Note: Descriptions are shown in the official language in which they were submitted.
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PLASTIC CONTAINER
Technical Field
The present invention relates generally to a plastic
container, and more particularly, to a retortable, plastic
container having a unique bottom configuration which, independent
of relative wall thickness, obviates paneling and other problems
heretofore associated with such containers when they are
subjected to sterilization.
Backaround Art
Many products which require sterilization, such as
nutritionals and pharmaceuticals, were originally packaged in
glass containers. Due in part to concerns for safety and
manufacturing costs, over the years changes in packaging resulted
in many of these products being packaged in metal containers.
Currently, the technology a~sociated with the sterilization of
metal containers is very well developed.
More recently however, consumers have indicated an
increasing preference for plastic containers, due to factors such
as cost and visibility of product. With respect to visibility of
product, some consumers, especially when it comes to the
purchasing of liquid nutritional product, believe that there is
an advantage in being able to visually inspect the product prior
to ingestion. The bases for these concerns are related to
factors such as food quality and spoilage.
Although consumers have indicated a preference for
plastic containers, until fairly recently the only plastic
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containers capable of being subjected to sterilization were
plastic bowls sterilized in batch or continuous batch systems.
Some of these bowls were formed with thick enough side walls that
deformation during the sterilization process was precluded.
Plastic containers manufactured in this manner possess several
drawbacks, including the excessive cost for materials, the
increased cost of shipping, and the inconvenience associated with
actual use due to the increased weight of the container. A
proposed alternative to the manufacture of containers with
relatively thick side walls has been the utilization of a vacuum
to retract the deformed end or, as in hot packing, the
maintenance in the sterilization system of a net vacuum.
The sterilization of plastic containers, which
containers initially and finally approxLmate the general shape of
a can, presents a particular problem known as paneling.
Typically when such containers are filled they have steam
injected into the container just prior to the container being
sealed. Duxing sterilization, problems can arise in the
deformation of the container due in part to the inter-relatedness
of product volume and headspace. The term "headspace" may be
; defined as the volume of gas (in a container) between the upper
surface of the product and the lower surface of the container's
top. For example, in a container packed without the use of.a
vacuum, the volume of product and the volume of headspace gas
equal the volume of the container. In a container packed under a
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Docket No. RSL 012 P2 - 3 -
vacuum, the volume of product plus the volume of headspace gas is
less than the volume capacity of the container when sealed. The
internal container volume or total fill equals the headspace
volume plus the product volume.
There are at least two critical performance
requirements in retortable, semi-rigid containers with respect to
bottom profile and panel strength, with panel strength being
defined as the net external pressure at which the sidewall
buckles inwardly. The first performance requirement is that at
minimum fill conditions, i.e., the lowest acceptable minimum
combination of product and headspace gas volume, and at low
temperature, i.e., the temperatures experienced at distribution,
sale, and consumption, the vacuum developed in a filled, sealed
and sterilized container must not exceed the panel strength, such
that the container sidewall does not buckle inwardly, a condition
known as paneling. The second critical performance requirement
is that at maximum fill conditions, i.e., the highest acceptable
product and headspace gas volume, the container bottom profile is
able to reform nearly to its original shape as the container
cools.
; With respect to the first performance requirement,
there is a tendency toward paneling in plastic retortable
containers. The problem is exacerbated when the container cannot
reform. Although the frequency of paneling during sterilization
due to the failure of the container bottom to reform may
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initially appear insignificant, for example one in every 5,000
cans, given the fact that millions of containers are sterilized
each year, the result is product waste due to the increased cost
of doing business, and lost potential revenue. For example,
problems with paneling typically result in jams in continuous
sterilizers causing the destruction of large quantities of
otherwise good product. However, in the best case scenario, such
a jam can cause 800 - 1,000 cans to be diverted onto the floor
during a 2-3 minute period while the jam is being unclogged. In
a worse case scenario, the entire system is forced to endure a
total shutdown which results in the destruction of the containers
and product in the system which can reach 20,000 containers.
To better appreciate the second critical performance
requirement, it may be desirable to more fully understand the
changes associated with the configuration of the container when
subjected to retort. Initially the plastic container is semi-
rigid. As its temperature increases, the pressure inside the can
; increases. Normally associated with this pressure increase is
the deformation of the container bottom as it expands outwardly,
similar to a balloon when inflated. Following actual
sterilization of the product, the temperature decreases.
Corresponding to the decrease in temperature is a decrease in the
pressure inside the container. As the pressure decreases, ~the
container bottom ideally will return to its original
configuration. Heretofore, based on trial and error efforts
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Docket No. RSL 012 P2 - 5 -
associated with the prior art, the presence of a recessed portion
associated with the container bottom, has been recognized as
being able to assist the reforming of the container in returning
to its pre-sterilization configuration.
These performance requirements impact on another
problem associated with plastic containers. The container must
be able to deform to provide a container volume increase of at
least 6% (corresponding to the thermoexpansion o~ the packaged
product) and preferably in excess of 15% without producing
catastrophic failure of the materials of construction.
One proposed solution to the long felt need of having a
retortable plastic container configured like a can is disclosed
in U.S. Patent No. 4,125,632. That particular patent proffers as
the solution to the problem the presence of localized thin spots
in the container wall to facilitate expansion and contraction of
the bottom profile during sterilization. ~he patent discloses
that it is critical that the thickness of the sidewall must be
thicker than the thickness of the base.
Unfortunately, due to the criticality of comparative
wall thickness the plastic container disclosed in U.S. Patent
4,125,632 can only be made using certain manufacturing methods.
For example, the container disclosed in the patent can not be
made by thermoforming. One hypothetical alternative which;could
allow for the necessary control of wall thickness would be
through the changing of the present can shapes. However, a
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Docket No. RSL 012 P2 - 6 -
problem would arise in that such changes in can size would most
probably necessitate the redesign of sterilization equipment.
The redesign option could be extremely expensive and entail the
purchase of new equipment. Thus, it is desirable to form a can
which can be sterilized in existing metal can sterilization
equipment.
It thus apparent that a need exists for an improved
plastic container capable of being used in conventional
sterilization equipment. It is also apparent that the need
exists for an improved plastic container able to survive retort
conditions.
Disclosure of the Invention
There is disclosed a body for a retortable, plastic
lS container having a diameter of two to four inches, which is
adapted, when closed, to hold a product under vacuum, said body
comprising a sidewall and a bottom wall integrally formed as a
single piece, said bottom wall having a heel portion and a
recessed center portion, said heel having a resting surface and
an inside corner, said recessed center portion having an outside
corner, said container having an outer surface, said bottom wall
having a low fill equilibrium pressure, also known as the low
temperature pressure of low fill or the normalized low fill,
equilibrium pressure index greater than or equal to the panel
~5 strength of the container such that the container will not panel
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Docket No. RSL 012 P2 - 7 -
during sterilization, and a net reforming pressure also known as
the normalized reforming pressure, inside the body always less
than the panel strength of the sidewall and greater than -0.68
p.s.i. such that the container will not panel during
sterilization, and food product packaged in said container.
The value for the low fill equilibrium pressure must
not exceed the panel strength of the container at low
temperature. The low fill equilibrium pressure index preferably
is greater than -2.54 p.s.i. with that low fill equilibrium
pressure index being equal to:
ClINT + ClA*A' + ClB*B' + ClC*C' + ClD*D' + ClE*E' +
ClF*F' I ClBF*B'*F' + ClCF*C'*F' + ClF2*F'*F'.
In the above equation: ClINT = -4.142753; ClA = -1.152504;
ClB = -2.125803; ClC = -1.832533; ClD = .460410; ClE = .478786;
ClF = 2.710596; ClBF = .499315; ClCF = .421809; and
ClF2 = -.454128.
The reforming pressure must not exceed the panel
strength of the container during reforming. Additionally, the
reforming pressure index should be greater than -0.68 p.s.i. with
the reforming pressure index being equal to:
C2INT + C2A*A' + C2B*B' + C2C*C' + C2D*D' + C2E*E'
+ C2F*FI + C2AB*A'*B' + C2AC*A'*C' + C2AD*A'*D' + C2BC*B'*C'
+ C2BF*B'*F' + C2CE*C'*E' + C2DE*D'*E' + C2DF*D'*F' + C2EF*EI*F'
+ C2A2*A'*A' + C2B2*B'*B' + C2D2*D'*D' + C2E2*E'*E'.
Docket No. RSL 012 P2 - 8 -
In the above equation: C2INT = 15.690630; C2A = -227.234510;
C2B = --12.565323; C2C = .236741; C2D = 16.780591;
C2E = 62.444483; C2F = .451248; C2AB = 55.363723;
C2AC = 56.165647; C2AD -- --74.140417; C2BC = --11.733167;
C2BF = -.303382; C2CE = 59.348338; C2DE = -76.524059;
C2DF = -3.159350; C2EF = 2.438579; C2A2 = 610.834990;
C2B2 = 2.487053: C2D2 = 60.327091; and C2E2 = -186.130720.
For said low fill equilibrium pressure and said
10 reforming pressure the ranges from A'-F' are as follows: A' is
between 0.0775" and 0.1435"; B' is between 1.2050" and 2.0000";
C' is between -0.0125" and 0.2385"; D' is between 0.0870" and
0.2610", E' is between 0.1200" and 0.2400", and F' is between
1.7110" and 4.0000".
In one embodiment, A' = .1270": B' = 1.5760":
C' = .0250"; D' = .2000"; E' = .1390" and F' = 2.3220", with the
low fill equilibrium pressure being equal to -1.8294 p.s.i. and r
the reforming pressure being equal to .1674 p.s.i. In the
preferred embodiment, A' = .0775"; B' = 2.0000"; C' = .0177";
~20 D' = .0870"; E' = .1200"; and F' = 2.3220", with the low fill
equilibrium pressure being equal to -2.2634 p.s.i. and the
reforming pressure being equal to .0506 p.s.i.
, In the container of the invention, A' is the average of
the radii of the circles associated with the curvature of the
outer surface of the inside corner of said heel and the circle
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Docket No. RSL 012 P2 - 9 -
associated with the curvature of the outer surface of the outside
corner of said recessed center portion. B' is the distance
between the points of intersection on the opposite sides of said
container of the circles associated with the curvature of the
outer surface of said inside corner of said heel and the line
forming part of the recessed center portion of said container,
said line defined as being tangent to both the circle associated
with the curvature of the outer surface of the inside corner of
said heel and the circle associated with the curvature of the
outer surface of the outside corner of the recessed center
portion.
Also, C' is the horizontal distance between the points
of tangency of the line connecting the inside corner of the heel
and the outside corner of said recessed center portion with the
respective circles associated with the curvature of the outer
surface of the inside corner of said heel and the curvature of
the outer surface of the outside corner of said recessed center
portion. D' is the perpendicular distance between said resting
surface of said container and the outside surface of said
~ 20 container at the vertical central axis of said container. E' is
;~ the perpendicular distance between the resting surface of said
container and the horizontal line tangent to the top of the
circle associated with the curvature of the outer surface of said
outside corner of s~id recessed center portion. F' is the
distance between the opposite outer edges of the resting surface.
Docket No. RSL 012 P2 - 10 -
Preferably the container is a low panel strength
container. Additionally, preferably the recessed center portion
is curved slightly convex outward. In one embodiment of the
invention, the recessed center portion is curved slightly concave
inward. In another embodiment of the invention, said recessed
center portion is relatively flat.
The container of this invention preferably is co-
extruded, has its sidewall and bottom wall formed in layers and
said layers of the container have a gas barrier therebetween. In
the preferred embodiment of the invention said container is
thermoformed.
There is also disclosed a packaged food product,
comprising a plastic container having a diameter of two to four
inches and food product, said container having a sidewall and a
bottom wall integrally formed as a single piece, said bottom wall
having a heel portion and a recessed center portion, said heel
having a resting surface and an inside corner, said recessed
center portion having an outside corner, said container having an
outer surface, said bottom wall having a low fill equilibrium
pressure of greater than the panel strength of the container and
a net reforming pressure inside the container always less than
the panel strength of the sidewall, and food product pac~aged
therein.
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The value for the low fill equilibrium pressure index
preferably is greater than -2.54 p.s.i. with the low fill
equilibrium pressure index being equal to:
ClINT + ClA*A' + ClB*B' + ClC*C' +ClD*D' + ClE*E' +
ClF*F' +ClBF*B'*F' + ClCF*C'*F' + ClF2*F'*F'.
In the above equation: ClINT = -4.142753; ClA = -1.152504;
ClB = -2.125803: ClC = -1.832533; ClD = .460410; ClE = .478786;
ClF = 2.710596; ClBF = .499315; ClCF = .421809; and
ClF2 = -.454128.
Similarly, the reforming pressure must not exceed the
panel strength of the container during reforming. Additionally
the reforming pressure index should preferably exceed -0.68
p.s.i., with the reforming pressure being equal to:
C2INT + C2A*A' + C2B*B' + C2C*C' + C2D*D' + C2E*E'
+ C2F*F' + C2AB*A'*B' + C2AC*A'*C' ~ C2AD*A'*D' + C2BC*B'*C'
+ C2BF*B'*F' + C2CE*C'*E' + C2DE*D'*E' + C2DF*D'*F' + C2EF*E'*F'
+ C2A2*A'*A' + C2B2*B'*B' + C2D2*D'*D' + C2E2*E'*E'. r
In the àbove equation: C2INT = 15.690630; C2A = -227.234510;
C2B = -12.565323; C2C = .236741; C2D = 16.780591;
C2E = 62.444483; C2F = .451248; C2AB = 55.363723;
C2AC = 56.165647; C2AD = -74.140417; C2BC = -11.733167;
C2BF = -.303382; C2CE = 59.348338; C2DE = -76.524059;
' C2DF = -3.159350; C2EF = 2.438579; C2A2 = 610.834990:
C2B2 = 2.487053; C2D2 = 60.327091; and C2E2 = -186.130720.
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Docket No. RSL 012 P2 - 12 -
For said low fill equilibrium pressure and said
reforming pressure the ranges for A'-F' are as follows: A' is
between 0.0775" and 0.1435"; B' is between 1.2050" and 2.0000";
C' is between -0.0125" and 0.2385"; D' is between 0.0870" and
0.2610"; E' is between 0.1200" and 0.2400"; and F' is between
1.7110" and 4.~000".
In one embodiment, A' = .1270"; B' = 1.5760";
C' = 0.250"; D' = .2000"; E' = .1390"; and F' = 2.3220", with the
low fill equilibrium pressure being equal to -1.8294 p.s.i. and
10 the reforming pressure being equal to .1674 p.s.i. In the
preferred embodiment, A' = .0775"; B' = 2.000"; C' = .0177";
D' = .0870"; E' - .1200"; and F' = 2.3220", with the low fill
equilibrium pressure being equal to -2.2634 p.s.i. and the
reforming pressure being equal to .0506 p.s.i.
In the container of this invention, A' is the average
of the radii of the circles associated with the curvature of the
outer surface of the inside corner of said heel and the circle
associated with the curvature of the outer surface of the outside
corner of said recessed center portion. B' is the distance
20 between the points of intersection on the opposite sides of said
container of the circles associated with the curvature of the
outer surface of said inside corner of said heel and the line
forming part of the recessed center portion of said container
said line defined as being tangent to both the circle associated
25 with the curvature of the outer surface of the inside corner of
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Docket No. RSL 012 P2 - 13 -
said heel and the circle associated with the curvature of the
outer surface of the outside corner of the recessed center
portion.
Also, C' is the horizontal distance between the points
of tangency of the line connecting the inside corner of the heel
and the outside corner of said recessed center portion with the
respective circles associated with the curvature of the outer
surface of the inside corner of said heel and the curvature of
the outer surface of the outside corner of said recessed center
portion. D' is the perpendicular distance between said resting
surface of said container and the outside surface of said
container at the vertical central axis of said container. E' is
the perpendicular distance between the resting surface of said
container and the horizontal line tangent to the top of the
circle associated with the curvature of the outer surface of said
outside corner of said recessed center portion. F' is the
distance between the opposite outer edges of the resting surface.
In the preferred embodiment of the invention, the
; packaged food product includes a container which is a low panel
strength container. Additionally, the packaged food product
includes a container wherein the recessed center portion is
curved slightly convex outward. In one embodiment of the
- invention, the recessed center portion is curved slightly c,oncave
inward. In another embodiment of the invention, said recessed
center portion is relatively flat.
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Docket No. RSL 012 P2 - 14 -
The present invention provides a plastic container
which does not experience paneling due to the pressures required
to reform the bottom profile of a container when the container is
subjected to retort conditions.
Yet another important aspect of this invention is to
provide a packaged food product comprising a retortable plastic
container whose bottom profile following being subjected to
retort conditions will reform very near to its original bottom
profile shape.
Other aspects and advantages of the invention will be
apparent from the following description, the accompanying
drawings, and appended claims.
; Brief Description of the Drawinqs
Fig. 1 is a partial vertical sectional view of a first
plastic container.
Fig. 2 is a partial vertical sectional view of a second
plastic container.
Fig. 3 is a partial vertical sectional view of a third
plastic container, formed in accordance with the present
invention.
Fig. 4 is a graph comparing net vacuum versus container
wall temperature, which graph discloses acceptable container
configurations.
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Fig. 5 is a partial vertical sectional view of a
plastic container made in accordance with the present invention.
Fig. 6 is a partial vertical sectional view of a
plastic container made in accordance with the present invention.
Fig. 7 is a partial vertical sectional view of the
preferred embodiment of a plastic container made in accordance
with the present invention.
Fig. 8 is a partial vertical sectional view of the
preferred embodiment of a plastic container made in accordance
with the present invention.
Detailed Description of the Drawinqs
Having reference to the drawings, attention is directed
first to Figs. 1, 2 and 3 which illustrate vertical cross
sectional views of three plastic containers. The partial
vertical sectional views of the plastic containers as shown in
Figs. 1, 2 and 3 do not, based solely upon their appearance,
provide any indication based on the prior art as to whether a
container made in accordance with the configurations shown in
Figs 1-3 would adequately perform when such container is
subjected to retort conditions. The type of containers shown are
known as low panel strength containers. In such containers, the
container itself is not altered through the addition of
strengthening items such as ribs.
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Docket No. RSL 012 P2 - 16 -
Fig. 4 graphically depicts a comparison of net vacuum
in pounds per square inch versus container wall temperature when
plastic containers made in accordance with Figs. 1-3 are
subjected to retort conditions. The sloping line is indicative
of the maximum values, above which line the container fails to
maintain integrity either during and/or following sterilization.
For example, the container bottom associated with Fig. 1 does not
perform acceptably when the container is heated to relatively
high temperatures, although the container performance at lower
temperature levels is acceptable. Similarly, the container
configuration shown in Fig. 2 performs acceptably during the high
temperature sterilization process, but fails to when the
container is subjected to lower temperatures associated with the
cooling process. Finally, the container configuration associated
with Fig. 3 can be seen as being fully able to perform so as not
to buckle, while being able to reform.
The container shown in Fig. 3 is able to successfully
meet the two critical performance criteria associated with
retortable plastic containers, notwithstanding the fact that the
container wall thickness is essentially uniform. Thus, the
container configuration shown in Fig. 3 permits the fcrmation of
a retortable plastic container independent of relative wall
thicknesses.
Heretofore, in low panel strength containers, the
problems associated with paneling and reforming have been
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Docket No. RSL 012 P2 - 17 -
tolerated along with the accompanying adverse economic impact,
since container design depended essentially on the success of
trial and error technique. It has been desirable to ascertain a
geometric container configuration or configurations, which would
not suffer from the problems associated with prior art plastic
containers, particularly those made with relatively uniform wall
thickness, such as by thermoforming.
It has been discovered that by manufacturing a
container with a bottom wall having a low fill equilibrium
pressure of greater than the panel strength of the container and
a net reforming pressure inside the container always less than
the panel strength of the container sidewall that the plastic
container can survive retort conditions. It has further been
discovered that there are a plurality of fairly critical
numerical values associated with certain perimeters of the
container which enable the generation of container bottoms which
will survive the retort conditions. The advantages associated
with the ability to ascertain whether a particular proposed
container configuration will produce acceptable results can best
be appreciated by the fact that there are literally millions of
theoretical container bottom configurations. The cost associated
with testing any given proposed configuration, whether by
computer simulation or by actual making of a mold, is relat;ively
inexpensive.
Docket ~o. RSL 012 P2 - 18 -
Figures 5 and 6 disclose partial vertical sectional
views of containers made in accordance with the present
invention. The container configuration shown in both of the
drawings is identical, with the only difference being with
respect to certain of the reference characters associated with
the teachings of this invention. In these drawings the plastic
container which could be used for the packaging of liquid or
solid nutritionals, or of medicinal products is designated by the
numeral 10. The container 10 is shown as including a sidewall 11
and a bottom wall 12. The container has an outer surface 13. At
the lower-most portion of the container 10 is a resting surface
14. The resting surface is shown as encircling the lower-most
portion of the container and is formed by the lower-most surface
of heel portion 15 of container 10.
Central of resting surface 14 is a recessed center
portion 16. The mid-point 18 of both the recessed center
portion, and preferably also the container 10, corresponds to the
center longitudinal axis of the container. The recessed center
portion 16 includes an outside corner 20, while the heel 15
includes an inside corner 22. It should be understood that it is
believed that in most configurations of containers formed in
accordance with the invention that the outside corner 20 and
inside corner 22 will actually be curved.
~s can be seen in Fig. 5, associated with the curvature
of the outer surface 13 at both the inside corner 22 of heel 15
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Docket No. RSL 012 P2 - 19 -
and the outside corner 20 of recessed center portion 16 are two
swing points Sl and S2. S1 and S2 serve as the centers of the
circles shown in Fig. 5, with both of these circles having the
same radius, namely A'. Thus, A' not only is the radius of the
circle associated with the curvature of the outer surface of the
inside corner of the heel, but it is also the radius of the
circle associated with the curvature of the outer surface of the
outside corner of the recessed area.
With respect to the two circles associated with the
inside corner of the heel, there is a distance between these two
circles which for purposes of this invention has been defined as
being B'. Put another way, B' is the distance between the points
of intersection on the opposite sides of the container of 1) the
circles associated with the curvature of the outer surface of the
inside corner of the heel, and 2) a point on the recessed center
portion of the container, with this point being one on a line
which is tangent to both the circle associated with the curvature
of the outer surface of the inside corner of the heel and the
circle associated with the curvature of the outer surface of the
outside corner of the recessed center portion.
Similarly, there is a distance between the outermost
portions of the circles associated with S2 on opposite sides of
the container. A distance C' is the difference in the horizontal
distance of B' and the distance between the outermost portions of
the circles associated with S2 on opposite sides of the
Docket No. RSL 012 P2 - 20 -
container. Put another way, C' is the horizontal distance
between the point of tangency of the line connecting the inside
corner of the heel and the outside corner of the recessed center
portion with the respective circles associated with the curvature
of the outer surface of the inside corner of the heel and the
curvature of the outer surface of the outside corner of the
recessed center portion.
There is also a distance D', with that being the
perpendicular distance between the resting surface 14 of the
container and the outside surface 13 of the container at the
vertical central axis 18 of the container. Finally, there is
shown a value for E', with that value being defined as the
perpendicular distance between the resting surface 14 of the
container and the horizontal line which is tangent to the top of
the circle associated with S2, i.e., the circle associated with
the curvature of the outer surface of the outside corner of the
recessed center portion. F' is the distance between the opposite
outer edges of the resting surface.
Figs. 5 and 6 disclose an embodiment of the invention
wherein: A' = .1270"; B' = 1.5760"; C' = .0250"; D '- .2000";
E' = .1390"; and F'- 2.3220", with the low fill equilibrium
pressure being equal to -1.8294 p.s.i. and the reforming pressure
being equal to .1~74 p.s.i.
Turning now to Fig. 6, there are shown the same swing
points Sl and S2, which points serve as the centers of circles
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Docket No. RSL 012 P2 - 21 -
associated with the outer surface at the outside corner of the
recessed center portion as well as at the inside corner of the
heel portion. There is shown a value for A, with this value and
definition being identical to A'. There is also shown a value
for D, with that value and definition being the same as D'.
There is a distance between the opposite points Sl or
the opposite centers of the circles associated with the curvature
of the inside corner of the heel. This value is defined as B.
Similarly, there is a distance between opposing points S2 with
this distance between the opposite centers of the circles
associated with the curvature of the outside corners of the
recessed area being defined as C. Finally, there is a value E
which is shown as being equivalent to the vertical distance
between the resting surface 14 of the container bottom to the
center of the circle associated with the curvature of the outer
surface of the inside corner of the heel, otherwise known as the
point S2.
For purposes of converting between the A'-E' values and
A-E values, the following equations may prove helpful:
C = B' - 2A' - 2C'
C' = B/2 - 2A - C/2
B' = B - 2A
E' = A + E
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Docket No. RSL 012 P2 - 22 -
It has also been found that for the container made in
accordance with this invention, the low fill equilibrium pressure
is equal to:
ClINT + ClA*A' + ClB*B' + ClC*C' + ClD*D' + ClE*E'
+ ClF*F' + ClBF*B'*F' + ClCF*C'*F' + ClF2*F'*F'.
In the above equation: ClINT = -4.142753; ClA = -1.152504;
ClB = -2.125803; ClC = -1.832533; ClD = .460410; ClE = .478786;
ClF = 2.710596; ClBF = .499315; ClCF = .421809; and
ClF2 = -.454128.
Similarly, it has been determined that the reforming
pressure is equal to:
C2INT + C2A*A' + C2B*B' + C2C*C' + C2D*D' + C2E*E'
+ C2F*FI + C2AB*A'*BI + C2AC*A'*C' + C2AD*A'*D' + C2BC*B'*C'
+ C2BF*B'*F' + C2CE*C'*E' + C2DE*D'*E' + C2DF*D'*F' + C2EF*E'*F'
+ C2A2*A'*A' + C2B2*B'*B' + C2D2*D'*D' + C2E2*E'*E'.
.: .
Docket No. RSL 012 P2 - 23 -
In the above equation: C2INT = 15.690630; C2A = -227.234510;
C2B = -12.565323; C2C = .236741; C2D = 16.780591;
C2E = 62.444483; C2F = .451248; C2AB = 55.363723;
C2AC = 56.165647; C2AD = -74.140417; C2BC = -11.733167;
C2BF = -.303382; C2CE = 59.348338; C2DE = -76.524059;
C2DF = -3.159350; C2EF = 2.438579; C2A2 = 610.834990;
C2B2 = 2.487053; C2D2 = 60.327091; and C2E2 = -186.130720.
For said low fill equilibrium pressure and said
reforming pressure the ranges of Al-F' have been found to be as
follows: A' is between 0.0775" and 0.1435"; B' is between
1.2050" and 2.0000"; C' is between -0.0125" and 0.2385"; D' is
between 0.0870" and 0.2610"; E' is between 0.1200" and 0.2400";
and F' is between 1.7110" and 4.0000". While th,e ranges of A',
B', C', D', E' and F' actually result in a low fill equilibrium
range of between -3.710 and .574 p.s.i. and a reforming pressure
range of between -2.808 to 4.062 p.s.i., preferably the low fill
equilibrium pressure is greater than -2.54 p.s.i. and the
reforming pressure is greater than -0.68 p.s.i.
The ability to utilize the equation associated with
- 20 this invention permits the prediction of acceptable container
design to be made with certainty.
Preferably the plastic container permits a food product
to be packaged in such container having a headspace between the
container top and the food product between 1 and 4 percent of the
volume of the container. Under the low fill pressure conditions,
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Docket No. RSL 012 P2 - 24 -
the fill is approximately 93%, while under high fill conditions,
the fill is approximately 97%. In the preferred embodiment, the
low temperature panel strength of the container is approximately
2.54 p.s.i., and the reforming panel strength is approximately
0.68 p.s.i.
Due to the unique geometric configuration associated
with the plastic container of this invention, the criticality of
wall dimensions and material properties are rendered essentially
irrelevant.
Best Mode
In actual utilization, a retortable plastic container
made in accordance with this invention is fabricated utilizing
the equation, constants, and parameters discussed above so as to
create a retortable, semi-rigid plastic container, which upon
being subjected to retort conditions exhibits reforming, but not
buckling. For example, Figs. 5 and 6 disclose an acceptable
plastic container bottom made in accordance with this invention.
In this particular embodiment, A' = .1270"; B' = 1.5760";
C' = .0250"; D' = .2000"; E' = .1390"; and F' = .2.3220" with the
low fill equilibrium pressure being equal to -1.8294 p.s.i. and
the reforming pressure being equal to .1674 p.s.i. As can be
seen, in this embodiment the container bottom is curved slightly
concave inward.
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Docket No. RSL 012 P2 - 25 -
Figs. 7 and 8 disclose what is believed to be a
preferred embodiment of the invention. In this embodiment, A' =
.0775"; B' = 2.0000"; C' = .0277"; D' = .0870"; E' = .1200"; and
F' = 2.3220", with the low fill pressure equilibrium being equal
to -2.2634 p.s.i. and the reforming pressure being equal to .0506
p.s.i. In this preferred embodiment the container bottom is
curved slightly convex outward. In other potential, acceptable
embodiments the recessed center portion is relatively flat.
The container of this invention is characterized by
flexibility with all blends of food grade polyolefin material,
including mono- and/or multi-layer barrier materials. Preferabiy
the material is an impact copolymer. Preferably the material is
; an impact copolymer. Preferably the outside layer of the
container is fabricated from a polyolefin material with a gas
barrier being interposed between the outside layer and the inside
layer, which is preferably formed of an ethylene vinyl alcohol
copolymer, or more preferably polypropylene. The container of
the preferred embodiment of this invention may have the
polyolefin outer layer formed from either an ethylene/propylene
copolymer or a polypropylene/polyethylene blend. Additionally,
~ the container made in accordance with this invention may be
; formed using one of several modes of manufacture, namely
extrusion blow molding, injection blow molding, injection
molding, or thermoforming.
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Docket No. RSL 012 P2 - 26 -
Industrial ApPlicabilitY
Annually, more than 200,000,000 units of pediatric
nutritional products alone are distributed in the U.S. The
majority of these products currently utilize glass or metal
containers. The industry has long sought ways to eliminate glass
and metal containers and move to a less expensive container such
as one formed from plastic, however the container must be
retortable. This invention solves this long sought need. The
container is not limited to usage in the pediatric nutritional
area, and could be utilized in such areas as adult nutritional
foods, or pharmaceutical products.
The product container formed by this invention can
be utilized in existing sterilization equipment. One advantage
of this is that in the continuous agitation sterilizers currently
utilized, the product can be heated and cooled faster due to the
rotation of the can during the sterilization process. This
possesses the ad~antage of there being less damage to the
product, especially where the product is heat sensitive such as
is the case with milk or soy based products, and consequently it
is important to minimize exposure to heat. In the above
nutritional products, overexposure to heat can result in poorer
color as well as decreased nutrition as the result of protein
degradation.
The performance of the container of this invention in
being able to deform at least 6~ and preferably in excess of 15
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Docket No. RSL 012 P2 - 27 -
without producing catastrophic failure permits the container to
function in batch sterilization which typically exposes the
containers within a batch to a diverse range of temperature and
pressure conditions, especially during the cooling portion of the
cycle.
As opposed to the container of U.S. Patent No.
4,125,632, which requires pressure to effectuate reforming, the
container of this invention can reform on its own without
additional application of pressure. While overpressure may be
utilized in the manufacture of containers in accordance with this
invention, it is applied to prevent localized catastrophic
failure, as opposed to being utilized solely for reforming.
While the form of apparatus herein described
constitutes a preferred embodiment of this invention, it is to be
understood that the invention is not limited to this precise form
of apparatus and that changes may be made therein without
departing from the scope of the invention which is defined in the
appended claims.
What is claimed is:
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