JP7790762B2 - Hollow structure and luggage board - Google Patents

Description

This disclosure relates to hollow structures and luggage boards.

Patent Document 1 describes a hollow structure used for protective materials and the like.
As shown in Figure 11, this hollow structure comprises a core layer obtained by folding a sheet material 50 having projections and recesses, and two skin layers bonded to both sides of the core layer. A plurality of cells are arranged within this hollow structure. The partition walls located between adjacent cells have a two-layer structure. One of the ends of this partition wall has a joint where the two layers are joined together, and the other end has a folded portion.

Patent No. 4368399

The hollow structures described above are required to have even greater impact resistance. The purpose of this disclosure is to provide a hollow structure with efficiently improved impact resistance.

A hollow structure according to one aspect of the present disclosure has a plurality of cells. The hollow structure comprises a core layer having a plurality of first walls, a plurality of second walls, and a plurality of partition walls, and first and second skin layers respectively bonded to both sides of the core layer. The plurality of cells includes a plurality of first cells and a plurality of second cells. Each of the first cells is partitioned by the first wall, a plurality of the partition walls extending from the first wall, and the second skin layer. Each of the second cells is partitioned by the second wall, a plurality of the partition walls extending from the second wall, and the first skin layer. The plurality of first cells aligned in one direction constitute a first cell row, and the plurality of second cells aligned in the one direction constitute a second cell row. The plurality of partition walls include a plurality of first partition walls having a two-layer structure located between adjacent first cells in the first cell row, and a plurality of second partition walls having a two-layer structure located between adjacent second cells in the second cell row. The first partition wall has a first joint at its end closer to the first wall, where the two layers constituting the first partition wall are joined together, and a first folded portion at its end farther from the first wall. The second partition wall has a second joint at its end closer to the second wall, where the two layers constituting the second partition wall are joined together, and a second folded portion at its end farther from the second wall. The joining strength of the first joint is greater than the joining strength of the second joint.

FIG. 1 is a perspective view of a hollow structure according to an embodiment. FIG. 1B is a cross-sectional view taken along line 1B-1B of FIG. 1A. FIG. 1C is a cross-sectional view taken along line 1C-1C of FIG. 1A. FIG. 1B is a schematic diagram showing the state of the sheet material constituting the core layer of the hollow structure of FIG. 1A before folding. FIG. 2B is a perspective view of the sheet material of FIG. 2A. FIG. 2C is a perspective view showing the sheet material of FIG. 2B in a folded state. FIG. 10 is a perspective view of a hollow structure according to a first modified example. FIG. 10 is a perspective view of a core layer according to a second modified example. FIG. 10 is a perspective view of a core layer according to a third modified example. FIG. 10 is a top view of a core layer according to a fourth modified example. FIG. 2 is a cross-sectional view of the sheet material and mold immediately after vacuum forming. 8 is an end view taken along line 8-8 of FIG. 6. 9 is an end view taken along line 9-9 of FIG. 6. FIG. 10 is a cross-sectional view of a core layer of a fifth modified example. FIG. 10 is a perspective view of a sheet material that constitutes a core layer in a conventional hollow structure.

An embodiment of the hollow structure will now be described.
In the specification and claims, terms such as "first,""second," etc. are used to distinguish between similar elements and do not necessarily denote a particular sequential or chronological order.

All features disclosed in the specification and/or claims are intended to be disclosed separately and independently of one another for purposes of the original disclosure and for purposes of limiting the claimed invention independently of any combination of features in the embodiments and/or claims.

The disclosed embodiments should not be construed as limiting the scope of the invention, and features of separate embodiments that perform equivalent or the same function may be interchanged between the disclosed embodiments within the scope of the amended claims. The recitation of numerical ranges by endpoints includes all numbers within that range. For example, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5.

As shown in FIG. 1A, the hollow structure 10 includes a core layer 20 and first and second skin layers 30, 40 bonded (e.g., welded) to both sides of the core layer 20. The core layer 20 has a plurality of first walls 21a, a plurality of second walls 21b, and a plurality of partition walls 23, which define a plurality of cells S having a hexagonal prism shape. The plurality of cells S includes a plurality of first cells S1 and a plurality of second cells S2. Each first cell S1 is defined by a hexagonal first wall 21a, a plurality of partition walls 23 extending from the first wall 21a toward the second skin layer 40, and the second skin layer 40. Each second cell S2 is defined by a hexagonal second wall 21b, a plurality of partition walls 23 extending from the second wall 21b toward the first skin layer 30, and the first skin layer 30.

The core layer 20 has a plurality of first cell rows S1a in which a plurality of first cells S1 are aligned along one direction (X-axis), and a plurality of second cell rows S2a in which a plurality of second cells S2 are aligned along one direction (X-axis). The X-axis, Y-axis, and Z-axis are mutually perpendicular axes, and the thickness direction of the hollow structure 10 is along the Z-axis. The first and second cell rows S1a, S2a extend in a direction perpendicular to the thickness direction Z.

As shown in Figures 1B and 1C, the multiple partition walls 23 include multiple first partition walls 23a, multiple second partition walls 23b, and multiple third partition walls 23c. The first and second partition walls 23a and 23b have a two-layer structure. The third partition wall 23c has a single-layer structure.

The first partition wall 23a is located between adjacent first cells S1 in the first cell row S1a. The first partition wall 23a has a first joint 24a at its first end in the thickness direction Z (the end closer to the first wall 21a) where the surfaces of the two layers constituting the first partition wall 23a are joined together by welding, and a first fold 25a at its second end in the thickness direction Z (the end farther from the first wall 21a). The two layers constituting the first partition wall 23a are not joined to each other between the first joint 24a and the first fold 25a.

The second partition wall 23b is located between adjacent second cells S2 in the second cell row S2a. The second partition wall 23b has a second joint 24b at its second end in the thickness direction Z (the end closer to the second wall 21b) where the two layers constituting the second partition wall 23b are joined together by welding, and a second fold 25b at its first end in the thickness direction Z (the end farther from the second wall 21b). The two layers constituting the second partition wall 23b are not joined to each other between the second joint 24b and the second fold 25b.

The two layers constituting the first partition wall 23a are not joined to each other near the center in the thickness direction Z. Therefore, a first communication portion 26a that connects the first cells S1 to each other may be formed between adjacent first cells S1 in the Y direction. Similarly, the two layers constituting the second partition wall 23b are not joined to each other near the center in the thickness direction Z. Therefore, a second communication portion 26b that connects the second cells S2 to each other may be formed between adjacent second cells S2 in the Y direction. Specifically, the first communication portion 26a is a gap that may be formed between two adjacent or abutting first partition walls 23a. Similarly, the second communication portion 26b is a gap that may be formed between two adjacent second partition walls 23b. In other words, even if the unjoined portions of the two layers appear to be in contact with each other, fluid can flow between the two layers.

The third partition wall 23c is located between the first cell S1 and the second cell S2. The first cell row S1a and the second cell row S2a share multiple third partition walls 23c and are arranged alternately along the Y axis, which is perpendicular to the X axis. The six partition walls 23 that define each first cell S1 include two first partition walls 23a and four third partition walls 23c, and the six partition walls 23 that define each second cell S2 include two second partition walls 23b and four third partition walls 23c.

The core layer 20 and the skin layers 30, 40 are made of a thermoplastic resin. The thermoplastic resins that make up the core layer 20 and the skin layers 30, 40 are conventionally known, and their materials are not particularly limited. Examples of thermoplastic resins include polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, and polybutylene terephthalate resin. The thermoplastic resins that make up the core layer 20 and the skin layers 30, 40 may be the same material or different materials. In this embodiment, the core layer 20 and the skin layers 30, 40 are both made of polypropylene resin.

The thicknesses of the first wall 21a, partition wall 23, and second wall 21b of the core layer 20 are not particularly limited, but are, for example, 0.1 mm to 0.5 mm. The thicknesses of the skin layers 30, 40 are not particularly limited, but are, for example, 0.3 mm to 0.6 mm.

The thickness of the first wall 21a may be greater than the thickness of the second wall 21b.
A method for manufacturing the hollow structure 10 will be described.
The manufacturing method of the hollow structure 10 includes a folding step, a heating step, and a lamination step.

(Folding process)
In the folding process, a core layer is produced by folding and forming a flat sheet material 200 as shown in Fig. 2A. The sheet material 200 is vacuum-formed to have predetermined concaves and convexes.

The sheet material 200 has first and second bulge portions 210, 220 in the shape of strips extending in the X direction. The first bulge portions 210 and second bulge portions 220 have a width in the Y direction and are arranged alternately along the Y axis. The first bulge portions 210 and second bulge portions 220 protrude in opposite directions along the Z axis. When the sheet material 200 is viewed in a plan view, the first bulge portions 210 and second bulge portions 220 have the same shape and are arranged at positions offset by 1/2 pitch along the X axis.

The first bulging portion 210 has a first bulging surface 210a, two partition surfaces 210b, and two end surfaces 210c. The cross-sectional shape of the first bulging portion 210 cut along a plane including the Y-axis and Z-axis is a trapezoid formed by bisecting a regular hexagon by its longest diagonal. The two end surfaces 210c are located at the boundary line P' shown in Figure 2A. The angle between the end surface 210c and the first bulging surface 210a is approximately 90°.

The second bulge portion 220 has a second bulge surface 220a, two partition surfaces 220b, and two end surfaces 220c. The cross-sectional shape of the second bulge portion 220 cut along a plane including the Y-axis and Z-axis is a trapezoid formed by bisecting a regular hexagon by its longest diagonal. The two end surfaces 220c are located at the boundary line Q' shown in Figure 2A. The angle between the end surface 220c and the second bulge surface 220a is approximately 90°. The length of the second bulge portion 220 along the X-axis, i.e., the length between the two end surfaces 220c, is the same as the length of the first bulge portion 210 along the X-axis, i.e., the length between the two end surfaces 210c. The end surface 220c of the second bulge portion 220 is located at the center of the first bulge portion 210 in the X-direction. The partition surface 210b of the first bulging portion 210 and the partition surface 220b of the second bulging portion 220 have the same shape. The core layer 20 is formed by sequentially folding the sheet material 200 along the boundary lines P' and Q'.

As shown in FIG. 2B, the sheet material 200 is mountain-folded along boundary line P' and valley-folded along boundary line Q'. As shown in FIG. 2C, the first bulging portion 210 is valley-folded along boundary line Q', which is located in the center in the X direction, so that the first bulging surfaces 210a divided by boundary line Q' abut each other. In the first bulging portion 210 folded in this manner, the abutting first bulging surfaces 210a form the first partition wall 23a, and the partition surface 210b forms the third partition wall 23c. At the first end (upper end in FIG. 2C) of the first partition wall 23a, the two end surfaces 210c aligned along the X axis form the single-layer first wall 21a. The second end (lower end in FIG. 2C) of the first partition wall 23a defines the first opening 27a.

The second bulging portion 220 is mountain-folded at boundary line P', which is located in the center in the X direction between adjacent boundary lines Q', so that the second bulging surfaces 220a divided by boundary line P' abut each other. When the second bulging portion 220 is folded in this manner, the abutting second bulging surfaces 220a form the second partition wall 23b, and the partition surface 220b forms the third partition wall 23c. At the second end (lower end in Figure 2C) of the second partition wall 23b, the two end surfaces 220c aligned along the X axis form the single-layer second wall 21b. The first end (upper end in Figure 2C) of the second partition wall 23b defines the second opening 27b.

In this way, during the folding process, a first cell S1 having a first opening 27a is defined by the first wall 21a and the partition wall 23 extending from the first wall 21a, and a second cell S2 having a second opening 27b is defined by the second wall 21b and the partition wall 23 extending from the second wall 21b. The surfaces of the first wall 21a and the second wall 21b are smooth. "Smooth surface" means a flat surface with no irregularities when visually observed.

When the sheet material 200 is vacuum-formed into an uneven shape, the thickness of the portions that are most deformed by the vacuum is thinner than the thickness of the remaining portions. Therefore, when vacuum-forming the sheet material 200, by vacuum-forming the second bulging portion 220 more strongly in the bulging direction, the thickness of the second wall 21b becomes thinner than the thickness of the first wall 21a. As a result, the thickness of the first wall 21a can be made relatively thicker than the thickness of the second wall 21b.

2A, when the back surface (bottom surface, not shown) of the sheet material 200 is placed facing the vacuum forming mold and molded, the two end surfaces 210c arranged on either side of boundary line P' become the first surface of the core layer 20 (the top surface in FIG. 1B), and the end surface 220c arranged on either side of boundary line Q' become the second surface of the core layer 20 (the bottom surface in FIG. 1B). Therefore, the thickness of the first wall 21a defining the first surface (end surface 210c) of the core layer 20 is thicker than the thickness of the second wall 21b defining the second surface (end surface 220c) of the core layer 20. The thickness of the first wall 21a is not particularly limited, but may be, for example, more than twice the thickness of the second wall 21b. The thickness of the partition wall 23 gradually increases from the second surface toward the first surface of the core layer 20.

On the first surface of the core layer 20, the multiple cells S are neatly aligned along the X and Y axes. Near the second surface of the core layer 20, the thickness of the partition walls 23 is thinner than near the first surface. Therefore, on the second surface of the core layer 20, the multiple cells S aligned along the Y axis are aligned in a slightly serpentine pattern. Near the second surface of the core layer 20, the two layers constituting the partition walls 23 can be compressed more to bring the two layers into close contact with each other. Therefore, in the heating process described below, the two layers constituting the partition walls 23 can be more reliably welded together near the second surface. Depending on the thickness of the partition walls 23, the multiple cells S aligned along the Y axis on the first surface of the core layer 20 may be aligned in a serpentine pattern, as shown in Figure 6.

(Heating process)
In the heating step, the core layer 20 produced in the folding step is pressed while being heated, thereby heat-welding (hereinafter simply referred to as "welding") the first end of the first partition wall 23a and heat-welding the second end of the second partition wall 23b.

One method for heating the core layer 20 is to heat the core layer 20 using a heating device while transporting it on a conveyor (not shown). For example, the first and second surfaces of the core layer 20 are sandwiched between first and second conveyors, respectively, and the core layer 20 is heated using heaters located inside the first and second conveyors. At this time, the core layer 20 is transported along the X-axis. By pressing the core layer 20 with the first and second conveyors, a load is applied to the core layer 20 along the X-axis. A load may also be applied to the core layer 20 along the Z-axis by sandwiching the core layer 20 between first and second conveyors aligned along the Z-axis.

By pressing the core layer 20 while heating it, the two layers that make up the first partition wall 23a are welded together near the first wall 21a, thereby forming the first joint 24a. Furthermore, the two layers that make up the first partition wall 23a are welded together near the second wall 21b, thereby forming the second joint 24b.

When pressing the core layer 20 from both sides, a load along the X axis is unlikely to be applied near the center of the first and second partition walls 23a, 23b. Therefore, the two layers constituting the first and second partition walls 23a, 23b are not welded to each other near the center in the Z direction. As a result, a first communication portion 26a that connects the first cells S1 adjacent to each other along the Y axis is formed near the center of the first partition wall 23a. Similarly, a second communication portion 26b that connects the second cells S2 adjacent to each other along the Y axis is formed near the center of the second partition wall 23b.

The thickness of the partition wall 23 near the first wall 21a is greater than the thickness near the second wall 21b. Therefore, when pressing the core layer 20 from both sides, a relatively greater load is applied near the first wall 21a than near the second wall 21b. That is, the length dimension along the X axis of the core layer 20 obtained by the folding process is longer at the position where it contacts the first wall 21a than at the position where it contacts the second wall 21b. Therefore, the load applied to the core layer 20 by the first and second conveyors is greater at the first end of the first partition wall 23a. Welding under a greater load results in a greater bonding force. Therefore, the bonding force of the first bonding portion 24a is greater than the bonding force of the second bonding portion 24b.

(Lamination process)
In the lamination process, first and second sheets (first and second skin layers 30, 40) are bonded to the first and second surfaces of the core layer 20, respectively. More specifically, the first and second sheets that will become the skin layers 30, 40 are heated and brought into contact with both surfaces of the core layer 20 for a predetermined time. This causes the first and second skin layers 30, 40 to be bonded (welded) to both surfaces of the core layer 20, respectively.

By going through the above manufacturing steps, a flat hollow structural body 10 including a plurality of cells S is fabricated.
The use of the hollow structure 10 is not particularly limited. Because the hollow structure 10 has a honeycomb structure, it has excellent impact resistance, sound insulation, and heat insulation. Therefore, the hollow structure 10 can be used appropriately for applications requiring these properties. Examples of applications of the hollow structure 10 include luggage boards, shelves, containers, etc.

When the hollow structure 10 is used in an application requiring a distinction between a front and a back, such as a luggage board or shelf board, the first skin layer 30 or the second skin layer 40 may be the front surface. Furthermore, of the first and second surfaces of the core layer 20, the one on which the multiple cells S are neatly aligned may be joined to the skin layer that will be the front surface, or the one on which the multiple cells S are arranged in a slightly meandering pattern may be joined to the skin layer that will be the front surface.

The operation and effects of this embodiment will be described.
(1) Because the bonding strength of the first bonding portion 24a is greater than the bonding strength of the second bonding portion 24b, the first bonding portion 24a can more effectively prevent the two layers constituting the first partition wall 23a from peeling off from each other. Therefore, the hollow structure 10 can improve impact resistance from one side, i.e., the side where the first bonding portion 24a is provided in the thickness direction. Therefore, impact resistance can be efficiently improved.

Furthermore, the bending strength of the hollow structure 10 can be improved compared to an embodiment in which the joining strength of the first joining portion 24a is the same as the joining strength of the second joining portion 24b.
(2) The thickness of the first wall 21a is relatively thicker than the thickness of the second wall 21b. This is because the thickness of the end surface 210c of the sheet material 200 that forms the core layer 20 is relatively thicker than the thickness of the end surface 220c. This allows the strength of the first wall 21a to be relatively increased. As a result, the hollow structure 10 has improved impact resistance from the first surface side in the thickness direction, i.e., the side where the first joint portion 24a is provided.

(3) The thickness of the first end of the partition wall 23 (the end intersecting with the first wall 21a) is relatively thicker than the thickness of the second end (the end intersecting with the second wall 21b). This allows the intersection of the partition wall 23 and the first wall 21a to be slightly crushed, more reliably joining (e.g., welding) this intersection to the first skin layer 30. In other words, even if the partition wall 23 is slightly crushed near its first end, the strength of the partition wall 23 itself is maintained, preventing excessive crushing of the partition wall 23. Furthermore, as shown in Figures 8 and 9, the thickness of the partition wall 23 continuously decreases from the first end to the second end. The thickness of the first end of the partition wall 23 is thicker than the thickness of the second end. Therefore, for example, when the core layer 20 is heated from both sides, the amount of resin melted near the first end of the partition wall 23 is greater than the amount of resin melted near the second end. This ensures a large amount of resin melts by heating, more reliably welding the first end of the partition wall 23. On the other hand, the second end of the partition wall 23 is relatively thin, making it more susceptible to heat from the heating device. This allows the second end of the partition wall 23 to be heated efficiently and welded more reliably.

(4) The first cell rows S1a and the second cell rows S2a are arranged alternately, which makes it possible to make the impact resistance more uniform on both sides of the hollow structure 10.
(5) The first joint 24a is a portion where two layers constituting the first partition wall 23a are welded together, and the second joint 24b is a portion where two layers constituting the second partition wall 23b are welded together. Therefore, the configurations of the first joint 24a and the second joint 24b can be simplified.

(6) A first communication portion 26a is formed between adjacent first cells S1 in the Y direction, and a second communication portion 26b is formed between adjacent second cells S2 in the Y direction. Therefore, when the hollow structure 10 is heated and bent, the heated air in the first cells S1 and the second cells S2 spreads throughout the hollow structure 10 through the first communication portion 26a and the second communication portion 26b. This makes it possible to suppress expansion of the first wall 21a and the second wall 21b.

This embodiment can be implemented with the following modifications. The configurations included in this embodiment and the following modifications can be implemented in combination with each other to the extent that no technical contradictions exist.

- The first and second joints 24a and 24b may be formed by applying adhesive between the two layers that make up the first partition wall 23a and/or between the two layers that make up the second partition wall 23b. In this case, the bonding strength of the first and second joints 24a and 24b can be changed by adjusting the type of adhesive and the state of application of the adhesive.

- The core layer 20 may not have at least one of the first communicating portion 26a and the second communicating portion 26b. The two layers that make up the first partition wall 23a may be bonded to each other over their entire surfaces. Similarly, the two layers that make up the second partition wall 23b may be bonded to each other over their entire surfaces.

- The hollow structure 10 does not have to be flat. At least a portion of the hollow structure 10 may be curved so that the outer surface defined by the first skin layer 30 is convex and the outer surface defined by the second skin layer 40 is concave. The hollow structure 10 can be curved as described above by press molding after the lamination process. This improves the impact resistance of the hollow structure 10 from the convex side. In such a curved portion of the hollow structure 10, the outer surface defined by the first skin layer 30 may be concave and the outer surface defined by the second skin layer 40 may be convex.

As in the first modified example shown in Figure 3, curved portions can be formed at any position by press-molding a portion of the hollow structure 10 after the lamination process. The height dimension of the convex surface 31 and the depth dimension of the concave surface 41 may be greater than the thickness dimension of the flat portion of the hollow structure 10. The hollow structure 10 may have multiple curved portions. In this case, the hollow structure 10 may have multiple curved portions that curve in different directions.

- At least one of the first wall 21a and the second wall 21b may have an uneven shape or uneven pattern on its outer surface. Such an uneven shape can create an anchor effect when joining (e.g., welding) the sheets that will become the skin layers. This can increase the bonding strength of the skin layers 30, 40. Increasing the bonding strength of the skin layers 30, 40 can improve the impact resistance of the hollow structure 10.

For example, as in the second modified example shown in Figure 4, the first wall 21a (end surface 210c) of the core layer 20 may have a linear recess 28a extending along the Y axis. This recess 28a is recessed in the direction of pulling during vacuum forming. The recess 28a can increase the welding area between the core layer 20 and the skin layers 30, 40.

Alternatively, as in the third modified example shown in Figure 5, the second wall 21b (end surface 220c) of the core layer 20 may have multiple wrinkle-shaped recesses 28b extending along the Y axis. Because the thickness of the end surface 220c is relatively thin, it is easily softened by heating in the heating process. The recesses 28b can be formed by setting the heating temperature in the heating process higher.

As in the fourth modified example shown in Figure 6, one of the first and second openings 27a, 27b (second opening 27b in Figure 6) does not have to be a regular hexagon. In Figure 6, the position of the first cell row S1a along the X axis is shifted, causing the shape of the second opening 27b to be distorted and no longer a regular hexagon. In this case, the cells S1 and S2 arranged alternately along the Y axis appear to be serpentine.

The cause of the meandering of the cells S1 and S2 will be described with reference to FIG.
7 schematically shows a mold 251 for vacuum-forming the sheet material 200 and the sheet material 200 immediately after vacuum-forming. The mold 251 has a plurality of suction holes 252 that suck the sheet material 200. The mold 251 may be a cylindrical drum. By transporting the sheet material 200 while wrapping it around the cylindrical mold 251, it is possible to continuously form a long sheet material 200.

The second bulge portion 220 is stretched by being sucked into the mold 251 through the suction holes 252, as shown by the white arrows in Figure 7. This makes the second bulge portion 220 relatively thinner than the first bulge portion 210. At this time, the intersections between the second bulge surface 220a and the two partition surfaces 220b and the two end surfaces 220c may not form sharp corners. In this case, the second bulge surface 220a, the two partition surfaces 220b, and the two end surfaces 220c of the second bulge portion 220 are curved so as to bulge outward toward the mold 251, and the second bulge portion 220 has four rounded corners. At this time, the first bulging surface 210a, the two partition surfaces 210b (partition surfaces 220b), and the two end surfaces 210c of the first bulging portion 210 are curved so as to be concave inward toward the mold 251, and the first bulging portion 210 has four sharp corners. In this case, the two first bulging surfaces 210a that make up the first partition wall 23a are curved so that their outer edges approach each other.

When the multiple first walls 21a and multiple first openings 27a are regular hexagons, the multiple second walls 21b and multiple second openings 27b are distorted hexagons. Alternatively, when the multiple second walls 21b and multiple second openings 27b are regular hexagons, the multiple first walls 21a and multiple second openings 27b are distorted hexagons.

In this way, the meandering state of the cells S changes depending on whether the first wall 21a or the second wall 21b becomes a regular hexagon. Even if distortion and meandering occur in multiple cells S, each cell S maintains its hexagonal column shape, so impact strength and bending strength are unlikely to decrease.

The distortion and meandering of the multiple cells S can occur, for example, because the first bulging surface 210a is curved or the second bulging portion 220 has rounded corners. In other words, even with a sheet material 200 having such characteristics, the core layer 20 can be formed while the cells S are distorted and meandering. This makes it possible to increase the molding speed of the sheet material 200 and core layer 20, thereby improving work efficiency and suppressing molding defects in the sheet material 200 and core layer 20.

The two second bulging surfaces 220a constituting the second partition wall 23b may be curved so that the centers of the surfaces approach each other, which improves the impact resistance of the second partition wall 23b.
As in a fourth modified example shown in Figures 8 and 9, at least one of the first wall 21a and the second wall 21b may have a protrusion. As shown in Figure 8, the protrusion 110 of the first wall 21a is a portion that melts and protrudes from the first wall 21a by increasing the heating temperature or the pressing force during the heating process. The protrusion 110 may protrude in the direction of extension of the first surface 20a of the core layer 20 (the surface that is bonded to the first skin layer 30), or in a direction intersecting the first surface 20a. The protrusion 110 allows the core layer 20 to be more reliably welded to the first skin layer 30.

Similarly, the first folded portion 25a may be heated or pressed to form a protrusion 111 protruding from the first folded portion 25a. The protrusion 111 serves as the portion that welds the first partition wall 23a (first folded portion 25a) to the second skin layer 40. This increases the welding area of the core layer 20 to the second skin layer 40, thereby increasing the strength of the weld.

As shown in Figure 9, the convex portion 113 of the second wall 21b is a portion that protrudes due to melting of the second wall 21b. The convex portion 113 may protrude in the direction in which the second surface 20b of the core layer 20 (the surface that is joined to the second skin layer 40) extends, or may protrude in a direction that intersects with the second surface 20b. The convex portion 113 allows the core layer 20 to be more reliably welded to the second skin layer 40.

Similarly, the second folded portion 25b may be heated or pressed to form a protrusion 112 protruding from the second folded portion 25b. The protrusion 112 serves as the portion that welds the second partition wall 23b (second folded portion 25b) to the first skin layer 30. This increases the welding area of the core layer 20 to the first skin layer 30, thereby increasing the strength of the weld.

By having the protrusions 111 and 112 protrude from the folded portions 25a and 25b, respectively, the opening areas of the first and second openings 27a and 27b can be narrowed. This improves the welding strength of the skin layers 30 and 40.

- The skin layers 30, 40 may be attached to both sides of the core layer 20 using an adhesive. In this case, the adhesive may be applied to the sheets that will become the skin layers 30, 40, or to the core layer 20.

The skin layers 30, 40 may be made of, for example, nonwoven fabric. Alternatively, nonwoven fabric may be attached to the outer surfaces of the skin layers 30, 40.
The hollow structure 10 may have a through-hole that penetrates through at least one of the core layer 20 and the skin layers 30, 40 in the thickness direction (Z direction).

The shape of the cells S of the hollow structure 10 is not limited to a hexagonal prism, and may be, for example, any polygonal prism, a circle, or an elliptical prism.
As in a fifth modified example shown in FIG. 10 , the outer edge of the hollow structure 10 may be crushed so as to bring the first skin layer 30 closer to the second skin layer 40. At this time, the outer edge of the first skin layer 30 and the outer edge of the first wall 21a curve closer to the first skin layer 30. In the crushed outer edge portion 105, the first skin layer 30, the first wall 21a, and the partition wall 23 are integrated into a solid shape. At this time, the first partition wall 23a is crushed near the first end, where it is thickest. Therefore, the strength of the solid outer edge portion 105 is higher and the surface of the outer edge portion 105 is smoother than when the first partition wall 23a is crushed near the second end, where it is relatively thinner.

The technical concepts that can be understood from the above embodiment are listed below.
(1) A hollow structure having a plurality of cells, the hollow structure comprising:
a core layer having a plurality of first walls, a plurality of second walls, and a plurality of partition walls;
first and second skin layers bonded to both sides of the core layer, respectively;
Equipped with
the plurality of cells includes a plurality of first cells and a plurality of second cells;
Each of the first cells is defined by the first wall and a plurality of the partition walls extending from the first wall,
each second cell is defined by the second wall and a plurality of the partition walls extending from the second wall;
the plurality of first cells aligned in one direction constitute a first cell row, and the plurality of second cells aligned in the one direction constitute a second cell row;
The plurality of partition walls are
a plurality of first partition walls having a two-layer structure positioned between adjacent first cells in the first cell row;
a plurality of second partition walls having a two-layer structure located between adjacent second cells in the second cell row,
the first partition wall has a first joint portion at an end closer to the first wall, where two layers constituting the first partition wall are joined to each other, and a first folded portion at an end farther from the first wall;
the second partition wall has a second joint portion at an end closer to the second wall where two layers constituting the second partition wall are joined to each other, and a second folded portion at an end farther from the second wall;
a bonding strength of the first bonding portion is greater than a bonding strength of the second bonding portion;
The thickness of the first wall is greater than the thickness of the second wall;
the first cell rows and the second cell rows are alternately arranged along a direction intersecting the one direction,
the two layers constituting the first partition wall are welded to each other at the first joint,
The two layers constituting the second partition wall are welded to each other at the second joint.
hollow structure.

(2) The plurality of cells arranged along a direction intersecting the one direction are arranged in a meandering manner, and each of the cells arranged in a meandering manner maintains a hexagonal prism shape.
The hollow structure described in (1) above.

(3) The second partition wall has a protruding portion protruding from the second folded portion along the first skin layer, and the protruding portion is welded to the first skin layer.
The hollow structure described in (1) above.

(4) the thickness of the first wall is at least twice the thickness of the second wall;
The thickness of the partition wall gradually increases from the second wall toward the first wall.
The hollow structure described in (1) above.

(5) At least a portion of the hollow structure is curved such that an outer surface defined by the first skin layer is a convex surface and an outer surface defined by the second skin layer is a concave surface.
A hollow structure according to any one of (1) to (4) above.

(6) A luggage board having the hollow structure described in any one of (1) to (5) above.

Claims (5)

A hollow structure having a plurality of cells, the hollow structure comprising:
a core layer having a plurality of first walls, a plurality of second walls, and a plurality of partition walls;
first and second skin layers bonded to both sides of the core layer, respectively;
Equipped with
the plurality of cells includes a plurality of first cells and a plurality of second cells;
Each of the first cells is defined by the first wall and a plurality of the partition walls extending from the first wall,
each second cell is defined by the second wall and a plurality of the partition walls extending from the second wall;
the plurality of first cells aligned in one direction constitute a first cell row, and the plurality of second cells aligned in the one direction constitute a second cell row;
The plurality of partition walls are
a plurality of first partition walls having a two-layer structure positioned between adjacent first cells in the first cell row;
a plurality of second partition walls having a two-layer structure located between adjacent second cells in the second cell row,
the first partition wall has a first joint portion at an end closer to the first wall, where two layers constituting the first partition wall are joined to each other, and a first folded portion at an end farther from the first wall;
the second partition wall has a second joint portion at an end closer to the second wall where two layers constituting the second partition wall are joined to each other, and a second folded portion at an end farther from the second wall;
a bonding strength of the first bonding portion is greater than a bonding strength of the second bonding portion;
The thickness of the first wall is greater than the thickness of the second wall;
the first cell rows and the second cell rows are alternately arranged along a direction intersecting the one direction,
the two layers constituting the first partition wall are welded to each other at the first joint,
the two layers constituting the second partition wall are welded to each other at the second joint,
the second partition wall has a protruding portion protruding from the second folded portion along the first skin layer, and the protruding portion is welded to the first skin layer.
hollow structure. The plurality of cells arranged along a direction intersecting the one direction are arranged in a serpentine manner, and each of the cells arranged in a serpentine manner maintains a hexagonal prism shape.
The hollow structure according to claim 1 . the thickness of the first wall is at least twice the thickness of the second wall;
The thickness of the partition wall gradually increases from the second wall toward the first wall.
The hollow structure according to claim 1 . At least a portion of the hollow structure is curved such that an outer surface defined by the first skin layer is convex and an outer surface defined by the second skin layer is concave.
The hollow structure according to any one of claims 1 to 3. A luggage board comprising the hollow structure described in any one of claims 1 to 4.