JP2004010128A - Upper lid and pallet box - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an upper lid which can exhibit excellent strength with a reduced weight and can be easily thinned, and a pallet box including the upper lid. <P>SOLUTION: The pallet box is formed to be a rectangular box including a pallet having a fork insertion hole, a rectangular parallelopiped sleeve 14 detachably standing on the periphery of a base of the pallet and the upper lid 15 in a form of a lidded rectangular parallelopiped for detachably closing the upper opening of the sleeve 14. The upper lid 15 is formed by injection-molding or press-molding and has numerous reinforcing ribs 51 extending like a lattice longitudinally and horizontally suspending from its lower surface. Peripheral dense rib structures 52 and center dense rib structures 53 are further formed on the lower surface periphery and the center of the upper lid 15. An engaging protrusion 54 is suspended from the lower end rim at both ends of a reinforcing rib 51 constituting the structure 52. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a synthetic resin upper lid formed integrally by injection molding or press molding and having a dense rib structure for reinforcement at a central portion, preferably at the central portion and a peripheral portion, and a lid made of the synthetic resin. And a pallet box provided.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an upper lid for this type of pallet box, a lid formed in a substantially flat plate shape by, for example, a vacuum forming method is known. This lid is vacuum-molded by heating and softening the thermoplastic resin sheet on the mold, and then extracting the air between the sheet and the mold, and the upper and lower surfaces of the sheet correspond to the surface of the mold. Are formed. The lid is provided with high rigidity in the whole or in a predetermined direction by forming a predetermined pattern including the large number of irregularities.
[0003]
[Problems to be solved by the invention]
However, in the above-mentioned conventional lid, it is extremely difficult to densely form an interval (distance) between adjacent convex portions or concave portions due to a technical limit in molding by a vacuum molding method. However, it has not been possible to locally reinforce portions where loads are applied intensively. Furthermore, in this lid, when molded for the purpose of imparting high rigidity to the whole, since the height of the entire unevenness, that is, the thickness of the lid becomes extremely large, the lid is very bulky. It also has disadvantages such as the workability of the desorption work is significantly deteriorated.
[0004]
The present invention has been made by paying attention to the problems existing in the prior art as described above. An object of the present invention is to provide an upper lid that can exhibit high strength while reducing the weight and that can be easily formed thin. Another object of the present invention is to provide a pallet box that can easily increase the strength of the entire upper lid while reducing the weight, and can easily form the upper lid thin.
[0005]
[Means for Solving the Problems]
To achieve the above object, the upper lid according to the first aspect of the present invention includes a top plate for closing an upper opening of a container formed in a bottomed cylindrical shape, and is provided with an injection molding method or a press molding method. A top lid integrally formed with the top plate, provided with a plurality of reinforcing ribs extending vertically and horizontally on a lower surface or an upper surface of the top plate, and a central portion dense rib at a center portion of the top plate having a narrow interval between adjacent reinforcing ribs. The structure is formed, and both ends of the dense rib structure are extended to the periphery of the top plate or to the vicinity of the periphery.
[0006]
According to a second aspect of the present invention, in the upper lid according to the first aspect, a peripheral edge dense rib structure in which a distance between adjacent reinforcing ribs is reduced is formed on a peripheral edge of the top plate. It is assumed that.
[0007]
The pallet box according to the third aspect of the present invention is the container according to the first or second aspect, wherein the container is formed in a cylindrical shape with a pallet and a side wall provided upright on a periphery of a mounting portion of the pallet. A pallet box including an upper lid, wherein the upper lid is configured to openably close an upper opening of the container.
[0008]
A pallet box according to a fourth aspect of the present invention is the pallet box according to the third aspect, wherein the lower end edge of the reinforcing rib constituting the dense rib structure is engageable with the upper end edge of the side wall. Characterized in that the engaging projections are suspended.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 2, the pallet box 11 of the embodiment includes a pallet 12, a square tubular sleeve 14 which is detachably provided on a peripheral edge of a mounting portion 13 of the pallet 12, and an upper opening of the sleeve 14. And a synthetic resin upper lid 15 for detachably closing the portion. The pallet box 11 is covered with the sleeve 14 and the upper lid 15 around the object placed on the receiver 13 of the pallet 12 to prevent the object from being collapsed during transportation. Used for Further, as shown in FIG. 5, a plurality of pallet boxes 11 can be stacked up and down.
[0010]
As shown in FIGS. 2, 5, and 6, the pallet 12 is integrally formed of a synthetic resin into a substantially square plate shape. The pallet 12 includes an upper deck 21 formed in a square plate shape, a long square pillar-shaped corner girder 22 and a center girder 23 suspended from the lower surface of the upper deck 21, and a single-sided two-way gap. It has a configuration of a single skid type (single surface type).
[0011]
On the upper surface of the upper deck 21, there is provided a placing portion 13 for placing a load on the pallet 12. The corner girder 22 is provided along a pair of opposing side edges of the upper deck 21, and the center girder 23 is provided on the lower surface at the center of the upper deck 21, that is, at the center position between the pair of corner girder 22. . A fork insertion hole 24 for inserting a forklift or a handlift fork is provided between the adjacent corner girder 22 and center girder 23. In addition, a plurality of locking plates 27 formed in a long rectangular plate shape are erected on the outer peripheral edge of the mounting portion 13 at predetermined intervals.
[0012]
The sleeve 14 is made of cardboard. As shown in FIGS. 2 and 5, the sleeve 14 is formed by bending a single corrugated cardboard formed in a long rectangular plate shape at a predetermined position to form a square tubular shape having a pair of opposing side walls 31. As shown in FIG. 6, it is configured so that it can be folded into a small flat plate and compact.
[0013]
As shown in FIG. 2, the upper lid 15 is integrally formed by an injection molding method or a press molding method. The upper lid 15 is formed as a covered quadrangular cylindrical shape from a top plate 41 formed in a square plate shape and a pair of side plates 42 hanging down from the periphery of the top plate 41. Further, each side plate 42 is formed in a tapered shape so as to slightly protrude outwardly of the upper lid 15 downward, that is, to slightly expand downward.
[0014]
A corner projection 44 and a side edge projection 45 as locking projections are protruded from an upper peripheral edge of the top plate 41. The corner projections 44 are formed on the upper surface of each corner of the top plate 41 so as to be substantially L-shaped in plan view, and the side edge projections 45 are formed in the center of each side edge of the top plate 41 with a flat rectangular shape. It is formed so that it becomes. Further, each corner of the upper lid 15 is provided with a corner recess 46 formed by recessing the upper surface of the corner of the top plate 41 so as to form an L-shape in a plane.
[0015]
The upper surface of the top plate 41 surrounded by the corner projections 44 and the side edge projections 45 serves as a girder mounting portion 47 for mounting the girders 22 and 23 of the pallet 12. The girder mounting portion 47 is provided on the upper surface of the central portion of the top plate 41 constituting the upper lid 15, and is formed in a flat “field” shape by a flat surface having the same height.
[0016]
As shown in FIGS. 1 and 3, on the lower surface of the top plate 41, a large number of reinforcing ribs 51 extending vertically and horizontally in a grid form are suspended and formed so that the interval between the adjacent reinforcing ribs 51 is reduced. A peripheral dense rib structure 52 and a central dense rib structure 53 are provided as a dense rib structure, and the strength of the top plate 41 is increased. The reinforcing rib 51 is provided over the entire lower surface of the top plate 41. In addition, the dense rib structures 52 and 53 are provided with spaces d1 and D1 between adjacent reinforcing ribs 51 provided at the center of the top plate 41 (the spaces d1 and D1 are drawn with the same length in FIG. 1). This is a structure in which adjacent reinforcing ribs 51 are provided at narrower intervals than in the case of FIG. Further, in the dense rib structures 52 and 53, it is preferable that the interval between the adjacent reinforcing ribs 51 is not more than half of the intervals d1 and D1.
[0017]
The peripheral edge dense rib structures 52 are formed along each side edge (peripheral edge) of the top plate 41, and four peripheral edge dense rib structures 52 are arranged in the entire top plate 41 so as to form a bottom surface square ring. I have. In the peripheral edge dense rib structure 52, the distances d2 and D2 between the adjacent reinforcing ribs 51 are each configured to be approximately half of the distances d1 and D1. The central dense rib structure 53 is configured to connect the central portions of the opposite side edges of the top plate 41 or the central portions of both end edges thereof, and a pair (two) of central portions crossing each other in the entire top plate 41. The dense rib structure 53 is arranged so as to have a bottom cross shape. In the central dense rib structure 53, the distances d3 and D3 between the adjacent reinforcing ribs 51 are each configured to be approximately one fourth of the distances d1 and D1.
[0018]
On the lower surface of each corner portion of the upper lid 15, the lower end edges at both ends of the two reinforcing ribs 51 located at the center of the plurality (four each) of the reinforcing ribs 51 forming the peripheral edge dense rib structure 52. The engagement projection 54 is hung down. Each of the engagement protrusions 54 is provided at a position separated by a predetermined distance d11 from the side plate 42, and the upper end of the sleeve 14 is attached to the lower end edge of the reinforcing rib 51 located between the side plate 42 and the engagement protrusion 54. The edge is configured to abut. The predetermined interval d11 is formed to be thicker than the thickness of the sleeve 14, for example, about twice as thick.
[0019]
On the other hand, each corner of the upper lid 15 is provided with a contact convex portion 61 as a contact portion formed in an L-shaped bottom surface so as to protrude from the inner surface of each side plate 42 by a predetermined width d12. These contact projections 61 are formed on the back surface of the corner recess 46, and the lower ends thereof are located below the reinforcing ribs 51 and the engagement projections 54. Further, one side surface of the contact convex portion 61 located on the inner side of the upper lid 15 is formed in a tapered shape slightly narrower upward as in the case of the side plate 42. That is, one side surface of the contact convex portion 61 is an inclined surface 62 formed so as to slightly protrude toward the inside of the upper lid 15 as it goes upward, and when the upper lid 15 is attached to the sleeve 14. The outer surface of the corner portion of the sleeve 14 (particularly, the corner of the sleeve 14) is configured to abut.
[0020]
The operation of the pallet box 11 will be described below.
As shown in FIG. 2, the pallet box 11 is brought into contact with the inner surface of the locking plate 27 at the peripheral edge of the pallet 12 by the outer surface of the lower end of the sleeve 14 assembled in a rectangular tube shape. It is assembled by covering the upper end (upper opening) with the upper lid 15 and locking the upper lid. As shown in FIG. 4 (a), when the upper lid 15 is engaged with the sleeve 14, each corner portion of the sleeve 14 assembled in a square tubular shape is brought into contact with the inclined surface 62 of the contact convex portion 61. This is done by letting
[0021]
At this time, each side plate 42 of the upper lid 15 is configured so as to be located on the outer side of the upper lid 15 than the inclined surface 62, and the sleeve 14 is positioned at the upper end of each side wall 31 as shown in FIG. The central portion of the edge is relatively easily bulged outward. Therefore, by smoothly bulging the center of the upper end edge of the side wall 31 into the gap 71 formed between the sleeve 14 and the center of the side plate 42, all four corners of the sleeve 14 Positioning at the time of contact with the contact protrusion 61 can be performed easily and quickly.
[0022]
The pallet box 11 in this assembled state is fixed with a fixing band 72 as shown in FIG. 5 if necessary, and then a fork of a forklift or a handlift is inserted into the fork insertion hole 24 opened at the lower end of the pallet 12. Inserted and transported. At this time, even if the object placed on the mounting part 13 of the pallet 12 shifts or collapses, the object is supported by the sleeve 14 surrounding the object, and the object is placed on the mounting part 13. There is no risk of falling from above.
[0023]
In particular, since the upper and lower ends of the sleeve 14 for preventing displacement and load collapse of the ornament are fixed by the pallet 12 and the upper lid 15, the sleeve 14 deforms while receiving the load applied from the ornament. Is easily suppressed. Further, the central portion of the side wall 31, which is the most susceptible portion of the sleeve 14, can move (bulge) a predetermined width in the horizontal (bulging) direction with respect to the upper lid 15 at the center of the upper edge of the side wall 31. Therefore, a certain degree of deformation can be tolerated. Therefore, the action of deforming the sleeve 14 is alleviated by, for example, the central portion of the side wall 31 bulging outward as shown in FIG. And bending (irregular bending) are significantly and effectively suppressed.
[0024]
On the other hand, as shown in FIG. 5, this pallet box 11 is configured such that another pallet box 11 is placed and stacked on the upper end portion (upper surface of the upper lid 15) of the pallet box 11 in an assembled state. At this time, the lower end surfaces (bottom surfaces) of the beams 22, 23 of the pallet 12 of the pallet box 11 located above are placed on the girder placement portion 47 of the top plate 41 of the pallet box 11 located below. I have. Further, the lower end of the outer side of each corner girder 22 of the upper pallet box 11 is engaged with the inner side surface of the corner projection 44 and the side edge projection 45 of the lower pallet box 11. I have. The front and rear ends of the center girder 23 of the upper pallet box 11 are engaged with the inner side surfaces of the side edge projections 45 of the lower pallet box 11. As a result, these upper and lower pallet boxes 11 are not easily displaced.
[0025]
Furthermore, in this stacked pallet box 11, the upper end of the sleeve 14 of the pallet box 11 located below and the lower end of the pallet 12 of the pallet box 11 located above are located at extremely close positions. . That is, there is only an interval between the upper end of the sleeve 14 and the lower end of the pallet 12 corresponding to the sum of the thickness of the top plate 41 and the height of the protruding ribs 51. Therefore, the overall height when a plurality of pallet boxes 11 are stacked up and down is easily reduced.
[0026]
Further, the stacked pallet boxes 11 have a structure that can easily and surely receive the load applied to the upper lid 15 of the pallet box 11 located below, and the pallet box 11 on which a heavy load is placed. 11 can be stacked upward in a plurality of stages. That is, on the lower surface of the top plate 41 constituting the upper lid 15 of the pallet box 11, a number of reinforcing ribs 51 extending vertically and horizontally in a grid form are hung down, and a substantially uniform strength is provided over the entire top plate 41. Have been. Further, a peripheral dense rib structure 52 and a central dense rib structure 53 are provided at the peripheral portion and the central portion of the top plate 41, respectively, so that a local load against the load applied from the pallet box 11 located above. Effective reinforcement effect. In particular, the peripheral dense rib structure 52 reinforces the load transmitted through the corner girder 22 of the pallet box 11 located above, and the central dense rib structure 53 reinforces the load transmitted through the central girder 23. It is supposed to do.
[0027]
On the other hand, the pallet box 11 separates the upper lid 15, the sleeve 14, and the pallet 12, then folds the sleeve 14 into a flat plate as shown in FIG. It is placed on top, and the top lid 15 is put on the placement part 13 to be stored small and compact. As shown in FIG. 6, another pallet box 11 can be placed and stacked on the upper end portion (the upper surface of the upper lid 15) of the pallet box 11 which is folded small and compact.
[0028]
The effects exerted by the above embodiment will be described below.
The pallet box 11 of the embodiment is configured such that a pallet 12, a side wall 31 erected on the periphery of the mounting portion 13 of the pallet 12, and a container formed in a rectangular tube shape with a bottom and a top opening of the container are attached and detached. It is formed in the shape of a square box from the upper lid 15 which is closed as much as possible. Further, the upper lid 15 is integrally formed by an injection molding method or a press molding method, and a large number of reinforcing ribs 51 hang down on the entire lower surface of the top plate 41 constituting the upper lid 15 so as to extend vertically and horizontally in a lattice shape. At the center of the lower surface of the top plate 41, a central dense rib structure 53 in which the interval between adjacent reinforcing ribs 51 is narrowed is formed. In addition, both end portions of each central portion dense rib structure 53 are extended to both side edges or both end edges of the top plate 41.
[0029]
For this reason, the upper lid 15 (top plate 41) of the pallet box 11 is formed by injection molding or press molding compared with the conventional lid formed by vacuum molding. It is easy to give high rigidity while forming thin. In particular, in the case of injection molding or press molding, the reinforcing ribs 51 provided to increase the strength of the upper lid 15 (top plate 41) can easily adjust the protrusion height arbitrarily over a fairly wide range. However, there is a technical limit that when forming a similar structure (irregularity) by vacuum forming, it must be limited to a considerably limited narrow range. Due to this technical limitation, in the case of vacuum forming, the thickness of the lid is increased more than necessary and it is easy to be bulky. However, in the upper lid 15 of this embodiment, it is extremely difficult to form the lid to a desired thickness. Easy.
[0030]
Furthermore, in the case of vacuum forming, since it is necessary to form irregularities on both surfaces (upper and lower surfaces) of the lid in order to increase the strength, one surface (upper surface or lower surface) of the lid is flat (the irregular surface). With no or little solid surface). For this reason, for example, the (many) irregularities formed on the upper surface of the lid easily accumulate rainwater, dust, dirt, and the like, and also cause a problem that the lid is significantly soiled.
[0031]
Further, on the lower surface of the upper lid 15 (top plate 41) of the pallet box 11, a large number of reinforcing ribs 51 extending vertically and horizontally in a grid form are hung down, and the strength of the entire top plate 41 is increased. In addition, since the central dense rib structure 53 is formed so as to locally reinforce the central portion of the weakest upper lid 15 (square plate-shaped top plate 41), the strength of the entire upper lid 15 is improved. Can be easily increased. Particularly, since the central dense rib structure 53 is extended along the center line of the top plate 41 so as to connect between the front and rear ends or between the left and right sides, the front and rear along the center line of the upper lid 15 or Exhibits extremely high strength in the left-right direction. Further, the central dense rib structure 53 can effectively receive the load from the central girder 23 of the pallet box 11 located above, and enhance the strength and stability of the stacked pallet boxes 11. it can. In addition, since the central dense rib structure 53 is configured to most effectively reinforce the upper lid 15 with a small configuration, the weight of the upper lid 15 can be easily reduced.
[0032]
The strength of the upper lid 15 can be further increased by forming the peripheral edge dense rib structure 52 on the peripheral edge of the upper lid 15 (top plate 41). In particular, the peripheral edge dense rib structure 52 can effectively receive the load from the corner girder 22 of the pallet box 11 located above.
[0033]
By providing an engaging projection 54 formed on the lower surface of the peripheral portion of the upper lid 15 so as to be able to engage with the central portion of the upper edge of the side wall 31, it is possible to easily significantly deform the side wall 31 in both the inside and outside directions. Can be regulated. In particular, in the pallet box 11, an engaging projection 54 is hung on the lower end edge of the reinforcing rib 51 constituting the peripheral edge dense rib structure 52. Since the top plate 41 at the portion where the peripheral edge dense rib structure 52 is formed is unlikely to be deformed when a load is applied, the engaging projection 54 is securely connected to the upper edge of the side wall 31 (sleeve 14). Can be engaged.
[0034]
A plurality of corner projections 44 and side edge projections 45 are provided on the peripheral edge of the girder mounting portion 47 to lock the side portions of the beams 22, 23 of the pallet 12 of the pallet box 11 located above. Pallet boxes 11 can be vertically stacked in a stable state. In particular, by providing these corner projections 44 and side edge projections 45 along the periphery of the upper lid 15, it is possible to effectively prevent the pallet box 11 located above from slipping and falling.
[0035]
The above embodiment can be embodied with the following modifications.
The sleeve 14 may be made of a synthetic resin plate that can be repeatedly washed, for example, a relatively hard foamed polypropylene sheet or a non-foamed polypropylene sheet (solid sheet).
[0036]
In addition to the bottomed cylindrical container composed of the pallet 12 and the sleeve 14 (side wall 31), for example, a folding type pallet box having a pair of side walls rotatably provided on the periphery of the pallet is provided. You may use it as a container of a shape. Further, a rectangular transport container (container) or a foldable transport container (foldable container) having no fork insertion hole at the lower end may be used as the bottomed cylindrical container.
[0037]
-As the bottomed cylindrical container, for example, a bottomed square tubular shape or a bottomed square tubular shape formed into a planar square shape with one side of 1 m or more, or a flat rectangular shape with a long side of 1 m or more. Is preferably used. Further, as disclosed in the above embodiment, a large container transported by a forklift or a handlift, that is, a large container that is difficult to transport by one person is suitably used.
[0038]
Instead of arranging the two central dense rib structures 53 so as to form a bottom cross shape, the two central dense rib structures are connected so as to connect opposed corner portions of the top plate 41 formed in a square plate shape. It may be arranged in a bottom X-shape.
[0039]
In the above embodiment, only one of the two central dense rib structures 53 formed in the shape of a bottom cross may be omitted.
Instead of arranging the two central dense rib structures 53 so as to have a bottom cross shape, the four central dense rib structures may be arranged so as to have a bottom cross-girder shape. The central dense rib structure in the form of a bottom girder is formed by combining two sets of dense rib structures each connecting the opposite side and end of the top plate 41.
[0040]
An engaging projection 54 is provided at both ends of the reinforcing rib 51 constituting the central dense rib structure 53.
-The engagement convex part 54 may be omitted.
[0041]
-The pallet 12, the sleeve 14, and the upper lid 15 may be formed in a flat rectangular shape.
The pallet 12 may be changed to a one-sided, four-sided skid type or a European type.
[0042]
Further, technical ideas that can be grasped from the embodiment will be described below.
5. The pallet box according to claim 3, wherein the pallet has fork insertion holes opened on a side surface and a bottom surface. 6.
[0043]
The top plate is provided with a girder mounting portion for mounting a pallet girder on its upper surface, and a dense rib structure is formed near a lower portion of the girder mounting portion. The pallet box according to claim 3 or 4, wherein the pallet box is provided.
[0044]
The top plate is provided with a girder mounting portion for mounting a pallet girder on an upper surface thereof, and also for locking a side portion of the pallet girder to a peripheral portion of the girder mounting portion. The pallet box according to claim 3 or 4, wherein a locking projection is provided.
[0045]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
According to the upper lid according to the first and second aspects of the present invention, it is possible to exhibit high strength while reducing the weight, and it is easy to form the lid thin.
[0046]
According to the pallet box according to the third and fourth aspects of the invention, it is possible to easily increase the strength of the entire upper lid while reducing the weight, and it is easy to form the upper lid thin.
[Brief description of the drawings]
FIG. 1A is a bottom view showing a part of an upper lid constituting a pallet box of an embodiment, and FIG. 1B is a cross-sectional view showing the upper lid as viewed from a line 1b-1b in FIG. 1A.
FIG. 2 is an exploded perspective view showing the pallet box of the embodiment.
3A is a cross-sectional view showing the upper lid taken along line 3a-3a in FIG. 1A, FIG. 3B is a cross-sectional view showing the upper lid also taken along line 3b-3b in FIG. 1A, and FIG. Sectional drawing which shows the upper lid seen from the 3c-3c line.
FIGS. 4A and 4B are bottom cross-sectional views each showing a part of a pallet box of the embodiment.
FIG. 5 is a view showing a state in which pallet boxes in an assembled state are stacked.
FIG. 6 is a view showing a state in which pallet boxes in a folded state are stacked.
[Explanation of symbols]
Reference Signs List 11 pallet box, 12 pallet forming container, 13 mounting portion, 14 sleeve forming side wall and container, 15 upper cover, 31 side wall, 41 top plate, 51 reinforcing rib, 52 dense Peripheral dense rib structure as a rib structure; 53, central dense rib structure as a dense rib structure; 54, engaging projections; d2, D2, d3, D3, intervals.

Claims (4)

With a top plate for closing the upper opening of the container formed in a bottomed cylindrical shape, an upper lid integrally molded by an injection molding method or a press molding method,
A plurality of reinforcing ribs extending vertically and horizontally are provided on a lower surface or an upper surface of the top plate, and a central dense rib structure in which a space between adjacent reinforcing ribs is narrowed is formed in a central portion of the top plate, and the dense rib structure is provided. Characterized in that both ends of the top cover extend to the periphery of the top plate or to the vicinity of the periphery. 2. The upper lid according to claim 1, wherein a peripheral edge dense rib structure in which a space between adjacent reinforcing ribs is narrowed is formed on a peripheral edge of the top plate. 3. A pallet box comprising a pallet, a container formed in a cylindrical shape with a bottom, and a side wall erected on the periphery of the mounting portion of the pallet, and an upper lid according to claim 1 or claim 2,
A pallet box, wherein an upper opening of the container is opened and closed by the upper lid. 4. The pallet according to claim 3, wherein an engagement protrusion configured to be able to engage with an upper end edge of the side wall is hung down on a lower end edge of the reinforcing rib constituting the dense rib structure. 5. box.

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