Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
FOAMED-WALL CONTAINER HAVING
A NON-TRANSPARENT APPEARANCE
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. Patent Application
Serial No. 11/384,979 filed on March 20, 2006, and International PCT
Application
No. PCT/US07/06264 filed on March 12, 2007.
FIELD OF THE INVENTION
[0002] The present invention relates generally to a foamed-wall polymer
container having a unique appearance. More particularly, the invention is
directed to a container comprising micro cellular foam, wherein the foam micro
cells contain a non-reactive gas such as nitrogen, and the container has a non-
transparent appearance. Also contemplated as a part of the present invention
is
a method of manufacturing the foamed-wall container having a non-transparent
appearance.
BACKGROUND OF THE INVENTION
[0003] Biaxially oriented single and multi-layered bottles may be
manufactured from polymer materials such as, for example, polyethylene
terephthalate (PET) using a hot preform process, wherein a single or multi-
layered preform is heated to its desired orientation temperature and drawn and
blown into conformity with a surrounding mold cavity. The preform may be
prepared by any conventional process such as, for example, by extruding a
preform comprising single or multiple layers of polymer, or by injecting
subsequent layers of polymer over a previously injection molded preform.
Generally, multiple layers are used for beverage containers, to add diffusion
barrier properties not generally found in single layer containers.
[0004] The various layers of polymers in the prior art multi-layered
containers
are generally in intimate contact with one another, thereby facilitating the
conduct
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of thermal energy through the walls of the containers. This allows the chilled
contents of the container to quickly warm to the ambient temperature.
Accordingly, such containers are often sheathed in, for example, a foamed
polystyrene shell to impart thermal insulating properties to the container.
[0005] It would be desirable to prepare an improved plastic container which is
opaque with unique visual properties without the addition of a coloring agent.
Further, it is deemed desirable to impart thermal insulating properties to the
improved plastic container. Also, it would be desirable to prepare an improved
plastic container having a non-transparent appearance without requiring the
addition of a coloring agent which would adversely affect the recycling
characteristics of the container.
SUMMARY OF THE INVENTION
[0006] Concordant and congruous with the present invention, a foamed-wall
container having a unique appearance has surprisingly been discovered. The
container comprises a micro cellular foamed polymer, and a non-reactive gas
contained within the micro cellular foam cells, wherein the container has a
non-
transparent appearance without the addition of a coloring agent. The colors
contemplated herein include a silvery appearance and a white appearance.
[0007] Also contemplated as an embodiment of the invention is a process for
preparing a foamed-wall container having a unique appearance. The process
comprises the steps of injection molding a polymer preform having a non-
reactive
gas entrapped within the walls thereof, cooling the preform to a temperature
below the polymer softening temperature, reheating the preform to a
temperature
above the polymer softening temperature, and blow molding the preform, to
prepare a container comprising a micro cellular foamed polymer having a non-
reactive gas contained within the micro cellular foam cells, wherein the
container
has a non-transparent appearance.
[0008] The container according to the present invention is particularly useful
for packaging carbonated beverages.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0009] The present invention is directed to a foamed-wall container having a
unique appearance, comprising a micro cellular foamed polymer, and a non-
reactive gas contained within the micro cellular foam cells, wherein the
container
has a silvery appearance.
[0010] Another embodiment of the present invention is directed to a process
for making a foamed-wall container having a unique appearance, comprising
injection molding a polymer preform having a non-reactive gas entrapped within
the walls thereof, cooling the preform to a temperature below the polymer
softening temperature, reheating the preform to a temperature above the
polymer
softening temperature, and blow molding the preform, to prepare a container
comprising a micro cellular foamed polymer having a non-reactive gas contained
within the micro cellular foam cells, wherein the container has a silvery
appearance.
[0011] Another embodiment of the present invention is direction to a a
foamed-wall container having a unique appearance, comprising a micro cellular
foamed polymer, and a non-reactive gas contained within the micro cellular
foam
cells, wherein the container has a white appearance.
[0012] Another embodiment of the present invention is directed to a process
for making a foamed-wall container having a unique appearance, comprising
injection molding a polymer preform having a non-reactive gas entrapped within
the walls thereof, cooling the preform to a temperature below the polymer
softening temperature, reheating the preform to a temperature above the
polymer
softening temperature, and blow molding the preform, to prepare a container
comprising a micro cellular foamed polymer having a non-reactive gas contained
within the micro cellular foam cells, wherein the container has a white
appearance.
[0013] Suitable polymers from which the container may be prepared include,
but are not necessarily limited to, polyethylene terephthalate (PET) and other
polyesters, polypropylene, acrylonitrile acid esters, vinyl chlorides,
polyolefins,
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polyamides, and the like, as well as derivatives, blends, and copolymers
thereof.
A suitable polymer for commercial purposes is PET.
[0014] Polymer flakes are melted in a conventional plasticizing screw
extruder, to prepare a homogeneous stream of hot polymer melt at the extruder
discharge. Typically, the temperature of the polymer melt stream discharged
from the extruder ranges from about 225 degrees Centigrade to about 325
degrees Centigrade. One ordinarily skilled in the art will appreciate that the
temperature of the polymer melt stream will be determined by several factors,
including the kind of polymer flakes used, the energy supplied to the extruder
screw, etc. As an example, PET is conventionally extruded at a temperature
from about 260 degrees Centigrade to about 290 degrees Centigrade. A non-
reactive gas is injected under pressure into the extruder mixing zone, to
ultimately cause the entrapment of the gas as micro cellular voids within the
polymer material. By the term "non-reactive gas" as it is used herein is meant
a
gas that is substantially inert vis-a-vis the polymer. Preferred non-reactive
gases
comprise carbon dioxide, nitrogen, and argon, as well as mixtures of these
gases
with each other or with other gasses.
[0015] According to the present invention, the extrudate is injection molded
to
form a polymer preform having the non-reactive gas entrapped within the walls
thereof. Methods and apparatus for injection molding a polymer preform are
well-known in the art.
[0016] It is well-known that the density of amorphous PET is 1.335 grams per
cubic centimeter. It is also known that the density of PET in the melt phase
is
about 1.200 grams per cubic centimeter. Thus, if the preform injection cavity
is
filled completely with molten PET and allowed to cool, the resulting preform
would not exhibit the proper weight and would have many serious deficiencies,
such as sink marks. The prior art injection molding literature teaches that,
in
order to offset the difference in the densities of amorphous and molten PET, a
small amount of polymer material must be added to the part after the cavity
has
been filled and as the material is cooling. This is called the packing
pressure.
Thus, about ten per cent more material must be added during the packing
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pressure phase of the injection molding cycle in order to insure that a
preform
made by injection molding is filled adequately and fully formed. The packing
pressure phase of the injection molding operation is likewise used for polymer
materials other than PET.
[0017] According to the present invention however, the polymer preform is
injection molded and simultaneously foamed using a non-reactive gas. The gas
is entrained in the material during the injection phase. Contrary to the prior
art
injection molding process, wherein additional polymer material is injected
during
the packing phase, the present invention utilizes minimal packing pressure. As
the polymer material is still in a molten state, the partial pressure of the
non-
reactive gas is sufficient to permit the release of the dissolved gas from the
polymer into the gas phase where it forms the micro cellular foam structure.
Thus, the preform made by the inventive process weighs less than, but has the
same form and geometry as, the polymer preforms produced by the conventional
injection molding operations that employ the packing process.
[0018] The micro cells may contain one or more of a variety of gases typically
used in processes for making micro cellular foam structures. In one
commercially acceptable embodiment, the non-reactive gas comprises carbon
dioxide in a concentration of at least ten percent by weight of the total
weight of
the non-reactive gas. This level of carbon dioxide concentration provides
adequate partial pressure to retard the diffusion of carbon dioxide from a
carbonated beverage within the inventive container to the exterior atmosphere.
Depending on certain injection and blow molding parameters which control the
size of the micro cells, the micro cellular foam tends to act as an effective
thermal
insulator, to retard the conduct of heat energy from the atmosphere to the
chilled
carbonated beverage within the container.
[0019] Upon completion of the injection molding step, the preform is cooled to
a temperature below the polymer softening temperature. For example, the
softening temperature for PET is approximately 70 degrees Centigrade. Thus,
the entrapped non-reactive gas is retained within the walls of the polymer
preform. This cooling step conditions the polymer and preserves its desirable
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properties for the successful preparation of a blow molded container. This
cooling step is also useful when employing polymers such as polyesters, which
cannot be blow molded directly from an extruded parison. This cooling step may
be effected by any conventional process used in the polymer forming art such
as,
for example, by passing a stream of a cooling gas over the surfaces of the
preform, or cooling the preform while in-mold by cooling the forming mold.
[0020] The preform is thereafter reheated to a temperature above the polymer
softening temperature. This heating step may be effected by well-known means
such as, for example, by exposure of the preform to a hot gas stream, by flame
impingement, by exposure to infra-red energy, by passing the preform through a
conventional oven, or the like. PET is generally reheated to a temperature
twenty to twenty-five degrees above its softening temperature for the
subsequent
blow molding operation. If PET is reheated too far above its glass transition
temperature, or held at a temperature above its softening temperature for an
excessive period of time, the PET undesirably will begin to crystallize and
turn
white. Likewise, if the preform is heated to a temperature above which the
mechanical properties of the material are exceeded by the increasing pressure
of
the non-reactive gas in the micro cells, the micro cells undesirably will
begin to
expand thus distorting the preform.
[0021] Finally, the preform is blow molded, to prepare a container, consisting
essentially of a micro cellular foamed polymer having a non-reactive gas
contained within the micro cellular foam cells. Methods and apparatus for blow
molding a container from a polymer preform are well-known.
[0022] The blow molded foamed-wall polymer container so produced has a
silvery appearance; as though the container were made of metal. The blow
molded container is silvery in color, and may exhibit Pantone Color Formula
Guide numbers in the range of about 420 through 425, 877, 8001, 8400, and
8420. In terms of the CIE L*a*b* Color Scale, the blow molded container is
silvery in color, and may exhibit L* values in the range of about 30 through
36, a*
values in the range of about 0.10 through 0.35, and b* values in the range of
about 2.40 through 3.70. While not wishing to be bound by any particular
theory
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regarding the reason that the ultimately produced container has a unique
silvery
appearance, it is believed that, as the preform cavity is being filled with
polymer,
bubbles of gas are formed at the flow front of the polymer due to the pressure
drop between the dissolved gas and the relatively lower pressure in the
preform
cavity. The bubbles formed at the flow front of the polymer material as it is
introduced into the preform cavity are subsequently deposited on the outside
and
inside surfaces of the preform.
[0023] According to another embodiment of the invention, polymer flakes are
melted in a conventional plasticizing screw extruder, to prepare a homogeneous
stream of hot polymer melt at the extruder discharge. Typically, the
temperature
of the polymer melt stream discharged from the extruder ranges from about 225
degrees Centigrade to about 325 degrees Centigrade. One ordinarily skilled in
the art will appreciate that the temperature of the polymer melt stream will
be
determined by several factors, including the kind of polymer flakes used, the
energy supplied to the extruder screw, etc. As an example, PET is
conventionally extruded at a temperature from about 260 degrees Centigrade to
about 290 degrees Centigrade. A non-reactive gas is injected under pressure
into the extruder mixing zone, to ultimately cause the entrapment of the gas
as
micro cellular voids within the polymer material. By the term "non-reactive
gas"
as it is used herein is meant a gas that is substantially inert vis-a-vis the
polymer.
Preferred non-reactive gases comprise carbon dioxide, nitrogen, and argon, as
well as mixtures of these gases with each other or with other gasses.
[0024] The extrudate is injection molded to form a polymer preform having the
non-reactive gas entrapped within the walls thereof. Methods and apparatus for
injection molding a polymer preform are well-known in the art.
[0025] According to the present invention, the polymer preform is injection
molded and simultaneously foamed using a non-reactive gas to utilize minimal
packing pressure. The gas is entrained in the material during the injection
phase. Contrary to the prior art injection molding process herein, wherein
additional polymer material is injected during the packing phase, the present
invention utilizes minimal packing pressure. As the polymer material is still
in a
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molten state, the partial pressure of the non-reactive gas is sufficient to
permit
the release of the dissolved gas from the polymer into the gas phase where it
forms the micro cellular foam structure. Thus, the preform made by the
inventive
process weighs less than, but has the same form and geometry as, the polymer
preforms produced by the conventional injection molding operations that employ
the packing process. It is understood that the micro cells may contain one or
more of a variety of gases typically used in processes for making micro
cellular
foam structures.
[0026] Upon completion of the injection molding step, the preform is cooled to
a temperature below the polymer softening temperature. For example, the
softening temperature for PET is approximately 70 degrees Centigrade. Thus,
the entrapped non-reactive gas is retained within the walls of the polymer
preform. This cooling step conditions the polymer and preserves its desirable
properties for the successful preparation of a blow molded container. This
cooling step is also useful when employing polymers such as polyesters, which
cannot be blow molded directly from an extruded parison. This cooling step may
be effected by any conventional process used in the polymer forming art such
as,
for example, by passing a stream of a cooling gas over the surfaces of the
preform, or cooling the preform while in-mold by cooling the forming mold.
[0027] The preform is thereafter reheated to a temperature above the polymer
softening temperature. This heating step may be effected by well-known means
such as, for example, by exposure of the preform to a hot gas stream, by flame
impingement, by exposure to infra-red energy, by passing the preform through a
conventional oven, or the like. PET is generally reheated to a temperature
twenty to twenty-five degrees above its softening temperature for the
subsequent
blow molding operation. If PET is reheated too far above its glass transition
temperature, or held at a temperature above its softening temperature for an
excessive period of time, the PET undesirably will begin to crystallize and
turn
white. Likewise, if the preform is heated to a temperature above which the
mechanical properties of the material are exceeded by the increasing pressure
of
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the non-reactive gas in the micro cells, the micro cells undesirably will
begin to
expand thus distorting the preform.
[0028] Finally, the preform is blow molded, to prepare a container, consisting
essentially of a micro cellular foamed polymer having a non-reactive gas
contained within the micro cellular foam cells. Methods and apparatus for blow
molding a container from a polymer preform are well-known.
[0029] The blow molded foamed-wall polymer container so produced has a
silvery appearance. The appearance of the blow molded container may vary as
the non-reactive gas in the mirco cells comprises a concentration of carbon
dioxide in excess of ten percent by weight of the total weight of the non-
reactive
gas. As the amount of carbon dioxide or other non-reactive in the micro cells
increases, the appearance of the resultant blow molded container will
transition
from a silvery appearance to a white appearance. The blow molded container
with a white appearance may exhibit CIE L*a*b* Color Scale numbers in the
ranges of: L* values in the range of about 41.5 through 46.0, a* values in the
range of about 0.10 through 0.25, and b* values in the range of about 2.20
through 3.10. While not wishing to be bound by any particular theory regarding
the reason that the ultimately produced container has a unique silvery
appearance, it is believed that, as the preform cavity is being filled with
polymer,
bubbles of gas are formed at the flow front of the polymer due to the pressure
drop between the dissolved gas and the relatively lower pressure in the
preform
cavity. The bubbles formed at the flow front of the polymer material as it is
introduced into the preform cavity are subsequently deposited on the outside
and
inside surfaces of the preform.
[0030] From the forgoing description, one ordinarily skilled in the art can
easily ascertain the essential characteristics of the invention, and without
departing from its spirit and scope, can make various changes and
modifications
to adapt the invention to various uses and conditions.
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