U.S. patent application number 10/843089 was filed with the patent office on 2005-11-17 for container having a metal end to which a membrane is sealed.
This patent application is currently assigned to Sonoco Development, Inc.. Invention is credited to McKnight, David, Morin, Jeremy E., Norris, Bernard Q. JR..
Application Number | 20050252918 10/843089 |
Document ID | / |
Family ID | 34941186 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050252918 |
Kind Code |
A1 |
McKnight, David ; et
al. |
November 17, 2005 |
Container having a metal end to which a membrane is sealed
Abstract
A container having an ethylene vinyl acetate-based or ethylene
methyl-acrylate-based sealant as the sealant layer for a flexible
membrane lid that is heat-sealed to a ring-shaped metal end on the
container. In some embodiments, the sealant comprises ethylene
vinyl acetate blended with a polyolefin. The polyolefin can
comprise a polyethylene such as low-density polyethylene. The metal
end can have a spot-coated surface or an uncoated (i.e., bare
metal) surface. A coating of a polypropylene-based composition is
provided on the metal end. The sealant layer of the lid is
heat-sealed to the polypropylene-based coating on the metal end to
form a peelable seal. The resulting seal allows the lid to be
peeled off the metal end by detachment of the sealant layer from
the polypropylene-based coating.
Inventors: |
McKnight, David; (Florence,
SC) ; Morin, Jeremy E.; (Florence, SC) ;
Norris, Bernard Q. JR.; (Byhalia, MS) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
Sonoco Development, Inc.
|
Family ID: |
34941186 |
Appl. No.: |
10/843089 |
Filed: |
May 11, 2004 |
Current U.S.
Class: |
220/359.3 ;
220/359.2 |
Current CPC
Class: |
B65D 15/18 20130101;
B65D 17/502 20130101; B65D 15/06 20130101 |
Class at
Publication: |
220/359.3 ;
220/359.2 |
International
Class: |
B65D 041/00 |
Claims
What is claimed is:
1. A container, comprising: a receptacle comprising a wall, the
wall having an upper edge extending about an opening of the
receptacle; a metal end affixed to the upper edge of the wall, the
metal end defining a central opening providing access to an
interior of the receptacle, the metal end defining an upper surface
facing away from the interior of the receptacle, the upper surface
being coated with a polypropylene-based composition; and a flexible
membrane lid comprising a substrate and a sealant layer, the
sealant layer defining a lower surface of the lid, the sealant
layer and the polypropylene-based composition on the upper surface
of the metal end being heat-sealed together so as to seal the lid
to the metal end, the sealant layer comprising a blend of ethylene
vinyl acetate and a polyolefin.
2. The container of claim 1, wherein the metal end comprises
tin-plated steel.
3. The container of claim 1, wherein the metal end comprises
spot-coated tin-plated steel.
4. The container of claim 1, wherein the polypropylene-based
composition comprises epoxy in which polypropylene is
dispersed.
5. The container of claim 1, wherein the polyolefin in the sealant
layer comprises polyethylene.
6. The container of claim 5, wherein the polyethylene comprises
low-density polyethylene.
7. A container, comprising: a receptacle comprising a wall, the
wall having an upper edge extending about an opening of the
receptacle; a metal end affixed to the upper edge of the wall, the
metal end defining a central opening providing access to an
interior of the receptacle, the metal end defining an upper surface
facing away from the interior of the receptacle, the upper surface
being coated with an epoxy-based composition; and a flexible
membrane lid comprising a substrate and a sealant layer, the
sealant layer defining a lower surface of the lid, the sealant
layer sealingly affixing the lid to the polypropylene-based
composition on the upper surface of the metal end so as to close
the central opening of the metal end, the sealant layer comprising
an ethylene vinyl acetate-based resin.
8. The container of claim 7, wherein the epoxy-based composition
consists essentially of epoxy.
9. The container of claim 7, wherein the epoxy-based composition
comprises epoxy in which polypropylene is dispersed.
10. The container of claim 7, wherein the sealant layer comprises
ethylene vinyl acetate blended with a polyolefin.
11. The container of claim 10, wherein the polyolefin comprises
polyethylene.
12. The container of claim 7, wherein the metal end comprises
electro-tin-plated steel to which the coating of epoxy-based
composition is applied.
13. The container of claim 7, wherein the metal end comprises
spot-coated electro-tin-plated steel to which the coating of
epoxy-based composition is applied.
14. A container, comprising: a receptacle comprising a wall, the
wall having an upper edge extending about an opening of the
receptacle; a metal end affixed to the upper edge of the wall, the
metal end defining a central opening providing access to an
interior of the receptacle, the metal end defining an upper surface
facing away from the interior of the receptacle, the upper surface
being coated with an epoxy-based composition; and a flexible
membrane lid comprising a substrate and a sealant layer, the
sealant layer defining a lower surface of the lid, the sealant
layer sealingly affixing the lid to the polypropylene-based
composition on the upper surface of the metal end so as to close
the central opening of the metal end, the sealant layer comprising
an ethylene methyl-acrylate-based resin.
15. The container of claim 14, wherein the epoxy-based composition
consists essentially of epoxy.
16. The container of claim 14, wherein the epoxy-based composition
comprises epoxy in which polypropylene is dispersed.
17. The container of claim 14, wherein the sealant layer comprises
ethylene vinyl acetate blended with a polyolefin.
18. The container of claim 17, wherein the polyolefin comprises
polyethylene.
19. The container of claim 14, wherein the metal end comprises
electro-tin-plated steel to which the coating of epoxy-based
composition is applied.
20. The container of claim 14, wherein the metal end comprises
spot-coated electro-tin-plated steel to which the coating of
epoxy-based composition is applied.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to containers for foods or other
consumer products, wherein a metal ring is affixed about the
opening of the container and the container is sealed by a flexible
membrane lid removably attached to the ring.
[0002] In such containers, the metal ring, also referred to as a
metal end, is attached to the top of the container, typically by
double-seaming the metal end to a flange at the top of the
container, and the flexible membrane lid is sealed to the metal end
so as to cover an opening defined therein. The lid generally
includes one or more layers providing strength and/or barrier
properties, and a sealant layer defining the lower surface of the
lid. The sealant layer's function is to seal to the metal end,
typically by heat sealing.
[0003] It is desirable for the lid to be sealed to the metal end
with sufficient strength to prevent inadvertent detachment of the
lid during shipping and handling prior to the consumer opening the
container. On the other hand, it is also desirable for the consumer
to be able to peel the lid off the metal end with relatively little
force, so that people of diverse ages and abilities can open the
container, and so that the lid comes off cleanly in one piece
rather than tearing. These objectives of high seal strength and low
peel force tend to be at odds with each other, but various
container closures that strike a balance between these dual
objectives have been developed. Some such closures have employed an
ionomer resin such as SURLYN.RTM. as the sealant layer of the
membrane lid. This sealant material is readily heat-sealable to the
spot-coated and non-spot-coated electro-tin-plated (ETP) steel ends
that are commonly employed. However, this material is one of the
most expensive sealants on the market, and also suffers from the
"age-up" phenomenon whereby the strength of the seal to the metal
end tends to increase with age, which is undesirable. SURLYN.RTM.
also has a relatively narrow heat-sealing temperature window; if
the temperature is too high, the seal strength is too great for
easy peelability of the lid, and if the temperature is too low, the
seal strength can be too low to keep the lid from inadvertently
detaching from the metal end. It can be difficult to control the
processing conditions so as to stay within the desired temperature
window. Further complicating this situation is the fact that
SURLYN.RTM. seals more readily to non-spot-coated ETP steel than to
spot-coated ETP steel. Thus, a lower sealing temperature must be
used for non-spot-coated metal ends than is used for spot-coated
metal ends. In a container processing plant that employs both types
of metal ends, it is thus necessary to have two different
processes.
[0004] Additionally, even for a given type of metal end, there can
be substantial variability in the surface characteristic of the
metal, which can affect the strength of the seal. Such variability
is not readily predicted or accounted for, and hence the strength
of the seals with the membrane lids tends to have substantial
variability.
[0005] Accordingly, an alternative sealant and closure system has
been sought. It is desired to provide a sealant and closure system
affording a wider temperature window for the heat-sealing
operation. It is also desirable for the closure system to be able
to use the same heat-sealing process conditions for both
spot-coated and non-spot-coated metal ends, and to produce
more-consistent seal strengths even under variable surface
characteristics of the metal ends.
BRIEF SUMMARY OF THE INVENTION
[0006] The present invention addresses the above needs and achieves
other advantages, by providing container closure systems having an
ethylene vinyl acetate-based or ethylene methyl-acrylate-based
sealant as the sealant layer for a flexible membrane lid. In some
embodiments, the sealant comprises ethylene vinyl acetate blended
with a polyolefin. The polyolefin can comprise a polyethylene such
as low-density polyethylene. The metal end can have a spot-coated
surface or an uncoated (i.e., bare metal) surface. A coating of a
polypropylene-based composition is provided on the metal end. The
polypropylene-based composition can comprise, as one example, epoxy
having polypropylene dispersed therein. The sealant layer of the
lid is heat-sealed to the polypropylene-based coating on the metal
end to form a peelable seal. The resulting seal allows the lid to
be peeled off the metal end by detachment of the sealant layer from
the polypropylene-based coating. This closure system is
less-sensitive to the heat-sealing temperature than the prior
SURLYN.RTM.-based closure and the seal strength is substantially
unaffected by the metal surface characteristics, since the seal's
failure mechanism is adhesive delamination between the lid and the
coating on the metal end.
[0007] In an alternative embodiment of the invention, the coating
on the metal end comprises an epoxy without any polypropylene
dispersed therein.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0008] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale, and wherein:
[0009] FIG. 1 is a perspective view of a container in accordance
with an embodiment of the invention;
[0010] FIG. 2 is a cross-sectional view along line 2-2 in FIG. 1,
showing the closure system; and
[0011] FIG. 3 is a magnified, exploded cross-sectional view of the
membrane and metal end in accordance with one embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present inventions now will be described more fully
hereinafter with reference to the accompanying drawings, in which
some, but not all embodiments of the invention are shown. Indeed,
these inventions may be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein;
rather, these embodiments are provided so that this disclosure will
satisfy applicable legal requirements. Like numbers refer to like
elements throughout.
[0013] A container 10 in accordance with an embodiment of the
invention is depicted in FIGS. 1-3. The container 10 includes a
receptacle 12 having a side wall 14 that encircles the interior of
the receptacle. The wall 14 can have various configurations and
cross-sectional shapes. A circular cross-section is shown, but
alternatively the receptacle can have other shapes such as oval,
square or rectangular, oblong, etc. The receptacle can be made of
various materials and by various processes. For instance, the
receptacle can be formed of plastic by thermoforming, blow-molding,
or injection-molding, or can be formed of composite materials
(e.g., paperboard with a liner of impervious material such as
polymer film and/or foil) by spiral-winding or convolute-wrapping
processes. The particular details of the receptacle are not
important to the present invention.
[0014] The container 10 also includes a closure system comprising a
metal end 16 and a flexible membrane lid 18. The metal end 16 is
ring-shaped so as to define a central opening 20 therethrough. The
opening 20 is encircled by a radially inner edge 22 of the metal
end; the inner edge 22 advantageously is curled or rolled as shown.
The metal end is affixed to the upper edge of the receptacle wall
14. The affixing of the metal end can be accomplished, for example,
by seaming together a curled radially outer edge of the metal end
and the upper edge of the receptacle wall as shown. A sealing
composition (not shown) can be disposed between the metal end and
receptacle wall in the seam region to make the seam hermetic. The
membrane lid 18 is sealed to the upper surface of the metal end 16
to seal the container closed at its top end. The lid advantageously
includes a pull tab 24 that is not sealed to the metal end so that
it can be readily grasped and pulled to remove the lid from the
metal end.
[0015] The membrane lid 18 comprises a substrate 26 and a sealant
layer 28. The sealant layer 28 forms the lower surface of the lid.
The substrate 26 can comprise various numbers of layers of various
materials such as metal foil, polymer film, metallized polymer film
(i.e., film having a very thin coating of substantially pure metal
deposited thereon), paper, etc. When the container contents must be
sealed against moisture and/or oxygen infiltration from the outside
environment, at least one layer of the substrate comprises a
barrier layer. Various materials can be used as barriers, including
metal foil, metallized polyester, non-metallized polymer film
(e.g., EVOH), and others. A combination of two or more such barrier
layers can be used. The particular structure of the substrate 26 is
not important to the present invention.
[0016] The sealant layer 28 comprises a heat-sealable material. The
heat-sealable material can comprise an ethylene vinyl acetate-based
(EVA-based) resin or an ethylene methyl-acrylate-based (EMA-based)
resin. Examples of suitable EVA-based and EMA-based resins include
various resins available from DuPont under the trademark
APPEEL.RTM..
[0017] In one embodiment, the sealant layer 28 comprises a blend of
an EVA-based or EMA-based resin with a polyolefin. The polyolefin
can comprise a polyethylene such as low-density polyethylene
(LDPE). As an example, the sealant layer can comprise a blend of
EVA and LDPE, or a blend of EVA, ethylene acrylic acid (EAA), and
LDPE. A suitable composition, for instance, can comprise about 80%
by weight of EVA having vinyl acetate content of about 28%, and
about 20% by weight LDPE.
[0018] In accordance with the invention, the metal end 16 is coated
on its upper surface with a coating 30 of a material that forms a
peelable heat seal with the sealant layer 28 of the lid. In one
embodiment of the invention, the coating 30 can comprise an epoxy.
An example of a suitable epoxy is available from Valspar as product
number 88X003C.
[0019] In another embodiment, the coating 30 can comprise an epoxy
in which polypropylene is dispersed. When this composition is
coated onto the metal end and cured, the surface of the resulting
coating 30 is characterized by a multitude of microscopic spaced
"islands" of polypropylene that are dispersed within the matrix of
the epoxy. These polypropylene islands comprise bonding sites to
which the membrane lid 18 can be sealed. The peel strength of the
bond between the lid and the metal end can be controlled by varying
the fraction of the total surface area of the coating 30 that is
made up of the polypropylene bonding sites or islands. This
fraction is a function primarily of the relative proportions of the
epoxy and polypropylene making up the coating 30.
[0020] The closure system of the invention can be employed with
various types of metal ends, including bare (i.e., uncoated) metal
as well as coated metal. As examples, the invention is applicable
to spot-coated electro-tin-plated (ETP) steel as well as uncoated
ETP steel. The invention is advantageous in that the blow-off
strength and peel-force characteristics of the seal between the lid
and the metal end are not affected to a substantial extent by the
surface characteristics of the metal end (i.e., whether it is
uncoated or coated, etc.), because the failure mechanism of the
seal is adhesive failure between the lid sealant layer and the
epoxy-based coating on the metal end. Furthermore, the EVA-based or
EMA-based sealant 28 has a relatively wide heat-sealing temperature
window. Consequently, the strengths of the seals to the membrane
lids tend to be more consistent than in prior closure systems.
[0021] Many modifications and other embodiments of the inventions
set forth herein will come to mind to one skilled in the art to
which these inventions pertain having the benefit of the teachings
presented in the foregoing descriptions and the associated
drawings. Therefore, it is to be understood that the inventions are
not to be limited to the specific embodiments disclosed and that
modifications and other embodiments are intended to be included
within the scope of the appended claims. Although specific terms
are employed herein, they are used in a generic and descriptive
sense only and not for purposes of limitation.
* * * * *