US3301462A

US3301462A - Collapsible and stackable carton

Info

Publication number: US3301462A
Application number: US423232A
Authority: US
Inventors: John R Starr
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-01-04
Filing date: 1965-01-04
Publication date: 1967-01-31
Anticipated expiration: 1984-01-31
Also published as: GB1065836A; FR1466651A

Description

Jan. 31,1967 J, R. STARR 3,301,462

COLLAPSIBLE AND STACKABLE CARTON Filed Jan. '4, 1965 2 Sheets-Sheet 1 INVENTOR John RSturr F G Ronald E. Barry Attorney 7 Jan. 31, 1967 J. R. STARR 3,301,462

COLLAPSIBLE AND STACKABLE CARTON Filed Jan. 4, 1965 2 Sheets-Sheet! 14 580 70 90a e30 600 am 1 92 9 930 640 9m A y: kg 2' 1" v; u r J l2 ;1 ?ZA Y I 1| I 62 was I 9. I MW .n: A b I A H 1 {In 5 M 6 52 I!!! Hi l 1/ g 70 90b (sob93 9|b 62b 14 90b 93b 64b 91b INVENTOR. Joh n R. Starr Ronald E. Barry Aflo rney United States Patent P 3,301,462 a COLLAPSIBLE AND STACKABLE CARTON John R. Starr, 37 Lawndale Stg, Belmont, Mass. '0217 8 :Filed'Jan. 4, 1965, Ser. No. 423,232-

12 Claims. (Cl. 229-37) This invention relates to containers having closure flaps which are secured together by pressure-sensitive adhesives and more particularly to containers'of the type which are collapsible and stackable.

The advantages of applying pressure-sensitive adhesives to the closure flaps of corrugated orsolid fiber type containers atrthe manufacturing point have been recognized forsome time. One of the 'principaladvantages is to the .user of such containers, who only hastto erect and close the flaps of the container, thus eliminating the problems incident 'to the use of adhesives and. adhesive applying apparata to seal the container. The principal disadvantage to the use of such containers has been the difficulty in collapsing and stacking containers which have been previously coated with the pressure-sensitive adhesive either on the inside or outside surfaces without overlapping any portion of the flaps having the pressure sensitive adhesive coated thereon.

Early efforts to overcome this problem were directed toward modifying the containers so that they could be collapsed and stacked with the pressure-sensitive adhesive coated flaps so located that they would not overlap. These modifications were not readily accepted by the container manufacturers since they necessitated a change in thebasic outline of the container with a corresponding change in the cutting and scoring apparatus for the container and could not be adapted to the more profitable standard type of containers.

Efforts to adapt pressure-sensitive adhesives to the standard type of containers have resulted in coating small areas of the portions ofthe flaps which are to be bonded together so that they will not overlap when the container is collapsed or stacked. This resulted in a reduction in the area of adhesive contact-between the fia-ps which are to be bonded together sincethe maximum area which can be coated with adhesive for collapsing or stacking the container is only fifty percent or less of the total area of contact between the flaps which are to be bonded together. This just barely meets the requirements established for sealing such containers. If line or spottype coatings of adhesive are used, the contact area will beeven less.

The principal object of the present invention is to provide a container which utilizes pressure-sensitive adhesives but overcomes the above disadvantages.

Another object of the present invention is to provide a regular slotted container having pressure-sensitive adhesive coated closure fi-aps which makes it possible to stack the containers in a collapsed condition without any of the containers sticking together or to each other.

Another object of the present invention is to provide a collapsible and stackable container having pressure-sensitive adhesive applied to the closure flaps which can be adhesively coated over substantially all of the contact area of the flaps which are to be bonded together.

Another object of the present invention is to provide a collapsible and stackable container having pressure-sensitive adhesive applied to the closure flaps at the point of manufacture without any substantial increase in the cost of manufacture of the container.

A further object of the present invention is to provide a collapsible and stackable container having pressuresensitive adhesive applied to its closure flaps which will be free from the adverse effects of dust and dirt.

In carrying out these objects, it should be noted that a regular slotted container having a pair of side walls and 33%,462 Patented Jan. 31, 1967 a pair of end walls with closure flaps being provided on both ends of the side and end walls is shown and described throughout the application but that the invention in its broadest concept can be used with any type of foldable material for a container. The side and end Walls may be of equal lengths or of unequal lengths. When the container is erected, the flaps, whether of equal or unequal lengths, will always have one portion overlapping another portion. In sealing the container, the best results are achieved when the entire overlapped portions of the side and end fiaps are secured together. A pressure-sensitive adhesive is applied to the portion of the ed portion of the flaps when the container is collapsed or stacked. If the flaps are coated on the inside surfaces and the container is collapsed, the pressure-sensi tive adhesive on the one set of flaps will overlie the release coating provided on the po1tion of the surface of the flaps opposite the adhesive coated flap. If the pressure-sensitive adhesive is coated on the outside of a portion of one set of the flaps, the portion of the other set of flaps which will overlap the adhesive coated portion of the first set of flaps will be coated with the release agent so that the containers can be stacked. The pressure-sensitive adhesive of this invention must be of the type which will remain tacky when in contact with the release coating and will readily adhere to an uncoated flap when the container is set up and sealed.

It is also within the ambit of this invention to apply a sheet of release paper to a previously pressure-sensitive coated flap at the time of manufacture of the container and to.remove the release paper when the container is to be used. This has particular significance to a container having the adhesive applied to the outer surface since the container can be randomly stacked and at the same time protected from dust or dirt. In either instance, the pressure-sensitive adhesive will remain sufiiciently tacky after the release coated flap or paper is removed to adhere to the surface of an uncoated flap. Using the pressure-sensitive adhesive release coating combination as disclosed herein, it is possible to obtain adhesion over a contact surface area that easily meets the standard requirements.

Other objects and advantages will become more readily apparent when the following detailed description is read in connection with the accompanying drawings, in which:

FIG. 1 is a view of a container blank cut and scored for a square container.

FIG. 2 is a perspective view of the container folded to a collapsed position for stacking.

FIG. 3 is a perspective view of the container folded to form a closed container.

FIG. 4 is a view of a container blank cut and scored for a rectangular container.

FIG. 5 is a perspective view of the blank shown in FIG. 4 folded to a collapsed position for stacking.

FIG. 6 is a perspective view of the blank shown in FIG. 5 opened to form a rectangular container with the release coated side wall flaps folded inward and the end wall flaps positioned for engagement therewith.

FIG. 7 is a perspective view of a collapsed container shown in a flat relation with a release coated strip applied to the outside surface of the pressure-sensitive coated flap so that the container can be stacked.

showing a modified arrangement for coating the flaps of the blank with adhesive and release coatings.

FIG. is a perspective view of the blank shown in FIG. 9 opened to form a rectangular container with the release coated end wall flaps folded inward and the adhesive coated side wall flaps positioned for engagement therewith.

FIG. 11 is a view of a broken section of a container blank showing an end wall-side wall flap arrangement in which an overlap will occur between adhesively coated areas of the side wall flap.

Referring more particularly to the drawings, a container blank 10 shown in FIG. 1 includes a number of

score lines

12, 14 and 16 which divide the blank into

end walls

18 and 22 and

side walls

20 and 24. Score lines 26 and 2 8 define

flaps

18a, 20a, 22a and 24a on one side and

flaps

18b, 20b, 22b and 24b along the other side, respectively. The flaps are separated by

slots

30, 32 and 34 so that they can be folded inward along

score lines

26 and 28 when the blank is folded to form a square container and are of substantially the same length. The flaps are generally designed so that one set abuts at the center of the container. This means that their height should not exceed one-half the length of the shorter side of the container.

As seen in FIGS. 13, a pressure-sensitive coating 36 is applied to the entire surface of

end wall flaps

20a, 24a, 20b and 2412. In this container, since it will be substantially square, a release coating 38 is applied to the entire surface of

side wall flaps

18a, 22a, 18b and 2211. When the container is folded along score line 14 to the collapsed position as shown in FIG. 2, the flaps having the release coating (18a, 22a, 18b and 2212) will be in face-to-face relation with the flaps coated with the pressure-sensitive adhesive (20a, 24a, 20b and 2411). If the proper adhesive release coating combination is chosen, the adhesive will not adhere to the release coated surface of the flap and will remain tacky until the collapsed blank is opened to form the container.

If the blank is folded along score line 14 or along

score

12 and 16 so that the coated flaps face outward, collapsing of the container will not be a problem. In stacking the collapsed containers as in FIG. 8, it will be seen that it is important to align the adhesive coated flaps with the release coated flaps or the tacky adhesive will adhere to the overlapped uncoated flap. In a square container, it does not make any difference which flaps are coated with which material because on closing, both sets of flaps can be designed to meet at the center so that their entire surfaces are engaged.

When a container having the inner surfaces coated is to be used, it is opened and the flaps having the release coating are folded inward so that the outer or uncoated portions of the flaps face outward. The flaps having the pressure-sensitive adhesive coated on the inside are then folded into engagement with the uncoated surfaces of the release coated flaps to seal the container. The entire contact area between the two interengaged flaps can be covered with the adhesive, providing a strong bond between the two surfaces. When a container having the outer surfaces of the flaps coated with a pressure-sensitive material is to be used, the flaps having the adhesive coated thereon are folded inward first and the side wall flaps folded on top so that the inner uncoated surface of the side wall flaps engages the adhesive coated outer surface of the other set of flaps.

In order to use a pie-applied pressure-sensitive adhesive on the closure flaps of a container as described above, it will be necessary to select an adhesive release coat combination that will be compatible with the container material. Since the adhesive is applied to only one surface of the two surfaces which are to be joined, the adhesive must remain sufiiciently tacky while in contact with the release coat to adhere to the uncoated closure flap. Tests which were conducted on various adhesives to determine if an effective seal were formed, were made on corrugated paperboard stock and were considered effective only if fiber tear occurred at rupture.

An example of suitable proprietary hot melt pressuresensitive adhesive is one which is compounded from Elvax (a copolymer of ethylene and vinyl acetate manufacture by Du Font) and a suitable tackifying resin. Suitable tackifying resins include, but are not limited to, triethylene glycol esters of hydrogenated resins, coumarone-indene resins and styrene resins. Suitable material rubber latices which are well known in the art can also be used. A twenty-five pound per ream coating of the adhesive was applied to the corrugated stock. All of these adhesives produced a goodto excellent adhesive to uncoated corrugated and a generally satisfactory bond;

A wide variety of conventionally used release agents were tested such as starch, polyvinyl alcohol, Quilon chrome complexes, natural and synthetic waxes, silicons and a number of resinous materials. Tests were conducted by placing the release agent in contact with an aggressively tacky adhesive and realizing that a high degree of release is needed for efiicient performance on packing lines. The most effective release agent found was the conventional silicone type release polymer such as polydimethylsiloxane to which may be added a small amount of carboxymethyl cellulose. It was found that an adequate release could be obtained if 0.22 gram of the agent per square foot of the corrugated stock were used.

In some. cases where a porous material such as kraft liner board is to be used, a ten pound per ream starch size was used for adequate hold out of the release agent. Sizing is only necessary where a porous lining is used and could be omitted where a denser board such as bogus liner board is to be used. The sizing is required merely to prevent penetration of the release coating into the board. If a faster curing silicone release polymer is developed, the sizing would not be necessary at all.

It should be noted that even though the best results were obtained with a silicone release polymer used with a hot melt pressure-sensitive adhesive, any other combination could be used. which produces the desired results.

The above general description of the use of this concept was directed to a square container. In actual practice, a rectangular container such as shown in FIGS. 4, 5 and 6 is most commonly used. The container blank 50 shown in FIG. 4 is divided by

score lines

52, 54 andv 56 into end wall 58, side wall 60, end wall 62 and side wall 64.

Score lines

66 and 68 define the closure flaps 58a, 60a, 62a and 64a on the top and 58b, 60b, 62b and 64]) on the bottom. Pairs of

slots

70, 72 and 74 are cut into each longitudinal edge of the blank to separate the flaps from each other. This, again, is a standard regular slotted rectangular container made according to standard dimensions.

In FIG. 4 the adhesive coating 76 is shown applied to the entire surface of the end wall closure flaps 58a, 62a, 58b and 62b. The release coating 78 is applied only to that portion of the inside surface of the side wall closure flaps 60a, 64a, 60b and 64b which will overlap the adhesive on the end wall flaps when the blank is folded on score line 54. In the collapsed position of the container with the coatings on the inside, the adhesive coating will be covered by the release coating and will protect the adhesive from any dust or dirt. It should be noted that the adhesive is applied to the end wall flaps and on erecting the container, the side wall flaps will be folded inward first and end wall flaps folded on top. It should also be noted that the entire contact area between the end wall flaps and the side wall flaps will be bonded together.

If the blank is folded along score line 54 with the coatings located on the outside of the blank, then an overlap will only occur on stacking of the carton as seen in FIG. 8.

In a container of this type, that is, with the adhesive material on the outside, the end wall flaps will be folded inward first and the side wall flaps folded on top of the end wall flaps. Again, the entire contact area between the end wall flaps and side wall flaps will be bonded together. This is generally the way that rectangular cartons are folded, that is, with the side wall flaps on the outside and in substantially abutting relation to present a smoother-looking container. ,7

There is one disadvantage to having the adhesive on the outer surface of the carton. Since the adhesive is always tacky, .it will readily adhere to any dust or dirt which might come in contact with it and also if the collapsed containers are randomly stacked, the adhesive coated surfaces could come into contact with each other. With the coated surfaces on the inside, the adhesive surface will be covered by the release coating and will be protected from dirt or dust at all times. It should also be obviousthat the containers can be stacked in any arrangement without any possibility of the adhesive coming into contact with uncoated of adhesive coated surfaces of the adjacent collapsed containers.

To overcome this disadvantage, it is possible to coat a container blank substantially as shown in FIG. 9 so that the coatings will be on the inside surfaces of the flaps. This blank is numbered the same as the blank shown in FIG. 4. This blank is folded to the collapsed position by folding end wall 58 on score line 52 into engagement with side wall 60 and side wall 64 on score line 56 into engagement with end wall 62 and side wall 60. The outer edges of end wall 52 will abut the outer edge of side wall 64 and can be secured together by any appropriate means. The

adhesive coatings

90a and 90b on the side wall flaps are located at the ends of the side wall flaps

adjacent score lines

52 and 56 and extend inward therefrom a distance equal to the height of the end wall flap. Normally the height of the flaps is equal to one-half the length of the shortest side so that the edges of the side wall flaps abut when the container is closed.

Adhesive coatings

91a and 91b are located at the opposite end of the side wall flaps and also extend inward a distance-equal to the height of the end wall flap. Referring to FIG. it can be seen that when the container is opened and the end wall flaps folded inward, the only contact area between the side wall flaps and end wall flaps will be the area coated with adhesive.

The

release coatings

92a and 92b on the end wall flaps are located

adjacent score lines

52 and 56 so that they overlap the adhesive coatings on the side wall flaps adjacent the same score lines 52 and 56. The release coatings 93a and 9,3!) are so located on the side wall flaps that they will overlap the adhesive coatings 91a and 9111 on the opposite ends of the side wall flaps. This arrangement of the adhesive and release coatings is most advantageously used with a container which has side walls at least twice as long as the end walls It should be noted that the blank could also be folded on score line 54 and the location of the release coatings changed to prevent the adhesive from adhering to the uncoated portions of the inner surfaces of the flaps. If the side walls are longer than the end walls but less than twice the length of the end wall, the adhesive coating 91a and 911) on the edge of side wall flaps 64a, 64b will come into contact with

adhesive coatings

91a and 91b on side wall flaps 60a and 60b when the container is collapsed. In a container that has a side wall less than twice the length of the end wall, the adhesive coatings could be reduced in length by reducing the length of each coating by an amount equal to one-half the amount of the overlap. This will be more clearly understood by referring to FIG. 11 where a section of the top flaps for a container blank are shown. The end wall flaps 100 and 104 are separated from the side wall flaps 102 and 106 by

slots

108, 110 and 112. When the blank is folded on score line 114, flaps 104 and 106 will overlie

flaps

102 and 100. The adhesive coated

areas

116 and 118 will overlie the adhesive release coated

areas

120 and 122,

respectively.

Areas

124 and 126 which would normally be entirely adhesive coated but with a container of these dimensions, these areas will overlap. These areas are, therefore, divided in half and areas 124a and 126a are coated with adhesive while areas 12% and 126b are coated with adhesive release coating. The outside strips 124a and 126a are coated with the adhesive so that on construction of the container, the outer edge will be secured to the end wall flap. When the container is erected, it should be understood that the end wall flaps are folded inward first. v The side wall flaps are then folded into engagement with the end wall flaps with the adhesive coated surfaces 116 and 126a in contact with one end wall and surfaces 118 and 124a in contact with the other end wall.

If it is desired to have the long or side wall closure flaps folded on the outside to produce a smoother-looking box, the adhesive can be located on the outside of the end wall flaps. As pointed out above, this will expose the tacky adhesive to dust and dirt. To prevent this, it is conceivable to apply a strip of release coated material over the adhesive material 82 on the end wall closure flap (FIG. 7). A small section of the strip 80a may be left extending over the edge of the flap to aid in removing the strip when the container is to be erected.

It should be noted that one of the primary advantages in this arrangement of the release adhesive coatings is to obtain an adhesive bond over the maximum contact area between the side wall flaps and end wall flaps. In all of the adhesive release coating arrangements shown above, more than half of the contact area of the end flap will be secured to one surface of the side wall flap.

This invention can be used with any type of container and the container need not be collapsible. A carton blank which is cut and scored and stacked fiat could also be used having the adhesive coating applied to one surface and the release coating applied to the-other side. When the blanks are stacked, the adhesive will always overlie the release coating located on the opposite side.

In containers which have side walls twice as long as the end walls or longer, the side wall flaps are often as wide as the length of the end walls. When this type of container is erected, one side wall flap will completely overlap the other side wall flap. The pressure-sensitive adhesive will only be applied to the inside surface of one of the side wall flaps. The adhesive release coating will be applied to the inner surface of the portions of the flaps overlapped by the adhesive coated flap when the container is collapsed.

Another important advantage of this invention is that the adhesive and release coatings can be applied to the same side of a container blank that is to be initially collapsed and then stacked. This eliminates any necessity for special equipment .or extra steps to apply adhesive and release coatings to sections of both sides of the blank.

In all of the above descriptions of the adhesive coatings, the entire area of the adhesive coated surface is shown coated with the adhesive. It should be understood that these areas can be either dotted or lined with adhesive if desired.

Although only a few modifications of the present invention have been shown and described, it should be obvious that various changes and modifications can be shown and described without departing from the scope of the appended claims.

What is claimed is:

1. A self-sealing container which is both collapsible and stackable and having opposed side and end panels hinigedly connected together to define a closed figure,

closure flaps extending from and hingedly connected to the edges of each of. said side and end panels, said flaps being substantially coextensive in length with respect to their connected panel,

said side panel flaps in the collapsed position of the container being disposed in face-to-face contacting relationship with the end panel flaps,

pressure-sensitive adhesive closure securing means applied to inner surface of one set of flaps, only, said securing means being capable of adhering to the uncoated portion of the container,

adhesive-release means applied to the portion of the inner surface of the other set of flaps disposed in facet-o-face relation with the adhesive securing means on the said one set of flaps to prevent the pressuresensitive adhesive from adhering to the inside surface of the other set of flaps when in the collapsed position.

2. A self-sealing container which is both collapsible and stackable and having opposed side and end panels hingedly connected together to define a closed figure, said side panels being longer than said end panels,

closure flaps extending from and hingedly connected to the edges of each of said side and end panels, said flaps being substantially coextensive in length with their respective panels,

pressure-sensitive adhesive closure securing means applied only to one surface of the closure flaps secured to the end panels of the container,

an adhesive release material applied to the portion of the surface of the .side panel flaps which overlies the adhesive securing means on said end panels flaps, whereupon said container blank can be collapsed with the pressure-sensitive adhesive securing means opposite the release material on the side wall flaps.

3. A self-sealing container which is both collapsible and stockable and having Opposed side and end panels hingedly connected together,

a closure flaps extending from and hingedly connected to the edges of each of said side and end panels, said flaps, when said container is collapsed and stacked, being disposed in face-to-face contacting relationship,

a pressure-sensitive adhesive coating on the outside surface of said end wall closure flaps, and

adhesive release means applied to the outside surface of the side wall flaps in the areas which will overlie the adhesive coating on the end wall' flaps when the container is collapsed and stacked to prevent said adhesive coated flaps from adhering to the side wall flaps of the container when said containers are collapsed and placed in a stacked position.

4. A container according to claim 2 wherein said adhesive release means is applied to the portion of the side wall flaps which comes in contact with the adhesive when the containers are in the collapsed or stacked position.

5. A container according to claim 2 wherein said adhesive release coat includes a silicon-type release polymer.

6. A container according to claim 5 wherein said adhesive includes proprietary hot-melt pressure-sensitive adhesive which will permanently adhere.

7. A container according to claim 5 wherein said adhesive includes a latex based pressure-sensitive adhesive which will permanently adhere to the container surface.

8. A self-sealing container according to claim 1 wherein said pressure-sensitive adhesive is applied to the entire inner surface of the end wall flaps only.

9. A self-sealing container according to claim 8 wherein said release coating includes a silicon release polymer.

10. A self-sealing container according to claim 9 wherein said adhesive includes a latex based pressure-sensitive adhesive which will permanently adhere to the container surface.

11. A self-sealing container which is collapsible and stackable and having opposed end walls and side walls, said side walls being at least twice as long as said end walls, closure flaps hingedly connected to the side and end walls and being substantially of the same length as the end and side walls and of a height equal to less than one-half the length of the end walls,

pressure-sensitive adhesive securing means applied to the ends only of the inside surfaces of each of said side wall flaps and extending inward a distance equal to the height of the end wall flaps said adhesive being .sufficiently tacky to adhere to the uncoated portions of the container, and

releasing means coated on the inside surfaces of the flaps in a position to overlap the adhesive securing means when the container is collpased, whereby on opening the container and closing the flaps, the side wall flaps will be bonded to the entire outer surface of the end wall flaps.

12. A self-sealing container which is collapsible and stackable and having opposed end walls and side walls, said side walls being longer than the end wall-s but less than twice as long as the end walls,

closure flaps hingedly connected to the side and end walls and being substantially of the same length as the end and side walls and of a height equal to less than one-half the length of the end walls,

pressure sensitive adhesive securing means applied to the portion of the end of the side wall flap inside surfaces adjacent the folded hinged connection of the container when the container is collapsed,

and pressure sensitive adhesive securing means applied to one-half. the portion of the other end of the inside side wall flaps which overlaps the opposite side wall flaps when the container is collapsed,

the pressure sensitive adhesive securing means being so located that it will engage the end wall flaps when the container is erected, and adhesive release means coated on the inside surface of the flaps in a position to overlie the portions of the side wall flaps coated with the adhesive securing means when the container is collapsed.

References Cited by the Examiner UNITED STATES PATENTS 1,094,451 4/ 1914 Martin. 2,217,757 10/ 1940 Lindley 229-37 2,874,891 2/1959 Kelsall 229-37 3,116,008 12/1963 Greene et al. 3,141,600 7/ 1964 Rosenthal. 3,184,144 5/1965 Greene et al 229-37 JOSEPH R. LECLAIR, Primary Examiner.

DAVIS T. MOORHEAD, Examiner.

Claims

1. A SELF-SEALING CONTAINER WHICH IS BOTH COLLAPSIBLE AND STACKABLE AND HAVING OPPOSED SIDE AND END PANELS HINGEDLY CONNECTED TOGETHER TO DEFINE A CLOSED FIGURE, CLOSURE FLAPS EXTENDING FROM AND HINGEDLY CONNECTED TO THE EDGES OF EACH OF SAID SIDE AND END PANELS, SAID FLAPS BEING SUBSTANTIALLY COEXTENSIVE IN LENGTH WITH RESPECT TO THEIR CONNECTED PANEL, SAID SIDE PANEL FLAPS IN THE COLLAPSED POSITION OF THE CONTAINER BEING DISPOSED IN FACE--TO-FACE CONTACTING RELATIONSHIP WITH THE END PANEL FLAPS, PRESSURE-SENSITIVE ADHESIVE CLOSURE SECURING MEANS APPLIED TO INNER SURFACE OF ONE SET OF FLAPS, ONLY, SAID SECURING MEANS BEING CAPABLE OF ADHERING TO THE UNCOATED PORTION OF THE CONTAINER, ADHESIVE-RELEASE MEANS APPLIED TO THE PORTION OF THE INNER SURFACE OF THE OTHER SET OF FLAPS DISPOSED IN FACETO-FACE RELATION WITH THE ADHESIVE SECURING MEANS ON THE SAID NE SET OF FLAPS TO PREVENT THE PRESSURESENSITIVE ADHESIVE FROM ADHERING TO THE INSIDE SURFACE OF THE OTHER SET OF FLAPS WHEN IN THE COLLAPSED POSITION.