Note: Descriptions are shown in the official language in which they were submitted.
CA 02235486 2006-04-21
78186-3
Improved Infrared Absorbing Polyester Packaging Polymer
Background of the Invention
Field of the Invention
The present invention relates to packaging polymers,
particularly bottles made from packaging polymer
compositions, and particularly polyester polymer compositions
which have an improved infrared (IR) absorption
characteristic. More specifically, the present invention
relates to a polyester polymer composition that includes
graphite as an infrared absorbing material. The present
invention envisions the use of the polyester polymer
compositions to make plastic bottles with acceptable color
and clarity, and with good physical properties, and with
improved infrared absorbing properties as the key
characteristics.
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Prior Art
The use of polyester compositions as a packaging
material, particularly compositions comprising polyethylene
terephthalate generally referred to as "PET" in the form of
fi:lms, plastic and other containers is well known. Plastic
bottles are used in containing pressurized fluids, such as
carbonated drinks, such as softdrinks or mineral waters, as
well as in non-carbonated, non-pressurized drinks. To form
plastic bottles, the polymer is extruded and then formed into
chips. The chips are employed to make a bottle preform by
injection molding as is well known in the industry. The
preform is then reheated and blown into a mold which provides
the: final shape of the bottle. The blow molding step causes
biaxial orientation of the polyester composition to occur at
least in the side walls and the bottom of the bottles, and to
a lesser degree in the neck. The biaxial orientation
provides strength to the bottle so that it can resist
deformation from internal pressure during use and adequently
contain the fluid over an industry standardized shelf-life.
To summarize, a conventional polyester chip based on a
modified P,ET resin is generally shipped to plastic bottle
manufacturers who injection mold the polymer to make a bottle
preform. The preform must: be heated to about 105 C and blow
molded into a bottle shape. To reduce the energy required to
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heat the preform and to cause the preform to quickly achieve
the desired blow molding temperature of about 105 C would be
particularly useful in the industry. Of course, the blow
molding temperature varies for different polyester
compositions, for example, polyethylene naphthalate would
recluire a different blow molding temperature.
Heating a conventional polyester preform to about 105 C
is typically achieved witt- commercially available quartz
infrared lamps which emit in the near infrared region (NIR)
as well as in the infrared region (IR) as will be more
clearly explained later. The absorption of infrared radiation
by PET is low because PET tends to absorb infrared radiation
only at certain frequencies as will be described later.
Thus, the rate of heating PET is very dependent upon the
ability of the polymer re=sin to absorb the infrared radiation
and any components within the PET composition which can
impirove the absorption of infrared radiation is commercially
useful for bottle manufacturers.
U.S. Patents 5, 409, 983; 5,419,936 and 5,529,744 to
Tinciale and assigned to ICI disclose a polyester composition
which includes an infrared radiation absorbing material
comprising suitable metals which intrinsically absorb
radiation in the wave-length region of 0.5 microns to 2
microns (NIR and IR) to substantially reduce the reheat time
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of' the polymer or bottle preform. The suitable metals
ir,Lclude antimony, tin, copper, silver, gold, arsenic,
cadmium, mercury, lead, palladium, platinum or a mixture of
two or more of these. For most applications, the metals
silver, gold, arsenic, cadmium, mercury, lead, palladium, and
platinum are either too expensive or environmentally
hazardous and these metals are not particularly preferred..
The more desired metals are one or more of antimony, tin or
copper with antimony being particularly advantageous.
U.S. Patents 4,408,004, and 4,535,118 to Pengilly and
initially assigned to Goodyear disclose a polyester having
improved infrared absorbing materials contained therein. The
only infrared absorbing material mentioned is carbon black
including specific types such as channel black and furnace
black. The carbon black"has an average particle size from 10
to 500 nanometers and a concentration from 0.1 to 10 parts by
weight per million parts by weight of the polyester employed.
This composition also substantially reduces ithe time to heat
the preform to approximately 105 C.
European Patent Application EPA 739,933 in the name of
Sh:Lmotsuma et al. and assigned to Teijin Limited discloses a
po]Lyester resin composition which contains, as a laser
serisitive material, graphite having an average particle size
of 0.1 to 50 microns. This patent does not recognize that
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graphite is useful for absorbing infrared radiation. This
patent also is not related to bottle preforms, packaging
materials, or plastic bottles. In fact, this patent relates
to a printing technique for electric or electronic parts.
Summary of the Invention
The present inventiozi, in the broadest sense,' includes a
polyester resin containing graphite, the size of the graphite
par'ticles are such that they are not readily visible to the
naked eye when uniformly dispersed in the resin and are
present in an amount from 3 to 60 parts by weight per million
by weight of the polyester resin (ppm).
In the broadest sense, the present invention includes a
method of heating either'a polyester resin or a polyester
bottle preform by: exposing the polyester resin or polyester
bottle preform to infrared radiation for a sufficient time to
heat the polyester resin or polyester bottle preform to
greater than ambient temperature, wherein the polyester resin
or polyester bottle preform contains 3-60 ppm graphite
particles, the graphite particles being not readily visible
to the naked eye when unif'ormly dispersed therein. =
In the broadest sense the present invention also
comprises a bottle preform. which can be heated with IR
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heaters to the desired blow molding temperature, and blow
molded in the form of a plastic bottle, said bottle preform
being made from polyester that contains graphite particles,
with the size of the graphite particles being sufficiently
small such that they are not readily visible to the naked eye
when uniformly dispersed within the bottle preform. The
graphite particles are present in an amount from 3 to 60 ppm
based upon the amount of polyester resin.
In the broadest sense, the present invention also
comprises a plastic bottle made from polyester that contains
graphite particles, said graphite particles being
sufficiently small.that they are not readily visible to the
naked eye upon uniform distribution within the plastic bottle
anci are employed in an amount of 3 to 60 ppm based on the
amount of polyester.
Brief Description of the Drawings
Figure 1 is a chart of the PET Absorption Spectrum where
IR wavelengths are plotted against the absorption coefficient
(1/cm) of PET.
Figure 2 is a bar graph of Percent Overall Power at Blow
Molding Window where the % overall power of IR lamps is
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plotted against the control and 5 ppm, 7.5 ppm, 10 ppm, 15
ppm and 20 ppm graphite/polymer compositions.
Figure 3 is a bar graph of the Blow Molding Window where
the preform temperature (in C) is plotted against the
control and 5 ppm, 7.5 ppm, 10 ppm, 15 ppm and 20 ppm
graphite/polymer compositions.
Figure 4 is a graph of the percent maximum power to heat
a bottle preform to 105 C vs. the amount of graphite in the
preform in ppm.
Description of the Preferred Embodiments
Infrared radiation covers wavelengths from 0.8
microns to 500 microns, and is generally divided into near
infrared (NIR 0.8 to 2.5 microns), middle IR (2.5 to 50
microns) and far IR (50 microns - 500 microns). Heating
occurs because the infrared radiation penetrates into the
interior of the polymer and vibrates the molecules without
subjecting the polymer to heating by conduction.
Polyester, and particularly polyethylene terephthalate
(PET) can be heated by infrared radiation generally faster
anci more uniformly than by conduction heating, but PET
absorbs only a small portion of the IR wavelength. As shown
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iri Figure 1, which is a:plot of the absorption coefficient (1
over centimeter, which is the depth of penetration of the IR
radiation) vs. IR wavelength, (in microns) it is clear that
PET primarily absorbs the IR wavelengths around 5.9 and about
8.7 to 9.1. These correspond to specific bonds in the
polyester which are excited by the infrared radiation. From
Figure 1 it is easy to visualize that if polyethylene
terephthalate could be modified such that it could absorb
more of the wavelengths of IR, it would require less time to
be heated to approximately 105 C in a preform and plastic
bottle operation.
Of course, it is also necessary that the formed plastic
bottle still exhibit gooci clarity. If the particles of the
IR absorbing material, iri the case of the present invention-
graphite, are too large in size, then the particles scatter
the visible light wavelerigths and causes the bottle to appear
hazy and not clear, particularly from an aesthetic viewpoint.
If it is desired to make a plastic translucent bottle which
is brown or green in color for certain specific types of
softdrinks or alcoholic beverages such as beer, then the size
and amount of the graphit:e particles is not so important.
However, the industry does not want any particles to be seen
with the naked eye even in translucent colored bottles.
No:ntranslucent colored bottles which are capable of masking
the graphite particles can employ a broader size range of
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graphite, so long as the graphite does not appear on the
surface of the bottle. Such bottles can achieve the primary
goal of using less energy to heat the bottle preform for
blow-molding.
Graphite, which is a crystalline allotropic form of
carbon, most commonly exist in platelet form. For clear
bottles, the graphite particles should be greater than about
0.5pm (microns) in the largest dimension, and not readily
visible to the naked eye(as an upper limit). A preferred
range for graphite particle size is 0.6-8ym.
The amount of graphit:e employed may range from 3 ppm up
to 60 ppm based upon the weight of the resin. However, when
a clear bottle is preferred, having approximately 40 ppm or
more graphite (based on the weight of the resin) produces a
bottle that is smoky gray to dark gray in color. While this
may be acceptable for colored bottles, which the present
invention is intended to cover, the preferred range of the
present invention is between 5 and 20 ppm graphite, and more
preferably between 8 and 12 ppm. If desired, master batches
of the polymer composition, or raw materials thereof
containing quantities of the graphite in far higher
concentrations can be made for subsequent blending with the
polymer to achieve the desired levels of graphite in the
polymer.
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Suitable polyesters are produced from the reaction of a
diacid or diester component comprising at least 65 mole %
terephthalic acid or C1 - C4 dialkylterephthalate, preferably
at least 70 mole %, more preferably at least 75 mole %, even
more preferably, at least 95 mole %, and a diol component
con-prising at least 65 mo:le % ethylene glycol, preferably at
least 70 mole %, more preferably at least 75 mole %, even
more preferably at least 95 mole %. It is also preferable
that the diacid component is terephthalic acid and the diol
component is ethylene glycol. The mole percentage for all of
the diacid component total.s 100 mole %, and the mole
percentage for all of the diol component totals 100 mole %.
Where the polyester components are modified by one or
more diol components othe'r, than ethylene glycol, suitable
diol components of the described polyesters may be selected
froin 1,4-cyclohexanedimethanol, 1,2-propanediol, 1,3-
propanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol,
1,6=-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol,
1,2=-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, Z,8-
bis(hydroxymethyl)-tricyclo-[5.2.1.0)-decane wherein Z
represents 3, 4, or 5; and diols containing one or more
oxygen atoms in the chain, e.g., diethylene glycol,
triethylene glycol, dipropylene glycol, tripropyl'ene glycol
or mixtures of these, and the like. In general, these diols
CA 02235486 1998-05-04
contain 2 to 18, preferably 2 to 8 carbon atoms.
Cycloaliphatic diols can. be employed in their cis or trans
configuration or as mixtures of both forms. Preferred
modifying diol component are 1,4-cyclohexanedimethanol or
diethylene glycol, or a mixture of these.
Where the polyester components are modified by one or
more acid components other than terephthalic acid, the
suitable acid components (aliphatic, alicyclic, or aromatic
dicarboxylic acids) of the linear polyester may be selected,
for example, from isophthalic acid, 1,4-
cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic
acid, succinic acid, glutaric acid, adipic acid, sebacic
acid, 1,12-dodecanedioic acid, 2,6-naphthalenedicarboxylic
acid, bibenzoic acid, or mixtures of these and the like. In
the polymer preparation,'-it is often preferable to use a
fuinctional acid derivative thereof such as the dimethyl,
diethyl, or dipropyl ester of the dicarboxylic acid. The
anhydrides or acid halides of these acids also may be
employed where practical,. These acid modifiers generally
retard the crystallization rate compared to terephthalic
acid.
Also particularly contemplated by the present invention
is a modified polyester made by reacting at least 85 mole %
terephthalate from either terephthalic acid or dimethyl
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terephthalate with any of the above comonomers. The mole %
of all diacids is 100 mole %, and the mole % of all diols is
100 mole %.
In addition to polyester made from terephthalic acid (or
dirnethyl terephthalate) and ethylene glycol, or a modified
po:Lyester as stated above, the present inventions also
includes the use of 100% of an aromatic diacid such as 2-6
naphthalene dicarboxylic acid or bibenzoic acid, or their
diesters, and a modified polyester made by reacting at least
85 mole % of the dicarboxylate from these aromatic
diacids/diesters with any of the above comonomers.
Conventional production of polyethylene terephthalate is
well known in the art and comprises reacting terephthalic
acid with ethylene glycol'at a temperature of approximately
200 to 250 C forming monomer and water. Because the reaction
is reversible, the water is continuous removed, driving the
reaction to the productiori of monomer. Next, the monomer
undergoes a polycondensation reaction to form the polymer.
During the reaction of the terephthalic acid and ethylene
glycol it is not necessary to have a catalyst present.
Generally, during the polycondensation reaction, a catalyst
is preferred such as antimony. Using diesters, other diacids
and other diols may conventionally employee various catalysts
as is well known in the art. The manner of producing the
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polyester of the present invention by any conventional manner
is acceptable for the present invention.
In the making of bottle preforms and plastic bottles
from the preforms, it is often desired to produce the
cleanest clearest polymer. Accordingly, the less additives
employed, the clearer the polymer produced. On the other
har.id, it is sometimes desirable to make a colored plastic
bottle or bottles with other desired characteristics, and
thus the use of a variety of conventionally known additives
is also within the scope of the present invention.
Accordingly, various pigments, dyes, fillers, branching
agents, crystallization retarding agents, and other typical
agents may be added to the polymer generally during or near
the end of the polycondensation reaction. The exact desired
additives and the place onL introduction in the reaction does
not form a part of this invention and this technology is well
known in the art. Any conventional system maybe employed and
those skilled in the art can pick and choose among the
various systems of introduction of additives to achieve the
desired result.
The graphite may be introduced into the polyester
production process at any time. For example, if a diacid and
a glycol are being reacted the graphite could be introduced
during the esterification reaction or during the
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78186-3
polycondensation reaction. Because graphite primarily exists
in a platelet like structure, it naturally orients itself in
the direction of injection molding for the bottle preforms
and in the direction of blow molding during the production of
plastic bottles. This means that the platelets align
themselves with the walls of the preform or with the walls of
the plastic bottle such that their major surface corresponds
with the major surface of the bottle preform or plastic
bottle. The advantage of such an alignment occurs when the
bottle preform is subjected to infrared radiation. The
radiation is absorbed better by the graphite which is
oriented in a manner exposing its largest surface to the
infrared radiation thereby capturing and absorbing radiation.
The amount of energy needed to reheat the preforms
depends on the optimum temperature for stretch-blow molding
of the bottle. If the temperature is too low, the bottle
will have a pearlescence appearance, and if the temperature
is too high, the bottle will have a hazy appearance. This
temperature difference is called the blow-molding window. In
commercial operations the energy of the IR heating lamps is
set to heat the preforms to a temperature in the middle of
the blow-molding window. Figure 4 shows the energy required
to heat the preforms containing graphite, in a Sidel SBO 2/3
production machine, to a temperature of 105 C, and
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il.lustrates the lower energy requirement as the graphite
concentration increases.
Test Methods
The relative viscosity (RV) was determined by mixing 0.2
grams of the amorphous polymer composition with 20
milliliters of solvent consisting of dichoroacetic acid at a
temperature of 25 C and using a Ubbelohde viscometer to
determining the viscosity.
The haze of the amorphous polymer composition was
determined by visual observation.
Brightness and yellowness of the amorphous polymer
composition were determin'ed by using a digital color monitor
such as Hunter Lab Scan 6000. Usually the range of
acceptable brightness is 25-35. The lower the number the
grayer the polymer. For yellowness, a negative number
inciicates more blueness and a positive number indicates more
yellowness. Preferably the yellowness number is between -3
to -8 (not yellow, but not too blue).
Analysis of the DEG (diethylene glycol) content in the
amorphous polymer resin was also determined. An appropriate
portion of the amorphous polymer was hydrolyzed with an
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aqueous solution of ammonium hydroxide in a sealed reaction
vessel at 220+5 C for approximately two hours. The liquid
portion of the hydrolyzed product is then analyzed by gas
chromatography. The gas chromatography apparatus, was a FID
Detector (HP5890, HP7673A) from Hewlett Packard. The
ammonium hydroxide is 28 to 30 % by weight ammonium hydroxide
from Fisher Scientific and is reagent grade.
The CEG (carboxyl end groups) value of the amorphous
polymer is determined by dissolving a sample of the amorphous
polymer in reagent grade benzyl alcohol and titrated to the
purple end point of phenol Red indicator with 0.03N sodium
hydroxide/benzyl alcohol solution. The results are reported
as milliequivelents sodium hydroxide per kilogram of the
sample.
The analysis of acetaldehyde (A/A) in the amorphous
polymer in parts per million is determined by obtaining a
representative sample of the amorphous polymer, cryogenically
grinding the polymer (using liquid nitrogen) such that the
amorphous polymer passes through a number ten mesh sieve but
collects on a 25 mesh sieve. A weighted portion is then
heated at 160 C for 90 miri. in a closed system to release the
acetaldehyde. The acetaldehyde content of the headspace in
the closed system is then analyzed by gas chromatography and
the parts per million acet.aldehyde is determined therefrom.
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The gas chromatography apparatus employed is the same as that
employed for the DEG analysis.
The determination of' the amount of catalysts and the
sequestering agent in the amorphous polymer is determined by
employing a DC plasma emissions spectrograph. The
spectrograph employed is manufactured by Spectrometric Inc.
of Andover MA and is Model Spectraspan III high voltage DC
Plasma Emission Spectrograph. A sample of the amorphous
polymer is placed in a cassette and the cassette is
introduced into the spectrograph and the based line and the
slope of each catalyst and se'questering agent present is
determined. The catalysts employed in the Example are
antimony (Sb), manganese (Mn), and cobalt (Co) and the
sequestering agent is phosphorous (P).
.,,
The glass transition temperature (Tg) , melt temperature
(Tm), the temperature of maximum crystallization rate (T,,)
wa:> also determined. A d:ifferential scanning calorimeter
(DSC) is used to determine the temperature at the glass,
crystallization rate, and melt point transition. The rate of
temperature increase/decrease is 10 C per minute. The DSC
employed was a Model 910 DSC from Perkins Elmer. The DSC was
purged with nitrogen at a rate of 50 ml per minute.
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The percent isophthalic acid (IPA) present in the
amorphous polymer was determined using a Hewlett Packard
Liquid Chromotograph (HPL('-) with an ultraviolet detector at
285 nanometers. An amorphous polymer sample was hydrolyzed
in diluted sulfuric acid (10 ml acid in 1 liter deionized
water) in a stainless steel bomb at 230 C for 3 hours. After
cooling, an aqueous solution from the bomb was mixed with
three volumes of methanol (HPLC grade) and an internal
standard solution. The mixed solution was introduced into
the HPLC for analysis.
The Example
The samples in the Example were produced in a 500 pound
pilot line reactor. The polymer was prepared from 199
kilograms of DMT with 135 kilograms of ethylene glycol, and
with 82 parts per million manganese (using manganese
acetate), and 250 parts per million antimony (using antimony
trioxide), and 65 parts per million cobalt (using cobalt
acetate), and 1.4 weight % diethylene glycol(based on the
weight of the polymer). Eight batches were prepared overall
with 0, 5, 7.5, 10, 15, 20, and 50 parts by weight graphite
per million parts by weight polymer. The maximum ester
interchange batch temperat-ure was 250 C. During the ester
interchange reaction, the methanol was removed. At the start
of the polycondensation reaction 69.7 parts by weight
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phosphorus per million parts by weight polymer was added in
form of polyphosphoric acid as a sequestering agent to arrest
the ester interchange catalytic activity. Additionally, 2.5
wt. $(based on the weight of the polymer) of isophthalic
ac:Ld was employed, thus forming the copolyester polyethylene
terephthalate isophthalate. The results of this Example are
set: forth in Table 1.
TABLE 1
AMORPHOUS POLYMER
TYPE RV Ydlowness Br(ghtnas DEG CEO A/A Sb Aln Co P Tg Tc Tm IPA
% PPM PPm PPm PPM PPM %
Cantrd 1.887 =7.1 31 1.51 22 73 216 75 64 67 78.4 168 245.3 2.29
GRAPHRE
Praplw1e-5 1.871 -5.3 26.3 1.55 20 104 196 79 60 60 79.1 158.4 246 2.3
Gaphits_7.5 1.893 -6.9 25 1.59 23 112 197 78 62 69 79.3 156.9 246.1 2.32
Graphits10 1.887 -5.8 24.8 1.68 22 73 214 76 68 70 78.8 166 245.4 2.34
GiaPhils15 1.892 46 24.1 1.54 23 83 202 76 63 72 78.8 162.6 245.7 2.31
Graphita20 1.900 -6.7 21.1 1.56 21 68 224 74 65 69 78.8 164.6 245.1 2.41
Gaphile50 1.892 -4.6 16.3 1.7 23 64 198 76 56 66 78.2 163.5 245.1 2.36
,= '
Table 1 shows that the various graphite samples (except for
the 50 ppm sample) have substantially the same features and
properties as the control. The 50 ppm sample actually had
the best (lowest) acetaldehyde level, but brightness
properties were not satisfactory for making clear bottles.
Green or brown colored plastic bottles may be produced with a
50 ppm graphite polymer.
The blow molding windows and preform reheat properties
of the PET control & PET containing 5, 7.5, 10, 15 and 20 ppm
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of graphite were analyzed at Plastic Technologies, Inc.
(Holland, OH). The bottles were blown on a Sidel SBO 2/3
production machine using a single 2-liter generic carbonated
soft drink bottle mold. First, the blow molding conditions
were optimized for an appropriate control resin. A "heat
scan" was then performed on the control resin by lowering and
raising the percent overa:Ll power of the quartz oven lamps in
2% increments. Ten bottles were blown at each percent
overall power and one of the middle bottles was observed for
amount of pearlescence or haze. The preform temperature at
the oven outlet of the SBC) machine was recorded using an
infrared pyrometer that reads the surface temperature of the
preform (the variability of the infrared pyrometer is about
1 C). The blow molding window of the resin was defined as
the temperature range of the preforms that yielded a slightly
pearlescent to a slightly hazy bottle. Using the control
pol.ymer's optimized blow molding conditions, heat scans were
thein performed on the other resins.
The control and the 5 ppm, 7.5 ppm, 10 ppm, 15 ppm and
20 ppm graphite polymer samples were injection molded into
bottle preforms and blown into plastic bottles.
Figure 2 shows the percentage of overall power employed
by the infrared lamps necessary to heat the samples, namely:
the control having no graphite, and the 5 ppm, 7.5 ppm, 10
CA 02235486 1998-05-04
ppm, 15 ppm and 20 ppm graphite samples. This Figure clearly
shows that less power is used by the IR lamps (in the Sidel
SBO 2/3 machine) to heat the polymer to a temperature such
that it can be blow molded into an acceptable plastic bottle
(approximately 105 C) when graphite is employed.
Figure 3 shows the blow molding window for the bottle
preforms (set forth in Figure 2) versus the preform
ternperature (in C) . The blow molding window is the
tennperature range where the preform can be blow molded into a
plastic bottle. If the temperature is too cool (generally
below approximately 100 C) blow molding will cause cold
stretching of the polymer, creating a whitish-color in the
bottle referred to as pearlesence. Obviously stretching at
too cold of a temperature is not desired as it affects the
physical properties, the-'ability of the bottle to properly
con.form to the shape of ttie mold when being blown, and the
overall appearance of the bottle. On the other hand, if the
temperature is too hot the bottle develops haziness and is no
longer transparent. For riontransparent colored bottles, for
example, slight haziness would be masked by the pigment.
Thus it is apparent that there has been provided, in
accordance with the invention, a product and process that
fully satisfies the objects, aims, and advantages set forth
above. While the invention has been described in conjunction
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with specific embodiments thereof, it is evident that many
alternatives, modifications, and variations will be apparent
to those skilled in the art in light of the foregoing
description. Accordingly, it is intended to embrace all such
alternatives, modifications, and variations as fall within
the spirit and broad scope of the appended claims.
,n
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