MOLD DELAY FOR INCREASED PRESSURE FOR FORMING CONTAINER
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Utility Application No.
13/230,246, filed on September 12, 201 1, and the benefit of U.S. Provisional
Application No. 61/382,1 23, filed on September 13, 201 0. The entire disclosures
of the above applications are incorporated herein by reference.
FIELD
[0002] This disclosure generally relates to molds for filling containers
with a commodity, such as a liquid commodity. More specifically, this disclosure
relates to molds for filling blown polyethylene terephthalate (PET) containers and
methods of using the same to increase pressure for forming containers.
BACKGROUND
[0003] This section provides background information related to the
present disclosure which is not necessarily prior art.
[0004] As a result of environmental and other concerns, plastic
containers, more specifically polyester and even more specifically polyethylene
terephthalate (PET) containers are now being used more than ever to package
numerous commodities previously supplied in glass containers. Manufacturers
and fillers, as well as consumers, have recognized that PET containers are
lightweight, inexpensive, recyclable and manufacturable in large quantities.
[0005] Blow-molded plastic containers have become commonplace in
packaging numerous commodities. PET is a crystallizable polymer, meaning
that it is available in an amorphous form or a semi-crystalline form. The ability of
a PET container to maintain its material integrity relates to the percentage of the
PET container in crystalline form, also known as the "crystallinity" of the PET
container. The following equation defines the percentage of crystallinity as a
volume fraction:
% Crystallinity =
where p is the density of the PET material; pa is the density of pure amorphous
PET material ( 1 .333 g/cc); and p is the density of pure crystalline material
( 1 .455 g/cc).
[0006] Container manufacturers use mechanical processing and
thermal processing to increase the PET polymer crystallinity of a container.
Mechanical processing involves orienting the amorphous material to achieve
strain hardening. This processing commonly involves stretching an injection
molded PET preform along a longitudinal axis and expanding the PET preform
along a transverse or radial axis to form a PET container. The combination
promotes what manufacturers define as biaxial orientation of the molecular
structure in the container. Manufacturers of PET containers currently use
mechanical processing to produce PET containers having approximately 20%
crystallinity in the container's sidewalk
[0007] Thermal processing involves heating the material (either
amorphous or semi-crystalline) to promote crystal growth. On amorphous
material, thermal processing of PET material results in a spherulitic morphology
that interferes with the transmission of light. In other words, the resulting
crystalline material is opaque, and thus, generally undesirable. Used after
mechanical processing, however, thermal processing results in higher
crystallinity and excellent clarity for those portions of the container having biaxial
molecular orientation. The thermal processing of an oriented PET container,
which is known as heat setting, typically includes blow molding a PET preform
against a mold heated to a temperature of approximately 250°F - 350°F
(approximately 12 1°C - 177°C), and holding the blown container against the
heated mold for approximately two (2) to five (5) seconds. Manufacturers of PET
juice bottles, which must be hot-filled at approximately 185°F (85 °C), currently
use heat setting to produce PET bottles having an overall crystallinity in the
range of approximately 25% -35%.
SUMMARY
[0008] This section provides a general summary of the disclosure, and
is not a comprehensive disclosure of its full scope or all of its features.
[0009] According to the principles of the present disclosure, a method
of fluid forming a container is provided. The method comprises positioning a
plastic preform into a mold cavity, wherein the mold cavity defines a first
configuration and a first volume. The method further includes injecting a fluid
within the plastic preform at a first fluid pressure urging the plastic preform into an
expanded shape. The method includes actuating the mold cavity into a second
configuration and a second volume, whereby the second volume is smaller than
the first volume, thereby resulting in a second fluid pressure within the plastic
preform being greater than the first fluid pressure.
[0010] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples in this
summary are intended for purposes of illustration only and are not intended to
limit the scope of the present disclosure.
DRAWINGS
[001 1] The drawings described herein are for illustrative purposes only
of selected embodiments and not all possible implementations, and are not
intended to limit the scope of the present disclosure.
[0012] FIG. 1 is a graph illustrating pressure versus time for a fluid
pressure within a container being formed in a conventional manner; and
[0013] FIG. 2 is a graph illustrating pressure versus time for a fluid
pressure within a container being formed according to the principles of the
present teachings.
[0014] Corresponding reference numerals indicate corresponding parts
throughout the several views of the drawings.
DETAILED DESCRIPTION
[0015] Example embodiments will now be described more fully with
reference to the accompanying drawings. Example embodiments are provided
so that this disclosure will be thorough, and will fully convey the scope to those
who are skilled in the art. Numerous specific details are set forth such as
examples of specific components, devices, and methods, to provide a thorough
understanding of embodiments of the present disclosure. It will be apparent to
those skilled in the art that specific details need not be employed, that example
embodiments may be embodied in many different forms and that neither should
be construed to limit the scope of the disclosure.
[0016] The terminology used herein is for the purpose of describing
particular example embodiments only and is not intended to be limiting. As used
herein, the singular forms "a", "an" and "the" may be intended to include the
plural forms as well, unless the context clearly indicates otherwise. The terms
"comprises," "comprising," "including," and "having," are inclusive and therefore
specify the presence of stated features, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of one or more
other features, integers, steps, operations, elements, components, and/or groups
thereof. The method steps, processes, and operations described herein are not
to be construed as necessarily requiring their performance in the particular order
discussed or illustrated, unless specifically identified as an order of performance.
It is also to be understood that additional or alternative steps may be employed.
[0017] When an element or layer is referred to as being "on", "engaged
to", "connected to" or "coupled to" another element or layer, it may be directly on,
engaged, connected or coupled to the other element or layer, or intervening
elements or layers may be present. In contrast, when an element is referred to
as being "directly on," "directly engaged to", "directly connected to" or "directly
coupled to" another element or layer, there may be no intervening elements or
layers present. Other words used to describe the relationship between elements
should be interpreted in a like fashion (e.g., "between" versus "directly between,"
"adjacent" versus "directly adjacent," etc.). As used herein, the term "and/or"
includes any and all combinations of one or more of the associated listed items.
[0018] Although the terms first, second, third, etc. may be used herein
to describe various elements, components, regions, layers and/or sections,
these elements, components, regions, layers and/or sections should not be
limited by these terms. These terms may be only used to distinguish one
element, component, region, layer or section from another region, layer or
section. Terms such as "first," "second," and other numerical terms when used
herein do not imply a sequence or order unless clearly indicated by the context.
Thus, a first element, component, region, layer or section discussed below could
be termed a second element, component, region, layer or section without
departing from the teachings of the example embodiments.
[0019] Spatially relative terms, such as "inner," "outer," "beneath",
"below", "lower", "above", "upper" and the like, may be used herein for ease of
description to describe one element or feature's relationship to another
element(s) or feature(s) as illustrated in the figures. Spatially relative terms may
be intended to encompass different orientations of the device in use or operation
in addition to the orientation depicted in the figures. For example, if the device in
the figures is turned over, elements described as "below" or "beneath" other
elements or features would then be oriented "above" the other elements or
features. Thus, the example term "below" can encompass both an orientation of
above and below. The device may be otherwise oriented (rotated 90 degrees or
at other orientations) and the spatially relative descriptors used herein
interpreted accordingly.
[0020] The present teachings provide for a blow mold device and
method of using the same to increase molding pressure for forming containers.
The blow mold design and method of the present teachings, unlike conventional
molds and methods, provides increased fluid pressure within the container being
formed for improved manufacturing.
[0021] As will be discussed in greater detail herein, the shape of the
mold of the present teachings and the container formed therewith can be formed
according to any one of a number of variations. By way of non-limiting example,
the mold of the present disclosure can be configured to hold any one or more of
a plurality of containers and be used in connection with a number of fluids and
commodities, such as beverages, food, or other hot-fill type materials, cold fill
materials, aseptic, carbonated, or just air.
[0022] It should be appreciated that the size and the exact shape of
the mold are dependent on the size of the container and the required operational
parameters. Therefore, it should be recognized that variations can exist in the
presently described designs. According to some embodiments, it should also be
recognized that the mold can comprise various features for use with containers
having vacuum absorbing features or regions, such as panels, ribs, slots,
depressions, and the like.
[0023] The present teachings relate to the forming of one-piece plastic,
e.g. polyethylene terephthalate (PET), PP, Polyethylene, or any other
thermoplastic resin capable of being injection blow molded, containers.
Generally, these containers, after formation, generally define a body that
includes an upper portion having a cylindrical sidewall forming a finish. Integrally
formed with the finish and extending downward therefrom is a shoulder portion.
The shoulder portion merges into and provides a transition between the finish
and a sidewall portion. The sidewall portion extends downward from the
shoulder portion to a base portion having a base. An upper transition portion, in
some embodiments, may be defined at a transition between the shoulder portion
and the sidewall portion. A lower transition portion, in some embodiments, may
be defined at a transition between the base portion and the sidewall portion.
[0024] The exemplary container may also have a neck. The neck may
have an extremely short height, that is, becoming a short extension from the
finish, or an elongated height, extending between the finish and the shoulder
portion. The upper portion can define an opening. Although the container is
shown as a drinking container and a food container, it should be appreciated that
containers having different shapes, such as sidewalls and openings, can be
made according to the principles of the present teachings.
[0025] The finish of the plastic container may include a threaded
region having threads, a lower sealing ridge, and a support ring. The threaded
region provides a means for attachment of a similarly threaded closure or cap
(not illustrated). Alternatives may include other suitable devices that engage the
finish of the plastic container, such as a press-fit or snap-fit cap, or a heat
induction seal, or other means of closing the container for example. Accordingly,
the closure or cap (not illustrated) engages the finish to preferably provide a
hermetical seal of the plastic container. The closure or cap (not illustrated) is
preferably of a plastic or metal material conventional to the closure industry and
suitable for subsequent thermal processing or withstanding the pressures
required by the commodity or process that the container is filled.
[0026] The container can be formed according to the principles of the
present teachings. A preform version of container includes a support ring, which
may be used to carry or orient the preform through and at various stages of
manufacture. For example, the preform may be carried by the support ring, the
support ring may be used to aid in positioning the preform in a mold cavity, or the
support ring may be used to carry an intermediate container once molded. At
the outset, the preform may be placed into the mold cavity such that the support
ring is captured at an upper end of the mold cavity. In general, the mold cavity
has an interior surface corresponding to a desired outer profile of the blown
container. More specifically, the mold cavity according to the present teachings
defines a body forming region, an optional moil forming region and an optional
opening forming region. Once the resultant structure, hereinafter referred to as
an intermediate container, has been formed, any moil created by the moil
forming region may be severed and discarded. It should be appreciated that the
use of a moil forming region and/or opening forming region are not necessarily in
all forming methods.
[0027] In one example, a machine places the preform heated to a
temperature between approximately 190°F to 250 °F (approximately 88 °C to
12 1 °C) (for PET, other ranges for alternate materials in accordance with the
chosen material) into the mold cavity. The mold cavity may be heated to a
temperature between approximately 250°F to 350°F (approximately 12 1 °C to
177°C) (or less or more depending on the resin, the process, and end product
desired). In some embodiments, an internal stretch rod apparatus stretches or
extends the heated preform within the mold cavity to a length approximately that
of the intermediate container thereby molecularly orienting the polyester material
in an axial direction generally corresponding with the central longitudinal axis of
the container. While the stretch rod extends the preform, fluid having a pressure
between 300 PSI to 600 PSI (2.07 MPa to 4.1 4 MPa) assists in extending the
preform in the axial direction and in expanding the preform in a circumferential or
hoop direction thereby substantially conforming the material to the shape of the
mold cavity and further molecularly orienting the material in a direction generally
perpendicular to the axial direction, thus establishing the biaxial molecular
orientation of the material in most of the intermediate container. The pressurized
air holds the mostly biaxial molecularly oriented material against the mold cavity
for a period of approximately one ( 1 ) to five (5) seconds before removal of the
intermediate container from the mold cavity. This process is known as heat
setting and results in a heat-resistant container suitable for filling with a product
at high temperatures.
[0028] In some embodiments, pressurized liquid can be injected into
the preform to urge the preform into its final shape. To achieve a desired final
shape, fluid pressure typically needs to be selected that is sufficiently high to
urge the preform into all portions of the mold cavity. Conventionally, depending
on the container to be formed and the difficulty of the desired shape, increased
fluid pressure may be necessary. However, obtaining these increased fluid
pressures may require costly upgrades in pumps and necessary machinery.
[0029] However, according to the principles of the present teachings,
increased fluid pressure can be achieved through the mechanical actuation of
the mold. That is, according to the principles of the present teachings, during a
liquid filling and forming process, a portion of the mold, such as the base
mechanism, can be retracted or otherwise extended away from the preform to
provide increased internal mold cavity volume. As the container is formed, the
pressure within the container begins to build in response to the fluid pressure of
the forming fluid. As the inflation process of the container nears its end
(potentially culminating in a pressure spike due to water hammer or hydraulic
shock), the base mechanism or other mold portion can be actuated to decrease
the volume of the mold cavity while simultaneously sealing the fluid from exiting
the mold cavity. The volume displacement (i.e. reduction) of the mold cavity
increases the pressure of the fluid within the container preform within the mold
cavity as the mold moves from a retracted position to a compressed position. In
this way, the fluid pressure within the container preform is mechanically
increased through the reduced volume displacement of the mold cavity, thereby
resulting in an internal fluid pressure within the mold cavity that is substantially
higher than that which could be achieved simply through fluid pumping capacity.
In other words, according to the principles of the present teachings, the fluid
pumps used for pumping the fluid within the mold cavity can be reduced in size
and cost without resulting in decreased fluid formation pressures. These fluid
formation pressures are thus still achieved through the mechanical volume
displacement of the mold cavity. The present teachings provide cost savings in
equipment purchase without sacrificing forming pressures and capability.
[0030] As can be seen in the graphs of FIGS. 1 and 2, employing the
principles of the present teachings and produce increased fluid pressure. By
way of non-limiting example, it can be seen that the final fluid pressure according
to the present teachings (FIG. 2) can be greater than about 120 psi compared to
techniques not employing the push-up or overstroke technique. It should be
noted, however, that in some embodiments it is desirable to minimize the time
between the completion of the fluid injection and the initiation of the mold
closure, generally indicated by the time difference A (FIG. 2). In some
embodiments, it has been found that this time difference A can be less than
about 2 seconds, and in some embodiments, as illustrated in FIG. 2 this time
difference A can be less than about 0.3 seconds. Time difference A can, in
some embodiments, be measured from the peak of a water hammer spike to a
peak of a mold push-up or overstroke.
[0031] In some embodiments, it has been found that in order to
achieve the desired increased fluid pressure within the preform or container, the
movement of the base mechanism can be moved about 10mm to about 15mm.
Although movement ranges above and below this stated range may be
acceptable for various container designs, a 10mm to 15mm range for an
exemplary 64oz round container has achieve the benefits of the present
teachings. In this regard, movement of the base mechanism has resulted in a
volume reduction of about 0.14%. However, this volume reduction can range
from about 0.1 % to about 5%. In many instances, the movement distance and
duration directly affects the quality of the resultant container. In some
embodiments, the base mechanism is actuated before the base is fully formed
and cooled, or unformable into the desired shape. This actuation occurs when
the container is greater than 90% formed and less than 100%. In some
embodiments, this operation results in a final pressure of about 40 bar or within
the range of about 20 bar to about 80 bar. The time duration of movement of the
base mechanism from the start of base mechanism actuation to completion can
be within the range of about 0.02 to 0.2 seconds, or particularly about 0.075
seconds.
[0032] In some embodiments according to the present teachings, a
method of fluid forming a container can comprise (a) positioning a plastic
preform into a mold cavity, (b) closing and sealing the mold cavity (and blow
nozzle) such that the mold cavity defines a first configuration and a first volume
such that a base portion of the mold cavity is in a first position, (c) injecting a
fluid within the plastic preform at a first fluid pressure urging the plastic preform
into an expanded shape against the mold cavity; and (d) moving the base portion
of the mold cavity into a compressed position thereby defining a second
configuration and a second volume of the mold cavity. The second volume is
smaller than the first volume resulting in a second fluid pressure within the
plastic preform being greater than the first fluid pressure. In some embodiments,
the step of moving the base portion of the mold cavity into the compressed
position includes mechanically moving the base portion of the mold cavity into
the compressed position to vary the mold cavity from the first volume to the
second volume. In some embodiments, the step of moving the base portion of
the mold cavity into the compressed position is performed after the step of
injecting the fluid within the plastic preform at the first fluid pressure urging the
plastic preform into the expanded shape against the mold cavity. In some
embodiments, the step of moving the base portion of the mold cavity into the
compressed position is performed at a predetermined time after injecting the
fluid within the plastic preform. This predetermined time can be less than about
2 seconds or even less than about 0.3 seconds. In some embodiments, the
second volume can be about 0.1 % to 5% smaller than the first volume.
[0033] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not intended to be
exhaustive or to limit the invention. Individual elements or features of a
particular embodiment are generally not limited to that particular embodiment,
but, where applicable, are interchangeable and can be used in a selected
embodiment, even if not specifically shown or described. The same may also be
varied in many ways. Such variations are not to be regarded as a departure from
the invention, and all such modifications are intended to be included within the
scope of the invention.

CLAIMS
What is claimed is:
1. A method of fluid forming a container, said method comprising:
positioning a plastic preform into a mold cavity, said mold cavity defining a
first configuration and a first volume;
injecting a fluid within said plastic preform at a first fluid pressure urging said
plastic preform into an expanded shape; and
actuating said mold cavity into a second configuration and a second volume,
said second volume being smaller than said first volume, thereby resulting in a
second fluid pressure within said plastic preform greater than said first fluid
pressure.
2. The method according to Claim 1 wherein said actuating said mold
cavity into said second configuration and said second volume comprises moving a
base portion of said mold cavity from a retracted position to a compressed position
to vary said mold cavity from said first volume to said second volume, said
movement resulting in a compression force being applied to said plastic preform.
3. The method according to Claim 1 wherein said actuating said mold
cavity into said second configuration and said second volume comprises sealing
said mold cavity to generally inhibit said fluid from flowing from said mold cavity
and moving a base portion of said mold cavity from a retracted position to a
compressed position to vary said mold cavity from said first volume to said second
volume.
4. The method according to Claim 1 wherein said actuating said mold
cavity into said second configuration and said second volume comprises
mechanically actuating a base portion of said mold cavity into a compressed
position to vary said mold cavity from said first volume to said second volume.
5. The method according to Claim 1 wherein said actuating said mold
cavity into said second configuration and said second volume is performed after
said injecting said fluid into said plastic preform at said first fluid pressure urging
said plastic preform into said expanded shape.
6. The method according to Claim 1 wherein said actuating said mold
cavity into said second configuration and said second volume is a predetermined
time after said injecting said fluid into said plastic preform at said first fluid pressure
to achieve a predetermined fluid pressure spike.
7. The method according to Claim 6 wherein said predetermined time is
less than about 2 seconds.
8. The method according to Claim 6 wherein said predetermined time is
less than about 0.3 seconds.
9. The method according to Claim 1 wherein said second volume is
about 0.1 % to 5% smaller than said first volume.
10. The method according to Claim 1 wherein said actuating said mold
cavity into said second configuration and said second volume occurs within a time
duration of about 0.02 seconds to about 0.2 seconds.
11. The method according to Claim 1 wherein said actuating said mold
cavity into said second configuration and said second volume occurs within a time
duration of about 0.075 seconds.
12. The method according to Claim 1 wherein said injecting a fluid within
said plastic preform at said first fluid pressure urging said plastic preform into said
expanded shape comprises injecting said fluid within said plastic preform at said
first fluid pressure urging said plastic preform into said expanded shape having a
volume less than 99% of a volume of said mold cavity.
13. The method according to Claim 1 wherein said injecting a fluid within
said plastic preform at said first fluid pressure urging said plastic preform into said
expanded shape comprises injecting said fluid within said plastic preform at said
first fluid pressure urging said plastic preform into said expanded shape having a
volume greater than 90% and less than 99% of a volume of said mold cavity.
14. A method of fluid forming a container, said method comprising:
positioning a plastic preform into a mold cavity;
closing and sealing said mold cavity, said mold cavity defining a first
configuration and a first volume such that a base portion of said mold cavity is in a
first position;
injecting a fluid within said plastic preform at a first fluid pressure urging said
plastic preform into an expanded shape against said mold cavity; and
moving said base portion of said mold cavity into a compressed position
thereby defining a second configuration and a second volume of said mold cavity,
said second volume being smaller than said first volume resulting in a second fluid
pressure within said plastic preform being greater than said first fluid pressure.
15. The method according to Claim 14 wherein said moving said base
portion of said mold cavity into said compressed position comprises mechanically
moving said base portion of said mold cavity into said compressed position to vary
said mold cavity from said first volume to said second volume.
16. The method according to Claim 14 wherein said moving said base
portion of said mold cavity into said compressed position is performed after said
injecting said fluid within said plastic preform at said first fluid pressure urging said
plastic preform into said expanded shape against said mold cavity.
17. The method according to Claim 14 wherein said moving said base
portion of said mold cavity into said compressed position is a predetermined time
after said injecting said fluid within said plastic preform at said first fluid pressure to
achieve a predetermined fluid pressure spike.
18. The method according to Claim 17 wherein said predetermined time
is less than about 2 seconds.
19. The method according to Claim 17 wherein said predetermined time
is less than about 0.3 seconds.
20. The method according to Claim 14 wherein said second volume is
about 0.1 % to 5% smaller than said first volume.
2 1. The method according to Claim 14 wherein said moving said base
portion of said mold cavity into said compressed position occurs within a time
duration of about 0.02 seconds to about 0.2 seconds.
22. The method according to Claim 14 wherein said moving said base
portion of said mold cavity into said compressed position occurs within a time
duration of about 0.075 seconds.
23. The method according to Claim 14 wherein said injecting a fluid
within said plastic preform at said first fluid pressure urging said plastic preform into
said expanded shape comprises injecting said fluid within said plastic preform at
said first fluid pressure urging said plastic preform into said expanded shape
having a volume less than 99% of a volume of said mold cavity.
24. The method according to Claim 14 wherein said injecting a fluid
within said plastic preform at said first fluid pressure urging said plastic preform into
said expanded shape comprises injecting said fluid within said plastic preform at
said first fluid pressure urging said plastic preform into said expanded shape
having a volume greater than 90% and less than 99% of a volume of said mold
cavity.