Kerins, Gerald J., Cincinnati, Ohio 45203, US; Collette, Wayne N., Merrimack, New Hampshire 03054, US; Piccioli, David, Auburn, New Hampshire 03032, US; Tacito, Louis D., Merrimack, New Hampshire 03054, US; Beck, Martin H., Merrimack, New Hampshire 03054, US; Clark, Richard E., St. Charles, Illinois 60174, US; Harry, Ieuan L., Nashua, New Hampshire 03060, US; Krishnakumar, Suppayan, Nashua, New Hampshire 03060, US; Miller, Bryan H., Nashua, New Hampshire 03062, US; Nichols, Richard, Tyngsboro, Massachusetts 08179, US; Worsowicz, Eileene M., Dublin, New Hampshire 03444, US
Containers formed from biaxially oriented PET materials in the shape
of narrow mouth bottles, wide mouth jars, and cans have found increased market
acceptance over the past few years.
For the most part, these containers have been limited to product
applications involving low to moderate fill temperatures such as soft drinks,
edible oils, mustards, tennis balls, etc. It has been estimated that 25% of the
20+ billion unit food package market (currently captive in metal and glass) could
be captured by polymer containers if the latter could provide acceptable performance
when hot filled with products in the 71.1-93.3°C (160-200°F) temperature range.
It is known, however, that two distinct distortion phenomenon occur
when PET (polyethylene terathylate) containers produced by conventional injection
blow, reheat blow and/or other techniques are hot filled and sealed.
The first involves excessive container thermal shrinkage and resulting
distortion when exposed to temperatures that approach or exceed the glass transition
(Tg) or softening temperature of PET (approximately 76.6°C (170°F)). The second
deforming phenomenon results from the partial internal vacuum generated in the
container after it is hot filled and then sealed with the contents still at or
near the filling temperature. As the product itself and its head space gases cool,
the resulting volume contractions induce a partial internal vacuum which in turn
creates a net inward force on the container sidewall which may cause the latter
to buckle or collapse.
The occurrance of either phenomenon renders conventionally produced
PET containers unacceptable for commercial applications involving elevated filling
As recognized in the art, thermal shrinkage can be alleviated through
the application of a post forming heat treatment process. It is well known that
the distortion temperature of PET (Tg) can be raised by increasing the percent
crystallinity of the "finished" polymer well above that of the amorphous or preform
state. In blown containers, the latter is achieved (1) by the preform orientation
process (which yields strain induced crystallization) as well as (2) by constrained
post blow conditioning in a heated blow mold at temperatures somewhat above the
expected product service temperature (which yields thermal induced crystallization).
Strain induced crystallization alone is known to increase percent crystallinity
to a substantial degree, but considerably less than the percent crystallinity
(i.e., Tg) levels attainable with heat set thermal conditioning.
As such prior art PET containers for hot fill applications have been
prepared using thermal conditioning techniques, as exemplified by US-A-4318882
which discloses the features of the precharacterising portion of claim 1. The
commercial viability of the latter (so called "heat set" process), however, is
diminshed by several key constraints which involve (1) the time required to thermally
condition and cool the container walls prior to removal from the blow mold and
(2) the crystallization properties of PET which vary considerably with chain morphology
and as such directly influence the visual aesthetics and physical properties in
the final container as a function of orientation or draw level.
For example, established methods of raising the Tg of PET container
walls, require relatively long mold residence times (on the order of 5-20 seconds)
to yield the desired level of thermal conditioning (usually defined as 1% maximum
container volume shrinkage when filled at 87.8°C (190°F)). The vast majority of
existing PET products, however, are formed on two stage, high output, intermittent
motion, reheat blow molding machines which would suffer a significant reduction
in productivity (i.e. throughput per unit time) if the above mold residence times
were employed. Similar throughput and/or other economic disadvantages exist with
rotary reheat and injection blow conversion techniques.
Beyond excessive mold residence times, the commercial viability of
know heat set techniques is also limited by the tendency of unoriented, essentially
amorphous PET to turn milky white and opaque when thermally crystallized. As such,
it is usually necessary to cool the low orientation neck finish, shoulder, and
base of a biaxially oriented PET container to prevent excessive crystallization
and whitening of these areas during heat set thermal conditioning, if a fully
transparent container is desired. The highly oriented bottle sidewalls, of course,
remain transparent despite high levels of thermal induced crystallization. These
morphological phenomenon force the bottle producer to (1) purposely crystallize
and whiten the unoriented container regions and risk potential problems with market
acceptance (visual asethetics) and loss of physical properties (reduced impact
resistance of unoriented crystalline regions) or (2) minimize unoriented material
crystallization and suffer probable thermal container distortion during hot filling.
(A common solution to the latter involves increasing the wall thickness of the
unoriented, uncrystallized regions to strengthen the latter and reduce the potential
of thermal distortion. Again, however, increased unit costs severely limit this
In addition to thermal distortion, prior art recognizes several approaches
to alleviating pressure induced vacuum collapse. Increasing container wall thickness
in conjunction with reinforcing ribs, beads, or other structural features can
be effective, however disadvantageous from a unit cost and/or geometric standpoint.
In addition, the patent literature also recognizes solutions involving intentional
thermoelastically deformable and pressure deformable container regions which move
inwardly under the influence of the product temperature, and resulting partial
internal vacuum to offset or eliminate the latter. The principal disadvantage
with this approach stems from the need to radically alter conventional container
geometry and the resulting marketing complications associated with product image,
consumer acceptance, etc.
An economically and commercially viable PET container which would
not exhibit either thermal or vacuum induced distortion would open substantial
new market segments to the lighter weight, transparent, and shatterproof PET packages.
The prior art provides various solutions to the above problems, however, they
do so only by compromising container economics (unit costs) and market acceptability
As such, it is the primary aim of the present invention to provide
an improved method of producing cost effective, hot fillable PET containers that
exhibit commercially acceptable thermal shrinkage with no vacuum collapse (when
hot filled and sealed at temperatures up to and including 93.3°C (200°F)) without
the need for post forming heat treatment and/or nonconventional container geometries.
A novel solution to the vacuum induced deformation problem for conventional
container geometries is provided through the application of specific process control
and product design techniques (in the container production and filling process)
to yield controlled levels of container shrinkage and "controlled" vacuum collapse
as required to achieve minimal internal vacuum levels with acceptable filled container
Accordingly, the present invention provides a method of forming a
thermal collapse resistant highly oriented polyester container suitable for use
in hot fill applications, the method comprising the steps of providing a polyester
preform (26), reheating the preform, placing the preform in a blow mould cavity,
and distending the preform to match the blow mould cavity to form a container,
characterised in that the total wall draw ratio of the preform is greater than
8 to 1 but less than 12 to 1 and the temperature of the reheated preform generally
ranges between 82.2°C (180°C) and 121.1°C (250°F) thereby to raise the side wall
density of the container to a density of from 1.350 to substantially but less than
1.370 grams/cubic centimeter, which density corresponds to 14 to 30% crystallinity.
The method of the present invention may be regarded as a partial
application of wide mouth PET container manufacturing technology as described in
U.S. Patent No. 4,496,064 to Beck et al.
The present invention also provides a thermal collapse-resistant
highly oriented polyester container suitable for use in hot fill applications,
the container having been stretch blow moulded from a preform, the container including
a finish portion, a container body portion having a sidewall, and a base portion,
characterised in that the sidewall density of the container is from 1.350 to substantially
but less than 1.370 grams/cubic centimeter, which density corresponds to 14 to
30% crystallinity, and the stretch ratio of the sidewall is greater than 8 to 1
but less than 12 to 1.
The above described wide mouth technology utilizes PET preforms produced
by conventional techniques to, in turn, produce wide mouth bottles and cans with
biaxially oriented thread and/or flange areas. The resulting container finish,
being oriented to a controlled degree, overcomes the disadvantages of non-oriented
amorphous polyester in heat set/hot fill processes as described earlier.
With the above and other objects in view that will hereinafter appear,
the nature of the invention will be more clearly understood by reference to the
following detailed description, the appended claims, and the several views illustrated
in the accompanying drawings.
Figure 1A is an elevational view of a polyester container produced
by a conventional technique.
Figure 1B is an elevational view of the same container after being
filled with a hot product at a temperature 87.8°C (190°F).
Figure 1C is an elevational view of the container of Figure 1 wherein
the container was improved by heat setting and then hot filled at 87.8°C (190°F)
with the container exhibiting a volume loss of 1% and having a convoluted, non-conventional
vacuum collapsed geometry.
Figure 2 is a half sectional view taken through a typical preform
utilized in conjunction with the present invention.
Figure 3 is a half sectional view taken through a standard mold defining
a blow cavity and having positioned therein the preform of Figure 2 prior to blow
Figure 4 is a half vertical sectional view of the resultant intermediate
article from blow molding the preform of Figure 2 in the mold cavity of Figure
Figure 5 is a half sectional view of a polyester can resulting from
the severing of the intermediate article of Figure 4 along the path of the arrow
Figure 6 is a half sectional view of a jar having a screw-threaded
neck finish, which jar is formed as part of an intermediate article in the same
general manner as shown in Figure 3.
Figure 7 is a half sectional view of the can of Figure 5 after filling
with a hot product at 87.8°C (190°F) and closing by securing an end unit thereto
utilizing a double seam, and where a 5% volume shrinkage is permitted to occur
after the double seaming.
Figure 8 is a half sectional view taken through the jar of Figure
6 after hot filling with a product at 87.8°C (190°F) and closing utilizing a cover
where 5% volume shrinkage is permitted to occur after closing.
Figure 9 is a graph showing typical wall density measurements and
calculated percent crystallinity for containers formed in accordance with the
aforementioned Beck et al patent vs. conventionally produced wide mouth jars.
Figure 10 is a half sectional view showing a can similar to that
of Figure 5 and closed in the manner shown in Figure 7 formed in accordance with
this invention and hot filled and sealed when less than 1% volume shrinkage is
Figure 11 is a half sectional view similar to Figure 10 but showing
a jar closed in the manner shown in Figure 8 and wherein less than 1% volume shrinkage
Fgiure 12 is a schematic elevational view of a spray cooling device
used to minimize container shrinkage during hot filling and seaming.
Figure 13 is a graph of polyester density as a function of draw ratio.
Figure 14 is a graph of polyester shrinkage at 87.8°C (190°F) as
a function of draw ratio.
Figure 15 is a graph of density vs. preform temperature at a fixed
Figure 16 is a graph of density vs. polyester comonomer contents
at a fixed preform temperature and draw ratio.
Figure 17 is a graph showing typical volume shrinkage curves as a
function of hot fill temperature for containers produced by various techniques.
Figure 18 is an enlarged fragmentary sectional view taken through
a typical preform wherein the preform is of a laminated construction.
Polyester containers when produced by conventional reheat or injection
blow techniques exhibit excessive thermal shrinkage of from 15-50% volume loss
when hot filled at 87.8°C (190°F). An example of such a container is shown in
Figure 1. As noted earlier, the prior art provides solutions to the polyester
thermal distortion problem by conditioning the blown container in a heated blow
mold to raise the polymer Tg (i.e. softening temperature) to somewhat above 87.8°C
(190°F). The heat set process accomplishes the above by increasing the polyester
percent crystallinity in the bottle sidewalls. The Tg of highly crystalline polyester
(i.e. above 50% crystallinity) is in excess of 176.7°C (350°F) (i.e. Tg increases
with increasing percent crystallinity). Density as measured by ASTM test method
#1505 is a useful measure of crystallinity as per:
= sample density in g/cm³
= 1.333 g/cm³ (amorphous)
= 1.455 g/cm³ (100% crystalline)
Figs. 1A, B Fig. 1C FINISH DENSITY (g/cm³)1.3411.388 FINISH % DIAMETER SHRINKAGE1.220.08 SIDEWALL DENSITY (g/cm³)1.3571.372 SIDEWALL % DIAMETER SHRINKAGE10.50.52 SIDEWALL % HEIGHT SHRINKAGE8.80.40
Table 1 above shows density vs. percent shrinkage data for the container
shown in Figure 1.
In general, heat set containers exhibit less than 1% volume loss
when filled at 87.8°C (190°F) and sidewall density measurements in excess of 1.365
g/cm³ and usually in excess of 1.370 g/cm³ (26% and 30% crystallinity
Although heat set containers exhibit acceptable thermal distortion
when filled at 87.8°C (190°F), they remain susceptible to pressure induced vacuum
collapse. Partial vacuum levels in excess of 5.52 x 10&sup4; - 11.03 x 10&sup4;
Pa (8-16 psi) (depending on fill level, product fill temperature, etc.) are typically
seen in rigid containers after the contents cool to ambient. To prevent the distortion
of the flexible polyester sidewalls, non-conventional container geometries such
as convoluted panels are utilized to control deformation usually in conjunction
with structural features such as ribs, beads and increased sidewall thickness.
In addition to increased unit costs the marketing disadvantages associated with
the radical geometries are substantial.
In addition, prior art heat set containers must prevent excessive
distortion of the finish region during hot filling to effect proper closure application
and sealing. Certain bottles, for example, utilize a pre-crystallized, opaque
finish to minimize distortion. Although effective, this method adds considerably
to unit costs. Other bottles maintain finish transparency by utilizing increased
wall thickness (vs. conventional non-hot fill containers) to minimize distortion.
The added costs associated with the latter approach limits its usefulness.
The following then demonstrates a novel method of producing hot fillable
polyester containers without the negatives associated with heat set approaches:
Figures 2-6 illustrate the manner in which cans, bottles and jars
molded from conventional single or multilayer injection or extrusion molded preforms
in accordance with the afore-described Beck et al patent and which exhibit highly
oriented flange and/or finish regions.
Reference is now specifically made to Figure 2 wherein there is illustrated
a preform particularly provided in accordance with this invention. The preform
is circular in cross section about a center axis 20 and includes an upper portion
22 which is open ended and is disposed above a support flange 24. As will be seen
in more detail in Figure 3, the flange and the neck portion 22 project out of
an associated blow mold. In a conventional molding operation, a blow tube fits
in the neck portion 22 and is sealed with respect thereto.
Immediately below the flange 24, the preform, which is generally
identified by the numeral 26, has a cylindrical portion 28 and thereafter increases
in thickness radially outwardly in an area identified by the numeral 30. Thereafter
the preform 26 is composed of an elongated cylindrical portion 32 which is slightly
tapered both internally and externally to facilitate withdrawal from the injection
mold and an associated core while remaining generally of a constant thickness.
The preform 26 has a substantially hemispherical bottom portion 34 which reduces
in thickness towards the center thereof.
It is to be understood, however, that the dimensions of the preform
will vary depending upon the particular immediately article which is to be formed.
Although there has been specifically illustrated an injection molded
preform 26, it is to be understood that the preform could be formed from an extruded
Reference is now made to Figure 18 wherein there is illustrated an
enlarged cross section through a typical preform which is of a laminated construction.
Such a preform would have exterior and interior layers 36 and 38 which are formed
of PET. Inward of these layers would be relatively thin barrier layers 40, 42,which
may be formed of materials such as SARAN (Registered Trade Mark). Finally there
will be a core 44 which may be formed of PET or a compatible polymer.
In Figure 3 there is schematically illustrated a typical blow mold,
which will be formed in split halves, and which is identified by the numeral 46.
The blow mold 46 will be provided with one or more blow cavities 48 which is shaped
to form an intermediate article of which a lower part is in the form of a can.
The preform 26 is clamped in the cavity 48 and supported by the flange 24. Suitable
conventional blowing apparatus including a blow stick (not shown) will be utilized
to direct blowing gas under pressure into the preform 26 and also to axially elongate
or stretch the preform 26. It is to be understood that the preform 26 will be
particularly configurated with respect to the cavity 48 to provide a preselected
draw ratio. Further, the axial elongation or stretching of the preform 26 with
respect to the cavity 48 and the expansion thereof due to the internal gas will
also be controlled so as to control the resultant thickness and draw ratio of
the body or sidewall of the resultant container.
In Figure 4 there is illustrated an intermediate article 50 which
has been formed from the preform 26 in the blow mold cavity 48. The lower part
of the article 50 will be in the form of a can which includes a bottom wall 54,
having integrally joined thereto a sidewall or body 56 with the sidewall 56 terminating
in an upper outwardly directed flange 58. If desired, the sidewall 56 may be provided
with internally directed vertically collapsible beads 60 to accommodate a decrease
in volume within the container as the product cools. The beads 60 will be formed
by internal ribs 62 of the blow mold 46.
The upper portion of the intermediate article 50 is generally identified
by the numeral 64 and will be considered an adaptor portion. The adaptor portion
64 is severed from the container or can 52 by cutting such as along the line defined
by the arrow A in Figure 4. This removed adaptor portion 64 may then be reground
and utilized in the forming of further preforms.
The separated container or can 52 is best illustrated in Figure 5
wherein the flange 58 becomes the customary flange utilized for double seaming
an end unit to the body 56.
It is to be understood that the configuration of the mold cavity
48 may be modified to form an intermediate article (not shown) of which the lower
part is in the form of a jar which is best illustrated in Figure 6 and is generally
identified by the numeral 66. The jar 66 will have a bottom wall 68 which closes
the lower end of a sidewall or body 70. The upper end of the body is open, but
in lieu of having the seaming flange 58, the upper end of the body is inwardly
directed to define an annular flange 72 which has extending axially upwardly therefrom
a neck finish 74 to which a conventional screw threaded or lug type closure cap
may be attached. If desired, the body 70 may be reinforced by hollow ribs 76 which
will be similar to the ribs 60.
In Figure 7, the can 52 is illustrated as having been filled with
a hot product 78 and closed by means of an end unit generally identified by the
numeral 80. The illustrated end unit is in the form of a metal or composite end
which is secured to the can by a conventional double seam 82 incorporating the
In Figure 8, the jar 66 is illustrated as being filled with a hot
fill product and being closed by an end unit 86. The end unit 86 is illustrated
as being in the form of a conventional closure having a depending skirt 88 which
is interlocked with the neck finish 74. It is to be understood that the end panel
portion of the closure 86 will be sealed relative to an end sealing surface 90
(Figure 6) of the neck finish 74.
As previously described, when the can 52 of Figure 5 and jar 66 of
Figure 6 are formed conventionally from a PET preform as described in the aforementioned
Beck et al patent, they are suitable to a high percentage of shrinkage when filled
with a hot product.
Figures 7 and 8 show a can and a wide mouth jar after hot filling
at 87.8°C (190°F). Total volume shrinkage for these containers produced by non-optimized
process conditions are typically in the 6-10% range vs. the 15-50% values exhibited
by prior art containers of the type shown in Figure 1.
The substantial improvement in performance results from elimination
of large, low orientation and essentially amorphous regions such as the closure
receiving finish and shoulder to sidewall transition regions which exist in containers
produced by conventional techniques.
Figure 13 is a typical graph of density vs. draw ratio for crystallizable
polyesters. Draw ratio is defined as:
= Max Bottle OD
= Min Preform ID
= length of bottle below finish
= length of preform below finish
By orienting the finish and shoulder regions of the final
container,the higher overall density (i.e. percent crystallinity and Tg) of such
containers (vs. conventional containers) as shown in Figures 5 and 6 results in
reduced thermal distortion when hot filled (without the need to thermally crystallize
or "heat set").
Figures 13 through 16 show graphs of various relationships relevant
to maximizing the density of polyester in finished containers with heat setting.
Those skilled in the art will recognize the role of, and interrelationships between;
tooling design, polyester composition, and process conditions (all non heat setting
variables) as they influence the polyester percent crystallinity in the finished
Figure 13, for example, shows how strain induced crystallization
raises the density of polyester to a maximum level somewhat less than 1.37 g/cm³
at a total draw ratio greater than 8 to 1 but less than 12 to 1 for typical polyesters.
Figure 14 shows the negative effect of excessive draw ratios beyond
that of maximum strain hardening on percent shrinkage. It is known that total
draw ratio is a controlling factor in density improvement. The ratio of axial
to hoop draw, for example, is of little consequence.
As further examples of known density optimization techniques, Figures
15 and 16 indicate the influence of process conditions and polyester composition
By combining the basic Beck et al oriented finish technology with
the prior art process techniques noted above, polyester containers with overall
volume shrinkage in the range of 3-5% (when hot filled at 87.8°C (190°F)) can
be produced without heat set thermal conditioning. The average sidewall and flange/finish
density of containers produced by such techniques range from 1.350 g/cm³
to 1.370 g/cm³ (14-30% crystallinity), more preferably from 1.360 to 1.370
g/cm³ (22 to 30% crystallinity).
Containers which exhibit 3-5% volume shrinkage at 87.8°C (190°F)
do not vary substantially in appearance vs. nonexposed containers and are, as
such, commercially viable for hot fill applications.
The 3-5% volume shrinkage can in fact be beneficial to reduce the
internal vacuum which is created when the container contents and head space gases
cool after sealing. In general, at a 87.8°C (190°F) fill temperature, a shrinkage
induced container volume reduction of from 2-5% is sufficient to neutralize the
pressure forces which tend to collapse the container. To effectively eliminate
the potential of vacuum collapse, it is desirable to minimize the container shrinkage
which occurs during hot filling and before sealing. This is best accomplished by
reducing the time interval between the onset of filling and the completion of
sealing to 5 seconds or less. If the latter is not practical due to filling line
and/or product constraints, it may be necessary to cool the exterior of the container
during filling and prior to sealing.
A spray system, as shown in Figure 12, has been found to effectively
increase the permissible fill/seam time interval by a factor of 10 or more.
Reference is now made to Figure 1 wherein there is illustrated the
manner in which a can, such as the can 52, but formed in accordance with this
invention, is filled and then sealed. There is schematically illustrated a support
90 on which the can 52, for example, is seated at which time it is seated beneath
a suitable filler 92 from which a hot fill product is dispensed into the can 52.
At the time the can 52 is being filled, it may simultaneously be cooled by means
of spray ducts 94. The spray ducts 94 may spray cool water on the can 52 or a
suitable cooling gas.
After the can 52 has been filled, it may be, after a suitable delay,
passed to a closing machine generally identified by the numeral 96 which applies
in a conventional manner the end unit 80 and forms the double seam 82. Only the
backup chuck 98 and one of the forming rolls 100 of the closing machine or double
seamer 96 is illustrated.
Associated with the closing machine and positioned to spray the can
52 as it is being closed are spray ducts 102. Like the spray ducts 94, the spray
ducts 102 may spray either cool water or a cooling gas onto the can 52 as it is
The above "controlled" shrinkage process effectively eliminates the
need for radial container geometries or excessive wall thicknesses. It is, however,
desirable to utilize the stiffening ribs or beads 60, 76, as shown in Figures
5 and 6, to prevent collapse due to long term water vapor transmission and the
resulting partial internal vacuum over extended product shelf life periods.
The following specific examples are intended to illustrate more fully
the nature of the present invention without limiting its overall scope:
This example demonstrates the production of a 411 x 501 polyester
can which exhibits 6-8% volume shrinkage when hot filled at 87.8°C (190°F). A
62 gram preform as shown in Figure 3 having a length of 12.57 cm (4.95 inches)
below the flange and an outside diameter of 3.96 cm (1.56 inches) with an average
wall thickness of 0.457 cm (0.180 inch) was produced from a PET copolymer (2%
by weight isophthalate) having an intrinsic viscosity of 0.80 ± 0.1.
The preform was reheated on a conventional stretch blow molding machine
equipped with a quartz IR reheat oven, at an overall machine cycle of 5.0 seconds.
The preform temperature just prior to stretch blowing was measured (using an IR
pyrometer) at 93.3°C (200°F). Blow mold temperature was maintained at 1.7°C (35°F).
The trimmed container was filled with water at 87.8°C (190°F) to
within 1.598 cm (0.625 inches) of the flange and allowed to cool to room temperature.
The total volume loss was then measured at 8.2%. The average sidewall density
averaged 1.348 grams/cm³ and as such a fully developed/strain thermally induced
crystalline structure was not achieved.
This example demonstrates the production of a polyester can as per
Example 1 with the tooling, material and process conditions optimized to yield
3-4% volume shrinkage when hot filled at 87.8°C (190°F).
The same preforms used in Example 1 were reheated at an identical
oven resident time, however, the quartz lamp energy outputs were increased to
raise the preform temperature prior to the onset of visible crystallinity). In
addition, the vertical preform temperature profile as well as the degree of axial
preform stretch prior to the onset of pressure expansion was altered to reduce
the wall thickness of the blown container to 0.038 cm (0.015 inches). All other
process and evaluation conditions were identical to those used in Example 1.
Total volume shrinkage was 4.2% and average sidewall density was
1.362 grams/cm³. As such, a fully developed, highly transparent, strain/thermally
induced crystalline structure was developed.
This example demonstrates the effectiveness of controlled container
shrinkage in preventing vacuum induced collapse.
Ten (10) polyester cans produced, as per Example 2, were hot filled
with water at 87.8°C (190°F) to a level 1.588 cm (0.625 inches) below the flange
and permitted to stand for 10 seconds prior to double seaming. All samples exhibited
vacuum induced collapse (as shown in Figure 10).
An additional ten (10) cans from the same lot were hot filled at
87.8°C (190°F), double seamed within 2 seconds, and immediately placed in a water
bath and cooled to ambient. All samples collapsed prior to removal.
A final group of ten (10) cans from the same lot were filled at 87.8°C
(190°F), seamed within 2 seconds and permitted to shrink under ambient conditions.
None of the samples exhibited vacuum induced deformation.
This example demonstrates the production of a polyester wide mouth
jar with controlled finish and sidewall shrinkage.
An 80 gram preform with a length below the finish of 16.03 cm (6.31
inches) and an average wall thickness of 0.470 cm (0.185 inch) was produced by
conventional injection techniques using a polyester homopolymer of 0.80 ± 0.1
The preform was reheated in a quartz oven to a temperature of 107.2°C
(225°F), with the vertical temperature profile and stretchblow conditions adjusted
to yield a 70mm CT, 680 gram (24 oz.) container (as shown in Figure 6) with a finish
wall thickness of 0.064 cm (0.025 inches) and an average sidewall thickness of
0.038 cm (0.015 inches).
Upon trimming and hot filling at 87.8°C (190°F) the overall volume
loss was 5.2% with a finish diameter reduction of 2.0% vs. a panel diameter reduction
of 3.2%. Average density of the finish and body sidewall areas were measured at
1.360 g/cm³ vs 1.356 g/cm³ respectively. Control containers using prior
art injection molded finishes as per Figure 1B showed unacceptable deformation
and overall volume loss.
This example demonstrates the synergistic effect of combining the
inherent Glastik oriented finish or flange advantages with known heat set techniques.
Preforms as utilized in Examples 1 and 2 and reheated as per Example
2 were stretch blown into the same blow mold as per Examples 1 and 2. The latter,
however, was maintained at 121°C (250°F) for 10 seconds (vs. 1.7°C (35°) for 1.5
seconds in Examples 1 and 2).
The resulting containers when hot filled exhibited 0.4% volume loss
at 87.8°C (190°F).
Preforms as utilized in Example 4 and reheated as per the same were
stretch blown into the same blow mold as per Example 4. The latter, however was
maintained at 121.1°C (250°F) for 10 seconds (vs 1.7°C (35°F) for 2.0 seconds
in Example 2).
The resulting containers exhibited transparent finish and shoulder
regions as well as 0.8% volume loss at 87.8°C (190°F).
By contrast, a 49 gram container of the same shape and size produced
by a conventional injection blow process heat set process exhibited a semi-opaque
finish and shoulder region and 1.6% volume loss at 87.8°C (190°F).
A graphic representation is shown in Figure 17. The curves represent
containers produced as follows:
Conventional non-heat set technology
Non-heat set Beck et al
Prior art conventional heat set
Heat set Beck et al
A method of forming a thermal collapse resistant highly oriented polyester
container suitable for use in hot fill applications, the method comprising the
steps of providing a polyester preform (26), reheating the preform, placing the
preform in a blow mould cavity, and distending the preform to match the blow mould
cavity to form a container, characterised in that the total wall draw ratio of
the preform is greater than 8 to 1 but less than 12 to 1 and the temperature of
the reheated preform generally ranges between 82.2°C (180°F) and 121.1°C (250°F)
thereby to raise the side wall density of the container to a density of from 1.350
to substantially but less than 1.370 grams/cubic centimeter, which density corresponds
to 14 to 30% crystallinity.
A method according to claim 1, characterised in that the average density of
the container is from 1.360 to 1.370 grams/cubic centimeter, which density corresponds
to 22% to 30% crystallinity.
A method according to claim 1 or claim 2 characterised in that the total wall
draw ratio of the preform is in the range of 8-10 to 1.
A method according to any one of claims 1 to 3 characterised in that the container
has a container volume shrinkage after hot filling at 87.8°C (190°F) of less than
A method according to any foregoing claim characterised by further comprising
the step of thermally conditioning at least the sidewall and finish of the container
by retaining the container for 2 to 5 seconds in the blow mold which is maintained
at a temperature above 87.8°C (190°F).
A method according to any one of claims 1 to 4, characterised by further comprising
the step of heat setting the container by retaining container in the blow mould.
A method according to claim 6 wherein the heat setting is carried out for a
period of around 10 seconds at a temperatures of around 121.1°C (250°F).
A method according to any foregoing claim, characterised in that the polyester
composition has an intrinsic viscosity on the order of 0.80 +/- 0.1.
A method according to any foregoing claim, characterised in that the temperature
of the reheated preform is on the order of 107.2°C (225°F) with there being an
axial temperature profile.
A method according to any foregoing Claim, characterised in that the provided
preform is of a multi-layer structure.
A method according to any foregoing claim, characterised by the step of internally
cooling the container prior to removing the container from the mold.
A method according to any foregoing claim, characterised by further comprising
the steps of hot filling the container with a hot fill product and closing the
A method according to claim 12 characterised in that the container volume shrinkage
resulting from the heating of the container during hot filling and the shrinkage
of the contents resulting from the cooling of the product in the closed container
are controlled so as substantially to eliminate deformation of the container.
A method according to claim 13 characterised in that the container shrinkage
after hot filling and before closing is minimised so as to eliminate collapse of
A method according to claim 14 characterised in that the container is closed
about 5 seconds or less after hot filling.
A method according to claim 15 characterised in that the container is closed
about 2 seconds after hot filling.
A method according any one of claims 14 to 16 characterised in that the hot
filled container is permitted to cool under ambient conditions.
A method according to any one of claims 1 to 13, characterised in that the
container is cooled during the hot filling and before closing to effect a substantial
portion of container shrinkage due to hot filling to occur after sealing.
A method according to claim 18, characterised in that the container cooling
is effected by fluid cooling of the water and gas type.
A thermal collapse-resistant highly oriented polyester container suitable for
use in hot fill applications, the container having been stretch blow moulded from
a preform, the container including a finish portion, a container body portion
having a sidewall, and a base portion, characterised in that the sidewall density
of the container is from 1.350 to substantially but less than 1.370 grams/cubic
centimeter, which density corresponds to 14 to 30% crystallinity, and the stretch
ratio of the sidewall is greater than 8 to 1 but less than 12 to 1.
A container according to claim 20, characterised in that the average density
of the container is from 1.360 to 1.370 grams/cubic centimeter, which density corresponds
to 22% to 30% crystallinity.
A container according to claim 20 or claim 21 characterised in that the total
wall draw ratio of the preform is in the range of 8-10 to 1.
A container according to any one of claims 20 to 22 characterised in that the
container has a container volume shrinkage after hot filling at 87.8°C (190°F)
of less than about 5%.
A container according to any one of claims 20 to 23, characterised in that
the polyester composition has an intrinsic viscosity on the order of 0.80 +/- 0.1.
A container according to any one of claims 20 to 24, characterised in that
the container is of a multi-layer structure.
A container according to any one of claims 20 to 25, characterised in that
the container is closed and has been hot filled with a product.
A container according to claim 26 characterised in that the container volume
shrinkage resulting from the heating of the container during hot filling and the
shrinkage of the contents resulting from the cooling of the product in the closed
container have been controlled so as substantially to eliminate deformation of