U.S. patent application number 10/861989 was filed with the patent office on 2004-11-18 for polyester compositions for hot-fill containers.
Invention is credited to Buehrig, Lavonna Suzanne, Estep, Robert Noah, Fischer, David Paul, Weinhold, Stephen.
Application Number | 20040228993 10/861989 |
Document ID | / |
Family ID | 26943835 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040228993 |
Kind Code |
A1 |
Weinhold, Stephen ; et
al. |
November 18, 2004 |
Polyester compositions for hot-fill containers
Abstract
Disclosed is a polyester composition comprising: I. a polyester
consisting essentially of (i) diacid residues consisting
essentially of terephthalic residues; and (ii) diol residues
consisting essentially of about 92 to about 98 mole percent
ethylene glycol residues, about 1 to about 4 mole percent
diethylene glycol (DEG) residues, and about 1 to about 4 mole
percent 1,4-cyclohexanedimethanol (CHDM) residues; and having an
inherent viscosity (IhV) which satisfies the equations IhV-X-Y=0.74
to 0.80, wherein X is the mole fraction of CHDM and Y is the mole
fraction of DEG; and II. at least one reheat enhancing aid in an
amount sufficient to provide between about 5 and about 25% reheat
improvement. Also disclosed are heat set containers suitable for
packaging hot-filled liquids and processes for the manufacture of
such heat set containers.
Inventors: |
Weinhold, Stephen;
(Kingsport, TN) ; Buehrig, Lavonna Suzanne;
(Kingsport, TN) ; Estep, Robert Noah; (Kingsport,
TN) ; Fischer, David Paul; (Kingsport, TN) |
Correspondence
Address: |
Steven A. Owen
Eastman Chemical Company
P.O. Box 511
Kingsport
TN
37662-5075
US
|
Family ID: |
26943835 |
Appl. No.: |
10/861989 |
Filed: |
June 4, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10861989 |
Jun 4, 2004 |
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09898621 |
Jul 3, 2001 |
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60254121 |
Dec 8, 2000 |
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Current U.S.
Class: |
428/35.7 ;
264/537; 428/473.5 |
Current CPC
Class: |
C08K 3/22 20130101; Y10T
428/31721 20150401; C08K 3/22 20130101; C08K 3/08 20130101; C08K
3/04 20130101; C08K 3/08 20130101; C08L 67/02 20130101; C08L 67/02
20130101; C08L 67/02 20130101; C08K 3/04 20130101; Y10T 428/1352
20150115; C08G 63/672 20130101 |
Class at
Publication: |
428/035.7 ;
428/473.5; 264/537 |
International
Class: |
B65D 001/00 |
Claims
We claim:
1. A polyester composition capable of producing a heat-set
container comprising: I. a polyester consisting essentially of: (i)
diacid residues consisting essentially of terephthalic residues;
and (ii) diol residues consisting essentially of ethylene glycol
residues, about 1 to about 4 mole percent diethylene glycol (DEG)
residues, and about 1 to about 4 mole percent
1,4-cyclohexanedimethanol (CHDM) residues; having an inherent
viscosity (IhV, in dl/g) which satisfies the equations IhV-X-Y=0.74
to 0.80, wherein X is the mole fraction, expressed as a decimal, of
CHDM and Y is the mole fraction, expressed as a decimal, of DEG;
and II. at least one reheat enhancing aid in an amount sufficient
to provide between about 5 and about 35% reheat improvement;
wherein said heat-set container exhibits less shrinkage when hot
filled if compared to containers produced from other polyester
compositions.
2. The composition of claim 1 wherein polyester component I
consists essentially of: (i) diacid residues consisting essentially
of terephthalic residues; and (ii) diol residues consisting
essentially of about 94.5 to about 97.5 mole percent ethylene
glycol residues, about 1.5 to about 3 mole percent DEG residues,
and about 1 to about 2.5 mole percent CHDM residues; and has an
inherent viscosity (IhV, in dl/g) which satisfies the equations
IhV-X-Y=0.76 to 0.80, wherein X is the mole fraction of CHDM and Y
is the mole fraction of DEG; wherein said heat-set container
exhibits less shrinkage when hot filled if compared to containers
produced from polyester compositions comprising diol residues
outside the range of about 1 to about 4 mole percent diethylene
glycol (DEG) residues, and outside the range of about 1 to about 4
mole percent 1,4-cyclohexanedimethanol (CHDM) residues.
3. The composition of claim 1 or 2 wherein said reheat enhancing
aid is selected from the group consisting of black and gray body
absorbers and near infrared absorbing dyes.
4. The composition of claim 3 wherein said reheat enhancing aid is
present in an amount of about 5 to about 150 ppm.
5. The composition of claim 4 wherein said reheat enhancing aid is
present in an amount of about 10 to about 100 ppm.
6. The composition of claim 1 wherein said reheat enhancing aid is
selected from the group consisting of carbon black, iron oxide,
antimony, tin, copper, silver, gold, palladium, platinum or a
mixture thereof.
7. The composition of claim 1 wherein said reheat enhancing aid is
selected from the group consisting of carbon black, black iron
oxide and antimony metal.
8. A polyester composition comprising: I. a polyester consisting
essentially of: (i) diacid residues consisting essentially of
terephthalic residues; and (ii) diol residues consisting
essentially of about 94.5 to about 97.5 mole percent ethylene
glycol residues, about 1.5 to about 3 mole percent diethylene
glycol (DEG) residues, and about 1 to about 2.5 mole percent
1,4-cyclohexanedimethanol (CHDM) residues; and has an inherent
viscosity (IhV, in dl/g) which satisfies the equations IhV-X-Y=0.76
to 0.80, wherein X is the mole fraction of CHDM and Y is the mole
fraction of DEG; and II. about 5 to about 150 ppm of at least one
reheat enhancing aid selected from carbon black, black iron oxide
and antimony metal; wherein said heat-set container exhibits less
shrinkage when hot filled if compared to containers produced from
polyester compositions comprising diol residues outside the range
of about 1 to about 4 mole percent diethylene glycol (DEG)
residues, and outside the range of about 1 to about 4 mole percent
1,4-cyclohexanedimethanol (CHDM) residues.
9. The composition of claim 1 further comprising at least one UV
absorbing compound which is thermally stable at polyester
processing temperatures and provides less than 20% transmittance of
UV light having a wavelength of 370 nm through a bottle wall 12
mils thick.
10. The composition of claim 9 wherein said UV absorbing compound
has formula I: 5wherein: R is hydrogen, alkyl, substituted alkyl,
aryl, substituted aryl, cycloalkyl, substituted cycloalkyl or
alkenyl; R.sup.1 is hydrogen, or a group such as alkyl, aryl, or
cycloalky, all of which groups may be substituted; R.sup.2 is any
radical selected from the group consisting of hydrogen, alkyl,
substituted alkyl, allyl, cycloalkyl or aryl; R.sup.3 is hydrogen
or 1-3 substitutents selected from alkyl, substituted alkyl,
alkoxy, substituted alkoxy and halogen, and P is cyano, or a group
such as carbamyl, aryl, alkylsulfonyl, arylsufonyl, heterocyclic,
alkanoyl, or aroyl, all of which groups may be substituted.
11. The composition of claim 10 wherein R.sup.2 is hydrogen, alkyl
and hydroxyalkyl; R is selected from hydrogen or an alkyl linking
group; and P is cyano.
12. The composition of claim 10 where said UV absorbing compound
comprises at least two compounds of formula I.
13. The composition of claim 10 wherein said UV absorbing compound
is present in an amount between 1 to about 5000 ppm by weight.
14. The composition of claim 10 wherein said UV absorbing compound
is present in an amount between about 2 ppm to about 1,500 ppm by
weight.
15. The composition of claim 10 wherein said UV absorbing compound
is present in an amount between about 10 and about 700 ppm by
weight.
16. A heat-set container comprising: I. a polyester consisting
essentially of: (i) diacid residues consisting essentially of
terephthalic residues; and (ii) diol residues consisting
essentially of ethylene glycol residues, about 1 to about 4 mole
percent diethylene glycol (DEG) residues, and about 1 to about 4
mole percent 1,4-cyclohexanedimethanol (CHDM) residues; and having
an inherent viscosity (IhV, in dl/g) which satisfies the equations
IhV-X-Y=0.74 to 0.80, wherein X is the mole fraction, expressed as
a decimal, of CHDM and Y is the mole fraction, expressed as a
decimal, of DEG; and II. at least one reheat enhancing aid in an
amount sufficient to provide between about 5 and about 35% reheat
improvement; wherein said heat-set container exhibits less
shrinkage when hot filled if compared to containers produced from
polyester compositions comprising diol residues outside the range
of about 1 to about 4 mole percent diethylene glycol (DEG)
residues, and outside the range of about 1 to about 4 mole percent
1,4-cyclohexanedimethanol (CHDM) residues.
17. The heat set container of claim 16 wherein polyester component
consists essentially of: (i) diacid residues consisting essentially
of terephthalic residues; and (ii) diol residues consisting
essentially of about 94.5 to about 97.5 mole percent ethylene
glycol residues, about 1.5 to about 3 mole percent DEG residues,
and about 1 to about 2.5 mole percent CHDM residues; and has an
inherent viscosity (IhV, in dl/g) which satisfies the equations
IhV-X-Y=0.76 to 0.80, wherein X is the mole fraction of CHDM and Y
is the mole fraction of DEG; wherein said heat-set container
exhibits less shrinkage when hot filled if compared to containers
produced from polyester compositions comprising diol residues
outside the range of about 1 to about 4 mole percent diethylene
glycol (DEG) residues, and outside the range of about 1 to about 4
mole percent 1,4-cyclohexanedimethanol (CHDM) residues.
18. The heat set container of claim 17 wherein said reheat
enhancing aid is selected from the group consisting of black and
gray body absorbers and near infrared absorbing dyes.
19. The heat set container of claim 18 wherein said reheat
enhancing aid is present in an amount of about 5 to about 150
ppm.
20. The heat set container of claim 4 wherein said reheat enhancing
aid is present in an amount of about 10 to about 100 ppm.
21. The heat set container of claim 16 wherein said reheat
enhancing aid is selected from the group consisting of carbon
black, iron oxide, antimony, tin, copper, silver, gold, palladium,
platinum or a mixture thereof.
22. The heat set container of claim 1 wherein said reheat enhancing
aid is selected from the group consisting of carbon black, black
iron oxide and antimony metal.
23. A heat set container comprising: I. a polyester consisting
essentially of: (i) diacid residues consisting essentially of
terephthalic residues; and (ii) diol residues consisting
essentially of about 94.5 to about 97.5 mole percent ethylene
glycol residues, about 1.5 to about 3 mole percent diethylene
glycol (DEG) residues, and about 1 to about 2.5 mole percent
1,4-cyclohexanedimethanol (CHDM) residues; and has an inherent
viscosity (IhV, in dl/g) which satisfies the equations IhV-X-Y=0.76
to 0.80, wherein X is the mole fraction of CHDM and Y is the mole
fraction of DEG; and p1 II. about 1 to about 300 ppm of at least
one reheat enhancing aid; wherein said heat-set container exhibits
less shrinkage when hot filled if compared to containers produced
from polyester compositions comprising diol residues outside the
range of about 1 to about 4 mole percent diethylene glycol (DEG)
residues, and outside the range of about 1 to about 4 mole percent
1,4-cyclohexanedimethanol (CHDM) residues.
24. The heat set container of claim 16 further comprising at least
one UV absorbing compound which is thermally stable at polyester
processing temperatures and provides less than 20% transmittance of
UV light having a wavelength of 370 nm through a bottle wall 12
mils thick.
25. The heat set container of claim 16 wherein said UV absorbing
compound has formula I: 6wherein: R is hydrogen, alkyl, substituted
alkyl, aryl, substituted aryl, cycloalkyl, substituted cycloalkyl
or alkenyl; R.sup.1 is hydrogen, or a group such as alkyl, aryl, or
cycloalky, all of which groups may be substituted; R.sup.2 is any
radical selected from the group consisting of hydrogen, alkyl,
substituted alkyl, allyl, cycloalkyl or aryl; R.sup.3 is hydrogen
or 1-3 substitutents selected from alkyl, substituted alkyl,
alkoxy, substituted alkoxy and halogen, and P is cyano, or a group
such as carbamyl, aryl, alkylsulfonyl, arylsufonyl, heterocyclic,
alkanoyl, or aroyl, all of which groups may be substituted.
26. The heat set container of claim 25 wherein R.sup.2 is hydrogen,
alkyl and hydroxyalkyl; R is selected from hydrogen or an alkyl
linking group; and P is cyano.
27. The heat set container of claim 25 where said UV absorbing
compound comprises at least two compounds of formula I.
28. The heat set container of claim 25 wherein said UV absorbing
compound is present in an amount between 1 to about 5000 ppm by
weight.
29. The heat set container of claim 10 wherein said UV absorbing
compound is present in an amount between about 2 ppm to about 1,500
ppm by weight.
30. The heat set container of claim 25 wherein said UV absorbing
compound is present in an amount between about 10 and about 700 ppm
by weight.
31. The heat set container according to claim 16, 17, 23, 24 or 25
wherein said container is a bottle.
32. A process for forming a heat-set container which comprises the
steps of: (1) injection molding the polyester composition of claim
1 to form a container perform; (2) reheating or temperature
conditioning the perform; and (3) stretch blow molding the preform
of step (2) into a mold heated at a temperature of about 90 to
160.degree. C.; wherein said container exhibits less shrinkage when
hot filled if compared to containers blown with compositions
comprising diol residues outside said range.
33. The process of claim 16 wherein step (3) comprises stretch blow
molding the preform of step (2) into a mold heated at a temperature
of about 100 to about 140.degree. C.
34. A heat set container formed from the composition of claim
1.
35. A heat set container formed from the composition of claim
5.
36. A process for forming a heat-set container which comprises the
steps of: (1) injection molding the polyester composition of claim
8 to form a container perform; (2) reheating the preform; and (3)
stretch blow molding the preform of step (2) into a mold heated at
a temperature of about 100 to about 140.degree. C.; wherein said
heat-set container exhibits less shrinkage when hot filled if
compared to containers produced from polyester compositions
comprising diol residues outside the range of about 1 to about 4
mole percent diethylene glycol (DEG) residues, and outside the
range of about 1 to about 4 mole percent 1,4-cyclohexanedimethanol
(CHDM) residues.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of copending U.S.
application Ser. No. 09/898,621, filed Jul. 3, 2001, which claims
priority to U.S. Provisional Application Ser. No. 60/254,121 filed
Dec. 8, 2000; both prior applications are hereby incorporated by
reference in their entirety to the extent that they do not
contradict statements herein.
FIELD OF THE INVENTION
[0002] The present invention pertains to certain polyester
compositions which are particularly suitable for the manufacture of
heatset-formed articles, such as containers. More specifically, the
present invention pertains to polyester compositions comprising
residues of terephthalic acid, ethylene glycol, diethylene glycol
(DEG) and cyclohexane dimethanol (CHDM), and a reheat enhancing
aid.
BACKGROUND OF THE INVENTION
[0003] It is well known in the art that poly(ethylene
terephthalate) (PET) and PET containing minor amounts of another
monomer such as isophthalic acid and/or CHDM is useful for many
packaging applications such as in the manufacture of beverage and
food containers. Containers for certain applications require a
special heat set process. For example, plastic containers which are
useful for many foods and juices are hot filled (the contents of
the container are at an elevated temperature when introduced into
the container). These "hot-fill" containers must be heat-treated or
"heat-set" to prevent unacceptable shrinkage or deformation of the
polyester container during the hot-fill process. Heat-setting
requires the use of heated blow molds and also requires the blow
molding process be slowed relative to the typical speeds used for
manufacturing non-heat-set containers to obtain a sufficiently long
contact time between the blow-molded container and the hot-blow
mold. This causes an increase in the cost of manufacturing heatset
containers as compared to the manufacture of non-heat-set
containers.
[0004] In the manufacture of containers such as bottles from
thermoplastic polyesters, a bottle preform is heated above the
glass transition temperature of the polyester and then positioned
in the bottle mold. A pressurized gas such as air then is fed or
injected into the heated preform through its open end causing the
preform to stretch and expand into the bottle mold. The bottle
preforms are test tube shaped articles prepared by injection
molding of the polyester. Such technology is well known to the art
as shown by U.S. Pat. No. 3,733,309. Any radiant energy source such
as quartz heaters, resistance heaters, and the like may be
employed.
[0005] The highest temperature to which a preform may be reheated
is limited by a number of factors which are dependent upon
characteristics of the polyester composition from which the
preforms are molded. Unfortunately, changing one of the factors to
improve a desired property frequently has a detrimental effect on
another property. For example, thermally induced crystallization of
the preform during reheat--that is, crystallization of the
polyester composition from the glass--increases rapidly with
temperature. Such crystallinity in the preform causes visible haze
in the resultant container, which is unacceptable. While the rate
of crystallization from the glass may be reduced by modifying the
polyester composition with various diacid or diol comonomers, such
modification reduces the level of strain induced crystallinity in
the blow molded container and increases the natural stretch ratio
of the polyester composition, making it difficult or impossible to
achieve good material distribution in the blow molded
container.
[0006] Other copolymer properties have similar countervailing
effects. Molecular weight or solution inherent viscosity (IhV) can,
within limits, reduce preform gravitational deformation (droop) and
the natural stretch ratio of the polyester composition.
Unfortunately, increasing IhV causes the polyester composition to
be more costly to manufacture and also, when the IhV exceeds a
certain level, dependent upon the particular injection molding
equipment used, increases the preform injection molding cycle time
due to the higher melt viscosity of the composition causing an
increase in the injection time.
SUMMARY OF THE INVENTION
[0007] The present invention provides a polyester composition
having improved processability in the manufacture of heat-set
containers and, thus, may be used to produce heat-set containers
having improved hot-fill stability; i.e., containers which exhibit
less shrinkage and deformation when hot-filled. The polyester
compositions of the present invention comprise:
[0008] I. a polyester consisting essentially of:
[0009] (i) diacid residues consisting essentially of terephthalic
residues; and
[0010] (ii) diol residues consisting essentially of about 92 to
about 98 mole percent ethylene glycol residues, about 1 to about 4
mole percent diethylene glycol (DEG) residues, and about 1 to 4
mole percent 1,4-cyclohexane dimethanol (CHDM) residues;
[0011] and having an inherent viscosity (IhV) which satisfies the
equations IhV-X-Y=0.74 to 0.80, wherein X is the mole fraction of
CHDM and Y is the mole fraction of DEG; and
[0012] II. at least one reheat enhancing aid in an amount
sufficient to provide between about 5 and about 35% reheat
improvement.
[0013] As used herein, inherent viscosity (IhV) is measured at
25.degree. C. using 0.5 grams of polymer per 100 ml of a solvent
consisting of 60% by weight phenol and 40% by weight
tetrachloroethane.
[0014] A second embodiment of the present invention concerns a
process for forming a heat-set container which comprises the steps
of:
[0015] (1) injection molding the above-described polyester
composition to form a container preform;
[0016] (2) reheating (in the case of two-stage blow molding) or
temperature conditioning of (in the case of single-stage blow
molding) the preform; and
[0017] (3) stretch blow molding of the preform into a mold heated
at a temperature of about 90 to about 160.degree. C.
[0018] Another embodiment of the present invention pertains to a
heat-set container formed from the above-described polyester
composition.
[0019] The improved polyester compositions of the present invention
may be injection molded to produce container preforms which are
capable of forming heat-set containers having low visual haze and
less than 3% volume shrinkage, even at reduced mold temperatures,
e.g., those less than 130.degree. C., and even those less than
110.degree. C. The present invention is based, in part, upon the
discovery that the temperature of the preform achieved during
reheat or conditioning is directly correlated to the hotfill
stability of the resultant container. More specifically, we have
found that the higher the temperature of the preform at the moment
it is blow molded into the container, the greater the hot-fill
stability of the container. It has further been discovered that
very hot preforms permit the temperature of the blow mold, i.e.,
the mold into which a heated preform is blown to form a container,
to be reduced while still producing containers having acceptable
hot-fill stability. Reducing the blow mold temperature provides
greater safety, lower energy consumption, less thermally-induced
degradation to components of the blow molding machine, less
shrinkage and deformation of the container within the blow mold
during the period after the high pressure blow air is exhausted
from the container and when the container is ejected from the mold,
and, potentially, the use of water instead of oil to heat the blow
molds. We also have found that the use of preforms molded from the
polyester compositions of the present invention enables the blow
molding machine to be operated at significantly higher speeds with
no reduction of container hot-fill stability.
[0020] The maximum temperature to which a preform can be reheated
is limited by the reheat rate of the polyester composition; i.e.,
the proportion of the incident radiation of infrared and visible
wavelengths to which the preform is exposed to during reheat which
is actually absorbed by the polyester composition. We have
discovered that increasing the reheat rate of the polyester
composition of the present invention produces advantageous results.
In particular, though bound by no theory, it is believed that
increasing the reheat rate of the polyester composition alters the
temperature profile through the wall of the preform during reheat
in a manner that beneficially affects the hot-fill stability of the
container. Also, increasing the reheat rate of the novel polyester
composition allows the preform to be reheated more quickly such
that it experiences for a shorter length of time the high
temperature at which crystallization from the glass occurs. Due to
the shorter required duration of high temperature exposure,
increasing the reheat rate of the polyester composition allows the
preform to be reheated to a higher temperature without
crystallization from the glass occurring. As mentioned above, this
improves the hot-fill stability of the container. The most
beneficial means to shorten the duration of reheat is to operate
the blow molding machine more quickly, such that the preform passes
through the oven more quickly. This reduces the cost of
manufacturing the container.
[0021] It can be appreciated from the foregoing discussion that the
many factors limiting the maximum preform temperature and the
resultant container hot-fill stability are complex and deeply
interrelated to the degree that a priori prediction of the
consequences of altering a characteristic of the polyester
composition is impossible even to those most skilled in the art.
Thus, it was surprising to discover an interdependent range of
copolymer modification, inherent viscosity, and reheat rate via the
addition of a reheat rate enhancing additive that yields polyester
compositions which produce heatset containers having markedly
superior hot-fill stability relative to containers made from
compositions outside of identified range.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The polyester component of our novel compositions consists
essentially of:
[0023] (i) diacid residues consisting essentially of terephthalic
residues; and
[0024] (ii) diol residues consisting essentially of about 92 to
about 98 mole percent ethylene glycol residues, about 1 to about 4
mole percent diethylene glycol (DEG) residues, and about 1 to about
4 mole percent 1,4-cyclohexanedimethanol (CHDM) residues;
[0025] and having an inherent viscosity (IhV, in dl/g) which
satisfies the equations IhV-X-Y=0.74 to 0.80, wherein X is the mole
fraction (as a decimal value) of CHDM and Y is the mole fraction
(as a decimal value) of DEG. The total mole percentage of all
components or residues of the polyester is 200 mole percent: 100
mole percent diacid residues and 100 mole percent diol residues. As
mentioned above, inherent viscosity (IhV) is measured at 25.degree.
C. using 0.5 grams of polymer per 100 ml of a solvent consisting of
60% by weight phenol and 40% by weight tetrachloroethane and is
given in dl/g units of measurement.
[0026] The polyester component preferably consists essentially
of:
[0027] (i) diacid residues consisting essentially of terephthalic
residues; and
[0028] (ii) diol residues consisting essentially of about 94.5 to
about 97.5 mole percent ethylene glycol residues, about 1.5 to
about 3 mole percent diethylene glycol (DEG) residues, and about 1
to about 2.5 mole percent 1,4-cyclohexane dimethanol (CHDM)
residues;
[0029] and has an inherent viscosity (IhV, in dl/g) which satisfies
the equations IhV-X-Y=0.76 to 0.80, wherein X is the mole fraction
(as a decimal value) of CHDM and Y is the mole fraction (as a
decimal value) of DEG.
[0030] The polyester component of the compositions of the present
invention is formed via conventional polyesterification. The three
polymerization stages are hereinafter referred to as the
esterification stage, the prepolymer stage, and the
polycondensation stage. The basic conditions which define these
three stages are set out below for convenience and clarity.
[0031] The polyesters and polyester containers made according to
this aspect of the present invention have an acceptable haze where
the haze ranges from 1 to 3 wherein the values given for haze
correspond to 0=no haze, 1=very slight haze, 2=slight haze, and
3=moderate haze. The polyester containers of the present invention
can be made using well known processes for producing containers
from polyesters. Such processes include injection stretch blow
molding and extrusion blow molding. Preferably, such containers are
made using a conventional blow molding process well known to
skilled artisans.
[0032] Generally during the hot-fill process, containers are filled
at a temperature between about 83.degree. C. to about 87.degree.
C., preferably between about 84.degree. C. to about 86.degree. C.
Containers can be condition by any means known in the art. For
example, bottles can be conditioned for at least 72 hours at about
50% relative humidity before hot filling.
[0033] As previously stated, to have maximum hot-fill stability,
one must heat the preform to its maximum temperature. This maximum
temperature is determined by a number of factors including, but not
limited to, type of container, acceptable haze or haze values, and
material distribution. One skilled in the art can determine this
temperature without undue experimentation. For example, one could
determine after a few trials of varying the preform temperature
what the maximum perform temperature would be to produce containers
with acceptable properties listed previously. The inventive
composition increases this maximum temperature as compared to other
polyester compositions. Thus, the improved composition allows for
greater hot-fill stability. This improvement is further illustrated
in the examples.
[0034] In the first stage of the melt-phase process to produce the
polyester composition, a mixture of polyester monomer (terephthalic
acid and diglycol esters thereof) and oligomers are produced by
conventional, well-known processes. The ester exchange or
esterification reaction is conducted at a temperature between about
220.degree. C. to about 250.degree. C. and a pressure of about 0 to
about 6.9 bars gauge (100 pounds per square inch--psig) in the
presence of suitable ester exchange catalysts such as lithium,
magnesium, calcium, manganese, cobalt and zinc, or esterification
catalysis such as hydrogen or titanium suitable forms of which are
generally known in the art. The catalysts may be used separately or
in combination. Preferably, the total amount of catalyst is less
than about 200 ppm on an elemental basis. Suitable colorants or
toners and/or ultraviolet (UV) light absorbers or stabilizers,
especially those that react or polymerize with the polyester
polymer, also may be added at this point to control the final color
or other properties of the polyester. The reaction is conducted for
about 1 to about 4 hours. It should be understood that generally
the lower the reaction temperature, the longer the reaction will
have to be conducted.
[0035] Generally, at the end of the esterification, a
polycondensation catalyst is added. Suitable polycondensation
catalysts include salts of titanium, gallium, germanium, tin, and
antimony, preferably antimony or germanium or a mixture thereof.
Preferably the amount of catalyst added is between about 90 and
about 350 ppm when germanium or antimony is used. Suitable forms
such as, but not limited to, antimony oxide are well known in the
art. The prepolymer reaction is conducted at a temperature less
than 280.degree. C., and preferably between about 240.degree. C.
and about 280.degree. C. at a pressure sufficient to aid in
removing reaction products such as ethylene glycol. The monomer and
oligomer mixture typically is produced continuously in a series of
one or more reactors operating at elevated temperature and pressure
less than one atmosphere. Alternatively, the monomer and oligomer
mixture may be produced in one or more batch reactors.
[0036] Next, the mixture of polyester monomer and oligomers
undergoes melt-phase polycondensation to produce a low molecular
weight precursor polymer. The precursor is produced in a series of
one or more reactors operating at elevated temperatures. To
facilitate removal of excess glycols, water, alcohols, aldehydes,
and other reaction products, the polycondensation reactors are run
under a vacuum or purged with an inert gas. Inert gas is any gas
which does not cause unwanted reaction or product characteristics
at reaction conditions. Suitable gases include, but are not limited
to CO.sub.2, argon, helium and nitrogen.
[0037] Temperatures for this step are generally between about
240.degree. C. to about 280.degree. C. and a pressure between about
0 and about 2 Torr. Once the desired inherent viscosity (IhV) is
achieved, the polymer is pelletized. Precursor IhV generally is
below about 0.7 dl/g to maintain good color. The target IhV
generally is selected to balance good color and minimize the amount
of solid stating which is required. The composition of the
polyester employed in the present invention was determined by
hydrolysis GC and .sup.1H-NMR. One of the benefits of the present
invention is that the polyester component may be prepared from
either terephthalic acid or dimethyl terephthalate based
polyesters.
[0038] The IhV of the polyester component typically is in the range
of about 0.76 to 0.88 dl/g provided that the IhV (in dl/g)
satisfies the equations IhV-X-Y=0.74 to 0.80, wherein X is the mole
fraction of CHDM and Y is the mole fraction of DEG. To illustrate,
if the diol component of the polyester contains 2 mole percent CHDM
residues and 2 mole percent DEG residues, the polyester has an IhV
0.78 to 0.84, e.g., 0.78-0.02-0.02=0.74 and 0.84-0.02-0.02=0.80.
The IhV of the polyester component preferably is in the range of
0.78 to 0.84 dl/g.
[0039] The polyester component of the compositions of the present
invention comprises residues of terephthalic acid, ethylene glycol,
diethylene glycol, and cyclohexanedimethanol. The term "residue" as
used herein to describe the composition of the polyester refers to
the moiety that is the resulting reaction product of the chemical
monomer in a particular reaction scheme, or subsequent formulation
or chemical product, regardless of whether the moiety is actually
obtained from the chemical species. For example, the terephthalic
acid residues may be derived from terephthalic acid, a diester of
terephthalic acid such as dimethyl terephthalate and
bis(2-hydroxyethyl) terephthalate, or a bis-acid chloride of
terephthalic acid such as terephthaloyl chloride. The
1,4-cyclohexanedimethanol used in the preparation of the polyester
component may be the cis, trans or cis/trans mixtures.
[0040] The polyester compositions of the present invention contain
at least one reheat enhancing aid in an amount sufficient to
provide between about 5 and about 35% reheat improvement as
compared to M&G 8006 PET. Reheat rate is defined as the change
in average temperature of a molded part as a function of exposure
to a radiant heat source for a specified time. Suitable reheat
rate-increasing additives are well known in the art and include,
preferably, black and gray body absorbers such as carbon black,
antimony metal, iron oxide and the like, as well as near infrared
absorbing dyes, including, but not limited to those disclosed in
U.S. Pat. No. 6,197,851, which is incorporated herein by
reference.
[0041] The reheat enhancing additive should be present in an amount
sufficient to improve the reheat rate of the unmodified polyester.
The actual amount of reheat rate-increasing additive will vary
depending on which additive is used. For the compositions of the
present invention the selected reheat enhancing aid should be
present in an amount sufficient to improve the reheat of the
polyester by at least 5% when compared to M&G 8006 PET.
Concentrations of about 1 to about 300 parts per million by weight
(ppmw), preferably about 3 to about 100 ppmw, normally are
sufficient. The reheat rate-increasing additive may be any reheat
rate-increasing additive used in the art, including, but not
limited to, carbon black, iron oxide, antimony, tin, copper,
silver, gold, palladium, platinum or a mixture thereof. However,
only very small amounts of black body absorbers, such as carbon
black, e.g., about 10 ppmw and less, and black iron oxide, e.g.,
about 50 ppmw or less, may be necessary to achieve the desired
reheat rate, but relatively large amounts of gray body absorbers
like antimony metal (about 100 ppmw or less) may be necessary to
achieve the same effect. Typically, the polymer composition may
comprise antimony metal in a concentration of at least 10 ppm.
[0042] The more effective concentration of the iron oxide, for
example, is from about 1 to about 100 ppmw, preferably from about 5
to about 50 ppmw with about 10 to about 30 ppmw being most
preferred. The iron oxide, which is preferably black, is used in
very finely divided form, e.g., from about 0.01 to about 200 .mu.m,
preferably from about 0.1 to about 10.0 .mu.m, and most preferably
from about 0.2 to about 5.0 .mu.m. Suitable forms of black iron
oxide include, but are not limited to magnetite and maghemite. Red
iron oxide is less preferred as it imparts an undesirable red hue
to the resultant polymer. Such oxides are described, for example,
on pages 323-349 of Pigment Handbook, Vol. 1, copyright 1973, John
Wiley & Sons, Inc. The reheat enhancing aid, e.g., iron oxide,
may be added to the polyester production system during or after
polymerization, to the polyester melt, or to the molding powder or
pellets from which the bottle preforms are formed. The heating
means used for heating the preforms according to the present
invention is a quartz lamp, Model Q-1P, 650 W., 120 V., by Smith
Victor Corp.
[0043] If the metal is used as the reheat rate-increasing additive,
the metal preferably is in particle form for ease of processing.
The metal particles are preferably sufficiently fine for them not
to be visible to the eye and have a range of sizes such that
absorption of radiation occurs over a relatively wide part of the
wavelength range and not just at one particular wavelength or over
a narrow band.
[0044] The amount of metal particles present in the thermoplastic
polymer composition, as it is to be used in this invention, is a
balance between the desired reduction in the reheat time of the
polymer, the crystallization of the polymer and the amount of haze
that is acceptable for a given application. Preferably, the amount
of metal particles is from about 1 ppm to 300 ppm, more
particularly from about 5 ppm to about 150 ppm, and especially from
about 10 ppm to about 100 ppm. If desired, masterbatches of the
polymer composition containing quantities of metal particles in far
higher concentrations can be made for subsequent blending with
polymer essentially free from the metal particles to achieve the
desired levels of particles.
[0045] When antimony is used it may be added to the polymerization
reactor in the form of antimony trioxide (antimony (III) oxide),
which is a catalyst for the polymerization of the monomers, with a
suitable reducing agent such as an acidic phosphorus compound,
e.g., phosphonic acid. The polyester monomer melt is a slightly
reducing environment, the polyesters may naturally have a very
minor proportion of antimony metal present, e.g., up to about 5-6
ppm. However, these low levels of antimony metal do not affect the
reheat time significantly, and thus, the reducing agent is
required. The use of antimony metal, and its generation in situ, is
disclosed in U.S. Pat. No. 5,419,936, which is incorporated herein
by reference.
[0046] The compositions of the present invention optionally may
contain one or more chemically reactive UV absorbing compounds;
that is, compounds which are covalently bound to the polyester
molecule as either a comonomer, a side group, or an end group.
Suitable UV absorbing compounds are thermally stable at polyester
processing temperatures, absorb in the range of from about 320 nm
to about 380 nm, and are nonextractable from said polymer. The UV
absorbing compounds preferably provide less than about 20%, more
preferably less than about 10%, transmittance of UV light having a
wavelength of 370 nm through a bottle wall 12 mils (305 microns)
thick. Suitable UV absorbing compounds include substituted methine
compounds of the formula 1
[0047] wherein:
[0048] R is hydrogen, alkyl, substituted alkyl, aryl, substituted
aryl, cycloalkyl, substituted cycloalkyl or alkenyl;
[0049] R.sup.1 is hydrogen, or a group such as alkyl, aryl, or
cycloalkyl, all of which groups may be substituted;
[0050] R.sup.2 is any radical which does not interfere with
condensation with the polyester, such as hydrogen, alkyl,
substituted alkyl, allyl, cycloalkyl or aryl;
[0051] R.sup.3 is hydrogen or 1-3 substitutents selected from
alkyl, substituted alkyl, alkoxy, substituted alkoxy and halogen,
and
[0052] P is cyano, or a group such as carbamyl, aryl,
alkylsulfonyl, arylsufonyl, heterocyclic, alkanoyl, or aroyl, all
of which groups may be substituted.
[0053] Preferred methine compounds are those of the above formula
wherein: R.sup.2 is hydrogen, alkyl, aralkyl, cycloalkyl,
cyanoalkyl, alkoxyalkyl, hydroxyalkyl or aryl; R is selected from
hydrogen; cycloalkyl; cycloalkyl substituted with one or two of
alkyl, alkoxy or halogen; phenyl; phenyl substituted with 1-3 of
alkyl, alkoxy, halogen, alkanoylamino, or cyano; straight or
branched lower alkenyl; straight or branched alkyl and such alkyl
substituted with 1-3 of the following: halogen; cyano; succinimido;
glutarimido; phthalimido; phthalimidino; 2-pyrrolidono; cyclohexyl;
phenyl; phenyl substituted with alkyl, alkoxy, halogen, cyano, or
alkylsufamoyl; vinyl-sulfonyl; acrylamido; sulfamyl;
benzoylsulfonicimido; alkylsulfonamido; phenylsulfonamido;
alkenylcarbonylamino; groups of the formula 2
[0054] where Y is --NH--, --N-alkyl, --O--, --S--, or
--CH.sub.2O--; --S--R.sub.14; SO.sub.2CH.sub.2CH.sub.2SR.sub.14;
wherein R.sub.14 is alkyl, phenyl, phenyl substituted with halogen,
alkyl, alkoxy, alkanoylamino, or cyano, pyridyl, pyrimidinyl,
benzoxazolyl, benzimidazolyl, benzothiazolyl, or a radical of the
formulae 3
[0055] --NHXR.sub.16, --CONR.sub.15R.sub.15, and
--SO.sub.2NR.sub.15R.sub.- 15 wherein R.sub.15 is selected from H,
aryl, alkyl, and alkyl substituted with halogen, phenoxy, aryl,
--CN, cycloalkyl, alkylsulfonyl, alkylthio, or alkoxy; X is --CO--,
--COO--, or --SO.sub.2--, and R.sub.16 is selected from alkyl and
alkyl substituted with halogen, phenoxy, aryl, cyano, cycloalkyl,
alkylsulfonyl, alkylthio, and alkoxy; and when X is --CO--,
R.sub.16 also can be hydrogen, amino, alkenyl, alkylamino,
dialkylamino, arylamino, aryl, or furyl; alkoxy; alkoxy substituted
with cyano or alkoxy; phenoxy; or phenoxy substituted with 1-3
alkyl, alkoxy, or halogen substituents; and
[0056] P is cyano, carbamyl, N-alkylcarbamyl,
N-alkyl-N-arylcarbamyl, N,N-dialkylcarbamyl, N,N-alkylarylcarbamyl,
N-arylcarbamyl, N-cyclohexylcarbamyl, aryl, 2-benzoxazolyl,
2-benzothiazolyl, 2-benzimidazolyl, 1,3,4-thiadiazol-2-yl,
1,3,4-oxadiazol-2-yl, alkylsulfonyl, arylsulfonyl or acyl.
[0057] In all of the above definitions the alkyl or divalent
aliphatic moieties or portions of the various groups contain from
1-10 carbons, preferably 1-6 carbons, straight or branched chain.
Preferred UV absorbing compounds include those where R and R.sup.1
are hydrogen, R.sup.3 is hydrogen or alkoxy, R.sup.2 is alkyl or a
substituted alkyl, and P is cyano. In this embodiment, a preferred
class of substituted alkyl is hydroxy substituted alkyl. A most
preferred polyester composition comprises from about 10 to about
700 ppm of the reaction residue of the compound 4
[0058] These compounds, their methods of manufacture and
incorporation into polyesters are further disclosed in U.S. Pat.
No. 4,617,374, the disclosure of which is incorporated herein by
reference. The UV absorbing compound(s) may be present in amounts
between about 1 to about 5,000 ppm by weight, preferably from about
2 ppm to about 1,500 ppm, and more preferably between about 10 and
about 300 ppm by weight. Dimers of the UV absorbing compounds may
also be used. Mixtures of two or more UV absorbing compounds may be
used. Moreover, because the UV absorbing compounds are reacted with
or copolymerized into the backbone of the polymer, the resulting
polymers display improved processability including reduced loss of
the UV absorbing compound due to plateout and/or volatilization and
the like.
[0059] The polyester component of the novel polyester compositions
consists essentially of residues of terephthalic acid, ethylene
glycol, diethylene glycol and 1,4-cyclohexanedimethanol, meaning
that the polyester component does not contain significant amounts
of other monomer residues which substantially affect the
characteristics and properties of the polyesters as described
herein. However, it is possible, although not normally desirable,
for the polyester component to contain minor amounts of residues of
additional monomers such as isophthalic acid and multifunctional
monomers such as trimethylolpropane, pentaerythritol, glycerol,
trimellitic anhydride, trimethylolpropane, pyromellitic
dianhydride, pentaerythritol, trimellitic acid, trimellitic acid,
pyromellitic acid and other polyester forming polyacids or polyols
generally known in the art.
[0060] Also, although not required, optional additives typically
used in polyesters may be used if desired. Such additives include,
but are not limited to, colorants, pigments, antioxidants,
stabilizers, crystallization aids, barrier-improving platelet
particles, compounds capable of improving planar stretch ratio,
acetaldehyde reducing compounds, oxygen scavenging compounds, and
the like.
[0061] The polyester compositions of the present invention are
suitable for forming a variety of shaped articles, including films,
sheets, tubes, preforms, molded articles, containers and the like.
Suitable processes for forming said articles are known and include
extrusion, extrusion blow molding, melt casting, injection molding,
stretch blow molding (SBM), thermoforming, and the like.
[0062] Heat set containers may be produced from the novel polyester
compositions of the present invention using known injection molding
and stretch blow-molding (SBM) processes. These known procedures
involve the steps of (i) injecting molding the polyester
composition to form a preform and (ii) blowing the heated preform
into a container shape. In the first step, the polyester
composition is melted in an extruder and the melt is injected into
a mold forming a preform, typically a test tube-shaped article with
threads molded at the open end. The second step involves blowing of
the preform heated at a temperature above the glass transition
temperature of the polyester, e.g., typically about 90 to about
140.degree. C., more typically about 100 to about 130.degree. C. In
a "single stage" SBM process, the preform is transferred from the
injection mold directly to a blow molding station. During the
transfer time, the preform cools to the proper blow molding
temperature. In a "two stage" SBM process, the preform is ejected
from the injection mold and then held at ambient temperatures for a
time long enough to achieve a consistent temperature within the lot
of preforms. In a separate step, the preforms are reheated to the
proper blow molding temperature before being blown into the desired
container shape. In the heat-set process, the preforms are blown
into a hot mold, usually at a mold temperature between about 90 and
about 160.degree. C., more typically between about 100 and about
140.degree. C. The hot mold is essential for manufacturing a
container having good hot-fill stability. During contact with the
hot mold, the crystallinity in the wall of the container is
increased and the in-plane orientation of polymer molecules induced
by blow molding is reduced. The specific type of process used is
determined by the volume of production, or the production rate
desired for a specific application, and the machine design and
capabilities.
EXAMPLES
[0063] The novel polyester compositions and their use in the
manufacture of containers are further illustrated by the following
examples. Unless indicated otherwise, parts are by weight,
temperature is in .degree. C. or is at room temperature and
pressure is at or near atmospheric.
[0064] The improvement in reheat rate is measured using injection
molded flat plaques having the dimensions 7.6 cm.times.7.6
cm.times.3.8 mm thick (3 inches.times.3 inches.times.0.15 inch
thick). The plaques were allowed to cool to ambient temperature. A
set of four plaques was prepared for each polyester material
evaluated. Each plaque was evaluated by placing a plaque in a
wooden holder that only contacted the plaque on the edges. The
temperature of the plaque in the holder was measured. This was the
initial temperature (T.sub.i). The holder was moved into position a
fixed distance 12.7 cm (5 inches) from the tip of a GE Quartzline
DYH 120V, 600 W, tungsten filament halogen lamp. The lamp
temperature during measurement was 3,200 degrees Kelvin. Each
plaque was exposed to the illuminated lamp for 35 seconds. The
temperature of the plaque then was measures by means of an infrared
pyrometer. The temperature was read from the face of the plaque
which was not illuminated to allow the heat absorbed by the front
surface of the plaque to penetrate through the plaque. The
temperature of the back side of the plaque rises at first to a
maximum temperature and then begins to fall slowly as the entire
plaque cools. The maximum temperature was recorded as the final
temperature (T.sub.f).
[0065] The temperature rise was recorded as .DELTA.T
(T.sub.f-T.sub.i). The change in temperature also was adjusted for
small differences in the thickness of the plaques. The average
.DELTA.T for the four plaques was determined from the adjusted
.DELTA.T to give a .DELTA.T.sub.avg for each polyester material.
The .DELTA.T.sub.avg for each polyester material was divided by the
.DELTA.T of the concurrently tested reference standard to provide
the improvement in reheat, or Reheat Index Value
(RIV)=(.DELTA.T.sub.avg Sample.div..DELTA.T.sub.avg Reference).
Example 1
[0066] A polyester consisting of terephthalic acid diacid residues
and diol residues consisting of approximately 95 mole percent
ethylene glycol residues, about 3.1 mole percent (0.031 mole
fraction) DEG residues, and 1.9 mole percent (0.019 mole fraction)
CHDM residues having an IhV of approximately 0.82 was prepared from
dimethyl terephthalate, ethylene glycol, DEG and CHDM according to
the procedures described above. The value of the expression
IhV-(mole fraction DEG)-(mole fraction CHDM)=0.82-0.031-0.019 is
equal to about 0.77.
[0067] Pellets of the above polyester were blended with pellets of
a reheat enhancing additive concentrate composed of 99.875 weight
percent of a poly(ethylene terephthalate) modified with
approximately 3.7 mole percent diethylene glycol (EASTAPAK
Polyester 9663) and 0.125 weight percent black iron oxide powder
(grade BK45 manufactured by Harcros Pigments, now known as
Elementis Pigments) compounded using a 30 mm Werner &
Pfleiderer extruder. Pellets of the polyester prepared as described
above (49 parts by weight) were blended with pellets of the reheat
enhancing additive concentrate (1 part by weight) yielding a
polyester consisting of terephthalic acid diacid residues and diol
residues consisting of approximately 95 mole percent ethylene
glycol residues, about 3.1 mole percent (0.031 mole fraction) DEG
residues, and 1.9 mole percent (0.019 mole fraction) CHDM residues
having an IhV of approximately 0.82 containing 25 ppmw of black
iron oxide.
[0068] The performance and properties of the polyester composition
of Example 1 were compared to those of the following
polyesters:
[0069] Comparative Polyester C-1--poly(ethylene terephthalate)
modified with approximately 3.7 mole percent DEG residues and
having an IhV of about 0.76 (EASTAPAK 9663, Eastman Chemical
Company).
[0070] Comparative Polyester C-2--a polyester consisting of diacid
residues consisting of about 97 mole percent terephthalic acid
residues and 3 mole percent isophthalic acid residues and diol
residues consisting of approximately 96.7 mole percent ethylene
glycol residues and about 3.3 mole percent (0.031 mole fraction)
DEG residues having an IhV of approximately 0.82 (PERMACLEAR Lot
61801, Wellman, Inc.).
[0071] Comparative Polyester C-3--the polyester prepared as
described in Example 1 which does not contain any reheat enhancing
additive.
[0072] The Reheat Index Value for the composition of Example 1 and
Comparative Polyesters C-1, C-2 and C-3 was determined relative to
a commercial poly(ethylene terephthalate) (Shell grade 8006
polyester) used in the manufacture of containers by stretch blow
molding processes. The Reheat Index Values thus determined were:
Example 1=1.17, Comparative Polyester C-1=0.99, Comparative
Polyester C-2=1.24, and Comparative Polyester C-3=0.99.
[0073] After first drying in a desiccant air dryer, pellets of the
polyester composition of Example 1 and Comparative Polyesters C-1,
C-2 and C-3 were each molded into preforms using a single cavity
Arburg injection molding machine. Each preform weighed about 49
grams and had finish diameter of 43 mm. The injection molding cycle
time for each of the four compositions was essentially
identical.
[0074] Each of the preforms was reheat stretch blow molded into
nominal 1 liter bottles using a Sidel SBO-2/3 blow molding machine.
This is a rotary blow molding machine having two blow molds and
three preform oven zones. The blow mold was designed to produce
bottles having vacuum panels, which prevent buckling or collapse of
the bottle due to the vacuum generated by hotfilling, sealing, and
cooling the bottles. For each composition, four sets of bottles
were produced at the following output rates and blow mold
temperatures:
[0075] 1. 800 bottles per hour per mold (BHM) during which oil at a
temperature of 138.degree. C. was circulated through the blow mold.
This oil temperature yielded a mold surface temperature of
120.degree. C.
[0076] 2. 1000 BHM during which oil at a temperature of 138.degree.
C. was circulated through the blow mold. This oil temperature
yielded a mold surface temperature of 120.degree. C.
[0077] 3. 800 BHM during which oil at a temperature of 118.degree.
C. was circulated through the blow mold. This oil temperature
yielded a mold surface temperature of 105.degree. C.
[0078] 4. 1000 BHM during which oil at a temperature of 118.degree.
C. was circulated through the blow mold. This oil temperature
yielded a mold surface temperature of 105.degree. C.
[0079] For each of these four conditions, blow molding machine
variables were adjusted to achieve the hottest possible preform
surface temperature without generating an objectionable level of
haze in the bottle wall, which is indicative of crystallization of
the preform during reheat. Additional adjustments to blowing
machine variables were also made to maintain the material
distribution in the containers, i.e., bottle section weights,
within specification. The blowing machine variables adjusted were
oven heater profile, overall oven power, preblow timing, preblow
air pressure, and preblow air flow rate. These variables and
adjustments are well known and understood to those skilled in the
art. The preform surface temperature was measured using an infrared
pyrometer immediately after the preform had exited the reheat oven.
Table 1 shows the preform surface temperature (.degree. C.) for the
preforms molded from the polyester compositions of Example 1 and
Comparative Polyesters C-1 through C-3 (Examples C-1, C-2 and
C-3).
1 TABLE I Preform Surface Temperature Example 800 BHM 1000 BHM 1
106 109 C-1 99 100 C-2 101 103 C-3 104 108
[0080] Table 1 shows that the preforms of Example 1 were heated to
substantially higher surface temperature (106 and 109.degree. C.)
than the preforms of Comparative Examples 1 (99 and 100.degree. C.)
and 2 (101 and 103.degree. C.), and to slightly higher surface
temperature than the preforms of Comparative Example 3 (104 and
108.degree. C.). Moreover, changing the oil temperature (and
therefore the mold temperature) did not have any significant impact
or influence on the preform surface temperature. The Examples
clearly show that the compositions of the present invention produce
preforms which can be heated to higher temperatures without forming
objectionable levels of crystalline haze than similar compositions
which are outside the scope of the present invention.
[0081] The bottles produced as described above from the composition
of Example 1 and Comparative Polyesters C-1, C-2 and C-3 were
examined visually for haze under conditions of typical indoor room
lighting. Table II shows the level of visual haze exhibited by the
bottles blown from the preforms heated to the surface temperatures
given in Table I wherein the values given for haze correspond to
0=no haze, 1=very slight haze, 2=slight haze, and 3=moderate haze.
The temperatures shown in Table II refers to the temperature of the
mold surface.
2 TABLE II Haze in Side-Wall of Blow Molded Bottles 800 BHM 1000
BHM Example 120.degree. C. 105.degree. C. 120.degree. C.
105.degree. C. 1 1 1 1 1 C-1 3 3 3 3 C-2 2 2 2 2 C-3 2 2 0 0
[0082] Table II shows that the level of haze exhibited by the
bottles of the Example 1 composition was substantially lower than
the level of haze in the bottles of Comparative Polyesters C-1 and
C-2 even though the preforms of the Example 1 composition were
heated to substantially higher surface temperature than the
preforms of Comparative Polyesters C-1 and C-2. The level of haze
in the bottles of the Example 1 composition was similar to the
level of haze in the bottles of Comparative Polyester C-3, being
slightly lower for bottles blown at the rate of 800 BHM and
slightly higher for bottles blown at the rate of 1000 BHM.
[0083] The hot-fill stability of the bottles produced as described
above was measured using the following procedure. First, the
bottles were stored under ambient conditions for a period of about
10 days after blowing to allow the bottles to age and to absorb
moisture from the atmosphere which is known to degrade hot-fill
stability. Then, the diameter of each bottle was measured at four
specified positions (upper bell, lower bell, upper bumper, lower
bumper) using a digital caliper. Next, the overflow volume of each
bottle was measured by filling it with cold tap water and measuring
the net weight of the water using a digital balance. Finally, each
bottle was subjected to the following hotfill procedure: (1)
quickly fill with water temperature controlled to 85.degree. C.;
(2) allow the unsealed bottle to rest on its base for 1 minute; (3)
seal the bottle with a threaded closure; (4) allow the sealed
bottle to rest on its base for an additional 1 minute; (5) immerse
the sealed bottle in a bath of cold tap water until it has cooled
to about room temperature.
[0084] After the bottles had cooled, they were removed from the
cooling bath and while still sealed the maximum and minimum
diameter was measured at each of the four specified positions.
Hot-fill-induced diameter shrinkage at each of the four positions
was calculated using the relation
Diameter Shrinkage=[Di-Dmean]/Di.times.100%
[0085] where Di is the initial diameter of the bottle and Dmean is
the arithmetic mean of the maximum and minimum diameters after
hotfilling. The arithmetic mean of the diameter shrinkage at the
four positions was calculated for a 10 bottle set for each
condition and is given as the Average Diameter Shrinkage (%) in
Table III.
3 TABLE III Average Diameter Shrinkage 800 BHM 1000 BHM Example
120.degree. C. 105.degree. C. 120.degree. C. 105.degree. C. 1 2.05
2.61 1.82 2.49 C-1 3.07 3.50 2.63 3.45 C-2 2.64 3.18 2.31 2.98 C-3
2.20 2.81 2.86 3.92
[0086] Table III shows that, for each of the blow molding output
rates (BHM) and blow mold temperatures (correlated to oil
temperature), the Average Diameter Shrinkage for the bottles of the
Example 1 composition was significantly less than that for the
bottles of Comparative Polyesters C-1, C-22, and C-3. It is
generally accepted in the industry that for a bottle to be deemed
to have acceptable hot-fill stability, the Average Diameter
Shrinkage determined by this procedure must be less than 3%. Table
III shows that the bottles of the Example 1 composition comfortably
meet this standard for all of the blowing conditions used, even at
the lower blow mold temperature. Conversely, the Average Diameter
Shrinkage of the bottles of Comparative Examples 1, 2, and 3 blown
using the lower mold temperature for the most part exceeds the 3%
limit and, in the best of cases, is below but very near the limit.
These results clearly show that the bottles of the Example 1
composition have hot-fill stability significantly superior to that
of the bottles of Comparative Polyesters C-1, C-2, and C-3.
[0087] Bottle ovality caused by hot-filling was calculated as the
difference between the maximum and minimum bottle diameters for
each of the four specified positions. It is a measure of the degree
to which a bottle becomes distorted upon hot-filling. The
arithmetic mean of the ovality at the four positions was calculated
for a 10 bottle set for each condition and is given in mm as the
Average Bottle Ovality in Table IV.
4 TABLE IV Average Bottle Ovality Caused by Hotfilling 800 BHM 1000
BHM Example 120.degree. C. 105.degree. C. 120.degree. C.
105.degree. C. 1 0.51 0.51 0.46 0.46 C-1 0.71 0.74 0.74 0.92 C-2
0.71 0.86 0.71 0.74 C-3 0.51 0.53 0.66 0.64
[0088] Table IV shows that, for each of the blow molding output
rates (BHM) and blow mold temperatures (correlated to oil
temperature), the Average Bottle Ovality for the bottles produced
from the Example 1 composition was significantly less than that for
the bottles produced from Comparative Polyesters C-1 and C-2, and
for the bottles of Comparative Polyester C-3 at the faster blow
molding output rate. This demonstrates that the bottles of the
Example 1 composition are more resistant to distortion during
hot-filling than are bottles made from commercial resins currently
being used in the industry to manufacture heat-set containers.
[0089] A different method to evaluate bottle shrinkage caused by
hot-filling is to measure the decrease in the bottle overflow
volume that occurs due to hot-filling. This measurement was carried
out as follows: (1) after aging but prior to hot-filling, the
overflow volume of each bottle was measured by weighing the empty
bottle on a digital balance; (2) completely filling the bottle with
cold tap water; and (3) weighing the filled bottle and subtracting
the weight of the empty bottle to calculate the weight of the
contained water. The volume of the bottle in cubic centimeters was
taken to equal the weight of water in grams. The bottles were
emptied of water, hot-filled with 85.degree. C. water as described
above, and the volume of the hot-filled bottles was determined in
the same manner as detailed above for the bottles prior to
hot-filling. The volume shrinkage for each bottle was calculated
using the relation:
Volume Shrinkage=[Vi-V]/Vi.times.100%
[0090] wherein Vi is the volume of the bottle before hot-filling
and V is the volume of the bottle after hot-filling. The arithmetic
mean of the volume shrinkage was calculated for a 10 bottle set for
each condition and is given as the Average Volume Shrinkage (%) in
Table V.
5 TABLE V Average Volume Shrinkage Caused by Hotfilling 800 BHM
1000 BHM Example 120.degree. C. 105.degree. C. 120.degree. C.
105.degree. C. 1 1.91 2.63 1.87 2.74 C-1 2.56 3.36 1.96 3.44 C-2
2.63 3.35 2.23 3.28 C-3 2.30 3.00 2.11 3.85
[0091] Table V shows that, for each of the blow molding output
rates (BHM) and blow mold temperatures (correlated to oil
temperature), the Average Volume Shrinkage for the bottles produced
from the Example 1 composition was significantly less than that for
the bottles produced from Comparative Polyesters C-1, C-2, and C-3.
It is generally accepted in the industry that for a bottle to be
deemed to have acceptable hotfill stability the Average Volume
Shrinkage determined by this procedure must be less than 3%. Table
V shows that the bottles of the Example 1 composition meet this
standard for all of the blowing conditions used, even at the lower
oil (blow mold) temperature. Conversely, the Average Volume
Shrinkage of the bottles of the Comparative Polyesters C-1, C-2 and
C-3 blown using the lower mold temperature is in each case greater
than the acceptable limit. These results clearly show that the
bottles of the Example 1 composition have hot-fill stability
significantly superior to that of the bottles of Comparative
Polyesters C-1, C-2, and C-3.
[0092] 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.
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