US 3312368 A
Description (OCR text may contain errors)
April 1967 w. G. REYNOLDS ETAL 3,312,368
EASY-OPEN CAN END Filed Sept. 9, 1964 FIG-l F|G.2
INVENTORS W\LL1AM GREYNOLDS BRUCE L. BAXTER ROBERT 5- DAVIDSON ATTORNEY 8 United States Patent O EASY-GWEN CAN END William G. Reynolds, Richmond, Bruce L. Baxter, Henrico County, and Robert S. Davidson, Richmond, Va., assignors to Reynolds Metals Company, Richmond, Van, a corporation of Deiaware Filed Sept. 9, 1964, Ser. No. 395,165 5 Claims. (Cl. 226-53) the consumer to effect opening of the can without requiring a conventional can opener or similar implements. Despite the develop'ement of easy-open metal end constructions which have met with fair marketing success, there remain problems which as yet have failed to be successiv'ely resolved in the practical design and commercial manufacture of such can ends; thus (1) The convenience to the user in being able to consume the beverage directly from the can to avoid the necessity for cups or glasses. For this purpose, the pouring or drinking aperature must be suiiiciently smooth and free of pro ections or burrs which might cause injury or annoyance to the user after opening of the container; and,
(2) Inasmuch as carbonated beverages such as beer develop gas pressure internally of the can in excess of 100 p.s.i., commonly reaching 130 psi. during pasturization, it is imperative that any easy-open end construction successfully withstand these pressures without leakage or accidental explosive rupture, while still providing a smooth pouring or drinking opening.
To achieve these results, it is manifestly desirable that a smooth pouring opening be pre-cut in the can end and have a separate removable closure or sealing tab applied thereover to seal the can. Prior to the present invention, however, such a construction has been deemed unfeasible for carbonated beverage cans due to leakage caused 'by the high internal pressure acting upon the seal tab at the precut cover aperture. While this leakage problem is overcome by the use of an imperforate can end having a scored rip strip or the like, it is found that the tearing of the scored metal strip from the initially imperforate end to pro- I vide a pouring opening often produces a slightly upturned and somewhat roughened edge surrounding the pouring aperture as a result of the upward force applied in pulling the tear strip from the relatively flexible light gauge aluminum or steel ends in which such scored removable sections are provided.
These and other advantages of prior art easy-open end closures are overcome by the simple yet highly effective can end structure of the present invention.
It is therefore a principal object of this invention to provide a can end having a pre-cut aperture therein and a single overlying tab which will not leak under high internal gaseous pressures commonly encountered with carbonated beverages.
It is an important object of this invention toprovide a can end closure wherein a pre-formed aperture in the can end is externally overlaid and sealed by a pull tab bonded therearound in a unique manner which is capable of withstanding internal gaseous pressure while permitting peel removal thereof.
It is a further object of the present invention to provide an easy-open can end wherein the pouring opening is free from any surface irregularity or similar roughness which might inconvenience or irritate the consumer.
It is a further object of this invention to provide a can end construction for carbonated beverages having a tearopen end, comprising only two elements, namely the aperture-d can end and the overlying peel strip bonded thereto which requires no additional securing means internally of the container as by way of an inner membrane or other more complex structure.
It is a further object of the present invention to provide an easy-open can end which obviates the necessity for scored areas which not only weaken the end but also contribute to irregularity or roughness when the can is opened.
It is a further object of this'invention to provide an apertured can end having an overlying pull strip bonded v thereto in a unique manner wherein the same is readily heat scalable to and peelabl'e from the can end, yet is sufficiently tightly bonded thereto as to prevent spontaneous peeling thereof due to internal high gaseous pressure.
Other objects and advantages of the present invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which FIG. 1 is a top plan view of a preferred form of can end of the present invention, the pre-cut aperture therein being shown in dotted lines.
FIG. 2 is a bottom plan view of the can end of FIG. 1, the pull strip thereof being indicated in dotted lines.
FIG. 3 is a fragmentary side elevation of the preferred can end.
P16. 4 is an enlarged diagrammatic showing of the apertured can end and pull tab in exploded relation, illustrating the bonding coatings thereon in more detail.
FIG. 5 is a top plan view of a first modified form of can end incorporating the invention.
FIG. 6 is a top plan view of a second modified form of the invention.
FIG. 7 is an enlarged section of a modified pull tab.
While the general concept of manufacturing a readily openable closure for metal containers by providing an apertured can end having a pull tab bonded thereto in overlying surrounding relation to the aperture is known, presently existing constructions of this type have proved unsuitable for beverage containers having considerable internal pressure for one or more of the following reasons:
(1) Soldered pull tabs as in the patents to Smith 2,034,007 or Grove 2,048,859 having a sufiiciently weak solder bond to permit manual rupture thereof in removing the tab, are likewise insufiiciently strong to withstand internal gas pressure on the order of -130 p.s.i. which commonly occurs during pasteurization;
(2) Further, solder-bonded tabs as in (1) when torn from the container, leave a roughened and irregular surface of torn solder surrounding the aperture which is undesirable and may irritate or annoy the user;
(3) Tabs secured as by a single-layer conventional heat-scalable adhesive as in the patent to Reynolds 2,629,- 534, for example, cannot withstand the continuing stress of internal pressure combined with constant wetting by the beverage at the aperture without yielding of the seal. Tests of such single-layer adhesives have resulted in failure of the seal at the metal-coating interface as if displaced from the metal surface by the beverage.
(4) Tabs of relatively quite flexible material such as paper, light-gauge aluminum foil or thin sheets of a flexible plastic as polyethylene, as for example in Huntting 2,740,547, either rupture under such internal pressures present at the aperture, or tend to bulge or bow outwardly at the aperture and cause spontaneous self-peeling of the tab commencing at the aperture edge and continuing peeling separation outwardly from the aperture in all directions.
Tabs of sturdy material can be bonded about the aperture solely by available strong adhesives, including for example recently developed epoxy or similar resins, and may withstand the internal pressure, but because of the excessive bond strength cannot be peeled from the can end but must be ruptured in place to gain access to the container, whereby such closures are commercially impracticable and unmarketable for beverage cans.
Accordingly, in the manufacture of easy-open beer can ends, reliance to the present time has been placed upon end structures incorporating either (1) a totally imperforate end suitably scored for a rip strip, as in Walsh 2,798,140, for example, or (2) an apertured end wherein however the overlying tab is of necessity secured to or formed integrally with an additional reenforcing barrier element disposed entirely internally of the can, thereby calling for more complex and expensive fabrication techniques, as evidenced by Houghtelling 2,870,935 or Livesay 3,119,509.
Despite the fact, then, that the teachings and development of the industry have hitherto led away from the concept of an apertured end having but a single overlying pull tab bonded only to the external surface of the can end, with 'no adjunct internal elements or cooperating structure therein associated with the external tab, the teachings of this invention provide such a single tab, apertured-end and easy-open closure which has proven effective in actual practice in withstanding the internal gas pressure of the container while yet permitting easy removability of the pull tab therefrom by peeling.
Accordingly, and referring to the drawings, the improved can end in its preferred form is shown at and includes a substantially conventional can end 11, which may be of aluminum, light-weight tinplate or conventional tinplate. The central panel of end 11 is cleanly pre-cut to define a substantially radially directed teardrop-shaped aperture 12 through which the contents of the can are to be dispensed. Externally overlying the substantially planar central panel of the can end 11 and in bonded peripheral relation to the aperture 12 is a pull strip 13 of generally hourglass or keyhole configuration as viewed in plan outline. The radially outermost portion 15 of the pull strip 13 which overlies and surrounds the pouring aperture 12 is peelably bonded to the can end surrounding the aperture by a unique adhesive means 14, FIGS. 3 and 4, to be described in more detail hereinafter. While the portion 15 is preferably planar, the same may have transverse beading or reenforcing ridges thereon. The innermost end 16 of the peel tab 13 is not bonded to the can end 11, but rather is free therefrom and may be slightly pre-bent to angle somewhat upwardly so as to enable the consumer to grasp the same. It is of course apparent that the free and unbonded end 16 of tab 13 if desired may be beaded for further rigidity or provided with an underfolded peripheral edge to minimize possible irritation to the fingers if desired in a manner known in the art, the essential requisite being that the tab portion 15 be of sufficient area so as to be readily grasped by the fingers of the user. The peel tab 13 is preferably of a light-gauge metal such as aluminum on the order of .009 but it is within the scope of the invention as seen in FIG. 7 that the tab at be of relatively stiff or rigid plastic 41 such as polystyrene or the like on the order of thickness and having a gas-barrier foil face 43 on the underside thereof. The gas barrier foil is coated with the adhesive system 14 on the surface that will be heat sealed to the can end. The plastic is tightly bonded to the exterior surface of the gas barrier foil with a resinous adhesive 42.
An essential feature of the peel tab and which con- .tributes materially to the success of the present invention is that the tab have sufficient rigidity and stiffness so as to remain substantially planar or in its initial unstressed configuration particularly along that portion 15 thereof as in FIG. 1 which overlies the pre-cut aperture 12 and does not bulge or tend to distort under the high gaseous pressures which may occur at aperture 12. This is for the reason that any bulging or doming of tab 13 at aperture 12 effects a spontaneous peeling of the adhesive 14 commencing at the edges of aperture 12 and continuing outwardly therefrom, whereby leakage or explosion rapidly occurs. With a sufficiently rigid tab 13 or 40, however, this self-peeling action does not occur, but rather the entire seal 14 remains in uniform tension and thus successfully withstand pressure at the aperture. The tab however possesses limited flexibility so that the tab end 16 thereof may be flexed upwardly and be readily grasped and pulled from the can by a peeling technique. As above noted, an aluminum tab on the order of .009 gauge meets these conditions.
In addition to the novel character of the peel tab which contributes to practicability thereof for high pressure beverage cans, another critical factor relates to the nature of the adhesive system 14 employed in bonding the tab to the can. It is old and well known in the art to bond two metallic or other elements together by means of a vinyl-base material wherein a heat seal can be readily effected between the members and yet be easily separated by a peeling action. While such adhesive material is quite suitable with respect to the highly desirable peeling action in non-pressure environments, the same has been found to be incapable of withstanding the -130 p.s.i. pressure within the beer cans in conjunction with constant wetting of the adhesive by the carbonated beverage and will leak or rupture as a result of a self-peeling action of the tab under such pressure and moisture conditions. Conversely other adhesives are known which are technically capable of effecting a most tight bond between the two members, but wherein the bond therebetween is of such magnitude that separation of the elements cannot be achieved without destruction or excessive deformation of one or both of the parts, and accordingly are manifestly undesirable.
The present invention uniquely combines the desirable attributes of both such types of adhesive to provide a tab-sealed apertured can end which will not only withstand the internal pressures in excess of 100 p.s.i., but will also permit ready peeling separation of the adhesively secured tab 13 from the can end 11 by the conjoint utili-- zation of a tight-bonding adhesive such as one in the class of epoxy resins and a readily heat scalable peelable adhesive such. as one of the vinyl resin type. Thus, as illustrated in the enlarged detail of FIG. 4, the external surface of can end 11 surrounding aperture 12 has initially applied thereto a layer of a tight bonding adhesive 19, as does the underside area of tab portion 15. The tight bonding adhesive 19 is on the order of 1 or 1 /2 mg./sq. in. in thickness. Applied thereover on both the tab and the can end is a coating of a readily peelable adhesive 17, which two as cooperatively associated comprise the novel adhesive assembly 14 of the present invention. A conventional internal lining 18 on the interior of the can is also illustrated in FIG. 4.
Among various adhesives of the character described, a specific example thereof which achieves the desired results comprises an epoxy primer for coating 19 marketed by Interchemical Corporation under the designation of B-1113 in association with a vinyl resinous coating 17 marketed by Stoner-Mudge Company, known as 8-988- 005.
More specifically, to further facilitate an understanding of the present invention, the epoxy coating B-1113 above referred to comprises a polyepoxide resin produced by the condensation of epichlorohydrin and 2,2-bis (phydroxyphenyl) propane and an alkoxy polyamine formaldehyde resin dissolved in suitable organic solvents.
This coating 19 is applied to the extent of about 1-1.5 mg./sq. in. on both the end 11 and tab portion 15. Further, the heat seal coating 17 of Stoner-Mudge constitutes a blend of vinylite resins formulated as a clear coating using Ketone and hydrocarbon solvents, applied to the extent approximating 3-6 mg/ sq. in.
Actual usage of the above as the adhesive coating 14 between end 11 and tab 13 has been found to repeatedly and successfully pass dry gas pressures of 100-125 p.s.i. as well as one hour pasteurization at l55-160 F. in contact with beer. Other comparable adhesives of this character may be employed, of which the foregoing are only exemplary.
The particular nature of the molecular interconnection between the coatings 17 and 19 when the tab is heat sealed to the can end 11 is not known, but has been found to be a reliable technique capable of withstanding such pressures without leakage. By the unique character of the present construction, however, the present invention provides a can end for carbonated beverages which will withstand developed internal pressure yet is readily openable wherein the closure comprises the inexpensively fabricated association of a conventional can end having a diecut aperture with a one-piece substantially planar tab element. It will be seen that inasmuch as no tearing of the metal is necessitated by virtue of the precut aperture 12, no ragged or rough metal edges will be created or will remain upon peeling to the annoyance of the consumer.
A further form of the invention incorporating the principles thereof is seen in FIG. 5. The can end 20 is provided with a pair of precut apertures, namely an elliptical pouring or drinking aperture 21 and a separate venting aperture 22 spaced therefrom. The two apertures are overlaid and sealed by a single peelable tab 23 of the same character as tab 13 and bonded to the can end in similar fashion. The tab 23 is provided with a terminal portion similar to tab poltion 16 which is free from bonded contact with the can end whereby the same may be grasped by the user to strip the tab from the can end.
The can end 30 of FIG. 6 is similar to that of FIG. 5 in providing like pouring and venting apertures 21 and 22 respectively wherein, however, separate sealing and pull tabs according to the teachings of the invention are employed at 25 and 26 respectively for individually sealing the apertures and which may be readily peeled therefrom for dispensing the container contents. As before each tab is provided with a terminal portion which is free from contact with the can end 30 for manual grasping.
The modified ends 20 and 30 are characterized by the elliptical pouring opening 21 of optimum convenience and efficiency wherein the major axis thereof is disposed substantially perpendicular to a can end radius.
What is claimed is:
1. An easy-open end for a hermetically sealed container subject to internal pressure substantially above atmospheric on the order of 100 p.s.i., said container end including a panel having a preformed aperture therein boundedby a smooth-faced panel portions, a pull tab having a first portion overlying said aperture and said panel portion surrounding said aperture and a second portion defining a finger grip for grasping said tab, non-metallic resinous adhesive means resistant to tension stresses bonding said first tab portion to said panel portions in a heat seal, said heat seal constituting the sole connection between said end and said tab, and with said tab and said adhesive means together constituting the sole sealing and pressure resistant closure means for said aperture,
said adhesive means comprising superimposed layers of a cross-linked polymer primer and a heat-fusible polymer overcoat provided on the contacting surfaces of both said panel and said pull tab, said first tab portion having sufficient rigidity to maintain its unstressed contour when subjected to container internal pressure substantially above atmospheric through said aperture thereby to stress said heat seal solely in tension, and said adhesive means being yieldable to peeling forces, whereby said tab may be peeled from said end upon grasping of said tab second portion to expose said aperture and said smoothfaced surrounding panel portion.
2. The end of claim 1 wherein said pull tab comprises a substantially planar sheet of aluminum stock on the order of .006-.010 thickness.
3. The end of claim 1 wherein said pull tab comprises a substantially planar plastic sheet on the order of thickness.
4. The container end of claim 1 wherein said crosslinked polymer primer constitutes an epoxy resin and said heat-fusible polymer overcoat comprises a vinyl resin.
5. Sealing means for an apertured beer can end capable of withstanding internal can pressures on the order of -130 p.s.i. at said aperture without leakage comprisa tab of sheet material overlying said aperture and bonded solely to the external surface of said can end surrounding said aperture by a heat sealable adhesive,
said adhesive comprising epoxy resins and vinyl resins,
said tab sheet material having sufficient rigidity to resist upward deformation thereof when subjected to said pressure at said aperture thereby to stress said adhesive solely in tension,
said tab including a finger grip portion free from bonded relation to said can end whereby said tab may be lifted thereby and pulled from sealing relation with said beer can end to expose said aperture.
References Cited by the Examiner UNITED STATES PATENTS 2,147,004 2/ 1939 Wark et al. 22047 2,719,647 10/ 1955 Freeman 22053 2,870,935 1/ 1959 Houghtelling 22053 3,182,851 5/1965 Taylor 22053 3,186,581 6/1965 Schneider et al. 22053 3,187,931 6/ 1965 Henchert 22054 3,251,515 5/1966 Henchert et al. 22048 THERON E. CONDON, Primary Examiner.
G, T. HALL, Assistant Examiner.