U.S. patent application number 11/670644 was filed with the patent office on 2007-06-21 for methods for making polyester resins having reduced frictional properties.
Invention is credited to Walter Lee Edwards, Sharon Sue Griffith, Tony Clifford Moore, Carl Steven Nichols, Robert Joseph Schiavone.
Application Number | 20070142537 11/670644 |
Document ID | / |
Family ID | 34811487 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070142537 |
Kind Code |
A1 |
Edwards; Walter Lee ; et
al. |
June 21, 2007 |
Methods for Making Polyester Resins Having Reduced Frictional
Properties
Abstract
The invention is a method for the late introduction of inert
particulate additives via a reactive carrier to achieve a polyester
resin that is capable of being formed into low-haze, high-clarity
bottles possessing reduced coefficient of friction. The invention
is also a polyester resin that includes between about 20 and 200
ppm of an inert particulate additive, such as surface-modified talc
or surface-modified calcium carbonate.
Inventors: |
Edwards; Walter Lee;
(Harrisburg, NC) ; Schiavone; Robert Joseph;
(Matthews, NC) ; Griffith; Sharon Sue; (Charlotte,
NC) ; Nichols; Carl Steven; (Waxhaw, NC) ;
Moore; Tony Clifford; (Charlotte, NC) |
Correspondence
Address: |
SUMMA, ALLAN & ADDITON, P.A.
11610 NORTH COMMUNITY HOUSE ROAD
SUITE 200
CHARLOTTE
NC
28277
US
|
Family ID: |
34811487 |
Appl. No.: |
11/670644 |
Filed: |
February 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10962167 |
Oct 8, 2004 |
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11670644 |
Feb 2, 2007 |
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10628077 |
Jul 25, 2003 |
6803082 |
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10962167 |
Oct 8, 2004 |
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09738150 |
Dec 15, 2000 |
6599596 |
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10628077 |
Jul 25, 2003 |
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Current U.S.
Class: |
524/451 ;
524/200; 524/605 |
Current CPC
Class: |
C08G 64/42 20130101;
B29K 2105/0002 20130101; Y10T 428/2913 20150115; C08G 63/78
20130101; Y10T 428/1369 20150115; C08G 63/80 20130101; C08J 2367/02
20130101; C08J 3/2056 20130101; C08G 63/91 20130101; Y10T 428/1352
20150115; C08G 69/28 20130101; C08G 69/04 20130101; C08G 64/20
20130101; C08J 3/226 20130101; Y10T 428/29 20150115; C08L 67/02
20130101; C08G 69/48 20130101; C08K 3/34 20130101; C08L 67/02
20130101; C08L 71/00 20130101; C08K 3/34 20130101; C08L 67/02
20130101 |
Class at
Publication: |
524/451 ;
524/605; 524/200 |
International
Class: |
C08K 3/34 20060101
C08K003/34; C08G 63/60 20060101 C08G063/60 |
Claims
1. A method for introducing surface-modified talc into polyethylene
terephthalate, comprising: forming polyethylene terephthalate
polymers via melt phase polycondensation; and thereafter
introducing between about 20 and 200 ppm of surface-modified talc
into the polyethylene terephthalate polymers via a reactive carrier
having a molecular weight of less than about 10,000 g/mol.
2. A method according to claim 1, wherein the surface-modified talc
comprises organosilane-treated talc having an average particle size
of less than about ten microns.
3. A method according to claim 1, wherein the surface-modified talc
has an average particle size of less than about two microns.
4. A method according to claim 1, wherein the step of introducing
surface-modified talc into the polyethylene terephthalate polymers
comprises introducing between about 40 and 150 ppm of
surface-modified talc.
5. A method according to claim 1, wherein the step of introducing
surface-modified talc into the polyethylene terephthalate polymers
comprises introducing less than about 100 ppm of surface-modified
talc.
6. A method according to claim 1, wherein the reactive carrier has
a molecular weight of more than about 300 g/mol.
7. A method according to claim 1, wherein the reactive carrier is a
liquid or slurry at near ambient temperatures.
8. A method according to claim 1, wherein the reactive carrier
possesses a carboxyl functional group, a hydroxyl functional group,
or an amine functional group.
9. A method according to claim 1, wherein the step of introducing
surface-modified talc via a reactive carrier comprises introducing
the reactive carrier into the polyethylene terephthalate polymers
in quantities such that bulk properties of the polyethylene
terephthalate polymers are not detrimentally affected.
10. A method according to claim 1, wherein the step of introducing
surface-modified talc via a reactive carrier comprises reacting the
reactive carrier with the polyethylene terephthalate polymers.
11. A method according to claim 1, wherein the reactive carrier is
introduced into the polyethylene terephthalate polymers via an
additive delivery system that does not employ an extruder to
introduce the reactive carrier into the polyethylene terephthalate
polymers.
12. A method according to claim 1, further comprising forming the
polyethylene terephthalate polymers into a preform.
13. A method according to claim 1, further comprising forming the
polyethylene terephthalate polymers into a container.
14. A method for introducing talc into polyethylene terephthalate
polymers, comprising: polymerizing polyethylene terephthalate
precursors via a continuous melt phase polycondensation process to
form a polyester melt comprising polyethylene terephthalate
polymers; and thereafter introducing into the polyester melt formed
during the continuous melt phase polycondensation process a
reactive carrier having a molecular weight of between about 300
g/mol and 10,000 g/mol, the reactive carrier being the delivery
vehicle for between about 20 and 200 ppm of talc.
15. A method according to claim 14, wherein the talc has an average
particle size of less than about ten microns.
16. A method according to claim 14, wherein the talc comprises
surface-modified talc having an average particle size of less than
about two microns.
17. A method according to claim 14, wherein the reactive carrier is
the delivery vehicle for less than about 150 ppm of
surface-modified talc.
18. A method according to claim 14, further comprising, after the
introduction of the reactive carrier and talc into the polyester
melt, forming the polyethylene terephthalate polymers into a
preform or a container.
19. A method for introducing talc into polyethylene terephthalate
polymers, comprising: polymerizing polyethylene terephthalate
precursors via a continuous melt phase polycondensation process to
form a polyester melt comprising polyethylene terephthalate
polymers having an intrinsic viscosity of at least about 0.45 dl/g;
thereafter introducing into the polyester melt formed during the
continuous melt phase polycondensation process a reactive carrier
having a molecular weight of between about 300 g/mol and 10,000
g/mol, the reactive carrier being the delivery vehicle for between
about 20 and 200 ppm of talc; and then continuing the melt phase
polycondensation of the polyethylene terephthalate polymers.
20. A method according to claim 19, wherein the talc has an average
particle size of less than about ten microns.
21. A method according to claim 19, wherein the talc has an average
particle size of less than about two microns.
22. A method according to claim 19, wherein the reactive carrier is
the delivery vehicle for between about 40 and 150 ppm of talc.
23. A method according to claim 19, further comprising, after the
step of continuing melt phase polycondensation, forming the
polyethylene terephthalate polymers into a preform or a container.
Description
CROSS-REFERENCE To RELATED PATENTS
[0001] This application is a voluntary division (i.e., a continuing
application) of commonly-assigned U.S. application Ser. No.
10/962,167 for Methods for Introducing Additives into Polyethylene
Terephthalate, which was filed Oct. 8, 2004, which is a
continuation-in-part of commonly-assigned U.S. application Ser. No.
10/628,077, now U.S. Pat. No. 6,803,082, for Methods for the Late
Introduction of Additives into Polyethylene Terephthalate, which
was filed Jul. 25, 2003, and which is a continuation of
commonly-assigned U.S. application Ser. No. 09/738,150, now U.S.
Pat. No. 6,599,596, for Methods of Post-Polymerization Injection in
Continuous Polyethylene Terephthalate Production, which was filed
Dec. 15, 2000. U.S. application Ser. No. 10/962,167, U.S. Pat. No.
6,803,082, and U.S. Pat. No. 6,599,596 are herein incorporated by
reference in their entirety.
[0002] This application, like its parent applications, incorporates
entirely by reference commonly-assigned application Ser. No.
09/738,619, now U.S. Pat. No. 6,500,890, for Polyester Bottle
Resins Having Reduced Frictional Properties and Methods for Making
the Same. This application includes material disclosed in
commonly-assigned U.S. Pat. No. 6,500,890 but does not introduce
new matter into the present invention disclosure.
[0003] This application further incorporates entirely by reference
the following commonly-assigned patents: Ser. No. 09/932,150, for
Methods of Post-Polymerization Extruder Injection in Polyethylene
Terephthalate Production, filed Aug. 17, 2001, now U.S. Pat. No.
6,569,991; Ser. No. 10/017,612, for Methods of Post-Polymerization
Injection in Condensation Polymer Production, filed Dec. 14, 2001,
now U.S. Pat. No. 6,573,359; Ser. No. 10/017,400, for Methods of
Post-Polymerization Extruder Injection in Condensation Polymer
Production, filed Dec. 14, 2001, now U.S. Pat. No. 6,590,069; Ser.
No. 10/176,737 for Polymer Resins Having Reduced Frictional
Properties, filed Jun. 21, 2002, now U.S. Pat. No. 6,727,306; and
Ser. No. 10/177,932 for Methods for Making Polyester Bottle Resins
Having Reduced Frictional Properties, filed Jun. 21, 2002, now U.S.
Pat. No. 6,710,158.
FIELD OF THE INVENTION
[0004] The invention relates to the late introduction of additives,
such as inert particulates, via reactive carriers during
polyethylene terephthalate production.
[0005] The invention further relates to polyester resins that
include small amounts of inert particulate additives, which reduce
the coefficient of friction in bottles formed from the polyester
resins while maintaining bottle clarity.
BACKGROUND OF THE INVENTION
[0006] Polyester resins, especially polyethylene terephthalate
(PET) and its copolyesters, are widely used to produce rigid
packaging, such as two-liter soft drink containers. Polyester
packages produced by stretch-blow molding possess high strength and
shatter resistance, and have excellent gas barrier and organoleptic
properties as well. Consequently, such plastics have virtually
replaced glass in packaging numerous consumer products (e.g.,
carbonated soft drinks, fruit juices, and peanut butter).
[0007] In conventional techniques of making bottle resin, modified
polyethylene terephthalate is polymerized in the melt phase to an
intrinsic viscosity of about 0.6 deciliters per gram (dl/g),
whereupon it is polymerized in the solid phase to achieve an
intrinsic viscosity that better promotes bottle formation. Before
1965, the only feasible method of producing polyethylene
terephthalate polyester was to use dimethyl terephthalate (DMT). In
this technique, dimethyl terephthalate and ethylene glycol are
reacted in a catalyzed ester interchange reaction to form
bis(2-hydroxyethyl)terephthalate monomers and oligomers, as well as
a methanol byproduct that is continuously removed. These
bis(2-hydroxyethyl)terephthalate monomers and oligomers are then
catalytically polymerized via polycondensation to produce
polyethylene terephthalate polymers.
[0008] Purer forms of terephthalic acid (TA) are now increasingly
available. Consequently, terephthalic acid has become an
acceptable, if not preferred, alternative to dimethyl terephthalate
as a starting material for the production of polyethylene
terephthalate. In this alternative technique, terephthalic acid and
ethylene glycol react in a generally uncatalyzed esterification
reaction to yield low molecular weight monomers and oligomers, as
well as a water byproduct that is continuously removed. As with the
dimethyl terephthalate technique, the monomers and oligomers are
subsequently catalytically polymerized by polycondensation to form
polyethylene terephthalate polyester. The resulting polyethylene
terephthalate polymer is substantially identical to the
polyethylene terephthalate polymer resulting from dimethyl
terephthalate, albeit with some end group differences.
[0009] Polyethylene terephthalate polyester may be produced in a
batch process, where the product of the ester interchange or
esterification reaction is formed in one vessel and then
transferred to a second vessel for polymerization. Generally, the
second vessel is agitated and the polymerization reaction is
continued until the power used by the agitator reaches a level
indicating that the polyester melt has achieved the desired
intrinsic viscosity and, thus, the desired molecular weight. More
commercially practicable, however, is to carry out the
esterification or ester interchange reactions, and then the
polymerization reaction as a continuous process. The continuous
production of polyethylene terephthalate results in greater
throughput, and so is more typical in large-scale manufacturing
facilities.
[0010] When the polymerization process is complete, the resulting
polymer melt is typically extruded and pelletized for convenient
storage and transportation. Thereafter, the polyethylene
terephthalate may be molded into preforms and bottles.
[0011] As will be understood by those having ordinary skill in the
art, polyethylene terephthalate is typically converted into a
container via a two-step process. First, an amorphous bottle
preform is produced from bottle resin by melting the resin in an
extruder and injection molding the molten polyester into a preform.
Such a preform usually has an outside surface area that is at least
an order of magnitude smaller than the outside surface of the final
container. The preform is reheated to an orientation temperature
that is typically 30.degree. C. above the glass transition
temperature. The reheated preform is then placed into a bottle mold
and, by stretching and inflating with high-pressure air, formed
into a bottle. Those of ordinary skill in the art will understand
that any defect in the preform is typically transferred to the
bottle. Accordingly, the quality of the bottle resin used to form
injection-molded preforms is critical to achieving commercially
acceptable bottles.
[0012] Polyethylene terephthalate bottles, especially
straight-walled two-liter soft drink bottles, often possess high
coefficients of friction (COF). This is a significant problem in
the bottling industry as excessive friction between adjacent
bottles prevents such bottles from easily and efficiently sliding
past one another as they are depalletized. To improve
depalletizing, bottlers conventionally resort to water misting and
line lubrication on a filling line.
[0013] There is a need for a polyester bottle that possesses
reduced coefficient of friction while retaining bottle clarity and,
therefore, a corresponding need for a method to achieve the
same.
OBJECT AND SUMMARY OF THE INVENTION
[0014] Accordingly, it is an object of the present invention to
provide a method of adding additives via a reactive carrier to a
continuous polyethylene terephthalate process after the melt-phase
polycondensation reactions are essentially complete.
[0015] It is a further object of the present invention to provide a
method of adding additives in a reactive carrier to a continuous
polyethylene terephthalate process to reduce polymer transition
times and eliminate upsets to the continuous process resulting from
changing polymer formulations.
[0016] It is a further object of the present invention to provide a
method of introducing additives into a continuous polyethylene
terephthalate process in a way that reduces the degradation or
volatilization of such additives.
[0017] It is a further object of the present invention to provide a
simplified additive delivery system wherein the reactive carrier is
a pumpable liquid or slurry at or near room temperature.
[0018] It is a further object of the present invention to provide a
simplified additive delivery system that does not require the use
of an extruder to deliver additives.
[0019] It is a further object of the present invention to provide a
method for making polyethylene terephthalate resin that can be
formed into high-clarity bottles possessing reduced coefficient of
friction.
[0020] It is a further object of the present invention to provide a
method for making polyethylene terephthalate preforms and bottles
possessing reduced coefficients of friction.
[0021] It is a further object of the present invention to provide a
polyester resin that is capable of being formed into high-clarity
bottles possessing reduced coefficient of friction.
[0022] It is a further object of the present invention to provide a
high-clarity polyester bottle including a surface-modified talc or
surface-modified calcium carbonate in concentrations that permit
the bottle to possess reduced coefficient of friction.
[0023] The foregoing, as well as other objectives and advantages of
the invention and the manner in which the same are accomplished, is
further specified within the following detailed description and its
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates the qualitative effect on bottle sidewall
haze and friction as a function of increasing concentration of the
reduced-COF additive.
[0025] FIGS. 2 and 3 illustrate the theoretical loss of intrinsic
viscosity of polyethylene terephthalate as a function of the
concentration of a reactive (additive) carrier at various molecular
weights.
DETAILED DESCRIPTION
[0026] In one aspect, the invention is a novel method for the late
introduction of additives into a continuous process for making
polyethylene terephthalate. The additives are introduced during,
and preferably after, the polycondensation of polyethylene
terephthalate polymers. In particular, the method employs a
reactive carrier that not only functions as a delivery vehicle for
one or more additives, but also reacts with the polyethylene
terephthalate, thereby binding the carrier in the polyethylene
terephthalate resin. This prevents the emergence of the carrier
from the polyethylene terephthalate during subsequent processing,
such as solid state polymerization and injection molding
operations. This also improves dispersion of the additive in the
polymer and reduces the tendency of the additive to emerge and
deposit in polymer processing equipment during solid state
polymerization.
[0027] In one embodiment, the invention is a method for making a
polyester resin that can be formed into high-clarity bottles
possessing reduced coefficient of friction. The method generally
includes reacting a terephthalate component and a diol component to
form polyethylene terephthalate precursors (e.g.,
bis(2-hydroxyethyl)terephthalate), which are then polymerized via
melt phase polycondensation to form polymers of polyethylene
terephthalate of a desired molecular weight. During
polycondensation, which is usually enhanced by catalysts, ethylene
glycol is continuously removed to create favorable reaction
kinetics.
[0028] Thereafter, inert particulate additives are introduced by
way of a reactive carrier into the polyethylene terephthalate
polymers (i.e., the reactive carrier functions as an additive
delivery vehicle). The reactive carrier, which has a molecular
weight of less than about 10,000 g/mol, not only facilitates
uniform blending of the inert particulate additives within the
polymer melt, but also reacts with the polyethylene terephthalate
polymers to ensure that the carrier does not emerge during
subsequent processes.
[0029] In another embodiment, the invention includes polymerizing
the polyethylene terephthalate precursors via melt phase
polycondensation to form polyethylene terephthalate polymers having
a target intrinsic viscosity of at least about 0.45 dl/g. Once the
polyethylene terephthalate polymers have achieved this target
intrinsic viscosity, inert particulate additives are introduced by
way of a reactive carrier having a molecular weight of less than
about 10,000 g/mol. Finally, the melt phase polycondensation of the
polyethylene terephthalate polymers is completed. Where inert
particulate additives are introduced during the polycondensation of
polyethylene terephthalate polymers, the target intrinsic viscosity
is preferably at least about 0.50 dl/g, more preferably at least
about 0.55 dl/g, and most preferably at least about 0.60 dl/g. At
an intrinsic viscosity of at least about 0.45 dl/g, the
polyethylene terephthalate polymer possesses sufficient molecular
weight, mechanical properties, melt strength, and crystallinity to
facilitate polymer processing.
[0030] The embodiments of the present invention as herein disclosed
are applicable regardless of whether the late addition of inert
particulate additives occurs after the polycondensation stage or
during the polycondensation stage (i.e., where the target intrinsic
viscosity of the polyethylene terephthalate polymers is at least
about 0.45 dl/g).
[0031] Accordingly, in a particular embodiment, the method is
characterized by the introduction of between about 20 and 200 ppm
of an inert particulate additive (e.g., talc or calcium carbonate)
that is capable of reducing the coefficient of friction in bottles
formed from the polyethylene terephthalate polymers. The
friction-reducing additive has an average particle size of less
than about ten microns and is preferably either surface-modified
talc or surface-modified calcium carbonate.
[0032] In another aspect, the invention is a polyester resin that
is capable of being formed into low-haze, high-clarity bottles
possessing reduced coefficient of friction. The bottle resin is
characterized by the inclusion of between about 20 and 200 ppm of
an inert particulate additive, preferably either talc (i.e., a
natural hydrous magnesium silicate of representative formula
3MgO.4SiO.sub.2.H.sub.2O)or precipitated calcium carbonate, having
an average particle size of less than about ten microns, more
preferably less than two microns. The inert particulate additive,
which is preferably surface-treated, is present in low
concentrations to ensure that bottles formed from the polyester
bottle resin possess low haziness. Such improved frictional
characteristics reduce, and can eliminate, the need to apply,
during filling operation, external lubricants to the surfaces of
containers formed from the present polyester resin.
[0033] Preferably, the polyester resin includes between about 40
and 150 ppm of the inert particulate additive, more preferably
between about 40 and 100 ppm of the inert particulate additive, and
most preferably between about 60 and 100 ppm of the inert
particulate additive.
[0034] Without being bound to a particular theory, it is believed
that the introduction of fillers can create discontinuous phases
within the polyethylene terephthalate resin. During stretch-blow
molding, such discontinuities lead to the formation of microvoids
around the filler particles. This causes bottle haze because of
differences in refractive index between the microvoid regions and
the polyethylene terephthalate matrix. The microvoids are
apparently caused by an inherent incompatibility of the filler
particles with the polyethylene terephthalate matrix.
[0035] According to the present invention, to improve compatibility
between the polyethylene terephthalate polymers and the inert
particulate additive, the inert particulate additive is preferably
treated with a coupling agent before its addition to polyethylene
terephthalate polymers. This has been found to significantly reduce
bottle haze while reducing bottle coefficient of friction (COF).
Without coupling agent treatment, the polyethylene terephthalate
polymers resist wetting of the inert particles. Thus, all things
being equal, surface treatment reduces polyester bottle haze.
[0036] Accordingly, the inert particulate additive is preferably
surface-modified talc or surface-modified calcium carbonate. In
particular, talc is preferably surface treated using silanes,
especially organosilanes such as 3-aminopropyl trimethoxy silane
and 3-aminopropyl triethoxy silane, at a loading of between about
0.5 and one weight percent. Calcium carbonate is preferably surface
treated using stearic acid at a loading of between about one and
two weight percent. Treatment with these coupling agents (e.g.,
organosilane and stearic acid) facilitates compatibility between
the inert particles and the polyethylene terephthalate polymer by
introducing covalent chemical bonding between the particle surface
and the polyethylene terephthalate polymer, or by introducing a
hydrophobic moiety that is compatible with the polyethylene
terephthalate to facilitate better polymer wetting of the
particle.
[0037] The inclusion of an inert particulate additive in the
polyethylene terephthalate resin reduces bottle friction, but also
increases bottle haze. FIG. 1 depicts the trade-off between reduced
friction and haze. In brief, concentrations of talc or calcium
carbonate greater than about 200 ppm (and in some instances even
100 ppm) will result in unacceptable hazy bottles, and
concentrations of talc or calcium carbonate much less than about 20
ppm will not noticeably reduce bottle coefficient of friction
(COF). As described previously, the polyester resin preferably
includes between about 40 and 150 ppm of the inert particulate
additive and most preferably between about 60 and 100 ppm of the
inert particulate additive.
[0038] The efficacy of the present invention is demonstrated by
testing that shows the addition of 100 ppm of surface-treated talc
reduces coefficient of friction by about 90 percent, as measured
using ASTM Test method D 1894.
[0039] Note that at any given weight fraction of inert particulate
additive, increasing particle size will exacerbate haziness with no
concomitant reduction in friction. An average particle size of much
more than ten microns generally causes unacceptable bottle haze. As
will be understood by those familiar with this art, particle size
is typically measured by techniques based on light scattering.
Particle sizes and distributions are often characterized using a
Hegman Fineness number determined from ASTM D1210-79.
[0040] As used herein, the term "diol component" refers primarily
to ethylene glycol, although other diols (e.g., polyethylene
glycol) may be used as well. It will be understood by those of
ordinary skill in the art that the diol component usually forms the
majority of terminal ends of the polymer chains and so is present
in the composition in slightly greater fractions. For example, the
molar ratio of the terephthalate component and the diol component
is typically between about 1.0:1.0 and 1.0:1.6.
[0041] As used herein, the term "terephthalate component" refers to
diacids and diesters that can be used to prepare polyethylene
terephthalate. In particular, the terephthalate component mostly
includes terephthalic acid and dimethyl terephthalate, but can
include diacid and diester comonomers as well. In this regard,
those having ordinary skill in the art will know that there are two
conventional methods for forming polyethylene terephthalate. These
methods are well known to those skilled in the art.
[0042] One method employs a direct esterification reaction using
terephthalic acid and excess ethylene glycol. In this technique,
the aforementioned step of reacting a terephthalate component and a
diol component includes reacting terephthalic acid and ethylene
glycol in a heated esterification reaction to form monomers and
oligomers of terephthalic acid and ethylene glycol, as well as a
water byproduct. To enable the esterification reaction to go
essentially to completion, the water must be continuously removed
as it is formed.
[0043] The other method involves a two-step ester exchange reaction
and polymerization using dimethyl terephthalate and excess ethylene
glycol. In this technique, the aforementioned step of reacting a
terephthalate component and a diol component includes reacting
dimethyl terephthalate and ethylene glycol in a heated ester
exchange reaction to form monomers and oligomers of terephthalate
and ethylene glycol, as well as methanol as a byproduct. To enable
the ester exchange reaction to go essentially to completion, the
methanol must be continuously removed as it is formed.
[0044] It will be understood by those having ordinary skill in the
art that the polyethylene terephthalate herein described may be a
modified polyethylene terephthalate to the extent the diol
component can include other glycols besides ethylene glycol (e.g.,
diethylene glycol, 1,3-propanediol, 1,4-butanediol and
1,4-cyclohexane dimethanol), or the terephthalate component
includes modifiers such as isophthalic acid, 2,6-naphthalene
dicarboxylic acid, succinic acid, or one or more functional
derivatives of terephthalic acid. In fact, most commercial
polyethylene terephthalate polymers are modified polyethylene
terephthalate polyesters.
[0045] An advantage of the present invention is that the inert
particulate additives may be added to any polyester bottle resin
formulation to reduce coefficient of friction (COF) in bottles made
therefrom. In this regard, bottle grade polyester resins will not
be discussed herein in detail as such resins are well known in the
art. For example, commonly-assigned, co-pending application Ser.
No. 09/456,253 filed Dec. 7, 1999, for a Method of Preparing
Modified Polyester Bottle Resins, now U.S. Pat. No. 6,284,866,
which discusses several U.S. patents that disclose various modified
polyethylene terephthalate resins. This application is hereby
incorporated entirely herein by reference.
[0046] While the present application is directed to polyester
resins, it is believed that non-polyester resins, such as
high-density polyethylene (HDPE), low-density polyethylene (LDPE),
linear low-density polyethylene (LLDPE), polyvinyl chloride (PVC),
and polyvinyl dichloride (PVDC), which are typically used in films,
show analogous frictional characteristics and thus benefit from the
use of inert particulate additives to reduce coefficient of
friction (COF).
[0047] In the present invention, the direct esterification reaction
is preferred over the older, two-step ester exchange reaction. As
noted, the direct esterification technique reacts terephthalic acid
and ethylene glycol to form low molecular weight monomers,
oligomers, and water.
[0048] For example, in a typical, exemplary process the continuous
feed enters a direct esterification vessel that is operated at a
temperature of between about 240.degree. C. and 290.degree. C. and
at a pressure of between about 5 and 85 psia for between about one
and five hours. The reaction, which is typically uncatalyzed, forms
low molecular weight monomers, oligomers, and water. The water is
removed as the esterification reaction proceeds to drive a
favorable reaction equilibrium.
[0049] Thereafter, the low molecular weight monomers and oligomers
are polymerized via polycondensation to form polyethylene
terephthalate polyester. This polycondensation stage generally
employs a series of two or more vessels and is operated at a
temperature of between about 250.degree. C. and 305.degree. C. for
between about one and four hours. The polycondensation reaction
usually begins in a first vessel called the low polymerizer. The
low polymerizer is operated at a pressure range of between about 0
and 70 torr. The monomers and oligomers polycondense to form
polyethylene terephthalate and ethylene glycol.
[0050] The ethylene glycol is removed from the polymer melt using
an applied vacuum to drive the reaction to completion. In this
regard, the polymer melt is typically agitated to promote the
escape of the ethylene glycol from the polymer melt and to assist
the highly viscous polymer melt in moving through the
polymerization vessel.
[0051] As the polymer melt is fed into successive vessels, the
molecular weight and thus the intrinsic viscosity of the polymer
melt increases. The temperature of each vessel is generally
increased and the pressure decreased to allow greater
polymerization in each successive vessel.
[0052] The final vessel, generally called the "high polymerizer,"
is operated at a pressure of between about 0 and 40 torr. Like the
low polymerizer, each of the polymerization vessels is connected to
a flash vessel and each is typically agitated to facilitate the
removal of ethylene glycol. The residence time in the
polymerization vessels and the feed rate of the ethylene glycol and
terephthalic acid into the continuous process is determined in part
based on the target molecular weight of the polyethylene
terephthalate polyester. Because the molecular weight can be
readily determined based on the intrinsic viscosity of the polymer
melt, the intrinsic viscosity of the polymer melt is generally used
to determine the feed rate of the reactants and the residence time
within the polymerization vessels.
[0053] Note that in addition to the formation of polyethylene
terephthalate polymers, side reactions occur that produce
undesirable by-products. For example, the esterification of
ethylene glycol forms diethylene glycol (DEG), which is
incorporated into the polymer chain. As is known to those of skill
in the art, diethylene glycol lowers the softening point of the
polymer. Moreover, cyclic oligomers (e.g., trimer and tetramers of
terephthalic acid and ethylene glycol) may occur in minor amounts.
The continued removal of ethylene glycol as it forms in the
polycondensation reaction will generally reduce the formation of
these by-products.
[0054] After the polymer melt exits the polycondensation stage,
typically from the high polymerizer, it is generally filtered and
extruded, preferably immediately after exiting the polycondensation
stage. After extrusion, the polyethylene terephthalate is quenched,
preferably by spraying with water or immersing in a water trough,
to solidify it. The solidified polyethylene terephthalate polyester
is cut into chips or pellets for storage and handling purposes. As
used herein, the term "pellets" is used generally to refer to
chips, pellets, and the like.
[0055] As will be known to those of skill in the art, the pellets
formed from the polyethylene terephthalate polymers may be
subjected to crystallization followed by solid state polymerization
(SSP) to increase the molecular weight of the polyethylene
terephthalate resin. (It should be noted that the method of the
invention does not adversely affect the SSP rate and often will
even increase the SSP rate.) The polyester chips are then re-melted
and re-extruded to form bottle preforms, which can thereafter be
formed into polyester containers (e.g., beverage bottles). The
levels of inert particulate additives (i.e., less than 200 ppm) do
not detrimentally affect cycle times during injection molding
operations.
[0056] The inert particulate additives are typically added after
the melt polymerization is complete (i.e., mixed with the molten
polymer stream after the final polymerization vessel). Such late
addition is desirable, for example, because esterification and
polycondensation conditions can cause a calcium carbonate additive
to dissolve in the polymer, which destroys its particulate nature.
Consequently, calcium carbonate is preferably added to the
polyethylene terephthalate polymer before extrusion and
pelletization.
[0057] Similarly, high polycondensation temperatures can strip
coupling agents (e.g., silane surface treatment) from talc. As talc
is not susceptible to dissolution in the polymer, its addition is
more adaptable than is the addition of calcium carbonate (i.e.,
talc itself can be added at any point during the
polymerization).
[0058] A particular advantage of the present invention is the
reduction of polymer transition times and elimination of upsets to
continuous processes that result from polymer formulation changes.
As will be known by those familiar with the art, conventional
polyester processing introduces additives in an ethylene glycol
solution or slurry. These ethylene glycol streams are added into
the esterification process or the first polycondensation vessel,
each of which have a high ethylene glycol content. To effect a
product change, the contents of each subsequent vessel must be
completely replaced. In standard continuous units, the required
transition time is on the order of four to eight hours.
[0059] Although the prior discussion assumes a continuous
production process, it will be understood that the invention is not
so limited. The teachings disclosed herein may be applied to
semi-continuous processes and even batch processes.
[0060] In a preferred embodiment, the method introduces the inert
particulate additive via a reactive carrier, rather than via an
inert carrier or no carrier at all. The reactive carrier, which
preferably has a molecular weight of less than about 10,000 g/mol
may be introduced during polycondensation, or more preferably,
after the polycondensation is complete. In either respect, the
reactive carrier should be introduced to the polyethylene
terephthalate polymers in quantities such that bulk polymer
properties are not significantly affected.
[0061] Most preferably, the reactive carrier has a melting point
that ensures that it is a liquid or slurry at near ambient
temperatures. Near ambient temperatures not only simplify the unit
operations (e.g., extruders, heaters, and piping), but also
minimize degradation of the inert particulate additives. As used
herein, the term "near ambient" includes temperatures between about
20.degree. C. and 60.degree. C.
[0062] As a general matter, the reactive carrier should make up no
more than about one weight percent of the polyethylene
terephthalate resin. Preferably, the reactive carrier is introduced
to the polyethylene terephthalate polymers in quantities such that
its concentration in the polymer resin is less than about 1000 ppm
(i.e., 0.1 weight percent). Reducing the reactive carrier to
quantities such that its concentration in the polymer resin is less
than 500 ppm (i.e., 0.05 weight percent) will further reduce
potential adverse effects to bulk polymer properties.
[0063] In general, reactive carriers having carboxyl, hydroxyl, or
amine functional groups are favored. Preferred are polyols,
especially polyester polyols and polyether polyols, having a
molecular weight that is sufficiently high such that the polyol
will not substantially reduce the intrinsic viscosity of the
polyethylene terephthalate polymer, and a viscosity that
facilitates pumping of the polyol. Polyethylene glycol is a
preferred polyol. Other exemplary polyols include functional
polyethers, such as polypropylene glycol that is prepared from
propylene oxide, random and block copolymers of ethylene oxide and
propylene oxide, and polytetramethylene glycol that is derived from
the polymerization of tetrahydrofuran.
[0064] Alternatively, the reactive carrier may include dimer or
trimer acids and anhydrides. In another embodiment, the reactive
carrier may possess, in addition to or in place of terminal
functional groups, internal functional groups (e.g., esters,
amides, and anhydrides) that react with the polyethylene
terephthalate polymers.
[0065] In yet another embodiment, the reactive carrier may include
esters without terminal functional groups, amides without terminal
functional groups, or anhydrides without terminal functional groups
that are capable of reacting into the polyethylene terephthalate
polymers during solid state polymerization and that will not cause
the polyethylene terephthalate polymers to suffer intrinsic
viscosity loss during injection molding processes.
[0066] In view of the foregoing, a preferred embodiment of the
invention includes reacting terephthalic acid and ethylene glycol
in a heated esterification reaction to form monomers and oligomers
of terephthalic acid and ethylene glycol, then polymerizing these
monomers and oligomers via melt phase polycondensation to form
polyethylene terephthalate polymers. Thereafter, between about 20
and 200 ppm of either surface-modified talc or surface-modified
calcium carbonate is introduced into the polyethylene terephthalate
polymers using a reactive carrier, which facilitates uniform
blending within the polymer melt. Preferably, the reactive carrier
is a polyol (e.g., polyethylene glycol) having a molecular weight
that permits the polyol to be pumped at near ambient temperatures
(e.g., less than 60.degree. C.) and that is introduced to the
polyethylene terephthalate polymers in quantities such that bulk
properties of the polyethylene terephthalate polymers are not
significantly affected. The polyethylene terephthalate polymers are
then formed into chips (or pellets via a polymer cutter) before
being solid state polymerized. Importantly, the polyol reactive
carrier combines with the polyethylene terephthalate polymer such
that it is non-extractable during subsequent processing operations
(e.g., forming polyester preforms or beverage containers).
[0067] As will be understood by those of ordinary skill in the art,
macromolecules are considered to be polymers at an intrinsic
viscosity of about 0.45 dl/g. This roughly translates to a
molecular weight of at least about 13,000 g/mol. In contrast, the
reactive carriers according to the present invention have molecular
weights that are less than about 10,000 g/mol. The molecular weight
of the reactive carrier is typically less than 6,000 g/mol,
preferably less than 4,000 g/mol, more preferably between about 300
and 2,000 g/mol, and most preferably between about 400 and 1,000
g/mol. As used herein, molecular weight refers to number-average
molecular weight, rather than weight-average molecular weight.
[0068] FIGS. 2 and 3 illustrate the theoretical loss of intrinsic
viscosity as a function of reactive carrier concentration at
several molecular weights. FIG. 2 depicts the impact of the
reactive carrier upon polyethylene terephthalate having an
intrinsic viscosity of 0.63 dl/g. Similarly, FIG. 3 depicts the
impact of the reactive carrier upon polyethylene terephthalate
having intrinsic viscosity of 0.45 dl/g. Note that at any
concentration, the reactive carriers having higher molecular
weights have less adverse effect upon intrinsic viscosity of the
polymer resin.
[0069] As used herein, the term "intrinsic viscosity" is the ratio
of the specific viscosity of a polymer solution of known
concentration to the concentration of solute, extrapolated to zero
concentration. Intrinsic viscosity, which is widely recognized as
standard measurements of polymer characteristics, is directly
proportional to average polymer molecular weight. See, e.g.,
Dictionary of Fiber and Textile Technology, Hoechst Celanese
Corporation (1990); Tortora & Merkel, Fairchild's Dictionary of
Textiles (.sup.7th Edition 1996).
[0070] Intrinsic viscosity can be measured and determined without
undue experimentation by those of ordinary skill in this art. For
the intrinsic viscosity values described herein, the intrinsic
viscosity is determined by dissolving the copolyester in
orthochlorophenol (OCP), measuring the relative viscosity of the
solution using a Schott Autoviscometer (AVS Schott and AVS 500
Viscosystem), and then calculating the intrinsic viscosity based on
the relative viscosity. See, e.g., Dictionary of Fiber and Textile
Technology ("intrinsic viscosity").
[0071] In particular, a 0.6-gram sample (.+-.0.005 g) of dried
polymer sample is dissolved in about 50 ml (61.0-63.5 grams) of
orthochlorophenol at a temperature of about 105.degree. C. Fiber
and yarn samples are typically cut into small pieces, whereas chip
samples are ground. After cooling to room temperature, the solution
is placed in the viscometer and the relative viscosity is measured.
As noted, intrinsic viscosity is calculated from relative
viscosity.
[0072] As noted, the invention embraces the late addition of
various kinds of additives via the reactive carrier. Late addition
is especially desirable where the additives are volatile or subject
to thermal degradation. Conventional additive injection during the
esterification stage or early during the polycondensation stage
subjects additives to several hours of high-temperature (greater
than 260.degree. C.) and reduced-pressure (less than 10 torr)
conditions. Consequently, additives that have significant vapor
pressure at these conditions will be lost from the process.
Advantageously, the method of the present invention significantly
reduces the time additives are exposed to high polycondensation
temperatures.
[0073] In addition to inert particulates (e.g., talc, calcium
carbonate, clays, or silicas), additives according to the present
invention can include, preform heat-up rate enhancers, stabilizers,
colorants, antioxidants, branching agents, oxygen barrier agents,
carbon dioxide barrier agents, oxygen scavengers, crystallization
control agents, acetaldehyde reducing agents, impact modifiers,
catalyst deactivators, melt strength enhancers, anti-static agents,
lubricants, chain extenders, nucleating agents, solvents, fillers,
and plasticizers.
[0074] Finally, as is understood by those familiar with polyester
packaging, ultraviolet (UV) radiation absorbers protect polymers
and the contents of packages formed from the same. Where UV
absorbers are added to the bottle resin during the injection
molding process, there is a tendency for such UV absorbers (and
when used, reactive carriers that deliver UV absorbers) to leave
deposits in the injection molds used for preforms. Such deposits
cause the preforms to stick in the injection molds slightly longer,
thereby slowing preform manufacturing efficiency.
[0075] Without being bound to any particular theory, it is believed
that the interaction between a UV absorber and the bottle resin
produces byproducts that in turn deposit on the molds in which
polyester bottle preforms are manufactured. These deposits cause
the preforms to stick in the mold, thereby slowing the production
rate of the preform-making process. Calcium carbonate and
especially talc have been found to have the beneficial effect of
reducing adherence to preform molds, thereby increasing the speed
and efficiency of the injection molding process. Accordingly, an
embodiment of the polyester resin includes both an inert
particulate additive as herein described and a UV absorber.
[0076] In the drawings and the specification, typical embodiments
of the invention have been disclosed. Specific terms have been used
only in a generic and descriptive sense, and not for purposes of
limitation. The scope of the invention is set forth in the
following claims.
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