U.S. patent application number 10/625605 was filed with the patent office on 2005-01-27 for container for hot fill food packaging applications.
Invention is credited to Mendez, Hernan, Peisach, Alberto.
Application Number | 20050017013 10/625605 |
Document ID | / |
Family ID | 34080241 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050017013 |
Kind Code |
A1 |
Peisach, Alberto ; et
al. |
January 27, 2005 |
Container for hot fill food packaging applications
Abstract
A plastic container suitable for hot-fill food packaging
applications is disclosed which is characterized by walls of
proportionately decreasing thickness from the mouth of the
container to a predetermined collapsible point. The wall thickness
is designed such that the container walls will collapse, or deform,
only at the collapsible point during cooling after hot-filling of
food product or during transportation of the container between
locations of varying altitudes and pressures. The container
preferably collapses in the base area such that the collapse is not
visible to the consumer and also the collapse does not affect
stability of the container while in use or during loading and
storage. The container of the invention is advantageous in that it
requires less plastic material to form than other known hot-fill
containers, and also can be formed out of any suitable food-grade
plastic material or by any process.
Inventors: |
Peisach, Alberto; (Golden
Beach, FL) ; Mendez, Hernan; (Bogota, CO) |
Correspondence
Address: |
HUNTON & WILLIAMS LLP
INTELLECTUAL PROPERTY DEPARTMENT
1900 K STREET, N.W.
SUITE 1200
WASHINGTON
DC
20006-1109
US
|
Family ID: |
34080241 |
Appl. No.: |
10/625605 |
Filed: |
July 24, 2003 |
Current U.S.
Class: |
220/609 |
Current CPC
Class: |
B65D 1/42 20130101; B65D
1/26 20130101 |
Class at
Publication: |
220/609 |
International
Class: |
A47G 019/00 |
Claims
What is claimed is:
1. A plastic container, comprising: a mouth; a bottom surface; and
a container wall between the mouth and the bottom surface, wherein
one of the bottom surface or the container wall flexes inward into
the cavity of the plastic container; wherein further the inward
flexing of the bottom surface of the container wall reduces a
pressure differential between the inside of the container and
atmospheric pressure when either the container is hot-filled with
food product or when the container is transported from a locale of
lower atmospheric pressure to higher atmospheric pressure; and
wherein further the non-flexing surface maintains the same form
from prior to hot-filling or transport.
2. The plastic container of claim 1, wherein the thickness of the
container walls decreases from a point substantially at the mouth
to a point substantially at the bottom surface.
3. The plastic container of claim 1, wherein the bottom surface
flexes inward into the container cavity.
4. The plastic container of claim 3, wherein the circumference of
the mouth is greater than the circumference of the bottom
surface.
5. The plastic container of claim 4, wherein the plastic comprises
a plastic suitable for solid phase pressure forming.
6. The plastic container of claim 5, wherein the plastic further
comprises polypropylene.
7. The plastic container of claim 6, wherein the plastic further
comprises a barrier enhancement agent.
8. The plastic container of claim 7, wherein the barrier
enhancement agent comprises ethylene vinyl acetate-vinyl
alcohol.
9. The plastic container of claim 8, wherein the plastic further
comprises an adhesive suitable for solid phase pressure
forming.
10. The plastic container of claim 9, wherein the adhesive
comprises an antioxidant
11. The plastic container of claim 5, wherein the plastic container
is formed from a plastic sheet comprising up to about 15 volume %
ethylene vinyl acetate-vinyl alcohol, about 80 to about 90 volume %
polypropylene and about 15 to about 20 volume % adhesive.
12. The plastic container of claim 1, wherein the plastic container
is formed from a plastic sheet having one or more layers, and
wherein further the thickness of the container walls are about
70-80 volume % of the thickness of the plastic sheet at a location
substantially adjacent to the container mouth and about 20-40
volume % of the sheet at a location substantially adjacent to the
bottom surface, and the thickness of the bottom surface is about
15-20 volume % of the thickness of the plastic sheet.
13. The plastic container of claim 12, wherein the container wall
thickness uniformly decreases from a location substantially
adjacent to the container mouth to a point substantially adjacent
to the bottom surface.
14. The plastic container of claim 13, wherein the container walls
are about 0.7 mm thick at a location substantially adjacent to the
container mouth and about 0.28 mm thick at a point substantially
adjacent to the bottom surface, and the thickness of the bottom
surface is about 0.16 mm.
15. A method for forming a plastic container, comprising: selecting
at least one polymer for a plastic container; and forming the
plastic container; wherein the plastic container comprises: a
mouth; a bottom surface; and a container wall between the mouth and
the bottom surface, wherein one of the bottom surface or the
container wall flexes inward into the cavity of the plastic
container; wherein further the inward flexing of the bottom surface
of the container wall reduces a pressure differential between the
inside of the container and atmospheric pressure when either the
container is hot-filled with food product or when the container is
transported from a locale of lower atmospheric pressure to higher
atmospheric pressure; and wherein further the non-flexing surface
maintains the same form from prior to hot-filling or transport.
16. The method of claim 15, wherein forming the container
comprises: heating the plastic sheet to its VICAT temperature; and
thermoforming the container.
17. The method of claim 15, wherein forming the container comprises
extrusion, vacuum forming, injection molding, blister packaging,
melt phase forming or blow molding.
18. A method of manufacturing a plastic container with a
selectively deformable surface, comprising: selecting at least one
polymer; heating the at least one polymer to its VICAT temperature;
and thermoforming a container from the heated polymer; wherein the
plastic container comprises: a mouth; a bottom surface; and a
container wall between the mouth and the bottom surface, wherein
one of the bottom surface or the container wall flexes inward into
the cavity of the plastic container; wherein further the inward
flexing of the bottom surface of the container wall reduces a
pressure differential between the inside of the container and
atmospheric pressure when either the container is hot-filled with
food product or when the container is transported from a locale of
lower atmospheric pressure to higher atmospheric pressure; and
wherein further the non-flexing surface maintains the same form
from prior to hot-filling or transport.
19. The method of claim 18, wherein the thickness of the container
walls decreases from a point substantially at the mouth to a point
substantially at the bottom surface.
20. The method of claim 18, wherein the bottom surface flexes
inward into the container cavity.
21. The method of claim 20, wherein the circumference of the mouth
is greater than the circumference of the bottom surface.
22. The method of claim 21, wherein the plastic comprises a plastic
suitable for solid phase pressure forming.
23. The method of claim 22, wherein the plastic further comprises
polypropylene.
24. The method of claim 23, wherein the plastic further comprises a
barrier enhancement agent.
25. The method of claim 24, wherein the barrier enhancement agent
comprises ethylene vinyl acetate-vinyl alcohol.
26. The plastic container of claim 25, wherein the plastic further
comprises an adhesive suitable for solid phase pressure
forming.
27. The plastic container of claim 26, wherein the adhesive
comprises an antioxidant
28. The plastic container of claim 22, wherein the plastic
container is formed from a plastic sheet comprising up to about 15
volume % ethylene vinyl acetate-vinyl alcohol, about 80 to about 90
volume % polypropylene and about 15 to about 20 volume %
adhesive.
29. The plastic container of claim 18, wherein the plastic
container is formed from a plastic sheet having one or more layers,
and wherein further the thickness of the container walls are about
70-80 volume % of the thickness of the plastic sheet at a location
substantially adjacent to the container mouth and about 20-40
volume % of the sheet at a location substantially adjacent to the
bottom surface, and the thickness of the bottom surface is about
15-20 volume % of the thickness of the plastic sheet.
30. The plastic container of claim 29, wherein the container wall
thickness uniformly decreases from a location substantially
adjacent to the container mouth to a point substantially adjacent
to the bottom surface.
31. The plastic container of claim 30, wherein the container walls
are about 0.7 mm thick at a location substantially adjacent to the
container mouth and about 0.28 mm thick at a point substantially
adjacent to the bottom surface, and the thickness of the bottom
surface is about 0.16 mm.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a plastic container suitable for
hot-fill food packaging applications, and a method of making the
container. The container is manufactured in a manner such that the
walls have a sufficient strength to withstand collapse upon cooling
of the container after sterilization, or during the transport of
the filled container between locations of varying altitude. A
collapsible point, preferably the bottom of the container, is
manufactured to selectively deform to compensate for the pressure
differentials experienced between the interior of the container and
atmospheric pressure after hot-filling, and during transport of the
container between locations of different altitudes. Also disclosed
is a method of forming a container having a selectively deformable
collapsible point, and walls that do not deform, after hot-filling
and during other pressure changes.
BACKGROUND OF THE INVENTION
[0002] The storage of food products in plastic containers is well
known. Further, it is known that food products can be hot-packed
into plastic containers and then sealed to satisfy requirements for
food products as well as to provide extended shelf life.
[0003] Typically, a food product is packed in the container while
the food product is at sterilization temperature and then the
container is fitted with a sealed cover. An air space exists
between the top level of the hot-packed food product and the seal.
As the food product cools, the reduction in temperature causes a
reduction in this air volume. This reduction in air volume results
in a corresponding reduction in pressure within the container, and
can cause the container to collapse due to the head space remaining
between the food product and the seal of the container after
sealing and cooling. In addition, any changes in the altitude of
the location of the packed container can cause similar expansion
and/or contraction of the container due to changing pressure
differentials between the interior of the container and the
atmospheric pressure at the different locations.
[0004] Such plastic containers must be designed to withstand
contraction inside the container caused by cooling of the
hot-filled food product, as well as those pressure changes that
occur during transport of the plastic containers. Container
deformation typically can occur at any location in the container
where the container wall cannot withstand the experienced pressure
differential between the inside of the container and the
atmospheric pressure. Although container deformation does not
necessarily affect the sterility and stability of the packed food
product, consumers tend to shy away from such products based on the
appearance that the containers are perhaps damaged or otherwise
spoiled. In addition, container deformation causes the containers
to be difficult to load and store due to the nonuniformity of the
walls or bases. Also, container deformation can make a container
unstable when used by the consumer, when for example the base is
deformed such that the container is not steady when placed on a
surface.
[0005] Many designs of plastic containers are known to fulfill
these requirements. One approach has been to design a plastic
container having wall design of sufficient rigidity to withstand
the pressure differentials. For example, U.S. Pat. Nos. 4,318,882
and 4,497,855 issued to Agrawal et. al. both titled "Method for
Producing a Collapse Resistant Polyester Container for Hot Fill
Applications," the disclosures of which are hereby incorporated by
reference in a manner consistent with this disclosure ("Agrawal"),
disclose a polyester container having at least one region that is
thermoelastically deformable inwardly after the container is hot
filled and sealed to offset the pressure forces which tend to
collapse the container as the contents cool and create an internal
vacuum. Agrawal discloses a process of forming this region by a two
step molding process in which the region is formed and heat set at
a first position and then reformed outwardly to a second position
and cooled in that position.
[0006] U.S. Pat. Nos. 6,062,409 and 6,347,717 issued to Eberle both
titled "Hot Fill Plastic Container Having Spaced Apart Ribs," the
disclosures of which are hereby incorporated by reference in a
manner consistent with this disclosure ("Eberle I"), disclose a
blow molded plastic container comprising a plurality of vacuum
panels having substantially arched upper and lower ends and vacuum
panel reinforcement means in a series of arched ribs. The design of
the container minimizes the stress placed on the corners of vacuum
panels and resists flexing when the container is filled with a hot
liquid.
[0007] Similarly, U.S. Pat. Nos. 5,178,289 and 5,279,433 to
Krishnakumar et. al. both titled "Panel Design for a Hot-Fillable
Container," the disclosures of which are hereby incorporated by
reference in a manner consistent with this disclosure
("Krishnakumar"), disclose a vacuum panel design for a hot-fill
container which resists the increase in container diameter which
may occur during hot-filling or when the container is dropped on a
hard surface.
[0008] U.S. Pat. No. 5,337,909 issued to Vailliencourt and titled
"Hot Fill Plastic Container Having a Radial Reinforcement Rib," the
disclosure of which is hereby incorporated by reference in a manner
consistent with this disclosure ("Vailliencourt"), discloses a
container of a heat set material having a plurality of elongated
vertically oriented vacuum panels in its sidewall and first and
second circumferentially extending inwardly directed reinforcement
ribs which permit the center portions of the panels to flex inward
during filling and sealing the container with a hot liquid but
resisting deformation of the container sidewall. U.S. Pat. No.
5,341,946 also issued to Vailliencourt et. al. and titled "Hot Fill
Plastic Container Having Reinforced Pressure and Absorption
Panels," the disclosure of which is hereby incorporated by
reference in a manner consistent with this disclosure
("Vaillencourt et.al."), discloses a container having a plurality
of vertically oriented vacuum absorption panels to prevent the
sidewall from taking a permanent set deflected inwardly.
[0009] Another approach is to use a specially designed base
configuration to provide stability to the container. For example,
U.S. Pat. No. 5,005,716 issued to Eberle titled "Polyester
Container for Hot Fill Liquids," the disclosure of which is hereby
incorporated by reference in a manner consistent with this
disclosure ("Eberle II"), discloses a polyester container having a
base configuration including an outer circular ring defining a
support plane for the container with a central outwardly concave
dome portion therein. The dome portion includes a number of
reinforcing rings formed along concentric tangent lines. The
configuration is designed to provide mechanical stability in
response to positive and negative pressures within the container
that tend to cause deformation of the container. Similarly, U.S.
Pat. No. 4,993,567 issued to Eberle Jr. titled "Involute Embossment
Base Structure for Hot Fill PET Container," the disclosure of which
is hereby incorporated by reference in a manner consistent with
this disclosure ("Eberle Jr."), discloses a base configuration for
a blow molded plastic container having a peripheral support ring
that is generally concentric with the container side walls and
connected to a central dome structure. A number of embossments
raised around the central disk to resist deformation induced by
stresses incurred during hot filling of the container.
[0010] Another approach has been to design plastic containers with
certain crystalline structures that are less susceptible to
deformation during the sterilization process. For example, U.S.
Pat. No. 5,106,567 issued to Demerest titled "Method for Producing
a Heat Set Article of Thermoformed Polyethylene Terephthalate," the
disclosure of which is hereby incorporated by reference in a manner
consistent with this disclosure ("Demerest"), discloses a article
made of polyethylene terephthalate ("PET") having a degree of
crystallinity of at least 20% giving the article more uniform and
reproducible impact resistance over amorphous PET articles.
[0011] U.S. Pat. No. 4,582,665 issued to Jabarin titled "Method of
Making Polyethylene Terephthalate Articles," the disclosure of
which is hereby incorporated by reference in a manner consistent
with this disclosure ("Jabarin"), discloses a method of making an
oriented and heat set thermoformed article of PET. The sidewalls of
the article have a specific density, and the article is quenched
after forming while under restraint in order to limit volume
shrinkage and to increase the onset-of-shrinkage temperature of the
article.
[0012] Yet another approach includes a combination of container
design and controlled treatment of the container after it has been
filled. See, e.g., U.S. Pat. Nos. 4,642,968 and 4,667,454 to
McHenry et. al. titled "Method Of Obtaining Acceptable
Configuration Of A Plastic Container After Thermal Food
Sterilization Process," the disclosure of which is hereby
incorporated by reference in a manner consistent with this
disclosure ("McHenry"). McHenry discloses a method of obtaining an
acceptable configuration of a thermally processed container packed
with food. The disclosure teaches that such a configuration can be
obtained by proper container design, by maintaining proper
headspace of gases in the container during thermal processing,
proper pressure outside the container during the cooking cycle and
cooling cycle of the process and/or by controlled reforming of the
bottom wall of the container. In addition, further improvements can
be obtained by controlling the thermal history of the empty
container.
[0013] U.S. Pat. No. 5,234,126 issued to Jonas et. al. titled
"Plastic Container," the disclosure of which is hereby incorporated
by reference in a manner consistent with this disclosure ("Jonas"),
discloses a plastic container made in accordance with equations
relating to reforming pressure and low fill equilibrium pressure
giving the container a unique bottom configuration which,
independent of wall thickness, obviates paneling and other
deformations of the container during sterilization.
[0014] Colombian Patent No. 25357 issued to Alberto, titled "Moving
Bottom Container," the disclosure of which is hereby incorporated
by reference in a manner consistent with this disclosure, discloses
a formed plastic container having a base design that collapses to
compensate for changes in pressure due to the effect of changes in
height relative to sea-level during transport, storage and sale of
the packed containers.
BRIEF SUMMARY OF THE INVENTION
[0015] The invention relates to a plastic container suitable for
the packaging of hot-filled food products that can withstand the
pressure changes caused by the cooling of the hot food product in
the sealed container, and also during transport of the packed
containers between locations having a pressure differential. The
invention also relates to a method of manufacture of the container.
The container of the invention includes walls designed by their
thickness to have a collapsible point, which collapsible point is
controllable by the manufacturing process. Preferably, the
collapsible point is designed to be located in the base of the
container such that it is not visible to the consumer after it
collapses, and also is designed such that the stability of the
container when standing is not affected.
[0016] Where the collapsible point is designed to be located in the
base of the container, the thickness of the container walls are
controlled such that the walls can withstand a designed pressure
force without deformation, except for the collapsible point. This
is done by controlling the manufacturing process to maintain the
desired wall and bottom surface thicknesses of the container. In
the preferred embodiment, the wall thickness decreases
proportionately from the area of the container substantially
adjacent to the mouth, to the bottom of the container, and the
thickness of the bottom is less than the thickness of the walls.
This is accomplished in the preferred forming process of
thermoforming by controlling the dimensions of the mold and the
counter-mold, and controlling the expulsion (ejection) pressure and
the temperature of the plastic sheet during forming. In addition,
the desired collapsible point may be further induced by a surface
design that will facilitate the collapse of that point at a lesser
pressure differential that can be withstood by other components of
the container. The collapse of the collapsible point reduces the
head space between the food product and the seal in the interior of
the container, and then reduces or eliminates the probability that
the walls of the container will also collapse, or otherwise
deform.
[0017] The container of the invention can be made of any plastic
materials that are suitable for food packaging, and any forming
method. For example, common plastic materials include polyethylene
terephthalate (PET), polyester, ethylene, polystyrene, low density
and high density polyethylene and polypropylene, or combinations of
these materials. Additives may be included with the plastic
materials to enhance properties desired in the final container. For
example, additional barrier materials, such as polyvinyldichloride
("PVDC"), polyvinylchloride ("PVC"), or ethylene vinyl
acetate-vinyl alcohol resins ("EVOH") may be added to decrease
permeability of the container to such undesirable materials as
oxygen and water vapor. Materials may be added to adapt the optical
properties. For example, materials may be added to decrease light
penetration into the container, or to increase clarity of the
container.
[0018] The container may be made by numerous known methods of
forming, such as blow molding, thermoforming, extrusion, injection
molding, blister packaging, vacuum forming or any other method of
forming.
[0019] One object of the invention is to provide a plastic
container suitable for hot-fill food packaging that can withstand
pressure differentials incurred after hot-filling and transport to
locales of varying altitudes without undesirable, or uncontrolled,
deformation of the container walls.
[0020] It is another object of the invention to provide a plastic
container suitable for hot-fill food packaging that has a
controlled collapsible point such that any deformation of the
container walls, and particularly the bottom surface, does not
affect the stability of the container when it is placed on a
surface for use.
[0021] It is another object of the invention to provide a plastic
container suitable for hot-fill food packaging that has a
controlled collapsible point such that any deformation of the
container walls does not affect the packing and handling
characteristics of the container for transport and storage.
[0022] It is another object of the invention to provide a plastic
container suitable for hot-fill food packaging that has a
controlled collapsible point that can be prepared by the various
forming processes.
[0023] Yet another object of the invention is to provide a plastic
container suitable for hot-fill food packaging having
proportionately decreasing wall thickness from the mouth of the
container to a predetermined collapsible point in the bottom
surface of the container such that the container does not collapse
during or after hot-filling or during transportation except at the
collapsible point.
[0024] It is another object of the invention to provide a plastic
container suitable for hot-fill food packaging that has a
controlled collapsible point such that the total amount of plastic
used to manufacture the cup is reduced over containers of
comparable size and application as manufactured by other currently
known processes.
[0025] It is another object of the invention to provide a method
for manufacturing a plastic container suitable for hot-fill food
packaging that has walls of proportionally decreasing thickness and
a controlled collapsible point such that any deformation of the
container walls do not affect the appeal of the container to the
consumer.
[0026] These and other objects will become apparent to those of
ordinary skill in the art through the description provided
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1a is a schematic of a filled container manufactured
according to previous technology.
[0028] FIG. 1b is a schematic of the bottom surface design of a
filled container manufactured according to previous technology.
[0029] FIG. 2a is a schematic of a container manufactured according
to one embodiment of the invention.
[0030] FIG. 2b is a schematic of the bottom surface design of a
filled container manufactured according to one embodiment of the
invention.
[0031] FIG. 3 is a graphical representation of a typical heat
treatment of a plastic sheet for solid phase plastic forming.
[0032] FIG. 4 is a flow scheme of the process of the invention for
manufacturing a container according to one embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The system and method of the invention relates to a
container suitable for hot-fill applications having walls that can
withstand the pressure differentials experienced during and after
sterilization, and also during transport of the packed containers
between locations having a pressure differential. A selected
collapsible point is designed into the container, typically the
bottom, that compensates for the pressure differentials experienced
during the sterilization process and transport between locales of
different pressures. The collapsible point may be designed such
that the point of collapse, or deformity of the container surface,
may easily be hidden from exterior view by placement of a sleeve
over the container, or by other means. Alternatively, the deformed
surface may be designed such that it collapses into the container
itself, where it is hidden from view. In this embodiment, the
container walls adjacent to the bottom surface should be designed
such that they do not collapse as well when the bottom surface
collapses. The bottom surface can be designed to have a surface
design that enhances its collapsing property, and reduce and/or
eliminate any collapsing of the adjacent walls.
[0034] In the preferred embodiment of the invention, the walls of
the container as made by the thermoforming process can withstand
pressure differentials between the interior of the sealed container
and the atmospheric pressure of 12 psi, while the bottom of the
container collapses between about 2.5 psi to about 10 psi pressure
differential between the interior of the sealed container and the
atmospheric pressure. In the preferred embodiment of the invention,
the collapsed bottom surface will typically not be able to "pop
out" again after collapsing into the container.
[0035] The collapsible point is preferably selected by designing
the thickness of the surface where the collapsible point is located
to withstand the least pressure differential between the interior
of the container and the atmospheric pressure, as compared to the
other surfaces of the container, such as the walls of the
container. Once the collapse of the collapsible point occurs, the
head space inside the container between the food product and the
seal is reduced, making it unlikely that the walls of the container
will collapse or otherwise deform. In addition, the other walls
should be designed to withstand pressure differentials between the
inside of the sealed container, both before and after the
collapsible point has collapsed, and the atmospheric pressure that
may be expected to occur after hot-filling and/or transport. One
method of designing the walls to have sufficient strength is by the
thickness of the walls. The thickness of the container walls may be
uniform, or preferably they may gradually decrease from a point
substantially adjacent to the mouth of the container to a point
substantially adjacent to the point where the container walls meet
the bottom surface. The decrease of the container wall thickness
may be uniform, although that is not a requirement. Additionally,
or alternatively, the container walls may include a design that
increases strength against collapse or deformation, as known to
those skilled in the art of container design. In the preferred
embodiment of the invention, such a structural wall design is
included at the area of the container wall substantially adjacent
to the bottom surface. This assists in preventing any buckling of
the walls in that area when the bottom collapses. In addition, the
container wall may include a decorative design that may or may not
add structural integrity to that surface.
[0036] If the container is manufactured by another method other
than thermoforming, such as injection molding, the container wall
and bottom surface thickness may be controlled by a mold design
that allows the walls to be of a thickness to withstand pressure
differentials between the inside of the sealed container, both
before and after the collapsible point has collapsed, and the
atmospheric pressure that may be expected to occur after
hot-filling and/or transport, and the bottom surface of the
container to be the selectively collapsible point by making the
bottom surface of lesser thickness than the walls. Alternatively, a
surface other than the bottom surface can be designed by the mold
to be the selectively collapsible point.
[0037] Preferably, the method of forming the container is by
thermoforming, and specifically solid phase pressure forming
("SPPF"), although other suitable methods such as melt phase
forming ("MPF"), blow molding, injection molding, blister
packaging, vacuum forming and extrusion may be used.
[0038] The plastics that may be used in forming include FDA
approved food grade acrylic, low density polyethylene ("LDPE"),
high density polyethylene ("HDPE"), polystyrene ("PS"),
polypropylene ("PP"), crystalline polyester ("CPET"), polyethylene
("PE") and combinations of these or other materials that are
currently used to achieve barrier properties listed as "other"
recycle code 7. Other suitable plastics may be selected that are in
compliance with 21 C.F.R. .sctn. 177.1360 of the FDA regulations,
and also 21 C.F.R. .sctn. 175.105, or regulations relating to food
grade plastics of the locale that the container is to be used.
Alternatively, if the container is not to be used for food
applications, the choice of starting raw materials is not so
limited.
[0039] Additives may be included with the plastic. For example,
materials to enhance barrier properties may be added, such as
ethylene vinyl acetate-vinyl alcohol copolymer ("EVOH"), PVDC, PVC,
nitrile barrier resin or Nylon.TM.. Barrier materials may be
desirable in applications where the designer needs to reduce the
permeation of oxygen and water vapor into the container. For
example, typically oxygen and water vapor transmission rates of
less than about 5 cc/mil/100 in.sup.2/24 hours/atmosphere at
23.degree. C./73.degree. F. and 75% RH is desirable for food
packaging applications. Also, typically an adhesive material is
included in the plastic material. One skilled in the art of forming
containers for food packaging will be able to select a suitable
adhesive, and level of adhesive, to be used in the plastic for the
forming of a container according to the invention. Suitable
adhesives include Antistatic 745-2AS.TM. and AS 745-5AS.TM.
available from Comai; Antioxidant CESA-STAT PPARFB12020.TM.
available from Clariant; AS ASPA-2485.TM. available from Shullman;
and Antistatic 40390.TM. available from Ampacet. Additives may also
include materials for aesthetic or other functional purposes, such
as clarity and blockage of light to the packed food product.
[0040] In thermoforming, sheet plastic is molded into the desired
shape via the pressing of formers, or molds, into a sheet of heated
plastic. Familiar products manufactured by thermoforming include
yogurt pots and simple trays. According to the preferred embodiment
of the invention, the plastic used to form the container comprises
a sheet of mixed EVOH, PP polymer and adhesive. A suitable EVOH is
EVAL.TM. J102B resin available from Eval Company of America,
located in Houston, Tex. EVAL.TM. J102B comprises approximately 32
mol % ethylene, with a Melt Index ("MI") of approximately 2.0 g/10
min @ 190.degree. C. and 2160 g, and 4.9 g/10 min @ 210.degree. C.,
2160 g, according to ASTM D1238. The density is approximately 1.17
g/cc according to ASTM D1505. The melting point and crystallization
temperature, as measured by differential scanning calorimetry, is
approximately 183.degree. C. and 161.degree. C., respectively. The
glass transition point, as measured by dynamic viscoelasticity, is
approximately 69.degree. C. The oxygen permeability, as measured by
ASTM D1434, is approximately 0.03-14 cc/mil/100 in.sup.2/24 hrs/atm
@ 65% relative humidity and 68.degree. F., and 1.8.times.10.sup.-14
cc/cm/cm.sup.2/sec/Hg @ 65% relative humidity and 20.degree. C. The
water vapor transmission rate, according to ASTM E96-E, is
approximately 3.8 g/mil/100 in.sup.2/24 hrs @ 90% RH and
100.degree. F., and approximately 50 g/30 .mu./m.sup.2/24 hrs @ 90%
RH and 40.degree. C. The gloss at 45.degree. is 85 as measured by
ASTM D2457. The haze is approximately 1.9% as measured by ASTM
D1003. The ultimate tensile strength is approximately 8200 psi and
the ultimate elongation is approximately 270%, as measured by ASTM
D882.
[0041] A suitable PP is PROPILCO.TM. 03H96, available from
Polipropileno del Caribe S.A. of Bogota, Colombia. The melt flow of
PROPILCO.TM. 03H96 is approximately 3 g/10 min, as measured by ASTM
D123 at 230.degree. C. and 2.16 kg. The tensile yield strength is
approximately 5300 ps, or 36.5 Mp and the tensile yield elongation
is approximately 9.3, as measured at 50 mm/min by ASTM D638. The
Rockwell hardness is approximately 102 as measured by D 785.
[0042] Preferably, the composition of the plastic sheet in the
preferred embodiment is approximately 0% to approximately 15% by
volume EVOH, and approximately 80% to approximately 100% by volume
PP, more preferably approximately 1% to approximately 7% by volume
EVOH, and approximately 85% to approximately 95% by volume PP, and
even more preferably approximately 1% to approximately 5% by volume
EVOH, and approximately 90% to approximately 95% by volume PP.
Additionally, adhesive may be included in amounts as determined by
those skilled in the art to form the container.
[0043] The plastic sheet is typically formed by extrusion, or
coextrusion where combinations of materials may be used to form the
plastic sheet. Typically, the various materials are extruded to
form a multilayer plastic sheet. For example, in the preferred
embodiment of the invention, the plastic sheet comprises five
layers of PP, adhesive, EVOH, adhesive and PP. However, other
additives may be added together during extrusion for use in a
single layer. Those skilled in the art of thermoforming will be
able to select suitable conditions for forming the plastic sheet
according to the desired properties of the finished container.
[0044] After the sheet of plastic that will be used to form the
container is formed, the sheet is preferably preheated to a
substantially uniform temperature distribution using methods and
equipment known to those skilled in the art of thermoforming. In
the preferred embodiment of the invention, an Illig 50K.TM. deep
draw cup forming thermoforming machine is used having a forming
area of about 500.times.280 mm. The Illig 50K.TM. is available from
ADOLF ILLIG Maschinenbau GmbH & Co. KG located in Heibronn,
Germany. The Illig 50K.TM. has five (5) heaters, each heater having
three zones. In the preferred embodiment, the sheet is heated by a
succession of a plurality of heaters comprising upper and lower
heaters. The heaters form a "tunnel" or "oven" through which the
plastic sheet passes on a belt conveyor. The heaters heat the
plastic sheet to its VICAT temperature according to methods and
processes known to those skilled in the art. Any heating equipment
or method can be used so long as it achieves a substantially
uniform temperature distribution throughout the sheet. Of course,
for different forming methods, other temperatures may be necessary.
For example, for injection molding, the plastic material must be
completely melted to pour into the mold.
[0045] Typically during thermoforming the plastic sheet undergoes
one or more heating and cooling cycles. The actual thermoforming
step comprises fitting a plug into a mold to form the desired
dimensions and shape of the container. After the container is
formed, it cools almost immediately and the formed containers are
typically stacked directly out of the thermoformer.
[0046] Once the container is formed, it may be used for hot-fill
food applications. The thickness of the walls of the container are
sufficient to withstand the pressure differences experienced during
the cooling of the hot-filled food product, and yet the thickness
of the bottom of the container allows the container to selectively
collapse at that point, where the deformation remains unnoticed by
the consumer or ultimate purchaser of the container. Similarly, the
deformation point may be designed to be located at a different
location in the container, and the artisan skilled in the art of
the selected forming process may adjust the forming conditions
appropriately to form the desired collapsible point. The advantage
of designing the collapsible point at the bottom of the container
is that the container may then be placed in a decorative outer
sleeve that shields the collapsed bottom from view. Alternatively,
and preferably, the bottom of the container is designed with a
surface design that allows mainly the center area of the bottom to
collapse, such that the edges of the bottom surface that do not
collapse provide stability for the container.
[0047] Turning now to the figures, FIG. 1a is a schematic of a
filled container manufactured according to previous technology.
FIG. 1a depicts a container 10 having a 11, a mouth 12, an inner
chamber 14, a bottom 15 and a side wall 16. The inner chamber 14 is
filled with a food material to level 13 that is hot-filled into the
container. The side walls 16 are designed to withstand the pressure
differentials between the interior of the sealed container and
atmospheric pressure. The bottom 15 is substantially level
following hot-filling and cooldown of the hot-filled food
product.
[0048] FIG. 1b depicts the bottom surface of the container of FIG.
1a having a bottom surface design 17. Typically, such a bottom
surface design 17 is designed to withstand the pressure
differentials between the interior of the sealed container after
hot-filling and atmospheric pressure.
[0049] A container manufactured according to the invention is
depicted in FIG. 2a. The container 10 includes a mouth 11, an inner
chamber 14, a bottom 15a, b and walls 16. A food product is
hot-filled in the inner chamber 14 to a level 13. The lower area of
the walls 16 substantially adjacent to the bottom 15a, 15b may
optionally, and preferably, include a design 18 that may provide
structural enhancements to that area of the wall 16 given its close
location to the collapsible bottom 15a, 15b. This design 18 may
also provide aesthetic enhancements, or may provide both aesthetic
and structural enhancements to the container 10.
[0050] In the container manufactured according to the invention,
the bottom 15a is not necessarily level after manufacture, although
the bottom 15a may be level. After hot-filling and cooling of the
food product, the bottom 15b of the container selectively deforms
by collapsing inward toward the inner chamber 14. When this occurs,
any head space that had been present between the level of the
packed food 13 and the top of the container is reduced and/or
substantially eliminated. Notably, the walls 16 remain
substantially uniformly tapered from the mouth 11 to the bottom
15b, and no deformation occurs. This is due to the increased wall
thickness of the walls 16 over the bottom 15a, b. The wall
thickness of the walls 16 and bottom 15a, b have been designed and
manufactured to allow only for deformation of the bottom 15a, b
after cooling of the hot-filled food product. This structural
integrity may be enhanced by design 18.
[0051] The bottom 15a, b preferably is designed to have a surface
design 17, shown in FIG. 2b, that further enhances the propensity
of the bottom 15a, b to collapse selectively over the walls 16. In
addition, the surface design 17 is situated such that only the
portion of the bottom 15a, b having the surface design 17 actually
collapses, permitting the uncollapsed outer edges of the bottom 19
to shield the collapsed bottom surface 15b from view, so that the
container does not appear to include "deformities" from the
perspective of a consumer. In addition, the uncollapsed outer edges
of the bottom 19 also provide stability to the container when
standing upright.
[0052] The desired wall thickness can be determined by methods
known to those skilled in the art of manufacturing containers for
hot-fill food packing applications by calculating the pressure
within the interior of the container after hot-filling and
subsequent cooling of the food product. The container of the
invention may also be designed to selectively deform at the bottom
15 and not the walls 16 for containers that are hot-filled at
locales of higher elevation, and then transported to locales of
lower elevation. The container of the invention may also be
designed to withstand pressure changes incurred during other
applications, such as transport of the containers in
non-pressurized airplane cargo holds.
[0053] FIG. 3 provides a graphical representation of a common heat
treatment for plastic sheets in preparation for thermoforming. This
graphical representation is exemplary only, and is not intended to
limit the invention in any manner. FIG. 3 demonstrates that those
skilled in the art of thermoforming typically follow a pattern of
rapidly increasing the temperature of the plastic sheet to be used
for forming to a temperature higher than the VICAT temperature, but
lower than the melting temperature. Then, the temperature is
allowed to slowly and slightly cool to the desired VICAT
temperature at which time the product is formed by punching the
plug into the mold in the thermoformer. This method of raising the
temperature of the plastic sheet to the VICAT temperature may be
used in the invention, although any other method that produces a
desirable thermoformed product may also be used.
[0054] A schematic of the thermoforming process of the preferred
embodiment invention is depicted in FIG. 4. At Step 410, the
plastic sheet that will be used in the thermoforming process is
prepared. Typically, the sheet is prepared by extrusion, or
coextrusion, according to principles and methods known to those
skilled in the art of plastics. The composition of the plastic
sheet is selected by the designer of the final product to include
the clarity and barrier properties desired. In Step 420, an
optional pretreatment of the plastic sheet may take place, if
necessary, prior to thermoforming. Again, the necessity and
conditions of the pretreatment step are selected by the designer of
the final product who is acquainted with the thermoforming of the
selected plastic sheet composition. In Step 430, the plastic sheet
is subjected to a heat treatment to achieve the VICAT temperature
of the plastic materials in the plastic sheet. In Step 440, the
container is punched from the plastic sheet by the molds of the
thermoforming machine. In Step 450, the formed container is cooled
and stacked where it may be used for hot-filling of food
products.
[0055] Although the container may be any dimension desired by the
designer, one common food packaging application is a four (4) ounce
cup. A typical four ounce cup made according to the preferred
embodiment of the invention weighs approximately 4.8 grams. The
wall dimensions range from about 0.71 mm adjacent to the mouth of
the cup, then proportionately decreasing to about 0.22 to about
0.34 mm or an average of 0.28 mm at the wall of the cup
substantially adjacent to the bottom of the cup. The bottom of the
cup is on the average about 0.16 mm thick. A typical cup is
approximately 79 mm wide, and approximately 52 mm in height.
[0056] One advantage of the container of the invention is that a
container of a certain size may be manufactured using less forming
material than previously known containers of comparable size,
resulting in cost savings in raw materials. For example, the four
ounce cup previously described weighs about 4.8 g. In contrast,
four ounce containers manufactured using currently known techniques
range from about 6.5 to about 6.7 grams. The raw material savings
in the container of the invention, for a comparable sized
container, can result in a savings of over 35% up to about 50% in
raw material costs. Further cost savings may be realized if raw
material costs increase.
[0057] This savings is realized because the containers previously
produced include walls throughout the cup of sufficient thickness
to prevent collapse at any point. By designing and manufacturing a
container with a selectively collapsible bottom by the system and
method of the invention, the manufacturer can realize significant
raw material cost savings while not experiencing increased
manufacturing costs, when using the same forming process.
EXAMPLES
[0058] The following example is provided as a further description
of one embodiment of the invention, and is not intended to be
limiting.
[0059] A four ounce cup was made according to the invention that
corresponds to the cup depicted in FIG. 1 by the thermoforming
process. The place of manufacture was Medellin, Colombia, having an
altitude above sea level of about 6500 feet. Note that the forming
conditions should be adjusted according to the ambient conditions
of the location of the manufacturing facility.
[0060] A starting plastic multilayer sheet comprising about 70-80
volume % EVAL.TM. J102B resin, about 20-40 volume % PROPILCO.TM.
03H96 PP and about 15-20 volume % Comai 745-2AS.TM. adhesive, based
on a total thickness of the multilayer sheet of about 1.02 mm, was
formed by coextrusion. The approximately 49 mm wide sheet was
continuously fed at a rate sufficient to mold four ounce cups, ten
cups at a time, 14 cycles per minute. The plastic sheet was fed
into an Illig 50K.TM. thermoforming machine where the first zone
heaters were set at about 350.degree. C./425.degree. C./300.degree.
C.; the second zone heaters were set at about 335.degree.
C./310.degree. C./370.degree. C.; and the first heater of the third
zone was set at about 335.degree. C. The cups were then formed from
the multilayer plastic sheet using a mold refrigerated to about
13.degree. C., and a countermold, also known as plug-assist,
refrigerated to about 11.degree. C. The cups were ejected by air
pressurized to about 5 psi from a distance of about 95 mm from the
cutting tool.
[0061] Each container was approximately four ounces, and about 79
mm in width and about 52 mm in height, with a weight of about 4.8
grams. The wall dimensions range from about 0.71 mm adjacent to the
mouth of the cup, then proportionately decreasing to about 0.22 to
about 0.34 mm or an average of 0.28 mm at the wall of the cup
substantially adjacent to the bottom of the cup. The bottom of the
cup is on the average about 0.16 mm thick. A typical cup is
approximately 79 mm wide, and approximately 52 mm in height. The
wall thickness was determined to provide sufficient rigidity to
withstand pressure differences between the interior of the
container and the atmospheric pressure of up to 12 psi. The bottom
of the container began to collapse at a pressure differential of
about 2.5 psi, and complete collapse was observed at about 10 psi
pressure differential. These pressure differentials have been
tested to meet or exceed the pressure differentials experienced by
cups used for hot-fill food product packaging under actual
conditions.
[0062] The foregoing embodiments have been presented for the
purpose of illustration and description only and are not to be
construed as limiting the scope of the invention in any way. The
scope of the invention is to be determined from the claims appended
hereto.
* * * * *