CA2058065A1 - Plastic container - Google Patents
Plastic containerInfo
- Publication number
- CA2058065A1 CA2058065A1 CA 2058065 CA2058065A CA2058065A1 CA 2058065 A1 CA2058065 A1 CA 2058065A1 CA 2058065 CA2058065 CA 2058065 CA 2058065 A CA2058065 A CA 2058065A CA 2058065 A1 CA2058065 A1 CA 2058065A1
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- Canada
- Prior art keywords
- container
- center portion
- heel
- recessed center
- curvature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Abstract
Docket No. RSL 012 P2 Abstract of the Disclosure There is disclosed a body for a retortable plastic container having a sidewall and bottom wall integrally formed as a single piece. The bottom wall has a heel portion and a recessed center portion. The heel has a resting surface and an inside corner. The recessed center portion has an outside corner. The container has an outside surface. The container is made in accordance with equations relating to reforming pressure and low fill equilibrium pressure and may be fabricated utilizing a variety of manufacturing modes since the providing of acceptable container configurations is not based on relative wall thicknesses.
Description
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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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- : , , Docket No. RSL 012 P2 - 2 -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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~1 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 . Ji , J
n Docket No. RSL 012 P2 - 4 -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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' ~1 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 J ~ t~, ,.
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 ,1 .
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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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Docket No. RSL 012 P2 - 11 -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.
~ 3 . i ~ ~ 3 ., 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 , ,:
~,~7 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.
~ ,, 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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Docket No. RSL 012 P2 - 15 -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.
.' `,' i ~ ~,' ' 3 t1 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 ' ~ ?
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 "
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 r ~, ~
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'.
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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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.',J'~ 3 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 ~` ~
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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~. , 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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- : , , Docket No. RSL 012 P2 - 2 -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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~1 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 . Ji , J
n Docket No. RSL 012 P2 - 4 -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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' ~1 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 J ~ t~, ,.
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 ,1 .
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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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Docket No. RSL 012 P2 - 11 -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.
~ 3 . i ~ ~ 3 ., 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 , ,:
~,~7 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.
~ ,, 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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Docket No. RSL 012 P2 - 15 -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.
.' `,' i ~ ~,' ' 3 t1 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 ' ~ ?
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 "
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 r ~, ~
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
.~
f~
j.
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, ' ~ ' .. ' .:
.
~. ' ' - :
.',J'~ 3 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.
':~
.3U
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.
, - - , .
,. . ~ . . ' ., :-' -: .
. :
- , . . . ~ , - . .
- ' .' ' ' ' ' . , . ~ : :
- . . : .
.. . ..
' ~ . , 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 ~` ~
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:
.. , ................. - .
- ' ,, i , ,
Claims (9)
1. A body for a retortable, plastic container which is adapted, when closed, to hold a product under vacuum, 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, characterized by said bottom wall having a low fill equilibrium pressure of greater than -2.54 p.s.i., and a reforming pressure greater than -0.68 p.s.i., said low fill equilibrium pressure being equal to:
C1INT + C1A*A' + C1B*B' + +C1C*C' +C1D*D' + C1E*E' + C1F*F' + C1BBF*B'*F' + C1CF*C'*F' + C1F2*F'*F', where C1INT = -4.142753; C1A = -1.152504; C1B = -2.125803;
C1C = -1.832533; C1D = .460410; C1E = .478786; C1F = 2.710596;
C1BF = .499315; C1CF = .421809; and C1F2 = -.454128, and said reforming pressure 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*DI*E' +
C2DF*D'*F' + C2EF*E'*F' + C2A2*A'*A' + C2B2*B'*B' +
C2D2*D'*D' + C2E2*E'*E', where 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, where for said low fill equilibrium pressure and said reforming pressure 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";
with A' being the radius of the circle associated with the curvature of the outer surface of the inside corner of said heel as well as the radius of the circle associated with the curvature of the outer surface of the outside corner of said recessed center portion, B' being 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 a point on the recessed center portion of said 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 said heel and the circle associated with the curvature of the outer surface of the outside corner of the recessed center portion, C' being the horizontal distance between the point 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' being 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' being the perpendicular distance between 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, and F' being the distance between the opposite outer edges of the resting surface.
C1INT + C1A*A' + C1B*B' + +C1C*C' +C1D*D' + C1E*E' + C1F*F' + C1BBF*B'*F' + C1CF*C'*F' + C1F2*F'*F', where C1INT = -4.142753; C1A = -1.152504; C1B = -2.125803;
C1C = -1.832533; C1D = .460410; C1E = .478786; C1F = 2.710596;
C1BF = .499315; C1CF = .421809; and C1F2 = -.454128, and said reforming pressure 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*DI*E' +
C2DF*D'*F' + C2EF*E'*F' + C2A2*A'*A' + C2B2*B'*B' +
C2D2*D'*D' + C2E2*E'*E', where 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, where for said low fill equilibrium pressure and said reforming pressure 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";
with A' being the radius of the circle associated with the curvature of the outer surface of the inside corner of said heel as well as the radius of the circle associated with the curvature of the outer surface of the outside corner of said recessed center portion, B' being 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 a point on the recessed center portion of said 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 said heel and the circle associated with the curvature of the outer surface of the outside corner of the recessed center portion, C' being the horizontal distance between the point 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' being 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' being the perpendicular distance between 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, and F' being the distance between the opposite outer edges of the resting surface.
2. A container according to claim 1 further characterized by said container being a low panel strength container.
3. A container according to claim 1 further characterized by said recessed center portion being relatively flat.
4. A container according to claim 1 further characterized by said recessed center portion being convex relative to said heel portion.
5. A container according to claim 1 further characterized by said recessed center portion being concave relative to said heel portion.
6. A container according to claim 1 further characterized by said container being co-extruded, said sidewall and bottom wall formed in layers, and said layers of the container having a gas barrier therebetween.
7. A container according to claim 1 further characterized by said container being thermoformed.
8. A container according to claim 1 further characterized by A' = .1270"; B' = 1.5760"; C' = .0250"; D' = .2000"; E' =
.1390"; F' = 2.3220", with the low fill equilibrium pressure being equal to -1.8294 p.s.i. and with the reforming pressure being equal to .1674 ps.i.
.1390"; F' = 2.3220", with the low fill equilibrium pressure being equal to -1.8294 p.s.i. and with the reforming pressure being equal to .1674 ps.i.
9. A container according to claim 1 further characterized by A' = .0775"; B' = 2.0000"; 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.
.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.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US63828191A | 1991-01-04 | 1991-01-04 | |
| US638,281 | 1991-01-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2058065A1 true CA2058065A1 (en) | 1992-07-05 |
Family
ID=24559380
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2058065 Abandoned CA2058065A1 (en) | 1991-01-04 | 1991-12-19 | Plastic container |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2058065A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112439108A (en) * | 2019-09-04 | 2021-03-05 | 肖特瑞士股份公司 | Closed end container and container assembly with same |
-
1991
- 1991-12-19 CA CA 2058065 patent/CA2058065A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112439108A (en) * | 2019-09-04 | 2021-03-05 | 肖特瑞士股份公司 | Closed end container and container assembly with same |
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