Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SLEEVE MULDI~TG
Field of the Invention
The present invention relates to a method and apparatus for
making multilayer injection-molded plastic articles such as preforms,
s wherein the successive molding of an inner sleeve and outer layer enables
cost-effective production of multilayer preforms for pasteurizable, hot-
fillable, and returnable and refillable beverage containers.
Background of the Invention
There is described in ZJ. S. Patent No. 4,609,516 to
to Krishnakumar et al a method for forming multilayer preforms in a single
injection mold cavity. In that method, successive injections of different
thermoplastic materials are made into the bottom of the mold cavity. The
materials flow upwardly to fill the cavity and form, for example, a five-
layer structure across the sidewall. This five-layer structure can be made
15 with either two materials (i.e., the first and third injected materials are
the
same) or three materials (i.e., the first and third injected materials are
different). Both structures are in widespread commercial u.se for beverage
and other food containers.
An example of a two-material, five-layer (2M, 5L) structure has
no inner, outer and core layers of virgin polyethylene terephthalate (PET),
and
intermediate barrier layers of ethylene vinyl alcohol (EVOH). An example
of a three-material, five-layer (3M, 5L) structure has inner and outer layers
of virgin PET, intermediate barrier layers of EVOH, and a core layer of
recycled or post-consumer polyethylene terephthalate (PC-PET). Two
25 reaSOIIS for the commercial success of these containers are that: (1) the
amount of relatively expensive barrier material (e.g., EVOH)
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can be minimized by providing very thin intermediate layers; and (2) the
container resists
delamination of the layers without the use of adhesives to bond the dissimilar
materials. Also, by
utilizing PC-PET in the core layer, the cost of each container can be reduced
without a
significant change in performance.
Although the above five-layer, and other three-layer (see for example U.S.
Patent
4,923,723) structures work well for a variety of containers, as additional
high-performance and
expensive materials become available there is an on-going need for processes
which enable close
control over the amount of materials used in a given container structure. For
example,
polyethylene naphthalate (PEN) is a desirable polyester for use in blow-molded
containers. PEN
JO has an oxygen barrier capability about five times that of PET, and a higher
heat stability
temperature -- about 250°F (120°C) for PEN, compared to about
175°F (g0°C) for PET. These
properties make PEN useful for the storage of oxygen-sensitive products (e.g.,
food, cosmetics,
and pharmaceuticals), and/or for use in containers subject to high
temperatures (e.g., refill or
hot-fill containers). However, PEN is substantially more expensive than PET
and has different
15 processing requirements: Thus, at present the commercial use of PEN is
limited.
Another high-temperature application is pasteurization -- a pasteurizable
container
is filled and sealed at room temperature, and then exposed to an elevated
temperature bath for
about ten minutes or longer. The pasteurization process initially imposes high
temperatures and
positive internal pressures, followed by a cooling process which creates a
vacuum in the
2o container. Throughout these procedures, the sealed container must resist
deformation so as to
remain acceptable in appearance, within a designated volume tolerance, and
without leakage. In
particular, the threaded neck finish must resist deformation which would
prevent a complete seal.
A number of methods have been proposed for strengthening the neck finish. One
approach is to add an additional manufacturing step whereby the neck finish,
of the preform or
25 container, is exposed to a heating element and thermally crystallized.
However, this creates
several problems. During crystallization, the polymer density increases, which
praduces a
volume decrease; therefore, in order to obtain a desired neck finish
dimension, the as-molded
dimension must be larger than the final (crystallized) dimension. It is thus
difficult to achieve
close dimensional tolerances and, in general, the variability of the critical
neck finish dimensions
3o after crystallization are approximately twice that prior to
crystallization. Another detriment is
the increased cost of the additional processing step, as it requires both time
and the application of
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energy (heat). The cost of producing a container is very important because
of competitive pressures and is tightly controlled.
An alternative method of strengthening the neck Enish is to
crystallize select portions thereof, such as the top sealing surface and
flange.
s Again, this requires an additional heating step. Another alternative is to
use
a high glass transition temperature (T~ material in one or more layers of the
neck finish. This also involves more complex injection molding procedures
and apparatus.
Thus, it would be desirable to provide an injection-molded article
zo such as a preform which incorporates certain high-performance materials,
and a commercially acceptable method of manufacturing the same.
FR-A-2538297 to Aoki describes a two-step molding process,
wherein a full-length inner sleeve of PET is formed in a first molding step
on a first core, and the core and sleeve are transferred to a second cavity
is where a full-length outer layer of polycarbonate is molded over the sleeve.
Aoki is directed to providing a specific molding apparatus in which a
plurality of neck molds are mounted for rotational movement on a rotating
platen, and a pair of injection cores are disposed for rotational movement
above inner and outer molding stations, so that one of the injection cores is
a o disposed above that portion of the rotating platen which is in line with
the
stopping position at the neck mold so that one of the injection cores can
pass through one of the neck molds before it is inserted into the inner
molding station.
GB-A-142956 to Bonis describes a two-step molding process,
a s wherein a full-length inner sleeve is formed in a first molding step on a
first
core, and the core and sleeve are transferred to a second cavity where a full
length outer layer is molded over the sleeve.
JP-5-73568 to Mitsubishi describes a two-step molding process,
wherein a full-length inner sleeve of PET is fon~ned at a first molding step
s o on a first core, and the core and sleeve are transferred to a second
cavity
where a full-length outer layer of a mixture of PET and gas barrier resin is
molded over the sleeve. Mitsubishi describes a specifac process having a
very long processing time, i.e., the inner layer is formed of a high
copolymer which is processed for 30 minutes in order to increase the
3 s density. The outer layer includes a gas barrier polymer mixed with PET in
order to improve the adhesion with the inner PET layer.
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Summary of the Invention
The present invention is directed to a method and apparatus for
making a multilayer injection-molded plastic article, such as a preform,
which is both cost-effective and enables control over the amounts of
s materials used in the various layers andlor pardons of the article.
According to a method/embodiment of the invention, an inner
sleeve is molded on a first core positioned in a first mold cavity. The inner
sleeve is only partially cooled before being transferred while still at an
elevated temperature to a second mold cavity where an outer layer is
lo molded over.the inner sleeve. By providing the inner sleeve in the second
mold cavity at the elevated temperature, bonding between the inner sleeve
and outer layer is enabled during the second molding step, such that layer
separation is avoided in the final molded article. The inner sleeve may
comprise a full-length inner sleeve, extending substantially the full length
i5 of the article, or alternatively may comprise only an upper portion of the
article, in which case the outer layer comprises a lower portion of the
article
and there is some intermediate portion in which the outer layer is bonded to
the inner sleeve.
In one embodiment, a first thermoplastic material is used to make
a o an inner sleeve which comprises a neck finish portion of the preforrn. The
first thermoplastic material is preferably a thermal resistant material having
a relatively high Tg, and/or forms a Crystallized neck finish during the first
molding step. In Contrast, a lower body portion of the preform is made of a
second thermoplastic material having a relatively lower thermal resistance
z 5 andlor lower crystallization rate Compared to the first material, and
forms a
substantially amorphous body-forming portion of the preform. In one
example, by achieving crystallization in the neck
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finish during the first molding step, the initial and finish dimensions are
the same so that the
dimensional variations caused by the prior art post-molding crystallization
step (and the expense
thereof) are eliminated. Also, a higher average level of crystallization can
be achieved in the
finish, by utilizing the higher melt temperatures andlor elevated pressures of
the molding
process.
In another embodiment, a full-length body sleeve is provided made of a high-
performance thermoplastic resin, such as PEN homopolymer, copolymer o~r blend.
The PEN
inner sleeve provides enhanced thermal stability and reduced flavor
absorption, both of which are
useful in refill applications. The amount of PEN used is minimized by this
process which
enables production of a very thin inner sleeve layer, compared to a relatively
thick outer layer
(made of one or more lower-performance resins).
Another aspect of the invention is an apparatus for the cost-effective
manufacture
of such preforms. The apparatus includes at least one set of first and second
molding cavities,
the first mold cavity being adapted to form the inner sleeve and the second
mold cavity adapted
to form the outer layer. A transfer mechanism includes at least one set of
first and second cores,
wherein the cores are successively positionable in the first and second
molding cavities. In one
cycle, a first core is positioned in a first mold cavity while a first inner
sleeve is molded on the
first core, while a second core, carrying a previously-molded second inner
sleeve, is positioned in
a second mold cavity, for molding a second outer layer over the second inner
sleeve. By
2o simultaneously molding in two sets of cavities, an efficient process is
provided. By molding
different portions/layers of the articles separately in different cavities,
different temperatures
and/or pressures may be used to obtain different molding conditions and thus
different properties
in the different portions/layers. For example, it is possible to mold the
crystallized neck finish
portion in a first cavity, while molding a substantially amorphous outer layer
in the second
cavity.
The resulting injection-molded articles, and/or e~tpanded injection-molded
articles, may thus have a layer structure which is not obtainable with prior
processes.
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The following chart provides temperature/time/pressure ranges for certain
preferred
embodiments, which are described in greater detail in the following sections:
a) for an inner sleeve of PEN polymer
material and an outer layer of PET
polymer
material
first moldin,~, step: range a(on the order ofl
core temperature 5-80C
mold cavity temperature 40-1 ~0C
to melt temperature 2?5-310C
cycle time 4-8 seconds
outer surface temperature of sleeve 60-120C
second molding step:
core temperature 5-8~C
~ 5 mold cavity temperature 5-60C
cycle time 20-50 seconds
pressure 8000-15,000 psi
b) for an inner sleeve of crystallized polyester material and an outer layer
of PET polymer
20 material
first molding, step: r_ar~~e~on the order of)
core temperature 5-60C
mold cavity temperature 80-150C
melt temperature 270-310C
25 cycle time 5-8 seconds
outer surface temperature of sleeve 80-140C
second molding stet:
core temperature 5-60C
mold cavity temperature 5-60C
30 cycle time. 20-35 seconds ,
pressure , 8000-15,000 psi '
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The present invention will- be more particularly set forth in the following
detailed
description and accompanying drawings.
brief Description of the Drawings
Figs. 1 A-1 D are schematic illustrations of a first method embodiment of the
present invention for making a preform having a full-length inner sleeve and a
single outer layer;
Figs. 2A-2B are schematic illustrations of an injection-molding apparatus and
the
sequence of operations for making a preform such as that shown in Fig. 1 D,
wherein a rotary
turret transfers two sets of cores between two sets of cavities; Fig. 2A shows
the cavities/cores in
a closed position and Fig. 2B shows the cavities/cores in an open position;
Fig. 3 is a time line showing the sequence of operations for the molding
apparatus
of Fig. 2;
Fig. 4A is a front elevational view of a returnable and refillable container,
partially in section, made from the preform of Fig. 1D, and Fig. 4B is an
enlarged fragmentary
1 s cross-section of the container sidewall taken along the line 4B-4B of Fig.
4A;
Figs. SA-SD are schematic illustrations of a second method embodiment of the
present invention for making a preform having a finish only sleeve and a
rnultilayer outer layer;
Figs. 6A-6D are schematic illustrations of an injection-molding apparatus and
sequence of operations for making a preform such as that shown in Fig. SD,
'wherein the transfer
2o mechanism is a reciprocating shuttle; Fig. 6A shows the shuttle in a first
closed position in first
and second mold cavities; Fig. 6B shows the shuttle in a second open position
after retraction
from the first and second mold cavities; Fig. 6C shows the shuttle in a second
opemposition
beneath the second and third mold cavities; and Fig. 6D shows the shuttle in a
fourth closed
position in the second and third mold cavities;
25 Fig. 7 is a time line of the sequence of operations shown in Fig. 6;
Fig. 8A is a cross-sectional view of a third preform embodiment of the present
invention having a full-thickness neck sleeve and multilayer body portion, and
Fig. 8B is an
enlarged fragmentary view of the neck finish of the preform of Fig. 8A;
Fig. 9A is a front elevational view of a hot-fill container made from the
preform
3o of Fig. 8A, and Fig. 9B is a fragmentary cross-section of the container
sidewal.l taken along line
9B-9B of Fig. 9A;
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Fig. 10 is a cross-sectional view of a fourth preform embodiment of the
present
invention, having a full-length body sleeve and multilayer outer layer;
Fig. 11 is across-sectional view of a fifth preform embodiment of the present
invention, including a full-length body sleeve and an extra outer base layer;
Fig. 12 is a cross-sectional view of a sixth preform embodiment of the present
invention, having a finish sleeve and a single layer outer Layer;
Figs. 13A and 13B are graphs showing the change in melting temperature (MP)
and orientation temperature (Tg) for various PEN/PET compositions; and
Fig. 14 is a schematic illustration of a three-station repeating apparatus,
including
I o IR heating stations A and ~ and RF heating station B.
Detailed Description
First Preform Embodiment refillable water
Figs. 1 A-1 D illustrate schematically one method embodiment for making a
preform with a full-length body sleeve and a single outer layer; this preform
is particularly useful
for making a returnable and refillable water bottle. Fig. 1 A shows a first
core 9 positioned in a
first mold cavity 11, and forming a chamber therebetween in which there is
formed an injection-
molded inner sleeve 20. The sleeve 20 is partially cooled and then the core 9
carrying sleeve 20 ,
2o is removed from the first mold cavity as shown in Fig. 1 B. While still
warm, the sleeve 20 on
core 9 is inserted into a second mold cavity 12 which forms an interior
molding chamber for
forming an outer layer 22 over the inner sleeve 20. After the second molding
step, a preform 30
has been formed including outer layer 22 and inner sleeve 20 as shown in Fig.
1 D. The inner
sleeve includes a top flange 21 which will form the top sealing surface of the
.resulting container
(see Fig. 4).
The first method embodiment will now be described in greater detail in regard
to
the apparatus shown in Figs. 2A-2B, and a time sequence of operations
illustrated in the time line
of Fig. 3.
As shown in Figs. 2A-2B, a four-sided rotatable turret 2 is interposed between
a
3o fixed platen 3 and a movable platen 4 on an injection-molding machine. The
turret 2 is mounted
on a carriage 5 which is slidable in the direction of platen motion (shown by
arrows Ai and A2).
The turret 2 is rotatable (shown by arrow A3) about an axis 6 disposed
perpendicular to the
.., . ..
,:. _.~ . _ . .
..,.i:"s. ...... f Y
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direction of platen motion. The turret is rotatable into two operative
positions spaced 180° apart.
In each of these positions, the two opposing faces 7, 8 of the turret carrying
furst and second sets
of cores 9, ' I 0 respectively, are received in a first set of cavities 1 I on
the movable platen 4, and a
second set of cavities 12 on the fixed platen 3. After a core set has been
successfully positioned
in each of the mold cavities, the finished preforms may be ejected from the
cores. Each of the
mold cavity and core sets include water passages 15 for heating or cooling of
the cavities/cores to
achieve a desired temperature during molding.
The sequence of operations for forming a particular preform v~rill now be
described. The preform has a full-body sleeve of a PEN polymer, such as
homopolymer PEN, or
1 o a PEN/PET copolymer or blend. The preform has a single outer layer made of
virgin PET.
In Fig. 2A, the movable platen 4 carrying the first set of mold cavities 11,
and the
carriage S carrying the turret 2, are each moved on guide bars (t:ie rods) 13,
14 to the left towards
the fixed platen 3 to close the mold (i.e., both cavities). The first set of
cores 9 on the left face 7
of the turret are positioned in the f rst cavity set I I (first molding
station); each first core/cavity
pair defines an enclosed chamber for molding an inner sleeve about the first
core. The PEN
polymer is injected via nozzle 16 into the first mold cavities to f~rm the
inner sleeve.
Simultaneously, the second core set 10 (on the second face 8 of the turret) is
positioned in the
second cavity set 12 (second molding station). 'Virgin PET is injected via
nozzle I7 into the
second set of cavities to form a single outer layer about a previously-formed
inner sleeve on each
of the second cores.
Next, the mold is opened as shown in Fig. 2B by moving both the movable platen
4 and carriage 5 to the left, whereby the first cores 9 are removed from the
first cavity 11 and the
second cores 10 are removed from the second cavity 12. Now, the finished
preforms 30 on the
second core set are ejected. The finished preforms 30 may be ejected into a
set of robot cooling
tubes (not shown) as is well known in the art. Next, the turret 2 is rotated
180°, whereby the first
set of cores 9 with the inner sleeves 20 thereon are now on the right side of
the turret (and ready
for insertion into the second set of cavities), while the second set of
(empty) cores 10 is now on
the left side of the turret (ready for insertion into the first set of anold
cavities). Again, the mold
is closed as shown in Fig. 2A and injection of the polymer materiials into the
first and second sets
of cavities proceeds as previously described.
In this embodiment, the farst and second cores are held at a temperature in a
range
on the order of 60-70°C, whether they are positioned in the first mold
cavities or the second mold
~~C.r e' ~~Pa ~. r' _... °.
i_- i ; . .. . ,_..
..
'> ;%~, d f~ ~R...
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cavities. The first mold cavities (for forming the inner sleevf;) are held at
.a temperature on the
order of 85-95°C. The melt temperature of the PEN polymer is on the
order of 285-295°C. The
cycle time in the first mold cavity is on the order of 6-7 seconds, i.e., the
time lapse between the
first and second injections. This is because, as shown in Fig. 3, the hold
a~zd cool stage is
substantially eliminated in the first mold cavities. The outer surface
temperature of the sleeve
(opposite the inner surface engaging the core) at the start of the second
injection is 100-110°C.
During the second molding step, the core temperature is again at 60-
70°C, but the
second mold cavity temperature is 5-10°C (much lower than the first
cavity temperature, to
enable quick cooling of the preform). The melt temperature of the virgin fET
is on the order of
1o 260 to 275°C; this is lower than the melt temperature of the PEN
polymer, but because the PEN
polymer is still warm (at a temperature of 100-110°C) during the second
molding step, there is
melt adhesion (including diffusion bonding and chain entanglement) which.
occurs between the
PEN polymer chains and virgin PET polymer chains (inner sleeve and outer
layer) respectively.
The cycle time for the second molding step is on the order of 35 to 37
seconds.
Fig. 3 is a time line with the cycle time along the x axis (time in seconds),
and the
sequence of steps in the second cavity set shown above the x axis, and the
sequence of steps in
the first cavity set shown below the x axis. At t = 0, the mold is closed (see
Fig. 2A) and the
pressure is built up. At t = 1.5 seconds, the second cavity (for forming the
outer layer) is filled,
the pressure boosted, and then the pressure reduced during the hold and
cooling stage; this
2o continues until t = 33 seconds in the second cavity. Meanwhile, no action
is required at t = 1.5
seconds in the first cavity ("no action period"); rather, it is not until t =
31 seconds that the first
cavity is filled and the pressure increased and held, until t = 33 seconds.
This substantial
elimination of the hold and cooling stage (in the first cavity) produces an
inner sleeve which is
still at an elevated temperature when it is subsequently is positioned in the
second cavity, and
enables melt adhesion between the outer surface of the inner sleeve and outer
layer. At t = 33
seconds, the mold is opened (see Fig. 2B), and the preforms from the second
cavity are ejected.
Then, at t = 35 seconds, the turret 2 is rotated so as to position the still-
warm sleeves (just made
in the first cavity) in a position to be inserted into the second cavity,
while the now-empty core
set (previously in the second cavity) is now positioned to be inserted in the
first caviri~. At t = 36
3o seconds, we are ready to begin the next cycle,
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The method and apparatus of Fig. 2 may be advantageously used to produce
multilayer preforms for a great variety of applications, including refill, hot-
fill and pasteurizable
containers: A number of alternative embodiments are described below.
The preform made according to the method and apparatus of Figs. 1-3 includes a
full-body inner sleeve 20 of PEN polymer, and a single outer layer 22 of
virgin PET. The
preform is substantially transparent and amorphous and may be repeated and
stretch blow-
molded to form a 1.5 liter returnable and refillable water bottle, such as
that shown in Fig. 4A.
The container 40 is about 13.2 inches (335 mm) in height and about 3.6 inches
(92 mm) in
widest diameter. The container body has an open top end with a. small diameter
neck finish 42
to having external screw threads for receiving a screw cap (not shown), and a
closed bottom end or
base 48. Between the neck finish 42 and base 48 is a substantially vertically-
disposed sidewall
45 (defined by vertical axis or centerline CL of the bottle), including a
substantially cylindrical
panel portion 46 and a shoulder portion 44 tapering in diameter i:rom panel 45
to neck finish 42.
The base 48 is a champagne-style base with a central gate portio:rl 51 and,
moving radially
~ 5 outwardly towards the sidewalk an outwardly concave dome 52, an inwardly
concave chime 54,
and a radially increasing and arcuate outer base portion 56 for a ;smooth
transition to the sidewall
panel 46. The chime 54 is a substantially toroidal-shaped area around a
standing ring (chime) on
which the bottle rests.
Fig. 4B shows in cross-section the multilayer panel portion 46, which includes
an
20 inner sleeve layer 41 (an expanded version of preform sleeve 20), and an
outer layer 43 (an
expanded version of preform outer layer 22). ~ne benefit of the present
invention is that the
layers 41 and 43 have bonded and will not separate during repeat stretch blow
molding or use of
the container, in this ease including the intended 20 or more refill cycles.
In addition, a flange 47
(same as flange 21 of the preform) forms a top sealing surface of the
container with increased
25 strength and thermal resistance.
Second Preform Embodiment~asteurizable beer)
Figs. SA-SD illustrate schematically a second method embodiment for making a
finish-only sleeve and a multiple outer layer preform; this preforan is
adapted for making a
30 pasteurizable beer container. Fig. 5A shows a core 207 positioned in a
first mold cavity 213;
together they form a first molding chamber in which a finish-only sleeve 250
is injection molded.
Fig. 5A shows an injection nozzle 211 in the mold cavity 213, through which a
molten
_. . . .
. .~ , .. _ ~ ,
.__ ~ =: " ..,~..~-''
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-11-
thermoplastic material is injected for forming the sleeve 250. Fig. 5B shows
the formed sleeve
250 on the core 207, the sleeve having been removed from first mold cavity 213
while it is still
warm. The core 207 carrying the sleeve 250 is then positioned in a second mold
cavity 214 as
shown in Fig. SC. The second mold cavity 2I4 and core 207 form a second
molding chamber
adapted to form an outer layer 252 over the inner sleeve 250. A plurality of
different
thermoplastic materials are injected through a gate 209 in the bottom of the
second mold cavity
214, to form the multiple outer layers. As shown in Fig. SD, tlhe outer layer
252 extends the full
length of the preform. A sequential injection process such as that described
in U.S. Patent No.
4,609,516 to Krishnakumar et al., may be used to form inner and outer layers
253, 254 of virgin
to PET, core layer 255 of recycled PET (which may include an oxygen scavenging
material), and
inner and outer intermediate layers 256, 257 of an oxygen barrier material,
between the
inner/core/outer layers. In this embodiment, only the virgin PET extends up
into the neck finish
of the preform, forming a single layer 25$ over inner sleeve 250. In the base
of the preform, a
final injection of virgin PET forms a plug 259 for clearing the nozzle before
the next injection
cycle.
Figs. 6A-6D illustrate a reciprocating shuttle apparatus, instead of the
rotatable
turret of Figs. 2A-2D, which comprises a second apparatus em'bodirnent. Tlgis
second apparatus
will now be described with respect to forming the preform of Fig. 5. Fig. 7
shows a time line of
the sequence of operations.
2o The apparatus (see Figs. 6A-6D) includes first and second parallel guide
bars 202,
203 on which a platen 205 is movably mounted in the direction of arrow Aq. The
platen 205
carries a platform or shuttle 206 which is movable in a transverse direction
across the platen 205
as shown by arrow A5. A fixed platen 212 at one end of the guide bars holds
three injection
mold cavity sets 213, 214 and 215 which are supplied by nozzles 218, 219 and
220 respectively.
The left (first) and right (third) cavity sets 213 and 21 S are used to form
neck portions of
preforms, while the middle (second) cavity set 214 is used for molding body-
forming portions.
Fig. 5A shows an arbitrarily-designated first step wherein the first core set
207 is
positioned in left cavity set 213 for forming a first set of preform neck
portions (sleeves).
Simultaneously, second core set 208 is positioned in middle cavity set 214 for
molding a set of
3o multilayer body-forming portions (over a second set of previously molded
neck portions). Fig.
5B shows the core sets following removal from the cavity sets, with a neck
sleeve 250 on each
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-I2-
core of core set 207, and a preform 260 om each core of core set 208. The
completed preforms
260 are then ejected from the core set 208.
In a second step (Fig. 6C}, the shuttle 206 is moved to the right such that
the first
core set 207 with neck sleeves 250 are now positioned below middle cavity 214,
while second
core set 208 with now empty cores 216 is positioned below right cavity set
215. Movable platen
205 is then moved towards fixed platen 2I2 so as to position first core set
2C~7 in middle cavity
set 214, and second core set 208 in right cavity set 215 (Fig. 6D). Again,
body-forming portions
are formed over the previously formed neck sleeves in middle cavity set 214,
while neck sleeves
are molded on each of the cores in the core set 208 in right cavity set 215.
The movable platen
20S is then retracted to remove the core sets from the cavity sets, the
finished preforms on the
first core set 207 are ejected, and the shuttle 206 returns to the left for
molding the next set of
layers.
Fig. 7 is a time line of the operations shown in Fig. 6, with time in seconds
along
the x axis, and the sequence of steps in the second cavity 214 shown above the
x axis, and the
sequence of steps in the first cavity 213 shown below the x axis. First, at t
= 0, the mold is
closed (Fig. 6A) and the pressure builds up. Then, at t = 1.5 seconds, the
second cavity 214 is
filled (forming the outer layer), the pressure increased, and the pressure
held while the preform
cools, until t = 21 seconds. Meanwhile, no action is required in the first
cavity at t = 1.5 seconds;
at t = 20 seconds, the first cavity 213 is filled with PEN polymer and the
pressure increased and
2o held until t = 21 seconds (again the hold and cooling stage has been
substantially eliminated in
the first cavity set by delaying the filling stage until near the end of the
hold and cooling stage for
the second cavity set). At t = 21 seconds, the mold is opened and the preforms
260 are ejected
from the second cavities. At t = 23 seconds, the shuttle 206 with the still
warm neck sleeves is
transferred to the second shuttle position as shown in Fig. 6C, and at t = 24
seconds the mold is
closed as shown in Fig. 6D.
In this particular embodiment, the first and second core sets 207, 208 are
held at a
temperature on the order of 60-70°C during bath of the first and second
molding steps. The first
mold cavity (for forming the neck finish sleeve) is on the order of 75-
85°C. The PEN polymer
has a melt temperature on the order of 275-285°C. The cycle time in the
first cavity is on the
order of 5-6 seconds; this is the time lapse between the first and second
injection steps. The
surface temperature of the sleeve at the time of the second injection is on
the order of 100-1 I O°C.
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In the second molding step, the core temperature is on the order of 60-
70°C, and
the second mold cavity is at a temperature om the order of S-10°C. The
cycle time in the second
mold cavity is on the order of 23-25 seconds. The elevated temperature at the
outer surface of
the sleeve, at the time of the second molding step, causes melt adhesion
(including diffusion
bonding and chain entanglement) between the PEN polymer of the sleeve and the
virgin PET of
the outer layer portion 258 which is adjacent the sleeve 250.
Third Preform Embodime t~(hot f l~
A further preform/container embodiment is illustrated in Figs. 8-9. Figs. 8A-
8B
to show a multilayer preform 330 and Figs. 9A-9B show a hot-fill beverage
bottle 370 made from
the preform of Fig. 8. In this embodiment, a first molded sleeve forms the
entire thickness of the
neck finish, and is joined at its lower end to a second molded body-forming
portion.
Fig. 8A shows a substantially cylindrical preform 330 (defined by vertical
centerline 332) which includes an upper neck portion or finish sleeve 340
bonded to a lower
is body-forming portion 350. The crystallized neck portion is a monolayer of
CPET and includes
an upper sealing surface 341 which defines the open top end 342 of the
preform, and an exterior
surface having threads 343 and a lowermost flange 344. CPET, sold by Eastman
Chemical,
Kingsport, TN, is a polyethylene terephthalate polymer with nucleating agents
which cause the
polymer to crystallize during the injection molding process. Beluw the neck
finish 340 is a
2o body-forming portion 350 which includes a flared shoulder-forming section
351, increasing
(radially inwardly) in wall thickness from top to bottom, a cylindrical panel-
forming section 352
having a substantially uniform wall thickness, and a base-forming section 353.
Body-forming
section 350 is substantially amorphous and is made of the following three
layers in serial order:
outer layer 354 of virgin PET; core layer 3S6 of post-consumer PET; and inner
layer 358 of
25 virgin PET. The virgin PET is a low copolymer having 3% comonomers (e.g.,
cyclohexane
dimethanol (CHDM) or isophthalic acid (IPA)) by total weight o:f the
copolymer. A last shot of
virgin PET (to clean the nozzle) forms a core layer 359 in the base.
This particular preform is designed for making a hot-fill beverage container.
In
this embodiment, the preform has a height of about 9b.3mm, and an outer
diameter in the panel-
30 forming section 352 of about 26.7mm. The total wall thickness at the panel-
forming section 352
is about 4mm, and the thicknesses of the various layers are: Quter layer 354
of about lmm, core
layer 356 of about 2mm, and inner layer 358 of about lmm. The panel-forming
section 3S2 may
REI~'TI'~1~. "L' ..~~t~~~T__
a~r~~'i~E
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be stretched at an average planar stretch ratio of about 10:1, as described
hereinafter. The planar
stretch ratio is the ratio of the average thickness of the preforn~ panel-
forming portion 352 to the
average thickness of the container panel 383, wherein the "average" is taken
along the length of
the respective preform or container portion. For hot-fill beverage bottles of
about 0.5 to 2.0 liters
in volume and about 0.35 to 0.60 millimeters in panel wall thickness, a
preferred planar stretch
ratio is about 9 to 12, and more preferably about 10 to 11. The hoop stretch.
is preferably about
3.3 to 3.8 and the axial stretch about 2.8 to 3.2. This produces a container
panel with the desired
abuse resistance, and a preform sidewall with the desired visual transparency.
The specific panel
thickness and stretch ratio selected depend on the dimensions of the hottle,
the internal pressure,
and the processing characteristics {as determined for example, by the
intrinsic viscosity of the
particular materials employed).
In order to enhance the crystallinity of the neck portion, a high injection
mold
temperature is used at the first molding station. In this embodiment, CPET
resin at a melt
temperature of about 280 to 290°C is injection molded at a mold cavity
temperature of about 110
to 120°C and a core temperature of about 5 to 15°C, and a cycle;
time of about 6 to 7 seconds.
The first core set, carrying the still warm neck portions (outer surface
temperature of about 11 S
to 125°C), are then transferred to the second station where multiple
second polymers are injected
to form the multilayer body-forming portions and melt adhesion occurs between
the neck and
body-forming portions. The core and/or cavity set at the second station are
cooled (e.g., S to
1 S °C core/cavity temperature) in order to solidify the performs and
enable removal from the
molds (cycle time of about 23 to 25 seconds) with acceptable levels of post-
mold shrinkage. The
cores and cavities at both the first and second stations include water
cooling/heating passages for
adjusting the temperature as desired.
As used herein, "melt adhesion" between the inner sleeve and outer layer is
meant
to include various types of bonding which occur due to the enhanced
temperature (at the outer
surface of the inner sleeve) and pressure (e.g., typical injection molding on
the order of 8,000-
15,000 psi) during the second molding step, which may include diffusion,
chemical, chain .
cntanglemcnt, hydrogen bonding, ctc. ~icncrally, difFusion and/or chain
cntanglcnaent will be
present to form a bond which prevents delamination of the layers in the
preform, and in the
3o container when filled with water at room temperature (25°C) and
dropped from a height of
eighteen inches onto a thick steel plate.
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Fig. 8B is an expanded view of the neck finish 340 of pref~rm 330. The
monolayer
CPET neck finish is formed with a projection 345 at its lower end, which is
later surrounded
(interlocked) by the virgin PET melt from the inner and outer layers 354,358
at the
second molding station. The CPET neck finish and outermost virgin PET layers
of the body are
melt adhered together in this intermediate region (between the lower end of
the neck finish
sleeve and the upper end of the body-forming region).
Fig. 9A shows a unitary expanded plastic preform container :370, made from the
preform of Fig. 8. The container is about 182.Omm in height and about 71.4mm
in (widest)
diameter. This 16-oz, container is intended for use as a hot-fill non-
carbonated juice container.
1o The container has an open top end with the same crystallized neck finish
340 as the preform,
with external screw threads 343 for receiving a screw-on cap (not shown).
Below the neck finish
340 is a substantially amorphous and transparent expanded body portion 380.
The body includes
a substantially vertically-disposed sidewall 381 (defined by vertical
centerline 372 of the bottle)
and base 386. The sidewall includes an upper flared shoulder portion 382
increasing in diameter
to a substantially cylindrical panel portion 383. The panel 383 has a
plurality of vertically-
elongated; symmetrically-disposed vacuum panels 385. The vacuum panels move
inwardly to
alleviate the vacuum formed during product cooling in the sealed container,
and thus prevent
permanent, uncontrolled deformation of the container. The base 386 is a
champagne-style base
having a recessed central gate portion 387 and moving radially outwardly
toward the sidewalk an
outwardly concave dome 388, an inwardly concave chime 389, and a radially
increasing and
arcuate outer base portion 390 for a smooth transition to the sidewall 381.
Fig. 9B shows in crass section the multilayer panel portion 383 including an
outer
layer 392, a core layer 394, and an inner layer 396, corresponding to the
outer 354, core 356 and
inner 358 layers of the preform. The inner and outer container layers 392, 396
(of virgin PET
copolymer) are each about O.lmm thick, and the core layer 394 (of post-
consumer PET) is about
0.2mm thick. The shoulder 382 and base 386 are stretched less and therefore;
are relatively
thicker and less oriented than the panel 383.
Fourth Preform Embodiment
3o A fourth preform embodiment is illustrated in Fig. 10. A multilayer,preform
130
is made from the method and apparatus of Figs. 1-2, and is adapted to be
reheat stretch blow-
molded into a refillable carbonated beverage bottle similar to that shown in
Fig. 4, but having a
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thickened base area including the chime for increased resistance to caustic
and pressure induced
stress cracking.
In Fig. 10' there is shown a preform 130 which includes a PEN inner sleeve
layer
120, and a three-layer outer layer comprising outermost (exterior) virgin PET
layer 123, first
intermediate (interior) PC-PET layer 124, and second intermediate (interior)
virgin PET layer
125. The inner sleeve layer 120 is continuous, having a body portion 121
extending the full
length of the preform and throughout the base. The sleeve layer further
includes an upper flange
122 which forms the top sealing surface of the preform. The outer layer
similarly extends the
full length and throughout the bottom of the preform.
to The preform 130 includes an upper neck finish 132, a flared shoulder-
forming
section 134 which increases in thickness from top to bottom, a panel-forming
section 136 having
a uniform wall thickness, and a thickened base-forming section 138. Ease
section 138 includes
an upper cylindrical thickened portion 133 (of greater thickness than the
panel section 136)
which forms a thickened chime in the container base, and a tapering lower
portion 135 of
reduced thickness for forming a recessed dome in the container base. A last
shot of virgin PET
(to clean the nozzle) forms a core Iayer 139 in the base. A pref~rrn having a
preferred cross-
section for refill applications is described in LJ.S. Patent 5,066,.'i28
granted November 19, 1991
to Krishnakumar et al., which is hereby incorporated by reference in its
entirety.
'This particular preform is designed for making a. refillable carbonated
beverage
2o container. The use of an inner sleeve 120 of a PEN homopoIymer, copolymer,
or blend provides
reduced flavor absorption and increased thermal stability far increasing the
wash temperature.
The inner PEN sleeve can be made relatively thin according to the method of'
Fig. I ~ The interior
PC-PET layer 124 can be made relatively thick to reduce the cost of the
container, without
significantly affecting performance. In this example, the preforrn has a
height of about 7.130
inches (181.1 mm), and an outer diameter in the panel-forming ;section 136 of
about 1.260 inches
(32.Omm). At the panel-forming section 136, the total wall thickness is about
0.230 inches (5.84
mm), and the thicknesses of the various layers are: inner layer 120 of about
0.040 inches ( 1.0
mm), outermost layer 123 of about 0.040 inches (1.0 mm), first intermediate
:layer 124 of about
0.130 inches (3.30 mm), and second intermediate layer 125 of albout 0.020
inches (0.5 mm). The
3o panel-forming section 136 may be stretched at an average planar stretch
ratio of about 10.5:1, as
described hereinafter. The planar stretch ratio is the ratio of the average
thickness of the preform
panel-forming portion 136 to the average thickness of the container panel (see
for example
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sidewall 46 in Fig. 4), wherein the "average" is taken along the length of the
respective preform
or container portion. For refillable carbonated beverage bottles of about 0.5
to 2.0 liters in
volume and about 0.5 to 0.8 millimeters in panel wall thickness, a preferred
planar stretch ratio is
about 7.5-10.5, and more preferably about 9.0-10.5. The hoop stretch is
preferably about 3.2-3.5
and the axial stretch about 2.3-2.9. This produces a container panel with the
desired abuse
resistance, and a preform sidewall with the desired visual transparency. The
specific panel
thickness and stretch ratio selected depend on the dimensions of the bottle,
the internal pressure
(e.g., 2 atmospheres for beer and 4 atmospheres for soft drinks), and the
processing
characteristics (as determined for example, by the intrinsic viscosity of the
particular materials
1o employed).
In order to provide a thin PEN sleeve layer (e.g. 0.5 to 1.0 mm), a suitable
mold
cavity temperature would be on the order of 100 to 110°C and core
temperature of about 5 to
15°C, for a PET melt temperature of about 285 to 295°C and cycle
time of about 6 to 7 seconds.
The first core set and warm inner layer are then immediately transferred to
the second station
where the outer layers are injected and bonding occurs between the inner and
outer layers (e.g.,
exterior surface of inner PEN sleeve layer at about 90 to 100°C and
innermost PET layer at
about 260 to 275 °C). The first core set and/or second cavity set at
the second station are cooled
(e.g., about 5 to 15 °C) in order to solidify the perform and enable
removal from the mold. The
cores and cavities at both the first and second stations include water
cooling/heating passages for
2o adjusting the temperature as desired.
In this embodiment, the inner sleeve layer 120 is made from a high-PEN
copolymer having 90% PEN/10°!° PET by total weight of the layer,
and in the container panel is
about 0.004 inches (0.10 mm) thick. The outermost layer 123 is a virgin PET
low copolymer
having 3% comonomers (e.g., CI-IDM or IPA), and in the container panel is
about 0.004 in (0.10
mm) thick. The first intermediate layer 124 is PC-PET, and in the container
panel is about 0.012
in (0.30 mm) thick. The second intermediate layer 125 is the same virgin PET
low copolymer as
outermost layer 123, and in the container panel is about 0.002 in (0.05 mm)
thick. The container
shoulder and base (see 44 and 48 in Fig. 4A) are stretched less and therefore
are thicker and less
oriented than the panel (see 46 in Fig. 4A).
3o Fifth Preform Embodiment
Fig. 11 illustrates another preform embodiment for making a refillable
carbonated
beverage container. This preform has an additional outermost layer in the base
only for
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increasing caustic stress crack resistance, 'while maximizing the use of
post..consumer PET for
reducing the cost. The preform 160 includes an upper neck finish 162,
shoa.~lder-forming portion
164, panel-forming section 166, and base-forming portion 16E~. The inner layer
170 has a body
portion 171 which is continuous throughout the length (including the bottom)
of the preform and
includes an upper flange 172 forming the top sealing surface. The inner layer
is virgin PET. An
outer layer 173 of PC-PET extends throughout the length of the preform, and
forms a single
outer layer in the neck finish and panel-forming section. In the base-forming
portion an
additional exterior layer 174 of high IV virgin PET is provided to enhance the
caustic stress
crack resistance of the blown container. A thin interior layer 175 of the
higlh IV virgin PET may
1o also be formed according to the sequential injection process previously
referenced. A last shot
176 of high IV virgin PET is used to clear out the PC-PET from the nozzle
section. The outer
base layer 174 is preferably a high IV virgin PET (hornopolymer or copolymer)
having an
intrinsic viscosity of at least about 0.76, and preferably in the range of
0.76 'to 0.84. The
resulting container rnay be either a footed or champagne base container.
Sixth Preform Embodiment
Fig. 12 shows another preforrn embodiment including a high.-temperature neck
finish sleeve 190 and a single outer layer 194 for forming a hot-fill
container. The preform I 80
includes a neck finish 182, shoulder-forming portion 184, panel-forming poa-
tion 186, and base
2o forming portion 188. The inner sleeve 190 includes a neck finish portion
191, extending
substantially along the length of the upper threaded neck finish portion 182
of the container, and
an upper flange 192 forming a top sealing surface. The inner sleeve is formed
of a thermal
resistant (high Tg) material such as a PEN homopolymer, copolymer or blend.
Alternatively, the
sleeve may be formed of CPET, sold by Eastman Chemical, Kingsport, TN, a
polyethylene
terephthalate polymer with nucleating agents which cause the polymer to
crystallize during the
injection molding process.
The outer layer 194 is made of virgin PET. This preform is intended for making
hot-fill containers, wherein the inner sleeve 190 provides additional thermal
stability at the neck
finish.
3o In further alternative embodiments, a triple outer layer of virgin PET, PC-
PET,
and virgin PET may be used.
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Alternative Constructions and Materials
There are numerous preform and container constructions, and many different
injection moldable materials, which may be adapted for a particular food
product and/or package,
filling, and manufacturing process. Additional representative examples are
given below.
Thermoplastic polymers useful in the present invention include polyesters,
polyamides and polycarbonates. Suitable polyesters include homopolymers,
copolymers or
blends of polyethylene terephthalate (PET), polybutylene terephthalate (PBT),
polypropylene
terephthalate (PPT), polyethylene napthaIate (PEN), and a cyclohexane
dime;thanoI/PET
copolymer, known as PETG (available from Eastman Chemical, Kingsport, 'I~1).
Suitable
polyamides (PA) include PA6, PA6,6, PA6,4, PA6, I 0, PA 11, PA 12; etc. Other-
useful
thermoplastic polymers include acrylic/imide, amorphous nylon,
polyacrylonitrile (PAN),
polystyrene, crystallizable nylon (MXD-6), polyethylene (PE), polypropylene
(PP), and
polyvinyl chloride (PVC).
Polyesters based on terephthalic or isophthalic acid are commercially
available
~5 and convenient. The hydroxy compounds are typically ethylene glycol and 1,4-
di-(hydroxy
methyl)-cyclohexane. The intrinsic viscosity for phthalate polyesters are
typically in the range of
0.6 to 1.2, and more particularly 0.7 to 1.0 (for O-chlorolphenol solvent).
0.6 corresponds
approximately to a viscosity average molecular weight of 59,000, and 1.2 to a
viscosity average
molecular weight of 112,000. In general, the phthalate polyester may include
polymer linkages,
2o side chains, and end groups not related to the formal precursors of a
simple phthalate polyester
previously specified. Conveniently, at least 90 mole percent wall be
terephthalic acid and at least
90 mole percent an aliphatic glycol or glycols, especially ethylene glycol.
Post-consumer PET (PC-PET) is a type of recycled PET prepared from PET
plastic containers and other recyclables that are returned by consumers for a
recycling operation,
25 and has now been approved by the FDA for use in certain food containers.
F'C-PET is known to
have a certain level of LV. (intrinsic viscosity), moisture content, and
contaminants. For
example, typical PC-PET (having a flake size of one-half inch maximum), has an
LV. average of
about 0.66 dl/g, a relative humidity of less than 0.25%, and the following
levels of contaminants:
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PVC: < 100 ppm
aluminum: < 50 ppm
olefin polymers (HDPE, LDPE, PP): < 500 ppm
paper and labels: < 250 ppm
colored PET: < 2000 ppm
other contaminants: < 500 ppm
PC-PET may be used alone or in one or more layers for reducing the cost or for
other benefits.
Also useful as a base polymer or as a thermal resistant and/or high-oxygen
barrier
0 layer is a packaging material with physical properties similar to PET,
namely polyethylene
naphthalate (PEN). PEN provides a 3-5X improvement in barrier property and
enhanced thermal
resistance, at some additional expense. Polyethylene naphthalate (PEN) is a
polyester produced
when dimethyl 2,6-naphthalene dicarboxylate (NDC) is reacted with ethylene
glycol. The PEN
polymer comprises repeating units of ethylene 2,6 naphthalate. PEN resin is
available having an
15 inherent viscosity of 0.67d1/g and a molecular weight of about 20,000 from
Amoco Chemical
Company, Chicago, Illinois. PEN has a glass transition temperature Tg of about
123°C, and a
melting temperature Tm of about 267°C.
Oxygen barrier layers include ethylene/vinyl alcohol (EVOH), PEN, polyvinyl
alcohol (PVOH), polyvinyldene chloride (PVDC), nylon 6, crysi:alli~able nylon
(MXD-6), LCP
20 (liquid crystal polymer), amorphous nylon, polyacrylonitrile (PAN) and
styrene acrylonitrile
(SAN).
The intrinsic viscosity (LV.) effects the processability of the resins.
Polyethylene
terephthalate having an intrinsic viscosity of about 0.8 is widely used in the
carbonated soft drink
(CSD) industry. Polyester resins for various applications may range from about
0.55 to about
25 1.04, and more particularly from about 0.65 to 0.85d1/g. Intrinsic
viscosity measurements of
polyester resins are made according to the procedure of ASTM D-2857, by
erriploying 0.0050 +
0.0002 g/ml of the polymer in a solvent comprising o-chlorophenol (melting
point OoC),
respectively, at 30°C. Intrinsic viscosity (LV.) is given by the
following formula:
LV. _ (ln(VSoIn.NSol.))/C
3o where:
VSo~n, is the viscosity of the solution in any units;
VSo~, is the viscosity of the solvent in the same units; and
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C is the concentration in grams of polymer per 100 mls of solution.
The blown container body should be substantially transparent. ~ne measure of
transparency is the percent haze for transmitted light through tlhe wall (HT)
'which is given by the
following formula:
HT = ~1'd~(Yd~Ys)] x 100
where Yd is the diffuse light transmitted by the specimen, and YS is the
specular light transmitted
by the specimen. The diffuse and specular light transmission values are
measured in accordance
with ASTM Method D 1003, using any standard color difference meter such as
model D25D3P
manufactured by Hunterlab, Inca The container body should have a percent haze
(through the
panel wall) of less than about 10%, and more preferably less than about 5%.
The preform body-forming portion should also be substantially amorphous and
transparent, having a percent haze across the wall of no more than about 10%,
and more
preferably no more than about 5%.
The container will have varying levels of crystallinity at various positions
along
t 5 the height of the bottle from the neck finish to the base. The percent
crystallinity may be
determined according to ASTM 1505 as follows:
crystallinity = [(ds - da)/(dc - da)] X 100
where ds = sample density in g/cm3, da = density of an amorphous film of zero
percent
crystallinity, and do = density of the crystal calculated from unit cell
parameters. The panel
portion of the container is stretched the greatest and preferably has an
average percent
crystallinity in at least the outer layer of at least about 15°/~, and
more preferably at least about
20%. For primarily PET polymers, a 1 S-25% crystallinity range is useful in
refill and hot-fill
applications.
Further increases in crystallinity can be achieved by heat setting to provide
a
combination of strain-induced and thermal-induced crystallization. Thermal-
induced
erystallinity is achieved at low temperatures to preserve transparency, e.g.,
holding the container
in contact with a low temperature blow mold. In some applications, a high
level of crystallinity
at the surface of the sidewall alone is sufficient.
As a further alternative embodiment, the preform may include one or more
layers
of an oxygen scavenging material. Suitable oxygen scavenging materials are
described in U.S.
Serial No. 08/355,703 filed December 14, 1994 by Collette et al., entitled
"Oxygen Scavenging
Composition For Multilayer Preform And Container," which is hereby
incorporated by reference
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in its entirety. As disclosed therein, the oxygen scavenger may be a metal-
catalyzed oxidizable
organic polymer, such as a polyamide, or an anti-oxidant such ;as phosphate or
phenolic. The
oxygen scavenger may be mixed with PC-PET to accelerate activation of the
scavenger. The
oxygen scavenger may be advantageously combined with other thermoplastic
polymers to
provide the desired injection molding and stretch blow molding characteristics
for making
substantially amorphous injection molded preforms and substantially
transparent biaxially
oriented polyester containers. The oxygen scavenger may be provided as an
interior layer to
retard migration of the oxygen scavenger or its byproducts, and to prevent
premature activation
of the scavenger.
l0 Refillable containers must fulfill several key performance criteria in
order to
achieve commercial viability, including:
1. high clarity (transparency) to permit visual on-line inspection;,
2. dimensional stability over the life of the container; and
3, resistance to caustic wash induced stress cracking and leakage.
t5 C'renerally, a refillable plastic bottle must maintain its functional. and
aesthetic: characteristics over
a minimum of 10 and preferably 20 cycles or loops to be econo'~ically
feasible. A cycle is
generally comprised of (1) an empty hot caustic wash, (2) contaminant
inspection (before and/or
after wash) and product filling/capping, (3) warehouse storage, (4)
distribution to wholesale and
retail locations and (5) purchase, use and empty storage by the consumer,
followed by eventual
20 return to the bottler.
A test procedure for simulating such a cycle would be as follows. As used in
this
specification and claims, the ability to withstand a designated number of
refill cycles without
crack failure and/or with a maximum volume change is determined according to
the following
test procedure.
25 Each container is subjected to a typical commercial caustic wash solution
prepared with 3.5% sodium hydroxide by weight and tap water. The wash solution
is maintained
at a designated wash temperature, e.g., 60°C. The bottles are submerged
uncapped in the wash
for 15 minutes to simulate the time/temperature conditions of a commercial
bottle wash system.
After removal from the wash solution, the bottles are rinsed in tap water and
then filled with a
3o carbonated water solution at 4.0 ~ 0.2 atmospheres (to simulate the
pressure in a carbonated soft
drink container), capped and placed in a 3~~C convection oven at 50% relative
humidity for 24
hours. This elevated oven temperature is selected to simulate longer
commercial storage periods
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- 23
at lower ambient temperatures. Upon removal from the oven, the containers are
emptied and
again subjected to the same refill cycle, until failure.
A failure is defined as any crack propagating through the bottle wall which
results
in leakage and pressure loss. Volume change is determined by comparing the
volume of liquid
s the container will hold at room temperature, both before and after each
refill cycle.
A refillable container can preferably withstand ait least 20 refill cycles at
a wash
temperature of 60°C without failure, and with no more than 1.5% volume
crzange after 20 cycles.
In this invention, a higher level of crystallization can be achieved in the
neck
fanish compared to prior art processes which crystallize outside the mold.
Tllus, the preform
1 o neck finish may have a level of crystallinity of at least about 30%. As a
furrlher example, a neck
finish made of a PET homopolymer can be molded with an average percent
crystallinity of at
least about 35%, and more preferably at least about 40% To facilitate bonding
between the neck
portion and body-forming portion of the preform, one rnay use a thread split
cavity, wherein the
thread section of the mold is at a temperature above 60°C, and
preferably above 75°C.
~ 5 As an additional benefit, a colored neck finish c~.n be produced, while
maintaining
a transparent container body.
The neck portion can be monolayer or multilayer and made o;f various polymers
other than CPET, such as arylate polymers, polyethylene naphthalate (PEN),
polycarbonates,
polypropylene, polyimides, polysulfones, acrylonitrile styrene, etc. As a
further alternative, the
20 neck portion can be made of a regular bottle-grade homopolymer or low
copolymer PET (i.e.,
having a Iow crystallization rate), but the temperature or other conditions of
the first molding
station can be adjusted to crystallize the neck portion.
Other benefits include the achievement of higher hot-fill temperatures (i.e.,
above
85°C) because of the increased thermal resistance of the finish, and
higher refill wash
25 temperatures (i.e., above 60°C). The increased thermal resistance is
also particularly useful in
pasteurizable containers.
Figs. 13A-13E illustrate graphically the change in melt temperature and
orientation temperature for PET/PEN compositions, as the weight percent of PEN
increases
from 0 to 100. There are three classes of PET/PEN copolymers or blends: (a) a
high-PEN
3o concentration having on the order of 80-100% PEN and 0-20% PET by total
weight, of the
copolymer or blend, which is a strain- hardenable,(orientable) and
crystallizable material; (b) a
mid-PEN concentration having on the order of 20-80% PEN and 80-20% PET, which
is an
CA 02436981 2003-08-21
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-24-
amorphous non-crystallizable material that will not undergo strain hardening;
and (c) a low-PEN
concentration having on the order of 1-20% PEN and 80-g9% PET, which is a
crystallizable and
strain-hardenable material. A particular PEN/PET polymer or 'blend can be
selected from Figs.
13A-13B based on the particular application.
Fig. 14 illustrates a particular embodiment of a combined infrared (IR) and
radio
frequency (RF) heating system for repeating previously molded and cooled
preforms (i.e., for use
in a two-stage repeat injection mold and stretch blow process). This system is
intended for
repeating preforms having layers with substantially different orientation
temperatures. For
example, in the fourth preform embodiment the high-PEN inner layer 120 has an
orientation
1 o temperature much higher than the virgin PET low copolymer and PC-PET outer
layers 123-125.
PEN homopolymer has a minimum orientation temperature on the order of
260°F (127°C), based
on a glass transition temperature on the order of255°F (123°C).
PEN homopolymer has a
preferred orientation range of about 270-2~5°F (132-146°C). In
contrast, PET homopolymer has
a glass transition temperature on the order of 175°F (80°C). At
the minimurrA orientation
15 temperature of PEN homopolymer, PET homopolymer would begin to crysta,Ilize
and would no
longer undergo strain hardening (orientation), and the resulting container
would be opaque and
have insufficient strength.
Returning to Fig. 14, this combined repeating apparatus may be used with
preforms having a substantial disparity in orientation temperatures between
layers. The preforms
20 130 are held at the upper neck finish by a collet 107 and travel along an
endless chain 115
through stations A, B and C in serial order. Station A is a radiant heating
oven in which the
preforms are rotated while passing by a series of quartz heaters. The heating
of each preform is
primarily from the exterior surface and heat is transmitted across the wall to
the inner layer. The
resulting heat or temperature profile is higher at the exterior surface of the
preform than at the
25 interior surface. The time and temperature may be adjusted in an attempt to
equilibriate the
temperature across the wall.
In this embodiment, it is desired to heat the inner PEN layer at a higher
temperature because of PEN's higher orientation temperature. Thus, the
preforms (across the
wall) are brought up to an initial temperature of about 160°F (71
°C) at station A, and are then
3o transferred to station B which utilizes microwave or radio frequency
heaters. 'These high-
frequency dielectric heaters provide a reverse temperature profile from that
of the quartz heaters,
with the interior surface of the preform being heated to a higher temperature
than that of the
CA 02436981 2003-08-21
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- 25
exterior surface. Fig. 14 shows the preforms 130 traveling bet;wean electrode
plates 108 and I 09,
which are connected to RF generator 110 and ground respectively. At station B,
the inner layer
is brought up to a temperature of about 295°F (146°C), and the
outer layer 1:o a temperature of
about 200°F (93°C). Finally, the preforms are passed to station
C, which is similar to station A.
At station C the quartz heaters bring the preforrns to a temperature of about
2g0°F (138°C) at the
inner layer and about 210°F (99°C) at the outer layer. The
repeated preforms are then sent to a
blow mold for stretch blow molding. A more detailed description of hybrid
repeating of
polyester preforms including a combination of quartz oven repeating and radio
frequency
repeating is described in U.S. Patent 4,731,513 to Collette entitled "Method
Of Repeating
Preforms For Forming Blow Molded I-lot Finable Containers," which issued March
15, 1988,
and is hereby incorporated by reference. In addition, additives may be
provided in either or both
of the PET and PEN layers to make them more receptive to radio frequency
heating.
In a preferred thin sleeve/thick outer layer embodiment, the thin inner layer
sleeve
may pave a thickness on the order of 0.02 to 0.06 inch (0.5 to 1.5mm), while
the thick outer layer
I5 has a wall thickness on the order of 0.10 to 0.25 inch (2.50 to 6.35mrn).
The inner layer may
comprise on the order of 10-20~/~ by total weight of the preforin. This
represents an
improvement over the prior art single injection cavity process for making
multilayer preforms.
Also, the weight of one or more outer layers (such as a layer o:f PC-PET) can
be maximized.
20 While there have been shown and described several embodiments of the
present
invention, it will be obvious to those skilled in the art that various changes
and modifications
may be made therein without departing from the scope of the invention as
defined by the
appending claims.
