Folding chair

Abstract

The folding chair according to the present application comprises a seat panel (10) and two X-shaped brackets symmetrically provided on the left and right sides of the seat panel (10). The X-shaped brackets comprise front legs (20) and rear legs (30) which are rotatably hingedly connected to each other. The front legs (20) and rear legs (30) are positioned on the outside of the seat panel (10), and the rear legs (30) are interposed between the side edges of the seat panel (10) and the front legs (20). The upper ends of the rear legs (30) are The folding chair further includes a slide link (40) which is hinged to a front portion of the outer edge of the seat panel (10) and has a slide part (42) slidably connected to the side edge of the seat panel (10), a fixed part (44) connected to the front leg (20), and a positioning plate (46) connected between the slide part (42) and the fixed part (44), the positioning plate (46) being located behind the front leg (20). After the folding chair is stored, the rear leg (30) can abut against the positioning plate (46) so as to be flush with the front leg (20) in the left-right direction, and the seat panel (10) does not interfere with the front leg (20) and the rear leg (30), so that the seat panel (10), the front leg (20), and the rear leg (30) can all be stored in an upright position, and there is an advantage that they can be placed flat after storage.

Description

[Technical field]

[0001] The present invention relates to a folding chair, and in particular to an X-shaped folding chair that can be folded flat. [Background technology]

[0002] Depending on the connection method of the front and rear support legs, folding chairs are divided into ``U-shaped'' folding chairs, in which the front and rear support legs are rotatably connected to the outside of the seat in an ``U'' shape, and ``X-shaped'' folding chairs, in which the front and rear support legs are rotatably connected to both the inside and outside of the seat in an ``X'' shape.

[0003] When a "L"-shaped folding chair is in the stored state, the front and rear support legs are folded over each other and cannot be stored on the same plane. Furthermore, because the front and rear support legs are hingedly connected to both side edges of the seat plate, the stored seat plate has an angle with the front and rear support legs. In other words, after storage, the front and rear support legs and the seat plate are on different planes, so the folding chair cannot be flat when stored and is also thick.

[0004] In the conventional X-shaped folding chair, the seat is folded over either the front or rear support legs when stored, so that the front and rear support legs and the seat are on different planes after storage, and the thickness is also large and it cannot be flattened. In addition, in the partially improved X-shaped folding chair, a relief groove is provided on the seat to increase the storage angle of the seat, which can reduce the thickness of the folding chair after storage to a certain extent, but the seat still abuts the front and rear support legs and their connection points, and the stored seat still has some angle with the front and rear support legs, so it cannot be stored completely flat, and providing the relief groove on the seat also reduces the strength of the seat to a certain extent. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention overcomes the shortcomings of the prior art and provides a folding chair that can be laid flat after folding. The technical aspects of the present invention for solving the technical problems are as follows: [Means for solving the problem]

[0006] The folding chair comprises a seat plate and two X-shaped brackets symmetrically installed on both the left and right sides of the seat plate, the X-shaped brackets including front and rear legs rotatably hinged, the front and rear legs being located on the outside of the seat plate, the rear legs being interposed between the side edge of the seat plate and the front legs in the lateral extension direction of the seat plate, and the upper ends of the rear legs being rotatably hinged to a front location of the outer edge of the seat plate, the folding chair further comprises slide links symmetrically installed on both sides of the seat plate, the slide links including a slide portion slidably connected to the side edge of the seat plate, a fixed portion connected to the front legs, and a positioning plate connected between the slide portion and the fixed portion, the positioning plate being located rearward of the front legs, and after the folding chair is stored, the rear legs can abut against the positioning plate so as to be flush with the front legs in the left-right direction. In the folding chair of the present invention, the front legs and rear legs are each located on the outside of the seat board, the front legs and the seat board are connected by a slide link, and a positioning plate is provided behind the front legs.By doing so, after the folding chair is stored, the rear legs can abut against the positioning plate so that they are flush with the front legs on the left and right sides.Furthermore, since the seat board does not interfere with the front and rear legs, the seat board, front legs and rear legs can be folded into a vertical position, which has the advantage that the folding chair can be placed flat after folding, without compromising the strength of the seat board.

[0007] In a preferred embodiment, the seat includes a plastic plate having a vertically downward edge around the periphery, and a frame located inside the edge, and a crimped edge is provided at the bottom of the frame, which wraps around the edge from below to the outside and crimps the lower edge of the edge. The seat uses a plastic plate, which has a very small thickness, saves material, and makes the product lighter, but the conventional structure with a recess cannot use the structure of the plastic plate. The improved structure of the present invention allows the plastic folding chair to be stored flat and achieves zero breakthrough.

[0008] In a preferred embodiment, the sliding part includes a connecting plate connected to the positioning plate and a sliding pin connected to the connecting plate, and a longitudinal sliding groove is provided on the side edge of the seat plate corresponding to the sliding pin, and the sliding pin protrudes into the frame. Since the sliding connection between the sliding part and the seat plate is realized by the sliding pin and the longitudinal sliding groove, the structure is simple and the assembly is easy.

[0009] In a preferred embodiment, the side edge of the seat plate is provided with a stopper pin at the rear side of the longitudinal slide groove for engaging the slide pin after the folding chair is unfolded.

[0010] In a preferred embodiment, the sliding part includes a connecting plate connected to the positioning plate and a sliding bush connected to the connecting plate by a connecting pin, the sliding bush is rotatable relative to the connecting plate, the sliding bush is fitted into the side edge of the seat plate from below, the sliding bush and the side edge of the seat plate are connected by sliding engagement, the side edge of the seat plate is provided with a stopper structure corresponding to the sliding part, and the stopper structure locks the sliding part after the folding chair is unfolded. Since the sliding bush is rotatable, it is realized that the sliding bush rotates a certain angle together with the seat plate when the seat plate is stored.

[0011] In a preferred embodiment, the inner surface of the sliding bush is provided with a lining with a pressing strip, and the inner edge of the frame is provided with a pressing shoulder, the pressing strip is located above the pressing shoulder to restrict the sliding bush in the vertical direction. The sliding bush fits into the side edge of the seat plate from below, and the pressing strip engages the pressing shoulder from above, so that the sliding bush and the side edge of the seat plate are stably connected to each other.

[0012] In a preferred embodiment, the fixing part is a flat plate structure and is connected to the inner edge of the front leg, the fixing part, the positioning plate and the connecting plate form a U-shaped groove, and the rear leg is received in the U-shaped groove after the folding chair is stowed.

[0013] In a preferred embodiment, the sliding part is provided with a sliding shaft, a rail groove is provided on the inside or outside of the side edge of the seat plate, the sliding shaft is slidably fitted into the rail groove, the sliding part is configured in a C-shape, the sliding part is hooked onto the side edge of the seat plate from below, and a stopper pin is provided at the rear part of the side edge of the seat plate to lock the sliding part after the folding chair is unfolded. It is a novel structure that the sliding part is hooked onto the side edge of the seat plate and slides by fitting the sliding shaft into the rail groove.

[0014] In a preferred embodiment, the lower edge of the side edge of the seat plate is provided with a bayonet at the rear side, and the slide engages with the bayonet after the folding chair is unfolded. Because the bayonet engages with the slide, the seat plate is more stable when fully unfolded.

[0015] In a preferred embodiment, the slide portion comprises a bottom frame connected to the lower part of the side edge of the positioning plate and a guide protrusion connected to the upper part of the side edge of the positioning plate, a notch is provided at the top of the bottom frame, the side edge of the seat plate is supported by the bottom frame, the notch restrains the side edge of the seat plate from below, the side edge of the seat plate is provided with a rail groove corresponding to the guide protrusion, and the guide protrusion is slidably fitted into the rail groove. The guide protrusion and the bottom frame cooperate to hold the side edge of the seat plate from above and below, resulting in a novel structure, which makes the structure of the side edge of the seat plate simpler and easier to manufacture.

[0016] In a preferred embodiment, a stopper block is provided on the side edge of the seat plate at the rear side of the rail groove, and a stopper pin is provided on the side edge of the seat plate at a rear portion, and after the folding chair is unfolded, the stopper block engages the guide protrusion, and the stopper pin engages the bottom frame.

[0017] In a preferred embodiment, the fixing portion is inserted into the front leg from the rear side of the front leg.

[0018] In a preferred embodiment, a downwardly recessed step is formed between the upper surface of the plastic plate and the edge, or the upper surface of the plastic plate and the edge are sequentially connected via a downwardly recessed step and a flange protruding laterally, or a downwardly recessed step is formed between the upper surface of the plastic plate and the edge, and flanges protruding outward are provided at the tops of the left and right edges, or a downwardly recessed step is formed between the left and right sides of the upper surface of the plastic plate and the edge, and flanges protruding outward are provided at the tops of the left and right edges. The step and flange not only increase the strength of the plastic plate, but also increase the support area of ​​the seat plate and improve the solidity of the product. [Brief description of the drawings]

[0019] The present invention will be further described below with reference to the drawings and examples. [Figure 1] 1 is a perspective view showing a first embodiment of a folding chair according to the present invention; [Diagram 2] FIG. 2 is another perspective view of the folding chair shown in FIG. 1. [Diagram 3] FIG. 2 is a partial exploded view of the folding chair shown in FIG. [Figure 4] 2 is a cross-sectional view of a slide link portion of the folding chair shown in FIG. 1. [Diagram 5] 2A to 2C are schematic diagrams showing the folding process of the folding chair shown in FIG. 1. [Figure 6] FIG. 2 is a cross-sectional view of the folding chair shown in FIG. 1 after it has been folded. [Figure 7] 2 is a local cross-sectional view of the seat plate of the folding chair shown in FIG. 1. [Figure 8] 1. FIG. 4 is a schematic diagram showing a modified example of the seat structure of the folding chair shown in FIG. [Figure 9] 1. FIG. 4 is a schematic diagram showing a further modified example of the seat structure of the folding chair shown in FIG. [Figure 10] FIG. 4 is a partial schematic view showing a second embodiment of a folding chair according to the present invention (slide link portion). [Figure 11] 11 is a cross-sectional view of a slide link portion of the folding chair shown in FIG. 10. [Figure 12] FIG. 11 is a cross-sectional view of the folding chair shown in FIG. 10 after it has been folded. [Figure 13] FIG. 11 is a perspective view showing a third embodiment of a folding chair according to the present invention. [Figure 14] FIG. 14 is another perspective view of the folding chair shown in FIG. [Figure 15] FIG. 14 is a cross-sectional view of the folding chair shown in FIG. 13 after it has been folded. [Figure 16] 14 is a schematic diagram showing a modified example of the seat structure of the folding chair shown in FIG. 13. [Figure 17] FIG. 11 is a schematic partial view showing a fourth embodiment of a folding chair according to the present invention (slide link portion). [Figure 18]FIG. 18 is a local cross-sectional view of the folding chair shown in FIG. 17 (at a slide link location). [Figure 19] FIG. 18 is a perspective view showing a slide link of the folding chair shown in FIG. [Figure 20] 18 is a schematic diagram showing another partial view of the folding chair shown in FIG. 17 (slide link portion). [Figure 21] 18 shows a further partial schematic diagram of the folding chair shown in FIG. 17 (at the slide link location). [Figure 22] FIG. 18 is a cross-sectional view of the folding chair shown in FIG. 17 after it has been folded. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In describing the present invention, the positions or positional relationships indicated by terms such as "front", "back", "left", "right", "direction", etc., are merely for the purpose of facilitating the description of the present invention, and do not expressly or imply that the devices shown have a particular position or must be configured or operated in a particular position, and therefore should not be construed as limiting the present invention. Those skilled in the art should understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0021] Example 1 1 to 6, the X-shaped folding chair includes a seat panel 10 and two X-shaped brackets arranged symmetrically on both the left and right sides of the seat panel and supporting the seat panel, the X-shaped brackets including front legs 20 and rear legs 30 that are rotatably hingedly connected, the front legs 20 and rear legs 30 both being located on the outside of the seat panel 10, and the rear legs 30 being interposed between the side edges of the seat panel 10 and the front legs 20, i.e., in the direction of extension outward of the seat panel, the side edges of the seat panel, the rear legs and the front legs, respectively. The upper ends of the rear legs 30 are hinged to be rotatable at the front locations on the outer sides of the seat plate 10, and further include slide links 40 that are disposed symmetrically on the outer sides of the seat plate and are connected between the front legs 20 and the seat plate 10, and the slide links 40 have slide parts 42 slidably connected to the side edges of the seat plate 10, fixed parts 44 connected to the front legs 20, and a positioning plate 46 connected between the slide parts and the fixed parts. Since the positioning plate 46 is located on the rear side of the front legs 20, after the folding chair is stored, the rear legs 30 can abut against the positioning plate 46 so as to be flush with the front legs in the left-right direction. In other words, since the front legs are on the outside of the rear legs and the rear legs are on the outside of the seat, when stored, the front legs, rear legs and seat do not interfere with each other; in other words, they can be folded horizontally or vertically so that the three are positioned on approximately the same plane when stored; further, the front legs and rear legs overlap at the connection points with the seat, so that they also overlap in height when folded.

[0022] 6, the seat panel 10 preferably includes a plastic plate 11 having a vertically downward edge 112 around the periphery, and a frame 12 located inside the edge, and a crimped edge 121 is provided at the bottom of the frame, which wraps around the outside of the edge 112 from below and crimps and fixes the lower edge of the edge. As a result, the frame is connected to the periphery of the plastic plate, increasing the strength of the seat panel, and the frame supports the sliding part 42, so that a thin sheet material formed by thermoforming can be used as the plastic plate.

[0023] Preferably, the sliding part 42 includes a connecting plate 421 connected to the positioning plate 46 and a sliding pin 422 connected to the connecting plate 421, and a longitudinal sliding groove 13 corresponding to the sliding pin 422 is provided on the side edge of the seat plate 10, and the sliding pin 422 protrudes into the inside of the frame 12. Specifically, in this embodiment, a cavity is formed inside the frame 12, and notches are provided in the edge part 112 and the frame 12, respectively, to form the longitudinal sliding groove 13, and the sliding pin 422 protrudes into the inside of the frame 12 through the notches, so that the frame 12 can provide a supporting force for the sliding pin 422.

[0024] Preferably, the side edge of the seat plate 10 is provided with a stopper pin 14 at the rear side of the longitudinal slide groove 13 for locking the slide pin 422 after the folding chair is unfolded, so that the folding chair is fully unfolded. It should be understood that the chair can be fully unfolded by the movement of the slide pin 422 to the tip of the longitudinal slide groove, and a stopper pin may not be provided.

[0025] Preferably, the fixed part 44 has a flat plate structure and is connected to the inner edge of the front leg, the fixed part 44, the positioning plate 46 and the connecting plate 421 form a U-shaped groove 48, and the rear leg 30 is accommodated in the U-shaped groove 48 after the folding chair is stored.

[0026] Preferably, referring to Fig. 7, the upper surface of the plastic plate 11 and the edge 112 are connected in sequence by a step 114 recessed downward and a flange 116 protruding outward from the side. Of course, as shown in Fig. 8, the edge may be directly formed on the outer edge of the upper surface of the plastic plate without providing the step and flange. Alternatively, as shown in Fig. 9, a step 114 recessed downward is formed between the upper surface of the plastic plate 11 and the edge 112.

[0027] Referring to FIG. 5, when the folding chair of the present invention is stored, the seat 10 moves backward (to the right side of the figure) and gradually flips downward, and the slide pin 422 gradually moves to the end of the elongated slide groove 13. After final storage is completed, the seat, front legs and rear legs are all placed vertically, so that the folding chair can be folded flat in the folded state as shown in FIG. 6, thereby minimizing the overall thickness.

[0028] Example 2 10 to 12, the difference between the second embodiment and the first embodiment is the structure of the slide portion 42. Specifically, in the second embodiment, the slide portion 42 includes a connecting plate 421 connected to the positioning plate 46 and a slide bush 423 connected to the connecting plate 421 by a connecting pin 424, the slide bush 423 is rotatable with respect to the connecting plate 421, is fitted into the side edge of the seat plate 10 from below, and the slide bush 423 is connected to the side edge of the seat plate by sliding fit. Also, the fixed portion 44, the positioning plate 46, and the connecting plate 421 form a U-shaped groove 48 in the same manner as in the first embodiment.

[0029] Preferably, a stopper structure is provided on the side edge of the seat plate 10 corresponding to the slide portion, and the stopper structure locks the slide portion 42 after the folding chair is unfolded.

[0030] Preferably, the inner surface of the slide bush 423 is provided with a lining 425 having a pressing strip 426, and a pressing shoulder 122 is provided at the inner edge of the frame 12, the pressing strip 426 being located above the pressing shoulder 122 to limit the slide bush 423 in the vertical direction.

[0031] Example 3 13 to 15, the difference between Example 3 and Example 1 is the configuration of the slide portion 42. Specifically, in Example 3, the slide portion 42 has a C-shaped structure, the slide portion 42 is hooked onto the side edge of the seat plate 10 from below, a slide shaft 427 is provided on the slide portion 42, a rail groove 15 is provided on the inner side of the side edge of the seat plate 10 (the rail groove is directly molded in the frame 12), and the slide shaft 427 is slidably fitted into the rail groove 15. As can be seen from FIG. 16, the rail groove 15 may be provided on the outer side of the side edge of the seat plate 10.

[0032] Preferably, a stopper pin is provided at the rear of the side edge of the seat plate 10 for locking the slide portion after the folding chair is unfolded.

[0033] Preferably, a bayonet 16 is provided on the rear lower edge of the side edge of the seat panel 10, and the slide portion 42 engages with the bayonet 16 after the folding chair is unfolded.

[0034] Preferably, the fastener 44 is inserted into the front leg 20 from the rear side of the front leg.

[0035] Preferably, downwardly recessed step portions 114 are formed between the left and right sides of the upper surface of the plastic plate 11 and the edge portions 112, and the left and right side edge portions 112 are provided at their tops with outwardly protruding flanges 116.

[0036] Example 4 17 to 22, the difference between the fourth embodiment and the third embodiment is the configuration of the slide portion 42. Specifically, in the fourth embodiment, the slide portion 42 includes a bottom frame 428 connected to the lower part of the side edge of the positioning plate 46 and a guide protrusion 429 connected to the upper part of the side edge of the positioning plate 46, a notch 4281 is provided at the top of the bottom frame 428, the side edge of the seat plate 10 is supported by the bottom frame 428, the notch 4281 restrains the side edge of the seat plate 10 from below, the side edge of the seat plate is provided with a rail groove 17 corresponding to the guide bump 429, and the guide protrusion 429 is slidably fitted into the rail groove 17. The guide tab 429 and the bottom chassis 428 respectively restrict the side edge of the seat plate from the up-down direction.

[0037] Preferably, a stopper block 18 for locking the guide protrusion 429 after the folding chair is unfolded is provided on the side edge of the seat plate 10 on the rear side of the rail groove 17, and a stopper pin 19 for locking the bottom frame 428 is provided on the rear part of the side edge of the seat plate. Of course, since positioning in the unfolded state is possible even when the guide protrusion 429 abuts against the rear end wall of the rail groove 17, the stopper block 18 and the stopper pin 19 do not have to be provided.

[0038] The above description is merely a preferred embodiment of the present invention, and therefore the scope of the present invention cannot be limited thereby; that is, any equivalent changes and modifications based on the claims and the contents of the specification of the present invention should be included within the comprehensive scope of the present invention. [Industrial Applicability]

[0039] The present invention discloses a folding chair, comprising a seat plate, two X-shaped brackets symmetrically provided on the left and right sides of the seat plate, the X-shaped brackets having front and rear legs rotatably hinged thereto, the front and rear legs being respectively located on the outsides of the seat plate, the rear legs being interposed between the side edges of the seat plate and the front legs, and the upper ends of the rear legs being rotatably hinged to the front portions of the outer edges of the seat plate, the folding chair further comprising a slide link comprising a slide part slidably connected to the side edges of the seat plate, a fixed part connected to the front legs, and a positioning plate connected between the slide part and the fixed part, the positioning plate being located on the rear side of the front legs. After the folding chair is stored, the rear legs can abut against the positioning plate so that they are flush with the front legs in the left-right direction, and the seat does not interfere with the front and rear legs, so the seat, front and rear legs can all be stored in an upright position and can be laid flat after storage, which has the advantage of being industrially applicable.

Claims

1. A folding chair comprising a seat plate and two X-shaped brackets symmetrically installed on both left and right sides of the seat plate, the X-shaped brackets including front and rear legs rotatably hinged, the front and rear legs being located on the outside of the seat plate, the rear legs being interposed between the side edge of the seat plate and the front legs in the lateral extension direction of the seat plate, the upper ends of the rear legs being rotatably hinged to a front location of the outer edge of the seat plate, and the chair further comprising slide links symmetrically installed on both sides of the seat plate, the slide links comprising a slide portion slidably connected to the side edge of the seat plate, a fixed portion connected to the front legs, and a positioning plate connected between the slide portion and the fixed portion, the positioning plate being located rear of the front legs, and after the folding chair is stored, the rear legs can abut against the positioning plate so as to be flush with the front legs in the left-right direction.

2. The folding chair according to claim 1, characterized in that the seat panel includes a plastic plate having a vertically downward edge around the periphery, and a frame positioned inside the edge, and a crimped edge is provided on the bottom of the frame that wraps around from the underside to the outside of the edge and crimps and fixes the lower edge of the edge.

3. The folding chair according to claim 2, characterized in that the sliding portion includes a connecting plate connected to the positioning plate and a sliding pin connected to the connecting plate, and a longitudinal sliding groove is provided on the side edge of the seat plate corresponding to the sliding pin, and the sliding pin protrudes into the inside of the frame.

4. 4. The folding chair according to claim 3, wherein a stopper pin is provided on the side edge of the seat plate at the rear side of the longitudinal slide groove to engage the slide pin after the folding chair is unfolded.

5. The folding chair of claim 2, characterized in that the sliding portion includes a connecting plate connected to the positioning plate and a slide bush connected to the connecting plate by a connecting pin, the slide bush is rotatable relative to the connecting plate, the slide bush fits into the side edge of the seat plate from below, the slide bush and the side edge of the seat plate are connected by sliding fit, the side edge of the seat plate is provided with a stopper structure corresponding to the sliding portion, and the stopper structure engages the sliding portion after the folding chair is unfolded.

6. 6. The folding chair according to claim 5, characterized in that the inner surface of the sliding bush is provided with a lining with a pressure strip installed thereon, and the inner edge of the frame is provided with a pressure shoulder, the pressure strip being located above the pressure shoulder to limit the sliding bush in the vertical direction.

7. The folding chair according to claim 3 or 5, characterized in that the fixing part has a flat plate structure and is connected to the inner edge of the front leg, the fixing part, the positioning plate and the connecting plate form a U-shaped groove, and the rear leg is accommodated in the U-shaped groove after the folding chair is stored.

8. The folding chair according to claim 2, characterized in that the sliding portion is provided with a slide shaft, a rail groove is provided on the inside or outside of the side edge of the seat plate, the slide shaft is slidably fitted into the rail groove, the sliding portion is configured in a C-shape, the sliding portion is hooked onto the side edge of the seat plate from below, and a stopper pin is provided at a rear portion of the side edge of the seat plate to engage the sliding portion after the folding chair is unfolded.

9. 9. The folding chair according to claim 8, wherein a bayonet is provided on the rear side of the lower edge of the side edge of the seat panel, and the sliding portion engages with the bayonet after the folding chair is unfolded.

10. 3. The folding chair of claim 2, wherein the sliding portion comprises a bottom frame connected to the lower part of the side edge of the positioning plate and a guide protrusion connected to the upper part of the side edge of the positioning plate, a notch is provided at the top of the bottom frame, the side edge of the seat plate is supported by the bottom frame, the notch restrains the side edge of the seat plate from below, the side edge of the seat plate is provided with a rail groove corresponding to the guide protrusion, and the guide protrusion is slidably fitted into the rail groove.

11. The folding chair according to claim 10, characterized in that a stopper block is provided on the side edge of the seat plate at the rear side of the rail groove, and a stopper pin is provided on the side edge of the seat plate at a rear portion, and after the folding chair is unfolded, the stopper block engages the guide protrusion portion, and the stopper pin engages the bottom frame.

12. 11. The folding chair according to claim 8 or 10, wherein the fixing portion is inserted into the front leg from a rear side of the front leg.

13. The folding chair of claim 2, characterized in that a downwardly recessed step is formed between the upper surface of the plastic plate and the edge, or the upper surface of the plastic plate and the edge are sequentially connected via a downwardly recessed step and a laterally protruding flange, or a downwardly recessed step is formed between the upper surface of the plastic plate and the edge, and an outwardly protruding flange is provided at the top of the edges on both the left and right sides, or a downwardly recessed step is formed between the left and right sides of the upper surface of the plastic plate and the edge, and an outwardly protruding flange is provided at the top of the edges on both the left and right sides.

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