JP7785282B2 - container - Google Patents

Description

This disclosure relates to a resin container.

One known container of this type is one in which the central region of the flat portion of the side wall is thicker than the outer edge region in order to prevent warping of the flat portion (see, for example, Patent Document 1).

JP 2019-69791 A (Figs. 1, 7, 9)

The outer surface of a container's sidewall is sometimes used as an information display surface, where labels can be affixed or inscriptions can be printed. However, with conventional containers, the thickened portion used to prevent warping described above creates a step on the outer surface of the sidewall, posing a problem in that the information display surface is restricted by the inside of the step, making it narrow. A solution to this problem is needed.

The invention of claim 1, which was made to solve the above problem, is a resin container that includes side walls with flat portions, each of which has a flat portion without a reinforcing rib inside the outer edge of the outer surface, in which a first step portion is formed in the back area of the flat portion near a pair of opposing outer edges, and a first thick portion inside the first step portion is thicker than a second thick portion outside the first step portion.

The invention of claim 2 is a container as described in claim 1, in which a second step portion is formed in the rear region at a position closer to the outside than the first step portion, and a third thick portion having the same thickness as the first thick portion or thicker than the first thick portion is provided outside the second step portion within the rear region.

The invention of claim 3 is the container described in claim 2, in which the first step portion and the second step portion are formed near the outer edges in both the vertical and horizontal directions, and the first thick portion is surrounded on all four sides by the second thick portion, and the second thick portion is surrounded on all four sides by the third thick portion.

The invention of claim 4 is a container according to claim 2 or 3, wherein the first step portion and the second step portion are inclined with respect to the thickness direction of the side wall with the flat portion.

The invention of claim 5 relates to a container according to any one of claims 1 to 4, wherein the side walls comprise a pair of first side walls that are separate from the bottom and upper frame of the container, and that are opposed to each other with their upper and lower ends hingedly connected to the bottom and upper frame, and that are foldable inward in half; and a pair of second side walls that are positioned between the pair of first side walls, have their upper ends hingedly connected to the upper frame, and are foldable upward and inward; and at least one of the pair of first side walls and the pair of second side walls is a side wall with a flat portion, and has a pair of outer edge projections at both lateral ends that extend vertically, form a groove-shaped cross section, and project outward.

The invention of claim 6 is a container described in claim 5 which is dependent on any one of claims 2 to 4, wherein at least the lower first side wall of the first side walls, which are folded in half and overlap each other, is a side wall with a flat portion, and has the first thick portion, the second thick portion, and the third thick portion thicker than the first thick portion in the back area of the flat portion, and the protrusion side wall of the outer edge protrusion located on the third thick portion side is inclined with respect to the third thick portion, and the inner surface of the lower first side wall is provided with a curved portion that smoothly connects the protrusion side wall and the third thick portion.

In the container of claim 1, a first step is formed in the back region of the flat portion of the outer surface of the side wall, and the first thick portion inside the first step is thicker than the second thick portion outside. In other words, in the container of claim 1, the inner surface of the side wall is thickened from the outer edge to form the first thick portion, and the resulting first step is formed on the inner surface of the side wall. Therefore, while providing a thick portion (first thick portion) to prevent warping, it is possible to eliminate the step that has been a problem in the past from the outer surface of the side wall, and expand the area of the outer surface of the side wall that can be used as an information display surface.

According to the configuration of claim 2, a second step portion is formed at a position closer to the outside of the first step portion, and a third thick portion having the same thickness as the first thick portion or a thickness thicker than the first thick portion is provided outside the second step portion. This balances the progress of the temperature drop in the resin across the entire flat portion of the side wall, and suppresses warping across the entire flat portion.

The first and second step portions may be provided only at a pair of positions near the outer edges of the back region that face each other in the vertical direction, or only at a pair of positions near the outer edges of the back region that face each other in the horizontal direction. Alternatively, as in the configuration of claim 3, they may be formed at positions near the outer edges in both the vertical and horizontal directions, with the first thick portion surrounded on all four sides by the second thick portion, and the second thick portion surrounded on all four sides by the third thick portion. In the configuration of claim 3, the first thick portion is surrounded on all four sides by the second thick portion, and the second thick portion is surrounded on all four sides by the third thick portion, balancing the progress of temperature drop in the resin throughout the entire flat portion.

In the container of claim 4, the first and second step portions are inclined relative to the thickness direction of the flat side wall, preventing items from getting caught and suppressing sudden changes in wall thickness, thereby reducing the occurrence of warping.

The container of claim 5 comprises a pair of first side walls that are separate from the bottom and upper frame, and are hinged at their upper and lower ends to the bottom and upper frame, facing each other, and can be folded inward in half; and a pair of second side walls that are hinged at their upper ends to the upper frame. The pair of second side walls can be folded upward and inward, and then the pair of first side walls can be folded in half inward to bring the entire container into a folded state. Furthermore, since at least one of the pair of first side walls and the pair of second side walls has a flat portion, and the container has the configuration of any one of claims 1 to 4, the outer surface of the pair of first side walls can be used as a wider information display surface than before.

In the container of claim 6, of the first side walls, the upper first side wall and the lower first side wall are folded in half and overlap each other, and at least the lower first side wall has a first thick portion, a second thick portion, and a third thick portion that is thicker than the first thick portion. This prevents the second side wall from getting caught on the first thick portion during rotation. In addition, the protruding side wall of the outer edge protrusion located on the third thick portion side is inclined with respect to the third thick portion, and the inner surface of the lower first side wall has a curved portion that smoothly connects the protruding side wall and the third thick portion. This also prevents the second side wall from getting caught on the third thick portion during rotation. This prevents a decrease in operability caused by the inclusion of a thick portion (first thick portion) on the inner surface of the container to prevent warping.

FIG. 1 is a perspective view of a container according to an embodiment of the present disclosure. A perspective view of the container in a folded state FIG. 10 is a perspective view of the container with the second side wall partially folded; FIG. 1 is a perspective view of a container with a first side wall partially folded; 1 is a perspective view of the outer surface side of the first side wall; 1 is a perspective view of the inner surface side of the first side wall; FIG. 1 is a perspective view of a first side wall with a partial cutaway; A partially cutaway cross-sectional view of the first side wall 1 is a cross-sectional side view of an upper end portion of a first side wall;

A container 10A according to one embodiment of the present disclosure will now be described with reference to Figures 1 to 9. As shown in Figure 1, the container 10A of this embodiment has, for example, a rectangular parallelepiped shape in plan view, and is divided into multiple components that are movably connected, allowing it to be changed between the assembled state shown in the figure and the folded state shown in Figure 2.

Specifically, the container 10A is divided into a bottom 11, an upper frame 12, a pair of first side walls 20, a pair of second side walls 40, a pair of door covers 13, and a pair of sliders 14. Each first side wall 20 (corresponding to the "side wall with flat portion" in this disclosure) is further divided into an upper first side wall 21 and a lower first side wall 22. Furthermore, these multiple components of the container 10A are injection-molded resin products, and the entire container 10A is made of resin. The specific structure of each component is described below.

As shown in Figure 3, the bottom 11 has a lower frame wall 11B that rises from the entire outer edge of a plate-shaped bottom wall 11A, and multiple hinge protrusions 11E on the inner surface of a pair of long sides of the lower frame wall 11B. The underside of the bottom wall 11A is provided with ribs extending inward from the outer edge, forming lower surface protrusions 11T (see Figure 4).

As shown in FIG. 4, the upper frame portion 12 comprises an outer frame wall 12B, an inner frame wall 12C, and an upper wall 12A connecting the upper ends thereof, and has a cross section shaped like a rectangular groove with an open bottom. The outer frame wall 12B is located directly above the lower frame wall 11B of the bottom portion 11, and when the folding structure is in the folded state as shown in FIG. 2, the outer frame wall 12B and the lower frame wall 11B abut against each other. As shown in FIG. 4, the lower end of the inner frame wall 12C is located above the lower end of the outer frame wall 12B, and the lower ends of the inner frame walls 12C on a pair of short sides of the upper frame portion 12 are located above the lower ends of the inner frame walls 12C on a pair of long sides. A plurality of hinge protrusions 12E (see FIG. 3) are provided between the lower ends of the inner frame walls 12C on each side of the upper frame portion 12 and the inner surface of the outer frame wall 12B.

As shown in FIG. 1, the upper surface of each of the pair of long sides of the upper frame portion 12 is provided with multiple hinge protrusions 12F, and the upper surface of each of the pair of short sides of the upper frame portion 12 is provided with a pair of positioning protrusions 12D. Side recesses 12M, 12N are formed at the center of each of the pair of short sides of the upper frame portion 12 and at both ends of each of the pair of long sides, by recessing the outer frame wall 12B and connecting it to the inner frame wall 12C. At the top end of the side recess 12M, a portion of the upper wall 12A remains as a handle 12L.

The pair of door lids 13 have hinge protrusions 13F at their base ends connected to hinge protrusions 12F of the upper frame 12, forming a so-called double door structure that opens and closes the top opening of the upper frame 12. Furthermore, when the door lids 13 are closed, the hinge protrusions 13F protrude upward from the main body 13H. The hinge protrusions 12F, 13F form positioning protrusions 12H on the top surface of a pair of long sides of the upper frame 12, and the positioning protrusions 12D on the top surface of a pair of short sides, allowing the bottom protrusions 11T (see Figure 4) of another container 10A to fit inside the positioning protrusions 12H and 12D on the top surface of a pair of short sides of the upper frame 12.

As shown in Figure 2, the leading edges of a pair of door lids 13 are curved to form a point symmetry, with half of the leading edge forming a protruding portion 13G that protrudes toward the other, while the other half forms a receiving portion 13J that receives the other protruding portion 13G. The receiving portion 13J also has a lower surface overlapping portion (not shown) that overlaps the underside of the other protruding portion 13G. A slider 14 slidably engages with the underside of each protruding portion 13G, and when each slider 14 is slid to the locked position, it engages with the other lower surface overlapping portion, locking the door lid 13 in the closed position.

As shown in Figure 1, the pair of second side walls 40 have a pair of outer edge projections 41 at both lateral ends, extending vertically and projecting outward with a groove-shaped cross section. As shown in Figure 3, the lower ends of the pair of outer edge projections 41 are connected by a pair of horizontal ribs 42A that project laterally from the outer surface of the second side wall 40, and the pair of horizontal ribs 42A are connected by multiple vertical ribs 42B. Although not shown, the upper ends of the pair of outer edge projections 41 are connected by a hinge support rib 26 that projects laterally from the outer surface of the second side wall 40, similar to the upper portion of the first side wall 20 described below (see Figure 5), and multiple hinge projections 21E are provided on the upper surface of the hinge support rib 26. The multiple hinge protrusions 21E on each second side wall 40 engage with the aforementioned hinge protrusions 12E on each short side of the upper frame 12, so that the upper end of the second side wall 40 is hingedly connected (rotatably connected) to the upper frame 12.

As shown in FIG. 3, a pair of locking claws 44 for attaching a card holder protrude from both sides of the lower end of the outer surface of the second side wall 40. Each outer edge protrusion 41 of the second side wall 40 has a pair of receiving recesses 43A formed in its vertically middle portion. The receiving recesses 43A open to the outer surface and tip surface of the outer edge protrusion 41, and a protrusion 43B protrudes slightly from the opening edge of the receiving recess 43A on the outer surface side of the outer edge protrusion 41.

As shown in Figure 5, the pair of first side walls 20 are divided into an upper first side wall 21 and a lower first side wall 22 at the vertical midpoint, which are hingedly connected. Both the upper first side wall 21 and the lower first side wall 22 have a pair of outer edge projections 23 at both lateral ends that extend vertically, have a groove-shaped cross section, and protrude outward.

The upper ends of a pair of outer edge protrusions 23 of the upper first side wall 21 are connected by a hinge support rib 26 that protrudes from the outer surface of the upper first side wall 21 and extends laterally, and a plurality of hinge protrusions 21E are provided on the upper surface of the hinge support rib 26. These hinge support ribs 26 have a slightly serpentine shape in the vertical direction to correspond to the plurality of hinge protrusions 21E, 22E. The lower ends of a pair of outer edge protrusions 23 of the lower first side wall 22 are also connected by a hinge support rib 26, and a plurality of hinge protrusions 22E are provided on the lower surface of the hinge support rib 26. The multiple hinge protrusions 21E on the upper first side wall 21 engage with the aforementioned hinge protrusions 12E on each long side of the upper frame 12, so that the upper end of the first side wall 20 is hingedly connected to the upper frame 12, and the multiple hinge protrusions 22E on the lower first side wall 22 engage with the aforementioned hinge protrusions 11E on each long side of the bottom 11, so that the lower end of the first side wall 20 is hingedly connected to the bottom 11.

The lower ends of the pair of outer edge projections 23 of the upper first side wall 21 are connected by a pair of horizontal ribs 25 (see FIG. 4) that protrude laterally from the outer surface of the upper first side wall 21, and the pair of horizontal ribs 25 are provided with multiple hinge projections 21F shown in FIG. 5 at multiple locations along their length. Meanwhile, the upper ends of the pair of outer edge projections 23 of the lower first side wall 22 are connected by outer edge projections 24 that have a groove-shaped cross section, extend laterally, and protrude outward, and the upper surface of the outer edge projections 24 is provided with multiple hinge projections 22F shown in FIG. 5 at multiple locations. The multiple hinge projections 21E at the lower end of the upper first side wall 21 engage with the multiple hinge projections 21F at the upper end of the lower first side wall 22, thereby hinge-connecting the upper first side wall 21 and the lower first side wall 22.

As shown in FIG. 6 , the upper first side wall 21 and the lower first side wall 22 are provided with a partition rib 28 that horizontally divides the interior of each outer edge protrusion 23 into two. The partition rib 28 is located laterally outward of the outer edge protrusion 23. Furthermore, in the region of the outer edge protrusion 23 outside the partition rib 28, near the vertical center of the first side wall 20, a side through-hole 29A is formed that penetrates the tip wall 23A of the outer edge protrusion 23. A pair of horizontal ribs 28A are provided on the upper and lower opening edges of the side through-hole 29A, connecting the partition rib 28 and the outer protrusion side wall 23D of the outer edge protrusion 23. Furthermore, an engagement piece 29 is provided on the opening edge of the side through-hole 29A opposite the partition rib 28, extending from a portion of the protrusion side wall 23D and bent at a right angle toward the partition rib 28. When the container 10A is in the assembled state, the engagement piece 29 is received in the receiving recess 43A of the second side wall 40, connecting the second side wall 40 and the first side wall 20. With this configuration, the container 10A can be switched between the assembled state and the folded state, as described above.

The first side wall 20 and the second side wall 40 are reinforced by an outer edge reinforcement portion consisting of a hinge support rib 26, a horizontal rib 42A, and outer edge protrusions 23, 24, and 41 that protrude from the main plate portions 30 and 49, which are the primary plate portions of the first side wall 20 and the second side wall 40. While some containers have ribs or groove-shaped structures on the inner side of the outer edge reinforcement portion, the container 10A of this embodiment does not have ribs or groove-shaped structures on the inner side of the outer edge reinforcement portion of the first side wall 20 and the second side wall 40. In the second side wall 40, a rectangular region inward from the outer edge reinforcement portion of the main plate portion 49, surrounded by the outer edge reinforcement portion consisting of the outer edge protrusions 41, the horizontal rib 42A, and the hinge support rib 26, is slightly thickened outward to form a thickened portion 45. This thickened portion 45 suppresses warping of the second side wall 40. The thick portion 45 also serves as the back support for the card holder that is attached to the pair of locking claws 44.

The mechanism by which warping is suppressed by providing the thickened portion 45 on the second side wall 40 is believed to be as follows. Specifically, if the portion of the main plate portion 49 of the second side wall 40 surrounded by the outer edge reinforcement is a flat plate of uniform thickness, the outer edge region of the flat plate cools more easily than the inner region, and the outer edge region shrinks more than the inner region. Therefore, the outer edge region hardens and shrinks before the inner region. The central region cannot absorb this shrinkage, and the resin in the central region bulges and hardens with no escape route, resulting in warping. Furthermore, if the flat plate does not have a uniform thickness, the thicker portion will shrink more than the thinner portion. Therefore, by providing the thickened portion 45, as in the case of the second side wall 40 of this embodiment, and making the inner region thicker than the outer edge region in the portion of the second side wall 40 surrounded by the outer edge reinforcement, the central region can shrink more than the outer region, thereby suppressing the bulging of the resin in the central region and suppressing warping, compared to when the thicknesses are uniform.

As shown in FIG. 6 , the upper first side wall 21 and the lower first side wall 22 have first thick portions 31 that protrude inward, corresponding to the thick portions 45 of the second side wall 40. As shown in FIG. 5 , in the upper first side wall 21 and the lower first side wall 22, the outer surface of the main plate portion 30, surrounded by the outer edge reinforcement portion consisting of the outer edge protrusions 23, horizontal ribs 25, outer edge protrusions 24, hinge support ribs 26, etc., forms a flat portion 39 without any irregularities. Hereinafter, to clarify that the flat portion 39 is the outer surface flat portion 39 and not the inner surface of the upper first side wall 21 and the lower first side wall 22, the flat portion 39 will be referred to as the "outer surface flat portion 39," and the area behind the outer surface flat portion 39 will be referred to as the "back region 39R," and the structure of the upper first side wall 21 and the lower first side wall 22 will be described in detail.

As shown in Figure 6, a first step portion 31S and a second step portion 33S are formed near the outer edge of the back region 39R of the upper first side wall 21. The first step portion 31S and the second step portion 33S form similar quadrangles, with the first step portion 31S located inside the second step portion 33S. As shown in Figures 7 and 8, there is a recess between the first step portion 31S and the second step portion 33S, and the first thick portion 31 inside the first step portion 31S is thicker than the second thick portion 32 between the first step portion 31S and the second step portion 33S. Additionally, the third thick portion 33 in the rear region 39R, located outside the second step portion 33S, is thicker than the first thick portion 31, and the inner surface of the third thick portion 33 is located closer to the inside of the container 10A than the inner surface of the first thick portion 31. The first step portion 31S and the second step portion 33S are gently inclined relative to the inner surface of the second thick portion 32.

Furthermore, on both sides of the upper first side wall 21, the protrusion side walls 23B of the outer edge protrusion 23 are inclined with respect to the thickness direction of the main plate portion 30, as shown in FIG. 8. An arc-shaped curved portion 33K is provided that smoothly connects the inner surface of the protrusion side wall 23B with the third thick portion 33. Furthermore, at both the upper and lower ends of the upper first side wall 21, the hinge support ribs 26 and horizontal ribs 25 protrude perpendicularly from the third thick portion 33, as shown in FIGS. 4 and 9. The wall thicknesses of the outer edge protrusion 23, horizontal ribs 25, outer edge protrusion 24, hinge support rib 26, etc. are close to those of the first thick portion 31 or the third thick portion 33.

The back side of the outer flat portion 39 of the lower first side wall 22 is similar to that of the upper first side wall 21. Furthermore, at the upper end of the lower first side wall 22, the protruding portion side wall 24B of the outer edge protrusion 24 rises vertically from the third thick portion 33, as shown in Figure 4.

This concludes the explanation of the configuration of the container 10A of this embodiment. Next, the effects of this container 10A will be described. In the container 10A of this embodiment, the inner surfaces of the upper first side wall 21 and the lower first side wall 22 are thickened from the outer edge to form the first thick portion 31, and the associated first step portion 31S is formed on the inner surface. Therefore, while the container 10A has a thick portion (first thick portion 31) for preventing warping, it is possible to eliminate the associated step portion (first step portion 31S) from the outer surface, thereby expanding the area of the outer surfaces of the upper first side wall 21 and the lower first side wall 22 that can be used as an information display surface.

Furthermore, by surrounding the thinner second thick portion 32 outside the first thick portion 31 with the thicker third thick portion 33, the progress of temperature drop in the resin is balanced across the entire outer flat portion 39 of the upper first side wall 21 and the lower first side wall 22, effectively suppressing warping across the entire outer flat portion 39. Moreover, because the third thick portion 33 is thicker than the first thick portion 31 and protrudes further inward than the first thick portion 31 into the container 10A (see Figure 8), the second side wall 40 is prevented from getting caught on the first thick portion 31 during rotation. Additionally, the protrusion side wall 23B of the outer edge protrusion 23 located on the third thick portion 33 side is inclined relative to the third thick portion 33, and the inner surfaces of the upper first side wall 21 and the lower first side wall 22 are provided with a curved portion 33K that smoothly connects the protrusion side wall 23B and the third thick portion 33. This also prevents the second side wall 40 from getting caught on the third thick portion 33 during rotation. This prevents a decrease in operability when folding and assembling the container 10A due to the inclusion of a thick portion (first thick portion 31) on the inner surface of the container 10A to prevent warping.

Furthermore, the first step portion 31S and the second step portion 33S are inclined in the thickness direction of the upper first side wall 21 and the lower first side wall 22, preventing luggage from getting caught and suppressing sudden changes in thickness, thereby reducing warping.

Other Embodiments
(1) In the container 10A of the above embodiment, the third thick portion 33 is formed on the outside of the second thick portion 32, but the third thick portion 33 may not be provided.

(2) In the container 10A of the above embodiment, the first thick portion 31 was surrounded on all sides by the first step portions 31S. However, the first step portions 31S may be provided only near the outer edges of either the top-bottom or bottom-bottom ends of the upper first side wall 21 or the lower first side wall 22, with the first thick portion 31 being the space between them. The same applies to the second step portions 33S. However, a configuration in which the first thick portion 31 is surrounded on all sides by the second thick portions 32, and the second thick portion 32 is surrounded on all sides by the third thick portions 33, as in the above embodiment, is preferable because it allows for a more balanced temperature drop in the resin throughout the entire outer surface flat portion 39.

(3) In the container 10A of the above embodiment, the first step portion 31S and the second step portion 33S are rectangular, but they may also be circular or elliptical.

(4) The container 10A in the above embodiment was a foldable container, but the above-mentioned first thick portion 31, second thick portion 32, third thick portion 33, etc. may be provided on the inner surface of the side wall of a non-foldable container. Also, the above-mentioned first thick portion 31, second thick portion 32, third thick portion 33, etc. may be provided on the lid or bottom wall.

(5) In the above embodiment, the first step portion 31S and the second step portion 33S were inclined with respect to the thickness direction of the first side wall 20, but they may also be parallel to the thickness direction.

Note that while the present specification and drawings disclose specific examples of technology included within the scope of the claims, the technology described in the claims is not limited to these specific examples and includes various modifications and variations of the specific examples, as well as parts of the specific examples taken independently.

10A Container 11 Bottom 12 Upper frame 20 First side wall (side wall with flat portion)
21 Upper first side wall (side wall with flat portion)
22 Lower first side wall (side wall with flat portion)
23 Outer edge protrusion 23B Protrusion side wall 31 First thick portion 31S First step portion 32 Second thick portion 33 Third thick portion 33S Second step portion 33K Curved portion 39 Flat portion 39R Back region 40 Second side wall

Claims (6)

In a resin container, a plurality of side walls include a flat side wall in which the flat portion has no reinforcing rib inside the outer edge of the outer surface,
A container in which a first step portion is formed near a pair of opposing outer edges in the back region of the flat portion, and a first thick portion inside the first step portion is thicker than a second thick portion outside the first step portion. A container as described in claim 1, wherein a second step portion is formed in the rear region at a position closer to the outside than the first step portion, and a third thick portion having the same thickness as the first thick portion or a thickness thicker than the first thick portion is provided outside the second step portion in the rear region. The container described in claim 2, wherein the first step portion and the second step portion are formed near the outer edges in both the vertical and horizontal directions, and the first thick portion is surrounded on all four sides by the second thick portion, and the second thick portion is surrounded on all four sides by the third thick portion. A container as described in claim 2 or 3, wherein the first step portion and the second step portion are inclined with respect to the thickness direction of the side wall with the flat portion. The plurality of side walls are separated from an upper frame portion which is a bottom portion and an upper portion of the container, and are composed of a pair of first side walls which are opposed to each other by being hingedly connected at their upper and lower ends to the bottom portion and the upper frame portion and can be folded inward in two, and a pair of second side walls which are disposed between the pair of first side walls and have their upper ends hingedly connected to the upper frame portion and can be folded upward and inward,
5. A container according to claim 1, wherein at least one of the pair of first side walls and the pair of second side walls is a side wall with a flat portion, and has a pair of outer edge protrusions at both lateral ends, which have a groove-shaped cross section, extend in the vertical direction, and protrude outward. Among the first side walls, at least the lower first side wall out of the upper first side wall and the lower first side wall that are folded in half and overlap each other is the side wall with the flat portion, and has the first thick portion, the second thick portion, and the third thick portion that is thicker than the first thick portion in the back region of the flat portion,
A container as described in claim 5, which is dependent on any one of claims 2 to 4, wherein the protrusion side wall of the outer edge protrusion located on the side of the third thick portion is inclined with respect to the third thick portion, and the inner surface of the lower first side wall is provided with a curved portion that smoothly connects the protrusion side wall and the third thick portion.