utilizing the plasticity of the flat sheet material is used to obtain an uneven sheet material 100 having a first bulge portion 110 formed by partially bulging the flat sheet material upward, and a second bulge portion 120 formed as a result of the first bulge portion 110 being bulged.

[0034] As shown in FIG. 3, in the core layer forming process, the uneven sheet material 100 is conveyed downstream by the first conveyor 63 while its vertical movement is restricted. At this time, the conveying speed by the first conveyor 63 is set to be slower than the rotation speed of the sheet roll 61 and the vacuum forming drum 62 arranged on the upstream side of the first conveyor 63. In other words, the conveying speed by the first conveyor 63 is set to be slower than the supply speed of the uneven sheet material 100 supplied from the upstream side. In addition, the first conveyor 63 is provided with a heating device 63a for heating the temperature between the first conveyor 63 to a predetermined temperature. Therefore, when the uneven sheet material 100 is conveyed between the first conveyors 63, it is folded while being compressed in the downstream direction while being heated, and the core layer 20 is formed. Then, when it is conveyed between the first conveyors 63, the core layer 20 is slightly compressed in the vertical direction while being heated.

[0035] 2(b) and (c), the conveying speed of the first conveyor 63 is slower than the supply speed of the embossed sheet material 100 supplied from the upstream side thereof, so that the embossed sheet material 100 is folded sequentially along folding lines P and Q. This forms the core layer 20. Specifically, as shown in FIG. 2(b), the embossed sheet material 100 is mountain-folded along folding line P and valley-folded along folding line Q.

[0036] As shown in Fig. 2(c), one first bulging portion 110 is folded at a folding line Q provided in the center portion in the X direction, so that the upper surface 110a on the right side in the X direction and the upper surface 110a on the left side in the X direction abut in an upright state. In the folded first bulging portion 110, the upper surface 110a on the right side in the X direction and the upper surface 110a on the left side in the X direction abut in an upright state to form a two-layered side wall portion 23 of the core layer 20, and the side surface 110b forms a one-layered side wall portion 23 of the core layer 20. At the upper end of the side wall portion 23, an upper wall portion 21 consisting of the end surfaces 110c of the adjacent first bulging portions 110 is formed, forming a first cell S1.

[0037] In addition, one second bulging portion 120 is folded at a folding line P provided in the center in the X direction between adjacent folding lines Q, and the lower surface 120a on the right side in the X direction and the lower surface 120a on the left side in the X direction abut in an upright state. In the folded second bulging portion 120, the lower surface 120a on the right side in the X direction and the lower surface 120a on the left side in the X direction abut in an upright state to form a two-layered side wall portion 23 of the core layer 20, and the side surface 120b forms a one-layered side wall portion 23 of the core layer 20. At the lower end of the side wall portion 23, a lower wall portion 22 consisting of the end surface 120c of the adjacent second bulging portions 120 is formed, forming a second cell S2.

[0038] In the core layer forming process, the first conveyor 63 is heated by the heating device 63a. Therefore, the folded core layer 20 is heated and pressed by the first conveyor 63. As a result, the upper and lower edges of the two-layered side wall portion 23 of the folded core layer 20 are heat-welded to form protrusions smaller than the protrusions 24, 25, 26, and 27, and the first side wall portion 23a and the second side wall portion 23b are connected to each other. On the other hand, the portions other than the upper and lower edges are not heat-welded, and a non-joint portion where the first side wall portion 23a and the second side wall portion 23b are not joined is formed in the vertical middle portion of the two-layered side wall portion 23.

[0039] In addition, when the core layer 20 is transported between the first conveyors 63, the core layer 20 is heated and slightly compressed in the vertical direction, so that in the first cell S1 where the lower wall portion 22 is not formed, the lower end of the side wall portion 23 is thermally melted and pressed in the vertical direction. As a result, the lower edge of the side wall portion 23 is partially thermally melted, and a protrusion 24, which is a burr-like protrusion extending toward the inside of the first cell S1, is formed. Similarly, in the second cell S2 where the upper wall portion 21 is not formed, the upper end of the side wall portion 23 is thermally melted and pressed in the vertical direction. As a result, the upper edge of the side wall portion 23 is partially thermally melted, and a protrusion 25, which is a burr-like protrusion extending toward the inside of the second cell S2, is formed.

[0040] Here, the two-layered side wall portion 23 that divides the first cell S1 is formed by the upper surface 110a of the first bulging portion 110, and the two-layered side wall portion 23 that divides the second cell S2 is formed by the lower surface 120a of the second bulging portion 120. The thickness of the lower surface 120a of the second bulging portion 120 is approximately the same as the thickness of the flat sheet material, while the thickness of the upper surface 110a of the first bulging portion 110 is thinner than the thickness of the flat sheet material. Therefore, the thickness of the two-layered side wall portion 23 that divides the first cell S1 is thinner than the thickness of the two-layered side wall portion 23 that divides the second cell S2.

[0041] Moreover, the thickness of the side surface 110b of the first bulging portion 110 is thinner than the thickness of the flat sheet material, and the thickness of the side surface 120b of the second bulging portion 120 is also thinner than the thickness of the flat sheet material. Therefore, the thickness of the side wall portion 23 of the single-layer structure that separates the first cell S1 and the second cell S2 is relatively thicker than the thickness of the first side wall portion 23a or the second side wall portion 23b formed between the first cells S1, and is relatively thinner than the thickness of the first side wall portion 23a or the second side wall portion 23b formed between the second cells S2.

[0042] Furthermore, the thickness of a pair of end faces 110c of the first bulging portion 110 is thinner than the thickness of the flat sheet material, and the thickness of a pair of end faces 120c of the second bulging portion 120 is also thinner than the thickness of the flat sheet material. Therefore, the thickness of the upper wall portion 21 of the first cell S1 and the thickness of the lower wall portion 22 of the second cell S2 are approximately the same.

[0043] When the core layer 20 is transported between the first conveyors 63, heat is transferred from the heating device 63a to the thickness direction end of the core layer 20. In the first cell S1, the upper surfaces 110a of the first bulging portions 110 are in contact with each other to form the side wall portion 23 having a two-layer structure, and the side surface 110b forms the side wall portion 23 having a one-layer structure. Therefore, more resin pools are formed on the lower edge of the side wall portion 23 having a two-layer structure than on the side wall portion 23 having a one-layer structure. After that, when the core layer 20 is cooled and the resin pools are solidified, the resin pools become the protrusions 24 as burr-like protrusions, and the lower edge of the side wall portion 23 having a two-layer structure forms a protrusion 24 that is relatively larger than the lower edge of the side wall portion 23 having a one-layer structure. Furthermore, the protruding length of the protruding portion 24 formed on the lower edge of the side wall portion 23 with a two-layer structure is greater than the protruding length of the protruding portion 24 formed on the lower edge of the side wall portion 23 with a one-layer structure. The protruding lengths of the protruding portions 24 formed on the lower edges of the side wall portion 23 with a two-layer structure are approximately the same width depending on the location, and the protruding lengths of the protruding portions 24 formed on the lower edges of the side wall portion 23 with a one-layer structure are approximately the same width depending on the location.

[0044] In the second cell S2, the lower surfaces 120a of the second bulging portions 120 come into contact with each other to form the side wall portion 23 having a two-layer structure, and the side surfaces 120b form the side wall portion 23 having a one-layer structure. Therefore, more resin pools are formed on the upper edge of the side wall portion 23 having a two-layer structure than on the side wall portion 23 having a one-layer structure. When the core layer 20 is then cooled and the resin pools solidify, the resin pools become protrusions 25 as burr-like protrusions, and the upper edge of the side wall portion 23 having a two-layer structure has a protrusion 25 that is relatively larger than the upper edge of the side wall portion 23 having a one-layer structure. In addition, the protrusion length of the protrusion 25 formed on the upper edge of the side wall portion 23 having a two-layer structure is greater than the protrusion length of the protrusion 25 formed on the upper edge of the side wall portion 23 having a one-layer structure. The protrusion length of the protrusion 25 formed on the upper edge of the side wall portion 23 having a two-layer structure is approximately the same width depending on the location, and the protrusion length of the protrusion 25 formed on the upper edge of the side wall portion 23 having a one-layer structure is approximately the same width depending on the location.

[0045] In addition, the two-layered sidewall portion 23 of the first cell S1 is relatively thinner than the two-layered sidewall portion 23 of the second cell S2. Therefore, it is more likely to melt by the heat from the heating device 63a. As a result, a larger resin pool is formed on the lower edge of the sidewall portion 23 of the first cell S1 than on the upper edge of the sidewall portion 23 of the second cell S2. When the core layer 20 is subsequently cooled and the resin pool solidifies, a larger burr-like protrusion is formed on the lower edge of the sidewall portion 23 of the first cell S1 than on the upper edge of the sidewall portion 23 of the second cell S2. As a result, the size of the protrusion 24 formed on the lower edge of the sidewall portion 23 of the first cell S1 is relatively larger than the size of the protrusion 25 formed on the upper edge of the sidewall portion 23 of the second cell S2.

[0046] A resin pool is formed on the upper edge of the side wall 23 of the first cell S1 by heating and pressing the core layer 20 while being transported between the first conveyors 63, resulting in the formation of a burr-like protrusion, a protrusion 26. Similarly, a resin pool is formed on the lower edge of the side wall 23 of the second cell S2 by heating and pressing the core layer 20 while being transported between the first conveyors 63, resulting in the formation of a burr-like protrusion, a protrusion 27.

[0047] In the skin layer bonding step, the skin layers 30 and 40 are bonded to the upper and lower surfaces of the core layer 20 . The core layer 20, which has been folded and has the protrusions 24 and 25 formed thereon, moves toward the second conveyor 66. The conveying speed of the second conveyor 66 is set to be equal to the conveying speed of the first conveyor 63. The second conveyor 66 is provided with a heating device 66a. Near the entrance of the second conveyor 66, sheet rolls 64 and 65, on which thermoplastic resin sheets to become the skin layers 30 and 40 are wound, are disposed. An adhesive (not shown) is applied to the sheets wound on the sheet rolls 64 and 65. The adhesive is preferably a hot melt adhesive made of a resin compatible with polypropylene resin, but the adhesive can be omitted. When the adhesive is omitted, for example, a low-melting thermoplastic resin layer made of the same material as the skin layers 30 and 40 may be formed. The adhesive and the low-melting thermoplastic resin layer can also be omitted.

[0048] As shown in Fig. 3, a thermoplastic resin sheet wound on a sheet roll 64, 65 is supplied to the upper surface 20a and the lower surface 20b of the core layer 20 passing between the second conveyor 66. The adhesive applied to the sheet is in a molten state. Since the second conveyor 66 is provided with a heating device 66a, the adhesive applied to the sheet is maintained in a molten state when the sheet passes through the second conveyor 66.

[0049] Next, the core layer 20 with the sheets disposed on both the top and bottom surfaces is moved downstream and cooled. This causes the adhesive applied to the sheets to cool and solidify, and the sheets are bonded to the top surface 20a and bottom surface 20b of the core layer 20. The sheet bonded to the top surface 20a of the core layer 20 becomes the skin layer 30, and the sheet bonded to the bottom surface 20b of the core layer 20 becomes the skin layer 40. In this way, a hollow structure 10 is obtained in which the skin layers 30, 40 are bonded to the top surface 20a and bottom surface 20b of the core layer 20.

[0050] Next, the function of the hollow structure 10 will be described with reference to FIG. As shown in Fig. 1(a), the core layer 20 formed by folding the embossed sheet material 100 has side walls 23 that divide the cells S and are erected in the thickness direction of the core layer 20 (hollow structure 10), and the multiple cells S are formed to extend in the thickness direction of the core layer 20 (hollow structure 10). Of the multiple cells S, the upper surface 20a of the core layer 20 is composed of the upper wall 21 of the first cell S1 and the upper edge of the side wall 23 of the second cell S2 and a protruding portion 25, and the protruding portion 25 is formed to protrude so as to extend inward of the second cell S2. A skin layer 30 is joined to the upper surface 20a of the core layer 20.

[0051] Since the skin layer 30 is joined to the upper wall portion 21 of the first cell S1 and the upper edge and protrusion 25 of the side wall portion 23 of the second cell S2, the bonding strength is stronger than when the protrusion 25 is not formed.

[0052] The lower surface 20b of the core layer 20 is composed of the lower end edge of the side wall portion 23 of the first cell S1 and the protruding portion 24 and the lower wall portion 22 of the second cell S2, and the protruding portion 24 is formed so as to protrude so as to extend inward of the first cell S1. A skin layer 40 is joined to the lower surface 20b of the core layer 20.

[0053] Since the skin layer 40 is joined to the lower wall portion 22 of the second cell S2 and the lower edge of the side wall portion 23 of the first cell S1 and the protrusion portion 24, the bonding strength is stronger than when the protrusion portion 24 is not formed.

[0054] Furthermore, the first side wall portion 23a or the second side wall portion 23b of the two-layer structure that separates the first cells S1 from each other is relatively thin, and the first side wall portion 23a or the second side wall portion 23b of the two-layer structure that separates the second cells S2 from each other is relatively thick, compared to the side wall portion 23 of the one-layer structure that separates the first cells S1 from each other. The side wall portion 23 of the two-layer structure between the first cells S1 is more likely to be thermally melted than the side wall portion 23 of the two-layer structure between the second cells S2 by heat from the heating device 63a of the first conveyor 63. As a result, the protrusion 24 formed in the first cell S1 is larger than the protrusion 25 formed in the second cell S2, so that the bonding strength of the skin layer 40 is relatively stronger on the lower surface 20b of the core layer 20 on which the protrusion 24 is formed than on the upper surface 20a.

[0055] According to the hollow structural body 10 of this embodiment and the manufacturing method thereof, the following effects can be obtained. (1) The hollow structure 10 of this embodiment includes a core layer 20 in which a plurality of cells S are arranged side by side and partitioned by a side wall portion 23 extending in the thickness direction. In the first cell S1 of the core layer 20, a protrusion 24 that protrudes toward the inside of the first cell S1 is formed on the lower edge of the side wall portion 23, and in the second cell S2 of the core layer 20, a protrusion 25 that protrudes toward the inside of the second cell S2 is formed on the upper edge of the side wall portion 23.

[0056] Therefore, in the portions where the protrusions 24, 25 are formed, the side wall portion 23 is reinforced, improving the strength of the core layer 20. A hollow structure having excellent strength is obtained. (2) The hollow structure 10 of this embodiment includes a core layer 20, and skin layers 30, 40 joined to the upper surface 20a and lower surface 20b of the core layer 20. The protrusion 24 protrudes along the lower surface 20b of the core layer 20 from the lower edge of the side wall portion 23 on the side where the skin layer 40 is joined. Moreover, the protrusion 25 protrudes along the upper surface 20a of the core layer 20 from the upper edge of the side wall portion 23 on the side where the skin layer 30 is joined.

[0057] Therefore, on the lower surface 20b of the core layer 20, the bonding area of ​​the core layer 20 to the skin layer 40 is increased by the protrusion 24, and on the upper surface 20a of the core layer 20, the bonding area of ​​the core layer 20 to the skin layer 30 is increased by the protrusion 25. This makes it possible to improve the bonding strength of the skin layers 30, 40 to the core layer 20.

[0058] (3) In the manufacturing method of the hollow structure 10, in the core layer formation process, the core layer 20 is compressed in its thickness direction while being heated, thereby forming protrusions 24, 25 on the side wall portion 23 that protrude toward the inside of the cell S.

[0059] Therefore, by compressing the thermoplastic resin core layer 20 in its thickness direction in a heated state and thermally melting the side wall portion 23, the protrusions 24, 25 can be formed integrally with the side wall portion 23. The strength of the side wall portion 23 can be improved more easily by using the protrusions 24, 25 to reinforce the side wall portion 23 than by joining other members.

[0060] (4) In the core layer forming process, a vacuum-formed thermoplastic resin embossed sheet material 100 is folded to form the core layer 20, while the core layer 20 is compressed in the thickness direction in a heated state.

[0061] Therefore, the core layer 20 and the protrusions 24, 25 can be formed in the same process, and the manufacturing process of the hollow structural body 10 having excellent strength can be simplified. Furthermore, the formation of the core layer 20 and the thermal welding of the upper and lower edges of the side wall portion 23 of the two-layer structure of the core layer 20 can be performed simultaneously.

[0062] (5) The hollow structural body 10 of this embodiment is manufactured through a vacuum molding process, a core layer forming process, and a skin layer bonding process. Each process is performed by the apparatus T in a series. Therefore, the hollow structural body 10 can be manufactured with excellent productivity and mass production, and at low cost.

[0063] (6) The transport speed of the first conveyor 63 constituting the core layer forming process is set to be slower than the rotation speed of the sheet roll 61 and the vacuum forming drum 62 arranged upstream of the first conveyor 63. In other words, the transport speed of the first conveyor 63 is slower than the supply speed of the corrugated sheet material 100 that has passed through the vacuum forming drum 62.

[0064] Therefore, the embossed sheet material 100 is folded sequentially along the folding lines P and Q. By moving the embossed sheet material 100, the core layer forming step can be easily carried out. Second embodiment Next, a hollow structure 11 according to a second embodiment of the present invention will be described. In the hollow structure 11 according to the second embodiment, the configuration of the corrugated sheet material 200 for forming the core layer 50 of the hollow structure 11 is different from that of the corrugated sheet material 100 according to the first embodiment. Therefore, the configurations of the upper wall portion 51, the lower wall portion 52, and the side wall portion 53 of the core layer 50 are different from those of the core layer 20 according to the first embodiment. Here, the portions different from the first embodiment will be mainly described.

[0065] As shown in Figs. 4(a) to (c), the core layer 50 of the second embodiment is formed by folding a single embossed sheet material made of thermoplastic resin molded into a predetermined shape. The cells S formed inside the core layer 50 include a third cell S3 and a fourth cell S4 having different structures. As shown in Fig. 4(b), in the third cell S3, a two-layered upper wall portion 51 is provided on the upper portion of the side wall portion 53. The layers of the two-layered upper wall portion 51 are bonded to each other. In addition, in the third cell S3, a one-layered lower wall portion 52 is provided on the lower portion of the side wall portion 53. On the other hand, as shown in Fig. 4(c), in the fourth cell S4, a one-layered upper wall portion 51 is provided on the upper portion of the side wall portion 53. In addition, in the fourth cell S4, a two-layered lower wall portion 52 is provided on the lower portion of the side wall portion 53. The layers of the two-layered lower wall portion 52 are bonded to each other.

[0066] As shown in Fig. 4(a), the third cells S3 are arranged in a row along the X direction. Similarly, the fourth cells S4 are arranged in a row along the X direction. The rows of the third cells S3 and the rows of the fourth cells S4 are alternately arranged in the Y direction perpendicular to the X direction. The third cells S3 and the fourth cells S4 form a honeycomb structure as a whole in the core layer 50. Note that the upper wall portion 51 and the lower wall portion 52 of the two-layer structure are not shown in Fig. 4(a).

[0067] 4(b) and 4(c), adjacent third cells S3 and adjacent fourth cells S4 are separated by sidewalls 53 having a two-layer structure. In the third cell S3 and the fourth cell S4, the two-layer sidewalls 53 are heat-welded to each other at both upper and lower ends, while the central portion in the thickness direction of the core layer 50 has a portion that is not heat-welded to each other. The adjacent third cell S3 and fourth cell S4 are separated by sidewalls 53 having a single layer structure that are formed perpendicular to the upper wall portion 51 and the lower wall portion 52.

[0068] The thicknesses of the first side wall portion 53a and the second side wall portion 53b constituting the side wall portion 53 of the two-layer structure formed between adjacent third cells S3 are approximately the same. The thicknesses of the first side wall portion 53a and the second side wall portion 53b constituting the side wall portion 53 of the two-layer structure formed between adjacent fourth cells S4 are approximately the same. On the other hand, the thicknesses of the first side wall portion 53a and the second side wall portion 53b formed between adjacent third cells S3 are relatively thinner than the thicknesses of the first side wall portion 53a and the second side wall portion 53b formed between adjacent fourth cells S4.

[0069] In addition, the thickness of the side wall portion 53 having a single layer structure is relatively thicker than the thickness of the first side wall portion 53a or the second side wall portion 53b formed between the third cells S3, and is relatively thinner than the thickness of the first side wall portion 53a or the second side wall portion 53b formed between the fourth cells S4.

[0070] As shown in FIG. 4(b), the side wall 53 of the third cell S3 has a thickened portion 54 at the upper end thereof, which is formed by partially thickening the side wall 53, and protrudes inwardly of the third cell S3. The thickened portion 54 is formed at the upper end edge of the side wall 53 so as to be integrated with the lower surface of the upper wall 51. As shown in FIG. 4(c), the side wall 53 of the fourth cell S4 has a thickened portion 55 at the upper end thereof, which is formed by partially thickening the side wall 53, and protrudes inwardly of the fourth cell S4. The thickened portion 55 is formed at the upper end edge of the side wall 53 so as to be integrated with the lower surface of the upper wall 51. The size of the thickened portion 54 formed at the upper end of the side wall 53 of the third cell S3 is relatively smaller than the size of the thickened portion 55 formed at the upper end of the side wall 53 of the fourth cell S4.

[0071] Next, a method for manufacturing the hollow structure 11 of this embodiment will be described with reference to Fig. 5, focusing on the differences from the first embodiment. The hollow structure 11 of the second embodiment is also manufactured using the device T used for manufacturing the hollow structure 10 of the first embodiment. Here, the shape of the embossed sheet material 200 formed in the vacuum forming process is different from that of the first embodiment. In other words, the shape of the outer circumferential surface of the forming die attached to the vacuum forming drum 62 in the vacuum forming process is different from that of the first embodiment.

[0072] 5(a), a concave-convex sheet material 200 is obtained in which a convex bulging region 220 is formed by vacuuming using a vacuum forming drum 62 from a flat sheet material made of thermoplastic resin wound around a sheet roll 61. The core layer 50 of the hollow structure 11 is formed by folding the concave-convex sheet material 200.

[0073] In the uneven sheet material 200, band-shaped flat regions 210 and bulging regions 220 are alternately arranged in the longitudinal direction (X direction) of the uneven sheet material 200. In the bulging region 220, a first bulging portion 221 having a cross section of a downward groove shape composed of an upper surface 221a and a pair of side surfaces 221b is formed over the entire extending direction (Y direction) of the bulging region 220. Note that the angle between the upper surface 221a and the side surface 221b of the first bulging portion 221 is preferably 90 degrees, and as a result, the cross section of the first bulging portion 221 is a downward U-shape. In addition, the width of the first bulging portion 221 (the length of the short side of the upper surface 221a) is set to be equal to the width of the flat region 210 and twice the length of the bulging height of the first bulging portion 221 (the length of the short side of the side surface 221b).

[0074] In addition, in the bulging region 220, a plurality of second bulging portions 222, each of which has a cross-sectional shape that is a trapezoid obtained by bisecting a regular hexagon at the longest diagonal, are formed so as to be perpendicular to the first bulging portion 221. The bulging height (height of upper surface 222a) of the second bulging portion 222 is set to be equal to the bulging height (height of upper surface 221a) of the first bulging portion 221. In addition, the interval between adjacent second bulging portions 222 is equal to the width of the upper surface 222a of the second bulging portion 222.

[0075] The first bulging portion 221 and the second bulging portion 222 are formed by partially bulging upward a flat sheet material by vacuum forming, utilizing the plasticity of the sheet. In the vacuum forming process, the first bulging portion 221 and the second bulging portion 222 are formed to bulge with respect to the flat sheet material, so that the thickness of the upper surface 221a of the first bulging portion 221 is thinner than the thickness of the flat sheet material. Also, the thickness of the pair of side surfaces 221b is thicker than the thickness of the upper surface 221a and thinner than the thickness of the flat sheet material. Furthermore, the thickness of the upper surface 222a of the second bulging portion 222 is thinner than the thickness of the flat sheet material and is approximately the same as the thickness of the upper surface 221a of the first bulging portion 221. The thicknesses of the side surfaces 222b and end surfaces 222c of the second bulging portion 222 are thicker than the thickness of the upper surface 222a and thinner than the thickness of the flat sheet material.

[0076] As shown in Figs. 4(b), (c) and 5(b), (c), in the core layer forming process, the uneven sheet material 200 is conveyed downstream by the first conveyor 63 while its vertical movement is restricted, and is folded. The uneven sheet material 200 is folded along the folding lines P and Q to form the core layer 50. Specifically, the uneven sheet material 200 is valley-folded at the folding line P between the flat area 210 and the bulging area 220, and mountain-folded at the folding line Q between the upper surface 221a and the side surface 221b of the first bulging portion 221, to be compressed in the X direction. Then, the upper surface 221a and the side surface 221b of the first bulging portion 221 are folded over, and the end surface 222c of the second bulging portion 222 is folded over the flat area 210, thereby forming one rectangular column-shaped partition 230 extending in the Y direction for one bulging area 220. The partitions 230 are successively formed in the X direction to form a hollow plate-like core layer 50 .

[0077] When the concave-convex sheet material 200 is compressed as described above, the upper surface 221a and the side surface 221b of the first bulge portion 221 form the upper wall portion 51 of the core layer 50, and the end surface 222c and the flat area 210 of the second bulge portion 222 form the lower wall portion 52 of the core layer 50. As shown in FIG. 4(c), a portion of the upper wall portion 51 where the upper surface 221a and the side surface 221b of the first bulge portion 221 are folded over to form a two-layer structure, and a portion of the lower wall portion 52 where the end surface 222c of the second bulge portion 222 and the flat area 210 are folded over to form a two-layer structure respectively become overlapping portions 231.

[0078] Further, the hexagonal columnar region formed by folding the second bulging portion 222 becomes the fourth cell S4, and the hexagonal columnar region formed between a pair of adjacent partitions 230 becomes the third cell S3. Therefore, the upper wall portion 51 of the third cell S3 is formed by the upper surface 221a and the side surface 221b of the first bulging portion 221, and the upper wall portion 51 of the fourth cell S4 is formed by the upper surface 221a of the first bulging portion 221. On the other hand, the lower wall portion 52 of the third cell S3 is formed by the flat region 210, and the lower wall portion 52 of the fourth cell S4 is formed by the end surface 222c of the second bulging portion 222 and the flat region 210. In other words, the upper wall portion 51 formed by the bulging portion is relatively thinner than the lower wall portion 52 formed by including a portion where the flat sheet material is not bulged. In addition, in the two-layer side wall portion 53, the side wall portion 53 of the fourth cell S4 formed by the upper surfaces 222a of the second bulge portions 222 abutting each other is thinner than the side wall portion 53 of the third cell S3 formed by the non-bulged portions of the bulge region 220 abutting each other.

[0079] In the core layer forming process, the first conveyor 63 is heated by a heating device 63a. Therefore, the folded and formed core layer 50 is heated and pressed by the first conveyor 63. As a result, the upper and lower edges of the two-layered side wall portion 53 of the folded core layer 50 are heat-welded, while the portion other than the upper and lower edges is not heat-welded.

[0080] In addition, when the core layer 20 is transported between the first conveyors 63, the core layer 20 is heated and slightly compressed in the vertical direction, so that heat from the heated upper wall portion 51 or lower wall portion 52 is transferred to the side wall portion 53, the thermoplastic resin is thermally melted, and thick portions 54, 55 are partially formed in the side wall portion 53. At this time, since the upper wall portion 51 of the core layer 50 is relatively thinner than the lower wall portion 52, the heat from the heating device 63a is more easily transferred to the side wall portion 53 through the upper wall portion 51 than through the lower wall portion 52. As a result, in the core layer forming process, a resin pool is easily formed at the upper end of the side wall portion 53 due to thermal melting of the side wall portion 53. The formed resin pool becomes the thick portions 54, 55 by subsequent cooling, and the thick portions 54, 55 protruding toward the inside of the third cell S3 and the fourth cell S4 are formed at the upper end of the side wall portion 53.

[0081] In addition, the two-layered sidewall portion 53 that separates the fourth cells S4 is thinner than the two-layered sidewall portion 53 that separates the third cells S3. Therefore, heat from the heating device 63a is more easily transferred to the two-layered sidewall portion 53 that separates the fourth cells S4 than to the two-layered sidewall portion 53 that separates the third cells S3. As a result, in the core layer forming process, a larger resin pool is more likely to be formed in the two-layered sidewall portion 53 that separates the fourth cells S4 than in the two-layered sidewall portion 53 that separates the third cells S3. As a result, the size of the thick portion 55 formed at the upper end of the sidewall portion 53 of the fourth cell S4 is relatively smaller than the size of the thick portion 54 formed at the upper end of the sidewall portion 53 of the third cell S3.

[0082] According to the hollow structural body 11 and the manufacturing method thereof of this embodiment, in addition to the effects (5) and (6) of the first embodiment, the following effects can be obtained. (7) The side wall portion 53 of the core layer 50 is formed with thick portions 54 and 55 .

[0083] Therefore, the strength of the side wall portion 53 is improved due to the presence of the thick portions 54 and 55 . (8) In the manufacturing method of the hollow structure 11, in the core layer formation process, the core layer 50 is compressed in its thickness direction while being heated, thereby forming thick portions 54, 55 in the side wall portion 53 which protrude toward the inside of the cell S.

[0084] Therefore, by compressing the thermoplastic resin core layer 50 in its thickness direction in a heated state and thermally melting the side wall portion 53, the thick portions 54, 55 can be formed integrally with the side wall portion 53. The strength of the side wall portion 53 can be improved more easily by using the thick portions 54, 55 for reinforcing the side wall portion 53 than by joining another member.

[0085] (9) In the core layer forming process, a vacuum-formed thermoplastic resin embossed sheet material 200 is folded to form the core layer 50, and the core layer 50 is compressed in the thickness direction in a heated state.

[0086] Therefore, the core layer 50 and the thick portions 54 and 55 can be formed in the same process, and the manufacturing process of the hollow structural body 11 having excellent strength can be simplified. Furthermore, the formation of the core layer 50 and the thermal welding of the upper and lower edges of the side wall portion 53 of the two-layer structure of the core layer 50 can be performed simultaneously.

[0087] The above embodiment can be modified as follows: The above embodiment and the following modified examples can be applied in combination with each other to the extent that there is no technical contradiction. The core layer 20 is not limited to being formed by folding a concave-convex sheet material. For example, it may be a concave-convex sheet material in which cylindrical or truncated cone-shaped bulges are formed by vacuum forming a single sheet material.

[0088] The core layer 20 is not limited to one in which columnar cells S are partitioned. For example, it may be one in which sheet layers are bonded to both the upper and lower surfaces of a core layer having a predetermined uneven shape. An example of a core layer having such a configuration is described in JP 2014-205341 A. Also, it may be a plastic cardboard with a harmonica-shaped cross section.

[0089] The core layer 20 does not have to be formed from a vacuum-formed uneven sheet material. For example, it may be formed from an uneven sheet material in which a plurality of strip-shaped sheets are bent and arranged at predetermined intervals to form the side walls of the cells.

[0090] Although the cells S are arranged in a hexagonal column shape inside the core layer 20, the shape of the cells S is not limited to this. For example, the cells S may be in a polygonal column shape such as a square column shape or an octagonal column shape. Furthermore, the cells do not have to be adjacent to each other, and there may be gaps (spaces) between the cells.

[0091] The core layer 20 may have cells of different shapes mixed therein. In the hollow structure 10 of the first embodiment, the thickness of the uneven sheet material 100 forming the core layer 20 does not have to vary depending on the location. Furthermore, the thickness of each portion may be different from that of the core layer 20 of the first embodiment. Similarly, in the hollow structure 11 of the second embodiment, the thickness of the uneven sheet material 200 forming the core layer 50 does not have to vary depending on the location. Furthermore, the thickness of each portion may be different from that of the core layer 50 of the second embodiment.

[0092] In the corrugated sheet material 100 forming the core layer 20 of the hollow structure 10 of the first embodiment, the thickness of the upper surface 110a in the first bulging portion 110 is thinner than the thickness of the flat sheet material. The thickness of the pair of side surfaces 110b is thicker than the thickness of the upper surface 110a and thinner than the thickness of the flat sheet material. Furthermore, the thickness of the pair of end surfaces 110c is also thicker than the thickness of the upper surface 110a and thinner than the thickness of the flat sheet material. The thicknesses of the upper surface 110a, the side surfaces 110b, and the end surfaces 110c are not limited thereto. For example, the thickness of the end surfaces 110c may be thinner than the thickness of the upper surface 110a. This is because, when the corrugated sheet material 100 is vacuum-formed from the flat sheet material wound on the sheet roll 61, the corners where the upper surface 110a and the end surfaces 110c are connected are the parts that are most pulled, and the end surfaces 110c may become thinner. Furthermore, each of the upper surface 110a, the side surface 110b, and the end surface 110c may not have a uniform thickness, but may gradually become thinner toward the corners.

[0093] In the concave-convex sheet material 100 forming the core layer 20 of the hollow structure 10 of the first embodiment, the thickness of the lower surface 120a in the second bulging portion 120 is equal to the thickness of the flat sheet material. The thickness of the pair of side surfaces 120b is thinner than the thickness of the lower surface 120a, that is, the thickness of the flat sheet material. Furthermore, the thickness of the pair of end surfaces 120c is also thinner than the thickness of the lower surface 120a, that is, the thickness of the flat sheet material. The thicknesses of the upper surface 110a, the side surfaces 110b, and the end surfaces 110c are not limited thereto. For example, the thickness of the lower surface 120a may be thinner than the thickness of the flat sheet material. This is because the flat sheet material may be stretched when the flat sheet material is heated by the vacuum forming drum 62.

[0094] In either case, in the core layer 20 folded in the folding process, the two-layered side wall 23 of the first cell S1 is relatively thinner than the two-layered side wall 23 of the second cell S2, and is more likely to be melted by the heat from the heating device 63a. As a result, a larger resin pool is formed at the lower edge of the side wall 23 of the first cell S1 than at the upper edge of the side wall 23 of the second cell S2.

[0095] In the core layer 20 of the hollow structure 10 of the first embodiment, the thickness of the upper wall portion 21 of the first cell S1 and the thickness of the lower wall portion 22 of the second cell S2 are approximately the same. This is not limited to the above, and for example, the thickness of the upper wall portion 21 of the first cell S1 may be thinner than the thickness of the lower wall portion of the second cell S2.

[0096] In the hollow structure 11 of the second embodiment, the thick-walled portions 54, 55 are formed at the upper end edge of the side wall portion 53 so as to be integrated with the lower surface of the upper wall portion 51, but the positions at which the thick-walled portions 54, 55 are formed are not limited thereto. They may be formed at positions on the side wall portion 53 that do not contact the upper wall portion 51. In this case, the upper wall portion 51 is relatively thinner than the lower wall portion 52, and heat from the heating device 63a is more easily transmitted to the side wall portion 53 through the upper wall portion 51 than through the lower wall portion 52, so that the thick-walled portions 54, 55 are easily formed at the upper end portions of the side wall portion 53.

[0097] In the side wall 23 of the hollow structure 11 of the second embodiment, in addition to the thick portions 54 and 55, protrusions similar to the protrusions 24 and 25 of the first embodiment may be formed. That is, the protrusions formed on the upper edge of the side wall 53 and the thick portions 54 and 55 formed on the upper end of the side wall 53 may coexist. In the core layer 50 of the second embodiment, the side wall 53 of the two-layer structure may also have a curved shape in top view in which the first side wall 53a and the second side wall 53b are slightly curved so that the center in the width direction bulges toward the inner side of the cell S. In this case, the protrusions on the upper edge of the side wall 53 are also formed along the curved shapes of the first side wall 53a and the second side wall 53b, similar to the protrusions 24 and 25 of the first embodiment. The two-layered side wall portion 53 has a curved shape when viewed from above such that the distance between the first side wall portion 53a and the second side wall portion 53b increases from both ends toward the center.

[0098] In the hollow structure 10 of the first embodiment, the protruding portion 25 may be larger than the protruding portion 24. Also, they may be about the same size. In the hollow structure 11 of the second embodiment, the thick portion 55 may be smaller than the thick portion 54. Also, they may be about the same size.

[0099] The thick portions 54, 55 may be formed in a portion other than the upper end of the side wall portion 53. They may be formed in the lower end or in the middle. Also, they may be formed in a plurality of places from the upper end to the lower end.

[0100] In order to reinforce the hollow structure 10, the cells S may be filled with a filler such as a foamed resin, a steel plate may be joined to any part of the main surface of the core layer 20, or a reinforcing member such as a metal rod may be inserted into the cells S.

[0101] At least one of the skin layers 30, 40 bonded to the hollow structure 10 may have a multi-layer structure instead of a single layer structure. For example, it may have a multi-layer structure including a low melting point film layer, a decorative layer with a printed pattern, a nonwoven fabric layer, etc.

[0102] At least one of the skin layers 30, 40 may be omitted. The thermoplastic resin constituting the core layer 20 and the skin layers 30, 40 may contain various functional resins. For example, flame retardancy can be improved by adding a flame retardant resin to the thermoplastic resin. It is also possible to use a thermoplastic resin containing various functional resins for all of the core layer 20 and the skin layers 30, 40, or to use a thermoplastic resin containing various functional resins for at least one of the core layer 20 and the skin layers 30, 40.

[0103] The skin layers 30, 40 are bonded to the core layer 20 by an adhesive, but may also be bonded to the core layer 20 by heat welding. In this case, the temperature of the heating device 66a of the second conveyor 66 may be adjusted taking into consideration the thermal melting temperature of the thermoplastic resin that constitutes the core layer 20 and the skin layers 30, 40.

[0104] In the above embodiments, the hollow structures 10 and 11 are described as being flat, but the hollow structures 10 and 11 do not have to be flat. For example, they may be formed into a curved plate shape by press molding or the like. In this case, because the peel strength of the hollow structures 10 and 11 is high, the surface can be formed flat even when they are formed into a curved plate shape. [Explanation of symbols]

[0105] 10, 11...hollow structure, 20, 50...core layer, 20a...upper surface (main surface), 20b...lower surface (main surface), 21, 51...upper wall portion, 22, 52...lower wall portion, 23, 53...side wall portion, 24, 25...protruding portion, 30...skin layer, 40...skin layer, 54, 55...thick portion, 100, 200...uneven sheet material, S...cell, S1...first cell, S2...second cell.

Claims

[Claim 1] A hollow structure made of a thermoplastic resin, comprising a hollow plate-like core layer in which a plurality of cells are arranged side by side and partitioned by side walls extending in a thickness direction, and a skin layer bonded to at least one main surface of the core layer, The cell has one end in a thickness direction closed by a wall portion and the other end open, a protrusion protruding toward an inner side of the cell is formed on the side wall of the core layer, the protrusion is formed by the side wall portion compressed in the thickness direction, the protrusion comprises a first protrusion formed on an edge of the side wall portion at the one end of the cell, and a second protrusion formed on an edge of the side wall portion at the other end of the cell and joined to the skin layer; A hollow structure, characterized in that the protruding amount of the second protruding portion is greater than the protruding amount of the first protruding portion.

Images