Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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T 4437
EASY OPENING PLASTIC PACKAGE
This invention relates to plastic packages,
especially those for food and other perishable items.
More specifically, the invention relates to plastic
packages sealed with a lid which may be easily removed
from the container portion of the package-.
Cup-like plastic containers for food and other
products have been in use for many years. Very often,
lids for such packages are formed from a metal foil
which is attached to the container with an adhesive. --It has been desirable to make such lids easily re-
movable from the container and this has commonly been
done by using an adhesive which allows the user to
easily remove the lid from the container and thus open
the package.
In recent years, there has been an increase in the
use of plagtic materials for lids for plastic -
containers. This has caused a number of problems
including the difficulty in manufacturing such a
package such that the lid may be easily removed from
the container. U.S. Patent 4,693,390 issued September
15, 1987 illustrates one attempted solution to this
problem. Therein the lid is scored (cut part of the
way through) at two points on the surface which is
bonded to an internal flange of the container. The
purpose of the scoring is to allow a major portion of
the lid to be relatively easily pulled away from the
container leaving a small portion of the lid attached
thereto.
It is an object of the present invention to
provide an easily openable plastic package wherein
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neither the lid nor the package are scored so that
there is a continuous layer of protective material both
on the inside and outside of both the lid and the
container to provide maximum protection for the
S contents of the package. This is especially
significant when oxygen barrier materials are in-
corporated into the plastic lid or container since it
is undesirable to have 6uch materials or the adhesives
by which they are bound to the protective layers come
into contact with food or other sensitive materials.
Furthermore, some of the oxygen barrier materials may
absorb moisture either from the outside or from the
inside of the package and this would decrease their
; effectiveness as a barrier to oxygen.
Another ob;ect of the present invention relates to
- the fact that there is no criticality in the location
of the seal between the lid and the container flange.
In a package which utilizes scoring, the adhesive seal
must be spaced from the scoring or else the container
will tend to break at the score. In the package of the
present invention, the burst strength of the package
does not depend on locating the adhesive in a
particular place with respect to the crimp, i.e. the
adhesive is used all the way throughout the container
flange including the area of the crimp.
The present invention relates to an easily opened
plastic package which comprises a flanged container
formed from a laminate comprising at least two plastic
layers bonded together by a relatively weak adhesive
layer which allows the plastic layers to be easily
pulled apart, wherein the container flange is formed
with a crimp which is thin enough to weaken the flange
sufficiently so that it breaks away easily when the
plastic layers are pulled apart, and a lid which is
strongly attached to the container flange. In the
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- preferred case of oxygen barrier packages, the
container will be formed of a laminate which comprises
~ an inner oxygen barrier layer and two outer protective
; layers bonded to the barrier layer by two adhesive
layers. One of the adhesive layers is strong and the
other i8 relatively weak to allow the outer layer with
which it is in contact to be easily peeled from the
barrier layer.
The base or protective layers are preferably
polypropylene but may also be selected from any thermo-
plastic which is capable of serving as a protective
outer layer. The oxygen barrier layer is preferably an
ethylene vinyl alcohol copolymer but may also be
polyvinylidene chloride or other barrier polymers.
Figure 1 is a cut away cross section of an oxygen
barrier package showing the flange of the container and
the various layers of the laminate from which it is
formed including the crimp and the lid attached
thereto.
Figure 2 illustrates another embodiment of the
invention wherein the container is formed of two base -
layers bonded together by a weak adhesive and also
illustrates how the peeling process is begun by pulling
upwardly on the extended end of the lid.
Figure 3 illustrates the embodiment wherein the
crimp is formed on the underside of the flange.
Figure 1 shows a portion of an oxygen barrier
container 10 and illustrates the details of the
container flange 12. The container 10 and flange 12
are formed of outer layers 14 of a base protective
material, an inner layer 16 of an oxygen barrier -
material, a layer 18 of the strong adhesive and a layer
20 of a relatively weak adhesive. The adhesives
provide the adhesion between the outer protective base
layers and inner barrier layers.
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The outer base protective layers are preferably
formed of polypropylene because it is inert to most
food products and does not affect the flavor or odor of
the product. Other inert strong polymers may also be
used. The barrier layer is preferably formed of a
copolymer of ethylene and vinyl alcohol because it has
excellent oxygen barrier properties and is easily
processable. Polyvinylidene chloride and other barrier
polymers may also be used.
The strong adhesive may be, for example, maleic
anhydride-modified polypropylene. The weak adhesive
may be, for example, maleic anhydride-modified poly-
ethylene or maleic anhydride-modified polypropylene
blended with polypropylene or even just a maleic
hydride-modified polypropylene with a low degree of
functionalization.
As can be seen in Figures 1, 2 and 3, the
container flange 12 has a crimp 22 therein. Figs. 1
and 2 show the crimp on the upper side of the flange
and Fig. 3 shows it on the underside of the flange.
The crimp 22 weakens that portion of the flange 12 but
still provides continuous unbroken base and barrier
layers 14 and 16. The crimp may be formed into the
container flange 12 in a secondary operation.
Preferably, the crimp is formed into the container
flange 12 during the forming process wherein the
container 10 is formed. This may be accomplished by a
variety of means including thermoforming and injection
molding.
The lid 24 is adhered to the upper portion of the
container flange 12. The seal between the lid 24 and
the flange 12 should be a so called "permanent"
seal-this means that the two layers should be extremely
difficult to pull apart. Such a seal between the lid
24 and the flange 12 can be accomplished by a variety
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of means including virtually any sealing method-
adhesion, ultrasonic, radio frequency, vibration
welding, thermal conduction and spin welding, for
example. In the case of the oxygen barrier package,
the lid must also include an oxygen barrier material
and preferably also include inner and outer protective
base layers. If oxygen barrier is not important, then
the lid may be formed of any plastic material, laminate
- or otherwise.
Figure 2 illustrates the non-oxygen barrier
embodiment of the present invention wherein the
container flange is formed of a laminate of two outer
base protective layers 14 adhered together by a layer
20 of a relatively weak adhesive. The lid 24 is
permanently sealed to the upper portion of the flange
12 and, as in Figure 1, extends outwardly beyond the
end of the flange 12.
As shown in Figure 2, to open this package, an
upward force is exerted on the extending end of the lid
24. Because of the strong adhesion between the lid 24
and the container flange 12, the upper base layer 14
does not peel away from the lid 24 but rather the two
base layers 14 peel away from each other at the
adhesive layer 20 because of the relatively weak
adhesion strength of that layer. When the peel reaches -
the crimp 22, the outward portion of the container -
flange 12 breaks off because the crimp 22 has weakened
the flange 12 sufficiently at that point for such
: breaking off to occur. This action provides the
: 30 opening of the package. The same type of thing happens
with the package of Fig. 1 except that the peel is
between the base and barrier layers which are bonded
together by the weak adhesive.
The characteristics of the weak adhesive are
important to the performance of the package of the
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present invention. In general, for shallow draw
containers, the adhesive strength should be at or above
0.5 pounds per linear inch (PLI) and for deep draw
containers, the adhesive strength should be at or above
1.0 PLI.
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