Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~7~1 15278
POLY(ETHYEENE TEREPHTHAL~TE) A~TICLES AND METHOD
This invention relates to improved methods of making hollow,
-- biaxially oriented, heat set partially crystalline articles. In
another aspect it relates to biaxially oriented, heat set hollow .
S poly(ethylene terephthalate) articles having a density o over
1.3860 and low permeabilities to carbon dioxide and oxy~en
gases, and also having a high "Qnset-of-shrinkage" temperature
compared with hollow articles heat set according to prior art
processes.
In order to i~.prove several physic:al properties ~f hollow
articles such as bottles made ~rom poly(ethylene terephthalate),
it has been suggested that biaxially oriented poly(ethylene
terephthalate) hollow articles, made by orientation blow molding
of a preform ~r parison under conditions to provide biaxial
orienta~ion and concomitant crystallization, be fur~her heat
treated at higher temperatures than the orientation blowing
temperature ~o further increase the density (or crystallinity)
of the hollow article. Such increasing of the density or
crystallinity by heating after shaping under orientation
conditions is commonly known as heat setting.
Wyeth et al. in U. S. Patent 3,733,309 suggests such a
process. However, the heat setting process is mentioned only in
passing and no speciic examples including heat setting are
present in the patent. Of course, the extra step would
ordinarily add considerable expense to the bottle making
process.
Collins in U.S. Patent 4,039,~41 discloses heat setting containers of an
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organic crystallizable synthetic thermoplastic polymeric
material. Among such materials di~closed are high density
polyethylene, polypropylene homopolymers and copolymers and
polyesters such as poly(ethylene terephthalate) and
poly(butylene terephthalate), including copolyesters such as
ethylene terephthalate/isophthalate copolymers. In a preferred
embodiment, heat setting is accomplished by blowing the plastic
parison in a heated blow mold, preheated to the heat setting
temperature.
It is stated in Collins that the heat setting temperature
used is that normally encountered in heat setting of oriented
films or fibers made from the given plastic material. It is not
stated, however, what heat setting tempeeatures are "normal" for
making oriented films or fibers from poly~ethylene
terephthalate). See Collins, infra. However, for this plastic
it is disclosed ;n Collins that the mold is preferably
~aintained at 130 to 220C.
It is disclosed in Collins that after heat setting, the
container should be cooled down to a temperature, for instance,
below about 60C. In one example of Collins, the heat setting
temperature of the mold is 200C. and in the other, it is 140C.
In unexamined Japanese Patent Application No. 146,175, laid
open November 15, 1980, containers are stretch blow molded under
conditions to biaxially orient the polyester molecules~ It is
explained that as a result of the stretch blow molding, the
residual strain was large and that when heated subsequent to the
molding, the residual strain was released, causing deformation
of the container. To solve this problem, the reference
recommends heat setting the containers after blow molding. It
is also recommended that the heat settang temperature in
unstretched areas such as the neck be held to 95-125C. so that
hazing will not occur in these areas. Other areas are heat set
at a higher temperature. It is recommended that the heat
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setting of the highly strained areas o the container be in the
range from 125~C. to 235~C. However, guenching of the heat set
container at lO~C. or above is not disclosed.
Unexamined Japanese Patent Application No. 77,672, laid open
'.! June 21, 1979, is similar except that it is not taught to heat
set unoriented parts at a lower temperature than other parts.
~he highest temperature disclosed for heat setting is 130C. and
in the only specific example the oriented blow molded bottle is
heat set by contacting with the hot blow mold kept at 130C. and
:~ then lowering the mold temperature to 100C. to prevent bottle
deformation when the bottle is discharged from the mold. In
~his reference, it is stated that hazing occurs when highçr heat
setting mold temperatures are used. The reference does not
disclose the present method or the novel products of the present
'1~ invention.
In unexamined Japanese Patent Application No. 21,463, laid
open February 17r 1979, a blown polSr(ethylene terephthalate)
bottle was heat set by heating the bottle to 140C. while still
within the blow mold.
~0 In unexamined Japanese Patent Application No. 78,~6~, laid
open June 11, 1978~ there is disclosed stretch blow ~olding a
thermoplastic resin, in the example specifically poly(ethylene
terephthalate~ to make a hollow article, and while the article
is still in the mold to introduce hot gases for purposes of heat
~5 setting. In the example, the hot gas is at 180~C~ The example
does not disclose cooling the heat set article before removal
from the mold, but the description of the drawing does describe
this as an alternative treatment, using normal temperature
compressed gas to cool the molded piece.
In unexamined Japanese Patent Application No. 66,968, laid
open May 29, 1979, methods of reducing residual strain in
biaxially oriented blown bottles are disclosed. The methods are
applied to unidentified, saturated polyester resins. In all of
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the methods the bottle is heated, a~ter being formed by biaxial
orientation blow molding by one method or another. After the
heat treatment the bottle i5 cooled, but the temperature to
which the bottle is cooled is not disclosed. The heating step
apparently includes heating the neck portion of the bottle,
since in one method the heating is by passing steam through
channels 8 which include channels 8 next to the neck, and in
another method heating is carried out by high temperature
pressurization of the interior of the bottle, which of course
includes the neck.
In unexamined Japanese Patent Application No. 78,268, laid
open June 11, 1978, a stretch blow molded hollow body, including
those made from poly(ethylene terephthalate) is heat set by
introducing hot ~as under pressure into the interior of the
bottle while in the mold. AEter the heat setting, normal
temperature gas can be optionally blown into the article to cool
the article before removal from the mold, or the heat set body
can simply be exhausted to atmospheric. In an example, the
heated gas ~or heat setting is at 200C. In the specific
example, no cooling before removal from the mold was disclosed.
Again, the heating includes heatin~ of the neck portion of the
bottle.
In unexamined Japanese Patent Application No. 41,973, laid
open April 3, 197g, it is disclosed to heat set stretch blow
molded containers, including those madP from poly~ethylene
terephthalate) by heating the blown containers at a high
temperature and then rapidly cooling them to room temperature.
Heat treatment can be within the mold while under pressure and
the heating can be by means of a hot mold. It is disclosed that
the heat treatment should be such that ~he density of the bottle
body following the heat treatment is no greater than 1.40
gms./cc. In the example given, steam at 179C. is used for
heating the mold in the heating step.
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' Sc~lett W.S. Pa-tent 2,823,421 discloses heat setting of pEr films using
heat setting temperatures of 150-250C. after orientation
stretching. This patent does not state, however, what "normal"
PET film heat setting temperatures are~ It does disclose that
for a film stretched three times in each direction that a heat
setting temperature of 200C. is preferred by Scarlett.
German Patent 2,540,930 discloses heat settmg of hollow articles.
The blank or parison is blow molded at 70-140C. and then cooled
in the mold to below 70C. Thereafter, the bottle can be
~0 reheated to heat setting temperature in that mold or in a
different mold. The heat setting temperature is said to be over
140C. or higher. In the disclosed process the entire bottle
including the neck is heated in the heat setting step to the
same temperature and the neck of the bottle crystallizes to an
opaque state.
In Brc~dy et al. U.S. Pa-tent 4,233 022 a bo-t-tle orien-ted by blow moldinq
PET at 75-100C. is heat set. Heat setting is accomplished in a
hot mold at a suitable heat setting temperature; examples of
such temperatures are given as 150 to 220C. The patent
features controlling di~ferent zones of the bottle at different
temperatures, so that all the sidewall of the bottle is at the
maximum heat setting temperatures being used, but the finish or
neck, for instance, is actually coolea to prevent
crystallization thereof. In this patent after the heat setting
step, it is stated that the bottle is cooled to a self-
sustaining condition.
In one embodiment the present process features biaxially
orienting a parison preheated to orientation temperature, by
inflating in a blow mold which has been preheated to the higher,
heat setting temperature and holding the bottle or other hollow
article against the mold wall for the short time necessary
to effect heat setting. The process of the present invention
also features thereafter cooliny the heat set hollow article or
,
bottle while under pressure but not below 100C. and then
exhausting the pressure in the bottle to essentially atmospheric
or ambient pressure before further coolin~ of the article below
100C~ takes place.
The prior art merely discloses that the bottle needs to be
cooled to a self-sustaining condition or it discloses that it
must be cooled to some specific temperature which is obviously
very low and at which such bottles are self-sustaining.
~or instance, Collins 4,039,641 specifically discloses
cooling to below 60C. and in one specific example cools to
40C., before releasing the gas pressure.
I have found that the "onset-of shrinkage" temperature for
the heat set sidewall of the poly(ethylene terephthalate) hollow
articles or containers of the invention depends on the density
of the sidewall and the temperature to which the hollow article
is cooled before the inflating pressure of the article is
exhausted to essentially atmospheric pressure.
The onset-of-shrinkage temperature referred to herein was
determined as described in Brady and Jabarin "Thermal Trea~ment
of Cold-Formed Poly(Vinyl Chloride) Polymer Engineering and
Science", pp. 686-90 of VolO 17, No. 9, September, 1977, except
that the samples were cut from the sidewalls of the bottles. No
thermal treatment was effected on the cut samples prior to the
tests.
~5 Ordinarily, when a PET bottle is blown in a blow mold, i~ is
cooled to guite a low temperature, a temperature very much below
the temperature at which the bottle would be selE-su~taining, in
~act much below the temperature at which the bottle will shrink
at all when the pressure is released. According to an important
feature of the present invention, I cool the heat set bottle,
while still under pressure preventing shrinkage, to a
temperat~re which will allow the volume of the hollow articl~ to
shrink no more than 6 percent, preferably 5 percent, when the
pressure is removed and allowed to cool to room temperature, but
no lower than 100C., before releasing the pressure to equalize
it with the ambient atmosphere. I have discovered that cooling
under pressure, i.e. when not allowing shrinkage, below 100C.
progressively reduces the onset-of-shrinkage temperature even
when the final room temperature volume remains the same and does
not decrease with decreasing "quench" temperature. Thus,
referring to the tables described hereafter, it will be seen
that the volume remains essentially constant for quench
temperatures of 90~C. and below but that the onset-o~-shrinkage
~empe~ature becomes progressively lower. It has also been found
that the trend continues above 100C. quench temperature, i.e.
that the onset-of-shrinkage temperature increases as the quench
temperature increases above lD0C~
One advantage of the present process is that a great
decrease in cycle time is obtained in my heat setting process
over processes disclosed or suggested in the prior art, because
the bottle is left in a mold only for the time necessary to cool
it to the relatively high temperature range before indicated, so
that the next cycle can be immediately started; or the bottle
can be immediately ~emoved from the mold in one embodiment
without cooling.
The process o~ the present invention, as well as the
product, is concerned with polymers of poly(ethylene
terephthalate3-having an inherent viscosity of at least 0.6.
Poly(ethylene terephthalate) polymers useful in the present
invention insluaes
polymers where at least 97% of the polymer contains the
repeating ethylene terephthalate units of the formula:
--OCH 2C H 20C ~ C--
I
. ,
.,
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. . _.. __.. _ _ . ... _ ... _.. .... .. .. . ..
t79~j~
.
with the remainder being minor amounts of ester-forming
components, and
copolymers of ethylene terephthalate wherein up to about 10
mole percent of the copolymer is prepared from the monomer units
selected from butane-1,4-diol; diethylene glycol; propane-1,3-
diol; poly tetramethylene glycol); poly ethylene glycol);
poly(propylene glycol); 1,4-hydroxymethylcyclohexane and the
like, substituted for the glycol moiety in the preparation of
the copolymer, or isophthalic; naphthalene 1,4- or 2,6-
dicarboxylic; adipic; sebacic; decane-l,10-dicarboxylic acids,
and the like, substituted for up to 10 mole percent of the acid
~oiety ~terephthalic acid) in the preparation of the copolymer.
Of course, the poly~ethylene terephthalate~ pclymer can
include various additives that do not adversely affect the
polymer. For instance, some such addi~ives are stabilizers,
e.g., antioxidants or ultraviolet light screening agents,
extrusion aids, additives designed to make the polymer more
degradable or combustible, and dyes or pigments. Moreover,
cross-linking or branching agents ~uch as are disclo~ed in U.S.
Patent 4,188,357 can be include~ in small amounts in order to
increase the melt strength of the polytethylene terephthalate).
It is an object of the present invention to provide an
improved manipulative process for produci~g poly(ethylene
terephthalate) hollow articles which are biax;ally oriented,
heat set and highly crystalline as indicated by density, which
process results in a maximum efficiency o~ production.
It is another object of the present invention to provide a
process for producing a poly(ethylene terephthalate) hollow
article having superior oxygen and carbon dioxide permeability
properties and having increased thermal stability (high onset-of-
shrinkage temperature~ It is a further object to provide such
poly~ethylene terephthalate) hollow articlès havin~ a
combination of such superior properties never before disclosed
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in the art~ The highly crystalline nature of such new products
and the permeability properties are directly related to their
density, so that the new products of the present invention have
high densities and consequently low permeabilities coupled with
higher onset-of-shrinkage temperatures not known in the prior
art for heat set poly(ethylene terephthalate) hollow articles.
Other objects, as well as aspects and advantages, of the
present invention will become apparent from a study of the
specification.
In one of its broadest aspects the process of the invention
comprises
(1) biaxially orienting the body of a hollow article by blow
molding a hollow poly(ethylene terephthalate) preform preheated
to a suitable orientation temperature range,
(2) while said article is still under pressure sufficient to
maintain its essential size and shape, heating to a higher
temperah~e in the range 200 to 250C. the portions thereof that
it is desired to crystallize, thereby increasing the density of
such portions, and
~ 3) while said article is still under a pressure sufficient
to maintain its essential size and shape, cooling said article
to a temperature at which it maintains its shape even without
internal pressure above atmospheric but not below 100~C., and
(4) thereafter exhausting the pressure from the hollow
article at said temperature and allowing the article to cool
further while not under internal pressure. Steps (3) and (4)
result in a heat set article having a higher "onset of
shrinkage" temperature tban i all cooling or guenching be done
under pressure down to ambient temperature.
According to an imp~rtant aspect of the present invention I
have provided a method of making a high density, partially
crystalline, biaxially vriented hollow poly~ethylene
i terephthalate~ plastic article having a neck or finish portion
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comprising
(1) enclosing a tubular paris~n of sa~d poly(ethylene
terephthalate), having a closed end and an open end destined to
form the neck or finish of the hollow article, within a blow
mold, which parison is at a first temperature range, which first
temperature range is conducive to orientation during stretching,
(2) while said parison is still at said first temperature
range expanding said parison into contact and conformance with
the blow mold walls by inflation with a gas under pressure to
make a hollow blown article, said stretching and expanding under
the resulting strain conditions resulting in biaxial orientation
and concomitant partial crystallization, and then while the
article walls are still inflated in contact with said mold
walls, raising the temperature of the article to a higher second
temperature in the range 200 to 250C., except for the neck or
finish portion of said article whic:h is kept at a low
temperature such that crystallizati.on is minimized or eliminated
so that the neck or finish portion remains transparent; this
temperature is usually in the range of 40-125C., more usually
40-~0C., but any non-crystallizing temperature o~ 125C. or
~elow can be used,
(3) wherein the heating in said second temperature range
heat se~s the body of said article by causing further
crystallization thereof as indicated by density increase,
(4) and while said hollow article is still at a shrinkage-
resisting pressure exceeding atmospheric, cooling said article
to a temperature at which it maintains its shape when not
pressurized but not ~elow lOO~C~, and
(53 thereafter reducing the gas pressure within said
article to essentially ambient pressure.
According to another aspect of the present invention, there
is provided new a product which is the product of the foregoing
process: a transparent hollow article of polytethylene
, . ~10--
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terephthalate) having an inherent viscosity of at least 0.6
dl.~gm., the body portion of said article being biaxially
oriented and heat set and having a density over 1.3860 gm./cc.
and an onset-of-shrinkage temperature of over 80~C.
In a preferred embodiment of the present process the heat
setting second temperature is in the range of 225 to 250~C. The
product of this preferred process is a transparent hollow
article of poly(ethylene terephthalate) having an inherent
viscosity of at least 0.6 dl./gm., the body portion of said
article being biaxially oriented and heat set and having a
density over 1.3930 gm./cc. and an onset-of-shrinkage
temperature of over 105~.
Thus, the present process of orientation blow molding and
heat setting not only produces articles with increased density
(crystallinity), with the known decrease in oxygen and carbon
dioxide permeabilities but it also has the following advantages
over the prior art:
(1) increased productivity rate because of decreased cycle
time,
t2) compared to prior art heat set PET bottles, higher
onset-of-shrinkage temperatures, important for hot-fill
packaging ~f flu~d products, and
(3) ener~y savings because of lack of necessity to
repeatedly cool the mold to low temperatures each cycle.
Figures 1, 2 and 3 ~re each the same view looking at the
~lat side of one-half of a split blow mold, each showing the
hollow plastic in various stages. Thus, in Figure 1 the
parison 1 is shown after it is enclosed in the two halves of the
split blow mold but before any air pressure has been applied.
Fi~ure 2 shows parison 1 extended by the blow pin and Figure 3
shows the completely blown bottle ?.
The apparatus shown in the drawings and the description of
its operation herein are suitable for effecting the process of,
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and making the product sf, the present invention, and were used
in the specific examples discussed hereafter. However, other
specific blow molding apparatus can of course be used to effect
the orientation blow molding at one temperture, heat setting at
a higher temperature and subsequent cooling under shrinkage-
resisting pressure to a desired temperature according to the
invention and, finally, the exhausting of the internal pressure
from the hollow article.
ln the drawings, 3 is body of the blow mold ~i.e., one-half
thereof), made ~p of neck ring 4, lower section 6 and upper
section 7. Sections 6 and 7 are mostly separated by air gap 8
to minimize heat conduction therebetween and 6 and 7 are in
physical contact only at narrow annular band 9. Lines 11 and 12
are provided for introducing cooling water into and from,
respectively, channels (not shown1 in 6. Lines 13 and 14 are
provided for introducing cooling water into and from,
respectively, neck ring 4 (one of the split halves of which is
depicted in the figures). Lines 1~ and 17 are for introduciny
oil ~or heating or cooling the mold, as the case may be, into
and from the mold, respectively. Each of 11, 13 and 16 are
connected to an appropriate source (not shown) of fluid under
pressure~
Electric resistance strip heater 18 encircles the bottom of
~ec~ion 7 and is used to help make up for loss of heat flowing
vertically ~rom section 7 to section 6.
Blow mandrel 19 is shown inserted in parison l; the blowing
air is introduced into parison 1 via line 27 through cylinder 21
and passageways (not shown~ in the end of mandrel 19, and the
same passageways serve ~or exhaustion of air from the blown
article. Cylinder 21 contains a mechanism which includes a
piston ~not shown) that has an O-rin~ that forms a seal against
the top of the mandrel during operation. St~etch rod 22 is
vertically movable through 21 and 19 by means not sh~wn.
.
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In operation, a preheated injection molded parison 1 is
enclosed in the split blow mold as shown in Figure 1 and the
mandrel is inserted. The upward progress of stretch rod 22 is
begun a split second before introduction of blowing air through
mandrel 19 and then the blowing air is introduced to blow the
bottle against the walls of the mold. The stretch rod during
initial blowing arrives at the position shown in Figure ~ and is
retracted before the blowing air is evacuated. The neck or
finish area during the entire process is kept cool by the
circulating cool water flowing through the halves of upper mold
sections 6 and neck ring halves 4. During the orientation
blowing and heat setting step, section 7 is maintained at the
desired heat setting temperature by circulating hot oil through
16, 7 and 17 and by heating the lower part of section 7 with
resistance heater 18.
While Pigure 2 shows parison 1 elongated without any
increase in the hoop direction, undoubtedly 1 is actually partly
inflated before it reaches the position shown in Figure ~, so
that axial mechanical stretching and pneumatic in~lation are
occurring together. Although my apparatus was run as described
here and as described in c~nnection with the examples, it ;s
equally possible (1) to complete the axial mechanical stretching
before beginning pneumatic inflation, or, on the other hand, ~2)
not to use any mechanical axial stretching with the stretch rod
at all; indeed, many commercial biaxially oriented bottles are
made by blow molding without the use of any ~echanical axial
stretching~
In the drawings 23 and 24 ~re thermocouples positioned as
shown and 1/8 inch from the mold cavity wall. In extensive
testing, it was shown that the temperature varied only about 4
to 5~. between the two thermocouples with the hottest
temperature being at 23 near the bottom of the bottle.
After heat setting for the desired time, the hot oil is
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. displaced by a continuous flow of room temperature oil to cool
the bottle to the desired "quench" temperature as determined by
the average of the two thermocouple temperatures. Then the
pressure is released and the mold opened.
In the apparatus described a series of bottles of the shape
shown in Figure 3 were blown under biaxial orientation
conditions, heat set by contact with the hot mold and guenched
to the temperature indicated in Tables 1 and 2. Then the
pressure was released and the mold was opened. In two minutes
each bottle, after release of the pressure, was filled with
room temperature water and the volume measured by measuring the
water used. Unless noted otherwise, each bottle was made from
poly(eth~lene terephthalate) having an inherent viscosity of
0.72 dl./gm. Various properties were obtained as indicated in
the tables.
For comparison or control purposes, a bottle was blown
identically to the others except that it was blown into a cold
mold and cooled to 23C. Thus, the! control had no heat setting
but was only biaxially oriented and not heat set, during the
course of which its density inrreased to 1.3634 gms./cc. Its
onset-of-shrinkage temperature was 45C.
The ~ottles in the examples represented by the data in
Tables 1 and 2 were made from injection molded parisons having
the general shape shown in Figure 1. They were 7.2 inches long
with a wall thickness of 145-150 mils and weighed 2~ gms. The
parisons were preheated to about l90DF. (outside surface l90~F.,
inside surface 188~F~). The parison at this temperature was
enclosed in the split halves of the blow mold, one-half of which
is shown in Figure 1. Then the stretch rod 22 was pushed
against the bottom o the parison for 0.15 second before the
blow pressure air was applied at 100 psig for 0.5 second, after
which it was increased to 300 psig, and the stretch rod was
maintained in the position shown on Figure 2 for 2 seconds and
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was then retracted~ At all times cold water circulated through
lower mold section 6 and neck ring 4 so that the unexpanded neck
was kept cold~ ~he blown bottle is of course blown against the
blow mold wall, which is maintained at the heat setting
temperature shown in Table 1 or 2 for the time shown in the
table. After this time, cold oil was circulated to replace the
hot oil for the length of time needed to l~wer the temperature
to the quench temperature shown in the tables. Once this
temperature was reached, the bottle was exhausted to atmospheric
and the mold was opened. The bottles are thereafter allowed to
cool, eventually to room temperature, without internal pressure.
In the examples summarized in Tables 1 and 2, the bottles
were all well-shaped unless indicatèd as "deformed". Also, the
nominal overflow volume of the bottles with no shrinkage is
about 522 cc.
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TABLE 1
Heat Quench Density(l) Volume ~nset
Setting Temp.. gm./cc. 2 min.C2) 24 hrs. Temp.~C.
~. ~ec. cubic centimeters
250 30148 1.4013
2S0 120148 1.4022
240 6lB0 1.3980 497O9 497.4
240 6170 1.3~80 501.9 501.6
240 6160 1.3980 506.2 506.1 184
240 6150 1.3980 509.3 509.2
240 6130 1.3978 513.9 514 172
2~0 6120 1.3978 516.1 515.9 16
240 6110 1.3978 518.5 518.4
240 6100 1.3g65 ~19.4 519.7 154
240 6 90 1.3970 520.8 S20.9 193
240 6 ~0 1.3g86 521.7 521.7 139
240 6 80 1.3982 none(3) 521.8
240 6 60 1.3982 521.8 522.1 132
230 6170 1.3950 493.1 493.6
230 6160 1.3950 499.5 498.8 168
230 6150 1.3950 ~04.1 503.8
230 ~14~ 1.3950 5~9.0 ~08.6
230 ~129 1~3950 512 511.6 148
~30 61~4 1.3947 514.1 ~13.7 ~3
230 6100 1.3g47 520.7 519.8 12~
230 6 85 1,3945 ~21.1 520.6 113
23~ 6 75 1.3945 521.4 520.9 10~
230 6 60 1.3950 521.8 521.B 88
(1~ at mid-sidewall
~2) overflow volume measured by fillin~ with LOOm kemperature
water 2 minutes a~ter opening mold.
(3) allowed to cool 24 hours in air without filling with water
until then.
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;.
TABLE_2
~eat Quench Density(l) Volume Onset
Setting Temp~C. gm./cc. ~ min.(~) 24 hrs. Temp.C.
C. Seo. cubic centimeters
220 6160 1.3912 Deformed
220 61~0 1.392~ 500.9 500.7
220 61~0 1.3910 502.9 502.9
220 6135 1.3912 506.0 505.8114
220 612~ 1.3914 513.9 513.6108
220 6110 1.3918 517.5 517.4100
220 61~0 1.3918 519.8 519.594
220 6 90 1.3923 520.5 520.588
220 6 ~0 1.3919 521.2 521.483
2~0 6 60 1.3922 521.5 521.576
200 6140 1.3867 Deformed
200 6130 1.3867 ~96.5 495.7102
200 6115 1.3868 513.0 513.095
200 6100 1.3877 519.9 519.884
200 6 90 1.3870 519.~ 520.080
~00 6 8~ 1.3860 520.8 520.478
200 6 60 1.3872 521.0 520.~74
130 6100 1.3702 509 508.474 (Deformed)
130 1~0100 1.3744 512.2 511.i74 ~Deformed)
(1) at mid-sidewall
(2) overflow volume measured by filling with room temperature
water 2 minutes after opening mold
(3) allowed to cool 24 hours in air without filling with water
until ~hen.
~he last two examples are a repetition of the example in Jap.
77,67Z, infra. The bottles were misshapen, i.e., they were
completely out of round, and of course, they have lower onset
temperatures and the densities are lower than the products of
the invention.
7 ~ 61
. The bottles made at 250C. heat setting temperature were
made of 0.9 inherent viscosity PET.
From the result~ shown in Tables l and 2 it will be seen
that I have discovered, surprisingly, that the onset-of-
shrinkage temperature (for a given density oriented and heat set
hollow article) becomes lower as the quench temperature becomes
lower, even when the volume stays constant. Thus, I have
discovered that higher quench temperatures, where the guenching
takes place while the hollow article is restrained against
shrinkager gives higher onset-of-shrinkage temperatures.
In Table 3 are shown results of tests for the permeation of
oxygen and of carbon dioxide for one~half liter bottles made
according to the invention.
The determination procedures were as follows:
Carbon dioxide barrier properties of containers were
determined by a gas chromatographic method. Containers were
placed in a test ~ixture in which carbon dioxide gas at one
atmosphere absolute was established and maintained at the
outside surface and dry nitrogen gas at one atmosphere absolute
at the inside surface. Carbon dioxide permeates through the
wall from the outside to the inside of the container. The
nitrogen gas inside the container was periodically sampled for
permeated carbon dioxide with a gas chromatograph. The rate of
carbon dioxide permeation was determined from the rate of
increase of CO2 concentration in the nitrogen gas inside the
container. The system was calibrated by using an assayed
calibrting gas of CO2 in nitrogen supplied by Matheson Gas
Products. Carbon dioxide test gas was moisturized to ~0-100%
relative humidîty in the test fixture by evapnration of water
~rom several sponges~ Test temperature was controlled by
- placing the entire apparatus in a closed room which was
controlled at 73 2F~
A method employing a Hersch coulometric detector was used to
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~1~7~6~
de~ermine oxygen barrier properties of containers. The
apparatus is similar to an Oxtran*100,Permeation Analyzer
manufactured by Modern Controls, Elk River, Minn. A test
fixture was used to establish oxygen and nitrogen gases at one
atmosphere absolute at the outside and inside surfaces of the
conta;ner respectively. Oxygen surrounding the outside sur~ace
was continuously replaced by a flowing gas stream which was
vented to the atmospheric environment. The nitrogen gas inside
the container was also a flowing system and served as a sweep
gas. Oxygen permeated through the wall from the outside to the
inside of the container where it was picked up by the nitrogen
sweep gas and carried to the coulometric detector for
mea~urement and ventin~ to atmosphere. The output of the
detector is directly proportional to the amount of oxygen it
receives and calibration is computed from well established laws
of electrochemistry. Both oxygen and nitrogen gases were
moisturi2ed by bubbling through tubes of water prior to entering
the test fixture. Test temperature was controlled by placing
the apparatus in a closed room which was maintained at 73 ~ 2F.
The results in the following Table 3 are for nominal one-
half liter bottles made from parisons each wei~hing about 25.85
grams and made a~ described for the bottles in connnection with
Tables 1 and 2. The control bottles were merely blown under
oriPntation conditions as before described and ~uenched to near
room temperature without heat ~etting while the heat set bottles
were heat set at 241C. as indicated.
*trademark
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7~361
TABLE 3
Heat Set Quench Oxygen Carbon Dioxide Den~ity
Temperature Temperature Permeation Permeation gms./cc.
C. ~C. (cc/day atm3 (cc/day atm)
control 0.126 0.830 1.3630
control 0~128 0.76~ 1.3630
control 0.125 -
control 0.125
average 0.126 0.795
241 147 0.093 0.49~ 1.3996
241 148 0.087
241 ~47 0.089 0.499 1.4000
241 147 0.0~0
average 0.090 0.498
Average Improvement 29% 37%
The results illustrate the magnitude o the recognized
improvement in the oxygen and carbon dioxide barrier properties
of PET with increased density obtained ~y heat setting.
In an especially advantageous embodiment of the process of
the invention the heat set hollow article is removea from the
mold at heat-setting temperature and is zoolea outside of the
heat settiny mold to the temperature of 100C. ~r higher before
designated prior to equalizing the internal pressure of the
hollow article with the ambient atmosphere. After heat setting
the pressure is reduced to a pressure which maintains its volume
abGut the same as when within the mold, the mold is opened, and
the bottle is cooled without confinement in a mold~ This
cooling can simply be air cooling in the room temperature air.
When the desired quench temperature of 100C. or higher is
reached/ the internal pressure is then released before further
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cooling. This specific process offers the shortest cycle time
since no blow mold time is spent for quenching; it also results
in the greatest energy savings since the blow mold can be kept
at constant temperature~
The data ~or the 1/2 liter bottles shown in Table 4 was
obtained using this embodiment of my process. The process was
effected exactly as described in connection with the discussion
of Tables 1 and 2, except modiied as described in the previous
two paragraphs herein. The pressure to which the bottles were
adjusted and automatically held during the quench step is as
shown. The cooling of the bottles to the "quench" temperature
took place outside the mold with the outside surface thereof
unrestrained so that the bottles simply cooled in the ambient
room temperature air. The temperatures were estimated rather
closely butr are not exact.
ABLE 4
Heat Setting Quench Density 'Volume Onset
C~ Sec. Press Temp. gms./cc. ccs. ~emp.
Psig ~.
.. . . . . .
230 6 23 170 1.3950 ~91 163
230 6 23 115 ~.3950 515 127
If one modifies this last embodiment of my invention -
wherein the hollow article is removed under some pressure from
the mold at heat setting temperature - so that the article
outside the heat setting mold is allowed to cool under ~hrinkage-
resisting pressure to below 100~C./ as low as room temperature,
e.g. 20~C., or even lower, the maximum benefit of hiyher onset-
of-shrinkage temperatures is not realized, but the advantages of
minimum cycle time and the energy savings still obt~in.
Accordingly, the invention includes this ~pecial embodiment;
usually one cools to below 80~C., often below 70~C., before
exhausting the air or other gas from the h~llow article.
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~ .. j ... .. _ _ ,. . _ ., . _ . _ ,~ ... ...... ~ .. . ." j_ ._. . ,__._ . , .. ___.... _, . ,.,_. ._ . . _ . __ ~_ ~ .
~79~1
Thus, in many instances the higher onset-of-shrinkage
temperature obtained when cooling to no lower than 100C.
before releasing the shrinkaye resisting pressure, as in
the principal embodiment of the invention, is not necessary
for the particular end use of the hollow axticle.
To illustrate this last embodiment, a bottle was made
in the same manner as in the 230C. bo-ttles summarized in
Table 4 except that the hea-t setting tempera-ture was 240C.
and the pressure was 17 psig and this pressure was not re-
leased until the bottle had cooled to about 70C. in the
ambient atmosphere. Its density was 1.3975 gms./cc., the
bottle volume was 520.5 cc. and the onset-of-shrinkage
temperature was 149C.
When inhexent viscosity is reerred to herein, it is
the viscosity as measured in a 60/40 weight ratio phenol/
ketrachloroethane solution at 25C. Density was deter-
mined by the method described in ASTM 1505, entitled
"Density Gradient Technique".
As will be evident to those skilled in the art,
various modifications of this invention can be made or
followed in the light of the foregoing disclosure and
discussion without departing from the spirit and scope
of the disclosure or from the scope of the claims.
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