Convenience Opening of Containers for Liquid Products

Containers of the general type under consideration are known. U.S. Pat. No. 3,292,828 illustrates a container can end with a plurality of openings which are sealed by a metal foil or plastic tape.

Heretofore it has not been possible to apply tape seals externally (without internal support) to highly pressurized containers. Tape seals have been used to cover pouring apertures in vacuumized products, such as the so-called "hot fill" items, where a resultant vacuum pulls the metalized tape against the end of the container. The same technique could not be applied to pressurized containers because the shear forces produced by the internal pressure would cause progressive peeling or shearing of the adhesive bond. In U.S. Pat. No. 3,292,828 both internal and external seals are required.

Another U.S. Pat. No. 2,870,935 is of interest in that it shows a large opening and suggests spraying the underside of the lid and the cover with adhesive to effectuate a satisfactory seal.

U.S. Pat. No. 3,338,462 illustrates the formation of a plastic plug with an outturned flange beneath the end panel. This construction would undoubtedly require excessive pull to remove if applied to small holes and is complicated to form, not to mention the possibility of pieces breaking off which would be objectionable.

In general, the closures of the instant type have not met with success in the pressurized beverage field because of the excessive requirements to perfect the seal.

This invention is directed to a novel arrangement for securing a strip of plastic or combination plastic coated metal foil (steel or aluminum) or a foil of steel or aluminum to a can end by an adhesive applied to the underside of the strip, the adhesive being forced into sealing engagement with the can end panel about a plurality of openings therein, the strip including a plastic layer which is extruded from the exterior toward the interior of the panel through the openings and the extrudate being set and formed under heat and pressure into hollow bosses having portions confined by the edges of the openings and including a peripheral rigidifying torus or bead.

A general object of the invention is to provide a pour opening in a can end panel in the form of a plurality of small openings as contrasted to one large opening, of a size and shape to permit sealing of a pressurized container by novel means only externally applied preferably in the form of a metalized tape and an adhesive.

A further object is to incorporate in the combination of a tape covering small openings in the can end, a peelable adhesive bonding or sealing means which provides for high bursting strength and relatively low peeling or shearing forces, and bonding the same by heat sealing, ultrasonic welding, high energy rate impact sealing or the like, the tape also being secured at one end to the can end by a non-peelable adhesive.

Another object is to form a tape which not only seals well to the container but which may be readily pulled away from the pour opening to permit drinking directly from the container.

These and other objects and advantages inherent in and encompassed by the invention wherein:

FIG. 1 is a fragmentary perspective view of a container with the novel closure in sealed position;

FIG. 2 is a perspective view of a container showing the closure in open position;

FIG. 3 is a top plan view of the structure shown in FIG. 1;

FIG. 4 is a top plan view of the structure shown in FIG. 2;

FIG. 5 is an enlarged cross-sectional view taken substantially on line 5--5 of FIG. 3;

FIG. 6 is an enlarged fragmentary view of a portion of FIG. 5;

FIG. 7 is an enlarged section taken substantially on line 5--5;

FIG. 8 is a graph of parameters for the tab and hole;

FIG. 9 is a top view of the opened container;

FIG. 10 is a side view of the container showing the tape draped against the side of the container;

FIG. 11 is an enlarged radial cross-sectional view of a plug section of the container end and tape; and

FIG. 12 is also an enlarged radial cross-sectional view of the container and tape.

Referring to the drawings, there is shown, a can 2 having a body 3 with double seam attachment 5 to an end panel 6.

In the embodiment shown, the panel 6, which is aluminum, is provided with a central straw-admitting vent opening 7, an anchor opening 8, which may be eliminated, and a plurality of small pour openings 10, located adjacent to the peripheral edge 11 of the can. These openings can be of various shapes having at least one rather short lateral dimension, but preferably are circular.

The openings 10, which may be arranged in any preferred pattern, are shown arranged in a circular array about one center opening 10 defining the center of the area and collectively form a pour aperture 10a.Each opening 10 has a raw edge 12 which, if the panel is steel, must be coated to prevent corrosion or contamination of flavor to the product in the container it being understood that the openings 10 are punched after the end panel is coated, if steel, by a suitable enamel as stated in the hereinafter disclosed U.S. patents.

A bendable or flexible, gas and liquid impervious, elongated strip or pull tab generally designated 14 of plastic or of thin aluminum or steel foil 15, which is coated with a plastic layer or film 15' of polypropylene resin, serves as a closure tab covering all of the openings. The tape 15 may be an oriented rubber-modified acrylonitrile polymer resin such as Barex or Cycopak material either metalized or not.

The polypropylene layer 15' as shown in the drawings (FIGS. 6 and 7) is adhered to the underside surface 18 of the foil 15 by a bond promoting agent 17. A bond promoting agent which has been found to provide superior results is a carboxylated polypropylene resin as more fully described in U.S. Pat. No. 3,616,047.

As shown in FIGS. 7 and 8 the strip 14 is applied to the exterior surface of the end panel with the polypropylene layer opposing the panel surface 20. To promote the bonding of the polypropylene layer 15' of the strip 14 to the end panel, an adhesive material 17' is applied, as by spot coating, to the end panel in the areas surrounding the openings. The adhesive 17' is preferably of a low peel strength type that is, the adhesive provides a high strength bond between the polypropylene layer and the end panel, but when removal of the strip is attempted, the strip is readily peelable or clearly separable from the end panel. A peelable adhesive material which has been found to be especially suitable for this application is a carboxylated polypropylene resin which has been treated with a different thermoplastic polymer such as ethylene/vinyl acetate, polymethylmethacrylate or polystyrene as is more fully disclosed in U.S. Pat. No. 3,671,356.

Upon or prior to application of the strip 14 to the peelable adhesive coated panel, the strip 14 is heated. Pressure is applied against its top side 21 preferably by a heated pressure plate or iron 22 which forces the tab or strip against the top side 20 of the end panel. A heated anvil (not shown) may be located beneath the panel, if desired. The pressure against the tape is of such magnitude that the heat-softened polypropylene layer 15' of the strip 14 is squeezed out from between the foil surface and top surface 20 about the openings and extrudes into the openings. The layer 15' about the openings is thinned out as at 17a thus materially improving the adhesive quality of the bond and beneficially improving the cohesive bond.

Bosses 31 and 32 having thick disk-like sections 27, 28 of the film material 15' are produced centered respectively in the openings 10 and 7. The disk-sections 27, 28 are respectively edged by a torus or annulus 29, 30 of thick cross-section. The torus extends from the corner edges 38 of the openings beneath the lower faces 31a of the disk center portions of the bosses to an area spaced above the lower corner edges 37 of the openings. This type of boss structure not only resists doming, but also inhibits development of cracks about the openings resulting from excessive doming caused by the pressure exerted thereagainst by the pressurized liquid in the container. Such doming, unless restrained, propagates incipient cracks and eventually causes failure of the bond. In actual constructions, the bosses or plugs can be seen and additionally can be felt by running a finger nail against the bottom side of the tape after opening. The structure of the bosses provide structural strength in the critical areas and independent tests have substantiated that the instant constructions have been eminently successful. The closures are required to withstand 100 p.s.i. The instant constructions with the torus shaped bosses have withstood pressures greatly in excess of these requirements, that is up to 270- 290 p.s.i. using treated carboxylated polypropylene resins as described in the aforesaid U.S. Pat. No. 3,671,356 as the adhesive bonding agents in the pour opening areas. The treated carboxylated polypropylene resin is applied over an enamel coating 25, which may be formed of a thermosetting resin such as epoxy, urea/formaldehyde epoxy/phenolic resin applied to the raw metal surface of the end panel.

By extruding the bosses as described, they are hollow and are stress resistant. Minimal amounts of materials are used. Any partial bonds between the edges of the openings and the extrudate afford a plus factor, although principal reliance is placed upon the bond between the top of the panel and the tape.

Of major concerns are the adhesive peel strength and foil thickness as a function of hole diameter. Assuming each hole to be circular, although they could be slots, arcuate or straight, each hole may be treated separately as long as the effect of one hole does not reach the adjacent hole.

In FIG. 7 a single hole is analyzed and requirements established. In the following analysis: P= internal pressure and D= diameter of each hole, we have the peel force F, per linear inch, as ##EQU1##

The contribution of the inplane component K to the peel force will be negligible, especially for the range of the hole sizes which are to be used. FIG. 8 shows the curve of F vs. D for p= 100 psi.

If 6063 aluminum foil is used, the shear strength is 10,000 psi. With a factor of safety of 2 (short time), the required foil thickness t is determined: ##EQU2##

This is also shown in the graph illustrated in FIG. 8.

The distance between holes should be such that the peel stress around one hole does not reach the next hole. This condition is achieved if the distance "l", between holes is greater than (.pi./n), ##EQU3## E.sub.1 = modulus of the adhesive E= modulus of the foil,

t= foil thickness,

and

h.sub.o = adhesive thickness.

For an example, assume the total pouring area= 0.75 in..sup.2, with 30 holes and the adhesive peel strength of 10#/in. ##EQU4## F = 4.4 lbs./in. t= 0.00089" (foil thickness) .apprxeq. 0.001".

Assume

E.sub.1 = 300,000 psi

E= 10.sup.7 psi

t= 0.001"

h.sub.o = 0.001"

So

n= 547

And

l= 0.006" = distance between holes

The tape should preferably be secured at its anchor end 40 to the end panel by an adhesive 41 (FIG. 3) such as a carboxylated polypropylene resin, an epoxy resin, ethylene-acrylic acid copolymer resin, or a phenol formaldehyde resin which may be applied in the areas of the opening 8. The adhesive 41 may be extruded through the opening 8 and thus form a plug or boss 42 with a torus 43 and a thick center disk 43a which additionally mechanically strengthens the area to prevent separation within the defined parameters.

The tape may be of greater length than the diameter of the end panel and may be folded at 44 in the groove against the chuck wall and have a free grasping end 45 laid over the adhered portion of the tape. The tape is preferably of a foil like material or metalized plastic that provides sufficient body and shape retention so that it can be bent and reshaped when peeled to be draped down the side of the container opposite the pour openings and closely accommodate itself to the container side wall as at 46 at shown in FIG. 10.

As best seen in FIGS. 4 and 9, the primary peelable attachment areas of the adhesive are located at 50 and 51, about the openings 7 and 10, respectively, and in laterally spaced strips 52,52 along the lateral margins of the strip in the region between the areas 50, 51 and also at 53,53 on the can top. This is accomplished by hollowing out the pressing iron 22 or roller. The function of this spot adhesion is to minimize the adhesion in non-critical areas so as to facilitate lifting of the tab to open position.

To open the can, the tape is grasped by the waffle patterned end 45 and peeled off openings 10 and 7 pulling out the hollow plugs or bosses from these openings. Since the tab is held at its anchor or tail end 40 it may be easily folded over the diametrically opposite side of the can so as not to interfere with drinking directly from the can.

Having described a preferred embodiment of the invention other forms will now become readily apparent to those skilled in the art and as set forth in the appended claims.