Note: Descriptions are shown in the official language in which they were submitted.
~L3534
COS-461 CIP
DC-528
THERMOPLASTIC FOOD CONTAINER
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BACKGROUND OF THE INVENTION
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The present invention generally relates to
` thermoplastic containers for receiving food products and
~ more particularly involve~ a thermoplastic container made
- from a multi-layered thermoplastic material.
; In the current state of food packaging many food
products such as soups and juices are still being packaged
primarily in metal cans. Because of the high acidity and
high susceptibility to spoilation from oxygen encroachment,
many food products must be packaged in metal containers
which exhibit some added chemical resistance to the acidity
- as well as being tightly and hermetically sealed. This
involves, in the case of metal cans r some interior coating
on the metal can to prevent the acidity in the ~ood product
from attacking the metal in the can.
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Other types of food packaging containers involve
glass containers with metal caps. The glass container
offers both chemical resistance to acidity and a highly
impermeable barrier to oxygen ingress into the container.
Unfortunately, the glass container is expensive to
manufacture and is subject to breakage and the accompanying
danger of glass injuries to the consumers. Both the metal
can with interior coating and the glass container are
measurably more expensive to manufacture and less desirable
than thermoplastic containers for the same food products~
Current food product packaging which utilizes
plastic containers suffers from the disadvantage that the
majority of plastic materials accepted by the FDA for
contact with products for human consumption do not offer
all the desired characteriistics for containers. For
example, one highly desirable material for food product
containers i5 polyethylene terephthalate (PET). This
polymer is a tough clear plastic material having good
strength characteristics and moderate barrier
characteristics. Unfortun-ately, the material does not
offer the impermeability needed to protect products which
are susceptible to oxygen encroachment and spoilation
therefrom. For example, soups and juices suffer rapid
spoilation when placed in straight PET containers because
of the relative porosity of PET to the ingress of oxygen
molecules. Thus, PET as a food container package leaves
much to be desired.
A~licant is aware of the manufacture of a laminated
container having ex-terior and interior layers of a
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structural polymer with a sandwiched barrier layer
therebetween. Whereas this container is an advancement
over the prior art its use is limited in the area of
hot-fill and retort since it has upper temperature limits
which, in some cases, would prevent hot filling and
retorting. In some cases where a high hot fill or retort
temperature is required, followed by chilling of the
product for retail sale, the polymers in the structural
layers become susceptible to trauma fracture which might
occur during packaging, shipping, stocking, or even by
dropping on the floor.
The present invention overcomes the disadvantages
of prior art containers by providing a multi-layered,
multi-segmented container which is highly impervious to the
transmission of gasses su~h as C02 and oxygen
therethrough, is tough and resilient, is inexpensive to
manufacture, and allows hotfilling and retorting without
degradation of the container's desirable qualities.
SUMMARY OF TE~E INVENTION
The present invention discloses a two-piece food
packaging container made of a multi-layered thermoplastic
material with an interior layer comprising a desirable
package polymer such as polyethylene terephthalate or
polypropylene, a layer of a barrier polymer such as
ethylene vinylalcohol (EVAL), and an exterior "girdle"
layer having enhanced fracture resistance. The container
of this invention may be manuEactured by coextruding the
barrier polymer inside a "sandwich" of the two structural
layers into a sheet material and then thermoforming the
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container in two separate sections which are then joined by
spin-welding.
In accordance with the present teachings, a composite
thermoplastic container for receiving hot-filled material
therein is provided. The container comprises a tapered
upper body section containing a filler opening at the top
end thereof and an open bottom end larger than the filler
section; and a tapered lower body section having a bottom
closure and an open upper end adapted for snug-fitting
relationship with the upper body portion. At least one of
the body sections comprises a multi-layered thermoplastic
material, at least one layer of which comprises a barrier
polymer having a low gas permeability and at least one other
layer comprises an impac-t copolymer; and, wherein the body
sections are friction-welded together to form a single
container.
In accordance with a further aspect of the present
teachings, a method is provided of forming a barriered,
nestable, composite thermoplastic container for receiving
hot-filled products and having vacuum compensating ability.
The method comprises coextruding a composite thermosplastic
sheet having at least one layer of a heat-resistant structural
polymer material, at least one impact layer of a tough
copolymer, and at least one layer of a barrier polymer. A
tapered upper body section having an opened larger end and
a narrower end with a filler opening is thermoformed from
the sheet. A papered lower body section having ~ larger
open upper end and a bot-tom closure is thermoformed from the
sheet with the bottom closure being thermoPormed to contain
a flanged, inwardly flexible diaphragm section arranged to
flex inward in response to a vacuum in the container. The
upper and lower body sections are friction-welded together
to form an integral container.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is partial cross-sectional ~ide view of
one embodiment of the container made according to the
present invention.
Figure 2 is an axial end view of the container of
Figure 1 taken at line 2-2 thereof.
Figure 3 is an axial bottom view of the container
of Figure 1.
Figure 4 is a partial cross-sectional side view
of the container of Figure 1 after the container has been
filled.
Figure 5 is a cross-sectional side view of an
alternate embodiment lid closure for the container of
Figure 1 and;
Figure 6 is a cross-sectional side view of the
container of Figure 5 after hot filling.
Figure 7 is a partial cross-sectional view of a
barriered container according to the present invention.
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DESCRIPTION OF THE PREFER~ED EMBODIMENTS
Referring to Figure 1, there is illustrated a
thermoplastic container 101 which is particularly
advantageous for packaging hot food products such as
vegetable juice. The container 101 comprises an upper body
portion 102 and a bottom portion 103. Upper body portion
102 comprises a tapered frustoconical wall section having
at its upper end an indented neck section 104 and a
peripheral rim 105. Rim 105 has located therein an
indented lip section 106 defining a fill opening 107.
Base cup 103 comprises an upwardly extending
frustoconical wall section 108 having at the upper end
thereof a peripheral spin-weld flange 109 integrally formed
thereon. Cup 103 has a bottom support rim 110 and a
diaphragm bottom section 111.
Diaphragm bottom 111 comprises a central
diaphragm disk 111 separated from rim 110 by a pair of
alternating flex-grooves 112 and 113. The provision of
disk 111 and grooves 112 and 113 allows a certain amount of
flexibility in the volume content of the container 101.
A flexible metal cap 114 is provided for
tight-fitting engagement over fill rim 105. Top 114
preferably is made of a ductile material such as aluminum
foil. A collapsable center section 115 slightly raised
from top 114 is formed therein to provide flex space above
the filled product in the container. A plurality of
indentations 116 are formed in the upper portion o~ the
conical section of body 102 and preferably at least three
indentations 116 are formed in the wall of the upper body
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portion. Likewise a set of indentations 117 are formed in
lower cup portion 103 and comprises at least three
indentations therein. The indentations 116 and 117 are
adapted for nested stack control so that several nested
components of the same configuration do not jam or lock
together prior to denesting and application.
The material preferred for forming the present
container consists of a multi-layered thermoplastic sheet
having an interior layer of polypropylene, an exterior
layer of a propylene/ethylene copolymer, and a central
layer of EVAL bonded therebetween. This sandwich effect
results in a waterproof layer on the interior of the
container formed of polypropylene and a tough, fracture-
resistant "girdle" layer ~f copolymer, with a captured or
"sandwiched" layer of EVAL between the two structural
layers. The layer of EVAL serves to provide an oxygen
barrier for the container to prevent the ingress of oxygen
and to protect the food product ~rom early spoilage. The
copolymer layer, comprising a propylene/ethylene copolymer,
acts as a reinforcement or "girdle" around the structural
barrier layers. The properties of the copolymer add the
extra toughness associated with the ethylene elastomer to
provide greatly enhanced fracture resistance to the
container, especially at low temperatures and after
heating. The inner layer of a homopolymer such as
polypropylene provides rigidity of the container during the
elevated temperatures of hot-filling or retorting while the
outer layer becomes rather soft. The copolymer outer layer
then provides toughness at the lower temperatures where the
homopolymer mlght be fracture-prone. In one preferred
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embodiment the multi-layered thermoplastic material was
extruded in a sheet coextrusion die such as those disclosed
in U. S. Patent 4,100,237
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and was thereafter thermoformed by means
:. such as blow molding into the final upper and lower body
portion. One method of thermoforming such containers which
also offers the additional advantage is obtaining biaxial
orientation in the containers';
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.. Other methods of thermoforming the container
~- portions such as vacuum molding and more conventional
- methods of blow forming can be utilized to form these
container portions. After the upper portion 102 is
-~ thermoformed a stamping machine can be utilized to cut top
opening 107 thereinO
After the upper and lower container portions are
~ formed from the composite sheet, each section is placed in
.' its respective spin-welding mandrel and they are joined~ together by spin-welding means to form a hermetically
:. sealed integral container 101. It is preferred that a
slight interference fit be designed into the container
~; sections between flange 109 and the lower skirt portion of
: conical wall 102. This allows for slight variations in
. sizing between the two respective container portions and
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further aids in their joining by spin-welding techniques.
The provision of polypropylene or polyethylene
terephthalate outer and inner layers in the two container
sections insures a good solid friction weld between the two
sections due to the susceptibility of these polymers to
spin-welding techniques.
Referring now to Figure 4, a container 101 is
illustrated in its filled and cooled state. One problem
with prior art containers is the shrinkage involved when
material which has been heated or retorted to sterilization
temperatures is placed in the food container ~a process
called "hot-filling"). The problem generally occurs when
hot food products at temperatures in excess of 200 F are
placed in the containers and the containers are then
sealed. As the heated material and the air above it in the
container cools it naturally contracts due to the change in
temperature. In many instances this could cause buckling
of the external walls or top and bottom of the containers.
This is particularly troublesome in thermoplastic
containers which have higher flexibility than glass and
metal. In the present invention this is overcome by the
provision of the unique diaphragm bottom section 111
containing expansion grooves 112 and 113 to allow flexing
upward of the bottom portion. Likewise the top seal 114
has a provision for compensating for the shrin~age of the
headspace air and of the products. As shown in Figure ~,
section 116 of top 114 is ductile enough to be drawn
downwardly into the container opening as the product
shrinks in response to being cooled. Thus as the product
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shrinks, the crown portion 115 of upper seal 114 is drawn
downward into the lip area 106, 107 of top portion 104.
Thus in Figure 4 it can be seen how top seal 114
has been drawn downward by cooling of the product and
bottom diaphram section 111 has flexed upward into the
container to of~set the shrinkage of the liquid. One of
the principal advantages of the present invention is that
these two effects are not obvious to the consumer. One of
the significant disadvantages of previous thermoplastic
container designs is that the shrinkage due to cooling
usually caused an uneven flexing inward of the side walls
or of the top/bottom sections. This flexing or l'buckling"
of the plastic container was often mistakenly perceived by
the consumer as indicating a spoiled product. Thus the
present invention, by providing the flex diaphram bottom
section and the collapsible top seal, compensates for the
effect of the shrinkage in the container contents. The
flexing of the bottom is indistinguishable to the average
consumer and the downward drawing of the top seal appears
to be the natural sealed condition of the top.
Figures 5 and 6 illustrate the preferred
embodiment of the invention wherein a different
construction for the metal foil lid is utilized. In the
lid illustrated in Figure 5, lid 214 comprises an outward
circular flange section 215 and a concentric ribbed
diaphram section 216. The rib 216 and the dome 217 extend
downward toward the container to eliminate most of the
headspace above the material in the container. This large
reduction in the headspace gives a reduction in the vacuum
effect when the contents and trapped air cool. This in
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turn will provide a more controlled downward flexure of the
foil lid as the product in the container cools. Figure 6
illustrates the ~inal downward position of the seal after
total collapse into the fill opening of the container.
Thus the present invention discloses a
thermoplastic food and beverage container manufactured from
a composite thermoplastic sheet material having a barrier
buried therein, which container is formed by thermoforming
an upper and a lower section from the multi-layered sheet
and then spin-welding the two sections into a single
integral container. The bottom section of the container
comprises a disguised flexible diaphram section and the top
section receives a collapsible foil seal to compensate for
the volume shrinkage due to cooling of the headspace air
and of the hot-filled product.
In addition to the advantages of the present
invention enumerated above, the design of the container
disclosed herein is particuarly advantageous for shipping.
Whereas most prior art conventional containers generally
are formed in a single operation and must be either formed
on location or shipped empty, the present invention
discloses a container which is nestable and can be shipped
at a fraction of the cost of conventional containers.
Since most conventional containers which are shipped must
be shipped empty the truck or railcar containing the
conventional containers is filled primarily with air.
For example, the average semi-trailer load of normal
products generally weighs about 20,000 pounds. A filled
semi-trailer load of empty plastic containers might weigh
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only 2,000 pounds. Thus the shipper of the containers is
paying for the cost of an entire truck load of containers
but is primarily shipping air. With the present invention
the containers may be shipped in separate parts, which due
to their frusticonical nature can be nested in a very
compact arrangement. The top sections 102 are nested
together and shipped in one container and the bottom
sections 103 may be nested together and shipped in a
separate container. Thus the user of the containers
realizes tremendous economies in shipping by the
nestability of the various components. The ~iller or
canner receives the nested portions and places them in a
relatively simple and inexpensive spin-welding device to
form the containers sectiotns into a single sealed integral
container. Spin-welding systems whlch are particularly
useful in welding the present container are disclosed in
U.S. Patents 3,800,40 to Mistarz et al; 3,799,821 to Jones;
3,708,376 to Mistarz; and RE 29,448 to Brown et al.
Although a specific perferred embodiment of the
present invention has been described in the detailed
~*scription above, the description is not intended to limit
the invention to the particular forms or embodiments
disclosed therein since they are to be recognized as
illustrative rather than restrictive and it will be obvious
to those skilled in the art that the invention is not so
limited. For example, whereas the container materials were
cited as being polyethylene terephthalate (PET) or
polypropylene, it is obvious that other known thermoplastic
container materials can be utilized. For example,
polyethylene, polyethylene terephthalate glycol (PETG),
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polyvinyl chloride, polystyrene, and various other poly
olefins and polyesters can be utilized for the container
material. Likwise other barriers can be utilized in the
sandwich between the wall polymers; for example such as
saran (PVDC) and barex. In one particular preferred
embodiment, a five layer coextruded sheet was manufactured
having a polypropylene such as Shell Chemical's 5225
homopolymer as the interior layer. The exterior layer was
formed from an impact copolymer manufactured by Northern
Petrochemical and designated as a reactor copolymer of
ethylene and propylene, product code 151OL~. The barrier
layer was EVAL "F" manufactured by Kuraray Chemical of
Japan and it was surrounded on each side by an adhesive
manufactured by Mitsui Chemical Industries of Japan and
designated as Admer QF-50~. Another copolymer which may be
utilized as the exterior layer is a propylene/ethylene
copolymer manufactured by Shell Chemical Co. and designated
as Shell 7921. One important criteria in selecting the
polymers for the copolymer appears to be that their melt
indices be very close together. In the preferred
embodiment above the polymer melt indices of the copolymer
are both both 0.6. In addition, whereas the container is
depicted as being generally cylindrical and is spin~welded
together, it is also possible to use other geometrical
cross-sectional shapes such as oval, elliptical or
polygonal, and to friction-weld them by means other than
spin-welding, i.e. by oscillatory bonding or welding. Thus the
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invention is declared to cover all changes and
modifications of the specific example of the invention
herein disclosed for purposes of illustration, which do not
.constitute departure from the spirit and scope of the
invention.
