US3647133A

US3647133A - Package, preferably for dry and frozen material, and an arrangement for the production of such a package

Info

Publication number: US3647133A
Application number: US65491A
Authority: US
Inventors: Od Wikar Christensson
Original assignee: Christenssons Maskiner and Patenter AB
Current assignee: Christenssons Maskiner and Patenter AB
Priority date: 1970-08-20
Filing date: 1970-08-20
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07

Abstract

A package of polygonal cross section having a thin end closure closing at least one end. The closure extends over onto and is attached to the sides of the package. Airtightness is improved by attaching the closure such that the end of the package is bent inwardly at least at the corner, in somewhat the form of a frustrum pyramid. An apparatus for closing such a package comprises a heatable tool having inwardly sloping sides to press the end closure onto the edge of the package end and concurrently force the end into the frustrum pyramid shape.

Description

I United States Patent [151 3,647,133 Christensson 1 Mar. 7, 1972 [54] PACKAGE, PREFERABLY FOR DRY 2,690,288 9/1954 Allen et a1 ..229/5.5 X

AND FROZEN MATERIAL, AND AN 2, 2,093 2/1959 Chap ARRANGEMENT FOR THE PRODUCTION OF SUCH A PACKAGE 3:050:229 8/1962 Neff ..229/51 TS X 72 l t: OdWikm-Chiste B 1 Stockholm, FOREIGN PATENTS 0R APPLICATIONS 284 648 11/1952 Switzerland ..229/37 E 3 l gm o [7 Ass'gnee gebohg, fifg f j f gfggg fi 902,601 8/1962 Great Britain ..229/55 Sweden 7 Primary Examiner-Davis T. Moorhead [22] Filed: Aug. 20, 1970 Attorney-Larson, Taylor and Hinds [21] Appl. No.: 65,491 [57] ABSTRACT 52] U S Cl 229/37 229/3 5 229/51 Ts A package of polygonal cross section having a thin end closure [51] B65d 6 365d 5/54 closing at least one end. The closure extends over onto and is [58] Fieid R 5 5 3 l l 5 R attached to the sides of the package. Airtightness is improved by attaching the closure such that the end of the package is bent inwardly at least at the comer, in somewhat the form of a [56] Reierences Cited frustrum pyramid. An apparatus for closing such a package comprises a heatable tool having inwardly sloping sides to UNITED STATES PATENTS press the end closure onto the edge of the package end and 2 41 l 622 1 H1946 G l I 229/3 5 concurrently force the end into the frustrum pyramid shape.

uyer et a 2,562,579 7/1951 Ringler ..229/37 E X 5 Claims, 6 Drawing Figures l8 I 7 IO PATENTEBMAR 1 m2 INVENIOI 00 W. CHRI STENSSON 9451604 Ja /w gar/s ATTORNEYS PACKAGE, PREFERABLY FOR DRY AND FROZEN MATERIAL, AND AN ARRANGEMENT FOR THE PRODUCTION OF SUCH A PACKAGE FIELD OF THE INVENTION This invention relates to packages, preferably for dry and frozen materials, and particularly to closures and manner of applying such closures.

BACKGROUND AND SUMMARY OF THE INVENTION Within the packaging industry, attention to a continuously increasing rate has been directed toward the task of achieving economical manufacture, and especially toward achieving economies in consumption of materials. One of the most opportune areas in which such economies may be achieved is in the design of the package blanks such that there will be a minimum wastage of material when the blanks are stamped out from a given piece of material,v such as cardboard. wastage of material commonly occurs in the corner surfaces and the like between the side surfaces of a package and its adjacent parts forming the closing flaps. The more closely a package blank approaches a completely rectangular outer contour, the less will be the wastage of material, and the greater will be the number of package blanks which may be stamped from a given piece of cardboard or the like.

Packages, however, must be reasonably tight. In many cases, such as where a vacuum exists inside of the package, complete tightness is required, and it is difficult to achieve this complete tightness while also effecting a reduction in the amount of material used. In other cases, although such complete tightness may not be required, it nevertheless is important to obtain the best possible tightness under the circumstances. This is especially so in those packaging instances where it is important to prevent passage of moisture from or to the interior of the package. For instance, when dried products are packed, it is important to prevent moisture entering the package from the outside air, and when frozen products are packaged, it is important to prevent leakage of moisture or liquid from the package. Such dried products might include cakes, roasted nuts, chips, etc. An example of a frozen product would include ice cream, for instance. An example of deep frozen products would include many different kinds of cooked vegetables, which may be frozen liquid in order to retain their moisture consistency.

Exemplary of packages which have been developed in an ef fort to achieve economies of material while at the same time achieving satisfactory tightness is a package of polygonal, preferably rectangular cross section, which is produced'by folding a piece of cardboard along given creasing lines, whereby pasting flips are arranged at the upper and perhaps also at the lower end of the package, an end closing piece of a thinner, easily bendable material being attached to the pasting flaps. In a package of this type, it is especially important to ensure tightness at the sides and the corners, where the cardboard of the sides meets the end closing piece. For achieving improved tightness in these areas, various solutions have been proposed. Included among these is a procedure wherein the closing flaps on the main part of the package, which is made of cardboard, are cut in inclined directions at their ends, sothat the slanting edges will contact each other when the cardboard blank has been folded into its form, polygonal in cross section. The cardboard piece may be made from cardboard covered by plastic on at least one side, but preferably on both sides, and the plastic by which the cardboard piece is covered may be heat weldable. Thereby the end closing parts may also comprise a thin foil of heat closable or weldable plastic. However, even in packages constructed in this manner, it has been found that the required tightness often is not achieved. Investigations have shown that this shortcoming apparently stems from the extremely small, but nevertheless relatively substantial, openings occurring at the corners of the package. The slot between the slanting flaps apparently acts as an air passage, directly into or from the comer, and the mouth of this air passage situated in the corner is notcovcred satisfactorily by the plastic foil lying over the package. It has, therefore, further been proposed to make the plastic foil bigger than the end surface of the package part made of cardboard, whereby an endpiece of the plastic foil will be available to be folded down onto the package sides. In this way, one would expect that a substantially better tightness would be achieved, but surprisingly enough, the tightness still is often unsatisfactory. Further investigations in this area form the basis of the instant invention.

To weld the plastic foil over the mouth of the package, it is necessary that the foil will be heated, at least in those areas which are to be welded. Upon heating, the plastic foil is weakened and made formable, but simultaneously it is subjected to temperature extension or expansion movement, which will not correspond to any similar extension of the central parts of the foil piece, and this will cause folding of the edge part of the plastic foil, folded around the upper and the lower edge of the package. When welded, this edge part will attach to the upper edge of the cardboard close to its mouth by such a strong bond that no sliding in the bond will be possible upon the subsequent cooling of the plastic foil. The consequence will be that folds will be created in the plastic foil, which on the one hand are so small that they generally cannot be observed by the naked eye, but'which, on the other hand, together represent a sufficient path between the interior of the package and the exterior air that communication will be created to a disturbing degree.

As a result of the investigation, and the detection of the apparent reason for the lack of tightness, a basic remedying feature of the present invention was developed, namely, during the welding when the plastic is still in a weak and forrnable state, to force the utmost edge part of the cardboard as well as the plastic foil inwardly under such a pressure that the folding tendency of the plastic foil will cause a flattening, by which the channels,which would otherwise be created, are avoided.

The present invention thus is directed to a package of polygonal, preferably rectangular, cross section, which is produced by folding a piece of cardboard along given creasing lines, whereby inwardly directed pasting flaps are-provided at the=upper and perhaps also at the lower end of the package, to which an end closing piece of a thinner, easily bendable material is attached. The pasting flaps on the main part of the package, which is made of cardboard, are cut in an inclined direction at their ends, so that the sloping ends will at least approximately contact each other when the cardboard blank is folded into its form, polygonal in cross section. The end closing part comprises a thin foil of a heat-scalable material, preferably of plastic, which may be welded to the preferably also plastic-covered cardboard of the package, and the end closing piece extends beyond the edge of the cardboard part of the package by a free edge part, which is intended to be folded down onto the cardboard sides and to be attached to them.

According to the invention, the free edge of the end closing piece along with the part of the cardboard piece of the package corresponding thereto, which was initially composed of four even sides, has, at least at the corners of the package but preferably all around the package, after the forming of the package, in connection with the'welding of the end closure to the cardboard, been formed as a short frustum of a pyramid with its sides sloping inwardly in the direction toward the end of the package, so that a flattening has taken place of the edges of the end closure, which were extended due to the heating to welding temperature, and consequently the tightness has been improved. The invention also relates to an arrangement for the production of such a package.

According to the invention, as it relates to such an arrangement, the arrangement contains a welding tool provided with inwardly turned sloped sides of such a form that they will simultaneously by pressure from their sloping sides provide the deformation of the upper part of the package duringreformation of this part to its frustum pyramidal form and add heat for providing the fixture of the free edge of the end closure to the side of the package by welding.

The invention will be further described below in connection with a preferred embodiment thereof illustrated in the attached drawings, but it is to be understood that the invention is not limited to this specific embodiment or form of execution, but that different modifications may occur within the framework of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows the cardboard blank of the package after it has been stamped out and creased.

FIG. 2 illustrates in perspective a finished package according to the previously proposed method for its closing.

FIG. 3 is a plan view of the end closing part.

FIG. 4 shows in increased scale a section through the edge part of the package which has been surrounded in FIG. 2 by a circle.

FIG. 5 shows the corresponding corner or edge part, modified according to the present invention.

FIG. 6 shows a tool for effecting the closure of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT The package blank according to FIG. 1 contains two short sides 10 and 11 and two

long sides

12 and 13, separated by means of creasing

lines

14, 15 and 16. Further there is a closing flap, comprising two

parts

17 and 18 mutually separated by means of a creasing line 19 and connected to the long side 13 by means of a second creasing line 20. The part 18 is intended to form the closing flap proper, which should be attached to the edge of the short side 10 when the package has been folded into its form rectangular in cross section, whereas the part 17 is intended as a grip tongue for opening the package. For making the opening of the package easier, a perforation device is also made. This may be of any kind known per se, and it may comprises cuts, arranged in pairs, which however do not run completely through the thickness of the cardboard. In each couple of such lines the one is cut in from the front side of the cardboard and the other one from the back side. For illustrating this, the line out from the outer side of the cardboard has been indicated in the drawing by means of a line, composed alternatively by one dash and one dot, whereas the line cut into the inner side of the cardboard has been indicated by alternatively one dash and two dots. The

two

lines

21 and 22 or 23 and 24 consequently will give a tearing device easy to open, at the opening of which the cardboard will be slotted between the two lines, contained in one single pair ofsuch lines.

At each end of the four sides 10, ll, 12 and 13 of the package, further pasting flaps 25-28 and 29-32, respectively are arranged. These flaps are cut in sloping direction in their ends, so that when the package is folded into its form rectangular in cross section, the edges will contact each other at 45 angles, as seen from FIG. 2.

In order that the part 17 shall serve as a grip tongue for an easy opening of the package, it should be free from the package in other parts than along the creasing line 19, and for this reason, at the stamping of the package

blank cuts

33 and 34 are arranged at the ends of the inner part of the grip tongue 17. The short pieces of the part 17 outside of these cuts therefore are attached to the surface of the closing flap 18 without perforation or creasing.

When folded the package blank according to FIG. 1 into a package, the four

sides

10, 11, 12 and 13 are bent perpendicularily to each other, and the flaps 25-28 and 29-32 are folded inwardly at least approximately at right angles to the levels of the sides concerned. The inner side of the flap 18 and/or the outer side of the edge of the side 10 is provided with paste, glue or some other means for joining together the package, and one then has a package, shaped as shown in FIG. 2, after the flaps 25-32 have been provided in the way indicated below with their end closing parts. One will see that the tearing tongue is inclined at a small angle, so that this tongue is easily available for opening the package.

In practice it will occur as a rule that the package has been produced by a given manufacturer of packages, delivering the package in evenly collapsed state to the enterprise, which will pack its products therein. Thereby it is quite natural, that the package is folded around full 180 along the

creasing lines

14 and 16, whereas, on the other hand, the creasing lines 15 and 20 are left unfolded, whereafter the gluing by means of the tongue flange 18 takes place. The user of the package thereafter has to break it up into its form, rectangular in cross section, before closing it in the below indicated way.

It is especially suitable to make the package blank from a cardboard, covered on both sides by a thermoplastic. The attachment along the flap 18 then takes place by plastic welding under addition of heat.

An end closure is shown in FIG. 3. This end closure is made from a rather thin and easily bendable and formable material, preferably also a plastic, which is heat weldable. It is applied over the still open mouth of the package according to FIG. 2, so that the dotted lines 35 will correspond to the creasing edges between the sides 10-13 of the package and the flaps 25-28 or 29-32, respectively, connected to them. One has cut the plastic piece somewhat bigger than the upper side of the package, so that it will have an edge all around to be folded down against the sides of the package. In this way one could by a minimum of stamping waste material provide a package, which one believed when carefully closed to be hermetically tight. To the question of this tightness we will return below.

FIG. 4 shows in enlarged scale the piece of FIG. 2, which has been surrounded by the circle 37. The creasing line 38, as one will see, is folded about a angle, so that the side 13 and the flap 28 will be normal to each other connected by a slight rounding, and the end closure will be attached to the flap 28 and the folded down edge part 36 to the side 13.

The tightness, which was expected to be created in a package according to the above, however, did not happen to occur. The investigations forming basis of the present invention have produced at least one explanation thereof. When welding the end closure 135 made of plastic to the package, it must be heated in the welded part to welding temperature. For practical reasons one cannot heat all of the piece 135 to this temperature, because it would in such a case be so weak, that it could thereafter no longer be kept in an even position over the mouth of the package. A great difference in temperature will therefore exist during the welding procedure, between the interior parts of the end closure 135, on the one hand, and the edge part 36 of same piece, on the other hand. This difference in temperature causes heat elongation of the edge parts, by which they are folded in wave form. The plastic is so weak and plastic, that after the welding is completed, and cooling is added, these waves will not again be equalized, but they will remain, and openings will therefore be created between the folded-down edge parts 36 of the plastic and the cardboard inside of this edge. At least, it is through these openings that the communication will later on be created between the interior of the package and the space outside of the package, so that said package will be untight.

The invention provides that one should press the extending edge parts 36 of the end closure inwardly onto the corresponding uppermost or lowermost edge part of the package side all around the package by means of a tool with a sloping pressure surface, so that the surplus of plastic in the edge parts 36 is pressed evenly under influence of an inwardly acting, wedge-formed applied pressure from a tool, and an outwardly acting pressure in the form of the resistance of the cardboard material against deformation, so that after completed welding of the parts of the end closure placed outside of the upper side of the cardboard, this specific edge part of the package will be inclined inwardly in the form of a thin frustum pyramid. The section through this pyramid is shown in FIG. 5 in a scale, corresponding to the one used in FIG. 4. The reference numerals are the same ones as used in FIG. 4. One will especially observe, that by the pressure of the uppermost edge part of the package sides no deformation needs to be created regarding the flaps 25-28, because all of this deformation may be received in the creasing line 38.

The arrangement used for causing the fixture of the end closure, of course, will either be the same or different at the lower end and at the upper end of the package. This depends the fact that the package is usually empty when it is closed at its lower end, but it is filled, when closed at its upper end. Consequently, one may if desired put a mandrel into the package when closing the lower end, but one would use suction nozzles at the closure of the upper end of the package. The closing of the end of the package under insertion of a mandrel is extremely well known, and therefore no specific description thereof would be required, but it is probable that it has not earlier happened that one used suction nozzles for keeping out the upper piece against being sucked down into the package, and therefore the arrangement according to FIG. 6 has been shown using this procedure.

The package 9 has been shown in FIG. 6, kept in place between a couple of

arms

40 and 41. Of course, it may also be supported on a table, which has not been shown in the drawing. The end closure 135 extends in a way already described outside of the upper edge of the package 9. This end closure is kept in place by means of a suction nozzle device 42 with a head 43, carried by a hollow shaft 44, so that it can be displaced along with the head 43 within a cavity 45 in the welding head 46. The welding head 46 in its turn is carried by a head 47, in which a second control shaft 48 meshes. Further, the welding head 46 carries by means of a thermally insulating piece 49 a coupling box 50, in which by means of the fixture 51 an electrical cable 52 is carried for feeding electrical current. The cable 52 runs to a connection plinth .53, from which conductors 54 run to one or a plurality of heater elements 55 in the interior of the welding head 46.

The arrangement now described functions in the following way: By means of the

arms

40, 41 the arrangement has caught a package 9, which is, or is to be, provided with an end closure 135, and has brought it into the position, in which his shown in FIG. 6. The welding head 46 has made a swinging movement about its shaft 48, so that it has moved completely outside of the range of the caught package 9. The conduit in the interior of the shaft 44 is thereafter put under vacuum, after the welding head has been brought into position above a column of ready cut end closures 135, so that the end closure is kept in correct position by the vacuum conduits 56. Thereafter the welding head 46 is again swung over the package 9 and is lowered down onto this package into a position as shown in FIG. 6.

Already earlier electrical current has been fed through the cable 52, the distribution plinth 53 and the cables 54 to the heater elements 55, so that the welding head 46 has assumed the temperature required for the welding. By means of the shaft 48 the welding head 46 is lowered down over the package 9 along with the end closure I35. Thereby the welding head 46 will by means of the wedge-formed, sloped surface 57 first press down the surplus part 36 of the end closure 135 against the sides of the package 9 and thereafter press the upper edge part of these sides along with the free edge 36 of the end closure 135, so that a deformation will take place simultaneously with a compression of all of the folds which could have been created in the edge part 36 of the end closure 135, and the package will in its upper part take the form which is shown in enlarged scale in FIG. 5.

It cannot be avoided that a given heat quantity is also transferred from the welding head 46 to the part of the end closure 135 which should remain even. The outermost parts of this even part of the end closure 135 therefore will also fold themselves under extension of surface, and it may then be important in some regular way to assume this folding action in order, when cooling the end closure again, to make the received part free. Amongst others, it is for this reason that the welding head has been provided inside of the sloped surface 57 with a teethformed border 58, running all around and so arranged that it will mesh inside of the edge of the package 9 and there weakly press the outermost part of the end closure 135 down for receiving its surface increased by heat development. This arrangement, however, has also a further purpose, .which may be regarded at least as important, viz, to make sure that the welding bond between the edge 36 of the end closure I35 and the edge of the package 9 will extend around the upper edge and thereby exist against the edge part of the outer side of the package as well against the narrow closing flaps, which may accidentally by the pressure from the tooth 58 be bent somewhat downwardly, but after lifting up the welding head will again by the resilient force in the creasing lines assume their position perpendicular to the packagesides.

When executing the invention as hitherto described, it has been found, however, that even now complete tightness could not be obtained in all treated packages. Certainly, the plurality of them have been tight to a satisfactory degree, but singular samples have, without the treatment having been in the slightest way different, proved to be untight. After substantial difficulty, it was found that this sporadically occurring untightness depended upon a specific occurrence in the corners of the package in connection with the used welding temperature.

In the corners of the upper edge of the package the sides are bent by the welding head in 90 angle. At the sides, they extend however in straight line on each side of each welding point. The consequence thereof will be, that heat is fed to the singular welding point over an angle of only 90 at the corners, but on the other hand over an angle of l at the sides. The heat feeding at the corners will therefore be less per unit of weight of the plastic material in the end closure I35. Simultaneously this end closure is bent down around the corner, so that a twofold folding will be created, viz firstly the folding, which also occurs at the sides, and which depends upon the heat enlargement of the material, and secondly also the folding required for receiving the surplus of material at the corners. The consequence will be, that one will simultaneously get a decreased feed of heat at the corners and a greater quantity of plastic receiving the heat which is fed, and that therefore the temperature of the plastic in the comer will be rather much lower than in the plastic along the sides. This in turn causes a risk of cold welding with consequent -untightcuess.

Assuming that this explanation of the existing untightness was sufficient and reliable, it was thereafter obvious, that one had in order to get the same welding relations for the plastic in the corners of the end closure and along its sides firstly to increase the temperature at the corners of the welding head, secondly also to decrease the quantity of plastic contained in the corner formations of the end closure. The first one is practically not possible to provide, because the welding head must be made from a good heat conducting material, and by the good heat conduction and equalization of temperature will take place. On the other side it is possible to decrease the quantity of plastic in the corner formations by cutting them off in a way, shown in FIG. 3 at 59.

Immediately, it proved that this visually unessential step caused the risk of leakage at the comers to be practically completely eliminated. By the cutting off, as a matter of fact, the heat consuming quantity of plastic was so strongly decreased, that the temperature exactly and surely would be above the limit temperature for cold welding, whereas it earlier balanced about this limit temperature and in some cases it was for reasons, which one could not find out,.below this limit temperature, in other cases however above the limit temperature.

When deciding how far the corner cutting of the upper piece should take place one was guided by the following pints of view: the stronger the corner cutting is, the less will the surplus of material be, which by assuming part of the welding heat causes a decrease of the welding temperature. Simultaneously, however, the distance from the corner 60 of the package to the cutting line 59 will be smaller, and this means that the surplus strip of plastic of the end closure in the corner will be less, with a risk that it will-be too narrow and cause a leakage in another way than the above mentioned one. In tests it proved that one will get a good compromise between these two points of view counteracting each other by cutting the comer of the end closure so that the distance between the proper corner 60 of the package and the cutting line 59 will be about equal to two thirds of the width of the surplus piece of the end closure along its straight sides.

in practical tests it has now proved that the leakage caused due to folding of the edge part 36 of the end closure 135 will be most difficult at the corners, and therefore one has also investigated the action of only pressing in the package along with the edge part of the end closure at the corners. Curiously enough, it was found thereby that the risk for leakage along the sides of the package was essentially smaller. It is not quite clear, what the reason to this may be, but one may assume that the folding at the sides at least in part has been caused by displacement tensions in the proper level of the plastic piece. By attaching the plastic piece in a more rigid way at the corner these displacement tensions are decreased, and one may in many a case achieve a completely satisfactory result without the middle parts of the upper edges of the package sides being subjected to the sloped pressing. The invention therefore also shall comprise such a partial use of the inventional idea.

I claim:

1. A package having a base portion of a polygonal cross section which is produced by folding a blank of stiff material such as cardboard or the like along creased lines such that at least one end of the package comprises inwardly directed pasting flaps, a thin foil end closure attached at said end, said pasting flaps being cut at their ends such that the ends of the flaps approximately contact each other when the cardboard blank is folded to its form, polygonal in cross section, the said end closure of the package at said end comprising a heat-scalable material capable of being heat sealed against the cardboard at the said end of the package and the end closure part including a free edge extending outside of the edge of the base portion of the package and adapted to be folded down against the outside of the sides of the base portion and to be attached to the sides thereof, the free edge of the said end closure, together with the part of the base portion connected thereto, at least adjacent to the corners between adjacent sides of the base portion and at said end, being bent inwardly towards the center of the package such that the bent end portions at said end form a frustrum pyramid with'the sides at least at said corners, sloping inwardly in the direction toward the end of the package such that a flattening takes place of the said free edges of the end closure against the base portion to provide an airtight connection between the free edge and the outside of the base portion at said end.

2. A package according to claim 1 wherein the base portion is bent inwardly all around its periphery at said end.

3. A package according to claim 1, wherein said package base portion is rectangular and wherein the stiff material is a plastic-coated cardboard and said end closure is a plastic film.

4. A package according to claim 1, in which a crease line is applied on the inner side of the stiff cardboard material of the base portion between the sides thereof and the pasting flaps, said crease line being arranged at least substantially to receive a portion of the material of the sides of the base portion when the part thereof adjacent said end is bent in to form said frustrum pyramid.

5. A package according to claim 1, wherein the outward extent of the free edge of the end closure is reduced at the corners of the package relative to its outward extent at the sides between said corners.

Claims

1. A package having a base portion of a polygonal cross section which is produced by folding a blank of stiff material such as cardboard or the like along creased lines such that at least one end of the package comprises inwardly directed pasting flaps, a thin foil end closure attached at said end, said pasting flaps being cut at their ends such that the ends of the flaps approximately contact each other when the cardboard blank is folded to its form, polygonal in cross section, the said end closure of the package at said end comprising a heat-sealable material capable of being heat sealed against the cardboard at the said end of the package and the end closure part including a free edge extending outside of the edge of the base portion of the package and adapted to be folded down against the outside of the sides of the base portion and to be attached to the sides thereof, the free edge of the said end closure, together with the part of the base portion connected thereto, at least adjacent to the corners between adjacent sides of the base portion and at said end, being bent inwardly towards the center of the package such that the bent end portions at said end form a frustrum pyramid with the sides at least at said corners, sloping inwardly in the direction toward the end of the package such that a flattening takes place of the said free edges of the end closure against the base portion to provide an airtight connection between the free edge and the outside of the base portion at said end.