Hollow structure

Abstract

To provide a hollow structure which is excellent in sound isolation property.SOLUTION: A hollow structure 10 has a plurality of cells arranged side by side therein. The hollow structure 10 includes a core layer 20 having a plurality of cells arranged side by side therein, an upper side sheet layer 30 arranged on an upper surface of the core layer 20, and a lower sheet layer 40 arranged on a lower surface of the core layer 20. The core layer 20 is composed of a base material blended with a thermoplastic resin. An upper side base material 32 of the upper side sheet layer 30 and a lower side base material 42 of the lower side sheet layer 40 are composed of a base material blended with inorganic fibers and thermoplastic resin fibers.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

[0002] Conventionally, a hollow structure in which a plurality of cells are arranged in parallel inside is known (for example, Patent Document 1). The hollow structure of Patent Document 1 is used, for example, for a luggage board placed in a luggage room for storing luggage behind an automobile.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a demand for further improvement in strength in the hollow structure of Patent Document 1. For example, in the hollow structure used for a luggage board, it is required not to plastically deform even when luggage is loaded on the upper surface. Therefore, there is still room for improvement in the hollow structure of Patent Document 1 from the viewpoint of strength.

Means for Solving the Problems

[0005] The hollow structure for solving the above problems is a hollow structure in which a plurality of cells are arranged in parallel inside, and includes a core layer in which the plurality of cells are arranged in parallel, and a sheet layer disposed on at least one surface of the upper and lower surfaces of the core layer. The core layer is composed of a material in which a thermoplastic resin is blended, and the sheet layer is composed of a material in which inorganic fibers and thermoplastic resin fibers are blended.

[0006] In the above configuration, the strength can be increased by blending inorganic fibers into the sheet layer of the hollow structure. Therefore, the strength of the hollow structure can be increased as compared with the case where the sheet layer is not provided on the hollow structure.

Advantages of the Invention

[0007] According to the present invention, a hollow structure excellent in strength can be obtained.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

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Figure 6

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Figure 10

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Figure 14

Best Mode for Carrying Out the Invention

[0009] An embodiment of the hollow structure will be described with reference to the drawings. <Luggage Board 1> As shown in FIGS. 1 and 2, the luggage board 1 is formed in a substantially rectangular plate shape that is long in the left-right direction. The luggage board 1 is provided symmetrically left and right. The luggage board 1 is placed on the bottom surface of the luggage compartment provided at the rear of the vehicle. The luggage board 1 is attached to the luggage compartment by being supported by a support portion provided in the luggage compartment.

[0010] The luggage board 1 includes a main body portion 2, a groove-shaped concave strip portion 3 provided on the lower surface of the main body portion 2, and a convex strip portion 4 provided on the upper surface of the main body portion 2. The concave strip portion 3 is formed by compressing the plate thickness of the hollow plate material constituting the luggage board 1 so that the plate thickness is made thinner. That is, the plate thickness of the portion of the luggage board 1 where the concave strip portion 3 is provided is thinner than the plate thickness of the portion of the luggage board 1 where neither the concave strip portion 3 nor the convex strip portion 4 is provided. Further, the concave strip portion 3 extends along the left-right direction.

[0011] The convex strip portion 4 is formed by increasing the plate thickness of the hollow plate material constituting the luggage board 1. That is, the plate thickness of the portion of the luggage board 1 where the convex strip portion 4 is provided is thicker than the plate thickness of the portion of the luggage board 1 where neither the concave strip portion 3 nor the convex strip portion 4 is provided. The convex strip portion 4 is provided on the rear side, which is one side with respect to the concave strip portion 3 in the main body portion 2. Further, the convex strip portion 4 extends along the left-right direction. Three convex strip portions 4 are provided on the upper surface of the main body portion 2. These three convex strip portions 4 are provided parallel to each other. Also, the convex strip portion 4 and the concave strip portion 3 are provided parallel to each other. For this reason, when the luggage board 1 is viewed from the up-down direction, the convex strip portion 4 is provided at a position shifted from the concave strip portion 3. The convex strip portion 4 has a function of preventing the luggage or the like placed on the upper surface of the main body portion 2 of the luggage board 1 from slipping off from the upper surface.

[0012] The main body part 2 has a first main body part 5 at the rear side which is one side based on the concave strip part 3 in the main body part 2, and a second main body part 6 at the front side which is the other side based on the concave strip part 3 in the main body part 2. The concave strip part 3 is configured such that the first main body part 5 can rotate relative to the second main body part 6 by being bent and deformed. By bending and deforming the concave strip part 3, when the first main body part 5 is lifted upward relative to the second main body part 6, tools and the like can be taken in and out of the space formed between the lower surface 1b of the luggage board 1 and the bottom surface of the luggage room. Further, the edge of the luggage board 1 has its plate thickness thinned so as to form an R shape.

[0013] Here, in the present embodiment, the thickness direction of the luggage board 1 is the same as the vertical direction of the vehicle. The surface located above the luggage board 1 is referred to as the upper surface 1a, and the surface located below the luggage board 1 is referred to as the lower surface 1b. Further, the front - rear direction of the luggage board 1 is the same as the front - rear direction in the traveling direction of the vehicle. Also, the left - right direction of the luggage board 1 is the same as the vehicle width direction of the vehicle.

[0014] As shown in FIG. 2, the upper surface 1a of the luggage board 1 is formed as a flat surface. The lower surface 1b of the luggage board 1 has a flat surface formed for the portion other than the concave strip part 3. Note that the upper surface 1a and the lower surface 1b of the luggage board 1 do not have to be flat surfaces. The hollow plate material constituting the luggage board 1 is constituted by a hollow structure 10 described later.

[0015] <Hollow structure 10> As shown in FIG. 3, the hollow structure 10 is a hollow plate material in which a plurality of cells S are arranged in parallel inside. The hollow structure 10 includes a core layer 20 in which a plurality of cells S are arranged in parallel inside, an upper sheet layer 30 disposed on the upper surface of the core layer 20, and a lower sheet layer 40 disposed on the lower surface of the core layer 20. The plurality of cells S are arranged in parallel so as to form rows along the direction X and the direction Y.

[0016] <Core layer 20> The core layer 20 is formed by folding a concavo-convex sheet material 100, which will be described later, having a predetermined concavo-convex shape. The concavo-convex sheet material 100 is configured by forming a predetermined concavo-convex shape on a flat sheet material.

[0017] The core layer 20 has an upper wall portion 21, a lower wall portion 22, and side wall portions 23 that are erected between the upper wall portion 21 and the lower wall portion 22 and partition the cell S into a hexagonal prism shape. The upper wall portion 21 and the lower wall portion 22 have a structure in which a single-layer structure and a two-layer structure are mixed. In FIG. 3, for the sake of convenience, the upper wall portion 21 and the lower wall portion 22 of the core layer 20 are shown as a single-layer structure.

[0018] As shown in FIGS. 3 to 5, in the cell S partitioned and formed inside the core layer 20, there are a first cell S1 and a second cell S2 having different configurations. As shown in FIG. 4, in the first cell S1, an upper wall portion 21 having a two-layer structure is provided at the upper part of the side wall portion 23. Each layer of the upper wall portion 21 having a two-layer structure is joined to each other. Due to the thermal shrinkage during the molding of the core layer 20, an opening (not shown) is formed in the upper wall portion 21 having a two-layer structure. In the first cell S1, a lower wall portion 22 having a single-layer structure is provided at the lower part of the side wall portion 23.

[0019] As shown in FIG. 5, in the second cell S2, an upper wall portion 21 having a single-layer structure is provided at the upper part of the side wall portion 23. In the second cell S2, a lower wall portion 22 having a two-layer structure is provided at the lower part of the side wall portion 23. Each layer of the lower wall portion 22 having a two-layer structure is joined to each other. Due to the thermal shrinkage during the molding of the core layer 20, an opening (not shown) is formed in the lower wall portion 22 having a two-layer structure.

[0020] As shown in FIGS. 4 and 5, between adjacent first cells S1 and between adjacent second cells S2, they are partitioned by side wall portions 23 having a two-layer structure, respectively. The side wall portions 23 of this two-layer structure have portions that are not thermally welded to each other at the central portion in the thickness direction of the core layer 20. Therefore, the internal spaces of the cells S in the core layer 20 communicate with the internal spaces of other cells S through the spaces between the side wall portions 23 of the two-layer structure. In FIGS. 4 and 5, reference numerals are attached to represent the leftmost cell S, but the same applies to other cells S.

[0021] As shown in FIG. 3, the first cells S1 are arranged in parallel so as to form columns along the X direction. The second cells S2 are arranged in parallel so as to form columns along the X direction. The columns of the first cells S1 and the columns of the second cells S2 are alternately arranged in the Y direction orthogonal to the X direction. The core layer 20 forms a honeycomb structure as a whole by the first cells S1 and the second cells S2.

[0022] The core layer 20 is composed of a material blended with a thermoplastic resin. Examples of the thermoplastic resin blended in the core layer 20 include polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, polybutylene terephthalate resin, and the like. In the present embodiment, the thermoplastic resin that is the material of the core layer 20 is polypropylene resin.

[0023] Inorganic materials are blended in the material of the core layer 20 in addition to the thermoplastic resin. Examples of the inorganic materials blended in the core layer 20 include talc, calcium carbonate, mica, glass fiber, magnesium hydroxide, aluminum hydroxide, and the like. In the present embodiment, the inorganic material that is the material of the core layer 20 is talc. That is, polypropylene resin and talc are blended in the material of the core layer 20 of the present embodiment.

[0024] <Upper sheet layer 30 and lower sheet layer 40> As shown in FIG. 6, the upper sheet layer 30 has a core layer side welding layer 31, an upper base material 32, a design side welding layer 33, and an upper nonwoven fabric 34. In FIG. 6, the hollow structure of the core layer 20 is shown with omission.

[0025] The upper base material 32 is disposed on the upper surface of the core layer 20 via the core layer side welding layer 31. The upper base material 32 has a flat sheet shape. As shown in FIG. 7, the upper base material 32 has a base material main body layer 32a, a core layer side resin layer 32b, and a design side resin layer 32c. The base material main body layer 32a is provided between the core layer side resin layer 32b and the design side resin layer 32c. The material of the base material main body layer 32a is blended with inorganic fibers, a foaming agent, and thermoplastic resin fibers. That is, the base material main body layer 32a is a composite material in which inorganic fibers, a foaming agent, and thermoplastic resin fibers are blended.

[0026] Examples of the thermoplastic resin fibers blended in the base material main body layer 32a include various fibers such as polypropylene fibers, polyamide fibers, polyethylene fibers, acrylonitrile-butadiene-styrene copolymer fibers, acrylic fibers, and polybutylene terephthalate fibers. In the present embodiment, the thermoplastic resin fibers that are the material of the base material main body layer 32a are polypropylene fibers. It is preferable that the thermoplastic resin fibers blended in the base material main body layer 32a and the thermoplastic resin blended in the core layer 20 are made of the same material.

[0027] Examples of the inorganic fibers blended in the base material main body layer 32a include various fibers such as glass fibers, carbon fibers, rock fibers, slag fibers, metal fibers, alumina fibers, and ceramic fibers. In the present embodiment, the inorganic fibers blended in the base material main body layer 32a are glass fibers. These inorganic fibers are blended to increase the strength of the base material main body layer 32a.

[0028] The blending ratio of the glass fiber and the polypropylene fiber is preferably set in the range of 40:60 to 70:30. The blending ratio of the foaming agent can be appropriately changed, and the blending ratio is set according to the required expansion performance and sound insulation performance. The base material body layer 32a is a so-called stampable sheet.

[0029] The core layer side resin layer 32b is disposed between the upper surface of the core layer side welding layer 31 and the lower surface of the base material body layer 32a. The core layer side resin layer 32b is a resin sheet having a flat sheet shape. The material of the core layer side resin layer 32b is blended with a thermoplastic resin. Examples of the thermoplastic resin blended in the core layer side welding layer 31 include polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, polybutylene terephthalate resin, and the like. In the present embodiment, the thermoplastic resin that is the material of the core layer side welding layer 31 is polypropylene resin. The core layer side resin layer 32b has less unevenness with respect to the lower surface of the base material body layer 32a.

[0030] The design side resin layer 32c is disposed between the upper surface of the base material body layer 32a and the lower surface of the design side welding layer 33. The design side resin layer 32c is a resin sheet having a flat sheet shape. The material of the design side resin layer 32c is blended with a thermoplastic resin. Examples of the thermoplastic resin blended in the core layer side welding layer 31 include polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, polybutylene terephthalate resin, and the like. In the present embodiment, the thermoplastic resin that is the material of the core layer side welding layer 31 is polypropylene resin. The design side resin layer 32c has less unevenness with respect to the upper surface of the base material body layer 32a.

[0031] As shown in FIG. 6, the core layer side welding layer 31 is disposed between the upper surface of the core layer 20 and the lower surface of the upper base material 32. A thermoplastic resin is blended in the material of the core layer side welding layer 31. Examples of the thermoplastic resin blended in the core layer side welding layer 31 include polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, polybutylene terephthalate resin, and the like. In the present embodiment, the thermoplastic resin that is the material of the core layer side welding layer 31 is polypropylene resin. The thermoplastic resin that is the material of the core layer side welding layer 31 is preferably a material that is compatible with the thermoplastic resin fibers blended in the upper base material 32 and the thermoplastic resin blended in the core layer 20.

[0032] The upper nonwoven fabric 34 is disposed on the upper surface of the upper base material 32 via the design side welding layer 33. The upper nonwoven fabric 34 has a flat sheet shape. The upper nonwoven fabric 34 is provided according to the required object and the design surface of the object. Examples of the material constituting the upper nonwoven fabric 34 include various conventionally known fibers such as polyamide fiber, aramid fiber, cellulose fiber, polyester fiber, polyethylene fiber, polypropylene fiber, rayon fiber, and glass fiber.

[0033] The design side welding layer 33 is disposed between the upper surface of the upper base material 32 and the lower surface of the upper nonwoven fabric 34. A thermoplastic resin is blended in the material of the design side welding layer 33. Examples of the thermoplastic resin blended in the design side welding layer 33 include polypropylene resin, polyamide resin, polyethylene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylic resin, polybutylene terephthalate resin, and the like. In the present embodiment, the thermoplastic resin that is the material of the core layer side welding layer 31 is polypropylene resin. The thermoplastic resin that is the material of the design side welding layer 33 is preferably a material that is compatible with at least one of the thermoplastic resin fibers blended in the upper base material 32 and the material constituting the upper nonwoven fabric 34.

[0034] The lower sheet layer 40 has a core layer side welding layer 41, a lower base material 42, a design side welding layer 43, and a lower nonwoven fabric 44. The lower base material 42 has a base material main body layer 42a, a core layer side resin layer 42b, and a design side resin layer 42c. Since the lower sheet layer 40 has the same material and the same structure as the upper sheet layer 30, the description thereof is omitted. Also, since the lower base material 42 has the same material and the same structure as the upper base material 32, the description thereof is omitted. Note that the materials and structures of the lower sheet layer 40 and the upper sheet layer 30 may be different. Also, the materials and structures of the lower base material 42 and the upper base material 32 may be different.

[0035] The upper surface of the core layer 20 and the upper base material 32 are joined by welding the core layer side welding layer 31. The upper base material 32 and the upper nonwoven fabric 34 are joined by welding the design side welding layer 33. Also, the lower surface of the core layer 20 and the lower base material 42 are joined by welding the core layer side welding layer 41. The lower base material 42 and the lower nonwoven fabric 44 are joined by welding the design side welding layer 43.

[0036] <Concave stripe portion 3> The core layer 20, the upper sheet layer 30, and the lower sheet layer 40 at the site where the concave stripe portion 3 is provided will be described.

[0037] As shown in FIG. 8, in the hollow structure 10, the plate thickness at the site where the concave stripe portion 3 is provided is made thinner by the manufacturing method of the luggage board 1 described later. Specifically, on the upper surface of the core layer 20, an engaging convex portion 20a is formed at a site corresponding to the concave stripe portion 3. Also, on the lower surface of the core layer 20, an engaging concave portion 20b is formed at a site corresponding to the concave stripe portion 3. The deepest part of the engaging concave portion 20b has a circular arc-shaped cross section. The depth of the engaging concave portion 20b is deeper than the height of the engaging convex portion 20a. In the core layer 20, the cells S are crushed between the engaging convex portion 20a and the engaging concave portion 20b.

[0038] The upper sheet layer 30 has a shape along the engaging convex portion 20a. The upper surface of the upper sheet layer 30 forms a flat surface. An engaging concave portion 30b is formed at a portion corresponding to the concave strip portion 3 on the lower surface of the upper sheet layer 30. The upper sheet layer 30 is crushed between its upper surface and the engaging concave portion 30b.

[0039] As shown in FIG. 9, specifically, among the upper sheet layer 30, the base material body layer 32a of the upper base material 32 is crushed. As a result, an engaging concave portion 30c corresponding to the concave strip portion 3 is provided on the lower surface of the base material body layer 32a. This is because the base material body layer 32a has a larger amount of deformation due to pressing in the manufacturing method of the luggage board 1 described later compared to the core layer side resin layer 32b, the design side resin layer 32c, the core layer side welding layer 31, the design side welding layer 33, and the upper nonwoven fabric 34 because it is spring-back. Also, because a foaming agent is blended in the base material body layer 32a, it has a larger amount of deformation due to pressing in the manufacturing method of the luggage board 1 described later compared to the core layer side resin layer 32b, the design side resin layer 32c, the core layer side welding layer 31, the design side welding layer 33, and the upper nonwoven fabric 34. Note that when the base material body layer 32a is spring-back, its thickness becomes thicker than the state before the heating process in the manufacturing method of the luggage board 1 described later. In the present embodiment, the engaging concave portion 30c of the base material body layer 32a corresponds to a concave engaging portion.

[0040] As shown in FIG. 8, the lower sheet layer 40 has a shape along the engaging concave portion 20b. An engaging convex portion 40a is formed at a portion corresponding to the concave strip portion 3 on the upper surface of the lower sheet layer 40. Also, an engaging concave portion 40b is formed at a portion corresponding to the concave strip portion 3 on the lower surface of the lower sheet layer 40. The deepest part of the engaging concave portion 40b has a cross-sectional arc shape. The lower sheet layer 40 is crushed between the engaging convex portion 40a and the engaging concave portion 40b. Although not shown in the figure, specifically, among the lower sheet layer 40, the base material body layer 42a of the lower base material 42 is crushed.

[0041] <Convex strip portion 4> The upper sheet layer 30 at the site where the convex strip portion 4 is provided will be described. As shown in FIG. 10, in the upper sheet layer 30, the thickness of the portion where the rib portion 4 is provided is increased by the manufacturing method of the luggage board 1 described later. Specifically, in the upper sheet layer 30, by pressing in the manufacturing method of the luggage board 1 described later, the thickness of the portion other than the rib portion 4 is made thinner than the thickness of the portion where the rib portion 4 is provided, so that the thickness of the portion where the rib portion 4 is provided is relatively increased. Specifically, among the upper sheet layer 30, the base material body layer 32a of the upper base material 32 is crushed. This is because the base material body layer 32a has a larger amount of deformation due to pressing in the manufacturing method of the luggage board 1 described later than the core layer side resin layer 32b, the design side resin layer 32c, the core layer side welding layer 31, the design side welding layer 33, and the upper non-woven fabric 34 because of the amount of springback. Also, the base material body layer 32a has a larger amount of deformation due to pressing in the manufacturing method of the luggage board 1 described later than the core layer side resin layer 32b, the design side resin layer 32c, the core layer side welding layer 31, the design side welding layer 33, and the upper non-woven fabric 34 because a foaming agent is blended.

[0042] On the upper surface of the base material body layer 32a, an engaging convex portion 32d is formed at a portion corresponding to the rib portion 4. The lower surface of the base material body layer 32a forms a flat surface. The engaging convex portion 32d has a cross-sectional arc shape.

[0043] The design side resin layer 32c has an engaging convex portion 32e along the engaging convex portion 32d of the base material body layer 32a. In the design side resin layer 32c, the thickness of the portion other than the portion corresponding to the rib portion 4 may be slightly thinner than the thickness of the portion corresponding to the rib portion 4.

[0044] The design side welding layer 33 has an engaging convex portion 32f along the engaging convex portion 32e of the design side resin layer 32c. In the design side welding layer 33, the thickness of the portion other than the portion corresponding to the rib portion 4 may be slightly thinner than the thickness of the portion corresponding to the rib portion 4.

[0045] The upper nonwoven fabric 34 has an engaging convex portion 32g along the engaging convex portion 32f of the design-side welding layer 33. In the upper nonwoven fabric 34, the thickness of the portion other than the portion corresponding to the rib portion 4 may be slightly thinner than the thickness of the portion corresponding to the rib portion 4. In the present embodiment, the engaging convex portion 32d of the base material main body layer 32a corresponds to a convex engaging portion.

[0046] <Method for manufacturing the luggage board 1> A method for manufacturing the luggage board 1 will be described with reference to FIGS. 11 and 12. The method for manufacturing the luggage board 1 can be divided into a core layer forming step, a heating step, a joining step, a forming step, and a post-processing step. The core layer forming step is a step of forming the core layer 20. The heating step is a step of heating the core layer 20, the upper sheet layer 30, and the lower sheet layer 40. The joining step is a step of joining the upper sheet layer 30 and the lower sheet layer 40 to the core layer 20. The forming step is a forming step of forming the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 to obtain an intermediate body 60. The post-processing step is a step of adjusting the shape of the end face of the intermediate body 60 to obtain the luggage board 1.

[0047] The core layer forming step will be described. The core layer 20 is formed by folding the concavo-convex sheet material 100. As shown in FIG. 11(a), the concavo-convex sheet material 100 is formed by shaping a single sheet of thermoplastic resin into a predetermined shape. In the concavo-convex sheet material 100, a belt-shaped planar region 110 and a bulging region 120 are alternately arranged in the X direction, which is the longitudinal direction of the concavo-convex sheet material 100. In the bulging region 120, a first bulging portion 121 having a downward groove-shaped cross section formed by an upper surface and a pair of side surfaces is formed over the entire Y direction, which is the extending direction of the bulging region 120. It is preferable that the angle formed by the upper surface and the side surface of the first bulging portion 121 is 90 degrees. As a result, the cross-sectional shape of the first bulging portion 121 is a downward C shape. Further, the length in the short hand direction of the upper surface, which is the width of the first bulging portion 121, is equal to the width of the planar region 110, and is set to be twice the length in the short hand direction of the side surface, which is the bulging height of the first bulging portion 121.

[0048] In the bulging region 120, a plurality of second bulging portions 122 having a trapezoidal cross-sectional shape obtained by bisecting a regular hexagon with its longest diagonal line are formed so as to be orthogonal to the first bulging portion 121. The bulging height of the second bulging portion 122 is set to be equal to the bulging height of the first bulging portion 121. Also, the interval between adjacent second bulging portions 122 is equal to the width of the upper surface of the second bulging portion 122.

[0049] Such first bulging portion 121 and second bulging portions 122 are formed by partially bulging the sheet upward by utilizing the plasticity of the sheet. Further, the concavo-convex sheet material 100 can be formed from a single flat sheet material by a well-known forming method such as a vacuum forming method or a shrink forming method.

[0050] As shown in FIGS. 11(a) and 11(b), the core layer 20 is formed by folding the concavo-convex sheet material 100 configured as described above along the boundary lines P and Q. Specifically, the concavo-convex sheet material 100 is valley-folded at the boundary line P between the planar region 110 and the bulging region 120, and mountain-folded at the boundary line Q between the upper surface and the side surface of the first bulging portion 121 and contracted in the X direction. As shown in FIGS. 11(b) and 11(c), when the upper surface and the side surface of the first bulging portion 121 are folded over and the end surface of the second bulging portion 122 and the planar region 110 are folded over, a prismatic partition body 130 extending in one Y direction is formed for one bulging region 120. By continuously forming such partition bodies 130 in the X direction, a hollow plate-shaped core layer 20 is formed.

[0051] When the concavo-convex sheet material 100 is contracted as described above, the upper wall portion 21 of the core layer 20 is formed by the upper surface and the side surface of the first bulging portion 121, and the lower wall portion 22 of the core layer 20 is formed by the end surface of the second bulging portion 122 and the planar region 110. As shown in FIG. 11(c), the portion where the upper surface and the side surface of the first bulging portion 121 in the upper wall portion 21 are folded over to form a two-layer structure is the overlapping portion 131. Also, the portion where the end surface of the second bulging portion 122 and the planar region 110 in the lower wall portion 22 are folded over to form a two-layer structure is the overlapping portion 131.

[0052] The hexagonal prism-shaped region where the second bulging portion 122 is folded and partitioned forms the second cell S2, and the hexagonal prism-shaped region partitioned between a pair of adjacent partition bodies 130 forms the first cell S1. In the present embodiment, the upper surface and side surfaces of the second bulging portion 122 constitute the side wall portion 23 of the second cell S2, and the side surface of the second bulging portion 122 and the flat portion located between the second bulging portions 122 in the bulging region 120 constitute the side wall portion 23 of the first cell S1. Then, the contact portions between the upper surfaces of the second bulging portions 122 and the contact portions between the flat portions in the bulging region 120 form the side wall portion 23 having a two-layer structure. In addition, when performing such a folding process, it is preferable to heat-treat the concavo-convex sheet material 100 to make it in a softened state.

[0053] Thereafter, the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are heated by a heating device (not shown). The heating device is set to a temperature at which the thermoplastic resin, which is the material of the core layer side welding layer 31 of the upper sheet layer 30 and the core layer side welding layer 41 of the lower sheet layer 40, melts. Then, with the upper sheet layer 30 and the lower sheet layer 40 in contact with both surfaces of the core layer 20, the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are placed in a mold (not shown) and the mold is clamped. Then, by closely adhering the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 in the mold for a predetermined pressure and time, the upper sheet layer 30 and the lower sheet layer 40 are joined to the core layer 20. Thereby, the hollow structure 10 is manufactured. Then, the manufactured hollow structure 10 is molded so as to have the size and shape corresponding to the luggage board 1, and the luggage board 1 can be obtained by adjusting the shape of the edge of the hollow structure 10.

[0054] The heating process will be described. As shown in Fig. 12(a), first, as the core layer 20 to be used for the luggage board 1, prepare a core layer 20 that was previously manufactured and cut into a shape larger than the luggage board 1. For example, as the core layer 20 to be used for the luggage board 1, prepare a rectangular shape that is about 50 mm larger than the size of the luggage board 1 in both the longitudinal and transverse directions. Note that in Figs. 12(a) to (f), the hollow structure of the core layer 20 is shown omitted. Also, in Figs. 12(a) to (f), the portions corresponding to the cross-sectional view taken along the δ-δ line in Fig. 1 are shown as schematic diagrams.

[0055] The upper sheet layer 30 and the lower sheet layer 40 to be used for the luggage board 1 are cut into a shape larger than the luggage board 1, specifically, a size similar to that of the core layer 20. As shown in Fig. 12(b), heat the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 respectively. When heating the core layer 20, place the core layer 20 in a heating furnace 71 set at a predetermined temperature and hold it for a predetermined time. Similarly, for the upper sheet layer 30 and the lower sheet layer 40, place the upper sheet layer 30 and the lower sheet layer 40 in a heating furnace 72 set at a predetermined temperature and hold them for a predetermined time. The temperatures inside the heating furnaces 71 and 72 are set to such an extent that the thermoplastic resin, which is the material of the core layer 20, the core layer side welding layer 31 of the upper sheet layer 30, and the core layer side welding layer 41 of the lower sheet layer 40, melts. In this case, the thicknesses of the upper sheet layer 30 and the lower sheet layer 40 become thicker than before the heating process due to springback. In Fig. 12(b), the thicknesses of the upper sheet layer 30 and the lower sheet layer 40 are exaggeratedly shown.

[0056] Next, the joining process and the forming process will be described. As shown in Fig. 12(c), the mold used for the joining process and the forming process includes an upper mold 51 and a lower mold 52. The upper mold 51 and the lower mold 52 of the present embodiment are maintained at room temperature without being heated as a whole.

[0057] The recess 52a formed in the lower mold 52 has a substantially rectangular shape in top view. The length of the recess 52a in the longitudinal direction is substantially the same as the length of the luggage board 1 in the longitudinal direction (left - right direction). The length of the recess 52a in the short - hand direction is substantially the same as the length of the luggage board 1 in the short - hand direction (front - back direction). Also, the depth of the recess 52a is about half of the thickness of the luggage board 1. The recess 52a is a part for forming the luggage board 1 in the molding process described later. It is preferable to set the size of the recess 52a in consideration of the thermal shrinkage of the core layer 20, the upper sheet layer 30, and the lower sheet layer 40. The same applies hereinafter.

[0058] In the recess 52a, a convex portion 52b having a shape corresponding to the concave strip portion 3 is provided. The length of the convex portion 52b in its length direction is substantially the same as the length of the luggage board 1 in the longitudinal direction. The height of the convex portion 52b is substantially the same as the depth of the concave strip portion 3. The height of the convex portion 52b is set higher than the depth of the recess 52a.

[0059] The recesses 51a, 51b formed in the upper mold 51 have a substantially rectangular - annular shape in top view. The depth of the recess 51a is about half of the thickness of the luggage board 1. Also, the depth of the recess 51b is substantially the same as the thickness of the shrinkage portion 61 of the intermediate body 60 described later. The recess 51a is a part for forming the luggage board 1 in the molding process described later, and the recess 51b is a part for forming the shrinkage portion 61 of the intermediate body 60. That is, when the upper mold 51 and the lower mold 52 are clamped, spaces of a size corresponding to the luggage board 1 are formed by the recess 51a and the recess 52a, and the recess 51b is located outside the outer edge of the recess 51a and the recess 52a.

[0060] In the recess 51a, three recesses 51c having a shape corresponding to the convex strip portion 4 are provided. The length of the recess 51a in its length direction is substantially the same as the length of the luggage board 1 in the longitudinal direction.

[0061] As shown in Fig. 12(c), first, the heated core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are placed on the recess 52a of the lower die 52 in the order from the bottom, i.e., the lower sheet layer 40, the core layer 20, and the upper sheet layer 30. Since the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are cut into a rectangular shape larger than the ledger board 1, in the state of being placed on the recess 52a, both longitudinal ends and both lateral ends protrude outward from the recess 52a. In the heating process, the surface temperature of the core layer 20 will be adjusted according to the height of the space between the upper die 51 and the lower die 52 during die clamping.

[0062] At this time, the thermoplastic resin, which is the material of the core layer side welding layer 31 of the upper sheet layer 30 and the core layer side welding layer 41 of the lower sheet layer 40, is in a state where a part of it is thermally melted. Therefore, the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are positioned in a temporarily joined state on the lower die 52.

[0063] Subsequently, as shown in Fig. 12(d), the upper die 51 is lowered toward the lower die 52 for die clamping, and the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are pressed to simultaneously perform the joining process and the forming process. A plurality of suction holes (not shown) are formed in the upper die 51 and the lower die 52. During die clamping, the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 can be attracted through the suction holes and closely adhered in a positioned state inside the upper die 51 and the lower die 52. The pressure and the pressing time during pressing can be set as appropriate.

[0064] As shown in Fig. 12(d), the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are formed into the inner surface shapes of the upper die 51 and the lower die 52, i.e., the shapes of the recesses 51a, 51b, and 52a, to become the intermediate body 60. At this time, the concave strip portions 3 and the convex strip portions 4 are formed.

[0065] As shown in Fig. 12(c), the recess 51b of the upper mold 51 is shallower than the recess 51a, and no recess is formed in the lower mold 52 at the corresponding position when the molds are clamped. Therefore, this part becomes a part where the height of the space between the upper mold 51 and the lower mold 52 during mold clamping is low. In this part, due to mold clamping, the thermoplastic resin constituting the core layer 20 melts and the core layer 20 thermally contracts, forming a shrinkage part 61 of the intermediate body 60. In the shrinkage part 61, the thermoplastic resins constituting the upper wall part 21, the lower wall part 22, and the side wall part 23 are melted and integrated.

[0066] In the recess 51a of the upper mold 51 and the recess 52a of the lower mold 52, they become parts where the height of the space between the upper mold 51 and the lower mold 52 during mold clamping is high, and in the heating process, parts adjusted to have a relatively low surface temperature are arranged. In this part, due to mold clamping, the thermoplastic resin constituting the core layer 20 becomes difficult to melt, and the core layer 20 maintains its height dimension.

[0067] When the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are pushed into the recess 52a of the lower mold 52 by mold clamping, the upper upper sheet layer 30 is bent toward the lower lower sheet layer 40 side, and its corner is formed in an R shape. Also, the lower lower sheet layer 40 is bent toward the upper upper sheet layer 30 side, and its corner is formed in an R shape.

[0068] As shown in Fig. 12(e), after separating the upper mold 51 from the lower mold 52 to cool the intermediate body 60, the intermediate body 60 is taken out from the lower mold 52. The intermediate body 60 obtained through the bonding process and the forming process has the upper sheet layer 30 bonded to the upper surface of the core layer 20 and the lower sheet layer 40 bonded to the lower surface of the core layer 20. In this case, the intermediate body 60 has a shape in which a shrinkage part 61 is formed over the entire circumference of the end of the part having the size and shape corresponding to the luggage board 1.

[0069] The post-processing process will be described. As shown in FIG. 12(f), the shrinkage portion 61 formed in the intermediate body 60 is cut with a cutting jig (not shown). Thereafter, the cut portion is polished, painted, etc. to adjust the shape of the end face. Note that a Thomson blade, a laser, or the like may be used as the cutting jig for cutting the shrinkage portion 61, and polishing, painting, etc. may not be performed.

[0070] The operation of this embodiment will be described. The strength can be increased by blending glass fiber, which is one of the inorganic materials, into the upper base material 32 of the upper sheet layer 30 and the lower base material 42 of the lower sheet layer 40.

[0071] The effects of this embodiment will be described. (1) The strength of the hollow structure 10 can be increased as compared with the case where the upper sheet layer 30 and the lower sheet layer 40 are not provided on the hollow structure 10.

[0072] (2) By blending a foaming agent into the upper base material 32 of the upper sheet layer 30 and the lower base material 42 of the lower sheet layer 40, the sound insulation of the hollow structure 10 can be increased as compared with the case where the upper sheet layer 30 and the lower sheet layer 40 are not provided on the hollow structure 10.

[0073] (3) Since the thermoplastic resin that is the material of the core layer 20, the thermoplastic resin fiber that is the material of the upper sheet layer 30, and the thermoplastic resin fiber that is the material of the lower sheet layer 40 are the same polypropylene resin, their compatibility with each other can be increased.

[0074] (4) The inorganic fiber that is the material of the upper base material 32 and the lower base material 42 is glass fiber. Glass fiber has a high tensile strength and elastic modulus among inorganic fibers and is relatively lightweight compared to metal fibers and the like. Therefore, while increasing the strength of the upper base material 32 and the lower base material 42, the weight reduction of the upper base material 32 and the lower base material 42 can be achieved.

[0075] (5) By blending talc into the material of the core layer 20, the bending rigidity of the core layer 20 can be further increased. (6) When the first main body portion 5 rotates with respect to the second main body portion 6, stress is likely to concentrate on the concave strip portion 3. The core layer 20, the upper sheet layer 30, and the lower sheet layer 40 are applied to the hollow structure 10 having the concave strip portion 3. Therefore, it is easier to maintain the function of the concave strip portion 3 than when the upper sheet layer 30 and the lower sheet layer 40 are not provided in the hollow structure 10.

[0076] (7) As a first comparative example, assume a hollow structure provided with each sheet layer without blending glass fibers. As a second comparative example, assume a hollow structure provided with each sheet layer without blending glass fibers and reinforced with a relatively thin steel plate. A loading test will be described for the luggage board 1 composed of the hollow structure 10 of the present embodiment, the hollow structure of the first comparative example, and the hollow structure of the second comparative example. In the loading test, when a weight of a predetermined mass and size is dropped directly above the concave strip portion 3 in the luggage board 1, it is tested whether the function of the concave strip portion 3 that rotates the first main body portion 5 with respect to the second main body portion 6 can be maintained.

[0077] In the luggage board 1 using the hollow structures of the first comparative example and the second comparative example, the function of the concave strip portion 3 that rotates the first main body portion 5 with respect to the second main body portion 6 could not be maintained. On the other hand, in the luggage board 1 using the hollow structure 10 of the present embodiment, the function of the concave strip portion 3 that rotates the first main body portion 5 with respect to the second main body portion 6 could be maintained. This is because in the hollow structure 10 of the present embodiment, the strength is increased by blending glass fibers in the upper base material 32 of the upper sheet layer 30 and the lower base material 42 of the lower sheet layer 40. Also, it was confirmed that the amount of deformation generated by the loading test in the luggage board 1 using the hollow structure 10 of the present embodiment was smaller than the amount of deformation generated by the loading test in the luggage board 1 using the hollow structures of the first comparative example and the second comparative example.

[0078] (8) The temperature change is significant inside the luggage compartment provided at the rear of the vehicle. If the linear expansion coefficient of the upper base material 32 is large, the hollow structure 10 may deform due to the thermal deformation of the upper base material 32. In this case, the luggage board 1 may shift with respect to the support portion provided in the luggage compartment. In this regard, the upper base material 32 in which glass fiber and polypropylene fiber are blended can have a smaller linear expansion coefficient compared to the upper base material blended with only polypropylene fiber. For this reason, the thermal deformation of the upper base material 32 can be suppressed, and thus, the displacement of the luggage board 1 with respect to the support portion can be suppressed. This also applies to the lower base material 42. That is, the upper base material 32 and the lower base material 42 disposed on both sides of the core layer 20 can suppress the deformation of both sides of the hollow structure 10. As described above, as an application destination of the hollow structure 10 using the upper base material 32 and the lower base material 42, the luggage board 1 placed in the luggage compartment is suitable. In particular, when the hollow structure 10 is applied to the luggage board 1 that is long in either the left-right direction or the front-rear direction, the effect is remarkable.

[0079] (9) In the base material body layer 32a of the upper base material 32 in which glass fiber and polypropylene fiber are blended, the ends of the respective fibers may be exposed on the surface of the base material body layer 32a. If the ends of the respective fibers are exposed on the surface of the upper sheet layer 30, there is a risk of damaging the manufacturing apparatus for manufacturing the hollow structure 10 or deteriorating the feel of the surface of the hollow structure 10. In this regard, in the present embodiment, by disposing resin layers on both the upper and lower surfaces of the base material body layer 32a, it is possible to suppress the exposure of the ends of the respective fibers on both the upper and lower surfaces of the upper sheet layer 30. This also applies to the lower sheet layer 40.

[0080] (10) In the present embodiment, by disposing the upper non-woven fabric 34 on the upper surface of the upper sheet layer 30, it is possible to improve the feel of the upper surface of the hollow structure 10 or improve the appearance of the upper surface of the hollow structure 10. This also applies to the lower surface of the hollow structure 10.

[0081] (11) By providing the engaging convex portion 32d and the engaging concave portion 30c in the base material main body layer 32a of the upper sheet layer 30, the bonding strength between the upper sheet layer 30 and the core layer 20 can be increased. In addition, it is possible to prevent an object placed outside from slipping on the surface of the hollow structure 10, or to position an object placed outside with respect to the surface of the hollow structure 10. For example, in the luggage board 1 using the hollow structure 10, the luggage placed on the upper surface of the luggage board 1 can be prevented from slipping by being caught by the engaging convex portion 32d.

[0082] The above embodiment may be modified as follows. In addition, the following other embodiments can be combined with each other as long as there is no technical contradiction. · The core layer 20 may not be formed through a folding process, but may be formed by bulging a plastic sheet material. For example, a plastic sheet material may be vacuum formed to form a core layer 20 having a shape in which a plurality of cells in a polygonal prism shape or a cylindrical shape bulge. Alternatively, a core layer 20 may be used which is formed by alternately forming a bulging region and a flat region by bending the sheet material.

[0083] · The core layer 20 is not limited to being formed by folding and molding a single thermoplastic resin sheet, and a plurality of sheets may be used to form the core layer 20. For example, the core layer 20 may be formed by bending a strip-shaped sheet at predetermined intervals and arranging a plurality of the curved and bent strip-shaped sheets facing each other. Further, the core layer 20 may be formed by stacking a plurality of sheets having cells formed thereon. That is, between the upper sheet layer 30 and the lower sheet layer 40, as long as a plurality of cells can be partitioned and formed by the sheet, the number of sheets constituting the core layer 20 and the mode of its bending and curving may be any.

[0084] ·In this embodiment, hexagonal columnar cells S were partitioned and formed inside the core layer 20. However, the shape of the cells S is not particularly limited, and for example, it may be a polygonal columnar shape such as a square columnar shape or an octagonal columnar shape, or a cylindrical shape. In that case, cells S having different shapes may be mixed inside the core layer 20. Also, the cells may not be adjacent to each other, and there may be a gap between the cells.

[0085] ·The core layer 20 is not limited to being partitioned into columnar cells S. For example, it may be a structure in which sheet layers are joined to both the upper and lower surfaces of a core layer having a predetermined uneven shape. Examples of the core layer having such a configuration include those described in Japanese Patent Application Laid-Open No. 2014-205341. Also, it may be a plastic corrugated board or the like having a harmonic cross-section.

[0086] ·In this embodiment, a single thermoplastic resin sheet was fold-molded to form the core layer 20 as a honeycomb structure in which hexagonal cells S were partitioned and formed inside the core layer 20. However, the molding method is not limited to this. For example, as described in Japanese Patent No. 4368399, the core layer 20 as a honeycomb structure may be formed by sequentially folding a three-dimensional structure in which a plurality of rows of convex portions having a trapezoidal cross-section are provided.

[0087] ·The number of laminated layers of the upper sheet layer 30 and the lower sheet layer 40 can be appropriately changed. ·As the thermoplastic resin that is the material of the core layer 20, the upper sheet layer 30, and the lower sheet layer 40, those added with various functional resins may be used. For example, by adding a flame-retardant resin to the thermoplastic resin, it is possible to enhance the flame retardancy. It is also possible to use those added with various functional resins for all of the core layer 20, the upper sheet layer 30, and the lower sheet layer 40. Further, it is also possible to use those added with various functional resins for at least any one of the core layer 20, the upper sheet layer 30, and the lower sheet layer 40.

[0088] · The material of the core layer 20 contains an inorganic material in addition to the thermoplastic resin, but at least the thermoplastic resin should be contained, and the inorganic material may not be contained. · The material of the upper base material 32 contains a foaming agent, but the foaming agent may not be contained. Even when the upper base material 32 does not contain a foaming agent, the upper base material 32 may become a porous member having a plurality of holes inside due to the occurrence of the springback or the like in the heating process. Also in such a case, similar to the above effect (2), the sound insulation property of the hollow structure 10 can be enhanced. The same applies to the lower base material 42.

[0089] · In the hollow structure 10, communication holes penetrating from the upper surface of the upper sheet layer 30 to the upper wall portion 21 of the core layer 20 may be provided by a needle or the like. In this case, by providing the communication holes, the sound absorption rate and the sound insulation property of the frequency in the low sound range can be particularly enhanced.

[0090] · Either or both of the core layer side resin layer 32b and the design side resin layer 32c of the upper base material 32 may be omitted. The same applies to the lower base material 42. · In the present embodiment, the upper sheet layer 30 and the lower sheet layer 40 are welded to both the upper and lower surfaces of the core layer 20, but the sheet layer may be welded only to one of the upper and lower surfaces of the core layer 20.

[0091] · The thicknesses of the upper sheet layer 30 and the lower sheet layer 40 may be different from each other. · Either or both of the upper nonwoven fabric 34 and the lower nonwoven fabric 44 may be omitted. In this case, the design side welding layers 33 and 43 can be omitted.

[0092] · The core layer side welding layer 31 disposed between the upper surface of the core layer 20 and the lower surface of the upper base material 32 may be omitted. In this case, the upper base material 32 is directly welded to the upper surface of the core layer 20. In this case, in particular, it is preferable that the thermoplastic resin blended in the upper base material 32 and the thermoplastic resin blended in the core layer 20 are compatible materials. Note that the core layer side resin layer 32b and the design side resin layer 32c of the upper base material 32 may function as a welding layer. The same applies to the core layer side welding layer 41 disposed between the lower surface of the core layer 20 and the upper surface of the lower base material 42, and the core layer side welding layer 41 may be omitted.

[0093] · The design side welding layer 33 may be omitted. In this case, the upper nonwoven fabric 34 is directly welded to the upper surface of the upper base material 32, and the lower nonwoven fabric 44 is directly welded to the lower surface of the lower base material 42. In this case, it is preferable that the thermoplastic resin blended in the upper base material 32 and the thermoplastic resin blended in the core layer 20 are compatible materials.

[0094] · The heating temperature in the heating step can be appropriately changed according to the material of the hollow structure 10. · In the heating step, the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 were heated in separate heating furnaces 71 and 72, but it is not limited to this. For example, the core layer 20, the upper sheet layer 30, and the lower sheet layer 40 may be heated in the same heating furnace.

[0095] · The heating in the heating step may be heating in an open environment instead of heating in the heating furnaces 71 and 72. For example, it may be heated with a burner, an IH heater, or an infrared heater.

[0096] · In this embodiment, the joining step and the molding step are performed simultaneously, but these steps may be performed separately. In this case, in the joining step, a hollow plate material can be obtained by joining the upper sheet layer 30 and the lower sheet layer 40 to the core layer 20. Then, in the molding step, an intermediate body 60 can be obtained from the hollow plate material using the upper mold 51 and the lower mold 52.

[0097] · The joining process and the molding process may be performed by heating the upper mold 51 and the lower mold 52. · The upper sheet layer 30 may be subjected to the heating process and the joining process without the upper nonwoven fabric 34 being provided. In this case, for example, the upper nonwoven fabric 34 will be disposed on the upper surface of the upper base material 32 via the design side welding layer 33 after the joining process. The same applies to the lower nonwoven fabric 44.

[0098] · The method for forming the concave stripe portion 3 can be changed as appropriate. The concave stripe portion may be provided, for example, using the springback generated by applying heat. Note that the timing at which the concave stripe portion 3 is provided may be when the springback occurs or after the springback has occurred. The same applies to the convex stripe portion 4, and the method for forming the convex stripe portion 4 can be changed as appropriate.

[0099] · A plurality of rows of the concave stripe portions 3 may be provided on the main body portion 2. In this case, the plurality of rows of concave stripe portions 3 may function, for example, as an anti-slip portion for making the luggage board 1 difficult to slide with respect to the luggage room, or as a positioning portion for positioning the luggage board 1 at a plurality of levels with respect to the luggage room.

[0100] · The number of the convex stripe portions 4 can be changed as appropriate. The convex stripe portions 4 may be provided in only one row, two rows, or four or more rows on the main body portion 2. Also, the shape of the convex stripe portions 4 can be changed as appropriate. The convex stripe portions 4 may extend, for example, in an L shape, a V shape, etc. when viewed from above.

[0101] For example, as shown in FIG. 13, the L-shaped rib portion 4 has a first rib portion 4a extending in the left-right direction and a second rib portion 4b extending in the front-rear direction. The first rib portion 4a extends from the right end portion in the left-right direction of the main body portion 2 to an intermediate position in the main body portion 2. The second rib portion 4b extends from the rear end portion in the front-rear direction of the main body portion 2 to the left end portion of the first rib portion 4a. Further, as shown in FIG. 10, in the rib portion 4 of this modification, the plate thickness of the portion where the rib portion 4 is provided is increased. By placing a load on the upper surface of the main body portion 2 surrounded by the L-shaped rib portion 4, the positioning of the load can be performed with respect to the upper surface of the luggage board 1.

[0102] A method of manufacturing the luggage board 1 of this modification shown in FIG. 13 will be described with reference to FIGS. 14(a) to (f). Here, the description will focus on the differences from the above-described embodiment. As shown in FIG. 14(c), the concave portion 51a formed in the upper die 51 is provided with a concave portion 51d having a shape corresponding to the rib portion 4. The concave portion 51d has a portion corresponding to the first rib portion 4a and a portion corresponding to the second rib portion 4b. Then, as shown in FIG. 14(d), by clamping the dies, the rib portion 4 is formed.

[0103] · The rib portion 4 may not be provided on the main body portion 2. In this case, the rib portion 4 is omitted in all three rows. · The groove portion 3 may be provided on the upper surface of the main body portion 2, or may be provided on both the upper surface and the lower surface of the main body portion 2. Further, the groove portion 3 may not be provided on the main body portion 2.

[0104] · The shape of the luggage board 1 is not limited to a substantially rectangular plate shape that is long in the left-right direction, and can be appropriately changed to a substantially square plate shape, a substantially circular plate shape, or the like. · The application destination of the hollow structure 10 is not limited to the luggage board 1, and can be appropriately changed to a door-shaped member having a groove portion 3, a sound absorption panel, or the like. Further, the application destination of the hollow structure 10 is not limited to a member having a groove portion 3, and can be appropriately changed to a floor structure having no groove portion 3, a sound absorption panel having no groove portion 3, or the like.

[0105] The technical ideas that can be derived from the above embodiments are as follows. · In the above hollow structure, it is preferable that the thermoplastic resin fiber which is the material of the sheet layer and the thermoplastic resin which is the material of the core layer are both polypropylene resins.

[0106] · In the above hollow structure, it is preferable that the inorganic fiber which is the material of the sheet layer is glass fiber. · In the above hollow structure, it is preferable that in addition to the thermoplastic resin, talc is blended in the material of the core layer.

[0107] In the above configuration, by blending talc in the material of the core layer, the bending rigidity of the core layer can be further increased. · In the above hollow structure, the sheet layer has a base material body layer composed of a material in which inorganic fibers and thermoplastic resin fibers are blended, and resin layers disposed on both surfaces of the upper and lower surfaces of the base material body layer, and it is preferable that the resin layer is composed of a thermoplastic resin.

[0108] When the base material body layer is composed of a material in which inorganic fibers and thermoplastic resin are blended, the ends of the respective fibers may be exposed on the surface of the base material body layer. In this regard, in the above configuration, by disposing resin layers on both surfaces of the upper and lower surfaces of the base material body layer, it is possible to suppress the exposure of the ends of the respective fibers on the surface of the sheet layer.

[0109] · In the above hollow structure, it is preferable that the sheet layer has concave or convex engaging portions provided on at least one surface of the upper and lower surfaces. In the above configuration, by providing engaging portions on the sheet layer, it is possible to increase the bonding strength between the sheet layer and the core layer, prevent an object placed externally on the surface of the hollow structure from slipping, or position an object placed externally on the surface of the hollow structure.

[0110] · In the above hollow structure, a main body portion composed of the core layer and the sheet layer, and a groove-shaped concave strip portion provided on at least one surface of the upper and lower surfaces of the main body portion are provided. When the concave strip portion is bent and deformed, a first main body portion on one side of the main body portion with reference to the concave strip portion is configured to be rotatable with respect to a second main body portion on the other side of the main body portion with reference to the concave strip portion, which is preferable.

[0111] In the concave strip portion, stress is likely to concentrate when the first main body portion rotates with respect to the second main body portion. The core layer and the sheet layer are applied to the hollow structure having the concave strip portion. Therefore, compared with the case where the sheet layer is not provided on the hollow structure, the function of the concave strip portion is easily maintained.

Explanation of reference numerals

[0112] 1… Luggage board 2… Main body portion 3… Concave strip portion 5… First main body portion 6… Second main body portion 10… Hollow structure 20… Core layer 30… Upper sheet layer 40… Lower sheet layer

Claims

1. A hollow structure in which a plurality of cells are arranged in parallel inside, a core layer in which the plurality of cells are arranged in parallel, and a sheet layer disposed on at least one surface of the upper and lower surfaces of the core layer, wherein the core layer is composed of a material in which a thermoplastic resin is blended, and the sheet layer has a base material composed of a material in which inorganic fibers and thermoplastic resin fibers are blended, and a non-woven fabric, which is a hollow structure.

2. The hollow structure according to claim 1, wherein the sheet layer has a welding layer between the base material and the non-woven fabric.

3. The hollow structure according to claim 1 or claim 2, wherein the blending ratio of the inorganic fibers and the thermoplastic resin fibers in the base material is higher for the inorganic fibers.

4. a main body portion composed of the core layer and the sheet layer, and a groove-shaped concave strip portion provided on at least one surface of the upper and lower surfaces of the main body portion, wherein when the concave strip portion is bent and deformed, a first main body portion on one side of the main body portion with respect to the concave strip portion is configured to be rotatable with respect to a second main body portion on the other side of the main body portion with respect to the concave strip portion, and the surface of the sheet layer on the core layer side has an engaging recess at a portion corresponding to the concave strip portion. The hollow structure according to any one of claims 1 to 3.

5. The thermoplastic resin fiber that is the material of the base material and the thermoplastic resin that is the material of the core layer are polypropylene resins, the inorganic fibers that are the material of the base material are glass fibers, and the material of the core layer contains talc in addition to the thermoplastic resin. The hollow structure according to any one of claims 1 to 4.

6. The hollow structure according to any one of claims 1 to 5, wherein the sheet layer has a concave engaging portion formed on the surface on the core layer side and a convex engaging portion formed on the surface opposite to the core layer side.

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