JP2026007714A - Method for joining cardboard sheets and furniture made from components using this method - Google Patents

Abstract

A method for joining two overlapping surfaces of cardboard sheets without adhesive and maintaining that state is provided.
[Solution] The outer joining surface 1a of the two surfaces to be joined has a trapezoidal insertion portion 1c with a wide tip and a narrow base, with both sides sloping, and protruding from a fold 1d at the top of the trapezoid. The inner joining surface 1b has a fixing portion protruding piece 1e, with a tip portion 1g that can be folded. The insertion portion 1c is inserted by pushing it into a hole created by folding the protruding piece 1e inward, and is fixed inside by standing it at about a right angle. The fixing portion protruding piece 1e is then pushed up from the inside to close the hole created by the insertion of the insertion portion 1c, and the tip portion 1g of the protruding piece is tightly attached to the insertion portion 1c, maintaining the fixed state.
[Selected Figure] Figure 2

Description

The present invention relates to a joining method that does not involve gluing two surfaces of cardboard sheets, a box-shaped component that uses this method, and cardboard furniture formed from this component.

When making rectangular tubular items using cardboard sheets, it is common to join both ends with adhesive, which requires a bonding process during manufacturing, and the bonded items become bulky when folded. Also, when combining multiple cardboard boxes, tape, string, etc. are generally required separately, making it difficult to join the boxes together.
Therefore, as a joining method that does not involve adhesive, (Patent Document 1) and (Patent Document 2) propose a method in which trapezoidal protrusions on both overlapping sheets are folded inward and fixed by tapered sides. (Patent Document 3) proposes a method in which ears are provided on the outer trapezoidal protrusions that are folded inward, thereby fixing the protrusions so that they do not easily come off. (Patent Document 4) proposes a method in which a square tube formed on the edge of a sheet is fixed with a trapezoidal protrusion. (Patent Document 5) proposes a method in which a square tube formed on the edge of a sheet is fixed in a rolled-up state.

Cardboard is also used for furniture such as beds, and is often stockpiled as an emergency measure in case of disasters, so there are a variety of types, including those specifically designed for beds, and those that can also be used as chairs and tables. All of them can be assembled in several parts, or they can be folded up and unfolded into pre-assembled pieces.
Most of them have a structure formed by two members with slits fitted together by the slits, as in (Patent Document 6), and are assembled with several types of members and parts. In (Patent Document 7), multiple boxes with this structure are used as a bed, chair, or table. In (Patent Document 8), an expandable product with this structure is proposed.

JP 2007-1594 A Patent No. 7046749 JP 2010-36958 A Patent No. 50431655 Utility Model Registration No. 3236422 JP 2022-169875 A Patent No. 6955737 Patent No. 6953008

In the joining method that does not involve adhesive (Patent Document 1), the trapezoidal protrusion that is pressed inward is not fixed in a folded upright position, and if force is applied and the upright part tilts, it will no longer be in a tightly adhered state.
In (Patent Document 2), a protrusion is provided at the base of the protruding piece to provide a catch, and joints are provided at two points on both sides to fix the two surfaces so that they do not shift, but if there is only one joint, the two surfaces will shift and if they move to the wider part of the hole, they will easily come out.
In (Patent Document 3), ears are provided to prevent them from easily coming out, and the ears can be folded to easily insert into the hole, but the ears can also be folded and come out, and even if the ears are held down by the protruding piece with the hole formed in them, the lower part of the ear is not fixed at all, so the two surfaces can separate, and it is not completely fixed, so if a strong force is applied it will come out.
In (Patent Document 4), a trapezoidal protrusion is pushed into a square hole and fixed at the wider part of the trapezoid, but this form is fine because this item is a cushioning material and the square tube formed by the wrapping is not subjected to any force that would separate it from the surface of the base, but if it were subjected to such force it would easily come out.
In (Patent Document 5), a square tube is wrapped around and fixed, but the bottom of the square tube is not joined to the sheet, and there are protruding pieces on the top surface and locking pieces on the sides, creating wasted space.

Regarding cardboard furniture, (Patent Document 6) shows that it is made by fitting slits together, but the number of parts is large and it is not intended for use as a bed. (Patent Document 7) shows that a box reinforced with partitions using slits inside is used, and it is intended for multi-purpose use, but part of the partitions and the outer frame of the box are glued at the edges, so it can be unfolded and assembled, but it is bulky when folded. (Patent Document 8) shows that the bed is extendable, but the length that it can be extended is fixed and it cannot be adjusted to any length.
When there are many different types and numbers of parts, working in a cluttered place can lead to parts being lost and making it impossible to assemble, and when packed, there can be wasted empty space. Packaging for assembled items tends to be large.
Most beds come in a fixed size, making them difficult for tall people to use, and none can be customized to fit a shorter woman or child.
Also, although the materials are inexpensive, there are many different parts and it requires processes such as gluing and folding, so it is not that cheap.

In consideration of the problems with the prior art described above, the present invention provides a joining method that joins two surfaces of cardboard sheets without adhesive and can reliably maintain this state. It also aims to use this joining method to form a three-dimensional component from a single rectangular sheet, and to connect multiple such components to provide inexpensive furniture such as cardboard beds that can be adapted to various uses.

This method of joining two overlapping surfaces of cardboard sheets does not involve gluing. The outer surface is provided with a folded, protruding insertion section with slopes on both sides as the tip widens and the folded section narrows. The inner surface is provided with a fixing section with a hole created by a folded, protruding protrusion, into which the insertion section is folded and inserted, protruding at a roughly right angle, and which has a means for fixing the insertion section to the position of the hole, which is wide enough not to slip out, by the protruding section.

The fixing part is shaped to fit the insertion of the insertion part, and the protruding piece of the fixing part is bent to fit the fixing position of the insertion part, with a tip that fits tightly to the insertion part. The protruding piece secures the insertion part with the folded tip while closing the hole created by the protrusion of the insertion part on the outer surface.

The protrusions of the fixing part have folds on both sides of the inclined edge of the insertion part that is inserted into the fixing part, and the two protrusions separated between the two sides have a hole pre-drilled in the part where the insertion part is fixed, or another protrusion is provided for creating a hole, and the insertion part is fixed at the base of the two protrusions on both sides.

One side has a protruding piece that splits into upper and lower halves, which are connected by folds on the left and right between the top and bottom. When one side is folded inward, the opposite side protrudes outward, narrowing at the tip to form an insertion section. On the other side, an insertion hole that can secure the insertion section vertically and horizontally is created by folding the protruding piece, and the inserted insertion section is folded so that it is secured by pressing down on the surface at the position of the protruding side.

A single rectangular sheet with cuts and creases, without holes or slits, is folded and assembled to form a box-shaped component with a rectangular top and an open bottom.

The upper parts of both short sides of the top surface of the component have a three-layer structure resembling the collar of a kimono, with the left and right sides of the innermost surface folded to narrow the width, forming a box-shaped component.

Cardboard furniture is formed by connecting or combining multiple of the above components.

The component is a box-shaped component with two rectangular cylindrical legs, with the open ends of the upper long sides of the component facing downwards in a U-shape.

This invention makes it possible to easily join two overlapping surfaces of cardboard sheets without adhesive and to firmly maintain this state. Furthermore, using this joining method, a single rectangular sheet with cuts and creases and no holes or slits can be assembled into a box-shaped member, and multiple such members can be connected to form cardboard furniture of various shapes depending on the intended use.

This is an example of the shape of the joining method, where the insertion part is trapezoidal, and A is an expanded view, and B is a front view of the state in which the insertion part and the fixing part overlap. 1A and 1B are assembly diagrams showing an example of the shape of the joining method when the insertion part is trapezoidal, where A is a perspective view and B is a cross-sectional view. This is an example of the shape of the joining method, where the insertion part is shaped like an extension of the lower base of a trapezoid, where A is an expanded view and B is a front view of the state in which the insertion part and the fixing part overlap. This is an assembly diagram of an example of a joining method in which the insertion part is shaped like an extension of the lower base of a trapezoid, where A is an oblique view and B is a cross-sectional view. This is an example of the joining method, in which the fixing part has two protruding pieces, where A is an expanded view and B is a front view of the state in which the insertion part and the fixing part overlap. This is an assembly diagram of an example of the joining method when the fixed part has two protruding pieces, where A is an oblique view, B is a partial front view of the fixed part seen from the inside, and C is an exploded view and oblique view of a small square tube. 1A and 1B are diagrams showing an example of a joining method in which the insertion portion protrudes inward and outward at the top and bottom, where FIG. 1A is a front view and FIG. 1B is a front view of the insertion portion and insertion hole. FIG. 10 is a perspective view of an example of a joining method in which the insertion portions protrude inward and outward at the top and bottom. Exploded view of a box-shaped component. FIG. FIG. This is a diagram of a box-shaped component, showing the side structure. A is an exploded view of the present invention on the left, a full view on the bottom right, and a top view on the top right. B is a diagram of a simple structure. A diagram of a box-shaped member, where A is a perspective view of one side and B is a perspective view of the other side. A diagram of a box-shaped member, showing a perspective view of the member joint. This is a perspective view of a box-shaped member, showing multiple members connected together. This is a perspective view of an example of the shape of a cardboard bed, where A is an example of a normal size with a shorter length, and B is an example of a wider width. 1A and 1B are perspective views of examples of applications of cardboard furniture, where A is a table and chair, and B is another example of a table. An exploded view of a box-shaped member with an open section. FIG. 10 is a perspective view of an assembly of a box-shaped member having an opening. FIG. 10 is a perspective view of an example of a box-shaped member having an opening used as a ladder.

Hereinafter, an embodiment of the present invention will be described.
The joining method of the present invention is a method for easily joining two overlapping surfaces of cardboard sheets without adhesive.
As shown in Figure 1A, the outer joint surface 1a of the two ends that are joined to form the square tube has an insertion portion 1c, which is trapezoidal in shape with a wide tip and a narrow base, with both sides sloping, and the upper base of the trapezoid is shaped as a fold 1d of the insertion portion, which protrudes due to this fold.The inner joint surface 1b has a protrusion 1e of the fixing portion, which is also trapezoidal in shape like the insertion portion 1c, and the lower base of the trapezoid is shaped as a fold 1f of the protrusion, which forms a trapezoid that is taller than the insertion portion 1c, as shown in Figure 1B, and the tip portion 1g is designed to be folded.

Figures 2A and 2B show the assembly diagram for this joint. The tip 1g of the fixed portion's protrusion 1e is folded inward, and the protrusion is folded at fold 1f, pushing the entire fixed portion's protrusion 1e into the interior of the tube to open a hole and prepare it for insertion of the insertion portion 1c. The outer joint surface 1a is then overlapped, and the insertion portion 1c is folded and inserted, pushing it in so that it forms a right angle inside. The fixed portion's protrusion 1e is then pushed up from the inside of the tube to close the hole opened by the insertion of the insertion portion 1c, and the tip 1g of the protrusion is pressed tightly against the insertion portion 1c to secure it in place. The tip 1g of the protrusion is folded in a position that allows it to tightly fit against the insertion portion 1c and not easily come off. This ensures a securely fixed state.

In FIG. 2, the protruding piece 1e of the fixing portion is pushed up from the inside of the tube to fix it, but if it is not possible to reach inside with one's hand, the following configuration can be used to fix it without reaching inside with one's hand.
As shown in Figure 3, the trapezoidal bottom base of the insertion part 1c is extended by the same width, and the tip part 1h of the extended insertion part is bent inward. The protrusion 1e of the fixing part is formed in a trapezoidal shape that is extended accordingly.
As shown in Figure 4, first fold the tip portion 1h of the insertion portion so that it is perpendicular to the inside, then fold the tip portion 1g of the protruding piece 1e of the fixing portion inward and fold the entire protruding piece 1e outward. When the outer joint surface 1a is placed over the inner joint surface 1b, fold the tip portion 1h of the insertion portion so that the protruding piece 1e protrudes from the hole. Now, push the insertion portion 1c into the hole so that it is approximately at a right angle inside. Then, insert the protruding piece 1e so that it closes the hole, and fasten the tip portion 1g tightly against the insertion portion 1c.
This allows assembly to be performed from the outside without having to reach inside.

2 and 4 show a form in which the open hole is closed while being fixed, but this requires the tip portion 1g of the protruding piece, which requires space. However, by leaving the hole open as described below, it is possible to join in a small space.
As shown in Figure 5, the insertion part 1c is shaped by extending the bottom base of a trapezoid. This could simply be a trapezoid, but when pressed inward, the width of the folded part of the trapezoid is small, and to fit the width of the finger, the width of the entire trapezoid must be increased. However, by inserting the bottom base of the trapezoid by folding it and extending it by the thickness that protrudes from the inner surface, the insertion part 1c can be made smaller.
As shown in Figure 5B, the fixing part is trapezoidal in size so that the insertion part 1c can be inserted, with folds on both sloping sides and two protruding pieces 1e separated between the sides. At the position where the insertion part 1c is inserted and protrudes, a triangular hole 1i is provided, with the position as the bottom and the point where the two protruding pieces 1e are separated as the vertex.

6A and 6B, first fold the two protrusions 1e inward, overlap the outer joining surface 1a with the inner joining surface 1b, push the insertion part 1c inward, spread the two protrusions 1e on both sides, and pass the protruding parts of the protrusions 1e and at the base of the protrusions 1e, the protrusions 1e on both sides are pressed down by the force that tries to close them, and they are fixed in a protruding and standing state. Also, by providing two protrusions 1e at the ends of the sheet as shown in Figure 6C, even small square tubes can be joined.
The fixed triangular hole 1i may be opened by bending the protrusion to make it protrude, and the insertion portion 1c may be fixed by being sandwiched between this triangular protrusion and two protrusions 1e.

7 and 8 show the joining of the surfaces of two members, one having a surface 2 on which an insertion portion is provided and the other having a surface 3 on which an insertion hole is provided.
The surface 2 on which the insertion section is provided has protrusions that are connected at the top and bottom as shown in Figure 8, and the lower protrusion is connected between folds 2a provided on the left and right sides of the base of the upper protrusion 2b, and when the upper protrusion 2b is folded at fold 2a and protrudes inward, the connected lower protrusion protrudes outward. The protruding inner and outer sides form a single flat surface, and the outer side is the insertion section 2c, with slopes on both sides and a narrowed tip.
The surface 3 provided with the insertion hole has a fold 3a of the protruding piece, causing the protruding piece 3b to protrude inward of the member, forming the insertion hole 3c. As shown in Figure 7B, the insertion hole 3c is shaped so that when the insertion part 2c is inserted, the upper part is fixed at the left and right ends and the lower part is fixed at the center, rather than the entire part. Normally, in this case, a long and narrow hole is made to match the thickness of the insertion part 2c, but with this shape, it is possible to fix it with a larger hole, which can be made by protruding the protruding piece.

Furthermore, the insertion hole 3c has a space at the top that is inclined to narrow in the direction of the fold 3a of the protrusion. As a result, when the insertion portion 2c is inserted into this space and the surface 2 and the surface 3 are brought into close contact, the inclination of this space and the inclination of the tip of the insertion portion 2c causes the insertion portion 2c to reliably move to the fixing position as shown in Figure 7B and be fixed up, down, left, and right.
The insertion portion 2c has a slit 2d aligned with the inside of the surface 3 where the insertion hole 3c is provided. Normally, it is not possible to fold it like this and create a slit at a position equal to the thickness of the sheet from the fold, but this is possible by making the inside and outside into one flat surface. As a result, by folding along the fold 2e of the insertion portion, the slit 2d presses down on the inside of the surface 3 where the insertion hole is provided, and the insertion portion 2c can be fixed not only vertically and horizontally but also front and back.
As with this joining method, the embodiments of Figs. 1, 3 and 5 are not limited to joining when forming a rectangular tube, but can also be used to join the surfaces of separate members.

By using these joining methods, a box-shaped component can be made from a single square sheet without adhesive.
A typical cardboard box has four sides joined together by glue on one side, and flaps extending from the sides to form the top and bottom lids have slits between them. However, the present invention uses only a single rectangular sheet with cuts and creases, no holes or slits, and no other components, as shown in Figure 9. The single sheet is assembled as shown in Figures 10 and 11, and joined on both sides to form a single box-shaped member with a rectangular top 4c and an open bottom.

Normally, when creating such a shape, the side surfaces would be as shown in Figure 12B, but in this shape, the innermost side surface 4d has the same width as the top surface 4c, so it protrudes to the left and right and is not flat. Simply narrowing the side surface 4d would make the inner side surface 4e and the outer side surface 4f higher than the top surface 4c.
In the present invention, the upper part of the side has a three-layer structure shaped like the collar of a kimono, as shown in Figure 12A. With this shape, protrusions can be provided on the left and right sides of the innermost side 4d, and by folding these protrusions, the width of the left and right sides can be narrowed to prevent any protrusions.
Also, since it is not joined by adhesive, the edge of the outer side surface 4f will lift up a little, but as shown in Figure 12B, it will lift up at the corner with the top surface 4c, and the edge will also warp, making it easier to get caught. Figure 12A is slanted at the bottom, so opening is also prevented.

The assembled box-shaped components have joints on both long sides of the top surface 4c to join the components, as shown in Figure 13. Insertion sections 2c are provided on surface 4a, and protrusions 3b, which form insertion holes 3c, are provided on surface 4b. Then, as shown in Figure 14, they are inserted and fixed. As shown in Figure 15, multiple components can be connected, and they can be used as a cardboard bed as shown in Figure 16. Since there is no limit to the number of components that can be connected, it can be made to fit the user's height. It can be made for people over 2 meters tall, as well as for small children. It can also be widened by adding more components horizontally, as shown in Figure 16B. While the figure shows a vertical head section, this can be removed to accommodate two small children. In this case, since the sides cannot be joined, tape can be used to secure the bed securely.
In this way, various configurations can be used to make effective use of space.

Depending on the number of pieces connected, it can be used as a chair or a table, as shown in FIG. 17A.
The sheet can also be used as is without assembling it in this way. In this case, if you tape the cut edges of the sheet, it can be used as a normal sheet for partitions, tabletops, etc.
This allows a small bed to be surrounded by sheets to create a baby bed. As shown in Figure 17B, a table with this top can be made with less assembly by taping the components together without connecting them, and it can be made taller than a table that is simply connected. Two of these tabletop components can be joined together to create a desk by adding several levels to increase the height. In this case, the open part of the component can be placed on the outside so that items can be placed inside.
In this way, two pieces of material can be joined together to create a thick wall-like partition. In this case, crumpled newspaper can be placed inside to provide heat and sound insulation.

Furthermore, as shown in Figure 18, the box-shaped member can be assembled by providing inward-folding portions on both long sides of the top surface 4c, to form a U-shaped open section at the bottom, as shown in Figure 19. The top surface 4g of the open section is supported by the side surfaces 4h of the open section, and the top surface 4g of the open section is folded upward, with the ends touching the top surface internally, making this section double, resulting in a structure that is strong against loads.
This material can be used to make beds, and also chairs and tables with openings that allow users to stretch or tuck their legs in. The part that folds inwards can be taped to eliminate the opening, so it can also be used as a thick, wall-like partition.
Also, by having an open section, it can be fixed with tape to take the form shown in Figure 20, and can be attached to a wall to be used as a ladder, or by adding inclines to both sides, it can be used as a stepladder.

In this way, a single rectangular sheet with cuts and creases, but no holes or slits, can be assembled into a single component by folding and joining without glue, and by connecting and combining these components, it can be used in a wider variety of forms than furniture made from regular cardboard.In addition, it can be used as is, and packaging requires only the rectangular sheet, so there is no need for other components or parts, which means there is no wasted space.
Since it is simply a die cut from a cardboard sheet, it can be provided at low cost.

1 Square tube 1a formed by joining Outer joining surface 1b Inner joining surface 1c Insertion portion 1d Insertion portion fold 1e Protrusion 1f of fixing portion Fold 1g of fixing portion Tip portion 1h of insert portion Tip portion 1i of fixing portion Hole 2 Surface 2a on which insertion portion is provided Folds 2b on the left and right Upper protrusion 2c Insertion portion 2d Insertion portion cut 2e Fold 3 Surface 3a on which insertion hole is provided Fold 3b of protrusion Protrusion 3c Insertion hole 4 Sheet 4a forming member Long side surface 4b Long side surface 4c Top surface 4d Most inner side surface 4e Inner side surface 4f Outer side surface 4g Top surface 4h of open portion Side of open portion

The present invention relates to a joining method that does not involve gluing two surfaces of cardboard sheets, a box-shaped component that uses this method, and cardboard furniture formed from this component.

When making rectangular tubular items using cardboard sheets, it is common to join both ends with adhesive, which requires a bonding process during manufacturing, and the bonded items become bulky when folded. Also, when combining multiple cardboard boxes, tape, string, etc. are generally required separately, making it difficult to join the boxes together.
Therefore, as a joining method that does not involve adhesive, (Patent Document 1) and (Patent Document 2) propose a method in which trapezoidal protrusions on both overlapping sheets are folded inward and fixed by inclinations on both sides. (Patent Document 3) proposes a method in which ears are provided on the outer trapezoidal protrusions that are folded inward, thereby fixing the protrusions so that they do not easily come off. (Patent Document 4) proposes a method in which a square tube formed on the edge of a sheet is fixed with a trapezoidal protrusion. (Patent Document 5) proposes a method in which a square tube formed on the edge of a sheet is fixed in a rolled-up state.

Cardboard is also used for furniture such as beds, and is often stockpiled as an emergency measure in case of disasters, so there are a variety of types, including those specifically designed for beds, and those that can also be used as chairs and tables. All of them can be assembled in several parts, or they can be folded up and unfolded into pre-assembled pieces.
Most of them have a structure formed by two members with slits fitted together by the slits, as in (Patent Document 6), and are assembled with several types of members and parts. In (Patent Document 7), multiple boxes with this structure are used as a bed, chair, or table. In (Patent Document 8), an expandable product with this structure is proposed.

JP 2007-1594 A Patent No. 7046749 JP 2010-36958 A Patent No. 50431655 Utility Model Registration No. 3236422 JP 2022-169875 A Patent No. 6955737 Patent No. 6953008

In the joining method that does not involve adhesive (Patent Document 1), the trapezoidal protrusion that is pressed inward is not fixed in a folded upright position, and if force is applied and the upright part tilts, it will no longer be in a tightly adhered state.
In (Patent Document 2), a protrusion is provided at the base of the protruding piece to provide a catch, and joints are provided at two points on both sides to fix the two surfaces so that they do not shift, but if there is only one joint, the two surfaces will shift and if they move to the wider part of the hole, they will easily come out.
In (Patent Document 3), ears are provided to prevent the ears from easily coming out, and the ears can be folded to allow easy insertion into the hole, but the ears can also be folded and come out, and even if the ears are held down with a protruding piece with a hole, the lower part of the protruding piece with the ears is not fixed at all, so the two surfaces can separate, and it is not completely fixed, so if a strong force is applied it will come out.
In (Patent Document 4), a trapezoidal protrusion is pushed into a square hole and fixed at the wider part of the trapezoid, but this form is fine because this item is a cushioning material and the square tube formed by the wrapping is not subjected to any force that would separate it from the surface of the base, but if it were subjected to such force it would easily come out.
In (Patent Document 5), a square tube is wrapped around and fixed, but the bottom of the square tube is not joined to the sheet, and there are protruding pieces on the top surface and locking pieces on the sides, creating wasted space.

Regarding cardboard furniture, (Patent Document 6) shows that it is made by fitting slits together, but the number of parts is large and it is not intended for use as a bed. (Patent Document 7) shows that a box reinforced with partitions using slits inside is used, and it is intended for multi-purpose use, but part of the partitions and the outer frame of the box are glued at the edges, so it can be unfolded and assembled, but it is bulky when folded. (Patent Document 8) shows that the bed is extendable, but the length that it can be extended is fixed and it cannot be adjusted to any length.
When there are many different types and numbers of parts, working in a cluttered place can lead to parts being lost and making it impossible to assemble, and when packed, there can be wasted empty space. Packaging for assembled items tends to be large.
Most beds come in a fixed size, making them difficult for tall people to use, and none can be customized to fit a shorter woman or child.
Also, although the materials are inexpensive, there are many different parts and it requires processes such as gluing and folding, so it is not that cheap.

In consideration of the problems with the prior art described above, the present invention provides a joining method that joins two surfaces of cardboard sheets without adhesive and can reliably maintain this state. It also aims to use this joining method to form a three-dimensional component from a single rectangular sheet, and to connect multiple such components to provide inexpensive furniture such as cardboard beds that can be adapted to various uses.

This is a method of joining two overlapping surfaces of cardboard sheets without gluing them together, in which an insertion section is provided on the outer surface that is folded and protrudes, with the tip widening and the folded section narrowing, resulting in slopes on both sides, and a fixing section is provided on the inner surface with a protruding piece that is folded and protrudes to form an open hole, and the insertion section is folded and inserted into the hole, protruding at approximately a right angle, and has a means for fixing by the protruding piece at the position of the hole that is wide enough that the insertion section will not slip out .

The fixing portion is shaped to fit the insertion of the inserting portion, and the protruding piece of the fixing portion is bent to fit the fixing position of the inserting portion, with a tip portion that fits tightly to the inserting portion, and the protruding piece closes the hole opened by the protrusion of the inserting portion on the outer surface, while the folded tip portion fixes the inserting portion.

The protrusions of the fixing part have folds on both sides of the inclined edges of the insertion part that is inserted into the fixing part, and the two protrusions separated between the two edges have a hole pre-made in the part where the insertion part is fixed, or another protrusion is provided for opening a hole, and the insertion part is fixed at the base parts of the two protrusions on both sides.

One side has a protruding piece that is divided into upper and lower parts, and is connected between the folds on the left and right between the top and bottom. When one side is folded inward, the other side that protrudes outward has a narrowed tip to form an insertion part, and on the other side, an insertion hole that can fix the insertion part vertically and horizontally is opened by the protruding protruding piece , and the protruding insertion part that is inserted into the insertion hole is folded so that it is fixed by pressing the surface at the cut line provided at the position of the surface on the protruding side.

A rectangular sheet is cut and folded, with no holes or slits, and assembled by folding to form a box-shaped member with a rectangular top and an open bottom.

The upper surfaces of both short sides of the upper surface of the member have a three-layer structure like the collar of a kimono, and the left and right sides of the innermost surface are folded to narrow the width, forming a box-shaped member.

A plurality of the above members are connected or combined to form cardboard furniture.

The component is a box-shaped component with two rectangular cylindrical legs, with the open ends of the upper long sides of the component facing downwards in a U-shape.

This invention makes it possible to easily join two overlapping surfaces of cardboard sheets without adhesive and to firmly maintain this state. Furthermore, using this joining method, a single rectangular sheet with cuts and creases and no holes or slits can be assembled into a box-shaped member, and multiple such members can be connected to form cardboard furniture of various shapes depending on the intended use.

This is an example of the shape of the joining method, where the insertion part is trapezoidal, and A is an expanded view, and B is a front view of the state in which the insertion part and the fixing part overlap. 1A and 1B are assembly diagrams showing an example of the shape of the joining method when the insertion part is trapezoidal, where A is a perspective view and B is a cross-sectional view. This is an example of the shape of the joining method, where the insertion part is shaped like an extension of the lower base of a trapezoid, where A is an expanded view and B is a front view of the state in which the insertion part and the fixing part overlap. This is an assembly diagram of an example of a joining method in which the insertion part is shaped like an extension of the lower base of a trapezoid, where A is an oblique view and B is a cross-sectional view. This is an example of the joining method, in which the fixing part has two protruding pieces, where A is an expanded view and B is a front view of the state in which the insertion part and the fixing part overlap. This is an assembly diagram of an example of the joining method when the fixed part has two protruding pieces, where A is an oblique view, B is a partial front view of the fixed part seen from the inside, and C is an exploded view and oblique view of a small square tube. 1A and 1B are diagrams showing an example of a joining method in which the insertion portion protrudes inward and outward at the top and bottom, where FIG. 1A is a front view and FIG. 1B is a front view of the insertion portion and insertion hole. FIG. 10 is a perspective view of an example of a joining method in which the insertion portions protrude inward and outward at the top and bottom. Exploded view of a box-shaped component. FIG. FIG. This is a diagram of a box-shaped component, showing the side structure. A is an exploded view of the present invention on the left, a full view on the bottom right, and a top view on the top right. B is a diagram of a simple structure. A diagram of a box-shaped member, where A is a perspective view of one side and B is a perspective view of the other side. A diagram of a box-shaped member, showing a perspective view of the member joint. This is a perspective view of a box-shaped member, showing multiple members connected together. This is a perspective view of an example of the shape of a cardboard bed, where A is an example of a normal size with a shorter length, and B is an example of a wider width. 1A and 1B are perspective views of examples of applications of cardboard furniture, where A is a table and chair, and B is another example of a table. An exploded view of a box-shaped member with an open section. FIG. 10 is a perspective view of an assembly of a box-shaped member having an opening. FIG. 10 is a perspective view of an example of a box-shaped member having an opening used as a ladder.

Hereinafter, an embodiment of the present invention will be described.
The joining method of the present invention is a method for easily joining two overlapping surfaces of cardboard sheets without adhesive.
As shown in Figure 1A, the outer joint surface 1a of the two ends that are joined to form the square tube has an insertion portion 1c, which is trapezoidal in shape with a wide tip and a narrow base, with both sides sloping, and the upper base of the trapezoid is shaped as a fold 1d of the insertion portion, which protrudes due to this fold.The inner joint surface 1b has a protrusion 1e of the fixing portion, which is also trapezoidal in shape like the insertion portion 1c, and the lower base of the trapezoid is shaped as a fold 1f of the protrusion, which forms a trapezoid that is taller than the insertion portion 1c, as shown in Figure 1B, and the tip portion 1g is designed to be folded.

2A and 2B show the assembly diagram of this joint. The tip 1g of the fixed portion's protrusion 1e is folded inward, and the protrusion is folded at fold 1f to push the entire fixed portion's protrusion 1e into the interior of the tube, creating a hole so that the insertion portion 1c can be inserted. The outer joint surface 1a is then overlapped, and the insertion portion 1c is folded and inserted, pushing it in until it forms a right angle inside. The fixed portion's protrusion 1e is then pushed up from the inside of the tube to close the hole created by the insertion of the insertion portion 1c, and the tip 1g of the protrusion is tightly attached to the insertion portion 1c, securing it in place. The tip 1g of the protrusion is folded in a position that allows it to tightly attach to the insertion portion 1c and not easily come off. This allows the fixed state to be firmly maintained.

In FIG. 2, the protruding piece 1e of the fixing portion is pushed up from the inside of the tube to fix it, but if it is not possible to reach inside with one's hand, the following configuration can be used to fix it without reaching inside with one's hand.
As shown in Figure 3, the trapezoidal bottom base of the insertion part 1c is extended by the same width, and the tip part 1h of the extended insertion part is bent inward. The protrusion 1e of the fixing part is formed in a trapezoidal shape that is extended accordingly.
As shown in Figure 4, first fold the tip portion 1h of the insertion portion so that it is perpendicular to the inside, then fold the tip portion 1g of the protruding piece 1e of the fixing portion inward and fold the entire protruding piece 1e outward. When the outer joint surface 1a is placed over the inner joint surface 1b, fold the tip portion 1h of the insertion portion so that the protruding piece 1e protrudes from the hole. Now, push the insertion portion 1c into the hole so that it is approximately at a right angle inside. Then, insert the protruding piece 1e so that it closes the hole, and fasten the tip portion 1g tightly against the insertion portion 1c.
This allows assembly to be performed from the outside without having to reach inside.

2 and 4 show a form in which the open hole is closed while being fixed, but this requires the tip portion 1g of the protruding piece, which requires space. However, by leaving the hole open as described below, it is possible to join in a small space.
As shown in Figure 5, the insertion part 1c is shaped by extending the bottom base of a trapezoid. This could simply be a trapezoid, but when pressed inward, the width of the folded part of the trapezoid is small, and to fit the width of the finger, the width of the entire trapezoid must be increased. However, by inserting the bottom base of the trapezoid by folding it and extending it by the thickness that protrudes from the inner surface, the insertion part 1c can be made smaller.
As shown in Figure 5B, the fixing part is trapezoidal in size so that the insertion part 1c can be inserted, with folds on both sloping sides and two protruding pieces 1e separated between the sides. At the position where the insertion part 1c is inserted and protrudes, a triangular hole 1i is provided, with the position as the base and the point where the two protruding pieces 1e are separated as the apex.

6A and 6B, first fold the two protrusions 1e inward, overlap the outer joining surface 1a with the inner joining surface 1b, push the insertion part 1c inward, spread the two protrusions 1e on both sides, and pass the protruding parts of the protrusions 1e and at the base of the protrusions 1e, the protrusions 1e on both sides are pressed down by the force that tries to close them, and they are fixed in a protruding and standing state. Also, by providing two protrusions 1e at the ends of the sheet as shown in Figure 6C, even small square tubes can be joined.
The fixed triangular hole 1i may be opened by bending the protrusion to make it protrude, and the insertion portion 1c may be fixed by being sandwiched between this triangular protrusion and two protrusions 1e.

7 and 8 show the joining of the surfaces of two members, one having a surface 2 on which an insertion portion is provided and the other having a surface 3 on which an insertion hole is provided.
The surface 2 on which the insertion section is provided has protrusions that are connected at the top and bottom as shown in Figure 8, and the lower protrusion is connected between folds 2a provided on the left and right sides of the base of the upper protrusion 2b, and when the upper protrusion 2b is folded at fold 2a and protrudes inward, the connected lower protrusion protrudes outward. The protruding inner and outer sides form a single flat surface, and the outer side is the insertion section 2c, with slopes on both sides and a narrowed tip.
The surface 3 provided with the insertion hole has a fold 3a of the protruding piece, causing the protruding piece 3b to protrude inward of the member, forming the insertion hole 3c. As shown in Figure 7B, the insertion hole 3c is shaped so that when the insertion part 2c is inserted, the upper part is fixed at the left and right ends and the lower part is fixed at the center, rather than the entire part. Normally, in this case, a long and narrow hole is made to match the thickness of the insertion part 2c, but with this shape, it is possible to fix it with a larger hole, which can be made by protruding the protruding piece.

Furthermore, the insertion hole 3c has a space at the top that is inclined to narrow in the direction of the fold 3a of the protrusion. As a result, when the insertion portion 2c is inserted into this space and the surface 2 and the surface 3 are brought into close contact, the inclination of this space and the inclination of the tip of the insertion portion 2c causes the insertion portion 2c to reliably move to the fixing position as shown in Figure 7B and be fixed up, down, left, and right.
The insertion portion 2c has a slit 2d aligned with the inside of the surface 3 where the insertion hole 3c is provided. Normally, it is not possible to fold it like this and create a slit at a position equal to the thickness of the sheet from the fold, but this is possible by making the inside and outside into one flat surface. As a result, by folding along the fold 2e of the insertion portion, the slit 2d presses down on the inside of the surface 3 where the insertion hole is provided, and the insertion portion 2c can be fixed not only vertically and horizontally but also front and back.
As with this joining method, the embodiments of Figs. 1, 3 and 5 are not limited to joining when forming a rectangular tube, but can also be used to join the surfaces of separate members.

By using these joining methods, a box-shaped component can be made from a single square sheet without adhesive.
A typical cardboard box has four sides joined together by glue on one side, and flaps extending from the sides to form the top and bottom lids have slits between them. However, the present invention uses only a single rectangular sheet with cuts and creases, no holes or slits, and no other components, as shown in Figure 9. The single sheet is assembled as shown in Figures 10 and 11, and joined on both sides to form a single box-shaped member with a rectangular top 4c and an open bottom.

Normally, when creating such a shape, the side surfaces would be as shown in Figure 12B, but in this shape, the innermost side surface 4d has the same width as the top surface 4c, so it protrudes to the left and right and is not flat. Simply narrowing the side surface 4d would make the inner side surface 4e and the outer side surface 4f higher than the top surface 4c.
In the present invention, the upper part of the side has a three-layer structure shaped like the collar of a kimono, as shown in Figure 12A. With this shape, protrusions can be provided on the left and right sides of the innermost side 4d, and by folding these protrusions, the width of the left and right sides can be narrowed to prevent any protrusions.
Also, since it is not joined by adhesive, the edge of the outer side surface 4f will lift up a little, but as shown in Figure 12B, it will lift up at the corner with the top surface 4c, and the edge will also warp, making it easier to get caught. Figure 12A is slanted at the bottom, so opening is also prevented.

The assembled box-shaped components have joints on both long sides of the top surface 4c to join the components, as shown in Figure 13. Insertion sections 2c are provided on surface 4a, and protrusions 3b, which form insertion holes 3c, are provided on surface 4b. Then, as shown in Figure 14, they are inserted and fixed. As shown in Figure 15, multiple components can be connected, and they can be used as a cardboard bed as shown in Figure 16. Since there is no limit to the number of components that can be connected, it can be made to fit the user's height. It can be made for people over 2 meters tall, as well as for small children. It can also be widened by adding more components horizontally, as shown in Figure 16B. While the figure shows a vertical head section, this can be removed to accommodate two small children. In this case, since the sides cannot be joined, tape can be used to secure the bed securely.
In this way, various configurations can be used to make effective use of space.

Depending on the number of pieces connected, it can be used as a chair or a table, as shown in FIG. 17A.
The sheet can also be used as is without assembling it in this way. In this case, if you tape the cut edges of the sheet, it can be used as a normal sheet for partitions, tabletops, etc.
This allows a small bed to be surrounded by sheets to create a baby bed. As shown in Figure 17B, a table with this top can be made with less assembly by taping the components together without connecting them, and it can be made taller than a table that is simply connected. Two of these tabletop components can be joined together to create a desk by adding several levels to increase the height. In this case, the open part of the component can be placed on the outside so that items can be placed inside.
In this way, two pieces of material can be joined together to create a thick wall-like partition. In this case, crumpled newspaper can be placed inside to provide heat and sound insulation.

Furthermore, as shown in Figure 18, the box-shaped member can be assembled by providing inward-folding portions on both long sides of the top surface 4c, to form a U-shaped open section at the bottom, as shown in Figure 19. The top surface 4g of the open section is supported by the side surfaces 4h of the open section, and the top surface 4g of the open section is folded upward, with the ends touching the top surface internally, making this section double, resulting in a structure that is strong against loads.
This material can be used to make beds, and also chairs and tables, with openings that allow users to stretch or tuck their legs in. The part that folds inwards can be taped to eliminate the opening, so it can also be used as a thick, wall-like partition.
Also, by having an open section, it can be fixed with tape to take the form shown in Figure 20, and can be attached to a wall to be used as a ladder, or by adding inclines to both sides, it can be used as a stepladder.

In this way, a single rectangular sheet with cuts and creases, but no holes or slits, can be assembled into a single component by folding and joining without glue, and by connecting and combining these components, it can be used in a wider variety of forms than furniture made from regular cardboard.In addition, it can be used as is, and packaging requires only the rectangular sheet, so there is no need for other components or parts, which means there is no wasted space.
Since it is simply a die cut from a cardboard sheet, it can be provided at low cost.

1 Square tube 1a formed by joining Outer joining surface 1b Inner joining surface 1c Insertion portion 1d Insertion portion fold 1e Protrusion 1f of fixing portion Fold 1g of fixing portion Tip portion 1h of insert portion Tip portion 1i of fixing portion Hole 2 Surface 2a on which insertion portion is provided Folds 2b on the left and right Upper protrusion 2c Insertion portion 2d Insertion portion cut 2e Fold 3 Surface 3a on which insertion hole is provided Fold 3b of protrusion Protrusion 3c Insertion hole 4 Sheet 4a forming member Long side surface 4b Long side surface 4c Top surface 4d Most inner side surface 4e Inner side surface 4f Outer side surface 4g Top surface 4h of open portion Side of open portion

The present invention relates to a joining method that does not involve gluing two surfaces of cardboard sheets, a box-shaped component that uses this method, and cardboard furniture formed from this component.

When making rectangular tubular items using cardboard sheets, it is common to join both ends with adhesive, which requires a bonding process during manufacturing, and the bonded items become bulky when folded. Also, when combining multiple cardboard boxes, tape, string, etc. are generally required separately, making it difficult to join the boxes together.
Therefore, as a joining method that does not involve adhesive, (Patent Document 1) and (Patent Document 2) propose a method in which trapezoidal protrusions on both overlapping sheets are folded inward and fixed by inclinations on both sides. (Patent Document 3) proposes a method in which ears are provided on the outer trapezoidal protrusions that are folded inward, thereby fixing the protrusions so that they do not easily come off. (Patent Document 4) proposes a method in which a square tube formed on the edge of a sheet is fixed with a trapezoidal protrusion. (Patent Document 5) proposes a method in which a square tube formed on the edge of a sheet is fixed in a rolled-up state.

Cardboard is also used for furniture such as beds, and is often stockpiled as an emergency measure in case of disasters, so there are a variety of types, including those specifically designed for beds, and those that can also be used as chairs and tables. All of them can be assembled in several parts, or they can be folded up and unfolded into pre-assembled pieces.
Most of them have a structure formed by two members with slits fitted together by the slits, as in (Patent Document 6), and are assembled with several types of members and parts. In (Patent Document 7), multiple boxes with this structure are used as a bed, chair, or table. In (Patent Document 8), an expandable product with this structure is proposed.

JP 2007-1594 A Patent No. 7046749 JP 2010-36958 A Patent No. 50431655 Utility Model Registration No. 3236422 JP 2022-169875 A Patent No. 6955737 Patent No. 6953008

In the joining method that does not involve adhesive (Patent Document 1), the trapezoidal protrusion that is pressed inward is not fixed in a folded upright position, and if force is applied and the upright part tilts, it will no longer be in a tightly adhered state.
In (Patent Document 2), a protrusion is provided at the base of the protruding piece to provide a catch, and joints are provided at two points on both sides to fix the two surfaces so that they do not shift, but if there is only one joint, the two surfaces will shift and if they move to the wider part of the hole, they will easily come out.
In (Patent Document 3), ears are provided to prevent the ears from easily coming out, and the ears can be folded to allow easy insertion into the hole, but the ears can also be folded and come out, and even if the ears are held down with a protruding piece with a hole, the lower part of the protruding piece with the ears is not fixed at all, so the two surfaces can separate, and it is not completely fixed, so if a strong force is applied it will come out.
In (Patent Document 4), a trapezoidal protrusion is pushed into a square hole and fixed at the wider part of the trapezoid, but this form is fine because this item is a cushioning material and the square tube formed by the wrapping is not subjected to any force that would separate it from the surface of the base, but if it were subjected to such force it would easily come out.
In (Patent Document 5), a square tube is wrapped around and fixed, but the bottom of the square tube is not joined to the sheet, and there are protruding pieces on the top surface and locking pieces on the sides, creating wasted space.

Regarding cardboard furniture, (Patent Document 6) shows that it is made by fitting slits together, but the number of parts is large and it is not intended for use as a bed. (Patent Document 7) shows that a box reinforced with partitions using slits inside is used, and it is intended for multi-purpose use, but part of the partitions and the outer frame of the box are glued at the edges, so it can be unfolded and assembled, but it is bulky when folded. (Patent Document 8) shows that the bed is extendable, but the length that it can be extended is fixed and it cannot be adjusted to any length.
When there are many different types and numbers of parts, working in a cluttered place can lead to parts being lost and making it impossible to assemble, and when packed, there can be wasted empty space. Packaging for assembled items tends to be large.
Most beds come in a fixed size, making them difficult for tall people to use, and none can be customized to fit a shorter woman or child.
Also, although the materials are inexpensive, there are many different parts and it requires processes such as gluing and folding, so it is not that cheap.

In consideration of the problems with the prior art described above, the present invention provides a joining method that joins two surfaces of cardboard sheets without adhesive and can reliably maintain this state. It also aims to use this joining method to form a three-dimensional component from a single rectangular sheet, and to connect multiple such components to provide inexpensive furniture such as cardboard beds that can be adapted to various uses.

A method of joining two overlapping surfaces of cardboard sheets that does not involve gluing, in which one surface has a folded, protruding insertion portion, and the other surface has a protruding, folded protrusion with a shape that matches the insertion of the insertion portion, and the insertion portion is inserted into the hole and protrudes at approximately a right angle, and the protruding portion or insertion portion forms a fixing portion that is fixed by folding at a position where the two surfaces are in close contact and both sides of the protruding insertion portion are in close contact with the hole, and in the case where the insertion portion has a shape in which the tip widens and the folded portion narrows so that both sides are inclined, the folded and inserted insertion portion is fixed by the folding of the protruding portion of the fixing portion .

The insertion part has a shape with inclined sides on both sides as the tip widens and the folded part narrows , and the protruding piece of the fixing part has a tip part that is folded to match the fixing position of the insertion part and comes into close contact with the insertion part, and the protruding piece closes the hole opened by the protrusion of the insertion part, and the insertion part is fixed by the folded tip part.

The insertion part has a shape with slopes on both sides as the tip widens and the folded part narrows, and the protrusions of the fixing part have folds on both sides of the sloping side of the insertion part to be inserted , and are two protrusions separated between the both sides, and a hole is pre-made at the position where the insertion part is inserted and protrudes, or another protrusion is provided for making a hole, and the insertion part is fixed at the folded part at the base of the two protrusions on both sides.

The insertion portion is divided into upper and lower portions by folds on the left and right , and one side of the protruding piece that is connected flatly at the top and bottom between the left and right folds is folded inward, so that the opposite side that protrudes outward has a narrowed tip for insertion , and the other surface has the hole that can fix the insertion portion vertically and horizontally, and the insertion portion that protrudes after being inserted into the hole becomes a fixed portion with a fold that holds the surface in place at the cut line on the surface on the protruding side.

Cuts and creases are made, and a single rectangular sheet without holes or slits is folded to form a box-shaped component with a rectangular top surface , an open bottom surface, and a three-layer structure resembling the collar of a kimono on both upper sides of the short side of the top surface, with the width narrowed by folding the left and right sides of the innermost surface .

Multiple of the above components are connected or combined to form cardboard furniture.

The component is a box-shaped component with two rectangular cylindrical legs, with the open ends of the upper long sides of the component facing downwards in a U-shape.

This invention makes it possible to easily join two overlapping surfaces of cardboard sheets without adhesive and to firmly maintain this state. Furthermore, using this joining method, a single rectangular sheet with cuts and creases and no holes or slits can be assembled into a box-shaped member, and multiple such members can be connected to form cardboard furniture of various shapes depending on the intended use.

This is an example of the shape of the joining method, where the insertion part is trapezoidal, and A is an expanded view, and B is a front view of the state in which the insertion part and the fixing part overlap. 1A and 1B are assembly diagrams showing an example of the shape of the joining method when the insertion part is trapezoidal, where A is a perspective view and B is a cross-sectional view. This is an example of the shape of the joining method, where the insertion part is shaped like an extension of the lower base of a trapezoid, where A is an expanded view and B is a front view of the state in which the insertion part and the fixing part overlap. This is an assembly diagram of an example of a joining method in which the insertion part is shaped like an extension of the lower base of a trapezoid, where A is an oblique view and B is a cross-sectional view. This is an example of the joining method, in which the fixing part has two protruding pieces, where A is an expanded view and B is a front view of the state in which the insertion part and the fixing part overlap. This is an assembly diagram of an example of the joining method when the fixed part has two protruding pieces, where A is an oblique view, B is a partial front view of the fixed part seen from the inside, and C is an exploded view and oblique view of a small square tube. 1A and 1B are diagrams showing an example of a joining method in which the insertion portion protrudes inward and outward at the top and bottom, where FIG. 1A is a front view and FIG. 1B is a front view of the insertion portion and insertion hole. FIG. 10 is a perspective view of an example of a joining method in which the insertion portions protrude inward and outward at the top and bottom. Exploded view of a box-shaped component. FIG. FIG. This is a diagram of a box-shaped component, showing the side structure. A is an exploded view of the present invention on the left, a full view on the bottom right, and a top view on the top right. B is a diagram of a simple structure. A diagram of a box-shaped member, where A is a perspective view of one side and B is a perspective view of the other side. A diagram of a box-shaped member, showing a perspective view of the member joint. This is a perspective view of a box-shaped member, showing multiple members connected together. This is a perspective view of an example of the shape of a cardboard bed, where A is an example of a normal size with a shorter length, and B is an example of a wider width. 1A and 1B are perspective views of examples of applications of cardboard furniture, where A is a table and chair, and B is another example of a table. An exploded view of a box-shaped member with an open section. FIG. 10 is a perspective view of an assembly of a box-shaped member having an opening. FIG. 10 is a perspective view of an example of a box-shaped member having an opening used as a ladder.

Hereinafter, an embodiment of the present invention will be described.
The joining method of the present invention is a method for easily joining two overlapping surfaces of cardboard sheets without adhesive.
As shown in Figure 1A, the outer joint surface 1a of the two ends that are joined to form the square tube has an insertion portion 1c, which is trapezoidal in shape with a wide tip and a narrow base, with both sides sloping, and the upper base of the trapezoid is shaped as a fold 1d of the insertion portion, which protrudes due to this fold.The inner joint surface 1b has a protrusion 1e of the fixing portion, which is also trapezoidal in shape like the insertion portion 1c, and the lower base of the trapezoid is shaped as a fold 1f of the protrusion, which forms a trapezoid that is taller than the insertion portion 1c, as shown in Figure 1B, and the tip portion 1g is designed to be folded.

2A and 2B show the assembly diagram of this joint. The tip 1g of the fixed portion's protrusion 1e is folded inward, and the protrusion is folded at fold 1f to push the entire fixed portion's protrusion 1e into the interior of the tube, creating a hole so that the insertion portion 1c can be inserted. The outer joint surface 1a is then overlapped, and the insertion portion 1c is folded and inserted, pushing it in until it forms a right angle inside. The fixed portion's protrusion 1e is then pushed up from the inside of the tube to close the hole created by the insertion of the insertion portion 1c, and the tip 1g of the protrusion is tightly attached to the insertion portion 1c, securing it in place. The tip 1g of the protrusion is folded in a position that allows it to tightly attach to the insertion portion 1c and not easily come off. This allows the fixed state to be firmly maintained.

In FIG. 2, the protruding piece 1e of the fixing portion is pushed up from the inside of the tube to fix it, but if it is not possible to reach inside with one's hand, the following configuration can be used to fix it without reaching inside with one's hand.
As shown in Figure 3, the trapezoidal bottom base of the insertion part 1c is extended by the same width, and the tip part 1h of the extended insertion part is bent inward. The protrusion 1e of the fixing part is formed in a trapezoidal shape that is extended accordingly.
As shown in Figure 4, first fold the tip portion 1h of the insertion portion so that it is perpendicular to the inside, then fold the tip portion 1g of the protruding piece 1e of the fixing portion inward and fold the entire protruding piece 1e outward. When the outer joint surface 1a is placed over the inner joint surface 1b, fold the tip portion 1h of the insertion portion so that the protruding piece 1e protrudes from the hole. Now, push the insertion portion 1c into the hole so that it is approximately at a right angle inside. Then, insert the protruding piece 1e so that it closes the hole, and fasten the tip portion 1g tightly against the insertion portion 1c.
This allows assembly to be performed from the outside without having to reach inside.

2 and 4 show a form in which the open hole is closed while being fixed, but this requires the tip portion 1g of the protruding piece, which requires space. However, by leaving the hole open as described below, it is possible to join in a small space.
As shown in Figure 5, the insertion part 1c is shaped by extending the bottom base of a trapezoid. This could simply be a trapezoid, but when pressed inward, the width of the folded part of the trapezoid is small, and to fit the width of the finger, the width of the entire trapezoid must be increased. However, by inserting the bottom base of the trapezoid by folding it and extending it by the thickness that protrudes from the inner surface, the insertion part 1c can be made smaller.
As shown in Figure 5B, the fixing part is trapezoidal in size so that the insertion part 1c can be inserted, with folds on both sloping sides and two protruding pieces 1e separated between the sides. At the position where the insertion part 1c is inserted and protrudes, a triangular hole 1i is provided, with the position as the base and the point where the two protruding pieces 1e are separated as the apex.

6A and 6B, first fold the two protrusions 1e inward, overlap the outer joining surface 1a with the inner joining surface 1b, push the insertion part 1c inward, spread the two protrusions 1e on both sides, and pass the protruding parts of the protrusions 1e and at the base of the protrusions 1e, the protrusions 1e on both sides are pressed down by the force that tries to close them, and they are fixed in a protruding and standing state. Also, by providing two protrusions 1e at the ends of the sheet as shown in Figure 6C, even small square tubes can be joined.
The fixed triangular hole 1i may be opened by bending the protrusion to make it protrude, and the insertion portion 1c may be fixed by being sandwiched between this triangular protrusion and two protrusions 1e.

7 and 8 show the joining of the surfaces of two members, one having a surface 2 on which an insertion portion is provided and the other having a surface 3 on which an insertion hole is provided.
The surface 2 on which the insertion section is provided has protrusions that are connected at the top and bottom as shown in Figure 8, and the lower protrusion is connected between folds 2a provided on the left and right sides of the base of the upper protrusion 2b, and when the upper protrusion 2b is folded at fold 2a and protrudes inward, the connected lower protrusion protrudes outward. The protruding inner and outer sides form a single flat surface, and the outer side is the insertion section 2c, with slopes on both sides and a narrowed tip.
The surface 3 provided with the insertion hole has a fold 3a of the protruding piece, causing the protruding piece 3b to protrude inward of the member, forming the insertion hole 3c. As shown in Figure 7B, the insertion hole 3c is shaped so that when the insertion part 2c is inserted, the upper part is fixed at the left and right ends and the lower part is fixed at the center, rather than the entire part. Normally, in this case, a long and narrow hole is made to match the thickness of the insertion part 2c, but with this shape, it is possible to fix it with a larger hole, which can be made by protruding the protruding piece.

Furthermore, the insertion hole 3c has a space at the top that is inclined to narrow in the direction of the fold 3a of the protrusion. As a result, when the insertion portion 2c is inserted into this space and the surface 2 and the surface 3 are brought into close contact, the inclination of this space and the inclination of the tip of the insertion portion 2c causes the insertion portion 2c to reliably move to the fixing position as shown in Figure 7B and be fixed up, down, left, and right.
The insertion portion 2c has a slit 2d aligned with the inside of the surface 3 where the insertion hole 3c is provided. Normally, it is not possible to fold it like this and create a slit at a position equal to the thickness of the sheet from the fold, but this is possible by making the inside and outside into one flat surface. As a result, by folding along the fold 2e of the insertion portion, the slit 2d presses down on the inside of the surface 3 where the insertion hole is provided, and the insertion portion 2c can be fixed not only vertically and horizontally but also front and back.
As with this joining method, the embodiments of Figs. 1, 3 and 5 are not limited to joining when forming a rectangular tube, but can also be used to join the surfaces of separate members.

By using these joining methods, a box-shaped component can be made from a single square sheet without adhesive.
A typical cardboard box has four sides joined together by glue on one side, and flaps extending from the sides to form the top and bottom lids have slits between them. However, the present invention uses only a single rectangular sheet with cuts and creases, no holes or slits, and no other components, as shown in Figure 9. The single sheet is assembled as shown in Figures 10 and 11, and joined on both sides to form a single box-shaped member with a rectangular top 4c and an open bottom.

Normally, when creating such a shape, the side surfaces would be as shown in Figure 12B, but in this shape, the innermost side surface 4d has the same width as the top surface 4c, so it protrudes to the left and right and is not flat. Simply narrowing the side surface 4d would make the inner side surface 4e and the outer side surface 4f higher than the top surface 4c.
In the present invention, the upper part of the side has a three-layer structure shaped like the collar of a kimono, as shown in Figure 12A. With this shape, protrusions can be provided on the left and right sides of the innermost side 4d, and by folding these protrusions, the width of the left and right sides can be narrowed to prevent any protrusions.
Also, since it is not joined by adhesive, the edge of the outer side surface 4f will lift up a little, but as shown in Figure 12B, it will lift up at the corner with the top surface 4c, and the edge will also warp, making it easier to get caught. Figure 12A is slanted at the bottom, so opening is also prevented.

The assembled box-shaped components have joints on both long sides of the top surface 4c to join the components, as shown in Figure 13. Insertion sections 2c are provided on surface 4a, and protrusions 3b, which form insertion holes 3c, are provided on surface 4b. Then, as shown in Figure 14, they are inserted and fixed. As shown in Figure 15, multiple components can be connected, and they can be used as a cardboard bed as shown in Figure 16. Since there is no limit to the number of components that can be connected, it can be made to fit the user's height. It can be made for people over 2 meters tall, as well as for small children. It can also be widened by adding more components horizontally, as shown in Figure 16B. While the figure shows a vertical head section, this can be removed to accommodate two small children. In this case, since the sides cannot be joined, tape can be used to secure the bed securely.
In this way, various configurations can be used to make effective use of space.

Depending on the number of pieces connected, it can be used as a chair or a table, as shown in FIG. 17A.
The sheet can also be used as is without assembling it in this way. In this case, if you tape the cut edges of the sheet, it can be used as a normal sheet for partitions, tabletops, etc.
This allows a small bed to be surrounded by sheets to create a baby bed. As shown in Figure 17B, a table with this top can be made with less assembly by taping the components together without connecting them, and it can be made taller than a table that is simply connected. Two of these tabletop components can be joined together to create a desk by adding several levels to increase the height. In this case, the open part of the component can be placed on the outside so that items can be placed inside.
In this way, two pieces of material can be joined together to create a thick wall-like partition. In this case, crumpled newspaper can be placed inside to provide heat and sound insulation.

Furthermore, as shown in Figure 18, the box-shaped member can be assembled by providing inward-folding portions on both long sides of the top surface 4c, to form a U-shaped open section at the bottom, as shown in Figure 19. The top surface 4g of the open section is supported by the side surfaces 4h of the open section, and the top surface 4g of the open section is folded upward, with the ends touching the top surface internally, making this section double, resulting in a structure that is strong against loads.
This material can be used to make beds, and also chairs and tables, with openings that allow users to stretch or tuck their legs in. The part that folds inwards can be taped to eliminate the opening, so it can also be used as a thick, wall-like partition.
Also, by having an open section, it can be fixed with tape to take the form shown in Figure 20, and can be attached to a wall to be used as a ladder, or by adding inclines to both sides, it can be used as a stepladder.

In this way, a single rectangular sheet with cuts and creases, but no holes or slits, can be assembled into a single component by folding and joining without glue, and by connecting and combining these components, it can be used in a wider variety of forms than furniture made from regular cardboard.In addition, it can be used as is, and packaging requires only the rectangular sheet, so there is no need for other components or parts, which means there is no wasted space.
Since it is simply a die cut from a cardboard sheet, it can be provided at low cost.

1 Square tube 1a formed by joining Outer joining surface 1b Inner joining surface 1c Insertion portion 1d Insertion portion fold 1e Protrusion 1f of fixing portion Fold 1g of fixing portion Tip portion 1h of insert portion Tip portion 1i of fixing portion Hole 2 Surface 2a on which insertion portion is provided Folds 2b on the left and right Upper protrusion 2c Insertion portion 2d Insertion portion cut 2e Fold 3 Surface 3a on which insertion hole is provided Fold 3b of protrusion Protrusion 3c Insertion hole 4 Sheet 4a forming member Long side surface 4b Long side surface 4c Top surface 4d Most inner side surface 4e Inner side surface 4f Outer side surface 4g Top surface 4h of open portion Side of open portion

Claims (8)

A method for joining two overlapping surfaces of cardboard sheets without gluing them together. The outer surface has a folded, protruding insertion section with slopes on both sides due to the tip widening and the folded section narrowing, and the inner surface has a fixing section with a protruding, folded protruding hole, into which the insertion section is folded and inserted at a substantially right angle, and which has a means for fixing the insertion section to the position of the hole with the protruding section, which is of a width that prevents it from slipping out. A method for joining two surfaces according to claim 1, wherein the fixing portion is shaped to accommodate the insertion of the insert portion, the protruding piece of the fixing portion is bent to match the fixing position of the insert portion, and a tip portion is provided that tightly contacts the insert portion, and the protruding piece fixes the insert portion with the folded tip portion while closing the hole opened by the protrusion of the insert portion on the outer surface. In the method for joining two surfaces of claim 1, the protruding pieces of the fixing part have folds on both sides of the inclined edges of the insertion part that is inserted into the fixing part, and the two protruding pieces separated between the two edges have holes pre-drilled at the position where the insertion part will be inserted and protrude, or another protruding piece is provided for drilling a hole, and the insertion part is fixed at the base of the two protruding pieces on both sides. A method of joining two overlapping surfaces of cardboard sheets without gluing them together. One surface has a protruding piece that splits into upper and lower sections, which connects between the folds on the left and right between the top and bottom. One side is folded inward, and the opposite side protrudes outward, narrowing at the end to form an insertion section. The other surface has an insertion hole created by folding the protruding piece, which can secure the insertion section vertically and horizontally. The inserted insertion section is folded so that it is held down and secured by a slit in the surface at the position of the protruding section. A box-shaped component formed using the joining method of claim 1 or 2, in which a single rectangular sheet with cuts and creases and no holes or slits is folded and assembled, resulting in a box-shaped component with a rectangular top and an open bottom. The box-shaped member of claim 5, wherein the upper portions of both short sides of the top surface of the member have a three-layer structure resembling the collar of a kimono, with the width of the innermost surface narrowed by folding the left and right sides. Cardboard furniture using the box-shaped member of claim 5, formed by connecting or combining multiple members. The cardboard furniture of claim 7, wherein both long sides of the upper surface of the member are box-shaped with the open U-shaped portions facing downward and two rectangular cylindrical legs.