U.S. patent application number 10/357119 was filed with the patent office on 2004-08-05 for extrusion blow molded articles.
Invention is credited to Connell, Gary Wayne, Pecorini, Thomas Joseph, Turner, Sam Richard.
Application Number | 20040151854 10/357119 |
Document ID | / |
Family ID | 32770957 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040151854 |
Kind Code |
A1 |
Pecorini, Thomas Joseph ; et
al. |
August 5, 2004 |
Extrusion blow molded articles
Abstract
Disclosed is a process for the manufacture of shaped articles by
extrusion blow molding comprising the steps of (1) extruding a
copolyester through a die to form a tube of molten copolyester; (2)
positioning a mold having the desired finished shape around the
tube of molten copolyester; and (3) introducing a gas into the tube
of molten copolyester, causing the extrudate to stretch and expand
to fill the mold; wherein the copolyester is a linear, copolyester
having an inherent viscosity (IV) of at least about 0.7 dL/g
measured at a temperature of 25.degree. C. at 0.25 g/dl
concentration in a solvent mixture of symmetric tetrachloroethane
and phenol having a weight ratio of symmetric tetrachloroethane to
phenol of 2:3 and comprising: (1) a diacid component consisting
essentially of 90 to 100 mole percent terephthalic acid residues
and 0 to about 10 mole percent isophthalic acid residues,
naphthalenedicarboxylic acid residues, biphenyldicarboxylic acid
residues or a combination of 2 or more of isophthalic,
naphthalenedicarboxylic or bipheyldicarboxylic acid residues; and
(2) a diol component consisting essentially of about 70 to 90 mole
percent 1,4-cyclohexanedimethanol residues and about 30 to 10 mole
percent neopentyl glycol residues; wherein the copolyester
comprises 100 mole percent diacid component and 100 mole percent
diol component. The process is particularly useful for the
manufacture of bottles or carboys having and interior volume of
about 2 to 50 liters.
Inventors: |
Pecorini, Thomas Joseph;
(Kingsport, TN) ; Turner, Sam Richard; (Kingsport,
TN) ; Connell, Gary Wayne; (Church Hill, TN) |
Correspondence
Address: |
B. J. Boshears
Eastman Chemical Company
P.O. Box 511
Kingsport
TN
37662-5075
US
|
Family ID: |
32770957 |
Appl. No.: |
10/357119 |
Filed: |
February 3, 2003 |
Current U.S.
Class: |
428/35.7 ;
264/540 |
Current CPC
Class: |
B29K 2067/00 20130101;
B29L 2031/7126 20130101; B29C 49/04 20130101; C08G 63/199 20130101;
B29C 49/0005 20130101; Y10T 428/1352 20150115 |
Class at
Publication: |
428/035.7 ;
264/540 |
International
Class: |
B29C 049/00 |
Claims
We claim:
1. Process for the manufacture of shaped articles by extrusion blow
molding comprising the steps of: (1) extruding a copolyester
through a die to form a tube of molten copolyester; (2) positioning
a mold having the desired finished shape around the tube of molten
copolyester; and (3) introducing a gas into the tube of molten
copolyester, causing the extrudate to stretch and expand to fill
the mold; wherein the copolyester is a linear, copolyester having
an inherent viscosity (IV) of at least about 0.7 dL/g measured at a
temperature of 25.degree. C. at 0.25 g/dl concentration in a
solvent mixture of symmetric tetrachloroethane and phenol having a
weight ratio of symmetric tetrachloroethane to phenol of 2:3 and
comprising: (1) a diacid component consisting essentially of about
90 to 100 mole percent terephthalic acid residues and 0 to about 10
mole percent isophthalic acid residues, naphthalenedicarboxylic
acid residues, biphenyldicarboxylic acid residues or a combination
of 2 or more of isophthalic, naphthalenedicarboxylic or
biphenyldicarboxylic acid residues; and (2) a diol component
consisting essentially of about 70 to 90 mole percent
1,4-cyclohexanedimethanol residues and about 30 to 10 mole percent
neopentyl glycol residues; wherein the copolyester comprises 100
mole percent diacid component and 100 mole percent diol
component.
2. The process of claim 1 wherein the copolyester comprises a
diacid component consisting essentially of at least 95 mole percent
terephthalic acid residues.
3. The process of claim 1 wherein the copolyester comprises a
diacid component consisting essentially of 100 mole percent
terephthalic acid residues.
4. Process according to claim 3 wherein the copolyester has an
inherent viscosity (IV) of about 0.9 to 1.2 dL/g.
5. Process according to claim 4 wherein the copolyester is
manufactured by a solid state polymerization process.
6. Process for the manufacture of a container having a volume of
about 2 to 50 liters by extrusion blow molding -comprising the
steps of: (1) extruding a copolyester through a die to form a tube
of molten copolyester; (2) positioning a mold having the desired
finished shape of the container around the tube of molten
copolyester; and (3) introducing a gas into the tube of molten
copolyester, causing the extrudate to stretch and expand to fill
the mold; wherein the copolyester is a linear, copolyester having
an inherent viscosity (IV) of at least about 0.9 to 1.2 dL/g
measured at a temperature of 25.degree. C. at 0.25 g/dl
concentration in a solvent mixture of symmetric tetrachloroethane
and phenol having a weight ratio of symmetric tetrachloroethane to
phenol of 2:3 and comprising: (1) a diacid component consisting
essentially of terephthalic acid residues; and (2) a diol component
consisting essentially of about 70 to 90 mole percent
1,4-cyclohexanedimethanol residues and about 30 to 10 mole percent
neopentyl glycol residues; wherein the copolyester comprises 100
mole percent diacid component and 100 mole percent diol
component.
7. Process according to claim 6 wherein the molten copolyester has
a temperature of about 250 to 300.degree. C.
8. An extrusion blow molded article produced from a linear
copolyester having an inherent viscosity (IV) of at least about 0.7
dL/g measured at a temperature of 25.degree. C. at 0.25 g/dl
concentration in a solvent mixture of symmetric tetrachloroethane
and phenol having a weight ratio of symmetric tetrachloroethane to
phenol of 2:3 and comprising: (1) a diacid component consisting
essentially of 90 to 100 mole percent terephthalic acid residues
and 0 to about 10 mole percent isophthalic acid residues,
naphthalenedicarboxylic acid residues, biphenyldicarboxylic acid
residues or a combination of 2 or more of isophthalic,
naphthalenedicarboxylic or biphenyldicarboxylic acid residues; and
(2) a diol component consisting essentially of about 70 to 90 mole
percent 1,4-cyclohexanedimethanol residues and about 30 to 10 mole
percent neopentyl glycol residues; wherein the copolyester
comprises 100 mole percent diacid component and 100 mole percent
diol component.
9. An extrusion blow molded article according to claim 8 wherein
the copolyester comprises a diacid component consisting essentially
of at least 95 mole percent terephthalic acid residues.
10. An extrusion blow molded article according to claim 8 wherein
the copolyester comprises a diacid component consisting essentially
of 100 mole percent terephthalic acid residues.
11. An extrusion blow molded article according to claim 10 wherein
the copolyester has an inherent viscosity (IV) of about 0.9 to 1.2
dL/g.
12. An extrusion blow molded article according to claim 8 wherein
the copolyester comprises a diacid component consisting essentially
of 100 mole percent terephthalic acid residues; the copolyester has
an inherent viscosity (IV) of about 0.9 to 1.2 dL/g; and the shaped
article is a bottle having a volume of about 2 to 50 liters.
Description
FIELD OF THE INVENTION
[0001] This invention relates to shaped articles produced by
extrusion blow molding of linear copolyesters containing
1,4-cyclohexanedimethanol and neopentyl glycol residues. More
particularly, this invention relates shaped articles such as
containers produced by extrusion blow molding of a crystallizable
copolyester containing 1,4-cyclohexanedimethanol and neopentyl
glycol residues that exhibit improved shear thinning behavior.
BACKGROUND OF THE INVENTION
[0002] Extrusion blow molding is a common process for creating
hollow articles from polymeric materials. A typical extrusion
blow-molding manufacturing process involves: 1) melting the resin
in an extruder; 2) extruding the molten resin through a die to form
a tube of molten polymer (i.e. a parison) having a uniform side
wall thickness; 3) clamping a mold having the desired finished
shape around the parison; 4) blowing air into the parison, causing
the extrudate to stretch and expand to fill the mold; 5) cooling
the molded article; and 6) ejecting the article of the mold.
[0003] In order to form good quality containers that have uniform
side wall thickness and to prevent tearing of the parison during
expansion (i.e. blowing), the polymer extrudate must have good
molten dimensional stability, also known as melt strength. A
material having good molten dimensional stability (i.e. high melt
strength) has a tendency to resist stretching and flowing as a
result of gravitational force when in the softened or molten state.
Excessive stretching of the extrudate parison causes the walls to
become too thin. This leads to lack of uniformity in the wall
thickness. Thin walls also have a greater tendency to tear under
the influence of the air pressure being used to expand the
extrudate into the mold walls.
[0004] In extrusion blow molding, the polymer melt usually is
extruded vertically from a die into a parison, whereby melt
strength can be determined by measuring the vertical length of an
extrudate after a certain amount of time to determine the extent to
which the extrudate stretches or "sags". When measuring sag, the
extruder output and die gaps are fixed, whereby a given volume and
weight of material is extruded over a fixed length of time. Given
these conditions, the extrudate of a polymer with low melt strength
will be long and thin. In contrast, the extrudate of a polymer with
high melt strength will be short and thick. In addition, the sag of
the extruded parison is directly related to the weight of the
parison, whereby larger and heavier parisons will have a greater
tendency to sag. Therefore, higher melt strength materials are
required to allow larger and heavier parisons, e.g., for making
larger bottles, and to maintain their shape. The higher the melt
strength, the larger the bottle that can be produced.
[0005] Since melt strength is related to slow flow induced
primarily by gravity, it can be related to viscosity of a polymer
measured at a low shear rate, such as 1 radian/second. Viscosity
can be measured by typical viscometers, such as a parallel plate
viscometer. Typically, viscosity is measured at the typical
processing temperature for the polymer, and is measured at a series
of shear rates, often between 1 radian/second and 100
radian/second. In extrusion blow molding, the viscosity at 1
radian/second at processing temperatures typically needs to be
above 30,000 poise in order to blow a bottle. Larger parisons
require higher viscosities.
[0006] Melt strength, however, only defines one of the processing
characteristics important in extrusion blow molding. The second
important characteristic is ease of flow at high shear rates. The
polymer is "melt processed" at shear rates ranging anywhere from
about 10 s.sup.-1 to 1000 s.sup.-1 in the die/extruder. A typical
shear rate encountered in the barrel or die during extrusion blow
molding or profile extrusion is 100 radians/second. These high
shear rates are encountered as the polymer flows down the extruder
screw, or as it passes through the die. These high shear rates are
required to maintain reasonably fast production rates.
Unfortunately, high melt viscosity at high shear rates can lead to
viscous dissipation of heat, in a process referred to as shear
heating. Shear heating raises the temperature of the polymer and
the extent of temperature rise is directly proportional to the
viscosity at that shear rate. Since viscosity decreases with
increasing temperature, shear heating decreases the low shear rate
viscosity of the polymer and thus its melt strength decreases.
[0007] Furthermore, a high viscosity at high shear rates, (for
example as found in the die) can create a condition known as melt
fracture or "sharkskin" on the surface of the extruded part or
article. Melt fracture is a flow instability phenomenon occurring
during extrusion of thermoplastic polymers at the fabrication
surface/polymer melt boundary. The occurrence of melt fracture
produces severe surface irregularities in the extrudate as it
emerges from the orifice. The naked eye detects this surface
roughness in the melt-fractured sample as a frosty appearance or
matte finish as opposed to an extrudate without melt fracture that
appears clear. Melt fracture occurs whenever the wall shear stress
in the die exceeds a certain value, typically 0.1 to 0.2 MPa. The
wall shear stress is directly related to the volume throughput or
line speed (which dictates the shear rate) and the viscosity of the
polymer melt. By reducing either the line speed or the viscosity at
high shear rates, the wall shear stress is reduced lowering the
possibility for melt fracture to occur. Although the exact shear
rate at the die wall is a function of the extruder output and the
geometry and finish of the tooling, a typical shear rate that is
associated with the onset of melt fracture is 100 radian/sec.
Likewise, the viscosity at this shear rate typically needs to be
below 30,000 poise.
[0008] To couple all of these desired properties, the ideal
extrusion blow molding polymer, from a processability standpoint,
will possess a high viscosity at low shear rates in conjunction
with a low viscosity at high shear rates. These attributes are also
useful in other melt processes. For injection molding, the low
viscosity at high shear rates will allow the polymer to easily flow
into the mold. However, once flow has stopped and the shearing
removed, the polymer rapidly becomes highly viscous so that the
part can be quickly removed from the mold. For profile extrusion, a
high viscosity at low shear rates maximizes melt strength while low
viscosity at high shear rates minimizes screw motor load, pumping
pressure, shear heating and melt fracture.
[0009] Fortunately, most polymers naturally exhibit at least some
degree of viscosity reduction between low and high shear rates,
known as "shear thinning", which aids in their processability.
Without the shear thinning, an extruder running a high melt
viscosity polymer would require extremely high motor loads and/or
very high melt temperatures, both of which can lead to polymer
degradation and excessive energy consumption. The ideal polymer
noted above would possess a high degree of shear thinning. Based on
the preceding discussion, one definition of shear thinning
important to the processes discussed in this invention would be the
ratio of the viscosity measured at 1 radian/second to the viscosity
measured at 100 radians/second. These viscosities would both be
measured at the same temperature, typical of the actual processing
conditions. This definition will be used to describe shear thinning
for the purposes of this invention.
[0010] Unfortunately, certain polymers such as polycarbonates and
polyesters such as poly(ethylene terephthalate) (PET) and
poly(ethylene-co-1,4-cyclohexylenedimethylene terephthalate) (PETG)
have a very low degree of shear thinning as compared to polymers
like PVC, polystyrene, acrylics and polyolefins. Since these other
polymers suffer from one or more of their own disadvantages (e.g.
cost, odor, clarity, toughness, chemical resistance), polyesters
would be ideal alternative materials in similar applications if
processing difficulties of polyesters could be overcome.
[0011] It is possible to increase the melt strength of a polymer by
lowering the melt temperature but, since the high shear rate
viscosity is also increasing, eventually the temperature will drop
to the point where melt fracture appears. Decreasing the
temperature also increases the degree of shear thinning so it does
make it possible to process articles of up to a certain size, but
the improved degree of shear thinning is usually insufficient to
enable the production of large articles.
[0012] It is also possible to increase the melt strength and degree
of shear thinning by increasing the molecular weight and molecular
weight distribution of the polyester through solid state
polymerization. Again, however, the improvement in shear thinning
obtained by this method is usually insufficient to allow the
production of large articles. Furthermore any polyester that can be
solid stated is crystallizable, whereby it can not be processed at
a temperature lower than its melting point. Certain solid stated
polymers may also exhibit a phenomenon referred to as "unmelts",
wherein a portion of the solid stated pellets possess a very high
melting point, or a very high viscosity whereby they do not
disperse in the melt pool. The resulting pellet sized particles are
easily observed in the parion and resultant bottle. These unmelts
are an unacceptable visual defect. In order to eliminate unmelts,
the material must be processed at higher temperatures, which often
results in an unacceptable reduction in melt strength.
[0013] A linear polyester is defined as a polyester that is
prepared from A-A and B-B monomers or A-B monomers or combinations
of these with the correct stoichiometric balance. A-A monomers can
represent dibasic acids such as terephthalic acid, isophthalic acid
and B-B monomers can represent diols such as ethylene glycol and
1,4-cyclohexanedimethanol. An A-B monomer can represent
p-hydroxybenzoic acid, etc. When the stoichiometry of these
polymerizing systems is correct, linear high molecular weight
polyesters are readily prepared. Diesters of the dicarboxylic acid
can be used instead of the dicarboxylic acids and high molecular
polyesters can be prepared by transesterification process.
[0014] It is possible to add a branching agent into the reactor so
that the resulting polymer chain is no longer linear. Branching
agents usually are defined by the number of functional groups
attached and can take the form of an A.sub.3 or B.sub.3 molecule
where A.sub.3 is a tricarboxylic acid or tricarboxylic acid ester
and B.sub.3 is a triol. Also A.sub.2B and AB.sub.2 monomers can be
employed to affect branching where A.sub.2B represents a monomer
with 2 acid functional groups and 1 alcohol and AB.sub.2 represents
a molecule of 1 acid functionality and 2 alcohol groups. Higher
functionality branching groups can also be employed for this
purpose including tetrafunctional groups, such as from
pentaerythritol and phromellitic dianhydride. The science related
to polyester branching is well known in the polyester art. Chain
branching is one of the most common methods for improving the melt
strength of a polymer, particularly polyesters. However, the use of
branching agents can lead to unacceptable gel formation in the
melt, especially if the branched material has been solid stated. A
gel is nothing more than a point in the polyester where too much
localized branching occurs, effectively creating a tightly
interconnected network of chains that cannot be easily melted. This
gel is present in the final molded/extruded part as an unacceptable
visual defect. To minimize gelling, the branching agents are added
at a low level with uniform dispersion throughout the reactor.
Thus, a branched polyester is difficult to produce and the increase
in melt strength is limited to the maximum amount of branching
agent that can be added without gel formation.
[0015] Amorphous copolyesters comprising terephthalic acid (T)
residues with different ratios of 1,4-cyclohexanedimethanol (CHDM)
and ethylene glycol (EG) residues are well known in the plastics
marketplace. As used herein, the abbreviation PETG is used for
compositions wherein the diacid component contains or comprises
terephthalic acid residues and the diol component comprises up to
50 mole percent CHDM residues with the remaining diol component
being ethylene glycol residues. PCTG is used herein to refer to
copolyesters wherein the diacid component comprises terephthalic
acid residues and the diol component comprises greater than 50 mole
percent CHDM residues with the remainder being ethylene glycol
residues.
[0016] Neopentyl glycol (NPG, 2,2-dimethyl-propane-1,3-diol) is
another common diol used in the preparation of polyesters. Similar
to CHDM, NPG has been used in combination with EG and terephthalic
acid to form useful amorphous copolyesters. However, the
combination of NPG and CHDM as the sole glycol components of the
copolyester has received minimal attention.
[0017] Several early references disclose polyesters containing both
CHDM and NPG residues with terephthalic acid residues as the diacid
compoent. Example 46 of U.S. Pat. No. 2,901,466 describes a
copolyester prepared from CHDM and NPG residues that was solid
stated to an IV of 1.06. The CHDM was described as being "75%
trans". The copolyester was reported to have a crystalline melting
point of 289-297.degree. C. The exact composition of this polyester
was not disclosed, but the melting point of this polymer is not
very different from that of pure poly(1,4-cyclohexylenedimethylene
terephthalate) (PCT, Tm=293.degree. C.).
[0018] U.S. Pat. No. 3,592,875 discloses polyester compositions
that contain both NPG and CHDM residues with an added polyol
present for branching. U.S. Pat. No. 3,592,876 discloses polyester
compositions that contain both EG, CHDM and NPG residues with the
level of NPG residues limited to up to 10 mole percent. U.S. Pat.
No. 4,471,108 discloses low molecular weight polyesters, some of
which contain CHDM and NPG residues but which also contain a
multifunctional branching agent. U.S. Pat. No. 4,520,188 describes
novel low molecular weight copolyesters with mixtures of aliphatic
and aromatic diacid residues with both NPG and CHDM residues
present.
[0019] U.S. Pat. No. 4,182,841 describes a composition containing
between 80 and 70 mole percent ethylene glycol and between 20 and
30 mole percent neopentyl glycol that also contains a
polyfunctional modifying material, i.e., a branching agent.
Terephthalic acid is the only acid used in the compositions. CHDM
was not mentioned. U.S. Pat. Nos. 5,523,382 and 5,442,036 describe
a branched copolyester suitable for extrusion blow molding. The
copolymer contains ethylene glycol (EG) residues in addition to 0.5
to 10 mole percent of CHDM residues and 3 to 10 mole percent
diethylene glycol (DEG) residues. The diacid component comprises
terephthalic acid residues with up to 40 mole percent isophthalic
acid (IPA) or 2,6-naphthalenedicarboxylic acid (NDA) residues. The
branching agent preferably consists of trimellitic acid or
anhydride. NPG is not mentioned.
[0020] U.S. Pat. No. 4,983,711 describes a branched copolyester
composed of EG and CHDM residues and consisting of from 0.05 to 1
mole percent of a tri-functional branching agent, preferably
trimellitic acid or anhydride. Preferred levels of the branching
agent are from 0.1 to 0.25 mole percent. This patent discloses CHDM
residue levels of 25 to 75 mole percent and is concerned with
extrusion blow molding applications. The prevention of melt
fracture is not mentioned. NPG is not discussed. U.S. Pat. No.
5,376,735 describes a branched poly(ethylene terephthalate)
modified with up to 3 mole percent IPA residues for use in
extrusion blow molding applications. A number of branching agents
are mentioned including TMA.
[0021] U.S. Pat. No. 5,235,027 describes a branched
co-poly(ethylene terephtalate) for extrusion blow molding. The PET
contains from 0.5 to 5 weight percent IPA residues, 0.7 to 2.0
weight percent DEG residues, 300-2500 ppm tri- or
tetrahydroxyalkane residues, 80-150 ppm Sb, phosphorous at least
25% by weight of the amount of Sb, red and blue toner (not
exceeding 5 ppm), and various branching agents with pentaerythritol
being preferred. NPG is not discussed.
[0022] U.S. Pat. Nos. 4,234,708, 4,219,527 and 4,161,579 describe
branched and end capped modified PET polyesters for extrusion blow
molding. A variety of chain branching agents (from 0.025 to 1.5
mole percent) and 0.25 to 10 equivalents of a non-ionic chain
terminator are described for controlling reaction conditions and
preventing gelling. NPG is not discussed. U.S. Pat. No. 4,398,022
describes a high melt strength copolyester consisting of
terephthalic acid and 1,12-dodecanedioic acid residues along with a
diol component comprising CHDM residues. No branching agent was
utilized. Japanese Patent Publication JP 3225982 B2 discloses
amorphous copolyesters said to be useful in the formulation of
coating compositions for steel sheet. The disclosed copolyesters
comprise a diacid component comprising mixtures of aliphatic and
aromatic acid residues and a diol component comprising NPG and CHDM
residues.
SUMMARY OF THE INVENTION
[0023] In view of the state of the art described above, there is a
need for shaped articles and extrusion blow molding processes which
produce such shaped articles utilizing a linear polyester having
improved processability for extrusion blow molding by
simultaneously having a higher melt strength without gel formation
and an increase in shear thinning. Accordingly, it is to the
provision of such articles, processes and polyesters that the
present invention is primarily directed. One embodiment of the
present invention is a process for the manufacture of shaped
articles by extrusion blow molding comprising the steps of:
[0024] (1) extruding a copolyester through a die to form a tube of
molten copolyester;
[0025] (2) positioning a mold having the desired finished shape
around the tube of molten copolyester; and
[0026] (3) introducing a gas into the tube of molten copolyester,
causing the extrudate to stretch and expand to fill the mold;
[0027] wherein the copolyester is a linear, copolyester having an
inherent viscosity (IV) of at least about 0.7 dL/g measured at a
temperature of 25.degree. C. at 0.25 g/dl concentration in a
solvent mixture of symmetric tetrachloroethane and phenol having a
weight ratio of symmetric tetrachloroethane to phenol of 2:3 and
comprising:
[0028] (i) a diacid component consisting essentially of about 90 to
100 mole percent terephthalic acid residues and 0 to about 10 mole
percent isophthalic acid residues, naphthalenedicarboxylic acid
residues, biphenyldicarboxylic acid residues or a combination of 2
or more of isophthalic, naphthalenedicarboxylic or
biphenyldicarboxylic acid residues; and
[0029] (ii)) a diol component consisting essentially of about 70 to
90 mole percent 1,4-cyclohexanedimethanol residues and about 30 to
10 mole percent neopentyl glycol residues;
[0030] wherein the copolyester comprises 100 mole percent diacid
component and 100 mole percent diol component. The linear polyester
chain consists essentially of the diacid and diol component defined
above meaning the polyesters are devoid or essentially devoid of
residues derived from monomers or reactants having three or more
functional groups that typically are present in branched-chain
polyesters. These copolyesters have been found to have unusually
high melt strength and degree of shear thinning for a linear
polyester. The significant shear thinning of these copolyesters
make them particularly well suited for extrusion blow molding
applications.
[0031] We have discovered that the above-defined linear
copolyesters are crystallizable. As used herein, the term
"crystallizable" means a copolyester that exhibits a substantial
crystalline melting point when scanned by differential scanning
calorimetry (DSC) at a rate of 20.degree. C./minute. These
crystallizable compositions are distinct from the amorphous
compositions in that they can be can be solid stated. Solid stating
is a process for increasing the IV of a polyester beyond what can
be easily be produced by standard melt phase polymerization. It has
been discovered that these solid stated, NPG-containing
copolyesters shear thin to a much greater degree than similar
linear solid stated polyesters that do not contain NPG. These solid
stated NPG-containing polyesters have rheological characteristics
that are particularly well suited for the extrusion blow molding of
large articles.
[0032] Another embodiment of the present invention is an extrusion
blow molded article produced from a linear copolyester having an
inherent viscosity (IV) of at least about 0.7 dL/g measured at a
temperature of 25.degree. C. at 0.25 g/dl concentration in a
solvent mixture of symmetric tetrachloroethane and phenol having a
weight ratio of symmetric tetrachloroethane to phenol of 2:3 and
comprising:
[0033] (i) a diacid component consisting essentially of about 90 to
100 mole percent terephthalic acid residues and 0 to about 10 mole
percent isophthalic acid residues, naphthalenedicarboxylic acid
residues, biphenyldicarboxylic acid residues or a combination of 2
or more of isophthalic, naphthalenedicarboxylic or
biphenyldicarboxylic acid residues; and
[0034] (ii) a diol component consisting essentially of about 70 to
90 mole percent 1,4-cyclohexanedimethanol residues and about 30 to
10 mole percent neopentyl glycol residues;
[0035] wherein the copolyester comprises 100 mole percent diacid
component and 100 mole percent diol component.
DETAILED DESCRIPTION OF THE INVENTION
[0036] In the first step of the extrusion blow molding process of
the present invention, the copolyester is extruded through a die to
form a tube of molten polyester. This step may be carried out using
a conventional extruder wherein the copolyester is heated to a
temperature of about 250 to 300.degree. C. to form a melt of the
copolyester. The melt then is extruded through a die, typically in
a downward direction, to form a tube of melted copolyester. The
width of the tube typically is in the range of about 50 to 200
mm.
[0037] In the second step of the extrusion blow molding process, a
mold having the desired finished shape is clamped or positioned
around the tube of molten copolyester that is suspended or hanging
from the die. In the third step of the process, a gas such as air
or nitrogen is fed into the tube of molten copolyester, causing the
extrudate to stretch and expand to fill the mold. The mold and
shaped article contained therein are cooled, e.g., to a temperature
of about 20 to 50.degree. C. and then the article is removed from
the mold. The extrusion blow molding process of the present
invention is especially useful for the manufacture of large
containers such as large bottles or carboys for the packaging of
liquids such as water. Because of the combination of desirable
properties possessed by the copolyesters employed in the present
invention, large containers, e.g., containers having a capacity of
from about 2 to 50 liters, can be produced by our novel
process.
[0038] The linear copolyesters utilized in the present invention
may be prepared by conventional polymerization processes known in
the art, such as disclosed by U.S. Pat. Nos. 4,093,603 and
5,681,918, the disclosures of which are herein incorporated by
reference. Examples of polycondensation processes useful in
preparing our novel copolyesters include melt phase processes
conducted with the introduction of an inert gas stream, such as
nitrogen, to shift the equilibrium and advance to high molecular
weight or the more conventional vacuum melt phase
polycondensations, at temperatures ranging from about 240 to about
300.degree. C. or higher which are practiced commercially. The
diacid residues of the copolyesters may be derived from either the
dicarboxylic acids or ester-producing equivalents thereof such as
esters, e.g., dimethyl terephthalate and dimethyl isophthalate, or
acid halides, e.g. acid chlorides. Although not required,
conventional additives may be added to the copolyesters of the
invention in typical amounts. Such additives include pigments,
colorants, stabilizers, antioxidants, extrusion aids, slip agents,
carbon black, flame retardants and mixtures thereof.
[0039] The polymerization reaction may be carried out in the
presence of one or more conventional polymerization catalysts.
Typical catalysts or catalyst systems for polyester condensation
are well-known in the art. Suitable catalysts are disclosed, for
Example, in U.S. Pat. Nos. 4,025,492, 4,136,089, 4,176,224,
4,238,593, and 4,208,527. Typical catalyst useful in
polyester-forming processes also are described by R. E. Wilfong,
Journal of Polymer Science, 54, 385 (1961). Preferred catalyst
systems include Ti, Ti/P, Mn/Ti/Co/P, Mn/Ti/P, Zn/Ti/Co/P, Zn/Al.
When cobalt is not used in the polycondensation, the use of
polymerizable toners may be required to control the color of these
copolyesters so that they are suitable for the intended
applications where color may be an important property. In addition
to the catalysts and toners, other additives, such as antioxidants,
dyes, etc. may be used in the copolyesterifications.
[0040] Solid-state polymerization is a process well known in the
art as described, for example, in U.S. Pat. No. 4,064,112. In this
process, amorphous precursor pellets that have been prepared by
melt phase polymerization are first crystallized at a temperature
10.degree.-100.degree. C. below their melt temperature and then
further held at a temperature of at least 10.degree. C. below their
melt temperature for a sufficiently long time, e.g., 2-40 hours, in
the presence of either vacuum or a flow of dry nitrogen to increase
their IV. These high temperatures are required to allow
polymerization to proceed at a relatively rapid and economical
rate. At these high temperatures, amorphous pellets would soften
and fuse together into a highly viscous block. In contrast,
crystalline pellets will not stick together at these temperatures.
Thus, solid state polymerization can only be performed on
crystallized pellets. Generally when molding grade pellets are
produced, either a batch or continuous process is used. In a batch
process, pellets are added to a large container heated according to
the two stage process described above. The container is
continuously rotated to provide uniform heating of the pellets, and
to prevent sticking of the pellets to the container walls during
the initial crystallization. In a continuous process, the pellets
first drop by gravity into a crystallizer unit, and then flow by
gravity through a large heated container which builds the IV.
Continuous processes are preferred for commercial operations for
reasons of economics. Normally, in solid stating pellets, particles
of regular or irregular shape may be used. The particles may be of
various shapes and sizes such as spherical, cubical, irregular such
as described in U.S. Pat. No. 5,145,742, cylindrical, or as
described in U.S. Pat. No. 4,064,112. "Particles" also includes
shapes which are generally flat.
[0041] Solid stating normally is accomplished by subjecting the
copolyester particles to a temperature of about 140.degree. C.
below the melting point to about 2.degree. C. below the melting
point of the polyester, preferably about 180.degree. C. below the
melting point to about 10 C.degree. C. below the melting point of
the polyester. The time of solid stating can vary over a wide range
(about 1 to 100 hours) according to temperature to obtain the
desired IV, but with the higher temperatures, usually about 10 to
about 60 hours is sufficient to obtain the desired I.V. or
molecular weight. During this period of solid stating, it is
conventional to flow a stream of inert gas through the pellets to
aid in temperature control of the polyester pellets and to carry
away reaction gases such as ethylene glycol and acetaldehyde.
Nitrogen is especially suitable for use as the inert gas because it
contributes to the overall economy of the process. Preferably, the
inert gas is recycled for economic reasons. Other inert gases which
may be used include helium, argon, hydrogen, and mixtures thereof.
It should be understood that the inert gas may contain some air or
oxygen-depleted air.
[0042] It is often observed in solid stating processes that the
rate of IV increase may slow considerably with time. Thus, the
maximum IV that can be obtained may be limited by the initial IV of
the precursor copolyester material. For this reason, the IV of the
copolyester precursor pellets prior to introduction into the solid
stating process typically is between 0.4 and 0.9, preferably
between 0.6 and 0.85, most preferably between 0.65 and 0.8.
[0043] The diacid component of the copolyesters employed in the
present invention preferably consists essentially at least 95 mole
percent, or more preferably 100 mole percent, terephthalic acid
residues. In a preferred embodiment, wherein the diacid component
of the copolyester consists essentially of terephthalic acid
residues, the IV of the solid stated copolyester ranges from about
0.9 to about 1.2 dL/g.
[0044] The second embodiment of our invention are shaped articles
prepared from the copolyesters described above. Examples of typical
shaped articles include containers, water cooler cabinets, toys,
cabinetry, medical devices, and appliance parts. The shaped
articles provided by the present invention preferably are bottles,
especially bottles having a capacity of about 2 to 50 liters,
prepared by the extrusion blow molding process described
herein.
EXAMPLES
[0045] The copolyesters provided by the present invention and the
preparation thereof are further illustrated by the following
examples. The inherent viscosities were measured at a temperature
of 25.degree. C. at 0.25 g/dl concentration in a solvent mixture of
symmetric tetrachloroethane and phenol having a weight ratio of
symmetric tetrachloroethane to phenol of 2:3. The first cycle
melting temperature (Tm1) was determined according to DSC at a
heating rate of 20.degree. C./minute to a temperature of
280-300.degree. C. The 2.sup.nd cycle glass transition temperatures
(Tg), crystallization temperature (Tch) and melt temperatures (Tm2)
were determined according to DSC at a heating rate of 20.degree.
C./minute to a temperature of 280-300.degree. C., quenching in
liquid nitrogen to 0.degree. C., and then rerunning the sample.
Final copolyester compositions were determined by proton NMR
analysis on a 600 MHz JEOL instrument. The melt viscosity was
determined by a Rheometrics Dynamic Analyzer (RDA II) with 25 mm
diameter parallel plates, 1 mm gap and 10% strain at the
temperatures indicated. The samples were dried at 60.degree. C. for
24 hours in a vacuum oven before the frequency sweep test. Bottles
were prepared using a 80 mm Bekum H-121 continuous extrusion blow
molding machine fitted with a barrier screw containing a Maddock
mixing section. The materials were dried for 12 hours at
121.degree. C. (250.degree. F.) prior to extrusion. The extruder
was run at 16 revolutions per minute (RPM). The materials were
extruded into water bottles having a volume of 3.785 liters (1 U.S.
gallon), using a 100 mm die. The bottles weighed between 145 and
160 grams. Melt Strength also was measured by recording the time
elapsed between when the parison emerged from the die to when it
reached a point 20 inches below the head. The parison was cut at
this time and weighed. The "melt strength" was recorded as the
product of the time and the weight of the parison drop, in units of
gram-seconds.
Example 1
[0046] A copolyester comprising a diacid component consisting of
100 mole percent terephthalic acid residues and a diol component
consisting of 83 mole percent CHDM residues and 17 mole percent NPG
residues (hereinafter referenced as 100T/83CHDM/17NPG) was
melt-phase polymerized in a 65 gallon (245 liter) stainless steel
batch reactor with intermeshing spiral agitators. To the reactor
was added 39.64 kg (87.39 pounds, 204.5 moles) of dimethyl
terephthalate, 11.48 kg (25.30 pounds, 110.4 moles) of neopentyl
glycol (NPG), 28.25 kg (62.27 pounds, 196.3 moles) of
1,4-cyclohexanedimethanol (CHDM) and 112.56 grams of a butanol
solution containing the titanium catalyst. The reactor was heated
to 200.degree. C. and held for 2 hours with agitation at 25 RPM.
The temperature was increased to 260.degree. C. and held for 30
minutes. The temperature was increased to 270.degree. C. and the
pressure was reduced at a rate of 13 torr per minute to full
vacuum. After the vacuum reached <4000 microns (<4 torr),
these conditions were held for 1 hour and 15 minutes at 25 RPM. The
RPM was reduced to 15 RPM and the conditions held to a wattmeter
peak. The pressure was increased to atmospheric with nitrogen and
the copolymer was pelletized. The copolymer had a melt phase
inherent viscosity (IV) of 0.758, color values of L*=68.50,
a*=-0.30, b*=6.47; and a composition by Nuclear Magnetic Resonance,
(NMR) of 100T/83CHDM17NPG. This polymer then was crystallized at
150.degree. C. for 2 hours and then solid state polymerized in a
static bed reactor with a nitrogen purge at 230.degree. C. for 24
hours. The IV of the solid stated material was 1.11 dL/g. The
polymer had a second cycle DSC glass transition temperature of
92.5.degree. C., a crystallization on heating (Tch) of
191.7.degree. C. (2.59 cal/g) and a melting point of 251.0.degree.
C. (3.08 cal/g). The first cycle melting point was 262.3.degree. C.
(10.01 cal/g). When measured at a temperature of 270.degree. C.,
the copolyester has a melt viscosity of 134880 poise at 1 radian
per second and a melt viscosity of 21162 poise at 100 radian per
second. The ratio of melt viscosity at 1 radian per second to the
melt viscosity at 100 radian per second is 6.37. Surprisingly, the
copolyester of Example 1 demonstrates a shear thinning behavior
that is superior to any of the other solid stated copolyesters.
Indeed, the shear thinning behavior of the Example 1 copolyester is
superior to even the branched copolyester described in Comparative
Example 2. The melt strength of the copolyester of Example 1 is
much higher than any of the other samples, even when examined under
conditions that produce approximately 23,000 poise viscosity at 100
radian/second (the onset of melt fracture). Bottles were prepared
at 260.degree. C. (500.degree. F.) barrel and head set
temperatures. The melt temperature was measured to be 282.degree.
C. (539.degree. F.). At these conditions, the material had
excellent melt strength and the resulting bottles contained no
unmelts or gels. The "melt strength" measured at this temperature
was 4775 gm-sec.
[0047] The following comparative examples provide melt viscosity
data for a number of copolyesters which are not within the scope of
the present invention. These samples were prepared using the same
general procedure as described in Example 1.
Comparative Example 1
[0048] A copolyester comprising a diacid component consisting of
terephthalic acid residues and a diol component consisting of 69
mole percent EG residues and 31 mole percent CHDM residues having
an IV of 0.74 dL/g was prepared by melt phase polymerization. It
was not solid stated. The polymer has a melt viscosity, measured at
210.degree. C., of 56396 poise at 1 radian per second and 21728
poise at 100 radian per second. The ratio of melt viscosity at 1
radian per second to the melt viscosity at 100 radian per second is
2.60. At this temperature, the viscosity at 1 radian/second is
sufficiently high to give the material marginal melt strength.
However, the copolyester can not be processed at lower
temperatures, as the viscosity at 100 radian/second has increased
to a limiting value. Experience with one particular but typical set
of tooling has shown that if the viscosity becomes greater than
approximately 23,000 at 100 radian/second, then the material will
experience melt fracture during extrusion blow molding. The melt
strength of this material at this temperature is sufficient to blow
smaller bottles, but is insufficient to produce large bottles.
Comparative Example 2
[0049] A copolyester comprising a diacid component consisting of
terephthalic acid residues and a diol component consisting of 69
mole percent EG residues and 31 mole percent CHDM residues and 0.18
mole percent trimelitic anhydrice residues having an IV of 0.74
dL/g was prepared by melt phase polymerization. It was not solid
stated. This polymer has a melt viscosity, measured at 217.degree.
C., of 99377 poise at 1 radian per second and 23232 poise at 100
radian per second. The ratio of melt viscosity at 1 radian per
second to the melt viscosity at 100 radian per second is 4.28. This
lower temperature represents the onset of melt fracture (relative
to the viscosity at 100 radian/second). However, at this
temperature, the melt strength of this material is almost twice the
melt strength of the polyester in Comparative Example 2. Thus, the
bottle size that can be produced with this material is much larger
than can be produced from the copolyester of Comparative Example 2.
However, this sample is branched.
Comparative Example 3
[0050] A copolyester comprising a diacid component consisting of
terephthalic acid residues and a diol component consisting of 97
mole percent EG residues and 3 mole percent CHDM residues was
prepared and solid stated to an IV of 0.98 dL/g. The copolyester
has a melt viscosity, measured at 265.degree. C., of 72000 poise at
1 radian per second and 23000 poise at 100 radian per second. The
ratio of melt viscosity at 1 radian per second to the melt
viscosity at 100 radian per second is 3.11.
Comparative Example 4
[0051] A copolyester comprising a diacid component consisting of
terephthalic acid residues and a diol component consisting of 19
mole percent EG residues and 81 mole percent CHDM residues having
an IV of 0.75 dL/g was prepared by melt phase polymerization. This
polymer has a melting point of 250.degree. C. and a melt viscosity,
measured at 270.degree. C., of 9166 poise at 1 radian per second
and 6842 poise at 100 radian per second. The ratio of melt
viscosity at 1 radian per second to the melt viscosity at 100
radian per second is 1.34. This polymer lacks sufficient melt
strength to be processed into large bottles, and can not be
processed at a lower temperature, as it will crystallize in the
extruder.
Comparative Example 5
[0052] A copolyester comprising a diacid component consisting of 74
mole percent terephthalic acid residues and 26 mole percent
isophthalic acid residues and a diol component consisting of 100
mole percent CHDM residues having an IV of 0.72 dL/g was prepared
by melt phase polymerization. This polymer has a melting point of
245.degree. C. and a melt viscosity, measured at 270.degree. C., of
5042 poise at 1 radian per second and 4274 poise at 100 radian per
second. The ratio of melt viscosity at 1 radian per second to the
melt viscosity at 100 radian per second is 1.18. This polymer lacks
sufficient melt strength to be processed into large bottles, and
can not be processed at a lower temperature, as it will crystallize
in the extruder.
Comparative Example 6
[0053] The copolyester prepared in Comparative Example 4 was solid
stated to an IV of 1.03 dL/g. This polymer has a melt viscosity,
measured at 270.degree. C., of 50482 poise at 1 radian per second
and 21434 poise at 100 radian per second. The ratio of melt
viscosity at 1 radian per second to the melt viscosity at 100
radian per second is 2.36. Bottles were prepared at 260.degree. C.
(500.degree. F.) barrel and head set temperatures. The melt
temperature was measured to be 283.degree. C. (541.degree. F.). At
these conditions, the material had marginal melt strength and the
resulting bottles contained many unmelts. The "melt strength"
measured at this temperature was 1830 gm-sec. Raising the
temperature removed the unmelts, but the parison lacked sufficient
melt strength to make a bottle.
Comparative Example 7
[0054] The copolyester prepared in Comparative Example 5 was solid
stated to an IV of 1.07. This polymer has a melt viscosity,
measured at 270.degree. C., of 49321 poise at 1 radian per second
and 23091 poise at 100 radian per second. The ratio of melt
viscosity at 1 radian per second to the melt viscosity at 100
radian per second is 2.14. Bottles were prepared at 260.degree. C.
(500.degree. F.) barrel and head set temperatures The melt
temperature was measured to be 283.degree. C. (542.degree. F.). At
these conditions, the material had marginal melt strength and the
resulting bottles contained many unmelts. The "melt strength"
measured at this temperature was 2000 gm-sec. Raising the
temperature removed the unmelts, but the parison lacked sufficient
melt strength to make a bottle. This melt strength is insufficient
to make large bottles.
[0055] The invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *