US2769589A - Closure construction for containers - Google Patents

Description

' Nov. 6, 1956 G. A. MOORE 2,769,589

CLOSURE CONSTRUCTION FOR CONTAINERS Filed May 12, 1954 INVENTOR. o

United States Patent CLOSURE CONSTRUCTION FOR CONTAINERS George Arlington Moore, New York, N. Y. Application May 12, 1954, Serial No. 429,232 3 Claims. (Cl. 229-37) This invention relates to a method of forming an improved closure structure for containers made primarily of substantially rigid fibrous board sheet material, the container blank having segments of wall portions adapted for being folded to form a container body with folded end closures that tightly close the container in such manner that avoids vulnerable weaknesses of the enclosure wall converging corner ends.

The present invention constitutes an improvement in the structure of my co-pending application Serial No. 292,226, filed June 7, 1952, now Patent No. 2,729,385, and has for its principal object to provide an improved closure structure for containers that avoids collision of bulk-forming folded material that would otherwise destroy the efliciency of the closure.

A further object of the invention is to provide a blank for a container having multiple wall segments arranged in a novel and improved manner that are integrally related with one another outwardly of the side wall defining areas of the blank and which may be folded in pairs without bulk collision.

Another object of the invention is to provide a folding carton type container with closure forming wall segments that may be folded in closure formation to hermetically seal the converging corner ends thereof in an improved manner.

A further object of the invention is to provide a means for forming a closure structure in which a portion of the closure forming segments construct a strong support upon which to form other portions of the enclosure walls to complete the closure.

A still further object of the invention is to provide a closure for containers having a pair of folded segments that resiliently co-act with another pair of folded opposing segments that are provided with means to mechanically interlock folded members to seal the closure structure.

Another object of the invention is to provide a closure for shipping cases of relatively heavy board material'that will render such cases suitable for transportation of granular or powdered materials without the use of inner bags or liners.

Further objects Will be apparent as the following description progresses.

Referring to the drawings:

Fig. 1 is a fragmentary view of a blank embodying the principal arrangement of closure forming end segments of the instant invention; the body portion of the blank being shown with a part broken away,

Fig. 2 is a fragmentary view in perspective of the blank of Fig. 1 formed into a container body and showing the open relationship of the closure forming end segments,

Fig. 3 is a fragmentary view in perspective of the com tainer showing an opposing pair of closure formingsegments folded inwardly of the container body wall,-and further showing one folded segment in dotted lines with a wing margin thereof in an intermediate position,

Fig. 4 is a fragmentary view in part cross-section of a part of the folded closure segments taken on line 44 1n Fig. 3,

Fig. 5 is another fragmentary view in part cross-section of another part of the opposing portions of folded segments taken along line 5-5 in Fig. 3, and showing the resilient relationship of the folded margins,

Fig. 6 is a fragmentary view in perspective of the container and closure showing an intermediately disposed folded closure panel and its relationship with the first folded segments,

Fig. 7 is a fragmentary view in perspective of the container showing the completed closure with the secondary closing means in overlapping panels in interlocking relationship, and

Fig. 8 is a fragmentary view in cross-section of a part of the completed closure taken on line 88 in Fig. 7.

Numerous attempts have been made to form containers of paper board material with corner pleats which are folded with the intention of sealing the converging corner ends of the container structure. Such pleats when folded of relatively stiff paper board material form a collision in the margins of the fold which produces an unruly lump of bulk forming material which holds the adjacent folded wall flaps apart by the springing characteristics of the folded pleats. It has also been discovered that the wall sections having the pleats can not be folded independently of its related adjacent walls without drawing the latter walls inwardly and downwardly to fold the pleats. This action causes the pleats to float in an'unruly manner away from its related wall portions while drawing all of the closure flaps in a downward movement from each of its respective base folding lines. Interior supporting means can not be provided in a filled container therefore, the folded bulk forming pleats can not be sufiiciently compressed to avoid a separation of the folded closure flaps adjacent to the folded pleats.

In my co-pending application heretofore mentioned there is disclosed corner forming pleats that are folded without altering the initial position of each of its respective depending wall panels while forming a pair of opposing closure sealing ledges for use of the said wall panels. The present invention provides structural embodiments that improves on the former invention to increase the efficiency of the closure construction of the container.

Referring first to Fig. 1 of the drawings, the numeral 4 indicates a blank of rigid or semi-rigid fibrous board material. The particular style of the blank selected for illustration is similar to those used to form folding cartons, the blank however having an improved arrangement of laterally opposed wall segments which are adapted to form fiat and tight end closures of nated corner closing pleats embodied therein.

The blank 4 is generally rectangular in shape and is provided with parallel vertical side edges 10 and 11, and between the side edges are crease lines 12, 13, 14 and 15 which are ruled suitably into the surface of the blank for accuracy of folding purposes. Crease line 12 is spaced inwardly of the side edge 10, crease line 13 is spaced from crease line 14 and crease line 15 is spaced inwardly of the container with larni-- Spaced between side edge and crease line 12 is a longitudinal body marginal portion'16 of the blank which provides for a body seam of the container when formed, marginal portion 16 is provided 'with a horizontal crease 1ine16.

The wall'portion'b'etween the crease lines 12'and 13 provides a side wall area 17 which is further defined with the horizontal crease line 18 which'may be opposed with another creaseline parallel theretoat the opposite end of the blank not shown. This will hold true in general for each of the segment wall portions of the blank as hereinafter described. a e

The wall portion between the crease lines 14 and provides another side wall area 19 which is further defined as having a horizontal creaseline 29, said side wall area 19 being adapted when folding the blank to be opposed to the side wall area 17.

The wall portion between the crease lines 13 and 14 provides another side wall area 21 which is further defined with a horizontal crease line 22 which is central of and. downwardly-of the crease lines 18 and 20.

Thevwall portion between the crease line 15 and side edge 11 provides another side wall area 23 further definedwith a horizontal creased line 24 which is positioned in line with crease line 22, and side wall area 23 being adapted to oppose the side Wall area 21 when folding the blank toform the container.

The side wall forming portion 17 of the blank provides a foldable end segment consisting of a closure'forming panel. 25 which extends upwardly of the crease line 18 and having two parallel outwardly extended crease lines 26 from each terminal end of said crease line 18. The terminal end of the crease line 26 joins with a continuing side edge 27 of panel 25. The crease lines 26 are extended into a slit line portion 28 and side edge portion 29, both of which lines form an opposite side edge of the panel 25, the said panel having a longitudinal end edge 30.

The panel 25 is provided with an opposing pair of foldable triangular shaped wall portions 31 each defined With a horizontal slit portion 32, the inner end of which forms of the triangular shaped wall portions 31 and 45 of panels of horizontal crease line 51 and upwardly and outwardly sloping edge 53 extending upwardly to form ends of hori zontm edge 54 of margin 50.

The side wall forming portion 23 of theblank 4 provides a foldable end segment 56, 57 that extends outwardly of horizontal crease line 24, marginal portions 56 and 57 being separated by horizontal crease line 58., The general arrangement, shape and area of segment 56, 57 is identical to end segment 49, 50 of panel 21 except side wall forming panel 23 and its end segment is provided with a straight an apex of a downwardly and outwardly sloping crease line 33 each terminating at the inner end of the horizontal crease line 16 and one end of the crease line 22 respectively. The slit lines 32 of the triangular shaped wall portion 31 adjacent creaseline 12 continues with a projected edge 34 defining the end of a .wall portion 35. One of the horizontal slit lines 32 terminates at vertical slit line 28. The pair of triangular defined wall portions 31 are provided in wall panel 25 for purpose hereinafter to be described.

The side wall forming portion 19 of the blank provides a foldable end segment panel 37 which extends outwardly of the crease line 2% and having two parallel outwardly extending crease lines 38 each of which lines extend into slit line 39 and edge 40 of the panel 37. The end of the panel 40 is defined with a centrally disposed horizontal edge 42 central between a pair of notches, each notch.

being defined with a vertical edge Y43 and an upwardly and outwardly sloping edge 44.

The panel 37 is also provided with a substantially iden-- tical pair of opposing foldable triangular shapedwall pdrtions 45 same as provided in the panel 25; Eachpair of triangular wall portions 45 being defined as'having' a hori- 4 zontal slit line 46 extending outwardly to verticalslit edges 39 and terminating inwardly of panel 37 to crease line 47 which slopes downwardly and outwardly to converging corner ends of crease lines 14, 22 and'15, 20 respectively. 1

' The side wall forming portion vided with a foldable end segment extendingoutwardly of crease line 22 and marginally sub-divided into two foldable wall sections 49 and 50 which are substantially 7 divided in two equal wall portions by a central horizontal crease line 51. Defining sides of the lower wall portion 49 extend outwardly in integral relationship with each 21 of the blank 15 m vertical edge 11 thus leaving one triangular wall portion 45 that extends into the adjacent panel segment 37.

The blank 4 may be coated with Wax or any other suitable resinous protective covering material having thermoplastic properties with which the seams of the container closures when formed, may be firmly sealed by application of heat and/or pressure. r a

The blank may be printed with a pattern of resinous adhesive material such as heat activated hot-melt compounds that contain dry solids and are solvent free and hence odor-free. The said pattern may comprise an adhesive coating upon selected areas of the blank as desired and that constitute the seam zones of the closure forming panels including the triangular shaped wall portions 31 and 45. The longitudinal seam of the container may be formed with a fast setting liquid'or viscous adhesive that may be used on conventional carton blank folding machines for rapid production of container folded bodies.

When coating the blank with wax, the closure forming panels 25 and 27 maybe adapted with means to lock the closure to avoid use of seam bonding adhesive if desired. In such case the panel 25 is provided with two opposed vertically slit lines 63 which extend downwardly of the horizontal end 30 of the said panel. The said slit lines 63 provide a tongue portion 64 betwcenthe slit lines. The

panel 37 is provided with a U-shape slit section'defined with a horizontal line 66 spaced upwardly of crease line 20 and a pair of vertical lines 67 extending upwardly from ends of line 66 that coincide in spaced relation to vertical slit lines 63 extending downwardly from edge 65 a in panel 25. V V

The body of the container may be formed by feeding the blanks through well known carton folding machines and shipped to packers'in collapsed space saving 'bulk,

The folded body may be opened to form the sidewalls of the container as illustrated by the container body 68 in Fig.2. The longitudinal se'amareas16 and'35 of the container are formed upon the inner surface of side wall 23 and a portion of the end segment wall'margin 56. The

tab portion 35 isrintegrally related to one of the triangular defined portions 31 disposed at right angles thereof. The

end edge 34 of wall portion 35 is spaced downwardly of' the crease line 58. This arrangement is important-to allow freedom for the folding of the wing-like rharginal portion 57 to double back when forming the closure of the container.

The body of container 68 may shaping mechanical form when it is desired to construct the container body and'a bottom closure thereof with accuracy of precision. The front side wall 19pof the: container is opposedto a back side wall 17. An ad jacent sidewall 23 is'opposed to another sidewall 21.

The front panel 37 of the side wall 19 is provided 'with a pair of the heretofore described triangular shaped wall '7 1 portions 45. The back panel 25 of the side wall 17 is provided with a pair of the heretofore described triangube formed over a body 7 lar shaped wall portions 31. This arrangement of triangular defined portions permits the marginally separated end segments 56, 57 and the opposing end segment 49 50 to be folded inwardly and downwardly in the mouth of the container body and double back the portions 31 and 45 without pulling each of the adjacent opposing panels 25, 37 inwardly and downwardly from their substantially vertically disposed position as illustrated in Fig. 3.

Each of the upper marginal portions 50 and 57 may be first folded outwardly anddownwardly on the crease lines 51 and 58 to primarily break the said crease lines prior to the folding of each of the lower portions 49 and 56 then being folded inwardly and downwardly on the crease lines 22 and 24 which momentarily straightens the pre-folded portions 50 and 57 so that opposing sides of each lower wall portion 49, 56 may carry inwardly an opposing pair of triangular wall portions 31 and 45 to form self-superimposed doubled back Wall portions disposed in right angular relationship with each of the two dependent wall portions 49, 56 and 25, 37 as illustrated in Figs. 3, 4, 5 and 6. Each of said pairs of doubled back folds 31, 45 are flatly compressed while in this position to prepare each doubled back fold portion with a relatively sharp base corner edge 73 including relatively sharp folded corner edges 33, 47. Each of said folds 31, 45 are now prepared to be folded uniformly and efficiently when folding the closure forming panel members 25 and 37. When relatively heavy gauge sheet is used for making the container, the crease lines 33 and 47 may be altered by employing cut scores which will facilitate the doubling back of these wall portions.

When the adhesive is applied to the surface of the blank as hereinbefore described, the superimposed layers of triangular shape folded portions 31 and 45 may be bonded upon corresponding surface portions of panels 25 and 37 when being compressed to provide strong support of the in-folded marginal wall portions 49, 50 and 56, 57 in substantially horizontal position. Each of the marginal portions 50 and 57 are then folded upwardly, outwardly and downwardly from their respective crease lines 51 and 58 to form doubled back wall margins that are resiliently active, said resilient margins being pressed downwardly and confined in fiat engagements with each of their respective dependent under wall portions 49 and 56 prior to the folding of the closure forming panel 37. The displaced side edges 71 taken from the slit portions 46 in the panel 37 lie in a vertical position. A bottom portion of each edge 71 is in substantial abutment with the horizontally disposed edges 52, 60 of the flattened doubled back margins 50, 57. The edges 52, 60 extend inwardly in line with the vertical edges 71. Each of the side edges 53, 61 of the said doubled back margins and edges 52, 60 recess in which to receive, in mortis fitting relationship, each inwardly disposed layer of the doubled back triangular wall portions 45 when folding the closure forming panel 37.

The in-folded opposed doubled back wall portions 49, 50 and 56, 57 have their respective side edges 28, 39 and 11 in edge to face abutments with interior marginal Wall portions of the opposing front side wall 19 and back side wall 17 adjacent to the folding lines 20, 18 respectively. The edges 28, 39 and corner edges 70 of each of the triangular folds 31 and 45 form sides of folded margins 49, 50 and 56, 57 one of the triangular folds 31 co-operating with the wall abutted edge portion 11 by virtue of the folded portion of the longitudinal body seam tab portion 35. The said lower sides 11, 28, 39 extend inwardly to folded corner lines 51 and 5:8, and turn upwardly, downwardly and outwardly to double back and provide the transversely disposed side edges 52, 60 and diagonal side edges 53 and 61. The end edge 54 of the folded wing 50 when flattened downthereof form a wardly, is disposed upon the top of corner edge of the end side wall 21. The end edge 59 of the folded wing 57 when flattened downwardly is disposed upon the top of corner edge of side wall 23. This defined arrangement adds materially to the supporting strength of the said pair of opposing iii-folded segments which now constitute sealing ledges having resiliently active margins uponwhich to form the closure of the container.

The illustrations of Figs. 4 and 5 clearly shows the principle of constructing the initial foundation upon which to build the enclosure walls of the container closure as hereinbefore described. Fig. 4 illustrates a typical corner portion of the container structure in preparation of forming the closure. The folded wall portion 56 with its self-superimposed folded portion 57 is supported in horizontal position by vertically disposed bracket-like folded wall portions 31. The related end edges 69 and 72 of the folds being positioned with respect to each other so that when the closure is completed the said relationship provide means to seal off these edge from being exposed within the interior of the container when completed and thus efiiciently seal the converging corners thereof.

Fig. 5 illustrates the relationship of the co-activ'e resiliency of the sealing ledge provided by the doubled back folded marginal wall portion 57 prior to being pressed downwardly to contact the wall portion 56 of the folded panel. The top margin '57 is shown in the same relative position as shown by the folded margin 50 in dotted lines illustrated in Fig. 3.

The panel 37 is folded inwardly and downwardly from its crease line 20 to overlap and make contact with each of the opposed outwardly and downwardly doubled back wings 56 and 57 as illustrated in Fig. 6. The pair of doubled back pleat portions having been flatly compressed when formed and fold with the panel in an orderly bend without swelling out and forming an unruly bulk of material which otherwise would form wall separating lumps of material. Such detrimental effect has been discovered as taking place when tried by those skilled in the art of making container of fibrous board material.

The inner disposed layer of each of the triangular folds 45 are 'mortised into each recess formed by the notch in a side of each folded wing portion and 57 as illustrated in Fig. 6. The edge 71 (Fig. 3) of the said folded portion 45 are disposed in abutment with edges 52 and 60 of notches in sides of folded margins 50 and 57 of said wings. Said abutment of edges are blocked off from exposure of the interior of the container by the in-most marginal-1y folded portions of the closure sealing ledges.

The end edge 42 of the folded panel 37 is engaged in edge to face abutment with an inner wall marginal portion of the back side wall 17 of the container, and adjacent the folding crease line 18 disposed therein for the folding of the opposing closure panel 25. The said abutment is not interfered with by the vertically positioned pair of side opposed doubled back folds 31 formed in the paned 25. The edges 43 of the notches in the folded panel 37 lie in abutment with inner end edges 72 which are takenfrom the initial slit lines 32 in the panel 25. A pair of the side edges 52 and 6!) of notches in the folded wings 50 and 57 respectively, lie in coplanar edge relationship with the edges 43 of notches. The other side edges 44 of the notches in the panel 37, and the other side edges 53 and 61 of the folded wing portions 59 and 57 each edge of aligned notches (Fig. 6) being disposed in coplanar surface relationship with each other to form a recess for mortis fitting engagement with each of the inner layer portions of triangular folded and compressed wall portions 31 when folding the panel 25. The said portions 31 are provided with relatively sharply folded corner edges due to having been compressed as hereinbefore described.

Adhesive maybe applied to the panel 37 prior to the V folding thereof should the container blank not be provided with-anlactivator .type of adhesive or protective coating as hereinbefore mentioned. The panel 25 in such case may receive an application of adhesive upon'the inner portions 31 will engage in mortis fitting relationship with each of the recesses formed by the previously folded closure forming members as hereinbefore'described so that adhesive coated surfaces of engaging panels will meet in uniform flat surface relationship.

The completed closure of the container 68 as shown in Fig. 7 presents the closure ashavingbeen closed without use of adhesive. This may be accomplished by providing the panel 37 of the closure with slit lines 66, 67 and the panel 25 with slit lines' 63 as hereinbefore described for the blank 4 in Fig '1. Such adaptation of means for closing the container without use of adhesive is particularly useful when forming the end closure of a waxed container. i

The closure is folded and formed in the manner hereinbefore described with the exception of a slight change in the manner offolding the panel member 25. When folding said panel 25 inwardly and downwa'rdlyfrom the folding crease line 18 thereof, the panel 25 is arched during the folding so that.the end edge portion 65 of the slit tongue portion 64 will enter into the yieldable wall portion provided by the slit lines 66 and 67 in the first tainer from pressure theclosure walls are rendered flatly disposed and securely retained in seam forming relationship.- a v v .p 7 The container shown in-Figs. 7 and 8 may be opened conveniently by lifting the tab portions 75 which will bend on each of'two crease lines '77 which may be provided in thepanel 2 5 if desired. The tabsmay be pulled upwardly toward the back of the container which withdraws the inserted tongue 64 from the slit portion 66 thus releasing the interlocking engagementsof the closure panels to open the container. 7 The closure may be folded again to reclose the container. This operation of opening and re-closing the container may be repeated many times without depreciating the efliciency of the closure structure of the container. The co-acting effects of the resiliently active sealing ledge portions and end closing panels of the closure structure is ever active during the normal use period of the container. 7 4 a Iclaim:

. 1. A closure for rectangular containershaving four side walls arranged in opposing pairs, two opposing side walls having a first pair of substantially like, foldable flaps, each of said flaps being divided alonga hinge line into two foldable marginal portions with an inner portion hinged to the outer portion, the two other opposing side walls having a second pair of foldable flaps connected thereto along fiapfold lines, each .of said second pair of flaps hav 'ing a pair of slit lines extending. inwardly a short distance from the side edges thereof in spaced, parallel relation to the flap fold line and av short crease line connecting each end of each slit line to a, corner of the container to define foldable triangular pleats integrally relatedwith a folded panel 37. Downward pressure upon the inserted v tongue portion 64 in the second folded panel 25 opens the slit'section 66 which is allowed toyield downwardly from the slit sides 67 thereof. Further downward pressure upon the whole of the folding panel 25 flattens the said panel and completes the insertion of the tongue portion 64 with its end edges 65 being in substantial abutment with an interior marginal portion of the front side wall 19 adjacent the upper longitudinal folded junction corner edge '20 thereof as illustrated in the cross-sectional view of this portion of the closure in Fig.8. 3 r

The arrangement thus described for locking the closure panels 25 and 37 each to the other is rendered effective by locating the slit line 66 relatively close to the folded corner edge 20 of the front side wall 19. The relatively narrow margin 76 (Fig. 7) between the edge 66 and longitudinal corner edge 20 provides strength of resistance to the said narrow margin which firmly secures the inserted tongue portion 64 engaged therewith. i

The simple means of retaining the inter-lockingrelationship of the overlapping panels 25 and 37 is efiiciently augmented by the co-acting effects of the pair of resilient superimposing wall portions 50 and 57 of the closure members. The resiliency of these folded members oppose the overlapping panels with ample resistance to close opposing marginal sides of the container adjacent the sealed converging corner ends of each opposing side wall 21 and 23 thereof, this augmenting resistance exerted against the corner sealed interlocked panels strengthens the securing arrangement provided in the end closing panels to retain the closure structure in seam forming relationship.

The container having been waxed or otherwise treated with wall protective plastic material, the closure formed thereto as above described may be subjected to heat while flap of said first pair, each of said first flaps being folded inwardly and downwardly to a substantially horizontal position, said pleats being superimposed upon said second flaps, each ofthe outer-most marginal portions of said first flaps being provided with a pair of opposed open notches cut inwardly of the side edges thereofwith an edge of each notch being parallelto and spaced outwardly of the dividing line of said first flaps, each said outer-most marginal portion being folded upwardly, outwardly and downwardly in self-superimposing relationship upon the inner-most marginal portion, the free side edge portions of each marginal portion being disposed in abutment upon an adjacent side wall of thecontainer, said parallel edge of each notch being positioned in the same plane as the slit edge of a pleat, each of said second flaps being folded inwardly and downwardly in overlapping container closing relationship, the outer edge of the first folded of said second flapsbeing provided with a pair'of open notches having edgesth'at' coincide with'one notch in each of said outer-most marginal portions and the pair of pleats in the otherfof .said second fiaps being morticed into'said pair of coinciding notches.

pressing the exterior surface of the panel 25 which compresses the intermediate disposed layers of the closure 7 structure. This action causes the wax or other wall proteetive material to soften by the heat imposed to the closure walls which has a tendency to blend the protective material in the seam forming marginsof the closure. While still under pressure the heat is withdrawn and the closure chilled to set and harden the protective material to augment the seal of the closure. After withdrawing the con- 1' 2. A flat blank of, foldable material adapted to be formed into a container having'a rectangular cross section and a closed end, saidblank compr sing asheet of said material being'cut and creasedfto form four side wall panelsarranged in series and having a glue panel positioned at one end, each of said side wall panels having outwardly extended foldable flaps defined by a longitudinal crease line, a first pair of spaced flaps. having lower portions thereof integral with the second pair of spaced flaps and one flap of said second pair having a lower portion integral with an extension of the glue panel, said first pair of flaps being substantially identical and each being a separated into inner and outer marginal portions by a V longitudinal score line spaced outwardly of the crease line, each side of the sccond fiaps having a short longitudinal slit line extending inwardly from'each side, edge, eachend of each slit;line being connected to the adjacent. corner. of a side wall panel by, a fold line, each outenmarginalr portion beingprovided with a pair of inwardly opposed triangular shaped open notches, each notch having a short longitudinal edge spaced outwardly. of said score and an upwardly and outwardly sloping edge terminating at an 7 Outer corner of the outer marginal portion, said score line being disposed substantially transversely midway between each slit line of said second flaps and each longitudinal edge of said notches, one end of said slit lines being connected to one end of said longitudinal edges by a transverse cut line, the outer end of one of second flaps being provided with a pair of open triangular shaped second notches, each second notch having a transverse edge spaced inwardly of a side edge of said one second flap and extending downwardly from said end and an edge therefrom sloping upwardly and outwardly to an outer corner of said one second flap, all of said slit lines being disposed in longitudinal alignment and the length of each slit line being substantially equal to the length of each said longitudinal edge and transverse edge of the triangular shaped notches.

3. A flat blank as set forth in claim 2 wherein the first foldable flap of said second pair being provided with a longitudinal slit line spaced outwardly of and substantially parallel with the fold line of the flap and each end of said slit line terminating in junction with an outwardly directed short transverse slit line thereby providing a yieldable wall portion in said flap with opposite ends thereof each being spaced inwardly transverse of each of said short longitudinal slit lines extending inwardly from each side edge of the flap, the second foldable flap of the second pair being provided with a pair of opposed short slit lines directed inwardly transverse from the longitudinal end edge of the flap and the length between said pair of transverse slit lines being substantially equal to the length between said transverse slit lines defining the yieldable Wall portion provided in said first foldable flap.

References Cited in the file of this patent UNITED STATES PATENTS 228,008 Wenzel May 25, 1880 1,482,857 Moore Feb. 5, 1924 1,921,150 Bomberger Aug. 8, 1933 2,297,571 Lowey Sept. 29, 1942 2,337,198 Holy Dec. 21, 1943 2,492,712 Ringler Dec. 27, 1949 2,553,803 Zinn May 22, 1951 2,553,804 Zinn May 22, 1951 2,596,224 Eaton et al. May 13, 1952 2,652,186 Zinn Sept. 15, 1953 2,729,385 Moore Jan. 3, 1956

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