Note: Descriptions are shown in the official language in which they were submitted.
g ~ O
POLYESTER/ZEOLITE ADM~ KES
FIELD OF THE INVENTION
This invention relates to a heat-molded or draw-
formed plastic article having improved flavor retainingproperties and clarity. More particularly, the present
invention relates to a plastic article prepared from a
polyester~small-pore or medium pore zeolite admixture
wherein the zeolite is present in a critical amount of
500 to 1000 parts per million based on the weight of the
polyester.
BACKGROUND OF THE INVENTION
Polyesters such as polyethylene terephthalate (PET)
are widely used for the production of light weight
plastic articles since PET is excellent in mechanical
properties such as formability and creep resistance and
can be biaxially molecularly oriented. However, during
molding or extrusion processes, acetaldehyde is formed
by thermal decomposition of the polyester and when the
polyester is formed into an article, the acetaldehyde in
the article walls migrates into the contents of the
article. Small amounts of acetaldehyde adversely affect
the flavor retaining property of foods and beverages,
and the fragrance retaining property of foods,
beverages, cosmetics, and other package contents. For
these reasons, it is desirable to minimize the migration
of acetaldehyde into package contents.
The use of zeolites in polyesters is disclosed in
U.S. Pat. Nos. 3,876,608, 4,391,971 and 5,104,965, and
PCT International Publication No. WO 90/03408.
U.S. Pat. No. 3,876,608 discloses the addition of
13X or 4A zeolite in polyesters as a inert filler to
increase surface roughness of polyester films. In this
disclosure, the molten polymer film is contacted with a
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cooling quench drum to obtain amorphous polymer prior to
biaxial orientation. Acetaldehyde is not mentioned.
U.S. Pat. No. 4,391,971 discloses a method for
reducing the acetaldehyde content in PET by passing the
PET through a bed of zeolite pellets. In this
disclosure, the zeolite is not admixed with the
polyester.
U.S. Pat. No. 5,104,965 discloses a process for
preparing a crystalline polyethylene terephthalate which
contains greater than 1000 ppm of a zeolite. No mention
is made of acetaldehyde or haze. In contrast, the
present inventors have determined that a
polyester~zeolite admixture wherein the zeolite is
present in a critical amount of 500 parts per million
(ppm) to 1000 ppm imparts adequate reduction in residual
acetaldehyde without imparting haze to the polyester and
thus improves the storage property, flavor retaining
property, and fragrance retaining property of containers
made from such polyesters. If smaller amounts of
zeolite is used, an acceptable level of haze can be
achieved, however, residual acetaldehyde is very large.
On the other hand, if larger amounts of zeolite is used,
residual acetaldehyde can be reduced but only at the
expense of haze.
PCT International Publication No. WO 90~03408
discloses a process for making oriented PET film
containing zeolites as slip additives. The use of
zeolites as polymerization catalysts in PET is also
disclosed. No mention is made of bottle or sheet
applications, only oriented film primarily for magnetic
tape applications. Acetaldehyde was not mentioned.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention
to reduce acetaldehyde contained in a polyester and
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improve the flavor retaining property and fragrance
retaining property of contents in a vessel formed from
the polyester without imparting haze to the polyester.
Another object of the invention is to provide
polyester/zeolite admixtures which exhibit excellent
mechanical properties such as impact resistance, stress
crack resistance and heat resistance, and which display
excellent melt flowability at the time of molding
thereof, and to provide processes for preparing said
polyester~zeolite admixture.
These and other objects are accomplished herçin by
a heat-molded or draw-formed plastic article having
improved flavor retaining properties and clarity which
comprises a thermoplastic polyester~zeolite composition
comprising:
(1) a polyester which comprises
(a) a dicarboxylic acid selected from the group
consisting of aromatic dicarboxylic acids, saturated
aliphatic dicarboxylic acids, cycloaliphatic
dicarboxylic acids, and combinations thereof, and
(b) a diol component comprising repeat units from
at least 50 mole percent ethylene glycol, based on 100
mole percent dicarboxylic acid and 100 mole p-ercent
diol; and
(2) 500 to 1000 parts per million based on the
weight of the polyester of a small-pore or medium pore
zeolite.
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DESCRIPTION OF THE-INVENTION
The polyester, component (1), of the present
invention includes copolyesters. The polyester may be
crystalline, semi-crystalline or amorphous. The
polyester contains repeat units from a dicarboxylic acid
and a diol, based on 100 mole percent dicarboxylic acid
and 100 mole percent diol. Dicarboxylic acids useful in
the present invention include aromatic dicarboxylic
acids preferably having 8 to 14 carbon atoms, saturated
aliphatic dicarboxylic acids preferably having 4 to 12
carbon atoms, and cycloaliphatic dicarboxylic acids
preferably having 8 to 12 carbon atoms. Specific
examples of dicarboxylic acids are: terephthalic acid,
phthalic acid, isophthalic acid,
naphthalene-2,6-dicarboxylic acid,
cyclohexanedicarboxylic acid, cyclohexanediacetic acid,
diphenyl-4,4'-dicarboxylic acid, succinic acid, glutaric
acid, adipic acid, azelaic acid, sebacic acid, and the
like. The polyester may be prepared from two or more of
the above dicarboxylic acids.
It should be understood that use of the
corresponding acid anhydrides, esters, and acid
chlorides of these acids is included in the term
"dicarboxylic acid".
The diol component contains repeat units from at
least 50 mole percent ethylene glycol. Examples of diol
comonomers which can be included with ethylene glycol
are cycloaliphatic diols preferably having 6 to 15
carbon atoms or aliphatic diols preferably having 3 to 8
carbon atoms. Specific diol comonomers are: diethylene
glycol, triethylene glycol, 1,4-cyclohexanedimethanol,
propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol,
hexane-1,6-diol, 3-methylpentanediol-(2,4),
2-methylpentanediol-(1,4), 2,2,4-trimethylpentane-
diol-(1,3), 2-ethylhexanediol-(1,3), 2,2-diethylpropane-
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diol-(1,3), hexanediol-(1,3), 1,4-di-(hydroxyethoxy)-
benzene, 2,2-bis-(4-hydroxycyclohexyl)-propane,
2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane,
2,2-bis-(3-hydroxyethoxyphenyl)-propane, and
2,2-bis-(4-hydroxypropoxyphenyl)-propane. The polyester
may be prepared from one or more of the above diols.
- The polyester may also contain small amounts of
trifunctional or tetrafunctional comonomers such as
trimellitic anhydride, trimethylolpropane, pyromellitic
dianhydride, pentaerythritol, and other polyester
forming polyacids or polyols generally known in th,e art.
For the purposes of the present invention, the
preferred polyester composition contains a dicarboxylic
acid component which consists essentially of repeat
units from terephthalic acid and a diol component which
consists essentially of repeat units from ethylene
glycol.
Polyesters useful as component (1) have an inherent
viscosity of 0.4 to 1.5 dL~g. Preferably, the polyester
has an inherent viscosity of 0.6 to 1.2 dL~g as measured
at 25C. using 0.50 grams of polymer per 100 ml of a
solvent consisting of 60% by weight phenol and 40% by
weight tetrachloroethane. The polyester may be prepared
by conventional polycondensation procedures well-known
in the art. Such processes include direct condensation
of the dicarboxylic acid(s) with the diol(s) or by ester
interchange using a dialkyl dicarboxylate. For example,
a dialkyl terephthalate such as dimethyl terephthalate
is ester interchanged with the diol(s) at elevated
temperatures in the presence of a catalyst.
The second component of the present invention is a
zeolite. Zeolites are crystalline alumino-silicates
with highly ordered crystalline structure. Cavities of
a defined size are formed in the rigid,
three-dimensional network composed of sio4 - and
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A104-tetrahedra. The lattice contains cavities of
varying diameters, depending on the type of zeolite. A
distinction is made between large-, medium-, and
small-pore zeolites. In the case of large-pore
Y-zeolites, for example, a cavity of this type having a
diameter of 7.4 angstroms is formed by twelve sio4
tetrahedra. In the case of small-pore A-zeolites, eight
tetrahedra form a ring of diameter 4.1 angstroms. The
medium-pore pentasil zeolites have a 10-ring system with
an ellipsoidal tubular diameter of 5.5 angstroms x
5.6 angstroms. All medium-pore zeolites are penta,sil
zeolites which contain uniform channels. Small-pore and
medium-pore zeolites are suitable for use in this
invention. Examples of small-pore zeolites include
A-zeolites such as 3A, 4A, and 5A, mordenite (small-pore
type) such as zeolites sold under the trademarks AW-300
and ZEOLON-300 which are available from Union Carbide
and Norton Company, erionite, chabazite, zeolite F such
as IONSIV F80, and zeolite W such as IONSIV W85.
IONSIV is a registered trademark of Union Carbide.
Examples of medium-pore zeolites include ZSM-5, ZSM-11,
ZSM-22, NU-10, Theta 1, ZSM-23, ZSM-48, TS-l, and
silicalite.
The present inventors have determined that addition
of small- or medium-pore zeolites in the range of 500 to
1000 parts per million (ppm) based on the weight of the
polyester to the polyester, component 1, reduces the
concentration of acetaldehyde in the polyester without
producing haze and thus improves the storage property,
flavor retaining property, and fragrance retaining
property of containers made from such polyester.
The polyester compositions of this invention are
prepared by mixing a polyester with small- or
medium-pore zeolites. The zeolites can be readily
incorporated into the polyester during the
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polymerization of the polyester or in a later step by
any suitable melt blending process such as batch mixing,
single screw, or twin screw extrusion. Preferably, the
zeolite is added during polymerization since this method
produces less haze then melt blending. Because zeolites
can absorb and release large amounts of water and hence
contribute to polymer hydrolysis on melt blending, it is
preferable to dehydrate the zeolites by heating to a
temperature of greater than 350C. before adding the
zeolites to the polyester melt.
This invention is useful for various packagi,ng
applications. Examples include, but are not limited to,
thermoformed or injection molded trays, thermoformed or
injection molded cups, extrusion blow molded bottles,
injection stretch blow molded bottles, extruded film,
and extruded sheet.
The materials and testing procedures used for the
results shown herein are as follows:
Acetaldehyde ge~eration (AA Gen) was determined by
the following method. After crystallizing for 30
minutes at 180C., the pelletized polyester~zeolite
admixture was dried overnight at 120C. in a vacuum
oven. A Tinius-Olsen melt indexer was loaded with 5
grams of the polyester or copolyester and held at the
test temperature (preferably 275-310C.) for five
minutes. The molten polyester was extruded into water
and stored at a temperature of -25C. until grinding.
The sample was ground to 20 mesh or finer and 0.5 grams
was placed in a sample tube which was immediately
sealed. The sample was analyzed by dynamic headspace
gas chromatographic analysis using a Hewlett-Packard
5890 Gas Chromatograph with a Perkin Elmer Automatic
Thermal Desorption ATD-50 as the injection system.
Acetaldehyde was desorbed by heating the sample at
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150C. for ten minutes. The gas chromatography column
had a 30 m by 0.53 mm inside diameter.
Haze was determined by ASTM D1003. Haze values
of less than 10% are acceptable for high quality
packaging.
The invention will be further illustrated by a
consideration of the following examples, which are
intended to be exemplary of the invention. All parts
and percentages in the examples are on a weight basis
unless otherwise stated.
EXAMPLES 1-14
Poly(ethylene terephthalate) was prepared by the
following procedure.
Dimethyl terephthalate, 145.5 grams, and 93.0 grams
of ethylene glycol were placed in a polymerization
reactor along with titanium tetraisopropoxide (20 ppm
Ti), manganese acetate (55 ppm Mn), antimony oxide (225
ppm Sb), and cobalt acetate (75-ppm Co). The amount and
type of zeolite indicated in Table I was also added.
The mixture was heated with stirring under nitrogen
atmosphere at 200 C. for 60 minutes, followed by
220 C. for 60 minutes at which time ZONYL A,-(120 ppm
phosphorus) which is available from DuPont, was added.
The reaction temperature was increased to 285 C. and
pressure was reduced to 0.3 mm Hg (0.3 torr). When the
polymer viscosity reached the desired level, the
polymerization was terminated by removing the heat
source and venting the reactor to ambient pressure. The
resulting polyesters had inherent viscosities of
O.50-0.68 dL/g. These polyesters were solid-state
polymerized to an inherent viscosity of 0.70-0.72 dL/g.
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TABLE I
ZEOLITE AA GEN HAZE
EXAMPLE (type) (ppm) 275C. 295C. (%)
1 NONE 5.413.4 4.43
2 4A 100 4.311.3 7.25
3 3A 500 4.612.1 6.20
4 13X 500 6.216.6 8.11
3A 500 4.413.0 8.43
6 ALUMINA500 5.412.9 5.72
7 3A 500 4.314.5 6.74
8 SILICA500 6.211.7 6.41
9 ALUMINA500 6.112.8 8.15
4A 5000 2.39.6 44.20
11 4A 500 3.611.2 4.34
12 4A 1000 3.48.4 7.48
13 NONE - 7.419.1 3.20
14 4A 2000 3.716.1 17.97
The results in Table I clearly indicate that
addition of small- or medium-pore zeolites, as opposed
to using large-pore zeolites such as 13X or similar
inorganic materials such as alumina and silica, in the
range of 100 to 1000 ppm to a polyester reduces the
concentration of acetaldehyde in the polyester without
producing an unacceptable level of haze. An
unacceptable level of haze has been defined as being
greater than 10%.
EXAMPLES 15-25
Poly(ethylene terephthalate) was prepared by the
following procedure.
Bis(2-hydroxyethyl) terephthalate, 190.5 grams, was
placed in a polymerization reactor along with antimony
oxide (225 ppm Sb), cobalt acetate (65 ppm Co) and
ZONYL A (80 ppm phosphorus). The amount and type of
zeolite indicated in Table II was also added. The
mixture was heated with stirring under nitrogen
atmosphere to 285 C. and pressure was reduced to
0.3 torr. When the polymer viscosity reached the
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desired level, the polymerization was terminated by
removing the heat source and venting the reactor to
ambient pressure. The resulting polyesters had inherent
viscosities of 0.57-0.62 dL~g. These polyesters were
solid-state polymerized to an inherent viscosity of
0.70-0.72 dL/g.
TABLE II
ZEOLITE AA GEN HAZE
EXAMPLE (type)(ppm) 275C. 295C. (%)
NONE - 2.7 10.52.34
16 NONE 3.7 12.93.28
17 4A 100 3.4 14.03.12
18 4A 250 2.3 14.13.04
19 4A 250 2.5 13.73.49
4A 500 2.5 13.38.03
21 4A 1000 2.5 13.610.47
22 4A 1000 2.3 15.76.51
23 4A 2000 2.1 11.413.54
24 4A 5000 1.7 10.940.18
NONE 3.2 13.02.74
The results in Table II clearly indicate that
addition of small- or medium-pore zeolites in the range
of 100 to 1000 ppm to a polyester reduce the
concentration of acetaldehyde in the polyester without
producing an unacceptable level of haze, as compared to
polyester compositions without zeolites. The addition
of small- and medium-pore zeolites to the polyester
prepared using the catalyst system in Examples 1-14 have
a greater effect in reducing the acetaldehyde than
adding the same types of zeolites to the polyester used
in Examples 15-25 which contain less catalyst metals.
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EXAMPLE 26
A polyester resin was prepared by mixing powdered
4A zeolite, 0.6 grams, with 599.4 grams of KODAPAK
PET 9921W which is available from Eastman Chemical
Company, and extruding~pelletizing in a Brabender
extruder at 275C. melt temperature. The zeolite was
heated at 500C. for 12 hours and the PET was dried at
150C. for 12 hours. The pelletized polyester~zeolite
resin was crystallized by heating at 180C. for 30
minutes and dried in a vacuum oven for 12 hours at
120C.
Acetaldehyde generation was 8.1 ppm at 275C. and
18.1 ppm at 29SC. compared to 11.0 ppm at 275C. and
25.5 ppm at 295C. without the zeolite additive.
EXAMPLE 26
A polyester resin was prepared by mixing powdered
4A zeolite, 6.0 grams, with 594.0 grams of KODAPAK PET
9921W and extruding/pelletizing in a Brabender extruder
at 275C. melt temperature. The zeolite was heated at
500C. for 12 hours and the PET was dried at 150C. for
12 hours. The pelletized polyester/zeolite resin was
crystallized by heating at 180C. for 30 min-and dried
in a vacuum oven for 12 hours at 120C.
Acetaldehyde generation was 6.7 ppm at 275C. and
12.7 ppm at 295C. compared to 11.0 ppm at 275C. and
25.5 ppm at 295C. without the zeolite additive.
Many variations will suggest themselves to those
skilled in this art in light of the above detailed
description. All such obvious modifications are within
the full intended scope of the appended claims.
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