Note: Descriptions are shown in the official language in which they were submitted.
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DELAMINATION-RESISTANT MULTILAYER CONTAINER PREFORM AND
METHOD OF MANUFACTURE
The present invention is directed to multilayer plastic containers and
preforms,
and to methods of manufacturing such containers and preforms.
Background and Summary of the Invention
Multilayer plastic containers and preforms typically include one or more
layers
of plastic resin such as polyethylene terephthalate (PET) alternating with one
or more layers of
bai7ier resin such as nylon or ethylene vinyl alcohol (EVOH) to resist
transmission of gas, water
vapor and/or flavorants, including odorants and essential oils, through the
container wall. An
important property of containers of this type is interlaminar adhesion to
resist delamination
between or among the various layers during filling and handling of the
containers by the
container manufacturer and the product paclcager, and during use of the
container by the
consumer. Various tecluziques have been proposed for increasing interlaminar
adhesion, which
generally result in a decrease in barrier properties, an increase in
manufacturing cost and/or an
increase in other undesirable container properties such as haze in the -
container wall. It is
therefore a general object of the present invention to provide a multilayer
container, a container
preform and a method of manufacture having improved adhesion characteristics
between the
layers of the container (and preform) wall without significantly affecting
container cost or other
parameters of manufacture.
A plastic container in accordance with one presently preferred aspect of the
invention includes a multilayer wall having at least one layer ofpolyester
resin, at least one layer
of barrier resin, and an adhesion-promoting material blended with the barrier
resin and/or the
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polyester resin to promote bonding between the barrier and polyester layers.
In the preferred
embodiments of the invention, the adhesion-promoting material is blended with
the barrier resin.
The adhesion-promoting material includes an organometallic coupling agent
based upon
titanium, zirconium or aluminum. The organometallic coupling agent preferably
has an amino
end group with an affinity for the carboxylic end group of the polyester, and
preferably is selected
from the group consisting of neopentyl(diallyl)oxy, tri(N-ethylenediamino)
ethyl titanate,
zirconate and aluminate. Coupling agents based upon titanium and zirconium are
particularly
preferred for containers having a clear (non-colored) wall.
The polyester resin preferably is selected from the group consisting of PET,
polyethylene naphthalate (PEN), blends and copolymers of PET and PEN, and
process regrind
that consists essentially of PET, PEN, or blends or copolymers of PET and PEN.
The barrier
resin preferably is selected from the group consisting of EVOH, nylon,
acrylonitrile copolymers,
blends of EVOH and nylon, nanocomposites of EVOH or nylon and clay, blends of
EVOH and
an ionomer, acrylonitrile, cyclic olefin copolymers, polyglycolic acid (PGA),
and blends thereof.
EVOH and m eta-xylylenediamine (MXD) nylon are p articularly p referred. A
ctive o xygen
absorbing barrier resins also may be employed in coinbination with or in place
of the listed
passive barrier resins.
Other aspects of the invention include a plastic container preform, methods of
malcing a plastic container and a preform, a barrier resin blend, a method of
processing a bairi.er
resin and a multilayer article in accordance with the invention.
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Brief Description of the Drawings
The invention, together with additional objects, features, advantages and
aspects
thereof, will be best understood from the following description, the appended
claims and the
accompanying drawings, in which:
FIGS. 1 to 4 are graplhic illustrations of test results on containers
fabricated in
accordance with exemplary einbodiments of the invention,
FIGS. 5A and 5B are schematic diagrams of a container preform in accordance
with one aspect of the invention, and
FIGS. 6A and 6B are schematic diagrams of aplastic container in accordance
with
another aspect of the invention.
Detailed Description of Preferred Embodiments
The Ken-React Reference Manual, published by Kenrich Petrochemicals, 2"a
edition 1993, Bulletin KR 0401, is incorporated herein by reference.
Containers and preforms in accordance with the present invention have a
multilayer wall with at least one layer of polyester resin alternating with at
least one layer of
barrier resin. (Additional layers not germane to the present invention may
also be included, such
as post consumer resin layers.) For example, a three-layer container or
preform may have a wall
with layers in the sequence polyester/barrier/polyester. A five-layer
container or preform may
have wall layers in the sequence
polyester/barrier/polyester/barrier/polyester. The barrier layer
or layers may extend throughout the bottom wall and the sidewall of the
container or preform,
or may be confined to a portion of the sidewall, for exanlple. The barrier
layers may or may not
extend into the fmish of the container or preform. FIGS. 6A and 6B are
schematic illustrations
of a five-layer container in accordance with the invention, the size and
geometry being for
illustrative purposes only. All exemplary test containers (and preforms) are
five-layer containers
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(and preforms) of the type illustrated in FIGS. 6A and 6B (and FIGS. 5A and
5B), In accordance
with one aspect of the present invention, an organometallic coupling agent
based upon titanium,
zirconium or aluminum is blended in each barrier layer and/or each polyester
layer to promote
adhesion between the barrier and polyester layers.
The polyester resin preferably is selected from the group consisting ofPET,
PEN,
blends and copolymers of PET and PEN, and process regrind that consists
essentially of PET,
PEN, or blends or copolymers of PET and PEN. In the examples discussed in the
present
application, the polyester resin was PET.
The barrier resin is a thermoplastic material that has a low gas and/or water
vapor
transmission rate, and/or exhibits a high barrier to transmission of
flavorants including odorants
and essential oils. The following materials are preferred: EVOH, nylon
(including amorphous
nylon and semicrystalline nylon such as MXD6), acrylonitrile copolymers,
blends ofEVOH and
nylon, blends of EVOH and an ionomer, cyclic olefin copolymers, PGA,
nanocomposites of
EVOH or nylon and clay, and blends thereof. EVOH and nylon are particularly
preferred.
MXD6 nylon and EVOH were employed as bairier resins in the examples discussed
in this
application.
The organometallic coupling agents employed in the present invention
preferably,
although not necessarily, are marlceted by Kenrich Petrochemicals Inc. of
Bayonne, New Jersey.
Coupling ageiits that are amino functionalized - i.e., that include. an amino
end group - are
ZO preferred. Such amino end groups in the coupling agent have an affmity for
polyester, carbonyl
and acid end groups in the structural resin layers. Neopentyl(diallyl)oxy,
tri(N-ethylenediamino)
ethyl titanate marlceted under the trade designation LICA-44 and
neopentyl(diallyl)oxy, tri(N-
ethylenediamino) ethyl zirconate marlceted under the trade designation NZ-44
are.particularly
preferred. Corresponding organometallic coupling agents based upon aluminum
can tint the wall
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of a clear (non-colored) plastic container, but may be employed where the
container is
intentionally colored and such tinting would not be an issue. Other coupling
agents marketed by
Kenrich and having amino end groups include isopropyl tri(N-ethylenediamino)
ethyl titanate
(KR-44), neopentyl (diallyl)oxy, tri(m-amino) phenyl titanate (LICA-97),
dineopentyl(diallyl)oxy, diparamino beneoyl zirconate (NZ-37)
andneopentyl(diallyl)oxy, tri(m-
amino)phenyl zirconate (NZ-97). NZ-44 and LICA- 44 coupling agents were
employed in the
examples discussed in this application.
It is currently preferred that the coupling agent be blended with the barrier
resin.
Because the barrier resin layers form a relatively small percentage by weight
of the overall
preform or container, a lesser quantity of coupling agent is required than if
the coupling agent
were blended with the polyester resin. However, the coupling agent could be
blended with the
polyester resin, or with both the polyester resin and the barrier resin, in
accordance with the
broadest aspects of the invention.
The organometallic coupling agent typically is in the form of a liquid, and
preferably is blended witli the barrier resin material prior to forming the
multilayer container.
In the tests described in this application, the liquid coupling agent additive
was blended with
particles ofthe barrier material (MXD6 or EVOH) at room temperature before
feeding the blend
to the extruder. This blending could also be done by master batch
concentration by the barrier
material supplier: The coupling agent acts as a melt phase modifier during the
manufacturing
process, w hich c an 1 ower t he p rocessing t emperature a nd/or p ermit u se
o f h igher i ntrinsic
viscosity (IV) barrier resins. Higher IV barrier resins tend to have better
barrier properties, and
thus the present invention facilitates improved barrier properties of the
resin without increasing
the thiclcness of the barrier resin layer. The following Table 1 shows plaque
screening test results
on MXD6 barrier material without coupling agent (control), or blended with
either LICA-44 or
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NZ-44 coupling agent, or blended with LICA-12 (neopentyl(diallyl)oxy,
tri(dioctyl)phosphato
titanate) or NZ- 12 (neopentyl(diallyl)oxy, tri(dioctyl)phosphato zirconate)
coupling agents also
supplied by Kenrich:
Table 1
Additive Additive Processing Test Resin RV Resin IV Plaque Plaque IV
% Temp ( C) (dl/g) RV (dl/g)
Control - 260 IV & Visual 1.8795 1.41 1.837 1.35
LICA-12 0.35 230 IV & Visual 1.8795 1.41 1.836 1.35
LICA-44 0.35 230 IV & Visual 1.8795 1.41 1.832 1.35
NZ-12 0.35 230 IV & Visual 1.8795 1.41 1.834 1.35
NZ-44 0.35 230 IV & Visual 1.8795 1.41 1.825 1.34
The plaques were made by injection molding at the processing temperatures
indicated in the
Table. The plaques were stepped plaques 6.25 in (15 8.75 mni) long by 1.75 in
(44.45 mm) wide.
The plaques had five equal sections of stepped thicknesses of 0.16 in (4.06
mm), 0.13 in (3.3
mm), 0.10 in (2.54 inm), 0.07 in (1.78 nun) and 0.04 in (1 mm). The visual
tests consisted of
observation whether the plaque mold had completely filled. The control sanlple
required a
processing temperature of 260 C to fill the plaque mold completely, while the
samples with
coupling agents required a processing temperature of only, 230 C to fill the
plaque mold
completely. It will also be noted that LICA-12 and NZ-12 coupling agents,
which have
phosphate end groups rather than amino end groups, also achieved the reduced
processing
temperature, although these additives would not be preferred forpromoting
adhesion to polyester
layers because of the absence of the amino end groups.
Table 1 also indicates the relative viscosities (RV) and intrinsic viscosities
(IV)
of the base resin and the plaques. These viscosities were measured in a
Viscotek model Y501 C
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viscometer employing standard dilute solution viscometrytechniques. Relative
viscosities were
measured at the "low" range of the equipment. Intrinsic viscosities were
measured as described
in the equipment manual with use of the Solomon-Gatesman equation. Resin
viscosities were
measured at 30 C in 60:40 Phenol:1,1,2,2 Tetrachloroethane. Thus, as shown in
Table 1, the
coupling agents permitted the processing temperature to be lowered 30 C and
still make good
plaques. The control (MXD6 without coupling agent) could not be processed at
temperatures
below 260 C in the equipment employed. (The same Arburg Model 320-210-500
molding
equipment was employed for all tests.) There were no significant differences
among the intrinsic
viscosities of the blends and the control, demonstrating that there was no
degradation of the
polymer molecular weight.
The following Table 2 demonstrates the increase in barrier properties
employing
an MXD6 barrier resin of higher intrinsic viscosity (IV), which was enabled by
blending the
barrier resin with the coupling agent. In test containers of Table 2, the
containers with M]XD6
barrier resin were of the five-layer construction of FIGS, 6A and 6B, with the
total weight
percentages of barrier resin (blended with coupling agent) being 3%, such that
each barrier layer
was approximately 1.5 wt % of the total container weight. That is, the NZ-44
coupling agent was
0.5 wt % of the total barrier resin, and the blend of coupling agent and
barrier resin was 3 wt%
of the containers.
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Table 2
Container Container
Construction MXD6 IV* (dUg) NZ-44 % Transmission**
(cc-CO2/day)
Monolayer PET N/A N/A 1.60
3% MXD6 1.41 0.5 1.00
3% MXD6 1.60 0.5 0.78
* Measured @ 30 C in 60:40 Phenol : 1,1,2,2 Tetrachloroethane en7ploying the
Viscotek
equipment and techniques discussed above.
28mm 500 ml beverage containers were filled at 3.0 gas volumes of C 02 b y c
hemical
carbonation techniques and were capped with 28 mm closures. These closures
were
polypropylene closures with ethylene vinyl acetate (EVA) liners as disclosed
in U.S. Patent
5,306,542. After being allowed to equilibrate for 14 days at 68F/50% RH
storage, the total
container CO2 transmission rate was measured by placing the container within a
sealed vessel
with a known capture volume. The sealed vessel had two ports through which
nitrogen carrier
gas flowed in through one of the ports and exited the vessel from the other
port.. The exit port
was directed to a Mocon C-IV CO2 test machine used for detecting the amount of
COa. The
quantity of COz was measured for a period of time, from which the COZ
transmission rate was
deternzined.
The process of container manufacture preferably involves manufacture of a
preform, followed by blow molding the preform to form the container. In the
examples discussed
in this application, the preform was fomzed in a sequential injection molding
operation of a type
illustrated in U.S. Patents 4,550,043, 4,609,516, 4,710,118 and 4,954,376.
FIGS. 5A and 5B are
a schematic illustrations of a preform in accordance with the invention, the
size and geometry
being for illustrative purposes only. However, the preform can also be formed
in a simultaneous
injection molding operation of a type illustrated in U.S. Patents 4,990,301
and 5,098,274, an
over-molding operation of a type illustrated in U.S. Patent 6,428,737, a
compression molding
operation of a type illustrated in U.S. published application 2002/0098310
using a mold cliarge
that includes the polyester resin and the barrier resin/coupling agent blend,
or in a coextrusion
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operation that produces a hollow tube having alternate layers ofpolyester
resin and barrier resin
blend. These specific citations are merely exemplary.
The amount of coupling agent blended with the barrier resin preferably does
not
exceed about 4% by weight of the blend. The amount of coupling agent more
preferably does
not exceed about 1.5% by weight of the blend. All percentages in this
application are by weight
unless otherwise indicated.
The presently preferred coupling agents identified above are well suited for
the
chemistries of the disclosed barrier and polyester resins. The chemical
functionalities of the
coupling agents do not affect the processability or barrier properties of the
barrierinaterial, other
than acting as a melt phase modifier as discussed above. The preferred
organometallic coupling
agents promote bonding between the polyester and barrier resin layers while
the materials are in
contact at elevated melt temperatures; it was difficult to separate the layers
of a preform after the
preform had cooled. While not being bound by any particular theory or
mechanism, one theory
is that the bonding between the polyester resin layers and the barrier resin
layers promoted by the
organometallic coupling agents includes covalent bonding, ionic bonding and/or
polar bonding
depending upon the type of barrier resin employed.
FIGS. 1-4 illustrate delamination test results on various container samples
constructed in accordance with the present invention. Each container had a
five-layer wall of
PET/MXD6/PET/MXD6/PET configuration (FIGS. 1-3B) or PET/EVOH/PET/EVOH/PET
:0 configuration (FIG. 4). In all tests, the containers were experimental
containers constructed for
comparison purposes only. The tests were arbitrarily devised to obtain
differentiation in data,
and do not reflect anyperfom7ance specification or conditions ofuse. In each
figure, the ordinate
indicates the percentage of containers in which delamination was observed by
visual inspection
as a result of the test, while the abscissa indicates the container structure,
specifically the total
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amount of barrier material by weight and the amount of NZ- 44 or LICA 44
coupling agent
employed. With the exception of the amount and type of coupling agent (NZ-44
or LICA-44),
and the type of barrier resin employed (EVOH or MXD6), all containers in each
test were
identical.
FIG. 1 illustrates the results of drop tests performed on twenty-four ounce
non-
round containers having a rounded rectangular cross section. The containers
were filled with
water, in which a blue dye was added to facilitate visual identification of
delaminations where
they occurred. The barrier layers totaled 1.5% of the containers by weight,
with the percentages
of NZ-44 or LICA-44 indicated in FIG. 1 (and in FIGS. 2A-4) being percentages
of the total
barrier layers -e.g., 0.20% of the 1.5% barrier layer or 0.003 % coupling
agent based upon the
total weight of the container. The filled containers were dropped onto a
cement base from a
height of three feet so that the containers iinpacted on their bottoms, and
then were examined
for delamination. As shown in FIG. 1, approximately 22% of the containers
showed
delainination without the NZ-44 or LICA-44 coupling agent in the barrier
layers. The containers
1.5 having MXD6 blended with 0.2 % LICA-44 showed delamination in 10% ofthe
containers. The
percentage of containers showing delainination progressively decreased in
container have 0.20%,
0,35% and 0.50% NZ-44. The last column in FIG. 1 shows delamination in 5% of
containers
when NZ-44 in the amount of 0.50% by weight was mixed with the MXD6 barrier
material. This
percentage ofNZ-44 zirconate coupling agent was then employed in subsequent
tests (FIGS. 2A-
4).
FIGS. 2A and 2B illustrate side-impact test results on 400 ml cylindrical
carbonated beverage containers. This side-impact testing involved a single
impact against the
container sidewall with a steel wedge and with the container clamped in
stationary position. The
energy of the impact was approximately 3.3 joules. FIG. 2A illustrates test
results with the
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containers filled with water, and FIG. 2B illustrates test results with the
containers filled with
water and carbonated at 3.0 GV (gas volumes). The barrier resin layers totaled
3% by weight of
the containers. In the sa.inples having a coupling agent, the coupling agent
was in the amount of
0.50% of the total barrier resin layers. Both FIGS. 2A and 2B show significant
percentages of
containers without the coupling agents of the present invention exhibiting
delainination after
testing, while containers in which the coupling agent was blended with the
barrier resin exhibited
no delamination after testing.
FIGS. 3A and 3B illustrate the results of drop tests on higllly embossed 500
ml
cylindrical beverage containers. These embossments were decorative design
details molded into
the container walls, and tend to act as stress concentrators and promote
delamination in the
container walls. In both of the tests ofFIG. 3A and 3B, the containers were
filled with water and
dropped onto a ceinent base to iinpact on their bottoms. FIG. 3A illustrates
the results of a three-
foot drop. The containers containing MXD6 barrier material exhibited
delamination in 6% of
the containers, while the containers having NIXD6 with 0.50% NZ-44 in the
barrier layers
exhibited no delamination. The drop height was then increased to six feet,
with the results being
illustrated in FIG. 3B. The containers without coupling agents exhibited
delamination in 42%
of the containers, while the containers with coupling agent exhibited
delamination in only about
8% ofthe containers. The coupling agent/barrier resin blend constituted 3% of
the total container
weight in the tests of FIGS. 3A and 3B.
FIG. 4 illustrates the results of a three-foot drop test on eight ounce
cylindrical
containers having 5% EVOH (or EVOH blended with coupling agent) as the barrier
layer. In the
three-foot drop test, in which the water-filled container was dropped onto its
base as described
above in connection with FIG. 1, FIG. 4 shows that there was a 20% reduction
in delamination
when the coupling agent was blended with the barrier material. In a side-
iinpact test, in which
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the water-filled container was impacted on its sidewall as described above in
connection with
FIG. 2A, the containers showed no delamination both with and without the
coupling agent.
There have thus been disclosed a multilayer container, a multilayer preform, a
barrier resin blend for use in a multilayer container, a method of making a
multilayerprefonn or
container, and a multilayer plastic article of manufacture that fully satisfy
all of the objects and
aims previously set forth. The container, barrier blend and method of
manufacture have been
disclosed in conjunction with a number of exemplary embodiments thereof, and
several
niodifications and variations have been discussed. Other modifications and
variations will
readily suggest themselves to persons of ordinary skill in the art. For
example, the invention in
its broadest aspects can also be applied to other articles of manufacture
having multilayer walls,
particularly walls with one or more barrier layers, such as container closures
and liners, or films
or sheets for later thermoforming, without departing from the scope of the
invention in its
broadest aspects. The invention is intended to embrace all such modifications
and variations as
fall within the spirit and broad scope of the appended claims.
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