U.S. patent application number 11/056218 was filed with the patent office on 2005-06-23 for method and apparatus for cooling during in-mold handle attachment.
This patent application is currently assigned to Graham Packaging PET Technologies Inc.. Invention is credited to Krishnakumar, Suppayan M., Piccioli, David.
Application Number | 20050136149 11/056218 |
Document ID | / |
Family ID | 25540794 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050136149 |
Kind Code |
A1 |
Krishnakumar, Suppayan M. ;
et al. |
June 23, 2005 |
Method and apparatus for cooling during in-mold handle
attachment
Abstract
Method and apparatus for in-mold handle attachment, wherein a
portion of a blow-molded container is formed about a retaining
member on a handle during blow molding. After forming the container
portion about the retaining member, a cooling medium is directed at
the location of the container portion in order to accelerate the
cooling rate at the container portion. There is achieved at least
one of an improvement in the security of the attachment of the
handle to the container, and a reduction in the blow-mold
processing time.
Inventors: |
Krishnakumar, Suppayan M.;
(Nashua, NH) ; Piccioli, David; (Auburn,
NH) |
Correspondence
Address: |
KUDIRKA & JOBSE, LLP
ONE STATE STREET
SUITE 800
BOSTON
MA
02109
US
|
Assignee: |
Graham Packaging PET Technologies
Inc.
York
PA
|
Family ID: |
25540794 |
Appl. No.: |
11/056218 |
Filed: |
February 11, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11056218 |
Feb 11, 2005 |
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09994555 |
Nov 27, 2001 |
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6855289 |
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Current U.S.
Class: |
425/526 ;
425/535 |
Current CPC
Class: |
B29L 2031/7126 20130101;
B29C 2049/2017 20130101; B29C 2049/5837 20130101; B29C 2049/6623
20130101; B29C 49/20 20130101; B29C 2049/2039 20130101; B29C 49/783
20130101; B29C 49/58 20130101; B29C 2049/6676 20130101; B29C
2049/4846 20130101; B29L 2031/7158 20130101; B29K 2067/00 20130101;
B29C 2049/6615 20130101; B29L 2031/463 20130101; B29C 49/06
20130101; B29C 49/66 20130101; B29C 49/12 20130101; B29K 2995/0041
20130101 |
Class at
Publication: |
425/526 ;
425/535 |
International
Class: |
B29C 049/58; B29C
049/64 |
Claims
1-7. (canceled)
8. An improved blow-molding apparatus of the type including a
stretch rod and blow-molding cavity, the improvement comprising:
the stretch rod having at least one port for directing a cooling
medium against a portion of a blow-molded container formed about a
handle in the blow-molding cavity.
9. The apparatus of claim 8, including a partial exhaust for
promoting flow of the cooling medium at the container portion.
10. The apparatus of claim 8, including: at least one high-pressure
source for supplying an expansion medium during blow-molding and
for supplying the cooling medium; and an exhaust promoting a flow
of the cooling medium in the blow-molding cavity.
11. The apparatus of claim 10, including at least one low-pressure
source for supplying a low-pressure expansion medium during a
preliminary expansion step.
12. The apparatus of claim 11, wherein the exhaust includes a slow
exhaust for promoting flow of the cooling medium and a rapid
exhaust for exhausting the blow-molding expansion medium.
13. A stretch rod for use in a blow-molding cavity, the stretch rod
including at least one port located at at least one select location
for directing a cooling medium against a portion of a blow-molded
container formed about a handle in the blow-molding cavity.
14-28. (canceled)
29. A stretch rod for a blow mold apparatus, the stretch rod
including at least one port located for directing a cooling medium
against a portion of a blow-molded container formed about a handle
in the blow mold.
30. The apparatus of claim 29, further including a source for
supplying the cooling medium to the stretch rod.
31. The apparatus of claim 29, further including a high pressure
source for supplying an expansion medium to the stretch rod.
32. The apparatus of claim 29, further including an exhaust for
promoting flow of the cooling medium to the blow mold.
33. The apparatus of claim 32, wherein the exhaust includes a slow
exhaust for promoting flow of the cooling medium and a rapid
exhaust for exhausting an expansion medium.
34. The apparatus of claim 29, comprising: at least one
high-pressure source for supplying an expansion medium to the blow
mold and for supplying the cooling medium; and an exhaust promoting
the flow of the cooling medium in the blow mold.
35. The apparatus of claim 29, including at least one low-pressure
source for supplying a low-pressure expansion medium during a
preliminary expansion of the container.
Description
DESCRIPTION OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to handled plastic containers,
wherein a handle is separately formed and then connected to a
container during the container blow-molding process, and more
particularly to an apparatus and method for cooling the handle
attachment portion(s) to improve one or more of the efficiency of
the blow-molding process and the integrity of the handle
attachment.
BACKGROUND OF THE INVENTION
[0003] Plastic containers for holding liquids such as beverages,
and other household items such as detergents, are in widespread
use. Plastics such as polyethylene terephthalate (PET) can offer
lightweight convenience, durability and transparency.
[0004] Larger-sized plastic containers, such as one- or two-liter
plastic containers, are typically provided with a handle for ease
of pouring. However, because of the increased weight of such
larger-sized containers, achieving secure handle attachment is
difficult. Also, a special mold is required in the production of
such bottles, as they are more difficult to blow mold than a
non-handled bottle, e.g., difficulties arise with stress
concentrations leading to possible container failure in areas near
the junction of the handle with the rest of the container.
[0005] Various attempts have been made to attach separate handles
to blow-molded containers formed from preforms, but these
attachment methods may not be successful in all applications. In
one method, a handle is connected to a plastic container by blow
molding the walls of the container around retaining portions
provided at opposing ends of the handle. This method is described
for example in PCT Publication WO97/43108 published 20 Nov. 1997
and assigned to Continental PET Technologies, Inc. In general, the
goals are to attach a separate handle to a plastic blow-molded
container by a method which enables relatively simple and rapid
manufacture and which method leads to the production of a handled
bottle having the handle firmly secured in position.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, an apparatus and
method are provided which allow enhanced in-mold cooling of select
locations of a blow-molded container by directing a cooling medium
at those locations. More specifically, the selected locations are
those portion(s) of the blow-molded container which engage
retaining member(s) on the handle during the blow-molding
process.
[0007] In one embodiment, a method of in-mold handle attachment is
provided wherein a portion of the blow-molded container is formed
about a retaining member on the handle during blow molding. After
forming the container portion about the retaining member, a cooling
medium is directed at the location of the container portion formed
about the retaining member in order-to accelerate the cooling rate
at that portion. In a more specific embodiment, the step of blow
molding includes injecting a pressurized medium (e.g., air) to form
the blow-molded container and hold the container in contact with
the mold cavity walls, followed by injecting a cooling medium at
select locations and enabling a partial exhaust to promote air flow
of the cooling medium at the select container locations, while
still maintaining the expanded container in contact with the mold
cavity walls. For example, the mold cavity walls may be heated in
order to thermally condition the container where the intended use
is as a hot-fill container.
[0008] One benefit of this method of in-mold handle attachment is a
reduction in the time for cooling of the blow-molded container
within the mold cavity. In spite of this reduction in cooling time
and resultant reduction in overall blow-molding process time, the
integrity of the handle attachment is maintained and preferably
improved by insuring that the container portion(s) formed about the
retaining member(s) on the handle are sufficiently rigidified prior
to removal of the finished container from the mold to ensure secure
handle attachment.
[0009] In another embodiment, an improved blow-molding apparatus is
provided, which includes a new type of stretch rod for the
blow-molding cavity. The stretch rod has at least one port for
directing a cooling medium against a select portion of the
blow-molded container formed in the blow-molding cavity.
Preferably, the at least one port directs a cooling medium at the
one or more portions of the molded container formed about one or
more retaining members on the handle. The blow-molding apparatus
may further include a partial exhaust circuit to enhance a flow of
the cooling medium in the blow-molding cavity.
[0010] In another embodiment, an improved stretch rod is provided
for use in a blow-molding cavity. The stretch rod includes at least
one port for directing a cooling medium into the blow-molding
cavity, in order to direct cooling air at select portions of the
container being formed about one or more retaining members on the
handle.
[0011] These and other features of the present invention will be
understood from the following detailed description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a graph of air pressure and stretch rod position
on the Y axis, versus time on the X axis, for a prior art
blow-molding process;
[0013] FIG. 2 is a graph of air pressure and stretch rod position
on the Y axis, versus time on the X axis, for one embodiment of a
blow-molding process of the present invention, showing the cooling
air blow with slow exhaust step;
[0014] FIG. 3 is a cross-sectional view of a blow mold with a
preform and handle positioned therein at the start of the
blow-molding process;
[0015] FIG. 4 is a cross-sectional view of the blow mold, similar
to FIG. 3 but later in the process wherein the preform has been
expanded to form the container and cooling air is directed out of
ports on the stretch rod toward the container engagement portions
with the handle; and
[0016] FIG. 5 is an air circuit diagram with three air supply and
two air exhaust lines as utilized in this embodiment of the
blow-molding process.
DETAILED DESCRIPTION
[0017] One embodiment of the present invention will now be
described for blow-molding a one-gallon hot-fillable PET container.
A prior art blow molding process for making such a container will
first be described for purposes of comparison. Additional aspects
of a process for making a hot-fillable container are described in
U.S. Pat. No. 4,863,046 issued 5 Sep. 1989 to Collette et al. and
U.S. Pat. No. 5,704,503 issued 6 Jan. 1998 to Krishnakumar et al.,
each of which are hereby incorporated by reference in their
entirety.
[0018] FIG. 1 is a graph illustrating a prior art blow-molding
process for making a one-gallon PET container. On the vertical Y
axis is indicated both the air pressure in psi within the blow
mold, and the relative stretch rod position (up and down) in the
blow mold. On the horizontal X axis is time in seconds. The graph
illustrates one cycle of the blow-molding process. During this
cycle a container would be blow-molded from a preform in a
blow-molding cavity similar to that shown in FIGS. 3-4.
[0019] There are essentially four stages in the prior art
blow-molding process, summarized below:
1 1. delay 0.4 secs 2. pre-blow 0.2 100-150 psi 3. high pressure
blow 5.0 550-600 4. rapid exhaust 0.3
[0020] At time "zero" on the X axis, a preform and handle have been
positioned in the blow mold and the blow mold cavity is closed.
Next, during a first delay stage of 0.4 seconds, a stretch rod
positioned inside the preform (such as shown in FIG. 3) is moved
downwardly. This causes axial stretching of the preform, where the
preform is at a temperature within the biaxial orientation
temperature range for PET. During a second optional pre-blow stage
of the process, beginning at 0.4 seconds and lasting 0.2 seconds,
low-pressure air is supplied around the stretch rod and within the
preform, such that the air pressure within the preform begins to
slowly rise and the preform begins to radially expand. The stretch
rod continues its downward descent during this second pre-blow
stage. At 0.6 seconds in the process, the end of the pre-blow
stage, the stretch rod has reached its lowest position where the
tip of the stretch rod is holding the central bottom portion of the
preform against the center of the blow mold base. This helps ensure
centering and even expansion of the preform into the container. The
preform is now partially expanded and has an internal air pressure
of 100 to 150 psi.
[0021] The process now enters a third stage, the high-pressure
blow, at 0.6 seconds. A supply of high-pressure air within the
preform is increased so that the preform very rapidly radially
expands to the final container dimensions. It is then held against
the walls of the mold cavity by the high pressure within the
cavity. This rapid expansion occurs on the order of 0.2 seconds and
the internal pressure reaches 550 to 600 psi. This pressure is held
for about five seconds, during which the fully expanded container
is held in contact with the warm walls of the blow mold cavity, in
order to thermally condition the container. This thermal
conditioning increases the amount of crystallization of the PET so
as to provide thermal stability when the container is hot-filled.
The stretch rod remains in its lowermost position holding the
center of the container against the center of the blow mold
base.
[0022] In a fourth stage of the process, beginning at about 5.6
seconds, there is a rapid exhaust of air from within the
blow-molded container, over a period on the order of 0.3 seconds.
At the same time, the stretch rod is contracted upwardly, returning
to its uppermost position. At the end of the fourth stage, the blow
mold cavity can be opened and the container removed from the
mold.
[0023] The blow-molding process of the present invention will now
be described with reference to FIGS. 2-5. FIG. 2 shows five stages
of the present embodiment with respect to air pressure and stretch
rod position over time, as follows:
2 1. delay 0.4 secs 2. pre-blow 0.2 100-150 psi 3. high pressure
blow 1.2 550-600 4. cooling air blow 1.4 450-500 5. rapid exhaust
0.3
[0024] FIG. 3 shows the preform and handle in the blow mold cavity
during the first stage of the process, and FIG. 4 shows the
container and handle within the blow mold during the fourth stage
wherein cooling air is directed to select portions of the container
engaging the handle. FIG. 5 is a schematic illustration of three
air supply lines and two exhaust lines for accomplishing this
embodiment of the blow-molding process.
[0025] At the beginning of the blow-molding process, designated as
time "zero" in FIG. 2, a preform and separate handle are positioned
within the blow-molding cavity as shown in FIG. 3. The preform 10
includes an uppermost neck finish 12 with external threads 14 and a
flange 16 at the bottom end of the neck finish. Below the neck
finish there is a short cylindrical transition (neck
finish-to-body) section 18, followed by a tapered shoulder or
dome-forming portion 20 of increasing thickness. Below this is the
panel-forming section 24 of the preform, which is substantially
cylindrical and of substantially even thickness. At the bottom
there is a closed base-forming section 26 having an upper tapered
section 28 decreasing in wall thickness and a lower generally
hemispherical central bottom portion 30. The preform of this
embodiment is designed in terms of wall thickness, length, width,
etc., for making a one-gallon hot-fillable container in accordance
with the dimensions defined by the blow-molding cavity. The preform
is of a single material and layer, and is made of commercially
available PET having an intrinsic viscosity of about 0.80.
[0026] As shown in FIG. 3, the preform 10 is positioned in a blow
mold unit 215 with a blow nozzle assembly 200 and stretch rod 208
in place for the start of the blow process. In FIG. 3, the stretch
rod 208 has already been extended down into the preform (within the
initial delay stage). The blow nozzle assembly includes a stuffer
(plug) 202 which engages the neck finish of the preform and has an
annular bore 204 for supplying fluid pressure to the interior of
the preform. The blow nozzle assembly further includes a pressure
relief valve (not shown) for controlling the fluid pressure within
the preform during the various expansion steps. The movable stretch
rod 208 enhances uniform expansion of the preform. The mold unit
215 includes a neck plate 216 which engages the flange 16 just
below the neck finish on the preform. An upper mold body 218 has an
inner surface 219 for forming the sidewall (upper dome, panel and
outer base) of the container. A lower mold body 220 has an inner
surface 221 for forming the central base of the container. The mold
portions 216, 218 and 220 are kept at various temperatures to
ensure appropriate thermal conditioning of the various portions of
the container.
[0027] Also positioned within the blow mold is a handle 40. The
handle is transferred into the blow mold by a transfer arm (not
shown but positionable within aperture 225 in the left-hand upper
mold body 218). The handle is held in place by handle-locating
section 223. The handle has an upper end 41 with a support platform
44 which includes an annular top flat surface 46, and an annular
curved inner surface 45 having a radius about the same as that of
an outer wall of the transition portion 18 of the preform, located
immediately below the flange 16. An upper retaining portion 48 is
provided, spaced beneath the support platform 44, and includes a
pair of vertically divergent tabs 49, 50 extending toward the
longitudinal axis 59 of the preform, container and mold cavity. As
later described, blow molding of the preform causes the plastic
material of a portion of the preform wall to be molded about the
upper retaining member 48 in order to hold the upper end 41 of the
handle against the underside of the flange 16. The specific
retaining member 48 shown herein is by way of example only; various
other attachment members of differing shape, size and location can
be utilized as well.
[0028] At a lower end 47 of the handle, below a central connecting
portion 42, is a lower retaining member 51. Member 51 will be
incorporated into a lower portion of the container dome by
blow-molding of the preform around the lower retaining member 51.
Similar to the upper handle retaining portion 48, the lower
retaining portion 51 has a diverging distal end 51 in order to
secure the handle to the container. Again, this is by way of
example only and not limiting.
[0029] At the start of the blow-molding process, the preform 10 is
generally hot, e.g., reheated to be within the orientation
temperature range of PET, except for the cold neck finish 12. The
preform will cool as it expands in the mold, and the mold sections
216, 218 and 220 are kept at different temperatures to control the
percent crystallinity in different portions of the expanded
container. The neck plate 216 engaging the neck finish is generally
kept at, e.g., 100.degree. F., the upper mold body 218 forming the
sidewall is kept warm, e.g., 190.degree. F., and the lower mold
body 220 forming the base of the container is kept cooler, e.g.,
50.degree. F. The expanded shoulder (dome) and panel sections of
the container thus achieve a substantially higher crystallinity
level than the base, which optimizes thermal stability in this
hot-fillable container.
[0030] As previously indicated, a hot-fillable container is
described in U.S. Pat. No. 4,863,046 to Collette et al., issued
Sep. 5, 1989, which is hereby incorporated by reference in its
entirety. Hot fill containers typically must withstand elevated
temperatures on the order of 180-190.degree. F. (the product
filling temperature) and positive internal pressures on the order
of 2-5 psi (the filling line pressure) without substantial
deformation, i.e., a volume change of no greater than about one
percent.
[0031] Returning to FIG. 2, the blow-molding cavity is closed (at
time "zero") and the blow-molding cycle begins with an initial
short delay stage. As previously described, the stretch rod is
extended axially downwardly (along vertical axis 59) to axially
extend the preform during this stage. During a second pre-blow
stage, the stretch rod continues its downward descent while an
initial low pressure air supply gradually increases the pressure
within the preform up to about 100 to 150 psi, over a period of 0.2
seconds. At 0.6 seconds, a third high-pressure blow stage begins,
with an initial rapid expansion of the container up to an internal
pressure of 550 to 600 psi. The container is now fully expanded and
held in contact with the cavity wall for about 1.2 seconds. Then,
in accordance with the present invention, the pressure within the
container is reduced to about 450 to 500 psi, and held for a period
of about 1.4 seconds, by supplying a cooling air flow with a slow
exhaust. As shown in FIG. 4, this cooling air is supplied via a
hollow central axial bore 210 and two air ports 212, 214 within the
stretch rod 208; the cooling air is directed by the ports toward
the two portions 61, 62 of container 60 which have formed around
and tightly engage the upper and low retaining portions 48, 47 of
the handle. This enables preferential cooling of these two portions
61, 62 of the container. This is particularly useful because these
two portions of the container have not been in contact with the
mold cavity walls, and thus are generally at a higher temperature
than the other portions of the container wall, i.e., the cavity
walls preferentially cool those portions of the container wall in
contact with the cavity walls. During this fourth cooling air blow
stage, the container is maintained in contact with the cavity walls
but there is some air flow allowed in order to cool the upper and
lower handle attachment portions 61, 62, based on the slow exhaust
of air from within the container. Again, this enables preferential
cooling of these two portions of the container.
[0032] In the final rapid exhaust stage, beginning at about 3.2
seconds and lasting for about 0.3 seconds, air pressure within the
container is rapidly reduced to zero (ambient) while the stretch
rod contracts to its uppermost position. The rapid exhaust stage is
over at 3.5 seconds and then the blow mold cavity can be opened and
the container removed from the cavity.
[0033] FIG. 5 is an air circuit schematic showing three air supply
lines and two exhaust lines for accomplishing the blow-molding
process as described herein. In this embodiment, each supply or
exhaust line is provided with a valve 102 which is timed to open
and close during the various portions of the cycle. During the
initial blow delay stage, all five air lines 104-108 are closed.
During the second pre-blow stage, the low-pressure air supply line
104 is open to gradually increase the pressure within the preform
and provide an initial radial expansion of the preform. During the
third stage of the process, all four air lines are closed except
for the high-pressure air supply line 105 which supplies
high-pressure air to rapidly expand the preform to the final
container dimensions, and hold it in contact with the cavity walls
for a period of 1.2 seconds. During the fourth cooling air-blow
stage, all lines are closed except for the cooling air line 106
which supplies high-pressure air to the two ports 212, 214 in the
stretch rod, and the slow exhaust line 107 which is open at the
same time to exhaust some of the high-pressure air in order to
provide an air flow about the two portions 61, 62 of the container
being cooled by the cooling air. Finally, during a fifth rapid
exhaust stage of the cycle, all air lines are closed except for the
rapid exhaust line 108 which is opened at the end of the cooling
stage in order to reduce the pressure within the container down to
zero (ambient), before opening the mold.
[0034] During the fourth cooling air blow stage, it is desirable to
provide some air flow in order to cool the two portions of the
container around the upper and lower handle attachment members, but
it is undesirable to drop the pressure within the container
substantially because the container would then pull away from the
cavity wall. This would substantially reduce the cooling occurring
at the cavity walls as well as the thermal conditioning required to
achieve the desired thermal stability in the hot-fillable
container. Also, it would be undesirable to provide a large air
flow by significantly exhausting air from the container as this
would use up large quantities of the high-pressure air, which is a
relatively expensive component of the process.
[0035] In accordance with the invention, there is achieved an
overall reduction in the blow-molding process time, as well as an
improved anchoring of the handle to the container. The reduction in
blow-molding process time is quite significant in the present
embodiment, which is seen by comparing FIGS. 1 and 2. In the prior
art process, the blow-molding process time was 5.9 seconds, whereas
in the embodiment of the present invention, the blow-molding
process time has been reduced to 3.5 seconds. This is a very
significant cost savings in the manufacture of the container.
[0036] In an alternative embodiment, the low pressure pre-blow
stage is eliminated. This would eliminate the need for the low
pressure air supply line. Generally, however, the pre-blow stage is
preferred because it improves the material distribution in the
container.
[0037] In another embodiment, a separate source of cooling air can
be eliminated; instead, the high pressure source is utilized during
the fourth cooling air blow stage, while opening of the slow
exhaust line achieves the desired reduction in air pressure and air
flow.
[0038] In yet another embodiment, additional cooling of the handle
can be achieved by circulating cooling media in the handle locating
section 223 of the blow mold.
[0039] In other embodiments, as previously indicated, the retaining
members on the handle may be of different size, shape and location.
In general, the goal is to achieve a secure connection between the
container wall and retaining members, typically by allowing the
container wall to conform to the external contour of the retaining
member, and also to reduce post-mold deformation at these portions
of the container wall by adequately cooling down the wall material
to its rigid state within the blow mold.
[0040] The container is not limited to either monolayer containers
or PET containers. Various other polymer resins can be used such as
polyesters (in addition to PET), polyolefins, polycarbonates,
nitrites, and copolymers of the same. Polyethylene naphthalate
(PEN) is another useful polymer with physical properties similar to
PET, but provides an improvement in barrier property and thermal
performance. The container may either be a monolayer or multilayer
construction, including layers of for example an oxygen barrier
material, a layer of reprocessed scrap material, or other
high-performance materials.
[0041] The container may not be a hot-fillable container, but
rather can be a carbonated beverage container, juice container,
ketchup container, liquid detergent container, etc.
[0042] The handle may be formed by any well-known technique, such
as injection molding. It is not necessary that it is made from the
same material as the container. It may be formed from a plastic
such as high-density polyethylene, polypropylene, PET, recycled
PET, glass reinforced PET or glass reinforced high-density
polyethylene.
[0043] Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with a
true scope and spirit of the invention being indicated by the
following claims.
* * * * *