U.S. patent application number 09/851240 was filed with the patent office on 2001-10-25 for method of preparing modified polyester bottle resins.
Invention is credited to Schiavone, Robert Joseph.
Application Number | 20010034431 09/851240 |
Document ID | / |
Family ID | 23812062 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010034431 |
Kind Code |
A1 |
Schiavone, Robert Joseph |
October 25, 2001 |
Method of preparing modified polyester bottle resins
Abstract
The present invention is a method of preparing a high molecular
weight copolyester bottle resin that has excellent melt processing
characteristics. The method includes the steps of reacting a diacid
or diester component and a diol component to form modified
polyethylene terephthalate, wherein diol component is present in
excess of stoichiometric proportions. Together, the diacid or
diester component and the diol component must include at least 7
percent comonomer. The remainder of the diacid component is
terephthalic acid or dimethyl terephthalate and the remainder of
the diol component is ethylene glycol. The modified polyethylene
terephthalate is copolymerized in the melt phase to an intrinsic
viscosity of between about 0.25 dl/g and 0.40 dl/g to thereby form
a copolyester prepolymer. Thereafter the copolyester prepolymer is
polymerized in the solid phase to form a high molecular weight
bottle resin that has an intrinsic viscosity of at least about 0.70
dl/g, and a solid phase density of less than 1.413 g/cc.
Inventors: |
Schiavone, Robert Joseph;
(Matthews, NC) |
Correspondence
Address: |
SUMMA & ALLAN, P.A.
11610 NORTH COMMUNITY HOUSE ROAD
SUITE 200
CHARLOTTE
NC
28277
US
|
Family ID: |
23812062 |
Appl. No.: |
09/851240 |
Filed: |
May 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09851240 |
May 8, 2001 |
|
|
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09456253 |
Dec 7, 1999 |
|
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Current U.S.
Class: |
528/308.8 ;
528/301; 528/308; 528/308.1; 528/308.3; 528/308.6; 528/308.7 |
Current CPC
Class: |
Y10T 428/1352 20150115;
Y10T 428/1397 20150115; C08G 63/80 20130101 |
Class at
Publication: |
528/308.8 ;
528/301; 528/308; 528/308.3; 528/308.1; 528/308.6; 528/308.7 |
International
Class: |
C08G 063/183; C08G
063/80; C08G 063/78 |
Claims
That which is claimed is:
1. A method of preparing a high molecular weight copolyester bottle
resin that has excellent melt processing characteristics,
comprising: reacting a terephthalate component and a diol component
to form a modified polyethylene terephthalate, wherein the
terephthalate component includes about 100 mole percent
terephthalic acid or dimethyl terephthalate, and the diol component
is present in excess of stoichiometric proportions and includes
between about 84 and 94 mole percent ethylene glycol, between about
2 and 6 mole percent diethylene glycol, and between about 4 and 10
mole percent cyclohexane dimethanol; thereafter copolymerizing the
modified polyethylene terephthalate in the melt phase to an
intrinsic viscosity of between about 0.25 dl/g and 0.40 dl/g to
thereby form a copolyester prepolymer having an average apparent
crystallite size of less than 9 nm; thereafter forming the
copolyester prepolymer into chips; and thereafter polymerizing the
copolyester prepolymer chips in the solid phase to form a high
molecular weight bottle resin, wherein the bottle resin has an
intrinsic viscosity of at least about 0.70 dl/g and a solid phase
density of less than 1.413 g/cc.
2. A method of preparing a high molecular weight copolyester bottle
resin according to claim 1, wherein the step of copolymerizing the
modified polyethylene terephthalate in the melt phase comprises
copolymerizing the modified polyethylene terephthalate in the melt
phase to an intrinsic viscosity of between about 0.30 dl/g and 0.36
dl/g.
3. A method of preparing a high molecular weight copolyester bottle
resin according to claim 2, further comprising forming the high
molecular weight bottle resin into bottle preforms.
4. A method of preparing a high molecular weight copolyester bottle
resin according to claim 1, wherein the step of forming the
copolyester prepolymer into chips comprises forming the copolyester
prepolymer into chips having an average minimum dimension of
between about 1 mm and 10 mm.
5. A method of preparing a high molecular weight copolyester bottle
resin according to claim 1, wherein the step of polymerizing the
copolyester prepolymer chips comprises copolymerizing the
copolyester prepolymer chips in the solid phase to form a high
molecular weight bottle resin having a solid phase density of
between 1.390 and 1.413 grams/cc.
6. A method of preparing a high molecular weight copolyester bottle
resin according to claim 1, wherein the step of polymerizing the
copolyester prepolymer chips comprises copolymerizing the
copolyester prepolymer chips in the solid phase to form a high
molecular weight bottle resin having an average apparent
crystallite size of 10 nm or less.
7. A method of preparing a high molecular weight copolyester bottle
resin according to claim 1, wherein the step of polymerizing the
copolyester prepolymer chips comprises copolymerizing the
copolyester prepolymer chips in the solid phase to form a high
molecular weight bottle resin having an average apparent
crystallite size of 9 nm or less.
8. A method of preparing a high molecular weight copolyester bottle
resin according to claim 1, further comprising forming the high
molecular weight bottle resin into bottle preforms.
9. A method of preparing a high molecular weight copolyester bottle
resin according to claim 8, wherein the step of forming bottle
preforms comprises forming the high molecular weight bottle resin
into bottle preforms at a haze temperature below 260.degree. C.
10. A method of preparing a high molecular weight copolyester
bottle resin according to claim 8, wherein the step of forming
bottle preforms comprises forming the high molecular weight bottle
resin into bottle preforms at a haze temperature below 250.degree.
C.
11. A method of preparing a high molecular weight copolyester
bottle resin according to claim 8, wherein the step of forming
bottle preforms comprises forming the high molecular weight bottle
resin into bottle preforms at a haze temperature below 240.degree.
C.
12. A method of preparing a high molecular weight copolyester
bottle resin that has excellent melt processing characteristics,
comprising: reacting a terephthalate component and a diol component
to form a modified polyethylene terephthalate, wherein the
terephthalate component includes about 100 mole percent
terephthalic acid or dimethyl terephthalate, and the diol component
is present in excess of stoichiometric proportions and includes
between about 84 and 94 mole percent ethylene glycol, between about
2 and 6 mole percent diethylene glycol, and between about 4 and 10
mole percent cyclohexane dimethanol; thereafter copolymerizing the
modified polyethylene terephthalate in the melt phase to an
intrinsic viscosity of between about 0.25 dl/g and 0.40 dl/g to
thereby form a copolyester prepolymer having an average apparent
crystallite size of less than 9 nm; thereafter forming the
copolyester prepolymer into chips; and thereafter polymerizing the
copolyester prepolymer chips in the solid phase to form a high
molecular weight bottle resin, wherein the bottle resin has an
intrinsic viscosity of at least about 0.70 dl/g, an average
apparent crystallite size of 10 nm or less, and a solid phase
density of between about 1.390 and 1.413 grams/cc.
13. A method of preparing a high molecular weight copolyester
bottle resin according to claim 12, wherein the step of
copolymerizing the modified polyethylene terephthalate in the melt
phase comprises copolymerizing the modified polyethylene
terephthalate in the melt phase to an intrinsic viscosity of
between about 0.30 dl/g and 0.36 dl/g.
14. A method of preparing a high molecular weight copolyester
bottle resin according to claim 13, further comprising forming the
high molecular weight bottle resin into bottle preforms.
15. A method of preparing a high molecular weight copolyester
bottle resin according to claim 12, wherein the step of forming the
copolyester prepolymer into chips comprises forming the copolyester
prepolymer into chips having an average minimum dimension of
between about 1 mm and 10 mm.
16. A method of preparing a high molecular weight copolyester
bottle resin according to claim 12, wherein the step of
polymerizing the copolyester prepolymer chips comprises
copolymerizing the copolyester prepolymer chips in the solid phase
to form a high molecular weight bottle resin having an average
apparent crystallite size of 9 nm or less.
17. A method of preparing a high molecular weight copolyester
bottle resin according to claim 12, further comprising forming the
high molecular weight bottle resin into bottle preforms.
18. A method of preparing a high molecular weight copolyester
bottle resin according to claim 17, wherein the step of forming
bottle preforms comprises forming the high molecular weight bottle
resin into bottle preforms at a haze temperature below 260.degree.
C.
19. A method of preparing a high molecular weight copolyester
bottle resin according to claim 17, wherein the step of forming
bottle preforms comprises forming the high molecular weight bottle
resin into bottle preforms at a haze temperature below 250.degree.
C.
20. A method of preparing a high molecular weight copolyester
bottle resin according to claim 17, wherein the step of forming
bottle preforms comprises forming the high molecular weight bottle
resin into bottle preforms at a haze temperature below 240.degree.
C.
21. Bottle resin chips of a high molecular weight copolyester
having excellent melt processing characteristics, comprising: about
a 1:1 molar ratio of a terephthalate component and a diol
component, said terephthalate component including about 100 mole
percent terephthalic acid or dimethyl terephthalate, and said diol
component including between about 84 and 94 mole percent ethylene
glycol, between about 2 and 6 mole percent diethylene glycol, and
between about 4 and 10 mole percent cyclohexane dimethanol; an
intrinsic viscosity of at least about 0.70 dl/g; a solid phase
density of between 1.390 and 1.413 grams/cc; an average apparent
crystallite size of less than 9 nm; a haze temperature of less than
about 250.degree. C.; and wherein said bottle resin chips have an
average minimum dimension of between about 1 mm and 10 mm.
22. Bottle resin chips of a high molecular weight copolyester
according to claim 21, wherein said bottle resin chips have a haze
temperature of less than about 240.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of copending
U.S. application Ser. No. 09/456,253, filed Dec. 7, 1999, which is
hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to polyester bottle resins and
methods of preparing polyester bottle resins. In particular, the
invention relates to methods of polymerizing modified polyesters in
the solid phase to yield bottle resins.
BACKGROUND OF THE INVENTION
[0003] Polyester resins, 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., such as carbonated soft
drinks, fruit juices, and peanut butter).
[0004] In conventional techniques of making bottle resin,
polyethylene terephthalate or its copolyesters are polymerized in
the melt phase to an intrinsic viscosity of about 0.6 deciliters
per gram (dl/g). The polyethylene terephthalate is then polymerized
in the solid phase to achieve a higher intrinsic viscosity that
promotes bottle formation.
[0005] 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 injection-molded preform is
critical to achieving commercially acceptable bottles.
[0006] Conventional polymerization techniques rely primarily on
melt-phase polymerization to produce polyester resins that
facilitate efficient preform molding. Melt phase polymerization,
however, is relatively expensive as compared to solid state
polymerization (SSP). In particular, melt-phase polymerization
requires a higher capital investment than does solid state
polymerization.
[0007] To reduce the costs associated with preparing bottle resins,
techniques have been developed to emphasize polymerization in the
solid phase rather than the melt phase. For example, there are
several patents assigned to DuPont that disclose modified
polyethylene terephthalate compositions and methods for preparing
the same. See, e.g., U.S. Pat. Nos. 5,510,454; 5,532,333;
5,540,868; 5,633,018; 5,714,262; 5,744,074; and 5,830,982. These
patents especially disclose polyethylene terephthalate compositions
having large crystallite sizes.
[0008] For example, U.S. Pat. No. 5,510,454 describes modified and
unmodified polyethylene terephthalate prepolymer having a degree of
polymerization of about 5 to about 35 (i.e., an intrinsic viscosity
ranging between about 0.10 dl/g and 0.36 dl/g), an average apparent
crystallite size of 9 nm or more, and a melting point of
270.degree. C. or less. The related U.S. Pat. No. 5,714,262 further
discloses a high molecular weight polyethylene terephthalate
composition polymerized in the solid phase from a low molecular
weight, large crystallite prepolymer, such as that disclosed by the
'454 patent. Both the '454 patent and the '262 patent teach that
polyethylene terephthalate can be modified by up to 10 mole percent
comonomers-but preferably less than 5 mole percent-provided that
the crystallization behavior of the polyester is substantially the
same as unmodified polyethylene terephthalate.
[0009] Accordingly, these DuPont patents teach away from modified
polyethylene terephthalate compositions that have substantially
different crystallization behavior from those of "homopolymer"
polyethylene terephthalate. This is critical because by embracing
only polyesters that behave like homopolymer polyethylene
terephthalate, the combined DuPont teachings yield high molecular
weight copolyester resins that not only have large crystallite
sizes, but also high crystallinity fraction. Polymer melt theory
suggests that this combination causes high haze point temperatures.
As will be understood by those of ordinary skill in the art, haze
point is the temperature at which large, light scattering
crystallites are present in the preform. This complicates the
conventional processing of resins produced according to the DuPont
teachings.
[0010] U.S. Pat. No. 4,165,420, which is assigned to Goodyear,
discloses low molecular weight polyester prepolymer in the form of
spherical beads that can be polymerized in the solid state to yield
a high molecular weight resin. The prepolymer has an intrinsic
viscosity of between about 0.1 dl/g and 0.35 dl/g. In accordance
with this Goodyear patent, to achieve discrete spherical beads
between 100 and 250 microns by employing either spray congealing or
atomization requires that the solid state polymerization begin at
an intrinsic viscosity of below 0.25 dl/g. The '420 patent also
results in prepolymer having relatively large crystallite
sizes.
[0011] Similarly, U.S. Pat. No. 4,755,587 and its
continuation-in-part, U.S. Pat. No. 4,876,326, both of which are
also assigned to Goodyear, disclose a method for producing high
molecular weight polyester resins from low molecular weight
prepolymers. In particular, the '587 patent discloses the solid
state polymerization of polyester prepolymers in the form of porous
pills. These prepolymers have an initial intrinsic viscosity
between about 0.15 dl/g and 0.7 dl/g-preferably less than 0.3
dl/g--for a time sufficient to yield a high molecular weight
polyester resin. The '587 patent also describes that a final
intrinsic viscosity of at least 0.65 dl/g is desirable, and
preferably an intrinsic viscosity of at least 0.7 dl/g. While the
'587 patent discloses that the invention is applicable to virtually
any polyester that can be solid state polymerized, it explains that
the most common kind of polyesters to be solid state polymerized
using the technique have about 75 mole percent of their acid
component provided by aromatic dicarboxylic acids.
[0012] In general, the cited Goodyear patents disclose modified
polyesters having both high and low molecular weight, as well as
solid state polymerization methods that employ copolyester
prepolymers. These patent disclosures, however, fail to teach the
present method for preparing copolyester bottle resins that have
excellent melt processing characteristics, specifically a low haze
point temperature. In particular, these Goodyear patents teach away
from using conventional pellets and instead employ very fine
spherical beads or porous pills (i.e., less than 1 mm). For
example, Goodyear's disclosed spray-congealing method produces
spherical polyethylene terephthalate particles in the 100-200 nm
range when the intrinsic viscosity is less than about 0.25 dl/g.
Goodyear's relatively greater surface area per weight of the fine
particles presumably promotes faster solid phase polymerization,
albeit at the cost of larger crystallite sizes. In this regard, the
heat treatment during the particle formation as taught by the
aforementioned U.S. Pat. No. 4,165,420 results in crystallite sizes
greater than about 9 nm. These Goodyear patents, however, fail to
appreciate that solid state polymerizing prepolymer having a
relatively large average crystallite size will result in resins
that possesses unacceptably high melt temperatures.
[0013] In summary, the prior art discloses solid state methods of
polymerizing low molecular weight polyester prepolymers to achieve
high molecular weight polyester compositions. These methods,
however, yield polyester compositions that possess unacceptably
high haze points. Processing such polyester compositions through
preform molding equipment at conventional temperature settings
results in hazy bottles. Consequently, preform equipment must be
operated at higher temperatures. This requires more cooling time,
which slows process throughput as compared to conventional
processes. Moreover, higher preform molding temperatures lead to
high levels of polyethylene terephthalate decomposition products,
such as acetaldehyde and color bodies. Therefore, there is a need
for a high molecular weight copolyester bottle resin that can be
polymerized primarily in the solid phase, and yet possesses
excellent melt processing characteristics.
OBJECT AND SUMMARY OF THE INVENTION
[0014] Accordingly, it is an object of this invention to provide a
cost-effective method of making a modified polyester bottle resin
that has excellent properties with respect to melt extrusion,
injection molding, and other kinds of melt processing.
[0015] In one aspect, the invention is a method of polymerizing
copolyester prepolymer to yield high molecular weight copolyester
possessing excellent melt processing properties. In contrast to
most conventional processes, the present method relies more on
solid state polymerization (SSP) and less upon melt polymerization
to increase molecular weight. In contrast to other solid state
processes, the present method yields a copolyester bottle resin
that can be manufactured into essentially haze-free bottle preforms
at significantly lower temperatures.
[0016] In another aspect, the invention is a low molecular weight
copolyester prepolymer composition that is useful for producing
higher molecular weight copolyester bottle resin having improved
melt-processing characteristics. Preferably, the copolyester
prepolymer composition is a modified polyethylene terephthalate
prepolymer having an intrinsic viscosity between about 0.25 dl/g
and 0.40 dl/g, and more preferably between about 0.30 dl/g and 0.36
dl/g. In yet another aspect, the invention is a high molecular
weight copolyester bottle resin made from the low molecular weight
copolyester prepolymer. This copolyester bottle resin has excellent
melt processing characteristics. Preferably, the copolyester bottle
resin is modified polyethylene terephthalate having an intrinsic
viscosity of at least 0.70 dl/g.
[0017] 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 drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 compares the haze point of a bottle resin prepared
from low intrinsic viscosity prepolymers with a conventional bottle
resin containing a similar fraction of total comonomer.
[0019] FIG. 2 compares, on a volumetric basis, the percent
crystallinity of a bottle resin prepared from low intrinsic
viscosity prepolymers with a conventional bottle resin containing a
similar fraction of total comonomer.
DETAILED DESCRIPTION
[0020] The present invention is a method of preparing a high
molecular weight copolyester bottle resin that has excellent melt
processing characteristics. The method includes the steps of
reacting a terephthalate component and a diol component to form a
modified polyethylene terephthalate. In this regard, the
terephthalate component and the diol component must together
include at least 7 mole percent comonomer substitution. The
modified polyethylene terephthalate is copolymerized in the melt
phase to an intrinsic viscosity of between about 0.25 dl/g and 0.40
dl/g to thereby form a copolyester prepolymer having an average
apparent crystallite size of less than 9 nm. With respect to this
melt phase copolymerization, the target intrinsic viscosity of the
prepolymer is preferably between about 0.30 dl/g and 0.36 dl/g. The
copolyester prepolymer is then formed into chips, which are
thereafter polymerized in the solid phase to form a high molecular
weight bottle resin that has an intrinsic viscosity of at least
about 0.70 dl/g and a solid phase density of less than 1.413
g/cc.
[0021] In one preferred embodiment, the step of reacting the
terephthalate component and the diol component is further defined
by the terephthalate component including at least about 4 mole
percent diacid or diester comonomer with the remainder being
terephthalic acid or its dialky ester, dimethyl terephthalate, and
the diol component being present in excess of stoichiometric
proportions and including at least about 2 mole percent diol
comonomer with the remainder being ethylene glycol. More
specifically, the terephthalate component preferably includes
between about 90 and 96 mole percent terephthalic acid or dimethyl
terephthalate and between about 4 and 10 mole percent diacid or
diester comonomer, and the diol component preferably includes
between about 94 and 98 mole percent ethylene glycol and between
about 2 and 6 mole percent diol comonomer. It will be understood
that diacid comonomer should be employed when the terephthalate
component is mostly terephthalic acid, and diester comonomer should
be employed when the terephthalate component is mostly dimethyl
terephthalate.
[0022] According to the invention, it has been determined that the
method yields a copolyester bottle resin that has excellent melt
processing characteristics when the 4 to 10 mole percent diacid
comonomer is a derivative of isophthalic acid, 2,6 naphthalene
dicarboxylic acid, and succinic acid, and the 2 to 6 mole percent
diol comonomer is diethylene glycol. In this respect, the term
"derivative" refers to the compound itself, its anhydrides, and its
dialkyl esters (e.g., succinic acid, its anhydride, or its dialkyl
ester).
[0023] In another preferred embodiment, the step of reacting the
terephthalate component and the diol component is further defined
by the terephthalate component including essentially no diacid or
diester comonomer--i.e., it is essentially 100 mole percent
terephthalic acid or dimethyl terephthalate--and by the diol
component including between about 84 and 94 mole percent ethylene
glycol, between about 2 and 6 mole percent diethylene glycol, and
between about 4 and 10 mole percent cyclohexane dimethanol.
[0024] In another aspect, the method of preparing a high molecular
weight copolyester bottle resin further includes forming the high
molecular weight bottle resin into bottle preforms. In this regard,
the invention facilitates formation of the bottle resin chips into
bottle preforms at a haze point temperature below 260.degree. C.,
preferably below 250.degree. C., more preferably below 240.degree.
C. (e.g., 235.degree. C.).
[0025] In yet another aspect, the method of preparing a high
molecular weight copolyester bottle resin includes copolymerizing
the copolyester prepolymer chips in the solid phase to form a high
molecular weight bottle resin having an average apparent
crystallite size of 10 nm or less, and more preferably 9 nm or
less.
[0026] The terms "melt viscosity" and "intrinsic viscosity" are
used herein in their conventional sense. Melt viscosity represents
the resistance of molten polymer to shear deformation or flow as
measured at specified conditions. Melt viscosity is primarily a
factor of intrinsic viscosity, shear, and temperature. As used
herein, the term "melt viscosity" refers to "zero-shear melt
viscosity" unless indicated otherwise.
[0027] 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
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 (7.sup.th Edition 1996). As used herein, average molecular
weight refers to number-average molecular weight, rather than
weight-average molecular weight.
[0028] Both melt viscosity and intrinsic viscosity, which are
widely recognized as standard measurements of polymer
characteristics, 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").
[0029] 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. As discussed herein, all intrinsic viscosities relating
to the invention are referenced to orthochlorophenol at 25.degree.
C.
[0030] The volume percent crystallinity of a polymer can be
calculated from the density of the polymer by Equation 1:
V.sub.C=(D.sub.M-D.sub.A).div.(D.sub.C-D.sub.A).multidot.100%, Eq.
1
[0031] wherein
[0032] V.sub.C=volume percent crystallinity
[0033] D.sub.M=measured polymer density
[0034] D.sub.A=100-percent amorphous polymer density
[0035] D.sub.C=100-percent crystalline polymer density
[0036] The measured density is typically determined according to
ASTM 1505-85 by employing a density gradient column that is
calibrated using glass bead density standards. The 100-percent
crystalline polymer density is estimated from the crystalline unit
cell of the polymer and the amorphous density is measured from the
amorphous polymer using a density gradient column. A 100-percent
crystalline polyethylene terephthalate polymer has a
generally-accepted calculated density of 1.455 grams/cc, and a
100-percent amorphous polyethylene terephthalate polymer has
generally-accepted measured density of 1.333 grams/cc.
[0037] As will be understood by those having ordinary skill in the
art, the amorphous density of polyethylene terephthalate is
modified by the introduction of comonomer units. In this regard,
the amorphous density of comonomer-modified polyethylene
terephthalate can be calculated by the Equation 2:
1.div.D.sub.A=((1-X.sub.CM).div..div.D.sub.APET)+(X.sub.CM.div.D.sub.ACM),
Eq. 2
[0038] wherein
[0039] D.sub.A=100-percent amorphous polymer density
[0040] X.sub.CM=weight fraction of comonomer unit
[0041] D.sub.APET=100-percent amorphous polyethylene terephthalate
density
[0042] D.sub.ACM=100-percent amorphous polymer density of the
polymer formed from the comonomer
[0043] Thereafter, volume percent crystallinity for the
comonomer-modified polyethylene terephthalate can be determined by
Equation 1 (above) using D.sub.A as calculated from Equation 2 and
using the 100-percent crystalline polymer density of polyethylene
terephthalate (i.e., D.sub.C=1.455 grams/cc).
[0044] With respect to isophthalic acid comonomer, the amorphous
density of polyethylene isophthalate is reported to be 1.356
grams/cc. See Amoco Chemicals GTSR-123, "Modification of PET with
Purified Isophthalic Acid." With respect to cyclohexane dimethanol
comonomer, the amorphous density for polycyclohexane dimethylene
terephthalate is reported to be 1.19 grams/cc. See H. Y. Yoo et
al., Polymer, Vol. 35 at p.117 (1994). With respect to 2,6
naphthalene dicarboxylic acid comonomer, the amorphous density of
polyethylene 2,6-napthalene dicarboxylate is 1.325 grams/cc. See
Amoco Chemicals GTSR-H, "Strain Hardening Characteristics and Basic
Properties of Naphthalate Containing Polyester Films." Finally,
with respect to succinic acid comonomer, the amorphous density of
polyethylene succinate is estimated to be 1.075 grams/cc. See J.
Erandrup and E. H. Immergut, Polymer Handbook, (3.sup.rd Ed.
1989).
[0045] The apparent crystallite size was determined by X-ray powder
diffractometry (XRD) using the procedure outlined in U.S. Pat. No.
5,714,262 with some minor modifications due to differences in
instrumentation. The pellets were powdered in a mini-mill, and the
powder was pressed into a disk 32 millimeters in diameter and
approximately one millimeter thick. The disks were placed in XRD
sample holders atop double-sided adhesive. The experiments were
performed in a Scintag XDS 2000 diffractometer that unlike the
Phillips instrument is designed to detect reflected X-rays rather
than transmitted X-rays. The initial experiments included runs with
the underside of the sample coated with a highly crystalline
material (LaB6 or Si). There was no evidence that any of the Cu
K-alpha X-rays penetrated completely through the sample to the
underlying adhesive. No corrections were needed for the adhesive
layer. The diffraction data was then collected from the rotated
sample over the range 150 to 20.degree. 2-theta using a step scan
at 0.05.degree./step, a 65 sec/step acquisition time, and 1.degree.
slits. No curved beam monochrometer was used and the X-ray scan was
run in step mode so a Lorenz-polarization correction was not
necessary. The apparent crystallite size was calculated using the
Sherrer equation on the 010 peak.
[0046] 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 (TA) and dimethyl terephthalate (DMT),
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. One method involves a two-step ester exchange
reaction and polymerization using dimethyl terephthalate and excess
ethylene glycol. The other method employs a direct esterification
reaction using terephthalic acid and excess ethylene glycol. These
methods are well known to those skilled in the art.
[0047] The present invention yields an intermediate, low molecular
weight copolyester prepolymer that includes selective substitution
of some terephthalic acid units with other diacid (or diester)
monomers and selective substitution of some ethylene glycol units
with other diol monomers. The diacid (or diester) and diol
reactants are polymerized in the melt phase until the prepolymer
achieves an intrinsic viscosity of between about 0.25 dl/g and 0.40
dl/g-more preferably an intrinsic viscosity of between about 0.30
dl/g and 0.36 dl/g-and an average apparent crystallite size of less
than 9 nm. The reaction can be controlled using cobalt-based and
antimony-based catalyst systems and phosphorous-based stabilizers.
In preferred embodiments, the reactants are chosen to yield the
following four preferred prepolymers:
[0048] (1) A low molecular weight copolyester prepolymer having a
terephthalate component including between about 4 and 10 mole
percent isophthalic acid or its dialkyl ester (i.e., dimethyl
isophthalate) with the remainder being terephthalic acid or its
dialkyl ester (i.e., dimethyl terephthalate), and a diol component
including between about 2 and 6 mole percent diethylene glycol with
the remainder being ethylene glycol.
[0049] (2) A low molecular weight copolyester prepolymer having a
terephthalate component including between about 4 and 10 mole
percent 2,6 naphthalene dicarboxylic acid or its dialkyl ester
(i.e., dimethyl 2,6 naphthalene dicarboxylate) with the remainder
being terephthalic acid or its dialkyl ester (i.e., dimethyl
terephthalate), and a diol component including between about 2 and
6 mole percent diethylene glycol with the remainder being ethylene
glycol.
[0050] (3) A low molecular weight copolyester prepolymer having a
terephthalate component including between about 4 and 10 mole
percent succinic acid, its dialkyl ester (i.e., dimethyl
succinate), or its anhydride (i.e., succinic anhydride) with the
remainder being terephthalic acid or its dialkyl ester (i.e.,
dimethyl terephthalate), and a diol component including between
about 2 and 6 mole percent diethylene glycol with the remainder
being ethylene glycol.
[0051] (4) A low molecular weight copolyester prepolymer having a
terephthalate component including about 100 mole percent
terephthalic acid or its dialkyl ester (i.e., dimethyl
terephthalate), and a diol component including between about 2 and
6 mole percent diethylene glycol and between about 4 and 10 mole
percent cyclohexane dimethanol with the remainder being ethylene
glycol.
[0052] Prior to the solid state polymerization step, the
copolyester prepolymer composition is formed into discrete
particles by conventional techniques (e.g., strand pelletization
and hot-cut pelletization-drops from a vibrating plate die, or
drops or pastillates from a rotating die or plate will not work
within the intrinsic viscosity range of the invention.) Such
discrete particles of modified polyethylene terephthalate
prepolymer are further polymerized in the solid state from a low
molecular weight (i.e., an intrinsic viscosity of between about
0.25 dl/g and 0.40 dl/g) to a high molecular weight (i.e., an
intrinsic viscosity of at least about 0.70 dl/g). Moreover, the
resulting high molecular weight bottle resin has a solid phase
density of less than 1.413 g/cc, which corresponds to a
crystallinity volume of less than about 65 percent. As will be
understood by those of ordinary skill in the art, the resulting
high molecular weight copolyester includes randomly substituted
diacid and diol monomer units.
[0053] As disclosed previously, the invention achieves a high
molecular weight copolyester bottle resin primarily via solid state
polymerization. In contrast, most conventional processes depend
mostly on melt phase polymerization to achieve high molecular
weight. For example, a standard method for preparing polyethylene
terephthalate bottle resin includes polymerizing polyethylene
terephthalate, which is modified by about 2.8 mole percent
isophthalic acid and 3.0 mole percent diethylene glycol, in the
melt phase to an intrinsic viscosity of about 0.6 dl/g. Thereafter,
the copolyester is further polymerized in the solid phase to a
somewhat higher molecular weight (e.g., 0.7 dl/g). This kind of
conventional process yields bottle resins that are suitable for
standard blow molding equipment. Unfortunately, polymerizing
copolyester resin in the melt phase to an intrinsic viscosity of
about 0.6 dl/g requires a significant capital investment.
[0054] Accordingly, this invention reduces bottle resin investment
costs by polymerizing copolyesters mostly in the solid phase rather
than in the melt phase. This is accomplished by initially
polymerizing a copolyester resin in the melt phase to an intrinsic
viscosity between about 0.25 and 0.40 dl/g. Thereafter, the
resulting polyester prepolymer is polymerized in the solid phase to
the desired molecular weight (i.e., an intrinsic viscosity greater
than about 0.70 dl/g).
[0055] While less expensive, employing solid state polymerization
rather than melt phase polymerization seems to increase the
crystallinity fraction of the resulting bottle resin. (This is
indicated by an increase in density relative to conventionally
produced polyester for a given composition). Unfortunately, higher
crystallinity fraction adversely affects haze point (i.e.,
increases haze point temperature). Thus, all things being equal,
beginning solid state polymerization of copolyester bottle resin at
a lower intrinsic viscosity will cause the resulting bottle resin
to possess a higher haze point. FIG. 1 shows that haze point
increases when the solid state polymerization is initiated at lower
intrinsic viscosities in accordance with the present invention as
compared to conventional processes. Likewise, FIG. 2 shows that
percent crystallinity increases when the solid state polymerization
is initiated at lower intrinsic viscosities in accordance with the
present invention as compared to conventional processes.
[0056] As will be understood by those having ordinary skill in the
art, polyester in the amorphous state is clear, whereas polyester
in the crystalline state-produced by thermal crystallization of the
amorphous phase-tends to be cloudy. Heating polyester above its
melting point and rapidly quenching it to a temperature below its
glass transition temperature destroys crystallinity, thereby
placing the copolyester in the amorphous state. Consequently, to
obtain clear bottle preforms, it is imperative that melting and
quenching put the bottle resin into a mostly amorphous state. (This
is especially important given that reheating bottle resin in a
blow-molding machine can promote crystallization.)
[0057] Therefore, a bottle resin possessing a low haze point is
desirable because it requires less heating to achieve an amorphous
state. A lower process temperature also means better heat transfer
and, thus, faster process throughputs. Lower temperatures minimize
the inadvertent production of unwanted decomposition by-products,
too.
1 Example 1 SSP Bottle Crystal- Haze Starting Resin linity Point
Density Copolyester I.V. I.V. volume % (.degree. C.) (g/cc) (A) PET
(2.8 mol % IPA 0.6 0.81 55 250 1.3988 and 3.0 mol % DEG) dl/g dl/g
(conventional) (B) PET (3.0 mol % IPA 0.3 0.81 67 260 1.4151 and
3.0 mol % DEG) dl/g dl/g
[0058] Example 1 (above) illustrates that initiating solid state
polymerization at a lower intrinsic viscosity tends to increase
crystallinity fraction and, thus, haze point temperature. This is
so even though the copolyester (B) polymerized in the solid phase
starting at about 0.3 dl/g had a somewhat higher comonomer fraction
as compared to the conventionally polymerized copolyester (A).
Ordinarily, a higher comonomer substitution should disrupt
crystallinity, thus depressing haze point. That is, all things
being equal, lower-not higher-comonomer molar fractions should
result in the formation of more perfect crystalline structures
during solid phase polymerization and, hence, higher haze points.
Here, however, the composition with the higher substitution (B) has
a higher crystallinity volume and higher haze point. This appears
to be a result of initiating solid state polymerization at a lower
intrinsic viscosity.
[0059] Other methods of producing bottle resins by primarily
relying on solid state polymerization can increase solid phase
polymerization rate. These methods, however, have failed to
appreciate the effect solid state polymerization has upon
crystallinity fraction and haze point. Accordingly, such methods
produce bottle resins having high melting points. This demands that
standard equipment achieve higher melt temperatures during molding
to facilitate haze-free production of bottle preforms. In short,
solid state polymerization requires less capital cost, but
ultimately yields resins that are difficult to process through
convention equipment.
[0060] To overcome this haze point problem caused by high
crystallinity, the present invention increases the comonomer
fraction as compared to conventional resins, such as that disclosed
in Example 1, when initiating SSP at a lower prepolymer intrinsic
viscosity. As discussed earlier, it is believed that higher
comonomer substitution, while somewhat slowing solid state
polymerization, advantageously reduces crystallite formation.
EXAMPLE 2
[0061] Polyester prepolymer with 3 mole percent isophthalic acid
and intrinsic viscosity between 0.30 and 0.35.
[0062] Terephthalic acid, 41.71 kg, isophthalic acid, 1.29 kg,
ethylene glycol, 17.58 kg, diethylene glycol, 0.08 kg, a 20%
solution of cobalt acetate tetrahydrate in water, 26.4 g, and 1.3%
antimony oxide in ethylene glycol, 1150.6 g, were blended together
to make a paste. This paste was transferred to an esterification
vessel heated to between 260.degree. C. and 270.degree. C. and
pressurized to 3 bar. The overhead system in the vessel column
separated and removed water produced during esterification from
glycol, and the glycol was returned to the esterification vessel.
The initial esterification batch provided a hot reactor heel to
which more paste was added to the esterification vessel for
efficient esterification. After the extent of esterification
reached 98% and the pressure in the reactor was reduced to 1 bar,
52.7 kilograms of ester was transferred to a polycondensation
vessel. After the transfer, 31.6 grams of a 10% phosphoric acid
solution was added to the ester, the pressure in the
polycondensation vessel was reduced to less than 1 mbar and the
temperature in the vessel was increased to 285.degree. C. After a
polycondensation time of 65 to 70 minutes, the vessel was brought
to atmospheric pressure. The product was extruded and quenched in a
water bath as an amorphous strand, and then cut into pellets.
EXAMPLE 3
[0063] Polyester prepolymer with 6.0 mole percent isophthalic acid
and intrinsic viscosity between 0.33 and 0.36.
[0064] Terephthalic acid, 40.42 kg, isophthalic acid, 2.58 kg,
ethylene glycol, 17.58 kg, diethylene glycol, 0.08 kg, 20% solution
of cobalt acetate tetrahydrate in water, 26.4 g, and 1.3% antimony
oxide in ethylene glycol, 1150.6 g, were blended together to make a
paste. This paste was transferred to an esterification vessel
heated to between 260.degree. C. and 270.degree. C. and pressurized
to 3 bar. The overhead system in the vessel column separated and
removed water produced during esterification from glycol, and the
glycol was returned to the esterification vessel. The initial
esterification batch provided a hot reactor heel to which more
paste was added to the esterification vessel for efficient
esterification. After the extent of esterification reached 98% and
the pressure in the reactor was reduced to 1 bar, 52.7 kilograms of
ester was transferred to a polycondensation vessel. After the
transfer, 31.6 grams of a 10% phosphoric acid solution was added to
the ester, the pressure in the polycondensation vessel was reduced
to less than 1 mbar and the temperature in the vessel was increased
to 285.degree. C. After a polycondensation time of 65 to 70
minutes, the vessel was brought to atmospheric pressure. The
product was extruded and quenched in a water bath as an amorphous
strand, and then cut into pellets.
EXAMPLE 4
[0065] Polyester prepolymer with 9.0 mole percent isophthalic acid
and intrinsic viscosity between 0.30 and 0.32.
[0066] Terephthalic acid, 39.13 kg, isophthalic acid, 3.87 kg,
ethylene glycol, 17.58 kg, diethylene glycol, 0.08 kg, 20% solution
of cobalt acetate tetrahydrate in water, 26.4 g, and 1.3% antimony
oxide in ethylene glycol, 1150.6 g, were blended together to make a
paste. This paste was transferred to an esterification vessel
heated to between 260.degree. C. and 270.degree. C. and pressurized
to 3 bar. The overhead system in the vessel column separated and
removed water produced during esterification from glycol, and the
glycol was returned to the esterification vessel. The initial
esterification batch provided a hot reactor heel to which more
paste was added to the esterification vessel for efficient
esterification. After the extent of esterification reached 98% and
the pressure in the reactor was reduced to 1 bar, 52.7 kilograms of
ester was transferred to a polycondensation vessel. After the
transfer, 31.6 grams of a10% phosphoric acid solution was added to
the ester, the pressure in the polycondensation vessel was reduced
to less than 1 mbar and the temperature in the vessel was increased
to 285.degree. C. After a polycondensation time of 65 to 70
minutes, the vessel was brought to atmospheric pressure. The
product was extruded and quenched in a water bath as an amorphous
strand, and then cut into a pellet.
EXAMPLE 5 (COMPARATIVE)
[0067] Polyester prepolymer with 6.0 mole percent adipic acid and
intrinsic viscosity between 0.32 and 0.36.
[0068] Terephthalic acid, 40.24 kg, adipic acid, 2.27 kg, ethylene
glycol, 17.58 kg, diethylene glycol, 0.08 kg, 20% solution of
cobalt acetate tetrahydrate in water, 26.4 g, and 1.3% antimony
oxide in ethylene glycol, 1150.6 g, were blended together to make a
paste. This paste was transferred to an esterification vessel
heated to between 260.degree. C. and 270.degree. C. and pressurized
to 3 bar. The overhead system in the vessel column separated and
removed water produced during esterification from glycol, and the
glycol was returned to the esterification vessel. The initial
esterification batch provided a hot reactor heel to which more
paste was added to the esterification vessel for efficient
esterification. After the extent of esterification reached 98% and
the pressure in the reactor was reduced to one bar, 52.7 kilograms
of ester was transferred to a polycondensation vessel. After the
transfer, 31.6 grams of a 10% phosphoric acid solution was added to
the ester, the pressure in the polycondensation vessel was reduced
to less than 1 mbar and the temperature in the vessel was increased
to 285.degree. C. After a polycondensation time of 65 to 70
minutes, the vessel was brought to atmospheric pressure. The
product was extruded and quenched in a water bath as an amorphous
strand and cut into a pellet. (This example shows that some
comonomer modifiers are less effective at disrupting crystallinity
relative to other comonomer modifiers, such as isophthalic
acid.)
EXAMPLE 6
[0069] Polyester prepolymer with 6.0 mole percent cyclohexane
dimethanol (CHDM) and intrinsic viscosity between 0.32 and
0.36.
[0070] Terephthalic acid, 43.00 kg, ethylene glycol, 16.60 kg,
cyclohexane dimethanol, 2.24 kg, diethylene glycol, 0,08 kg, 20%
solution of cobalt acetate tetrahydrate in water, 26.4 g, and 1.3%
antimony oxide in ethylene glycol, 1150.6 g, were blended together
to make a paste. This paste was transferred to an esterification
vessel heated to between 260.degree. C. and 270.degree. C. and
pressurized to 3 bar. The overhead system in the vessel column
separated and removed water produced during esterification from
glycol, and the glycol was returned to the esterification vessel.
The initial esterification batch provided a hot reactor heel to
which more paste was added to the esterification vessel for
efficient esterification. After the extent of esterification
reached 98% and the pressure in the reactor was reduced to 1 bar,
52.7 kilograms of ester was transferred to a polycondensation
vessel. After the transfer, 31.6 grams of a 10% phosphoric acid
solution was added to the ester, the pressure in the
polycondensation vessel was reduced to less than 1 mbar and the
temperature in the vessel was increased to 285.degree. C. After a
polycondensation time of 65 to 70 minutes, the vessel was brought
to atmospheric pressure. The product was extruded and quenched in a
water bath as an amorphous strand, and then cut into pellets.
EXAMPLE 7
[0071] The copolyester prepolymer, 200 kg containing 3 mole percent
isophthalate from Example 2 was blended together in a rotary-vacuum
tumble dryer for solid state polymerization. The copolyester was
heated in the tumble dryer to 227.5.degree. C. with a vacuum of
less than 1 millibar. After 54 hours under these conditions, the
copolyester had a final intrinsic viscosity of 0.81 dl/g and a
density of 1.4151 g/cc, which corresponds to a volume percent
crystallinity of 67.1 percent. The apparent crystal size was 8.2
nm, as determined by powder X-ray diffraction.
EXAMPLE 8
[0072] The copolyester prepolymer, 200 kg, containing 6 mole
percent isophthalate from Example 3 was blended together in a
rotary-vacuum tumble dryer for solid state polymerization. The
copolyester was heated in the tumble dryer to 226.degree. C. with a
vacuum of less than 1 millibar. After 40 hours under these
conditions, the copolyester had a final intrinsic viscosity of 0.81
dl/g and a density of 1.4124 g/cc, which corresponds to a volume
percent crystallinity of 64.7 percent. The apparent crystal size
was 9.1 nm, as determined by powder x-ray diffraction.
EXAMPLE 9
[0073] The copolyester prepolymer, 150 kg, containing 9 mole
percent isophthalate from Example 4 were blended together in a
rotary-vacuum tumble dryer for solid state polymerization. The
copolyester was heated in the tumble dryer to 225.degree. C. with a
vacuum of less than 1 millibar. After 79 hours under these
conditions, the copolyester had a final intrinsic viscosity of 0.81
dl/g and a density of 1.4008 g/cc, which corresponds to a volume
percent crystallinity of 54.8 percent. The apparent crystal size
was 9.2 nm, as determined by powder X-ray diffraction.
EXAMPLE 10 (COMPARATIVE)
[0074] The copolyester prepolymer, 200 kg, containing 6 mole
percent adipate from Example 5 was blended together in a
rotary-vacuum tumble dryer for solid state polymerization. The
copolyester was heated in the tumble dryer to 225.degree. C. with a
vacuum of less than 1 millibar. After 60 hours under these
conditions, the copolyester had a final intrinsic viscosity of 0.81
dl/g and a density of 1.4126 g/cc, which corresponds to a volume
percent crystallinity of 65.0 percent. The apparent crystal size
was 8.7 nm, as determined by powder x-ray diffraction.
EXAMPLE 11
[0075] The copolyester prepolymer, 200 kg, containing 6 mole
percent cyclohexane dimethanol from Example 6 was blended together
in a rotary-vacuum tumble dryer for solid state polymerization. The
copolyester was heated in the tumble dryer to 229.degree. C. with a
vacuum of less than 1 millibar. After 45 hours under these
conditions, the copolyester had a final intrinsic viscosity of 0.80
dl/g and a density of 1.3945 g/cc, which corresponds to a volume
percent crystallinity of 55.2 percent. The apparent crystal size
was 8.6 nm, as determined by powder X-ray diffraction.
2 Example 12 Crystal- Crystal- Apparent Pre- lization lization
Crystallite polymer temperature time Size Copolyester I.V.
(.degree. C.) (hours) (nm) Polyethylene 0.6 180 2 7.0 terephthalate
(2.8 mol % dl/g IPA and 3.0 mol % DEG) (conventional) Polyethylene
0.3 180 4 7.3 terephthalate (3.0 mol % dl/g IPA and 3.0 mol % DEG)
Polyethylene 0.3 180 4 7.5 terephthalate (6.0 mol % dl/g IPA and
3.0 mol % DEG) Polyethylene 0.3 180 4 8.3 terephthalate (9.0 mol %
dl/g IPA and 3.0 mol % DEG) Polyethylene 0.3 180 4 8.0
terephthalate (6.0 mol % dl/g adipic acid and 3.0 mol % DEG)
Polyethylene 0.3 180 4 6.2 terephthalate (6.0 mol % dl/g CHDM and
2.7 mol % DEG)
[0076] Example 12 (above) illustrates the effect of crystallization
conditions on copolyester prepolymer crystal size. In contrast to
the method described in the aforementioned DuPont patents, the
present invention employs much longer crystallization times.
Without being bound to a particular theory, it is believed that
polymer crystallization starting from lower temperature and longer
crystallization times promote the formation of more nuclei, which
results in relatively smaller crystallite size.
3 Example 13 SSP Crystal- Apparent Start- Bottle linity Haze
Crystallite ing Resin volume Point Size Density Copolyester I.V.
I.V. % (.degree. C.) (nm) (g/cc) Polyethylene 0.6 0.81 55 250 8.0
1.3988 terephthalate dl/g dl/g (2.8 mol % IPA and 3.0 mol % DEG)
(conventional) Polyethylene 0.3 0.81 67 260 8.2 1.4151
terephthalate dl/g dl/g (3.0 mol % IPA and 3.0 mol % DEG)
Polyethylene 0.3 0.81 65 245 9.1 1.4124 terephthalate dl/g dl/g
(6.0 mol % IPA and 3.0 mol % DEG) Polyethylene 0.3 0.81 55 235 9.2
1.4008 terephthalate dl/g dl/g (9.0 mol % IPA and 3.0 mol % DEG)
Polyethylene 0.3 0.81 65 255 8.6 1.4126 terephthalate dl/g dl/g
(6.0 mol % adipic acid and 3.0 mol % DEG) Polyethylene 0.3 0.80 55
240 8.7 1.3945 terephthalate dl/g dl/g (6.0 mol % CHDM and 2.7 mol
% DEG)
[0077] Example 13 (above) illustrates that despite initiating SSP
at a low intrinsic viscosity, the invention produces bottle resins
with melt characteristics that are equal or better to those of
bottle resins produced by conventional techniques.
[0078] The theoretical mechanism for this improved melt processing
behavior is not completely understood, but may be related to the
crystalline morphology of the copolyester compositions in the solid
phase. It is believed that the addition of relatively high
fractions of certain kinds of comonomer disrupts polymer
crystallinity. This permits the polyester to be melted and extruded
at a lower temperature while completely destroying the molded
preform haze that is associated with thermal crystallinity. In this
regard, it has been observed that adipic acid does not seem to
disturb crystallinity as copolyester bottle resin primarily
modified with adipic acid has a relatively high haze point.
Alternatively, the theoretical mechanism for this improved melt
processing behavior may also be related to the crystallization rate
of these copolyester compositions while in the melt phase.
[0079] As noted, an objective of the invention is to produce a high
molecular weight bottle resin that can be readily processed using
convention equipment. In this regard, it is instructive to compare
the copolyester composition of the present invention with a
conventional copolyester bottle resin. A polyethylene terephthalate
bottle resin modified by about 5 mole percent isophthalic acid or
its dialkyl ester (i.e., dimethyl isophthalate) and 3 mole percent
diethylene glycol and melt polymerized to an intrinsic viscosity of
only about 0.32 dl/g prior to being polymerized in the solid phase
will possess melt processing characteristics similar to those of a
conventional polyethylene terephthalate bottle resin modified by
about 2.8 mole percent isophthalic acid and 3.0 mole percent
diethylene glycol and melt polymerized up to 0.6 dl per gram prior
to being polymerized in the solid phase:
4 Example 14 SSP Bottle Haze Starting Resin Crystallinity Point
Copolyester I.V. I.V. mole % (.degree. C.) PET (2.8 mol % IPA, 0.6
0.80 55 250 3.0 mol % DEG) dl/g dl/g (conventional) PET (5.0 mol %
IPA, 0.32 0.80 65 250 3.0 mol % DEG) dl/g dl/g
[0080] It is reemphasized that the copolyester of the present
invention is produced by a process (i.e., primary reliance on SSP)
that requires significantly less capital investment. Accordingly, a
major benefit of the present invention is the ability to produce
bottle resins that perform at least as well as conventional bottle
resins, while lowering required capital expenditures.
[0081] In direct contrast to the cited DuPont prior art, which
teaches solid state polymerization of polyester prepolymer having
large apparent crystallite size in the prepolymer, this invention
reduces the negative impact of crystallinity upon haze point
temperature by employing smaller crystals in the prepolymer (i.e.,
less than 9 nm). More specifically, according to the invention, it
has been determined that while larger crystal sizes in the
prepolymer (i.e., 9 nm or more) appear to speed solid state
polymerization steps by facilitating higher SSP temperatures,
larger crystals negatively affect bottle resin characteristics. In
particular, bottle resins having larger crystal sizes process
poorly because they possess elevated haze point temperatures. This
is especially true when such bottle resins have a comonomer
substitution of less than about five weight percent isophthalic
acid, or a similarly effective comonomer.
[0082] While not wanting to be bound by any particular theory, it
is believed that crystalline polymers comprised of smaller crystals
melt at lower temperatures as compared to resins comprised of
larger crystals. Although smaller crystals may somewhat slow solid
phase polymerization, the resulting bottle resins are capable of
formation into preforms at a lower haze point. As a practical
matter, this simply means that the present invention actually
achieves a bottle resin that can be processed through conventional
injection molding conditions and equipment.
[0083] In another aspect, the invention is bottle resin chips of a
high molecular weight copolyester having excellent melt processing
characteristics. The copolyester chips comprises about a 1:1 molar
ratio of a terephthalate component and a dial component. The
terephthalate component and the dial component together include at
least 7 mole percent comonomer. In addition, the copolyester chips
have an average minimum dimension (i.e., the shortest side of the
chip) of between about 1 mm and 10 mm, and possess an intrinsic
viscosity of at least about 0.70 dl/g, a solid phase density of
less than 1.413 g/cc, an average apparent crystallite size of less
than 9 nm, and a haze temperature of less than about 250.degree.
C.
[0084] Note that these copolyester chips are significantly larger
than the spherical beads and porous pills disclosed by the
aforementioned Goodyear patents. In fact, the particle sizes
disclosed by those patents (<1 mm) are essentially fines with
respect to the present copolyester chips.
[0085] As will be understood by those of ordinary skill in the art,
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. This is what is meant by the phrase "about a 1:1
molar ratio of a terephthalate component and a diol component," as
used herein. For example, the molar ratio of the terephthalate
component and the diol component is between about 1.000:1.010 and
1.000:1.005.
[0086] In one embodiment of the bottle resin chips, the
terephthalate component includes at least about 4 mole percent
diacid or diester comonomer with the remainder being terephthalic
acid or dimethyl terephthalate, and the diol component includes at
least about 2 mole percent diol comonomer with the remainder being
ethylene glycol. More specifically, the terephthalate component
preferably includes between about 90 and 96 mole percent
terephthalic acid or dimethyl terephthalate and between about 4 and
10 mole percent diacid or diester comonomer; and the dial component
includes between about 94 and 98 mole percent ethylene glycol and
between about 2 and 6 mole percent diol comonomer.
[0087] In this formulation, the bottle resin chips preferably have
a solid phase density of between 1.401 grams/cc and 1.413 grams/cc,
which is greater than the density of bottle resins produced
according to conventional methods (i.e., those that rely primarily
on melt phase polymerization to produce polyester resins), and less
than the density of bottle resins produced according to other
previously cited methods that emphasize in the solid phase
polymerization rather than the melt phase polymerization.
[0088] In one preferred embodiment, the high molecular weight
copolyester bottle resin chips have a terephthalate component
including between about 4 and 10 mole percent isophthalic acid or
its dialkyl ester (i.e., dimethyl isophthalate) with the remainder
being terephthalic acid or its dialkyl ester (i.e., dimethyl
terephthalate), and a dial component including between about 2 and
6 mole percent diethylene glycol with the remainder being ethylene
glycol.
[0089] In another preferred embodiment, the high molecular weight
copolyester bottle resin chips have a terephthalate component
including between about 4 and 10 mole percent 2,6 naphthalene
dicarboxylic acid or its dialkyl ester (i.e., dimethyl
2,6-naphthalene dicarboxylate) with the remainder being
terephthalic acid or its dialkyl ester (i.e., dimethyl
terephthalate), and a dial component including between about 2 and
6 mole percent diethylene glycol with the remainder being ethylene
glycol.
[0090] In another preferred embodiment, the high molecular weight
copolyester bottle resin chips have a terephthalate component
including between about 4 and 10 mole percent succinic acid, its
dialkyl ester (i.e., dimethyl succinate), or its anhydride (i.e.,
succinic anhydride) with the remainder being terephthalic acid or
its dialkyl ester (i.e., dimethyl terephthalate), and a dial
component including between about 2 and 6 mole percent diethylene
glycol with the remainder being ethylene glycol.
[0091] In another preferred embodiment, the high molecular weight
copolyester bottle resin chips have a terephthalate component
including about 100 mole percent terephthalic acid or its dialkyl
ester (i.e., dimethyl terephthalate) and essentially no diacid or
diester comonomer, and a diol component including between about 2
and 6 mole percent diethylene glycol and between about 4 and 10
mole percent cyclohexane dimethanol with the remainder being
ethylene glycol. In this particular formulation, the bottle resin
chips have a solid phase density of between 1.390 grams/cc and
1.413 grams/cc.
[0092] In another embodiment, the copolyester bottle resin chips
comprise about a 1:1 molar ratio of a terephthalate component and a
dial component. The terephthalate component includes at least about
9 mole percent isophthalic acid or its dialkyl ester (i.e.,
dimethyl isophthalate) with the remainder being terephthalic acid
or its dialkyl ester (i.e., dimethyl terephthalate), and the diol
component includes at least about 2 mole percent diethylene glycol
with the remainder being ethylene glycol. In addition, the
copolyester chips have an average minimum dimension of between
about 1 mm and 10 mm, and possess an intrinsic viscosity of at
least about 0.80 dl/g, a solid phase density between 1.390 grams/cc
and 1.413 grams/cc, an average apparent crystallite size of less
than 10 nm, and a haze temperature of less than about 240.degree.
C.
[0093] The excellent melt processing characteristics of these high
molecular weight copolyester bottle resins is somewhat surprising
because they have much higher crystallinity as compared to
conventionally produced copolyester having a similar comonomer
fraction. One of ordinary skill in the art would expect the high
crystallinity of these copolyester compositions to complicate melt
extrusion. Instead, the high molecular weight copolyester
compositions possess improved melt processing properties. It
appears that a high crystallinity, which tends to increase haze
point, is not problematic when the apparent crystallite size is
kept below about 9 nm.
[0094] The disclosed copolyester compositions are especially useful
as bottle resins because they can be manufactured into haze-free
bottle preforms at low temperatures. Forming preforms at lower
temperatures reduces the creation of unwanted byproducts, such as
aldehydes and color bodies. As will be known to those skilled in
the art, aldehydes, even at low concentrations, adversely affect
bottle taste. Color bodies affect the aesthetics of the bottles
produced from the preforms and is commercially undesirable for
color control. Moreover, as discussed previously, lower melt
temperatures promote efficient heat transfer.
[0095] 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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