U.S. patent application number 09/905310 was filed with the patent office on 2002-05-02 for can with peelably bonded closure.
Invention is credited to Ball, Melville Douglas, Furneaux, Robin C., Hamstra, Peter, Moulton, James D., Scott, Tom E., Smith, Christopher Robert.
Application Number | 20020050493 09/905310 |
Document ID | / |
Family ID | 26939038 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020050493 |
Kind Code |
A1 |
Ball, Melville Douglas ; et
al. |
May 2, 2002 |
Can with peelably bonded closure
Abstract
A metal can for holding a carbonated or otherwise pressurized
beverage or the like, having a rigid metal lid formed with an
eccentrically disposed, upwardly projecting frustoconical annular
flange defining an aperture of average diameter between about 0.625
inch and about 1 inch, and a flexible metal foil closure extending
over the aperture and peelably bonded by a heat seal to the sloping
outer surface of the flange.
Inventors: |
Ball, Melville Douglas;
(Kingston, CA) ; Scott, Tom E.; (Port Angeles,
WA) ; Furneaux, Robin C.; (Banbury, GB) ;
Moulton, James D.; (Kingston, CA) ; Smith,
Christopher Robert; (Aurora, IL) ; Hamstra,
Peter; (Kingston, CA) |
Correspondence
Address: |
COOPER & DUNHAM LLP
1185 Ave. of the Americas
New York
NY
10036
US
|
Family ID: |
26939038 |
Appl. No.: |
09/905310 |
Filed: |
July 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09905310 |
Jul 13, 2001 |
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09603004 |
Jun 26, 2000 |
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09603004 |
Jun 26, 2000 |
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09247999 |
Feb 10, 1999 |
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Current U.S.
Class: |
220/359.2 ;
220/359.4 |
Current CPC
Class: |
B65D 2517/5032 20130101;
B65D 2517/0013 20130101; B65D 2517/5083 20130101; B65D 2517/5054
20130101; B65D 2517/0062 20130101; B65D 17/502 20130101; B65D
2517/0056 20130101 |
Class at
Publication: |
220/359.2 ;
220/359.4 |
International
Class: |
B65D 041/00 |
Claims
What is claimed is:
1. A can comprising: (a) a metal can body having an open upper end;
(b) a substantially rigid metal can lid peripherally secured to and
closing said can body end, said lid having an upper surface; (c) a
frustoconical annular flange formed in a portion of said lid and
projecting upwardly from said lid upper surface, said flange having
an upwardly sloping outer surface and an annular inner edge lying
substantially in a plane and defining an aperture with an average
diameter between about 0.625 inch and about 1 inch, said flange
outer surface being oriented at an angle of slope between about
12.5.degree. and about 30.degree. to said plane; and (d) a flexible
closure member of a material comprising a metal foil, extending
entirely over said aperture and peelably bonded by a heat seal to
said flange outer surface entirely around said aperture.
2. A can as defined in claim 1, wherein said can has a geometric
axis, said lid upper surface is substantially flat, said aperture
is circular and said flange is disposed in a portion of said lid
eccentric to said geometric axis.
3. A can as defined in claim 1, wherein said closure member and
heat seal have a tear/shear force resistance of at least about 25
lb./in., and wherein said average diameter of said aperture and
said angle of slope of said flange are mutually selected such that
when the closure member is subjected to differential pressure of a
given value between about 50 and about 100 p.s.i. within the can,
the tear/shear force exerted on the closure member and heat seal
does not exceed said tear/shear force resistance.
4. A can as defined in claim 3, wherein said tear/shear force
resistance is between about 25 and about 75 lb./in.
5. A can as defined in claim 1, wherein said closure member
material is deformable, and wherein said average diameter of said
aperture, said angle of slope of said flange, and the deformability
of said material are mutually selected such that said closure
member, when subjected to differential pressures up to at least
about 90 p.s.i. in the can, bulges upwardly with an arc of
curvature such that a line tangent to said arc at said inner edge
of said flange lies at an angle to said plane not substantially
greater than said angle of slope of the flange outer surface.
6. A can as defined in claim 1, wherein said closure member
material is deformable, and wherein said average diameter of said
aperture, said angle of slope of said flange, and the deformability
of said material are mutually selected such that said closure
member, when subjected to differential pressures up to at least
about 100 p.s.i. in the can, bulges upwardly with an arc of
curvature such that a line tangent to said arc at said inner edge
of said flange lies at an angle to said plane not substantially
greater than said angle of slope of the flange outer surface.
7. A can as defined in claim 1, wherein said closure member and
heat seal have a tear/shear force resistance of at least about 75
lb./in., and wherein said average diameter of said aperture and
said angle of slope of said flange are mutually selected such that
when the closure member is subjected to differential pressure of
not more than about 90 p.s.i. within the can, the tear/shear force
exerted on the closure member and heat seal does not exceed said
tear/shear force resistance.
8. A can as defined in claim 1, wherein said closure member and
heat seal have a tear/shear force resistance of at least about 75
lb./in., and wherein said average diameter of said aperture and
said angle of slope of said flange are mutually selected such that
when the closure member is subjected to differential pressure of
not more than about 100 p.s.i. within the can, the tear/shear force
exerted on the closure member and heat seal does not exceed said
tear/shear force resistance.
9. A can as defined in claim 5, wherein said closure member and
heat seal have a tear/shear force resistance of at least about 75
lb./in., and wherein said average diameter of said aperture and
said angle of slope of said flange are mutually selected such that
when the closure member is subjected to differential pressure of
not more than about 90 p.s.i. within the can, the tear/shear force
exerted on the closure member and heat seal does not exceed said
tear/shear force resistance.
10. A can as defined in claim 6, wherein said closure member and
heat seal have a tear/shear force resistance of at least about 75
lb./in., and wherein said average diameter of said aperture and
said angle of slope of said flange are mutually selected such that
when the closure member is subjected to differential pressure of
not more than about 100 p.s.i. within the can, the tear/shear force
exerted on the closure member and heat seal does not exceed said
tear/shear force resistance.
11. A can as defined in claim 1, wherein said heat seal has a
90.degree. peel strength between about 8 N and about 20 N.
12. A can as defined in claim 1, wherein said annular inner edge is
formed with a reverse bead curl.
13. A can as defined in claim 12, wherein said reverse bead curl is
substantially tangent to the upwardly sloping outer surface of the
flange.
14. A can as defined in claim 1, wherein said metal foil is
aluminum alloy foil.
15. A can as defined in claim 14, wherein said aluminum alloy foil
has a thickness between about 0.003 inch and about 0.004 inch.
16. A can as defined in claim 1, wherein said heat seal is formed
as an annulus surrounding said aperture and having a width between
about 0.079 inch and about 0.118 inch.
17. A can as defined in claim 1, wherein said closure has a tab
portion with a manually graspable free end and an extension
overlying said lid in opposed relation to said tab portion, said
heat seal including an annulus surrounding said aperture and a
further seal portion bonding said extension to said lid such that
the peel force required to separate the extension from the lid is
greater than that required to separate the closure member from the
lid at the annulus, whereby the aperture can be opened by peeling
back the closure member while the closure member remains secured to
the lid by said further seal portion.
18. A can as defined in claim 17, including a body of
fragrance-providing material disposed between the closure member
and the lid and surrounded by the heat seal such that when the
closure member is subjected to a peel force effective to open the
aperture, the body of fragrance-providing material becomes
exposed.
19. A can as defined in claim 1, including a body of
fragrance-providing material disposed between the closure member
and the lid and surrounded by the heat seal such that when the
closure member is subjected to a peel force effective to open the
aperture, the body of fragrance-providing material becomes
exposed.
20. A can as defined in claim 1, wherein said body is a drawn and
ironed metal can body for holding a carbonated beverage; wherein
the lid is formed with a peripheral rim engaging the open upper end
of the can body and projecting upwardly above the upper surface of
the lid; wherein the body is formed with an outwardly concave lower
end, the rim and body lower end being mutually shaped and
dimensioned to permit stable vertical stacking of the can with
other identically shaped and dimensioned cans; wherein the flexible
closure member is domed so as to rise to a height above the annular
flange; and wherein the height of the rim, the concavity of the
body lower end, and the height to which the closure rises above the
annular flange are such that there is sufficient clearance between
the lid upper surface of the can and the concave bottom of another
identical can stacked above it to accommodate the domed
closure.
21. A can lid member mountable on a metal can body having an open
upper end so as to be peripherally secured to and to close said can
body end, said lid comprising a substantially rigid unitary metal
member having an upper surface with a frustoconical annular flange
formed in a portion of said lid and projecting upwardly from said
lid upper surface, said flange having an upwardly sloping outer
surface and an annular inner edge lying substantially in a plane
and defining an aperture with an average diameter between about
0.625 inch and about 1 inch, said flange outer surface being
oriented at an angle of slope between about 12.5.degree. and about
30.degree. to said plane, said flange being arranged and configured
to be closed by a flexible closure member extending entirely over
said aperture and peelably bonded to said flange outer surface
around said aperture.
22. A can lid mountable on a metal can body having an open upper
end so as to be peripherally secured to and to close said can body
end, said lid comprising a substantially rigid unitary metal can
lid member having an upper surface with a frustoconical annular
flange formed in a portion of said lid and projecting upwardly from
said lid upper surface, said flange having an upwardly sloping
outer surface and an annular inner edge lying substantially in a
plane and defining an aperture with an average diameter between
about 0.625 inch and about 1 inch, said flange outer surface being
oriented at an angle of slope between about 12.5.degree. and about
30.degree. to said plane defining an aperture; and a flexible metal
foil closure member extending entirely over said aperture and
peelably bonded by a heat seal to said flange outer surface
entirely around said aperture.
23. A carbonated, or otherwise pressurized, beverage package
comprising: (a) a can including a metal can body having an open
upper end and a substantially rigid metal can lid peripherally
secured to and closing said can body end, said lid having an upper
surface; (b) a body of a carbonated, or otherwise pressurized,
beverage contained within said can; (c) a frustoconical annular
flange formed in said lid and projecting upwardly from said lid
upper surface, said flange having an upwardly sloping outer surface
and an annular inner edge lying substantially in a plane and
defining an aperture with an average diameter between about 0.625
inch and about 1 inch, said flange outer surface being oriented at
an angle of slope between about 12.5.degree. and about 30.degree.
to said plane; and (d) a flexible metal foil closure member
extending entirely over said aperture and peelably bonded by a heat
seal to said flange outer surface entirely around said
aperture.
24. A method of producing a can containing a carbonated, or
otherwise pressurized, beverage, comprising: (a) filling a drawn
and ironed metal can body, having an open upper end, with a
carbonated, or otherwise pressurized, beverage, and (b) closing
said open upper end of said can body by peripherally securing a
substantially rigid metal can lid to said can body end, said lid
having an upper surface and a frustoconical annular flange formed
in said lid and projecting upwardly from said lid upper surface,
said flange having an upwardly sloping outer surface and an annular
inner edge lying substantially in a plane and defining an aperture
with an average diameter between about 0.625 inch and about 1 inch,
said flange outer surface being oriented at an angle of slope
between about 12.5.degree. and about 30.degree. to said plane, and
a flexible metal foil closure member extending entirely over said
aperture and peelably bonded by a heat seal to said flange outer
surface entirely around said aperture.
25. A can for holding liquid, comprising: (a) a metal can body
having an open upper end; (b) a substantially rigid metal can lid
peripherally secured to and closing said can body end, said lid
having an upper surface and defining an aperture therein for
pouring or drinking liquid from the can; and (d) a flexible closure
member extending entirely over said aperture and peelably bonded by
a heat seal to said lid entirely around said aperture; wherein the
improvement comprises: (e) said closure including a tab portion
with a manually graspable free end and an extension overlying said
lid in opposed relation to said tab portion, said heat seal
including an annulus surrounding said aperture and a further seal
portion bonding said extension to said lid such that the peel force
required to separate the extension from the lid is greater than
that required to separate the closure member from the lid at the
annulus, whereby the aperture can be opened by peeling back the
closure member while the closure member remains secured to the lid
by said further seal portion.
26. A can for holding liquid, comprising: (a) a metal can body
having an open upper end; (b) a substantially rigid metal can lid
peripherally secured to and closing said can body end, said lid
having an upper surface and defining an aperture therein for
pouring or drinking liquid from the can; and (d) a flexible closure
member extending entirely over said aperture and peelably bonded by
a heat seal to said lid entirely around said aperture; wherein the
improvement comprises: (e) a body of fragrance-providing material
disposed between the closure member and the lid and surrounded by
the heat seal such that when the closure member is subjected to a
peel force effective to open the aperture, the body of
fragrance-providing material becomes exposed.
27. A can as defined in claim 1, wherein the can lid is formed of
the same alloy as the can body.
28. A can as defined in claim 27, wherein said alloy is AA3104
alloy or AA 3004 alloy.
29. A can as defined in claim 1, wherein the can lid is formed of
AA3104 alloy or AA 3004 alloy.
30. A can as defined in claim 1, wherein the can lid is formed of
steel.
31. A can as defined in claim 1, wherein the can lid has a diameter
of less than two inches.
32. A can as defined in claim 31, wherein the can lid has a gauge
of less than 0.0082 inch.
33. A can as defined in claim 31, wherein the can lid is
substantially free of countersinking.
34. A can comprising: (a) a metal can body having an open upper
end, a lower portion with a maximum diameter and an upper portion
formed as a neck of reduced diameter relative to said maximum
diameter; (b) a substantially rigid metal can lid peripherally
secured to and closing said can body end, said lid having an upper
surface; (c) a frustoconical annular flange formed in a portion of
said lid and projecting upwardly from said lid upper surface, said
flange having an upwardly sloping outer surface and an annular
inner edge lying substantially in a plane and defining an aperture;
and (d) a flexible closure member of a material comprising a metal
foil, extending entirely over said aperture and peelably bonded by
a heat seal to said flange outer surface entirely around said
aperture.
35. A can as defined in claim 34, wherein said body is a drawn and
ironed metal can body having an initially cylindrical sidewall with
an upper portion, and wherein said neck is produced by forming said
sidewall upper portion.
36. A can as defined in claim 34, wherein said body is a drawn and
ironed metal can body having a generally cylindrical sidewall, an
initially closed end portion integral therewith, and an open second
end; wherein said neck is produced by forming said end portion;
wherein said open second end is closed by seaming a can end
thereto; and wherein said open upper end is produced by forming an
endwise opening in said neck.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of copending U.S.
patent application Ser. No. 09/603,004, filed Jun. 26, 2000, which
is a continuation-in-part of U.S. patent application Ser. No.
09/247,999, filed Feb. 10, 1999 (now abandoned), the entire
disclosures of both of the aforesaid applications being
incorporated herein by this reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to cans, and more particularly to
metal cans having an apertured lid with a heat-sealed, peelable
closure for the aperture. In an important specific aspect it is
directed to heat-sealed-closure type cans for holding carbonated
beverages or like contents that exert a positive internal pressure
on the closure, and also to lids for such cans, carbonated
beverage-containing packages including such cans, and methods of
producing such cans containing carbonated beverages.
[0003] Heat sealable containers are widely used for a variety of
high quality food products. Non-retorted products packaged with
heat sealable foil lidding include many types of jams, preserves,
yogurt and dairy products, peanuts and snack foods. A wide variety
of retortable fish and meat products (including many varieties of
pet food) are also packaged using heat sealed foil lidding. In some
instances, the entire lid of a can or like container may be
removably bonded by heat sealing to a flange formed at an open
upper end of the container body, so as to enable the lid to be
completely removed, for access to the contents of the container.
Other containers, exemplified by cans of tomato or like quiescent
fruit juices, have a lid permanently secured to the container body
and formed with an aperture (for pouring out the contents) covered
by a heat sealed closure or, more commonly, by a closure bonded
with a pressure sensitive adhesive. Such a closure is commonly a
thin, flexible element, e.g. an aluminum foil-polymer laminate,
peripherally bonded by heat sealing to a flange defining the
aperture, and has a tab that enables the closure to be peeled
manually from the flange; the flange may be a flat portion of the
can lid surrounding the aperture and coplanar with the aperture
edge.
[0004] For easy opening, typical peel forces (at 90.degree. to the
flange) for a heat sealed closure are in a range between about 2
lbs. (.apprxeq.9 Newtons) and 4 lbs. (.apprxeq.18 Newtons) and
preferably about 21/2lbs. (.apprxeq.11.3 Newtons).
[0005] Some containers with heat sealed closures are subjected to a
retorting process after filling to sterilize the food or beverage.
The retort process involves pressure differentials (from inside to
outside) of up to 30 psi (.apprxeq.2 bar), although for many
applications, a counter pressure system is used to prevent the lid
or closure from bursting off the container. This is necessary
because of the reduction in bond strength which generally occurs at
the elevated retort temperatures. Moreover, in the case of
containers with a lid or closure heat sealed to a flange which is
coplanar with the container aperture, internal pressure will cause
the lid or closure to bulge over the aperture and, in turn, this
bulging exerts a peel force on the heat seal.
[0006] Carbonated soft drinks require a container capable of
withstanding internal pressures of 90 psi or higher. Such
pressures, or even substantially lesser positive internal
pressures, would exert on a conventional heat sealable closure a
peeling force more than sufficient to cause burst failure.
Increasing the strength of the heat seal bond sufficiently to
withstand such forces would make manual peeling of the closure
difficult or virtually impossible for many consumers. Consequently
heat sealable closures have not had wide commercial use with canned
carbonated beverages. In present-day commercially available
carbonated soft drink cans, having a so-called drawn-and-ironed
aluminum alloy can body and an aluminum alloy can lid peripherally
secured to the open upper end of the body, the can end is commonly
formed with a scored area and provided with a riveted tab system
which, when lifted, creates a lever action and exerts a downward
force that generates a fracture along a scored line thereby
creating an aperture. The region of the lid that lies within the
scored area is simultaneously bent down into the top of the
container.
[0007] A conventional can end or lid provided with a riveted tab
and scored area must be fabricated from sheet which has sufficient
strength and formability to meet the requirements. In particular,
the gauge, alloy and temper must be chosen to meet the demands of
the rivet-forming operation, to enable the scoring (which typically
has a depth equal to about half the thickness of the lid) to
withstand internal pressures which may exceed 90 psi (.apprxeq.6
bar), and to impart sufficient strength to the rivet area of the
lid so that the score line can be ruptured by manual application of
a leveraged force using the tab. The aluminum alloy designated
AA5182, rolled to about 0.0086" (.apprxeq.218 .mu.) gauge currently
meets these requirements in the most cost effective way. However,
compared to some other sheet alloy products (for example, AA3104
can body sheet), it is quite costly. This is due in part to the
comparatively high magnesium content (.apprxeq.4.5% by weight) and
also due to the more costly rolling practices which are necessary
for this alloy. Moreover, during recycling and remelting
operations, magnesium is preferentially oxidized, and therefore
lost in the dross. This means that metal from recycled used
beverage containers (UBCs) is not suitable for can end sheet
production unless costly additions of magnesium are made to
compensate for this magnesium loss.
[0008] In addition, the full can end must have sufficient strength
and rigidity when attached to the can so that it will not buckle,
reverse or deflect excessively under the stresses applied by the
internal pressure from the contained beverage; the larger the area
of a can lid, the greater is the strength necessary to prevent
deflection and buckling or reversal. In recent years, there has
been some reduction in commercial can end (lid) diameter, with
concomitant reduction in lid gauge and area, affording savings in
amount of metal used per lid. However, a conventional can lid must
have a diameter large enough to accommodate the tab and the
centrally positioned rivet as well as a scored area of sufficient
size to provide the desirably large aperture currently preferred
for pouring or drinking; this consideration has constrained the
extent to which the diameter of conventional lids can be reduced.
Also, even with the limited lid diameter reduction heretofore
achieved, a conventional lid is ordinarily formed with a peripheral
countersink to aid in minimizing deflection and reduce the
likelihood of buckling or reversal of the lid, although the
presence of the countersink (unavoidably near the location of
drinking or pouring) is disadvantageous from a hygienic standpoint
in that, especially during storage, it may collect dirt and foreign
matter.
[0009] Another disadvantage of the riveted tab--scored area system
is that the score line is vulnerable to corrosive attack. Scoring
of the can end cuts through the protective layer of lacquer and
exposes a crevice of unprotected metal. Any spillage or
contamination of this score line by a beverage or other liquid may
initiate localized corrosive attack.
[0010] Alternative structures have heretofore been proposed or
produced with the objective of enabling use of heat sealable
closures with containers for carbonated beverages or other
substances that create elevated internal pressure. For instance, it
has been proposed to provide a spherically domed (rather than
planar) lid having an aperture covered by a similarly spherically
curved closure member bonded thereto, or to provide a container in
which the entire lid is heat-sealed to an angled (rather than
planar) flange around the container periphery. In a further
alternative, a can lid has been provided with plural small holes
(rather than a single aperture) covered by a single foil laminate
seal with a pull tab. These alternatives, however, have various
limitations or drawbacks.
[0011] U.S. Pat. No. 3,889,844 describes a can closure in which a
can end is shaped to impart a frustoconical area around a pour hole
sealed with an adhesive tape tab so that the forces acting on the
tape (exerted by can contents under pressure, such as carbonated
beverages) tend to place the adhesive in shear instead of in peel.
The size of the pour hole described in this patent provides a pour
rate which is low as compared to present-day conventional
carbonated beverage cans with scored can ends, and the attainment
of long shelf life at pressures as high as 90 psi is not shown.
SUMMARY OF THE INVENTION
[0012] The present invention, in a first aspect, broadly
contemplates the provision of a can comprising a metal can body
having an open upper end; a substantially rigid metal can lid
peripherally secured to and closing the can body end, the lid
having an upper surface; a frustoconical annular flange formed in a
portion of the lid and projecting upwardly from the lid upper
surface, the flange having an upwardly sloping outer surface and an
annular inner edge lying substantially in a plane and defining an
aperture with an average diameter between about 0.625 inch and
about 1 inch, the flange outer surface being oriented at an angle
of slope between about 12.5.degree. and about 30.degree. to the
plane; and a flexible closure member of a material comprising a
metal foil, extending entirely over the aperture and peelably
bonded by a heat seal to the flange outer surface entirely around
the aperture.
[0013] In currently preferred embodiments of the invention, the lid
has a substantially flat upper surface. It is also strongly
currently preferred that the aperture be circular, because in
noncircular apertures there are locations around the perimeter
where the tendency of the closure member to peel (burst) is
enhanced. The "average diameter" in the case of a circular aperture
is, of course, simply the diameter of the aperture.
[0014] It will be understood that directions such as "upper" or
"upwardly" are used herein with reference to a can standing upright
with the lid at the top. The term "angle of slope" refers to the
acute angle formed between the plane of the aperture edge and the
line representing the flange outer surface as seen in a vertical
plane intersecting the aperture edge at a point at which the line
tangent to the aperture edge in the plane of the aperture edge is
perpendicular to the vertical plane.
[0015] When the can is filled with a carbonated beverage, the
closure member is subjected to a differential pressure
(herein-after sometimes designated .DELTA..sub.p), i.e. a positive
difference between the pressure within the can and ambient pressure
outside the can, in some circumstances as high as 90 psi or even
more. This differential pressure exerts, on the closure member and
heat seal, a force having a tear/shear component (i.e., tending to
tear the closure member and shear the heat seal, such component
being hereinafter referred to as the tear/shear force and being
sometimes designated .gamma.), and in some cases also a peel
component.
[0016] In currently preferred embodiments of the invention, the
closure member material is deformable, and the average diameter of
the aperture, the angle of slope of the flange, and the
deformability of the material are mutually selected such that the
closure member, when subjected to differential pressures up to at
least about 90 psi (preferably up to at least about 100 psi) in the
can, bulges upwardly with an arc of curvature such that a line
tangent to the arc at the inner edge of the flange lies at an angle
(to the plane of the flange inner edge) not substantially greater
than the angle of slope of the flange outer surface, thereby to
eliminate any peel component of the force exerted by the
differential pressure on the closure member and heat seal.
[0017] Also, in some currently preferred embodiments, the closure
member and heat seal have a tear/shear force resistance of at least
about 75 lb./in., and the average diameter of the aperture and the
angle of slope of the flange are mutually selected such that when
the closure member is subjected to differential pressure of up to
at least about 90 psi (preferably up to at least about 100 psi)
within the can, the tear/shear force exerted on the closure member
and heat seal does not exceed the aforesaid tear/shear force
resistance.
[0018] As a further particular feature of the invention, in
currently preferred embodiments, the annular inner edge of the
flange is formed with a reverse bead curl, which may be
substantially tangent to the upwardly sloping outer surface of the
flange.
[0019] Conveniently and advantageously, in at least many instances,
the metal foil of the closure member is aluminum alloy foil, e.g.
having a thickness between about 0.002 inch (.apprxeq.50 .mu.) and
about 0.004 inch (.apprxeq.100 .mu.). Also advantageously, the heat
seal may be formed as an annulus surrounding the aperture and
having a width between about 0.079 inch and about 0.118 inch (about
2 to 3 mm). This width of heat seal is found to be sufficient to
withstand tear/shear forces encountered in use, and at the same
time it facilitates manual peeling of the closure member to open
the aperture. To enable such peeling without difficulty, the
90.degree. peel strength of the heat seal is between about 8 and
about 20 N, preferably between about 10 and about 16 N. The closure
may be provided with a tab portion having a manually graspable free
end.
[0020] In contrast to the riveted tab structure of conventional
carbonated beverage cans, a heat-sealable closure member may become
completely separated from the can upon opening, and may then be
separately discarded, creating environmental problems. To avoid
this consequence, and further in accordance with the invention, the
closure may be provided with an extension overlying the lid in
opposed relation to the aforementioned tab portion, and the heat
seal may include both an annulus surrounding the aperture as
described above and a further seal portion bonding the extension to
the lid such that the peel force required to separate the extension
from the lid is greater than that required to separate the closure
member from the lid at the annulus, the aperture being easily
opened by peeling back the closure member from the flange while the
closure member remains secured to the lid by the further seal
portion. This promotes retention of the closure member on the lid,
as desired for environmental reasons. Moreover, the peeled but
retained metal foil closure member can be folded over the aperture
to provide a measure of coverage and protection for the contents of
a can which has been only partially emptied.
[0021] Additionally, a body of fragrance-providing material may be
disposed between the closure member and the lid and surrounded by
the heat seal such that when the closure member is subjected to a
peel force effective to open the aperture, the body of
fragrance-providing material becomes exposed. The fragrance thereby
released, in proximate relation to the nostrils of a person
drinking from the can, enhances the effective flavor sensed by the
drinker.
[0022] The can body may be a drawn and ironed metal can body for
holding a carbonated beverage. The lid may be formed with a
peripheral rim engaging the open upper end of the can body and
projecting upwardly above the upper surface of the lid, the body
being formed with an outwardly concave lower end, and the rim and
body lower end being mutually shaped and dimensioned to permit
stable vertical stacking of the can with other identically shaped
and dimensioned cans. In such a structure, although the flexible
closure member (bulging because of the internal pressure) is domed
so as to rise to a height above the annular flange, the height of
the rim, the concavity of the body lower end, and the height to
which the closure rises above the annular flange are such that
there is sufficient clearance between the lid upper surface of the
can and the concave bottom of another identical can stacked above
it to accommodate the domed closure.
[0023] Metal foil as used for the closure (e.g. as a lacquered foil
or as part of a foil-polymer laminate) has the advantage of
affording excellent gas barrier properties, so that the shelf life
and quality of the product are comparable to that which is obtained
with a normal can, or a glass bottle, and superior to most other
beverage container systems (including PET bottles and other polymer
containers). Aluminum foil, for instance, is an effectively perfect
barrier for oxygen (important for beer to prevent development of
off-flavors owing to oxidation) and for carbon dioxide (important
where carbonation levels need to be maintained). It is also an
effective barrier to prevent migration and loss of fragrance and
flavor components.
[0024] The aperture defined by the flange preferably extends over a
minor fraction of the area of the open end of the can body.
Especially for holding contents such as carbonated beverages, in
cans wherein the open end of the can body has a center of symmetry
(e.g. being circular), the annular flange and the aperture are
disposed eccentrically of the can body open end so as to be
relatively close to the periphery of the lid, for ease of pouring
or drinking. That is to say, the flange is disposed in a portion of
the lid eccentric to the geometric axis of the can, i.e., close to
a side of the can.
[0025] Although the shape of the aperture can take different forms,
noncircular apertures are nonpreferred, and, in particular, angular
apertures or aperture shapes with very small radii of curvature are
not suitable for the present invention. If, instead of a circular
aperture, an elliptical or irregularly shaped aperture is provided,
e.g. having an aspect ratio between about 1.1 and 1.5, the flange
is not strictly frustoconical; it will be understood that the term
"frustoconical" is used broadly herein to define an upwardly
convergently sloping flange continuously surrounding an aperture,
whether the aperture is circular or not.
[0026] In further aspects, the invention embraces a can lid member
as described above, mountable on a metal can body having an open
upper end so as to be peripherally secured to and to close the can
body end; the combination of this lid member with a flexible
closure member extending entirely over the aperture and peelably
bonded to the flange outer surface around the aperture; a
carbonated beverage package comprising a can as described above in
combination with a body of a carbonated beverage contained within
the can; and a method of producing a can containing a carbonated
beverage, comprising filling a drawn and ironed metal can body,
having an open upper end, with a carbonated beverage, and closing
the open upper end of the can body by peripherally securing thereto
a metal can lid member as described above having a flexible closure
member extending entirely over the aperture defined by its annular
flange and peelably bonded to the flange outer surface around the
aperture.
[0027] In the can of the invention, the provision of the
frustoconical annular flange defining the can aperture, and the
securing of the flexible closure member by peelable bonding to the
upwardly sloping outer surface of this flange, enable the use of a
peelably bonded closure member on an otherwise conventional
carbonated beverage can, despite the high differential pressure
(positive internal pressure) acting on the closure through the
aperture and the resultant outward bulging or doming of the
flexible closure member. This is because the angle of slope of the
flange can be made steep enough so that a line tangent to the arc
of curvature of the domed closure member at the inner edge of the
flange lies at an angle (to the plane of the flange inner edge)
which is not substantially greater than, and is preferably less
than, the angle of slope of the flange outer surface. In such case,
the internal pressure acting on the closure member does not exert
any significant component of peeling force that would tend to
separate the closure member from the flange by peeling. Instead,
the forces acting on the peelably bonded flange area owing to
tension in the closure member are predominantly shear in character.
Heat seal bonds, for instance, are strong under shear loading,
especially at ambient temperature; the inability of conventional
heat sealed closures to withstand internal pressure in carbonated
beverage cans has been caused by the substantial peeling forces
exerted on such closures when the closures bulge, under the
elevated pressure within a can of carbonated beverage, at a
substantial angle to a planar horizontal flange surrounding an
aperture.
[0028] For a given internal pressure condition, aperture dimension,
and closure member, the minimization or elimination of peeling
force exerted on a closure bond by elevated pressure within the can
is dependent on the angle of slope of the flange. Stated generally,
the greater the angle of slope, the easier it is to provide a
bonded closure that will not burst from internal pressure yet can
be easily manually peeled by a consumer, having regard to the
extent of doming of practicable flexible foil closure members under
the pressures within a carbonated beverage can. With the flat lid
surface and upwardly projecting frustoconical flange of the present
invention, any desired angle of slope can readily be provided, in
contrast to the range of angles permitted by other geometries such
as a uniformly spherically domed lid having an aperture therein.
Moreover, the arrangement of flange, aperture, and domed closure of
the invention, occupying only a portion of the area of the can end,
enables the height of the closure to be restricted to an extent
compatible with convenient vertical stacking of cans.
[0029] The use of a can end or lid having an aperture with a
peelable heat-sealed closure, in accordance with the present
invention as described above, affords additional advantages in that
the strength and/or the size of the lid may be reduced (without
decreasing the desired size of the aperture for pouring or
drinking), as compared to a conventional can lid having a riveted
tab and scored area. This is because the strength and size
requirements imposed on the lid by the riveted tab and scoring are
eliminated. In addition, the forming operations for the flange and
aperture of the present invention are less demanding than for a
riveted tab, the most critical being the formation of the reverse
bead curl, in embodiments of the invention including that
feature.
[0030] Reduction in strength requirements enables use of a less
expensive alloy for the lid than the AA5182 currently used, and/or
a reduction in lid gauge, thereby affording savings in metal cost.
For example, in particular embodiments of the invention, the lid
may be fabricated of an alloy similar in composition to AA5182, but
with a reduced concentration of magnesium. Alternatively, AA3104 or
3004 alloys, which are the alloys most commonly used for the can
body, could be used. In each case, the gauge of the sheet would be
selected to provide the desired property combination. For the case
of AA3104 alloy, the can end and can body would be the same alloy
and this is advantageous in several respects. For example, the
recycling of used beverage cans (UBCs) benefits from the reduced
magnesium oxide dross formation. Furthermore, there are benefits to
be gained during metal processing. For example, since only one
alloy is used for the can end and can body, the casting and rolling
scheduling can be greatly simplified and rolling mill schedules can
be optimized for a single alloy, allowing improvements in mill
productivity. Similarly, it should be possible to reduce metal
inventories. Alternatively, the lid may be made of other metals,
such as steel, that are unsuitable for a riveted tab and scored
area opening system.
[0031] Reduction in size requirements, a result of the elimination
of the need to accommodate the riveted tab at a central location on
the lid while also affording adequate area for a pouring/drinking
opening of preferred large size, further reduces strength
requirements. Whereas a lid diameter of about 2 1/8 inches
represents a currently practicable lower limit for a can with a
riveted tab and a scored area providing a desirably large opening,
with the present invention the lid diameter can advantageously be
reduced to less than 2 inches, indeed substantially less, yet
without reducing the size of the pouring/drinking aperture. Since a
reduced lid size will have a reduced tendency to buckle when
pressurized, the gauge of metal used can be reduced by at least
about 5% below the current value of 0.0086 inch (.apprxeq.218 .mu.)
used with 2 1/8inch diameter AA5182 alloy lids. Alternatively, the
design of the lid can be modified to eliminate the countersink
recess which is conventionally formed in the peripheral area of can
lids to prevent stiffening and thereby to prevent excessive
deflection and buckling. In yet a further alternative, the reduced
tendency of a smaller diameter lid to buckle can be exploited by
using a lower strength alloy than AA5182, with the advantages in
cost and recycling mentioned above.
[0032] The reduction in lid size attainable with the invention
requires a reduction in diameter, or formation of a neck, in the
upper portion of the can body on which the lid is mounted, so as to
conform to the small lid diameter without detracting from the fluid
capacity of the can. To this end, the upper part of the sidewall of
a conventional drawn and ironed can body may be subjected to one or
more neck-forming operations that reduce the upper body diameter to
conform to the lid. Alternatively, the drawing and ironing
operation may be modified so as to form the necked portion from the
bottom portion of the can body (which is of higher gauge than the
sidewall), forming an open end for the neck, and closing the other
end of the can body (which, in this embodiment, is the lower end)
by seaming a plain can end thereto before filling. The reduced
diameter lid with the flanged aperture and heat-sealed closure is
then seamed onto the open neck after the can is filled.
[0033] Further features and advantages of the invention will be
apparent from the detailed disclosure hereinbelow set forth,
together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a perspective view of a can embodying the present
invention in a particular form;
[0035] FIG. 2A is an enlarged and somewhat simplified fragmentary
elevational sectional view of a portion of the lid member of the
can of FIG. 1, including the aperture-defining flange and closure
member;
[0036] FIG. 2B is a highly simplified and schematic representation
of the same view as FIG. 2A;
[0037] FIG. 3 is a view similar to FIG. 2A of a flexible closure
member bonded to a conventional planar flange defining an
aperture;
[0038] FIG. 4 is a fragmentary view similar to FIG. 3 of a portion
of the flange and closure member of the embodiment of the invention
shown in FIGS. 2A and 2B;
[0039] FIG. 5 is a simplified and somewhat schematic top plan view
of the can of FIG. 1;
[0040] FIG. 6 is an exploded diagrammatic elevational sectional
view of the can lid and closure member of FIG. 5;
[0041] FIG. 7 is a plan view of the closure member of FIG. 5;
[0042] FIG. 8 is a side elevational view, partly broken away, of
two cans having the structure shown in FIG. 1, illustrating the
ability of the cans to be stacked vertically;
[0043] FIG. 9 is a view similar to FIG. 2B illustrating a condition
of excessive bulging of the closure member;
[0044] FIG. 10 is a graph representing the relationship between
sealing temperature and peel strength in Example 2 described
below;
[0045] FIG. 11 is a graph representing the relationship between
heat seal temperature and burst pressure in the same example;
[0046] FIG. 12 is an enlarged fragmentary sectional elevational
view of a portion of a lid member embodying the present
invention;
[0047] FIG. 13 is a schematic fragmentary sectional elevational
view of a lid member embodying the invention;
[0048] FIG. 14 is a graph showing bulge height of an exemplary
closure member as a function of pressure within the can (i.e.,
differential pressure .DELTA..sub.p);
[0049] FIG. 15 is a schematic plan view of a can lid embodying the
invention and having a "stay-on" closure member;
[0050] FIG. 16 is a graph showing 90.degree. peel force as a
function of displacement of the closure member of FIG. 15;
[0051] FIGS. 17A and 17B are highly schematic fragmentary
elevational sectional views in illustration of a further embodiment
of the invention including a fragrance reservoir;
[0052] FIG. 18 is a sectional elevational view of one form of can
lid embodying the invention and including a fragrance
reservoir;
[0053] FIGS. 19 and 20 are views similar to FIG. 15 of two can lids
embodying the invention and including both a stay-on closure member
and a fragrance reservoir;
[0054] FIG. 21 is a sectional view of another form of can lid
embodying the invention, in which the conventional countersink is
omitted;
[0055] FIG. 22 is an elevational view of a further embodiment of
the can of the invention, having a reduced-diameter body neck and
lid;
[0056] FIG. 23 is an enlarged fragmentary perspective view of the
upper portion of the can of FIG. 22, showing the lid with the
heat-sealed closure member in place;
[0057] FIG. 24 is a view similar to FIG. 23 with the closure member
removed;
[0058] FIG. 25 is an elevational view of another embodiment of the
can of the invention;
[0059] FIG. 26 (prior art) is an exploded and highly schematic
sectional view in illustration of a system for producing a
conventional drawn and ironed can body;
[0060] FIG. 27 is a fragmentary view, similar to FIG. 26, of one
form of modification of the system of FIG. 26 for producing the
body of the can of FIG. 25;
[0061] FIG. 28 is an elevational view of the can body as formed by
the system of FIG. 27; and
[0062] FIG. 29 is a view similar to FIG. 27 of an alternative
modification of the system of FIG. 26 for producing the body of the
can of FIG. 25.
DETAILED DESCRIPTION
[0063] The container of the invention will be described, with
reference to the drawings, as embodied in a metal can 10 for
holding a carbonated beverage such as soda or beer. The can 10
includes a one-piece can body 11 constituting the bottom 12 and
continuous, upright, axially elongated, generally cylindrical side
wall 14 of the can, and a lid 16 which, after the can has been
filled with the beverage, is peripherally secured to the open top
end of the can body to provide a complete, liquid-tight
container.
[0064] In this embodiment, the body 11 may be an entirely
conventional drawn-and-ironed aluminum alloy can body, identical in
structure, alloy composition, method of fabrication, configuration,
gauge, dimensions and surface coatings to can bodies currently
commercially used for carbonated and other beverages
(alternatively, for example, the body may be a steel can body, such
as are in common use in Europe). In particular, and in common with
known can bodies, the bottom 12 of the body 11 is externally
concave and the open top end of the body has a circular edge 18
lying in a plane perpendicular to the vertical geometric axis of
the side wall 14. The terms "aluminum" and "aluminum alloy" are
used interchangeably herein to designate aluminum metal and
aluminum-based alloys.
[0065] Except as hereinafter described, the lid 16 may also be a
generally conventional aluminum alloy lid member of the type
currently commercially used for beverage cans having drawn and
ironed one-piece can bodies such as the body 11. Thus, the alloy of
which it is constituted, the steps and procedures employed in its
fabrication (with the exceptions noted below), and its general
overall configuration, dimensions, gauge and surface coatings as
well as the manner in which it is secured to the top edge 18 of the
can body 11, may all be the same as in the case of present day can
lids well-known in the art.
[0066] It should be noted, however, that since the can lid of the
present invention is not subjected to the rivet-forming and scoring
operations that must be performed on currently conventional can
lids, since the strength and rigidity necessary for the
conventional rivet and tab area to withstand the lever action are
not required, and since gauge and strength requirements related to
the presence of a score line do not apply, the invention permits
the use of nonconventional can lid alloys, materials and/or lid
gauges. For example, coated steel can lids, which are normally too
difficult to open by the conventional scoring mechanisms, could be
used in the practice of the invention. The current gauge used for
AA 5182 alloy lids could be reduced and/or the alloy composition
could be modified by reducing the proportion of Mg, thereby
lowering costs. Similarly, AA 5182 alloy could be replaced as the
alloy of the lid with a lower cost, lower strength alloy such as AA
3104 alloy or AA3004 alloy, commonly used for can bodies (but not,
heretofore, for can lids). Used at an appropriate gauge, AA 3104
alloy or AA 3004 alloy may have sufficient strength for the lid
structure of the present invention; it could offer the advantages
of lower cost as compared to the AA 5182 alloy currently used for
can lids and would also afford benefits for recycling, in that the
can lid and body would be made of the same alloy.
[0067] In particular, the lid 16 in this illustrated embodiment is
substantially rigid, and has a substantially flat upper surface 20
with a circular periphery, around which is formed a raised annular
rim 22 projecting upwardly above the plane of the flat upper
surface 20. When the lid is mounted on the open upper end of a
beverage-filled can body, in known manner, the rim 22 engages the
upper edge 18 of the can body; the circular flat surface 20 lies
substantially in a horizontal plane, perpendicular to the vertical
geometric axis of the cylindrical side wall 14, and is centered
with respect to the latter axis.
[0068] The lower end 14a of the side wall 14 of the can 10 is
shaped (tapered) to interfit with the rim 22 of the lid of another
identical can 10a, when the can 10 is stacked vertically on top of
the can 10a as shown in FIG. 8. A multiplicity of the cans may thus
be stably vertically stacked, one on another, as is true of
present-day conventional cans of the same general type. The
elevation of the lid rim 22 above the flat upper surface 20 of the
lid, together with the concavity of the can bottom 14,
cooperatively define a central g.DELTA..sub.P or space between the
lid of one can and the bottom of the next can above it, in such a
stacked arrangement.
[0069] Also in common with present-day conventional lid members
used with one-piece drawn-and-ironed aluminum alloy beverage can
bodies, the lid 16, when secured to the beverage-filled can body,
provides therewith a complete sealed enclosure holding the
beverage. The lid is thus subjected to elevated internal pressure
within the can (i.e., pressure higher than ambient atmospheric
pressure) if the beverage is carbonated. However, the formed
aluminum alloy lid is substantially rigid, so that it undergoes at
most only a small deflection of its upper surface as a result of
this pressure condition, and the upper surface 20 remains
substantially flat notwithstanding the internal pressure acting on
the lid.
[0070] The lid 16 is arranged to provide an aperture through which
the beverage contained in the can may be poured or removed by
drinking directly from the can, either with a straw inserted
through the aperture or by juxtaposition of the consumer's mouth to
the aperture. Heretofore, in cans for holding carbonated beverages
or other such contents at elevated pressure, the aperture-providing
feature has conventionally included a scored portion of the metal
of the lid member and a riveted pull tab system for parting the lid
metal along the score line to open the aperture.
[0071] The present invention, in contrast, provides a pre-formed
open aperture 24 in the lid, and a peelable, flexible closure
member 28 covering the aperture. In order to achieve adequate burst
resistance without requiring excessive force to peel the closure
member, a shallow frustoconical annular flange 30 is formed in the
lid within the area of the flat upper surface 20, to surround and
define the aperture 24 and to provide a seat for the closure
member.
[0072] More particularly, the flange 30 projects upwardly from the
upper surface 20 of the lid, and has an upwardly sloping outer
flange surface 32 and an annular inner edge 34 defining the
aperture 24, which is illustrated as being of circular
configuration but is not limited to a circular shape. The inner
edge 34, as shown in FIGS. 2A and 2B, is preferably formed as a
bead 36 with a reverse curl, which is tangent to a horizontal plane
represented by line P (FIGS. 2A and 2B) and to the line of slope of
the outer flange surface 32 so that, once the closure member 28 is
heat-sealed to the flange surface, the cut metal (typically an
aluminum alloy) at edge 34 cannot come into contact with the
contained beverage. This is advantageous because the cut metal at
the edge (unlike the major surfaces of the lid) has no protective
coating, and would be attacked by acidic or salt-containing
beverages if it were exposed thereto. The reverse curl of bead 36
also prevents a drinker's lips from touching and being injured by
the cut metal at edge 34, and avoids any possibility of damage to
the closure member by contact with the cut metal. However, the
invention may also be embodied in a can wherein the aperture has a
standard (not reverse) bead curl, which also affords such benefits
as safety for the consumer, it being noted that where the cut edge
of the metal is not kept from contact with the contained liquid by
a reverse curl, it may be protected by application to the cut edge
of a lacquer.
[0073] The flexible closure member 28 is constituted of a sheet
material comprising metal foil, e.g. aluminum foil; in the
described embodiment of the invention, the closure member is
fabricated of a suitably lacquered aluminum foil sheet or an
aluminum foil-polymer laminate sheet. Stated more broadly,
materials that may be used for the closure member include, without
limitation, lacquer coated foil (where the lacquer is a suitable
heat seal formulation); extrusion coated foil (where the polymer is
applied by a standard or other extrusion coating process); the
aforementioned foil-polymer laminate, wherein the foil is laminated
to a polymer film using an adhesive tie layer; and
foil-paper-lacquer combinations such as have heretofore been used
for some low-cost packaging applications.
[0074] The closure member extends entirely over the aperture 24 and
is secured to the flange outer surface 32 by a heat seal extending
at least throughout the area of an annulus entirely surrounding the
aperture. Since the reverse curl bead 36 does not project beyond
the slope of the flange outer surface, the closure member smoothly
overlies this bead as well as the flange outer surface, affording
good sealing contact between the closure member and the flange.
[0075] The closure member, in the described embodiment of the
invention, is bonded by heat sealing to the flange 30, covering and
closing the aperture 24, before the lid member 16 is secured to a
can body 11 filled with a carbonated beverage. Once the lid has
been mounted on the body to complete the enclosure of the beverage,
elevated pressure generated by the beverage acts on the inner
surface portion of closure member 28 which is exposed through the
aperture to the interior of the can, causing the flexible closure
member to bulge outwardly. Further in accordance with the
invention, however, the angle .theta. (FIG. 2A) of slope of the
flange outer surface relative to the plane of the annular edge 34
(i.e., plane P) is selected to be such that a line tangent to the
arc of curvature of the bulged closure member at the inner edge of
the flange lies at an angle to plane P not substantially greater
than the angle .theta. of slope of the flange outer surface. As
indicated in FIG. 2B, since the upper surface 20 of the lid member
16 is flat and horizontal (and thus parallel to plane P), .theta.
may alternatively be defined as the angle of slope of the flange
outer surface to the flat lid surface 20.
[0076] Preferably the angle .theta. is between about 12.5.degree.
and about 30.degree. to the plane P, and more preferably at least
15.degree.. In currently particularly preferred embodiments, the
angle .theta. of slope is between about 18.degree. and about
25.degree. to the plane P.
[0077] In FIGS. 2A and 2B, A is the diameter of the aperture 24 in
plane P, R is the radius of curvature of the bulged or domed
closure member 28, and h is the maximum vertical height of the
domed closure member above the aperture plane P. In these figures,
the foil closure is shown domed to the point at which the flange is
tangential to the arc of the domed foil closure member 28, i.e., at
which the line of slope of the flange surface 32 as seen in a
vertical plane is tangent to the arc of curvature of the closure 28
(as seen in the same vertical plane) at the edge of aperture
24.
[0078] For the closure configuration illustrated in FIGS. 2A and
2B, the forces acting on the heat sealed flange area due to the
tension in the foil, are predominantly shear in character, with no
significant peel force component. In this case, the burst
resistance will depend on the shear strength of the heat seal joint
or the bulge strength of the foil or foil laminate itself. This
ensures that the burst resistance of the lid is enhanced
significantly compared to that of a standard heat sealed
container.
[0079] Heat seal bonds are strong under shear loading, especially
at ambient temperature, and an annular heat seal about 2 mm -3 mm
wide is sufficient to resist the anticipated shear forces which
result from the internal pressure. If the foil is domed to a lesser
extent than shown in FIGS. 2A and 2B, relative to the flange slope
angle .theta., the foil laminate will tend to hold down the heat
seal bond with a corresponding additional enhancement of the burst
resistance. If, however, the foil were domed to a greater extent
than is shown in FIGS. 2A and 2B, relative to the flange slope
angle, a peel force component would arise at the inner edge of the
aperture, with an increased likelihood of burst failure.
[0080] The frustoconical aperture-defining flange enables provision
of a flange slope angle .theta. sufficient to accommodate the
extent of doming or bulging of the closure member to be used
therewith, under the elevated internal pressures for which the can
is designed, and thereby enables the burst resistance to be
enhanced significantly, for a closure with a peel force which is
acceptable to the consumer. The peel force is dependent both on the
inherent peel properties of the selected heat seal lacquer system,
and on geometric effects associated with the complex bending and
distortion which the closure foil undergoes during peeling.
[0081] As will therefore be clear, the flange slope angle and the
form of the foil closure strongly influence the burst
resistance.
[0082] In addition to the flange slope angle and extent of doming
of the closure, not only the resistance of the heat seal bond to
shear forces but also the strength of the foil of the closure
member are selected to withstand the forces acting thereon. If the
flange slope angle, in accordance with the invention, is such as to
substantially avoid any substantial peel force component of forces
acting on the heat sealed area owing to tension in the foil from
the internal pressure acting on the closure member, and if the heat
seal bond and the shear resistance of the bond are adequate, burst
failure could occur by failure of the foil itself. The shear force
required to break the heat seal bond can be adjusted either by
increasing the width of the heat sealed region, or by selecting
laminates or coating formulations which achieve a higher shear
strength. Both of these expedients, however, would increase the
peel force required to open the container.
[0083] The effect of heat sealing the closure member 28 to a
sloping flange surface rather than a horizontal flange surface,
will be apparent from a comparison of FIGS. 3 and 4. FIG. 3
represents an aperture 40 in a conventional lid member 41 wherein
the flange 42 around the aperture is simply a flat horizontal
portion of the lid upper surface, coplanar with the aperture edge
43. A flexible closure member 44 covering the aperture 40 and
bonded by heat sealing to the coplanar flange 42 will bulge, in the
same manner as the closure member 28 in FIG. 2A, if the lid member
41 is mounted on a can body filled with a carbonated beverage or
other pressure-generating contents. Assuming that equal elevated
pressures exist within the cans of FIGS. 2A and 3, that the
diameters of apertures 24 and 40 are equal, and that the same
flexible sheet material is used for the closure members 28 and 44,
the extent of bulging of the closure members (defined by h and R)
should be essentially identical in both cans. In the case of the
planar flange of FIG. 3, the consequent tension force F.sup.T
acting on the heat-seal-bonded portion of the closure member 44 at
the edge of the aperture 40 will have a substantial peeling force
component F.sub.P acting at 90.degree. to the plane of the flange
surface. In the case of the sloping flange of the invention,
however, as shown in FIG. 4, owing to the above-described relation
of angle .theta. to the angle of the tangent to the arc of
curvature of the domed closure member 28 at the aperture edge 34
(in which, in FIG. 4, the reverse curl is omitted for simplicity of
illustration), the same tension force F.sub.T (which acts in the
direction of the aforementioned tangent at the edge of the
aperture) has no significant peeling force component F.sub.P acting
in direction D at 90 to the plane of the (sloping) flange surface
32.
[0084] Under the pressures that may obtain within a can of
carbonated beverage, the peeling force component F.sub.P acting on
a flange that is coplanar with the aperture edge can be sufficient
to cause the closure member to progressively separate from the
flange by peeling until it bursts open, at least if the strength of
the heat seal bond is within conventional limits as desired for
ease of peeling by a user. The sloping of the flange prevents this
from happening, and thereby increases the burst resistance of the
heat-sealed closure member sufficiently to enable its safe use on a
carbonated beverage can without having to increase the heat seal
bond strength to a point which would make the closure member
difficult to remove by a user.
[0085] It will be understood that the extent of bulging of the
closure member under the influence of pressure within the can, and
thus the angle of the tangent (relative to plane P) to the bulged
or domed closure member at the aperture edge, is dependent on the
pressure within the can and the elastic deformability of the
closure member. Desirably, the slope angle .theta. of the flange
surface 32 should be chosen to be sufficiently large so as to be
compatible with the bulging characteristic of the chosen closure
member material. The provision of the flange, which serves as a
seat for the heat sealing of the closure member, as a frustoconical
projection from a (preferably substantially flat) upper surface of
a substantially rigid lid, facilitates this provision of a
relatively large slope angle. At the same time, by making the
aperture area a minor fraction of the total area of the can open
end, the height h of the domed closure may readily be kept
sufficiently small to be accommodated between the lid of one can
and the concave bottom of another when the cans are stacked
vertically as shown in FIG. 8.
[0086] Further, it will be understood that the benefits of the
invention may be realized even if the flexible closure member
bulges slightly beyond the ideal limit of tangency to the slope of
the flange. In such a case, the peel component of force will start
to grow, but may still be insufficient to cause failure of the
bond. FIGS. 5-7 illustrate further the configuration and
arrangement of the flange, aperture and closure member at the top
of the can in the embodiment of FIG. 1. With a circular can lid
member 16 having a diameter of 48 mm, mountable on a can body
having a correspondingly dimensioned circular open upper end, a
circular aperture 24 having a diameter of 20 mm is defined by a
frustoconical annular flange 30 having a maximum diameter (in the
plane of lid surface 20) of 30 mm. As best seen in FIG. 7, the
foil-polymer laminate closure member 28 has a circular central
portion 32 mm in diameter (large enough to completely overlie the
sloping outer surface of the flange), with a short projection 28a
on one side for overlying part of the flat upper surface of the lid
and an integral tab portion 28b on the opposite side which,
outwardly of the flange 30, is not heat sealed but is free to be
bent and pulled. The exploded diagrammatic elevational view of FIG.
6 indicates the relative positions of the can lid 16 and the
closure member 28, as well as the folding of the tab. The closure
member is subjected to a preliminary forming step to impart a
frustoconical shape (also indicated in FIG. 6) to its circular
central portion for proper seating on and sealing to the flange
30.
[0087] The aperture 24 is shown in FIG. 5 as being disposed
eccentrically of the geometric center (center of symmetry) of the
can lid 16, i.e., relatively close to the edge of the lid, so that
a user can easily bring the aperture to his or her mouth for
drinking the contained beverage directly from the can. However,
depending on use and contents, different positions for the aperture
may be employed. Also, if desired, aperture configurations other
than the circular shape shown may be provided.
[0088] The manufacture of the can of the invention, including
particularly the lid and closure, may (as stated) be in many
respects generally conventional. However, certain modifications of
conventional practice and equipment, now to be described, are
employed to achieve the novel flange shape and the heat sealing of
the closure member thereto.
[0089] Illustratively, but without in any way limiting the
invention thereto, the foil closure stock may be a suitable
aluminum foil (e.g. made of alloy AA3104 or of a conventional foil
alloy such as AA3003, 8011, 8111, 1100, 1200) with a foil gauge of
0.002"-0.004" (.apprxeq.50 .mu. to 100 .mu.) which is either
lacquered on one side with a suitable heat sealable lacquer, or
laminated on one side with a suitable heat sealable polymer film
(e.g., polyethylene, polypropylene, etc.), 0.001"-0.002"
(.apprxeq.25 .mu. to 50 .mu.) thick. The other (outwardly exposed)
side should have a suitable protective lacquer coating. It may be
desirable to print onto the foil using rotogravure, flexographic or
another known printing method. It may also be desirable to emboss
the laminate, or just the pull tab portion thereof, to provide an
attractive surface texture which enhances the appearance of the
closure and assists in opening by making the closure easier to
grip.
[0090] In order to seal to the aperture, the closure members 28
with their described integral pull tabs are formed and stamped out
from the foil laminate stock using a suitable press (standard
presses can be used with tooling specifically designed for these
closure members). In the embodiment where the frustoconical flange
is preformed, the foil closure members are preshaped (by a drawing
process) so that they will fit over the raised aperture of the
lid.
[0091] A heat sealing machine with suitable tooling is used to heat
seal the closures to the can lid. In the case where the
frustoconical flange is preformed, the heat seal tooling is
designed to conform to the flange shape. That is to say, the
tooling is angled to match the flange (and the formed closure
member). The exact heat sealing conditions are dependent on the
polymer and heat seal coating formulation used. The temperature of
the bottom heat sealing tool should be selected so that the coating
on the inside of the lid member should not be significantly
softened or melted during the heat sealing operation. For the
commonly used can end coatings and for heat seal dwell times of
about 0.3 sec. or less, the temperature should be less than about
220.degree. C. and preferably about 200.degree. C. or below. The
upper tool temperature is set to ensure that the heat seal bond is
achieved in an acceptably short time. Typical commercial heat
sealing machines have dwell times of 0.3 sec. The dwell time,
pressure and temperatures may be optimized for the particular heat
seal application. Heat sealing the closure to the lid involves use
of a customized heat sealing line (such as those built by Hans
Rychiger AG, Steffisburg, Switzerland), with appropriately
constructed heat seal tooling provided to bond the closure to the
angled aperture.
[0092] The forming of the can lid member 16 itself with the
frustoconical flange 30 and aperture 24 as described is relatively
straightforward, using modified can end forming tooling, with
provision for forming the reverse curl bead 36. The can lids of the
invention do not require the formation of a rivet or tab.
[0093] The lids, complete with heat sealed closures, are
substantially compatible with existing can filling lines and will
be a direct replacement for the currently commercially used lids
for cans for carbonated beverages and the like. Modifications may
be made in the lid handling equipment to minimize or eliminate the
possibility of damaging the raised aperture and closure.
[0094] Alternatively, in the currently preferred method of
fabrication, the can lid may initially be provided with the
aperture 28 and reverse curl bead 36 around the edge thereof, and
the closure member 28 may be heat sealed to the upper surface of
the lid in covering relation to the aperture, before the upwardly
sloping frustoconical configuration is imparted to the flange
portion of the lid immediately surrounding the aperture. Forming of
the frustoconical flange 30 then proceeds, with concomitant
deformation of the already heat sealed foil closure member,
followed by mounting of the lid on a can body already filled with
carbonated beverage.
[0095] As initially applied to the can lid, the portion of the
closure member 28 extending across the aperture may be
substantially planar as indicated at 28c in FIG. 12, which shows a
frustoconical flange 30 having an angle of slope .theta. of
23.degree.. When the lid is mounted on a can body filled with a
carbonated beverage, so as to completely enclose the beverage, the
resultant pressure within the can creates a positive differential
pressure .DELTA..sub.P causing the deformable closure member to
bulge upwardly. FIG. 13 illustrates the location of the heat seal
annulus 46 on the sloping outer surface of the frustoconical flange
30.
[0096] A particular feature of the present invention is the
dimension of the aperture 24. There is a consumer preference for
cans with good pouring characteristics (good pour rate with a
smooth, streamlined flow). Cans with large opening ends (LOEs) have
been introduced in recent years and have been successful,
especially for beverages with lower carbonation levels (e.g.
lemonade and iced tea), although in the case of highly carbonated
beverages, problems with score line failure and burst resistance
have been encountered. A conventional shape of apertures for
beverage cans is approximately oval with an aspect ratio between
about 1.1 and about 1.5. A standard aperture is 0.7 inch in
diameter and an LOE is 1 inch.times.0.7 inch; thus, the current
aperture size for a carbonated beverage container, expressed as
average diameter, is from about 0.7 inch to about 0.875 inch.
[0097] Some can designs have also provided a separate vent hole in
the lid to improve pouring and drinking characteristics, but the
inclusion of the vent hole adds to manufacturing cost and may
complicate the opening process for the consumer.
[0098] The aperture size and shape are important in determining
pouring and drinking characteristics. In general, larger aperture
sizes give better flow rates with a more even flow. The relation
between aperture and flow rates is illustrated by the following
test data obtained in experimental pouring tests with the can
tilted from the upright position through an angle of 120.degree.,
so that the can walls make an angle of 30.degree. to the
horizontal, and oriented so that the aperture is at its lowest
point on the can end:
1 TABLE 1 Aperture Pour Rate (g./sec.) Standard can aperture 56 LOE
70 0.5625" (14.3 mm), flat flange 18 0.625" (15.9 mm), flat flange
31 0.750" (19.0 mm), flat flange 50 0.875" (22.2 mm), flat flange
75 0.5625" (14.3 mm), angled flange 24 0.625" (15.9 mm), angled
flange 35 0.750" (19.0 mm), angled flange 56 0.875" (22.2 mm),
angled flange 93
[0099] In the above table, "angled flange" means an upwardly
sloping frustoconical flange as provided in the present invention;
"flat flange" means that the portion of the lid surrounding the
aperture is substantially coplanar with the aperture edge, as in
conventional can lids.
[0100] As will be apparent from Table 1, for equivalent hole sizes,
the pour rate for "angled flange" apertures is higher by about 10
to 15% at a 30.degree. tilt than that for "flat flange" apertures.
The 0.750" angled flange aperture has a pouring rate at 30.degree.
tilt approximately the same as that of the current standard can
aperture. The 0.5625" aperture (with both flat and angled flanges)
has a significantly lower pour rate than that of the current
standard can aperture. The 0.875" angled flange aperture provides a
higher pour rate than the LOE design (which, like the standard can,
has a flat flange). For the aperture range of interest, the pour
rate is approximately proportional to aperture area.
[0101] As hereinafter further explained, the tear/shear forces
acting on the closure member and seal tend to increase with
aperture size, so that the maximum aperture diameter is limited by
the need to provide a can with adequately high burst pressure or
burst resistance (i.e., the pressure at which the closure member
and seal rupture or fail). Therefore, the range of average aperture
diameter in accordance with the present invention is between about
0.625 inch and about 1 inch, to afford satisfactory pour rates
(without any separate vent hole) and at the same time to achieve
high burst resistance without sacrifice of other characteristics
such as peelability.
[0102] Another important characteristic, for attainment of
adequately high burst resistance, is the tear/shear force imposed
on the heat seal and closure member by a given differential
pressure. The tear/shear force .gamma. (lb./in.) is determined by
the differential pressure .DELTA..sub.P (psi), aperture diameter A
(inches) and angle of slope .theta. of the frustoconical flange 30,
in accordance with the relation 1 = A P 4 sin ( 1 )
[0103] In particular instances, depending (for example) on the
degree of carbonation of the contained beverage and the consequent
magnitude of differential pressure that the can, closure and seal
must be designed to withstand, the design value of tear/shear force
resistance for a can in accordance with the invention (i.e., the
value that the closure member and heat seal must be able to
withstand) may range from less than (or about) 25 lb./in. to about
(or even somewhat more than) 75 lb./in., a tear/shear resistance of
about 75 lb./in. being currently preferred in many cases. Typical
filling line pressures for carbonated beverages are between about
50 and about 60 psi, though for some beverages (sports drinks,
lemonade, etc.), lower carbonation levels are used. However, in
order to take account of extreme conditions (temperature,
agitation, etc.) a minimum test burst pressure requirement of 90
psi is currently specified for many applications, and a burst
resistance of 100 psi would be even more desirable.
[0104] Table 2 sets forth values calculated using relation (1)
above for tear/shear force .gamma. (lb./in.) for various aperture
diameters A and flange slope angles .theta. at a differential
pressure .DELTA..sub.P of 100 psi.
2 TABLE 2 .gamma.(lb./in.) A = .theta..degree. 0.500" 0.625" 0.750"
0.875" 1.000" 1.125" 1.250" 2.5 286.6 358.2 429.9 501.5 573.1 644.8
716.4 5 143.4 179.3 215.1 251.0 286.8 322.7 358.6 7.5 95.8 119.7
143.6 167.6 191.5 215.5 239.4 10 72.0 90.0 108.0 126.0 144.0 162.0
180.0 12.5 57.8 72.2 86.6 101.1 115.5 129.9 144.4 15 48.3 60.4 72.4
84.5 96.6 108.7 120.7 17.5 41.6 52.0 62.4 72.7 83.1 93.5 103.9 20
36.5 45.7 54.8 64.0 73.1 82.2 91.4 22.5 32.7 40.8 49.0 57.2 65.3
73.5 81.7 25 29.6 37.0 44.4 51.8 59.2 66.5 73.9
[0105] These are the minimum strength requirements (lb./in.) for
the closure member and heat seal to withstand a pressure
differential .DELTA..sub.P of 100 psi without rupture or failure
(bursting), for each specified combination of aperture diameter A
and slope angle .theta.. As is apparent, for a given differential
pressure, the tear/shear force strength requirement decreases with
increasing flange angle and increases with increasing aperture
diameter.
[0106] By way of illustration, an aperture diameter of 0.875 inch
and a flange angle of about 22.50 would require a closure foil with
a breaking strength in excess of 57.2 lb./in. and an equivalent
minimum heat seal shear strength, for burst resistance of 100
psi.
[0107] Typical aluminum lidding foils of 0.003 inch thickness can
withstand a tear force in excess of 75 lb./in. Practicable heat
seals capable of withstanding a shear force of 75 lb./in. can also
readily be provided, in configurations suitable for the heat seal
46. Therefore, combinations of A and .theta. in Table 2 for which
the calculated value of .gamma. is 75 lb./in. or less enable
satisfactory and practicable attainment of a burst resistance of
100 psi in the can of the present invention.
[0108] As already stated, to avoid a peel component in the force
exerted on the closure member and heat seal by the differential
pressure .DELTA..sub.P, the bulge height h of the closure member
above the plane P of the aperture 24 should not exceed a value
h.sub.max at which the slope of the flange 30 is tangent to the arc
of the bulging closure at the edge of the aperture. This upper
limiting value h.sub.max (in inches) is, again, determined by the
angle of slope .theta. of the flange and the aperture diameter A
(in inches) of the aperture 24; in the case of a circular aperture,
such limiting value can be calculated using the relation 2 h max =
A 2 ( 1 sin - 1 tan ) ( 2 )
[0109] It will be seen that the maximum permitted bulge height, to
achieve the described freedom from any peel component, increases
with aperture diameter and also increases with flange angle.
[0110] The actual bulge height in a closure member 28 produced by a
given differential pressure .DELTA..sub.P is dependent on the
properties of the closure foil related to deformation, i.e., the
deformability of the foil, as well as on the aperture diameter.
FIG. 14 illustrates the relationship of bulge height h (here given
in mm) to pressure .DELTA..sub.P for a 7/8inch aperture diameter
and an exemplary aluminum foil 100 .mu. (0.004 inch) thick. The
Figure has been corrected for the small initial displacement of the
foil relative to the flange (i.e., the foil was not perfectly flat
after the forming and springback). The measurements were made with
a lid clamped into place in the "buckle-tester." The position of
the center of the foil covered aperture was measured carefully
(using a precision laser measurement device) and the pressure was
gradually increased. Measurements were taken at intervals of 10 psi
up to 80 psi and the displacement at each pressure was computed and
plotted in FIG. 14.
[0111] Examples of the maximum permitted bulge height (inches) as
defined above, calculated for a circular aperture using relation
(2), for various combinations of A (in inches) and .theta., are set
forth in Table 3:
3 TABLE 3 h.sub.max (in.) A (in.) .theta..degree. = 17.5 20 22.5 25
27.5 30 0.625 0.048 0.055 0.062 0.069 0.076 0.084 0.750 0.058 0.066
0.075 0.083 0.092 0.100 0.875 0.067 0.077 0.087 0.097 0.107 0.117
1.000 0.077 0.088 0.099 0.111 0.122 0.134
[0112] For an aperture diameter of 0.875 inch with a flange slope
angle of 22.5.degree., the maximum bulge height should be 0.087
inch to avoid peel force components.
[0113] If the bulge height exceeds the critical value, FIG. 14 can
be used to determine the angle of the tangent to the arc of the
bulging closure foil at the edge of the aperture. If the stress
within the foil can be determined, the peel component of the stress
can be estimated. Provided that this component is less than the
measured peel stress for the closure material, failure by peeling
will not occur. However, it is preferred that the lid parameters be
chosen to ensure that the bulge height does not exceed the
above-defined limiting value at least for differential pressures up
to 90 psi, more preferably for differential pressures up to 100
psi.
[0114] Metal foils have comparatively good creep resistance over
the range of temperatures that may be experienced in service, and
therefore afford an important advantage over polymeric closure
member materials with respect to creep susceptibility and
consequent short shelf life. Since creep is dependent on applied
stress, increasing the thickness of the closure material can reduce
or eliminate creep. For aluminum foil closure members, a thickness
between about 0.003 and about 0.004 inch (about 75-100 .mu.) is
sufficient to virtually eliminate creep.
[0115] The performance of the bond between the closure membrane and
the lid flange is dependent on the properties of the adhesive layer
and on the design of the joint. The flange angle is designed to
ensure that the forces between the closure membrane and the flange
are predominantly shear in character under the fully pressurized
conditions of use. However, the shear stress in the joint can be
affected by the width of the heat seal; i.e., increasing the width
of the bond spreads the load and thereby reduces the stress
intensity.
[0116] It is desirable for the width of the heat seal to be less
than about 0.118 inch (3 mm) and preferably about 0.079 inch (2
mm). If the width is increased above about 0.118 inch (3 mm), the
peel force required to open the container will be increased.
[0117] Furthermore, an increased heat seal (and flange) width would
mean that the drinking aperture has to be located further from the
container edge, detracting from the convenience of the consumer by
making the container less comfortable and more inconvenient to
drink from.
[0118] Experimentally, it is found that a 0.079 inch (2 mm) wide
heat seal annulus for the foil closure performs well in the can of
the invention (see Example 4 below). Fully pressurized cans (60-70
psi) have been stored at ambient temperature (.apprxeq.20.degree.
C.) for several months, with no detectable sign of creep in either
the foil or in the adhesive bond joint.
[0119] In containers for beverages and the like with manually
peelable closures, the peel force required to open the container
should preferably fall within the range between about 1.8 lb. and
4.5 lb. (8N and 20N), and still more preferably within the range
between about 2.25 lb. and 3.6 lb. (10N and 16N) as measured by a
90.degree. peel test. The peel force required is dependent on the
peel strength of the bond and on the effective width of the seal
during the peeling procedure. In the case of an angled flange,
there will also be a geometrical factor, which will affect the
final peel force required. The strength and gauge of the foil will
also contribute to peel strength since the peel action requires the
foil to be bent and deformed.
[0120] In the case of heat seal bonding, the peel strength is
influenced by the particular lacquer formulations on the two mating
surfaces, and on the heat sealing conditions which are used. For
example, in one preferred embodiment, the outer can end panel
surface has a thin vinyl lacquer coating (Valspar Unicoat, up to
about 2 .mu. thick) and the aluminum foil closure material has a
vinyl based heat seal lacquer (Alcan Rorschach TH388, between about
5 and 8 .mu.thick).
[0121] For this combination of coatings, the peel strength falls
within an acceptable range for peelability. At the same time,
provided the closure foil has sufficient strength, the heat seal
bond can meet the requirements for shear strength.
[0122] Variations in peel strength can be obtained by changes to
the heat sealing temperature, the heat sealing pressure and/or the
dwell time for sealing.
[0123] In addition to the aforementioned vinyl based lacquer
systems, various other combinations of can end lacquer and heat
seal coatings have been found to be suitable for the present
invention. These are exemplified, without limitation, as
follows:
4 Can lid coating (exposed side) Foil Closure coating Epoxy coating
(solvent based lacquer) Polypropylene (extrusion coated)
Polypropylene based heat sealed lacquer Laminated polypropylene
Polypropylene formula- tion: extrusion coated Polyester coated
(e.g. extrusion Polyester compatible coated) heat seal coating
Polystyrene/polyester blend
[0124] It should be recognized that the combination of specific
coating formulations on the can lid (exposed side) and on the foil
closure material (product side) needs to be carefully selected to
provide the desired combinations of peel strength and shear
strength. Furthermore, the coatings must also provide adequate
protection from any corrosive attack of the metal by the product.
The coatings must also comply with applicable food/beverage contact
regulations.
[0125] The coatings, at the thicknesses applied, must also be
capable of maintaining integrity during the forming operations to
which the components of the lid are subjected. In particular, the
coating on the lid must survive the bead curl forming
operation.
[0126] It is found that coating formulations based on the classes
of coatings listed above are able to meet all of these
requirements. As will be seen from the above list, at least one of
the two coating formulations (and preferably both) have a
thermoplastic polymer as a major component (e.g. vinyl,
polypropylene, polystyrene, polyester) and heat sealing is the
preferred method of attaching the closure.
[0127] It will also be noted that the adhesion between the
lacquers/coatings and the metal surfaces is important and suitable
cleaning and, optionally, pretreatment of the foil surface prior to
coating is recommended.
[0128] As already stated, for the peelable closures of the present
invention, it is desirable that the foil closure be relatively easy
for the consumer to peel back from the pouring/drinking aperture.
However, it is also desirable to design the closure in such a way
that the consumer is discouraged from removing the closure foil
completely, since it may then be discarded as litter. A preferred
design of closure for this purpose is illustrated in FIG. 15, which
shows a can lid 116 having a flat upper surface and an
eccentrically disposed aperture 124 surrounded by an angled flange
to which a foil closure member 128 is bonded by an annular portion
146a of a heat seal. On the side of the aperture adjacent the lid
edge, the closure member has an integrally formed pull tab 128b
(folded back over the aperture, with its unfolded position
indicated at 128b'). The closure member also has an integral
"stay-on" extension 128a positioned in opposed relation to tab 128b
(with respect to the aperture) and overlying the flat upper surface
of the lid. Extension 128a is bonded to the lid by a further heat
seal portion 146c, which is so dimensioned as to require a
substantially greater peeling force (for separating extension 128a
from the lid) than that required by annular heat seal portion 146a
(for separating the closure member from the angled flange around
the aperture).
[0129] In other words, the closure member 128 of FIG. 15 includes a
"stay-on" tab area or extension 128a which is sealed to the lid
panel 116 by portion 146c of the heat seal that has a size and
shape which requires a substantially higher peel force (greater
resistance to peeling) than the annular seal portion 146a
surrounding the aperture 124, thereby discouraging the consumer
from completely removing the closure foil. As a result of this
design, when the consumer peels open the closure, the peel will
initially be within the targeted range for each opening, e.g. from
about 2.25 lb. to 4.5 lb. (about 10-20N). Then as the aperture is
completely opened, the peel force will fall to a very low value so
that the consumer will sense that the opening is completed. If the
consumer continues to pull the closure, the required peel force
will rise rapidly to a value which exceeds the normally accepted
easy peel range, i.e. to >5.5 lb. (about 25N). An example of the
peel characteristics of a closure of this invention is given in
FIG. 16.
[0130] This variation in peel force requirement can be achieved
most readily by careful design of the seal region, in particular by
appropriately selecting the dimensions of the heat seal portions
146a and 146c. In the case of a heat sealed closure, this is easily
achieved by the design of the heat seal tooling. With a pressure
sensitive adhesive, it would be more difficult and would require
the adhesive to be printed onto the closure film in the desired
pattern.
[0131] FIG. 16 is a graph showing a typical variation of peel force
(90.degree. peel test) as the closure is peeled open. As the peel
is initiated, the force rapidly increases as the foil peels away
from the region of the flange on the pull tab side 128b. As the
foil is peeled from the remainder of the flange and opens the
aperture, the peel force remains fairly constant, rising to a
second maximum at the end of the aperture. At this point, the foil
is not sealed to the lid, and the peel force falls quickly to a low
value. At the start of the "stay-on" extension region, the peel
force rises to a high value to discourage the consumer from
completely removing the closure foil.
[0132] Further control of the peel force can be obtained by varying
the heat sealing conditions in the different regions of the
closure. For example, if the temperature of the heat seal in the
stay-on extension region were increased, a high peel strength would
result. It is also possible to use a different heat seal lacquer,
with a higher inherent peel strength, in the "stay-on" extension
region. Yet another method of increasing the peel force requirement
in the "stay-on" tab region is by the use of one or more ridges or
other profiled features (not shown). Such features would serve to
increase the effective area of the seal and to provide a degree of
mechanical keying for the closure.
[0133] As discussed above with reference to FIG. 15, the peel force
varies as the closure is peeled back. The detailed variation of the
peel force required can be adjusted and controlled by the various
methods described. The variation shown in FIG. 16 corresponds to a
desirable behavior for the consumer, in that the uniform peel force
after an initial higher start force provides ease of opening for
the container; the subsequent drop in peel force gives the consumer
an indication (by feel) that the aperture is completely opened;
and, finally, the rapid rise of the force due to the "stay-on"
extension signals the consumer that the closure is intended to stay
on and be folded back for drinking.
[0134] With an aluminum foil closure material, employing a
"stay-on" arrangement as described, the closure can be easily
folded down so that it does not significantly interfere with the
drinking experience of the consumer. Furthermore, since the foil
has good dead-fold characteristics (i.e. it does not exhibit any
noticeable spring back), the closure can be folded back over the
aperture if desired. Although this does not reseal the can, it
would prevent the undesired ingress of dirt or insects into the
beverage between drinks, and may also reduce the spillage if a can
is accidentally tipped.
[0135] Yet another advantageous feature of the invention, in
particular embodiments as illustrated in FIGS. 17-20, is the
incorporation of a source of a fragrance or aroma in the can lid,
so that peeling of the closure member to open the can also acts to
expose a small quantity of an oil or wax based aroma concentrate,
located on the lid in a position which is in close proximity to the
nostrils of a person drinking from the can aperture. The aroma is
selected to enhance or complement the taste of the beverage.
[0136] It is well known that the senses of smell and taste are
closely related, and in particular that the sense of smell can
significantly enhance the taste experience. Preservation or
enhancement of a smell associated with a particular beverage,
thereby improving the aroma of the product, may serve to increase
the overall enjoyment of the product. Fragrances which may be thus
provided may include (by way of nonlimiting illustration) lemon,
orange, lime, mint, etc.
[0137] The aroma-enhancing feature may, for example, advantageously
be incorporated in a can lid 116 having a "stay-on" foil closure
member 128 as described above with reference to FIGS. 15-16. A
small part of the lid area, initially covered by the foil closure
member (FIG. 17A) but exposed upon peeling of the closure member
(FIG. 17B), is modified so as to receive a small quantity 156 of an
oil- or wax-based fragrance. This can be achieved by forming a
small upwardly opening depression or reservoir 158 in the lid 116
(FIG. 18) and/or by forming a similar receptacle indentation
(facing the lid; not shown) in the foil closure member itself.
[0138] The reservoir, and hence the supply of fragrance, are
disposed on the side of the aperture 124 away from the edge of the
lid so as to be close to the nostrils of a person drinking from the
can. This location is between the aperture 124 and the stay-on heat
seal portion 146c and is thus covered by the closure extension 128a
when the closure member is sealed on the lid.
[0139] A wide variety of concentrated fragrances are readily
available and, for the described use, the volume required is about
one drop (less than 0.01 ml). Since the fragrance is sealed between
the lid 116 and the closure member 128, there is little if any loss
of fragrance during storage, owing to the excellent barrier
properties of aluminum.
[0140] When the foil closure member is peeled back (FIG. 17B) to
open the can it exposes the fragrant oil 156, releasing the aroma.
As will be apparent from the drawings, the fragrance reservoir 158
is positioned on the can lid in close proximity to the nose of a
person drinking straight from the can, to maximize the
effectiveness of the aroma.
[0141] For use with a lid having a fragrance reservoir, the heat
seal 146 securing the closure member 128 to the lid 116 is
configured to fully surround the reservoir 158 containing the
supply of fragrance. Two specific heat seal designs for this
purpose are respectively shown in FIGS. 19 and 20. In FIG. 19, the
heat seal area 146a around the aperture 124 is contiguous with the
heat seal area 146b surrounding the fragrance reservoir or well 158
and the heat seal portion 146c that secures the "stay on" extension
128a of the closure member to the lid; the design is such that as
the lid is peeled back from the aperture, there is a high
probability that the fragrance-containing depression 158 in the lid
will be partially or fully exposed and the fragrance will start to
be released. In FIG. 20, the heat seal area 146d surrounding the
fragrance containing reservoir is isolated from the heat seal
portions 146a (around the aperture) and 146c (bonding the stay-on
closure member extension to the lid), but again, the action of
peeling back the closure member results in partial or complete
opening of the reservoir to release the fragrance. In the case of
FIG. 20, by isolating the fragrance reservoir 158 from the main
heat seal areas 146a and 146c, the probability of premature
evaporation of the fragrance owing to heat input from the heat
sealing tools is significantly reduced.
[0142] In brief summary, the present invention provides a novel can
end with a safe and convenient aperture and a heat sealable foil
closure, suitable for use with carbonated beverages or similar
products. Among the benefits and advantages that may be achieved
with the cans of the invention are the following:
[0143] improved sanitary characteristics, because no external
exposed surface is introduced into the beverage, as occurs when
present-day scored lids are opened with a riveted pull-tab
system;
[0144] enhanced aesthetics, in that the peelable foil closure can
be embossed and printed (inside and/or outside);
[0145] increased selection of aperture size and shape since, while
there will be some limitations, a wider range of aperture sizes and
shapes will be possible than is the case with present-day scored
lids;
[0146] greater safety, in particular because the reverse curl of
the aperture-defining bead eliminates sharp edges;
[0147] ease of opening, and concomitant consumer satisfaction,
since marketing studies in the food industry indicate that
consumers prefer easy-peel closures to the scored ends of
present-day carbonated beverage cans as well as to the use of can
openers;
[0148] ease of use, since a can with this end design has better
pouring characteristics and may be easier to drink from
directly.
[0149] Especially preferred embodiments of the invention are
carbonated beverage cans with readily peelable closure members
characterized by a burst resistance of at least about 90 psi (or
higher, e.g. 100 psi or above) and a shelf life of at least six
months or more. The creep resistance and barrier properties of foil
closures, together with the shear strength of heat seals, enable
attainment of the desired extended shelf life.
[0150] Still further features and advantages of the invention
reside in the provision of cans with lids having the above
described angled flange aperture and heat sealed closure member,
wherein the lid diameter (hence, also, the lid area) is smaller
than that of present-day conventional cans with riveted tabs and
scored areas for opening, yet without any reduction in the size of
the opening for pouring and/or drinking.
[0151] In recent years, the diameter of the can end (lid) used for
carbonated and noncarbonated beverages has been significantly
reduced. Most recently the size has been reduced from "204" size
(about 2 1/4inches in diameter) to "202" size (about 2 1/8inches in
diameter). This size reduction alone represents a significant
potential saving to can makers and fillers. However, a number of
additional benefits can also be realized as a result of this size
reduction. For example, it is well known that a reduced diameter
lid is less susceptible to buckling under the internal pressure.
This can be exploited in a number of ways (the choice or
combination depending on economic, aesthetic and other (e.g.,
hygiene, recycling, etc.) considerations. Essentially, a reduced
lid diameter enables the lid profile design, alloy, temper and
gauge to be reconsidered.
[0152] Furthermore, the smaller size means that adequate buckle
strength can be achieved with a thinner gauge. For "204" size ends,
the typical gauge was about 0.009 inch and for "202" ends, the
gauge requirement is about 0.0086 inch.
[0153] As mentioned above, AA 5182, the currently preferred lid
alloy, is a premium alloy (due to the Mg content) and is costly and
difficult to roll. Moreover, for can end (lid) applications, the
sheet must be coated on both sides. For these reasons, there is a
significant economic incentive for can makers to reduce the lid
size and gauge as much as possible.
[0154] The trend for cans to have larger opening ends (LOE) means
that, with conventional riveted tab lids, the opportunity for
further reduction in end diameter is very limited, since the tab
and the centrally positioned rivet require the lid to be of a
certain minimum diameter.
[0155] By use of the angled flange aperture and heat sealed foil
closure system of the present invention, the lid diameter can be
significantly reduced (e.g. to below 2 inches in diameter), while
still retaining a large pouring opening. The reduction in lid
diameter also enables the gauge of the lid to be further reduced
(or, alternatively, enables use of a lower strength and lower cost
alloy), since buckle resistance is easier to achieve with a smaller
diameter lid.
[0156] With this approach, it should be possible to reduce the can
end diameter by at least 5% to the "200" size (about a 10% area
reduction, compared to the current "202" size), with an additional
reduction of about 5% in gauge (to a gauge of less than 0.0082
inch), while still meeting the target buckle resistance of the can
lid. Thereby significant savings in metal may be achieved, although
an extra necking stage must be incorporated into the can body
making operation to conform the upper end of the can body
dimensionally to the reduced-diameter lid, adding an expense that
would partially offset the cost savings.
[0157] The reduction in can lid diameter attainable with the
invention also affords opportunities to reduce or eliminate the
"countersink" feature of the can lid, which is advantageous, since
the countersink (formed around the periphery of the lid) is prone
to contamination by dust or debris. FIG. 21 illustrates a lid 160
embodying the invention and free of countersinking, i.e., having no
peripheral countersink (such as is shown, for example, at 162 in
each of FIGS. 12 and 18); the substantially planar upper surface
164 of the lid extends all the way to the raised annular rim 166.
It will also be recognized that the reduction or elimination of the
countersink feature also reduces the metal usage (by up to about
5%), providing further potential cost savings.
[0158] It should be noted that, where it is desired to be able to
stack cans on each other, a smaller diameter lid may require some
redesign of the can body. In previous can designs, the bottom
profile has been designed to stack against the lid. However, as lid
diameters have decreased, it is becoming more difficult to achieve
this. With the current "202" size lid, the can bottom design has
been modified to achieve this stackability. However, the narrowing
of the base is approaching the point where the stability of the can
(to tipping) is becoming a concern. If the lid is further reduced
in size it may therefore be necessary to redesign the can base
further to enable stable stacking.
[0159] FIGS. 22-24 illustrate a specific embodiment of the
invention in a beverage can including a one-piece can body 170 with
a narrow neck 172 and a reduced-diameter can end or lid 174 (which
has an angled flange aperture 176 and foil bonded heat sealed
closure 178) with no countersink or recess.
[0160] The domed bottom 180 and sidewall 182 of the body 170 are
formed with the draw and iron procedure currently in widespread
use. The can body sidewall is then necked as shown at 172 to a
small diameter of approximately 1 to 1.5 inches, and flanged to
enable attachment of the lid 174. After the can is filled, the
small diameter lid with the peelable foil bonded closure 178 as
described above is seamed to the open upper end of the necked
can.
[0161] The main purpose of the countersink in current can lid
designs is to minimize deflection and also to reduce the
probability of buckling or reversal of the can end under internal
pressure. In the embodiment of FIGS. 22-24, the lid has a small
diameter, and therefore will not deflect as much as a larger
diameter end would. For that reason, there is no need for a recess
or countersink. Since there is no countersink or recess, can end
failure will not involve buckling. The maximum internal pressure
for the end will be determined by the strength and gauge of the can
end and the foil closure material, the bonding strength between the
foil and end, and the seam integrity. Hence the can end material
can be made from much lower gauge metal than that (e.g. AA 5182)
which is currently used. The alloy used could also be the same as
that used for the can body, for instance, AA 3104 alloy.
[0162] The narrow neck 172 gives the can a bottle shape, which may
be preferred by many consumers for aesthetic reasons, especially if
this shape is enhanced with graphics and/or embedded design
elements (not shown).
[0163] Illustrative dimensions of the can of FIG. 22 include a
maximum can body diameter (bottom portion) of 2.60 inches, a neck
tapering upwardly to receive a lid having an outer diameter of 1.56
inches, and an aperture with a diameter of 0.75 inch, the overall
height of the can being 6.50 inches.
[0164] Another exemplary embodiment of the invention in a necked
can with a reduced diameter lid 188 having an angled flange
aperture and heat sealed closure is shown in FIG. 25. The can
comprises a body 190 with an integral neck 192. The base of the
container consists of a panel 194 similar to a conventional can lid
(but lacking any rivet, tab, scored area or other opening system)
and is seamed onto the open lower end of the can body in the same
way as conventionally utilized to join a lid to the upper end of a
drawn and ironed can body.
[0165] The forming of the body 190 may be understood by reference
to the can body maker tooling shown in FIG. 26 and the alternative
modifications thereof respectively illustrated in FIGS. 27 and 29.
FIG. 26 shows, in simplified schematic cross-section, a standard
can body maker (known in the prior art) comprising a hollow mandrel
200 with a shaped end cap 202, a series of ironing rings 204a,
204b, 204c, and a "domer" 206. The domer and the shaped end of the
mandrel are designed to generate the familiar outwardly concave can
bottom dome profile. This can body making operation results in a
significant thinning of the metal sidewalls due to the ironing
process, but the thickness of the metal in the bottom of the can is
not significantly reduced.
[0166] FIG. 27 shows one modification for producing the body of the
can of FIG. 25. The features of particular significance are the
domer tool 208 which is designed to generate the neck 192 of the
new can body 190, and the end cap 210 of the mandrel 212 which is
shaped so as to match the shape of the domer tool (allowing a
suitable clearance).
[0167] The detailed shape of this tooling is optimized so as to
control metal flow during the forming operation, and to minimize
the likelihood of metal failure (tearoffs and the like). In
particular, small radii of curvature are avoided and the extent of
the deformation is kept to a minimum consistent with the
requirements for a neck. The neck 192 itself is slightly tapered so
that the finished body 190 can be easily removed from the mandrel
212. The can body 190, complete with neck 192, is shown in FIG.
28.
[0168] With this formed shape as a starting point, a number of
additional steps are employed to produce the final can of FIG. 25.
The additional steps include trimming or punching an opening in the
upper end of the neck 192 to constitute an open upper end of the
can body, on which the lid 188 is to be secured; trimming the other
end 214 of the can to remove earing scrap; and attaching a plain
metal can end shell 194 to the latter end by a seaming operation.
The can body is then filled, for example with a carbonated
beverage, and the lid 188 with its angled flange aperture and heat
sealed closure member is secured to the open upper end of the neck
192.
[0169] In addition to this preferred method, two alternative
processes for producing the modified can body will be described. In
the first alternative, the can body 190 with formed neck 192 is
produced using a double action forming process shown schematically
in FIG. 29. The features of particular significance are that the
domer tool of FIG. 27 is replaced by a tool 220 which is designed
to generate the neck of the new container (as before), and the end
cap of the mandrel is replaced by an annular piece 222. In the
center of this a second movable tool 224 is introduced so the
complete configuration operates as a double action press tool, with
the outer annular portion generating the outer profile of the neck
region, and the inner tool applying an additional second forming
step to form the neck of the can body. The press itself needs to be
modified to give the appropriate "double action" operation (double
action presses and forming operations are well known in, for
example, the cup forming process). The additional steps for
trimming, forming of the opening and application of the can bottom
end and lid would be similar to those described in the preferred
method.
[0170] The second alternative method (not illustrated in the
drawings) involves the production of a modified can body with a
convex domed end, by a standard drawing and ironing process and a
subsequent hydroforming operation similar to that described by
Belvac Production Machinery Inc., Lynchburg, Va., for shaping of
can walls. This hydroforming process involves the use of a high
pressure jet of fluid such as water and a shaped mold, to complete
the forming of the neck region of the can. By using a split mold,
the sidewall could optionally be shaped for decorative
purposes.
[0171] It should be recognized that embodiments such as that of
FIG. 25 may offer the following advantages:
[0172] The can body and neck are formed in a single high speed
process and can utilize existing can body makers (with different
tooling).
[0173] The neck is formed from metal which has not been thinned by
the ironing process.
[0174] Although some re-tooling would be required, it should be
relatively straightforward to modify filling lines to handle cans
of this design, since they would be similar in shape to glass or
PET bottles.
[0175] It will be recognized that this design and process will
require changes to the tooling and container handling and
inspection systems. However added costs due to these factors will,
partly or completely, be offset by the savings listed above.
[0176] By way of further illustration of the invention, reference
may be made to the following specific examples, in which Example 1
is a hypothetical example and Examples 2 and 3 describe burst
resistance tests performed on actual samples of can lids with
heat-sealed closures embodying features of the invention, while
Example 4 describes actual tests related to shelf life. In these
Examples, identifications of aluminum alloys by four-digit numbers
with the prefix "AA" refer to designations of aluminum alloy
compositions registered with the Aluminum Association, as will be
understood by persons skilled in the art.
EXAMPLE 1
[0177] An illustrative can end (lid) embodying the present
invention with a heat sealed foil/polymer laminate closure might be
constructed with the following specification:
5 Aperture diameter (A): 1" Flange angle 0-25.degree. Laminate
.004" foil (AA 3104) + .001" polymer (e.g., polyethylene,
polypropylene, polyester) Heat seal width 0.1" Can lid sheet 0.009"
(AA 5182 alloy) with a heat sealable coating
[0178] It will be understood that a range of values for each
parameter should be possible. The target burst resistance for such
a lid would be>90 psi and the target peel force (at 90.degree.
to the plane of the aperture) would be<4 lbs.
EXAMPLE 2
[0179] Tests were performed to determine peel strength and burst
resistance for can ends (lids) of "202" can end size (a standard
can size designation) in accordance with the invention, having an
annular frustoconical flange with an 18.degree. angle of slope
defining an aperture 3/4" in diameter, covered by a foil closure
heat sealed to the flange around the aperture. The lids were formed
from can end sheet of AA5182 aluminum alloy at a gauge of 0.0086",
and their outer surfaces were coated with "Valspar" unicoat at a
coating weight of 1.5 mg/in.sup.2 (approximately 1.5 .mu. thick).
The closures were made from heat sealable stock of 50 .mu. foil of
AA3105 aluminum alloy, coated on its inner surface (the surface in
contact with the aperture-defining frustoconical flange) with
Rorschach TH388 vinyl heat seal lacquer at a coating weight of 6
g/m.sup.2 (about 6 .mu. thick). Heat sealing was performed at
various selected tool temperatures (on the side of the foil
closure) of from 230.degree. to 280.degree. C., with a pressure of
975 N and a time of 0.3 sec.
[0180] Initially, to determine peel strength, T-peel test pieces
were prepared from the can end sheet and heat sealable foil stock
described above by heat sealing 15 mm wide strips of the foil stock
to 15 mm wide can end sheet samples for different heat seal
temperatures (as listed in FIG. 10). Results, summarized in FIG.
10, show that the peel strength can be adjusted for this
combination of materials by modifying the heat seal temperature. As
mentioned above, a peel force of between about 10 N and about 15 N
is generally regarded as acceptable for an easy opening container.
Since the anticipated width of the heat seal for closures embodying
the present invention may be typically or conveniently
approximately 15 mm, the peel forces will fall within this
acceptable range.
[0181] To test burst resistance, a number of formed and heat sealed
can ends as described were subjected to a standard burst test in
which the rim of the can end is clamped to a rubber gasket seal and
a gradually increasing air pressure is applied to the inner lid
surface. The deformation of the lid and seal can be observed during
the test and the maximum pressure at failure is recorded. After
testing the lids are examined to determine the mode of failure.
[0182] The results of these burst tests are shown in FIG. 11. For
these tests, burst pressures of approximately 60 psi were recorded.
During the tests it was noted that the foil closure 28 stretched
and "domed" to a point where the tension in the foil had developed
a significant peel component, i.e., the tangent (in a vertical
plane) to the bulged foil closure 28 at the edge of the aperture 24
exceeded the 18.degree. slope angle of the flange 30, as
illustrated diagrammatically in FIG. 9. Failure of the seal
occurred by a peel initiated at the inner edge of the aperture.
[0183] A 60 psi burst resistance is sufficient for low levels of
carbonation or for normally carbonated beverages under standard
conditions of use. However, since carbonated products must be
capable of tolerating varying degrees of extreme conditions
(elevated temperature, agitation, etc.), the normal targeted burst
resistance is generally 90 psi or higher. In the case of the
materials employed in this Example, higher burst resistance should
be achieved with this gauge of foil if a higher flange angle (e.g.
25.degree.) were to be used.
EXAMPLE 3
[0184] A further series of can ends in accordance with the
invention were prepared and tested. The lid members were the same
(dimensions, gauge, alloy, coating, flange slope angle and aperture
diameter) as in EXAMPLE 2, but the closures were made of heat
sealable foil stock of 70 .mu. foil of AA9802 aluminum alloy with
an inner surface coated with a vinyl heat seal lacquer of unknown
formulation. Heat sealing was performed with a tool temperature (on
the foil closure side) of 280.degree. C., under the same pressure
and time conditions as in EXAMPLE 2.
[0185] These materials (can end sheet and foil closure) were
subjected to peel strength testing. Peel strengths of greater than
20 N/15 mm were recorded for these samples. This is too high for
convenient peeling and indicates that the vinyl lacquer was not a
suitable formulation.
[0186] Samples of the lids and closures were formed, subjected to
heat sealing, and tested for burst resistance. Burst resistance was
found to be>90 psi. During the burst tests, the foil closures
bulged to form a shallow dome, but the distortion was not
sufficient to create a significant peel component to the resultant
tension force.
[0187] Failure of the lids eventually occurred by distortion of the
can end shell metal. The foil and the heat seal survived the test
satisfactorily.
[0188] With the thicker foil of this Example, the doming which
occurs at pressures below 90 psi (for the 3/4" aperture) was below
the level at which a peel component of force would arise.
EXAMPLE 4
[0189] A further series of can ends in accordance with the
invention were prepared and tested. The lid members differed from
those of EXAMPLES 2 and 3 in having a flange slope angle of about
23.degree. and an aperture diameter of 7/8. The can end lacquer was
Valspar Unicoat (vinyl based) lacquer as before, at a thickness of
between 1.5 and 2 .mu.. The closures were made of heat sealable
foil stock of 80 .mu. gauge foil of AA3104 aluminum alloy with an
inner surface coated with a polystyrene/polyester blend heat seal
lacquer designated TH312 (Alcan Rorschach) applied at 8 g/m.sup.2.
Heat sealing was performed with a top tool temperature of
200.degree. C., a bottom tool temperature of 200.degree. C., a
dwell time of 0.3 second, and a heat seal width of 0.079 inch (2
mm). Heat sealing was carried out before the angled flange was
formed.
[0190] Burst tests were performed on the lids. In tests performed
before the angled flange was formed, failure of the heat seal
occurred at between 40 and 55 psi. In tests performed after forming
the flange, using a standard can end bulge test, failure by
buckling of the can end occurred at between 85 and 90 psi. In tests
also performed after forming the flange but using a modified
clamping tool to prevent end buckling, failure of the heat seal
occurred between about 110 psi and 120 psi (the lowest value
recorded was 106 psi).
[0191] Peel strength was tested using a 90.degree. peel test. The
peel force varied during the test but was within the range between
about 2 1/2 lbs (.apprxeq.11.3 Newtons) and 4 lbs (.apprxeq.18
Newtons).
[0192] To test shelf life, can ends of this Example were used for
cans filled with carbonated soft drinks at an estimated filling
pressure of .apprxeq.60 psi and stored at ambient temperature.
Samples prepared and tested in this way have maintained full
pressurization for over six months.
EXAMPLE 5
[0193] The shelf life of cans in accordance with the invention was
tested by preparing a can having a lid in accordance with the
invention, including an angled flange having an 18.degree. angle of
slope and defining a circular aperture 0.750 inch in diameter. The
closure was aluminum foil 0.004 inch (100 .mu.) thick, with a
vinyl/acrylic lacquer ("TH 388") used for the heat seal, which had
a width of 0.079 inch (2 mm). The internal pressure of the can was
50 psi. The can was examined weekly for over eight weeks.
Throughout this period, there were no detectable changes in bulge
height of the foil closure and there was no detectable change in
the heat seal joint (i.e., no sliding).
[0194] In a further test, another can was prepared, having a lid in
accordance with the invention, including an angled flange having an
18.degree. angle of slope and defining a circular aperture 0.875
inch in diameter. The closure was aluminum foil 0.004 inch (100
.mu.) thick, with a vinyl/acrylic lacquer ("TH 388") used for the
heat seal, which had a width of 0.079 inch (2 mm). The internal
pressure of the can was 60 psi. The can was examined weekly for
over six weeks. Throughout this period, there was no change in
bulge height of the foil closure and no detectable change in the
heat seal joint (i.e., no sliding).
[0195] It is to be understood that the invention is not limited to
the features and embodiments hereinabove specifically set forth,
but may be carried out in other ways without departure from its
spirit.
* * * * *