Packaging box

Abstract

To provide a robust packaging box in which side panels can be easily held upright. [Solution] A packaging box 1 is assembled by folding a sheet material, and the sheet material has front and rear side sections 3 consisting of outer panels 12, 16, upper edge panels 13, 17, and inner panels 14, 18 connected to the front and rear sides of a rectangular central panel via folding parts, and left and right side sections 4 consisting of the outer panel, upper edge panel, and inner panel connected to the left and right sides. A first engagement protrusion 31 is provided on the left and right sides of the inner panel of the front and rear side sections. A connecting plate 20 is connected between the adjacent front and rear side sections and the left and right side sections via folding parts, and an insert plate 21 is connected to the front and rear sides of the inner panel of the left and right side sections. The inner panel of the left and right side sections is cut to provide a first surface section. When the folding parts of the sheet material are folded and assembled, the first surface section is released from the inner panel of the left and right side sections to form a first holding piece. A hole formed in the inner panel of the left and right side sections forms a first engagement recess 61. The first engagement protrusion is engaged with the first engagement recess to hold the front and rear side sections and the left and right side sections upright.

Description

[Technical field]

[0001] The present invention relates to a packaging box that is easy to assemble and sturdy. [Background technology]

[0002] Conventionally, packaging boxes have been known which are formed by erecting side panels consisting of outer and inner panels around a rectangular bottom panel. For example, a box has been known in which an outer panel, an upper edge panel, an inner panel, and a laminated panel are connected to the left and right sides and the front and rear sides of the bottom panel of a single blank sheet via folded sections, connecting panels are connected between the left and right outer panels and the front and rear outer panels, an extension panel is connected to the front and rear inner panels via folded sections, protrusions are provided on the front and rear end edges of the left and right inner panels and the laminated panels, and a cutout is provided near the folded sections between the front and rear inner panels and the extending panels. In assembling this packaging box, the front and rear side panels are raised relative to the bottom panel, the extension panels and connecting panels are positioned between the outer and inner panels of the left and right side panels, the front and rear and left and right laminated panels are stacked on the bottom panel, and the protrusions are engaged with the cutouts to restrict the swinging of the front and rear and left and right inner panels, thereby completing the assembly (see Patent Document 1). [Prior art documents] [Patent documents] [Patent Document 1] Utility Model Registration No. 3220875

[0003] However, with the above-mentioned packaging box, there have been cases where the side panels could not be maintained upright because the protrusion could not be inserted into the cutout, the protrusion could bend and break when being inserted into the cutout, or the locked state could be released. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above problems. The object of the present invention is to provide a sturdy packaging box that can easily hold the side panels of the packaging box in an upright position. [Means for solving the problem]

[0005] The problem to be solved by the present invention is as described above, and the means for solving this problem will now be described.

[0006] In the first invention, a packaging box is assembled by folding a sheet material, The sheet material has front and rear side portions connected to front and rear edges of a rectangular central plate, and left and right side portions connected to left and right edges of the central plate, the front and rear side portions have an outer plate, an upper edge plate, and an inner plate connected in order to the front and rear edges of the central plate via bent portions, and first engagement protrusions are provided on the left and right edges of the inner plate of the front and rear side portions, the left and right side portions have an outer plate, an upper edge plate, and an inner plate connected in order to the left and right edges of the central plate via bent portions, and connecting plates are provided between the left and right edges of the outer plate of the adjacent front and rear side portions and the front and rear edges of the outer plate of the left and right side portions via bent portions. a connecting plate is connected to the front and rear edges of the inner plate of the left and right side portions via a bent portion, the inner plate of the left and right side portions is cut into the inner plate of the left and right side portions from the bent portion between the inner plate of the left and right side portions and the insert plate to provide a first surface portion, the bent portion of the sheet material is folded to erect the left and right side portions against the central plate, the connecting plate is folded toward the inside of the box, and the insert plate is folded into an angled shape, the connecting plate and the insert plate are sandwiched between the outer plate and the inner plate of the front and rear side portions, and the front and rear side portions are erected against the central plate, This packaging box is characterized in that, when the insertion plate is bent into an angle shape, the first surface portion is released from the inner plate of the left and right side portions to form a first retaining piece that is positioned between the outer plate and the inner plate of the left and right side portions, and together with the formation of the first retaining piece, a hole formed in the inner plate of the left and right side portions forms a first engagement recess, and the first engagement protrusion is engaged with the first engagement recess to maintain the upright position of the front and rear side portions and the left and right side portions.

[0007] The second invention is a packaging box which is the first invention, characterized in that the first surface portion has an inclined cut-out portion which extends from the folded portion between the inner panel of the left and right side portions and the insertion plate toward the opposite side to the side where the inner panel of the left and right side portions is connected to the upper edge panel, and a sloped portion of the same shape is formed in the first engagement recess, and the first engagement convex portion abuts against and engages with the sloped portion of the first engagement recess.

[0008] The third invention is the first or second invention, wherein a pressure plate is connected via a folding portion to the side opposite to the side where the upper edge plate of the inner plate of the front and rear side portions is connected, second engagement protrusions are provided on the left and right sides of the pressure plate of the front and rear side portions, a pressure plate is connected via a folding portion to the side opposite to the side where the upper edge plate of the inner plate of the left and right side portions is connected, the folding portions of the sheet material are folded to erect the left and right side portions against the central plate, the pressure plate is overlapped on the central plate, the connecting plate is folded toward the inside of the box, the insertion plate is folded at an angle, the connecting plate and the insertion plate are sandwiched between the outer plate and the inner plate of the front and rear side portions to erect the front and rear side portions against the central plate, the pressure plate is overlapped on the central plate, and the second engagement protrusions are engaged with the first engagement recesses to maintain the front and rear side portions and the left and right side portions upright.

[0009] The fourth invention is the third invention, wherein a second surface portion is provided by cutting into the inner panels of the left and right side portions up to the folded portions between the inner panels of the left and right side portions and the pressure plate, the folded portions of the sheet material are folded to erect the left and right side portions against the central plate, and when the pressure plate is overlapped on the central plate, the second surface portion is released from the inner panels of the left and right side portions and positioned between the outer panels and the inner panels of the left and right side portions, and holes formed in the inner panels of the left and right side portions form second engagement recesses, and the second engagement protrusions are engaged with the second engagement recesses to maintain the front and rear side portions and the left and right side portions erected.

[0010] The fifth invention is the third invention, wherein the inner panels of the left and right side portions are cut to provide a third surface adjacent to the first surface, the folded portions of the sheet material are folded to erect the left and right side portions against the central panel, and when the pressure plate is placed on top of the central panel, the third surface portion is released from the inner panels of the left and right side portions to form a second retaining piece, which is located between the outer panels and the inner panels of the left and right side portions and below the first engagement recess, and wherein together with the formation of the second retaining piece, a hole formed in the inner panels of the left and right side portions forms a first engagement recess.

[0011] The sixth invention is the fourth invention, wherein the inner panels of the left and right side portions are cut to provide a third surface adjacent to the first surface, the folded portions of the sheet material are folded to erect the left and right side portions against the central panel, and when the pressure plate is placed on top of the central panel, the third surface portion is released from the inner panels of the left and right side portions to form a second retaining piece, which is located between the outer panels and the inner panels of the left and right side portions and below the first engagement recess, and wherein together with the formation of the second retaining piece, a hole formed in the inner panels of the left and right side portions forms a first engagement recess. Effect of the Invention

[0012] According to the present invention, the side panels of the packaging box can be easily held upright, resulting in a sturdy packaging box.

[0013] [Brief description of the drawings]

[0014] [Figure 1] 1 is a simplified perspective view of a packaging box 1 according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a plan view showing the sheet material 2 of the packaging box 1. [Diagram 3] FIG. 2 is a simplified perspective view showing the packaging box 1 in the process of being assembled. [Figure 4] An enlarged view of a portion near FIG. 2A. [Diagram 5] An enlarged view of a portion near FIG. 1B. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, an embodiment of the present invention will be described. As shown in FIG. 1, the assembled packaging box 1 of this embodiment has front and rear side portions 3 on the front and rear sides of a central plate 11, left and right side portions 4 on the left and right sides, and an opening at the top.

[0016] The packaging box 1 can be made of thick paper such as paperboard or corrugated cardboard, but in this embodiment, a paperboard having a thickness of about 0.4 mm is used. The packaging box 1 is formed by assembling sheet materials 2 shown in FIG. 2, and the sheet materials 2 are shown with the front side of the page as the inner side of the box. In the present embodiment, the folding portion refers to a streak-like portion provided for folding the sheet material. Examples of the folding portion include a crease, a cut line, a perforation line, etc., and are illustrated by dashed lines.

[0017] First, a description will be given of the sheet material 2 shown in Fig. 2. The packaging box 1 shown in Fig. 1 is completed by folding and assembling the sheet material 2.

[0018] For the sake of explanation, the short sides of the center plate 11 will be referred to as the front and rear sides, and the long sides of the center plate 11 will be referred to as the left and right sides. In addition, when the packaging box 1 is assembled and placed with the center plate 11 facing down, the up-down direction will be referred to as the center plate 11 side being the lower side and the opening side being the upper side.

[0019] The central plate 11 of the sheet material 2 forms the bottom of the packaging box 1 , and the outer plates 12 , the upper edge plate 13 , the inner plate 14 and the pressing plate 15 form the front and rear side portions 3 . Additionally, the outer plate 16 , the upper edge plate 17 , the inner plate 18 and the pressing plate 19 constitute the left and right side portions 4 .

[0020] The sheet material 2 has outer plates 12 connected to the front and rear sides of a rectangular central plate 11 via bent portions. An upper edge plate 13 is connected to the outer plate 12 via a bent portion. In this embodiment, the front-to-rear width of the upper edge plate 13 is set to 6 mm. Further, the inner plate 14 is connected to the side of the upper edge plate 13 opposite to the side where the outer plate 12 is connected via a bent portion. On the left and right end edges of the inner plate 14 opposite to the side where the inner plate 14 is connected to the upper edge plate 13, first engagement protrusions 31 having a generally U-shape and protruding from the left and right edges are provided. The first engagement protrusions 31 are portions that engage with first engagement recesses 61 described below in the assembly process. In this embodiment, the front-to-rear width of the first engagement protrusions 31 is set to 13 mm, and the left-to-right width (the length protruding from the left and right end edges of the inner plate 14) is set to 2 mm. Further, a pressing plate 15 is connected via a bent portion to the side opposite to the side where the upper edge plate 13 of the inner plate 14 is connected. A substantially U-shaped second engagement protrusion 32 protruding from the left and right edges is provided on the left and right edges of the pressing plate 15. This second engagement protrusion 32 is a portion that engages with a first engagement recess 61 and a second engagement recess 62 described below in the assembly process. In this embodiment, the front-to-rear width of the second engagement protrusion 32 is set to 8 mm, and the left-to-right width (the length protruding from the left and right edges of the inner plate 14) is set to 2 mm.

[0021] Further, outer plates 16 are connected to the left and right sides of the center plate 11 via bent portions. An upper edge plate 17 is connected to the outer plate 16 via a bent portion. In this embodiment, the left and right width of the upper edge plate 17 is set to 6 mm. An inner plate 18 is connected to the upper edge plate 17 via a bent portion on the side opposite to the side to which the outer plate 16 is connected. Further, a pressing plate 19 is connected to the inner plate 18 via a bent portion on the side opposite to the side to which the upper edge plate 17 is connected.

[0022] Additionally, a connecting plate 20 is connected to the adjacent outer plates 12 and 16 via a bent portion. A bent portion is formed in the connecting plate 20 in the diagonal direction from a corner of the central plate 11, and the connecting plate 20 is formed so that when the outer plates 12 and 16 are erected against the central plate 11, the connecting plate 20 is folded from this bent portion toward the inside of the box. Further, an insertion plate 21 is connected to the front and rear sides of the inner plate 18 via bent portions.

[0023] Further, a first surface portion 41 is provided on the inner plate 18 by cutting the inner plate 18 from the bent portion between the inner plate 18 and the insertion plate 21 . 4, the first surface portion 41 is divided into an inclined cutout portion 41a that extends from the vicinity of the bent portion between the inner plate 18 and the insertion plate 21 toward the side opposite to the side where the inner plate 18 is connected to the upper edge plate 17, a cutout portion 41c that is connected to the inclined cutout portion 41a and extends linearly toward the pressing plate 19, a short cutout portion 41b that extends from the end of the inclined cutout portion 41a opposite to the side where the cutout portion 41c is connected to the bent portion between the inner plate 18 and the insertion plate 21, and a cutout portion 41d that extends from the end of the cutout portion 41c toward the insertion plate 21. In this embodiment, the front-rear width W1 of the first surface portion 41 from the imaginary extension line of the bent portion between the inner plate 18 and the insertion plate 21 to the cutout portion 41c is 5.5 mm, which is approximately the same as the left-right width (6 mm) of the upper edge plate 17. The length of the cutout 41c is 5 mm, and the length of the cutout 41b is 1.5 mm.

[0024] Further, the inner plate 18 is provided with a second surface portion 42 that is connected to the cut portion 41c of the first surface portion 41 and cuts into the bent portion between the inner plate 18 and the pressing plate 19. The second surface portion 42 is partitioned by a cutout portion 42a continuing to the cutout portion 41c of the first surface portion 41, a cutout portion 42b parallel to the bent portion between the inner plate 18 and the pressing plate 19, and a short cutout portion 42c extending from the cutout portion 42b to the bent portion between the inner plate 18 and the pressing plate 19. In this embodiment, the length of the cutout portion 42a is 4 mm, the length of the cutout portion 42b is 5 mm, and the length of the cutout portion 42c is 1.5 mm.

[0025] Further, the inner plate 18 is provided with a third surface portion 43 adjacent to the first surface portion 41 by cutting into the inner plate 18 . The third surface portion 43 is divided into a cutout portion 41d common to the first surface portion 41, a cutout portion 43a connected to the cutout portion 41d and separating the third surface portion 43 from the insertion plate 21, and a cutout portion 42a common to the second surface portion 42. In this embodiment, the left-right width W2 of the third surface portion 43 from the imaginary extension line of the bend between the inner plate 18 and the pressure plate 19 to the cut-out portion 41d is 5.5 mm, which is approximately the same as the left-right width of the upper edge plate 17 (6 mm).

[0026] Further, the inner plate 18 is cut into a generally U-shape from the bent portion between the inner plate 18 and the pressing plate 19 to provide a fourth surface 44. The left-right width W3 of the fourth surface 44 from an imaginary extension line of the bent portion between the inner plate 18 and the pressing plate 19 to the cut is 5.5 mm, which is approximately the same as the left-right width of the upper edge plate 17 (6 mm).

[0027] Next, the process of assembling the sheet material 2 will be described. First, as shown in Fig. 3, the bent portion between the central plate 11 and the outer plate 16 is bent to make the outer plate 16 stand up relative to the central plate 11. Also, the bent portion between the outer plate 12 and the connecting plate 20 is bent to make the connecting plate 20 stand up. Next, the bent portion between the outer plate 16 and the upper edge plate 17 and the bent portion between the upper edge plate 17 and the inner plate 18 are bent to make the inner plate 18 and the outer plate 16 face each other. In addition, the bent portion between the inner plate 18 and the pressing plate 19 is folded, and the pressing plate 19 is placed on the central plate 11. At this time, as shown in FIG. 5, the second surface portion 42 is separated from the inner plate 18 in conjunction with the bending operation of the pressing plate 19 and is positioned on the opposite side to the pressing plate 19. The third surface portion 43 also becomes detached from the inner plate 18 in conjunction with the bending operation of the presser plate 19, and this detached portion forms a second holding piece 52. The second holding piece 52 is positioned on the opposite side to the presser plate 19, that is, between the inner plate 18 and the outer plate 16. Since the left-right width W2 of the second holding piece 52 is 5.5 mm and the left-right width of the upper edge plate 17 is 6 mm, if the inner plate 18 attempts to move toward the outer plate 16, its tip abuts against the inner surface of the outer plate 16 to restrict the movement and maintain the space between the inner plate 18 and the outer plate 16.

[0028] Furthermore, when the second surface portion 42 and the third surface portion 43 are separated from the inner plate 18, holes formed in the shapes of the cutout portions 42a, 42b, and 42c in the inner plate 18 form the second engagement recess 62. Furthermore, holes formed in the shapes of the cutout portions 43a, 41d, and 42a form a part (lower side) of the first engagement recess 61.

[0029] Furthermore, the fourth surface portion 44 also becomes detached from the inner plate 18 in conjunction with the bending operation of the presser plate 19, and this detached portion forms a third holding piece 53. The third holding piece 53 is also positioned on the opposite side to the presser plate 19, that is, between the inner plate 18 and the outer plate 16. Since the left-right width W3 of the third holding piece 53 is 5.5 mm and the left-right width of the upper edge plate 17 is 6 mm, if the inner plate 18 attempts to move toward the outer plate 16, its tip abuts against the inner surface of the outer plate 16 to restrict the movement and maintain the space between the inner plate 18 and the outer plate 16.

[0030] Next, the bent portion between the central plate 11 and the outer plate 12 is folded so that the outer plate 12 stands up relative to the central plate 11. Also, the bent portion between the outer plate 16 and the connecting plate 20 is folded, and the diagonal bent portion is folded so that the connecting plate 20 is folded towards the inside of the box. Additionally, the insertion plate 21 is bent at an angle toward the inside of the box. At this time, the first surface portion 41 is released in conjunction with the bending operation of the insertion plate 21 to form a first holding piece 51. This first holding piece 51 is positioned opposite the insertion plate 21, that is, between the inner plate 18 and the outer plate 16. The left-right width W1 of the first retaining piece 51 is 5.5 mm, and the left-right width of the upper edge plate 17 is 6 mm, so that if the inner plate 18 attempts to move toward the outer plate 16, its tip will abut against the inner surface of the outer plate 16, restricting the movement and maintaining the space between the inner plate 18 and the outer plate 16.

[0031] In addition, when the first surface portion 41 is separated from the inner plate 18, the hole shape formed by the inclined cut portion 41a, the cut portion 41b, the cut portion 41c, and the cut portion 41d form a part (upper side) of the first engagement recess 61 in the inner plate 18. 5, in this state, the first engagement recess 61 is configured as a hole formed when the first surface portion 41 and the third surface portion 43 are separated from the inner plate 18. In detail, the hole shape is formed by the inclined cut portion 41a, the cut portion 41b, the cut portion 41c, and the cut portion 42a. The length from the cut portion 41b of the first engagement recess 61 to the lower end of the first engagement recess 61 is 15 mm.

[0032] In addition, the bent portion between the outer plate 12 and the upper edge plate 13, and the bent portion between the upper edge plate 13 and the inner plate 14 are bent to make the inner plate 14 and the outer plate 12 face each other, the bent portion between the inner plate 14 and the pressing plate 15 is bent to overlap the pressing plate 15 on the central plate 11, and the connecting plate 20 and the insert plate 21 are sandwiched between the inner plate 14 and the outer plate 12. At this time, the first engagement protrusion 31 provided on the inner plate 14 engages with the first engagement recess 61 provided on the inner plate 18, and the second engagement protrusion 32 provided on the pressing plate 15 engages with the first engagement recess 61 and the second engagement recess 62 provided on the inner plate 18, thereby maintaining the upright position of the front and rear side portions 3 and the left and right side portions 4.

[0033] The upright holding of the front and rear side portions 3 and the left and right side portions 4 will now be described in detail. When the first engaging protrusion 31 and the second engaging protrusion 32 are fitted into the first engaging recess 61 and the second engaging recess 62, the first engaging protrusion 31 and the second engaging protrusion 32 move toward the first engaging recess 61 and the second engaging protrusion 62 while slightly rubbing against the inner plate 18. At this time, the inner plate 18 is pressed toward the outer plate 16, but the left and right side portions 4 are positioned near the first engaging recess 61 and the second engaging recess 62, as described above, between the outer plate 16 and the inner plate 18, with the first holding piece 51 and the second holding piece 52 positioned near the first engaging recess 61 and the second engaging recess 62. In detail, the lower side of the first engaging recess 61 is in contact with the outer plate 16, and the upper side of the first engaging recess 61 is in contact with the outer plate 16, restricting the movement of the inner plate 18 toward the outer plate 16. Therefore, the inner plate 18 near the first engagement recess 61 and the second engagement recess 62 is restricted from moving toward the outer plate 16, and the first engagement protrusion 31 and the second engagement protrusion 31 can be received in the first engagement recess 61 and the second engagement recess 62, so that the engagement is not incomplete and the engagement can be ensured.

[0034] Furthermore, when the first engagement protrusion 31 and the second engagement protrusion 32 are fitted into the first engagement recess 61 and the second engagement protrusion 62, the first engagement recess 61 has a larger hole shape than the elongated cutout portion as shown in the prior art document mentioned above, so that by moving the first engagement protrusion 31 and the second engagement protrusion 32 closer to the first engagement recess 61, they can be easily fitted into the first engagement recess 61 and the second engagement recess 62 without having to look closely at the hole. On the other hand, the front-rear width of the first engaging protrusion 31 is 13 mm, the length from the cutout 41b of the first engaging recess 61 to the lower end of the first engaging recess 61 is 15 mm, and once the first engaging protrusion 31 is fitted into the cutout 41b, the inclined portion 61a of the first engaging recess 61 abuts against the upper side of the first engaging protrusion 31 to restrict movement, so that even if a large hole is formed, the inner plate 14 does not move and the lock is released. Even after the lock is released, the first holding piece 51 and the second holding piece 52 restrict the movement of the inner plate 18, so that the inner plate 18 does not move toward the outer plate 16 and the lock is released, and the front-rear side portions 3 and the left-right side portions 4 are maintained upright to form a sturdy packaging box.

[0035] Furthermore, when the first engaging protrusion 31 and the second engaging protrusion 32 are fitted into the first engaging recess 61, the inner plate 14 is pushed slightly toward the outer plate 12 and moves, and in this state the first engaging protrusion 31 and the second engaging protrusion 32 are fitted into the first engaging recess 61. Then, when the moved inner plate 14 returns to the inside of the box due to repulsion, the second engaging protrusion 32 also moves together with it and is fitted into and locked in the second engaging recess 62. Therefore, the front and rear side portions 3 and the left and right side portions 4 can be held upright in an extremely simple and strong manner to provide a sturdy packaging box.

[0036] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. The technical scope of the present invention broadly covers the entire range of the technical ideas truly intended by the invention, which are apparent from the matters described in this specification and the drawings. [Explanation of symbols]

[0037] 1 Packaging box 2 Sheet material 3 Front and rear sides 4 Left and right side 11 Bottom plate 12, 16 Outer plate 13, 17 Upper edge plate 14, 18 Inner plate 15, 19 Retaining plate 20 Connecting plate 21 Insertion plate 31 First engaging protrusion 32 Second engagement protrusion 41 First page 41a Slanted notch 41b, 41c, 41d notch 42 Second surface part 42a, 42b, 42c notch 43 Third side part 43a Cutting section 44 Fourth side 51 First holding piece 52 Second holding piece 53 Third holding piece 61 First engagement recess 61a Slope 62 Second engagement recess

Claims

1. A packaging box that is assembled by folding a sheet material, The sheet material has front and rear side portions connected to front and rear sides of a rectangular central plate, and left and right side portions connected to left and right sides of the central plate, The front and rear side portions are provided by connecting an outer plate, an upper edge plate, and an inner plate in order to the front and rear sides of the central plate via bent portions, First engagement protrusions are provided on the left and right sides of the inner plate of the front and rear side portions, The left and right side portions are provided with an outer plate, an upper edge plate, and an inner plate, which are connected in sequence to the left and right sides of the central plate via bent portions, A connecting plate is provided between the left and right sides of the outer plates of the adjacent front and rear side portions and the front and rear sides of the outer plates of the left and right side portions via a bent portion, An insert plate is connected to the front and rear sides of the inner plate of the left and right side portions via a bent portion, The inner plates of the left and right side portions are cut from the bent portions between the inner plates of the left and right side portions and the insertion plate to provide first surface portions; The folding portions of the sheet material are folded to erect the left and right side portions relative to the central plate, the connecting plate is folded toward the inside of the box, and the insertion plate is folded in an angle shape to sandwich the connecting plate and the insertion plate between the outer plate and the inner plate of the front and rear side portions, and the front and rear side portions are erected relative to the central plate; When the insertion plate is bent into an angle shape, the first surface portion is separated from the inner plate of the left and right side portions to form a first holding piece, which is positioned between the outer plate and the inner plate of the left and right side portions, In addition to the formation of the first holding pieces, holes formed in the inner plates of the left and right side portions form first engagement recesses, The first engaging protrusions are engaged with the first engaging recesses to hold the front and rear side portions and the left and right side portions upright.

2. 2. The packaging box according to claim 1, wherein the first surface portion has an inclined cut-out portion extending from the bent portion between the inner panel of the left and right side portions and the insertion panel toward the opposite side to the side where the inner panel of the left and right side portions is connected to the upper edge panel, and a sloped portion of the same shape is formed in the first engagement recess, and the first engagement protrusion abuts against the sloped portion of the first engagement recess to engage.

3. A pressing plate is connected to the inner plate of the front and rear side portions via a bent portion on the opposite side to the side where the upper edge plate is connected, Second engagement protrusions are provided on the left and right sides of the pressing plate of the front and rear side portions, A pressing plate is connected to the inner plate of the left and right side portions via a bent portion on the opposite side to the side where the upper edge plate is connected, The folding portion of the sheet material is folded to erect the left and right side portions relative to the center plate, and the pressing plate is placed on the center plate. The connecting plate is folded toward the inside of the box, the insert plate is bent into an angle shape, and the connecting plate and the insert plate are sandwiched between the outer plate and the inner plate of the front and rear side portions, the front and rear side portions are erected relative to the central plate, and the pressing plate is overlapped on the central plate; 3. The packaging box according to claim 1, wherein the second engaging protrusions are engaged with the first engaging recesses to hold the front and rear side portions and the left and right side portions upright.

4. A second surface portion is provided by cutting the inner plate of the left and right side portions to a bent portion between the inner plate of the left and right side portions and the pressing plate, the second surface portion being connected to the first surface portion, When the folded portions of the sheet material are folded to erect the left and right side portions relative to the central plate and the pressing plate is placed on the central plate, the second surface portion is released from the inner plate of the left and right side portions and positioned between the outer plate and the inner plate of the left and right side portions, and holes formed in the inner plate of the left and right side portions form second engagement recesses, 4. The packaging box according to claim 3, wherein the second engaging protrusions are engaged with the second engaging recesses to hold the front and rear side portions and the left and right side portions upright.

5. The inner plates of the left and right side portions are cut to provide third surface portions adjacent to the first surface portions, 4. The packaging box according to claim 3, wherein when the folded portions of the sheet material are folded to erect the left and right side portions against the central plate and the pressing plate is overlapped on the central plate, the third surface portion is released from the inner plate of the left and right side portions to form a second retaining piece, the second retaining piece being positioned between the outer plate and the inner plate of the left and right side portions and below the first engagement recess, and further wherein, together with the formation of the second retaining piece, a hole formed in the inner plate of the left and right side portions forms a first engagement recess.

6. The inner plates of the left and right side portions are cut to provide third surface portions adjacent to the first surface portions; 5. The packaging box according to claim 4, wherein when the folded portions of the sheet material are folded to erect the left and right side portions against the central plate and the pressing plate is overlapped on the central plate, the third surface portion is released from the inner plate of the left and right side portions to form second retaining pieces, the second retaining pieces being positioned between the outer plate and the inner plate of the left and right side portions and below the first engagement recesses, and together with the formation of the second retaining pieces, holes formed in the inner plate of the left and right side portions form first engagement recesses.

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