Note: Descriptions are shown in the official language in which they were submitted.
WO 99/61514 PCT/US99/11659
METHOD OF PRODUCING A THERMOPLASTIC POLYMER PREFORM
AND AN ARTICLE PRODUCED THEREFROM
This application claims priority to provisional patent application Serial No.
60/086,924, filed May 27, 1998, which is incorporated herein by reference in
its
entirety.
Background of the Invention
Field of the Invention
The present invention relates generally to the field of processing
thermoplastic polymers and forming thermoplastic articles, and more
particularly to
a method of crystallizing a thermoplastic polymer by introducing a repeat rate-
increasing additive into the thermoplastic polymer and processing same.
Descrip~:ion of Related Art
Repeat Rate-Increasing Additives in Blow Molding Applications
The use of polymer compositions, particularly compositions comprising
polyethylene terephthalate) or copolymers thereof' (hereinafter collectively
referred
to as "PET"), for example in the form of films, bottles and other containers
is well
known. When bottles or other containers (hereinafter collectively referred to
as
"containers") are used for containing fluids, e.g., water, juices and
carbonated drinks,
container-forming compositions, in the form of polymer chips or pellets, are
usually
formed into the container shape in a two stage process. First, a container
preform is
injection molded; and second, either immediately or after a short storage
period, the
container preform is blown using compressed air into a mold which is in the
final
shape of the container. In the second stage of the process, the container
preform is
usually at or near ambient temperature, and it has to be heated to a
temperature (for
PET) of from about 85 ° C to about 120 ° C for the blow molding
step. It is this
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"reheat" step which is usually the rate-determining step in the second stage
of the
process.
Accordingly, to increase the output of the container-forming processes,
known energy-absorbing materials have been added to polymer compositions to
increase the "reheat" rate of the polymer preform to be processed and made
into a
container. By increasing the reheat rate, less energy and time is required to
heat the
polymer preform to its glass transition temperature (Tg) and blow mold the
preform
thereby forming a container. Thus, the output of the container-forming
processes is
increased and less energy is required when using reheat rate-increasing
additives.
I 0 Examples of such known energy-absorbing materials or reheat rate-
increasing
additives and compositions containing same are illustrated in U.S. Patents
4,408,004; 4,476,272; 4,535,118; 4,420,581; 5,419,936; and 5,529,744.
However, none of the processes utilizing reheat rate-increasing additives in
thermoplastic polymers incorporate a reheat additive in a process where
1 S crystallization of a polymer containing the additive is carried out.
Previously, it was
thought that there was no correlation or connection between reheat rate-
increasing
additives and polymer crystallization. In fact, prior to the present
invention, there
was no indication or expectation that such additives would have a significant
affect
on polymer crystallization, crystallization rates, or crystallization
processes.
20 ?. Crystallization in Blow Molding Applications
Thermoplastic polymers are often heat-treated to modify their material
characteristics for improved performance when farming thermoplastic articles.
For
example, the finishes (i.e., the upper portion typically comprising an opening
and
threads for engaging a cap) of PET preforms made to be blow molded into heat-
set
25 containers are commonly crystallized by heating the finish of the preform,
typically
by exposure to infrared (IR) radiation. The purpose of subjecting heat-set
preforms
to this process, known as the Yoshino Process (U.S. Patent 5,261,545), is to
convert
the amorphous material in this region of the container to crystalline form,
and
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thereby prevent or reduce distortion of the finish of the heat-set container
during hot
filling.
In the Yoshino Process, an injection-molded preform is placed in a carrier
which shields the body of the prefonm against exposure to crystallizing heat,
but
leaves the finishes exposed. The carrier containing the preform passes through
an
oven, where the preform finish is exposed to infrared energy for a sufficient
amount
of time to allow the finish to highly crystallize. High crystallinity provides
dimensional stability to the finish and allows the resulting article or
container to be
hot-filled without suffering from thermal distortion in the finish.
However, not all polymers can be used for forming containers according to
the Yoshino process. Copolymers, for example, have much slower crystallization
rates than homopolymers. Therefore, using copolymers in the Yoshino process
provides less throughput and requires more energy than homopolymers. Prior to
the
present invention, homopolymers were the predominant polymer used in
crystallization processes.
Moreover, unfortunately, crystallizing a thermoplastic polymer preform is an
additional step in the conventional container-forming process. An additional
step, of
course, creates longer and less efficient processing. Several factors effect
the rate at
which the crystallizing machine can process preforms, including polyester
resin
properties, oven efficiency, temperature the preform attains in the oven, and
time
spent in the oven. Accordingly, increasing efficiency by minimizing the amount
of
time and additional energy required to complete the container-forming process
having a crystallization step is still needed.
Thus, heretofore, efficiency of a manufacturing facility crystallizing (at
least
a portion thereof) preforms processed under a Yoshino-type process was not
enhanced by increasing the crystallization rate of preforms through the use of
a
reheat rate-increasing additive. In addition, only homopolymers were useful in
applications requiring faster crystallization because copolymers were limited
by their
slower crystallization rates. Moreover, there was no indication or expectation
that a
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4
reheat rate-increasing additive would have any affect on, let alone increase
polymer
(homopolymer and copolymer) crystallization, crystallization rates, or
crystallization
processes.
Summary of the Invention
The method of the present invention uses a polymer/reheat rate-increasing
additive composition to increase the rate of the polymer crystallization and,
thus, the
efficiency of a conventional container-forming process.
In accordance with the purposes) of this invention, as embodied and broadly
described herein, this invention, in one aspect, relates to a method of
producing a
thermoplastic polymer preform having at least a crystalline finish portion
comprising
(i) providing a thermoplastic polymer composition comprising a thermoplastic
polymer and at least one reheat rate-increasing additive; (ii) forming a
preform from
the thermoplastic polymer composition, wherein the preform comprises a finish
portion and a body portion; and (iii) exposing at least the finish portion of
the
preform to energy until crystallized.
In another aspect, the present invention relates to a method of producing a
thermoplastic polymer container having at least a crystalline finish portion,
the
method comprising (i) providing a thermoplastic polymer composition comprising
a
thermoplastic polymer and at least one reheat rate-increasing additive; (ii)
forming a
preform from the thermoplastic polymer composition, wherein the preform
comprises a finish portion and a body portion; (iii) exposing at least the
finish
portion of the preform to energy until crystallized; and (iv) blow molding the
preform into a container, wherein the container has at least a crystalline
finish
portion.
In another aspect, the present invention relates to a method of crystallizing
at
least a finish portion of a thermoplastic polymer container comprising (i)
providing a
thermoplastic polymer container comprising a thermoplastic polymer and at
least
one reheat rate-increasing additive, wherein the container has a finish
portion and a
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US 009911659
body portion; and (ii) exposing at least the finish pardon of the container to
energy until crystallized.
In yet another aspect, the present invention relates to a methed of
crystallizing a
theranoplsstic polymer composition comprising (i) providing a thermoplastic
polymer
composition comprisipg a thermoplastic polymer and at least one repeat rate
increasing
additive; az~d (ii) exposing at least a portion of the composition to energy
until
crystallized.
In still anflther aspect, the prosent invention relates to a method for
forming
id caatainers comprising ahcat-set finish as n pardon of the container
comprising (i)
molding a container from a polymer comprising at least one repeat fate-
improving
addidva; and (ii) heat-setting at least a portion of the finish of the
container.
Iu yet another aspect, the present invention re3ates to a container formed
from a
thermoplastic polymer comprising a body and a finish, wherein the finish is
crystalline
and contains a repeat rate-inareaeing additfve.
In other aspects, the present irwentiort relates to products made by the
processes
of the pzeseni invention
Additional advantages of the inventionwill be act forth in part in the
detailed
description, including the figuxes, which follows, and is part will be obvious
from the
description, or may be teamed by practice of the invention, The advantages
ofthe
invention will be realized and attained by means of the eletneets and
cotnhinations
particularly pointed ou; in the appended claims. Yt is to be understood thact
bath the
fflrcgoing general description and ttie following detailed dsscriptian are
exemplary $nd
oxplenatory of preferred embodiments of the invention, and are not restrictive
of the
invention, as claimed.
AMENDED SHEET
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- u-~ui:bd~~ hiom:nrtu~t r~ ~istnatK~;,"r.c. "'~''"' ~ 4U4tilfai~~fUu~~~U~ i
uui r ni US 009911659
27-06-2000
6
Detailed Descrip~on of the Invention
The present invention may be understood mare readily by reference to the
following detailed description of the invention, including the appended
figures referred
S to heceia, and t_~e examples provided therein. It is to be understflod that
this invention
is not limited to the specific processes and conditions described, as spxific
processes
andJar process conditions for processing plastic articles as such may, of
course, vary. It
is also to be understood that the terminology used herein is for the purpose
of
describing particular embodiments only and is not intended to be timitiag.
i0 It must also be noted that, as usod in the specification and the appended
claittu,
the singular forces "a," "an" and "the" include plural referents unless the
context clearly
dictates otherwise. For example, reference to processing a thermoplastic
°'prcfann,"
"article," "contains" or "bottle" is intended to include the processing of a
plurality of
thermoplastic preforms, articles, containers or bottles.
1 ~ Ranges niay be expressed herein as from "about" or "approximately" one
particular value aadlor to "about" or "approximately" another particular
value. When
such a range is expressed, another embodiment includes from the one particular
value
andlar tc the other particular value. Similarly, when value: are expressed as
approximations, by use of the antecedent about, it will be understood that the
particular
20 value forms another embodiment.
It has been disc:wercd that the rate card percent of crystallization of au
amorphous th..~rmoplaatic polymer can be increased by incorporating into the
AMENDED SHEET
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7
polymer a reheat rate-increasing additive before processing by a
crystallization
machine. "Amorphous," for purposes of further defining the polymers of the
present
invention prior to crystallization, shall mean substantially noncrystalline. A
substantially noncrystalline polymer typically may have less than about S to 7
weight percent crystallinity. In particular, and by way of example,
significant
increases in the efficiency of processing heat-set PET container prefotms
having a
crystallized finish portion using the Yoshino process may be obtained by means
of
the method described herein.
In a broad sense, the process aspects of the invention may be defined as a
method of producing molded articles comprising preparing a prefonn of
thermoplastic polymer admixed with a reheat rate-increasing additive,
subjecting the
preform to radiant energy for a period of time necessary to raise its
temperature to
above the glass transition temperature of the polymer, and subsequently
forming the
preform into a desired shape. The term "glass transition temperature" is
defined
generally as the temperature at which the polymer changes from a glass-like
material
to a rubbery or leathery material.
The present invention is highly useful because 1 ) the method increases the
amount of reheat energy which is absorbed by the preforms, and 2) the method
increases (nucleates) the spherulitic crystalline growth rate during the step
of
preform/container crystallization. Spherulitic crystalline growth may be
defined as
the increase in spheroid crystalline bodies in the amorphous polymer.
Moreover, it has been surprisingly found that conventional reheat additives
improve crystallization from the glass (providing improved processing during
the
finishing step), but do not noticeably affect the crystallization from the
melt. This is
particularly important because significant changes in crystallization from the
melt
would result in narrowed processing windows, which would make container
production more difficult and less forgiving.
Thus, the method of the present invention provides preforms/containers
having a higher or increased degree of crystallinity in a shorter processing
time. The
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method of the present invention further provides a container-forming and/or
container-processing step having increased output rates.
Presentlv Preferred Embodiments
Briefly described, in one presently preferred embodiment, the present
invention comprises a method of producing a thermoplastic polymer preform
having
at least a crystalline finish portion. The method comprises (i) providing a
thermoplastic polymer composition comprising a thermoplastic polymer and at
least
one reheat rate-increasing additive; (ii) forming a preform from the
thermoplastic
polymer composition, wherein the preform comprises a finish portion and a body
portion; and (iii) exposing at least the finish portion of the preform to
energy until
crystallized. The invention also relates to a preform produced by the method
of this
embodiment.
In a second embodiment, the present invention relates to a method of
producing a thermoplastic polymer container having at least a crystalline
finish
portion. This method comprises (i) providing a thermoplastic polymer
composition
comprising a thermoplastic polymer and at least one reheat rate-increasing
additive;
(ii) forming a preform from the thermoplastic polymer composition, wherein the
preform comprises a finish portion and a body portion; (iii) exposing at least
the
finish portion of the preform to energy until crystallized; and (iv) blow
molding the
preform into a container, wherein the container has at least a crystalline
finish
portion. Preferably, the preform in step (iv) is at a temperature of from
80°C to
125 °C for blow molding. The invention also relates to a container
produced by the
method of this second embodiment.
In a third embodiment, the present invention relates to a method of
crystallizing at least a finish portion of a thermoplastic polymer container
comprising (i) providing a thermoplastic polymer container comprising a
thermoplastic polymer and at least one reheat rate-increasing additive,
wherein the
container has a finish portion and a body portion; and (ii) exposing at least
the finish
portion of the container to energy until crystallized. This embodiment differs
from
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9
that of exposing a preform to energy until crystallized. In this embodiment,
at least
the finish portion of a container, not a preform, is exposed to crystallizing
energy.
The invention also relates to a container crystallized by the method of this
third
embodiment.
In yet another embodiment, the present invention relates to a method of
crystallizing a thermoplastic polymer composition. The method comprises (i)
providing a thermoplastic polymer composition comprising a thermoplastic
polymer
and at least one reheat rate-increasing additive; and (ii) exposing at least a
portion of
the composition to energy until crystallized. This embodiment is different in
that at
least a portion of a composition having an additive is exposed to
crystallizing energy
and not a finish of a preform or a container. Preferably, the thermoplastic
polymer
composition is in the form of an article, more preferably a container, and
even more
preferably a bottle. Moreover, the invention relates to a bottle crystallized
by the
method of this embodiment.
In yet another embodiment, this invention relates to a method for forming
containers comprising a heat-set finish on a portion of the container
comprising (i)
molding a container from a polymer comprising at least one reheat rate-
improving
additive; and (ii) heat-setting at least a portion of the finish of the
container.
Preferably, the reheat rate-improving additive is carbon black, iron oxide or
antimony metal. More preferably, the polymer comprises antimony metal in a
concentration of about 20 ppm (ppm = parts per million by weight) or more,
iron
oxide in a concentration of less than about 12 ppm or carbon black in a
concentration
of less than about 10 ppm. The invention also relates to a container formed
from the
method of this embodiment.
In another embodiment, the present invention relates to a container formed
from a thermoplastic polymer. The container comprises a body and a finish,
wherein
the finish is crystalline and contains a reheat rate-increasing additive.
Preferably, the
finish is at least 25 weight percent crystalline. Preferably, the
thermoplastic polymer
used for forming the container is polyethylene terephthalate) or a copolymer
thereof. The reheat rate-increasing additive preferably includes, but is not
limited to,
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carbon black, iron oxide, antimony, tin, copper, silver, gold, palladium,
platinum or
a mixture thereof.
In all of the embodiments of this invention, the thermoplastic polymer
composition is preferably transparent. Further, the thermoplastic polymer may
comprise a homopolymer or comprise a copolymer. Preferably, the polymer is a
polyester, and more preferably polyethylene terephthalate) or a copolymer
thereof.
Exposure to energy to crystallize at least the finish portion of the preform
or
container having the additive is effected for about 25 seconds. The finish of
the
preform is at least 20 weight percent crystalline after exposure to
crystallizing
10 energy. Preferably, the crystallizing radiant energy is at least partially
within the
infrared region of the energy spectrum. Further, at least a portion of the
preform
crystallizes at a rate faster than that of a prefonm without a reheat rate-
increasing
additive.
Thermo~astic Polvmers
The thermoplastic polymer used in the invention is most usually a polyester,
particularly a partially aromatic polyester, especially a polyester derived,
at least
mainly, from an aromatic diacid and an aliphatic (including cycloaliphatic)
diol. A
preferred partially aromatic polyester is one which comprises at least 50 mole
%,
preferably at least 70 mole %, of ethylene terephthalate residues. The
polyester may
also contain residues derived from ethylene isophthalate, ethylene
naphthalate,
ethoxyethylene terephthalate, ethoxyethylene isophthalate or ethoxyethylene
naphthalate.
Typically, polyesters such as polyethylene terephthalate polymer (PET) are
made by reacting a glycol with a dicarboxylic acid as the free acid or its
dimethyl
ester to produce a prepolymer compound which is then polycondensed to produce
the polyester. If required, the molecular weight of the polyester can then be
increased further by solid state polymerization.
Suitable polyesters for the method of the present invention include
crystallizable polyester homopolymers or copolymers that are suitable for use
in
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containers and packaging, and particularly food packaging. The present
invention
provides accelerated crystallization rates for any thermoplastic resins, e.g.,
PET
containing a reheat rate-increasing additive. Suitable polyesters are
generally known
in the art and may be formed from aromatic dicarboxylic acids, esters of
dicarboxylic acids, anhydrides of dicarboxylic esters, glycols, and mixtures
thereof.
More preferably, the polyesters are formed from repeat units comprising
terephthalic
acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate,
dimethyl-2,6-
naphthalenedicarboxylate, 2,6-naphthalenedicarboxylic acid, ethylene glycol,
diethylene glycol, 1,4-cyclohexane-dimethanol, 1,4-butanediol, and mixtures
thereof.
The dicarboxylic acid component of the polyester may optionally be
modified with one or more different dicarboxylic acids. Such additional
dicarboxylic acids include aromatic dicarboxylic acids preferably having 8 to
14
carbon atoms, aliphatic dicarboxylic acids preferably having 4 to I2 carbon
atoms,
or cycloaliphatic dicarboxylic acids preferably having 8 to 12 carbon atoms.
Examples of dicarboxylic acids to be included with terephthalic acid are:
phthalic
acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid,
cyclohexanedicarboxylic
acid, cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid, succinic
acid,
glutaric acid, adipic acid, azelaic acid, sebacic acid, mixtures thereof and
the like.
Preferably, the amount of said second dicarboxylic acid is less than 30 mole%
and
more preferably less than about 15 mole%.
In addition, the glycol component may optionally be modified with one or
more different glycols other than ethylene glycol. Such additional glycols
include
cycloaliphatic diols preferably having 6 to 20 carbon atoms or aliphatic diols
preferably having 3 to 20 carbon atoms. Examples of such glycols include:
diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, propane-1,3-
diol,
butane-1,4-diol, pentane-I,S-diol, hexane-1,6-diol, 3-methylpentanediol-(2,4),
2-
methylpentanediol-(1,4), 2,2,4-trimethylpentane-diol-(1,3), 2-ethylhexanediol-
(1,3),
2,2-diethylpropane-diol-(1,3), hexanediol-(1,3), 1,4-di-(hydroxyethoxy)-
benzene,
2,2-bis-(4-hydroxycyclohexyl)-propane, 2,4-dihydroxy-1,1,3,3-tetramethyl-
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cyclobutane, 2,2-bis-(3-hydroxyethoxyphenyl)-propane, 2,2-bis-(4-
hydroxypropoxyphenyl)-propane, mixtures thereof and the like. Polyesters may
be
prepared from two or more of the above glycols. Preferably, the amount of the
second glycol is less than 30 mole% and more preferably less than about 15
mole%.
The thermoplastic resin may also contain small amounts of trifunctional or
tetrafunctional comonomers such as trimeliitic anhydride, trimethylolpropane,
pyromellitic dianhydride, pentaerythritol, and other polyester forming
polyacids or
polyols generally known in the art.
Rehear Rate-Increasing dditives
As described above, the thermoplastic polymers according to this invention
include at least one reheat rate-increasing additive. Reheat rate is defined
as the
change in average temperature of a molded part as a function of exposure to a
radiant heat source for a specified time. Suitable reheat rate-increasing
additives are
well known in the art and include, preferably, black and gray body absorbers
such as
carbon black, antimony metal, iron oxide and the like, as well as near
infrared
absorbing dyes, including, but not limited to those disclosed in U.S.
97/15351,
which is incorporated herein by reference.
The reheat rate-increasing additive should be present in an amount sufficient
to improve the reheat rate of an unmodified polymer. The actual amount of
reheat
rate-increasing additive will vary depending on which additive is used.
Typically, in
order to achieve the presently preferred crystallization of a preform or
container, the
thermoplastic polymer composition comprises the reheat rate-increasing
additive in
a concentration of about 1 to 300 ppm. The reheat rate-increasing additive may
be
typically any reheat rate-increasing additive used in the art, including, but
not
limited to, carbon black, iron oxide, antimony, tin, copper, silver, gold,
palladium,
platinum or a mixture thereof. However, only very small amounts of black body
absorbers, like carbon black and iron oxide (about 10-12 ppm or less) may be
necessary to achieve the desired crystallinity, but relatively large amounts
of gray
body absorbers like antimony metal may be necessary to achieve the same
effect.
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Typically, the polymer composition may comprise antimony metal in a
concentration of at least 10 ppm.
The more effective concentration of the iron oxide, for example, is from
about 1.0 to about 100 ppm, preferably from about 1 to about SO ppm with 1-30
ppm
being most preferred. The iron oxide, preferably Fe,03 is used in very finely
divided
form e.g., from about 0.01 to about 200 pm, preferably from about 0.1 to about
10.0
~tm, and most preferably from about 0.2 to about 5.0 pm. Such oxides are
described,
for example, on pages 323-349 of Pigment Handbook, Vol. 1, copyright 1973,
John
Wiley & Sons, Inc.
Iron oxide, for example, can be added to the polyester reactant system,
during or after polymerization, to the polyester melt, or to the molding
powder or
pellets from which the bottle preforms are formed. For purposes of
clarification, the
bottle preforms are test tube shaped, injection moldings which are heated
above the
glass transition temperature of the polymer and then positioned in the bottle
mold to
receive the pressurized air through its open end. Such technology is well
known to
the art as shown in U.S. Pat. No. 3,733,309. Any radiant energy source may be
employed, and the one used for heating the preforrns according to this
invention is a
quartz lamp, Model Q-1P, 650 W., 120 V., by Smith Victor Corp.
Suitable preferred metals for use as the additive according to the method of
this invention include antimony, tin, copper, silver, gold, palladium and
platinum or
a mixture of two or more of these. It should also be appreciated that
additional gray
and black body absorbers including, but not limited to arsenic, cadmium,
mercury
and lead can also be used. However, for most applications, silver, gold,
arsenic,
cadmium, mercury, lead, palladium and platinum are either too expensive or
environmentally hazardous and these metals are, consequently, not particularly
preferred. Preferably, the metal is one or more of antimony, tin or copper
with
antimony being particularly advantageous.
Moreover, if metal is used as the reheat rate-increasing additive, the metal
preferably is in particle form for ease of processing. The metal particles are
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preferably sufficiently fine for them not to be visible to the eye and have a
range of
sizes such that absorption of radiation occurs over a relatively wide part of
the
wavelength range and not just at one particular wavelength or over a narrow
band.
The amount of metal particles present in the thermoplastic polymer
S composition, as it is to be used in this invention, is a balance between the
desired
reduction in the reheat time of the polymer, the crystallization of the
polymer and
the amount of haze that is acceptable for a given application. Preferably, the
amount
of metal particles is from about 1 ppm to 300 ppm, more particularly from
about 5
ppm to 150 ppm, and especially from about 10 ppm to 100 ppm. If desired,
masterbatches of the polymer composition containing quantities of metal
particles in
far higher concentrations can be made for subsequent blending with polymer
essentially free from the metal particles to achieve the desired levels of
particles.
In polyester compositions, antimony is especially preferred because, in the
form of antimony trioxide (antimony (III) oxide), it is a catalyst for the
polymerization of the monomers used in the preparation of polyesters such as
polyethylene terephthalate). As the polyester monomer melt is a slightly
reducing
environment, the polyesters may naturally have a very minor proportion of
antimony
metal present, e.g., upt o about 5-6 ppm. However, these low levels of
antimony
metal do not affect the reheat time significantly.
Also, although not required, additives and/or lubricants normally used in
polyesters may be used if desired. Such additives include catalysts,
colorants,
pigments, glass fibers, fillers, impact modifiers, antioxidants, stabilizers,
processing
aids, flame retardants, acetaldehyde reducing compounds and the like.
Typical Techniaue Jfor Producing a Thermoplastic Container
The method of the present invention is particularly suited for use in the
production of a heat-set thermoplastic polymer (e.g., polyester) container. A
polyester preform, for example, is molded in the injection molding machine
from a
polyester resin containing a reheat rate-increasing additive. The preform is
molded
according to known techniques, whereby polyester pellets are dried and
injection
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molded to produce clear, amorphous polyester preforms. The amorphous or
"glassy"
preforms preferably comprise a threaded finish portion and a body portion. The
finish portion is crystallized according to the present invention to prevent
distortion
of the finish upon further processing of the preform to produce a container,
or upon
heat-filling of the container. The body portion of the preform is typically
processed,
as by heated blow molding, to form a container having a desired shape and
size.
According to the present invention, a portion of the preform is crystallized.
Preferably, only the finish is crystallized. Crystallization of the finish is
usually an
optional, and, until now, predominantly cumbersome stage of a preform-forming
10 process. However, by using a reheat rate-increasing additive in accordance
with this
invention, crystallization rates are dramatically increased rendering a
crystallization
stage more desirable in many container-forming applications.
Generally, crystallization involves exposing at least a portion of the preform
finish to radiant heat from lamps in a row of ovens (across a spectrum which
may
15 include the IR range) while protecting the body of the preform.
More particularly, after forming the preform, the preform is transported to a
crystallization machine. The preforms are preferably loaded into carriers
which
shield the bodies of the preforms against exposure to crystallizing heat, but
leave the
finishes exposed. The Garners, containing the preforms, are passed through the
crystallizing machine, where the preform finishes are exposed to infrared
energy for
a sufficient amount of time to allow the finishes to crystallize. This stage
preferably
involves exposing at least a portion of the preforrn finish to radiant heat
from lamps
in a row of ovens (across a spectrum that may include the IR range) while
protecting
the body of the preform. The finish is heated to temperatures at which the
selected
polyester crystallizes rapidly (for PET about 150°C to about
180°C). This results in
a highly crystalline finish, i.e., spherulitic crystallinity levels at a
minimum of about
20 weight percent. These high levels of crystallinity give dimensional
stability to the
finish that enable the resulting container to be hot-filled without suffering
from
thermal distortion in the finish region. Moreover, at least a portion of the
preform
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16
crystallizes at a rate faster than that of a preform without a repeat rate-
increasing
additive.
Crystallization of the finish can be performed either to the preform (as in
the
Yoshino process), to a pre-bottle (as in the Sidel SRCF process outlined in
U.S.
Patent No. 5,382,157), or to the actual heat-set bottle.
The desired container is preferably blow molded from the preform and heat-
set, according to known techniques. In particular, the preform body (with or
without
the crystallized finish) is exposed lamps emitting radiant heat (which may
include
the IR range of the spectrum) until the preform has reached the appropriate
temperature range for bottle blowing (from about 85 °C to about
120°C for PET).
The preform is removed from the oven and placed into a warm or hot blow mold
and
pressurized. The prefonm is thereby stretched into a container, preferably a
bottle
which is held against the warm or hot blow mold (therefore, the name "heat-
set").
These bottles are typically designed to withstand hot-filling without
shrinkage
greater than about 1 % by volume. It is also desirable, although not required,
to
achieve a large degree of spherulitic crystallinity in the bottle sidewall in
order to
resist thermal distortion upon hot-filling of the bottle.
Crystallization of the bottle prefonms occurs through crystal nucleation.
Crystal nucleation in the preform is primarily heterogeneous. That is, the
initial seed
crystal forms at the surface of a pre-existing foreign particle in the resin,
in the
present case, a repeat rate-increasing additive. The additive, in accordance
with the
present invention, is a component intentionally added to promote increased
repeat
rates and nucleation. The density of crystal nucleation is controlled by the
density of
the additive as well as the rate at which seed crystals of polymer form at the
surface
of the additive, which is in turn influenced by material variables and
temperature.
The following examples and experimental results are included to provide
those of ordinary skill in the art with a complete disclosure and description
of
particular manners in which the present invention can be practiced and
evaluated,
CA 02332984 2000-11-22
WO 99/61514 PCT/US99/11659
17
and are intended to be purely exemplary of the invention and are not intended
to
limit the scope of what the inventors regard as their invention. Efforts have
been
made to ensure accuracy with respect to numbers (e.g., amounts, temperature,
etc.);
however, some errors and deviations may have occurred. Unless indicated
otherwise, parts are parts by weight, temperature is in °C or is at
ambient
temperature, and pressure is at or near atmospheric.
Thus, it has been discovered that incorporating a reheat rate-increasing
additive into PET, for example, dramatically accelerates the crystallization
rate of
PET from the glass. However, the decisive factor in determining whether this
effect
is useful in commercial package manufacturing processes is how long the PET
article must be exposed to crystallizing energy. In general, the longer the
required
exposure time to achieve accelerated crystallization, the less the process is
commercially attractive.
The following example(s), in addition to the figures discussed above,
illustrate that the required exposure time to achieve accelerated
crystallization is
much less for those compositions containing a reheat rate-increasing additive
than
those compositions without the additive.
Production of Heat-Set Thermoplastic Po[~rmer~ EST) Preforms
1 ) Injection Molding
A polymer preform was injection molded. Specfically, preblended polymer
(PET Homopolymer or modified PET) pellet concentration @ 50:1 let down ratio
resulting in a 12 ppm level of black iron oxide was formed. Preforms were
molded
from the blend on a standard injection molding machine (4-cavity Husky LX-
160).
This injection molding machine is well known to one of ordinary skill in the
art and,
as such, need not be described in detail here.
2) Reheat - Crystallizing
The prefonms were crystallized on standard reheat equipment (Sidel SBO
2/3), which typically can be a stretch blow molding machine. This equipment is
CA 02332984 2000-11-22
' i'-uy:o4 ~ r~om:nrrmr ~ Kustn~rrcu;~N.i; '''.'''' . auabr~~ddu~~~~"" uui a i
i US 009911659
27-06-2000
18
well la~awn td one Qf ordinary skill in the art and, as such, need not be
described in
detail here. To sitnalate finish crystallization process, preforms v,~ere subj
ccted to the
fohowing various heating times andlor energy exposure levels to a point at
which
crystallization of the preform body oocurred:
(1) the radiant energy exposure was changed while holding production
output rate constant (32.2 second periody (energy range: 250,000 to
475,000 watts); and
(2) the exposure time was changed by varying production output rate while
holding lamp intensity constant (output range: 8-13.5 partshninute}.
3) 'Testing
'The crystahinity ofthc preforrns was determiner! by fast measuring gradient
tube density, then converting density to weight percent crystallinity using
the equations
standard to the industry. Both measuring gradient tube density and converting
density
to cryatallinity using standard eQuatious are lmown to one of ordinary skill
in the art
and, as such, need not be described in detail here.
Comp~irstive Example
A PET Homopolymer prefonn with approximately 12 ppm black iron oxide was
24 prepared by the method outlined above and subjected to approximately
475,000 watts
of exposure of Iit over a 32.Z second period. The preform do~relopod 41 weight
percent
crystallinity.
The suns PET Homopolyrnex preform was prepared without the black iron
oxide and subjected to the same exposure conditions. This prefortn developed
only 10
2S weight percent crystatlinity.
lrxpeximental results were plQttcd, demonstrating the crysfallinity (weight
percent) of various fortes of PET after exposure to radiant energy (watts)
over the 32.2
second reheat period, and
AMENDED SHEET
CA 02332984 2000-11-22
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27-06-2000
19
demonstrating the crystatlinity (weight p ercent) of the PET Forms versus the
production
rate of the prefonns. The results refer to the following fortes of PET
manufactured and
used by Eastman Chemical Corporation of Ki:~gspor~, Tennessee, U_B.A.:
a) 0.8 Its' (intrinsic viscosity) PET homopolymer (EASTAPAK p663) with
and without a repeat rate-increasing additive;
b) 0.S IfV CHI3M (cyclohexane dimetlianol) modified PET (FASTAPAK (R)
copolyester 992 iW) ~c~ith and without a repeat rate-increasing additive, and
c) 4.8 ItV IPA (isapthalic acid) modified PET (at Eastman Chemical Company
IO referred to internally as EA~TA.PAK (R) copolyester B-l I) with and
without a repeat rate-increasing additive.
Threa forms of PET (all with 0.S It'd contpin a repeat rate-increasing
additive
in accordance with the method of this irwention: PET Homopolymer; CF~M
Modified
PET; and IP 4 Modified PET. At the cod of the rehear period (32.2 seconds),
wherein
I ~ the PET forms are exposed to a final radiant energy of approximately
x.50,000 watts,
the three above-mentioned PET fotZns having the relxcat additive clearly have
a higher
crystal'linity than those without the repeat additive.
In addition, it is particularly surprising that the PET capoiymers ~CIrIDM and
IPA modified) have a higher crystallinity tran the PET homapolymer without a
repeat
20 additive. Copolymers, in general, do not crystallize as fast as
homopolymers.
Therefore, the addition of a repeat rate-increasing additive dramatically
increases the
crystallinity of a homopalymer and a copolymer. Lxpcrimental evidence conf
rntcd
this proposition because the PET hornopolymer havitte the additivo has a
higher
crystallinity at the end of the r~heat period than the PET copolymers with an
additive.
25 This result is to be expected given the crystallization rates of
hcmopolymers versus
copolymers.
AMENDED SHEET
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uui r. ni US 009911659
A plot of crysta11i2ation of the PET polymers versus the production rate
indicates again that the crystallization of the PBT polymers having the rcheat
rate-
increasirg additive is markedly increased over those PET polytrtcrs without
the
5 additive. For example, at lower production rates (8-IO partsltuinute), the
0.8 PET
Hotnopolyrner and Q.81tV CHDM modified PET having the reheat additive show
over
double (at 8 parts/ntinute) the crystallinity of those PET polymers without
the additive.
These results strongly suggest that 1 ) the rats of erystallizauon of the PET
polymers
with tl~e additive is significantly higher than thaw without the additive, and
2) the
10 rehear rate-incrcasino additivo is the raesan for the dramatio increase is
the rate of
crystatli~ation. First, the PET palymexs are the same (i_e., 0.8 ItV and
modiftGd vvth
the same copolymers). Second, the processing conditions are the same (i.e.,
temperature, time, rate, exposure to et~~. Therefore, tine only experimental
variable
that distin~tishcs the results is the reheat rate-increasing additive, and the
results show
15 that the additive dramatically improves crystallization of the PET
polymers.
Throughout this applicaxion, various publications are referenced. The
disclosures of these publications in their entireties are hereby incorporated
by reference
into this application in order to more fully describe the state of the art to
which This
invention pertains.
20 It will be apparent to those skilled in the art that various
rraodifications and variations
can oe made in the present invention without departing from fete scope or
spirit of the
invention. Other embodiments of the invention will be apparent to thaw sldiled
in the
art from consideration of the spec'tftcatian and practice of the invention
disclosed
herein. It is intended that the specification and examples be considered as
exemplary
only, with a true scope and spirit of the invention being indicated by the
following
claims.
AMENDED SHEET
CA 02332984 2000-11-22
