Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to the manufacture of
containers having sidewalls of oriented thermoplastic polymeric
materials. More particularly, the invention relates to plastic
bottles having in their sidewall a high level of circumferential
orientation as measured by circumferential orientation release
stress (ORS), as hereinafter defined, and to the manufacture of
such bottles from closed-end tubes or parisons by blow-molding.
This application is a divisional application of co-
pending application No. 185,069, filed November 5, 1973.
~olecular orientation of thermoplastic polymeric
materials is not new. Molecularly oriented film and sheet are
widely used and have improved physical properites, including
superior impact resistance, increased resistance-to creep, in-
creased stiffness, increased resistance to stress rupture and
reduced stress crazing, when compared to their unoriented coun-
terparts. Examples of such materials are given in U.S. Patent
3,141,912.
For a given polymer and end use application, there is
an optimum level of orientation, which may be below the maximum
20 possible orientation level. For example, impact strength may
reach a maximum value as the amount of orientation is increased,
with addition orientation resulting in a decreased impact strength.
Another example of a property which may deteriorate with attempts
to achieve high levels of orientation is optical transparency;
certain polymers "stress whiten", giving them a milky appearance.
The amount of orientation in an article formed from a
polymeric material is affected by the conditions under which the
material is oriented. For example, in a tubular article higher
levels of circumferential orientation result from increasing the
amount of stretch in either the circumferential or axial direc-
tion, by increasing the stretching rate, and by decreasing the
stretching temperature.
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It has been proposed to form plastic bottles by blow-
molding a parison, or closed-end tube. While such proposals
have met with some success, it has not generally been economically
practicable to form bottles for carbonated beverages by this
technique. The reason has been that if the bottle is oriented,
by stretching, sufficiently to develop the creep resistance re-
quired of containers for carbonated beverages (assuming a wall
thickness thin enough to be economic), stress whitening has been
observed to occur, making the container unsalable. Impact
strength is also found to be undesirably low.
Further analysis of this phenomenon has brought the
realization that stress whitening and reduced impact strength
which develop primarily at the inner portion of the bottle wall,
is due to the fact that the inside of the parison is stretched
to a much higher extent, proportionally, than the outside. It ~
has been found that the degree of orientation is not constant ~ -
; - ~ ,. -
across the bottle wall thickness, but on the contrary varies
, . .
substantially across the wall, and at or near the inner portion
of the wall is sufficiently high to give rise to the stress
j 20 whitening and low impact strength.
In accordance with the invention of copending appli-
cation No. 185,069, these deficiencies are overcome in a self-
..
supporting container, such as a bottle, having a tubular side-
wall made of an oriented, polymeric, thermoplastic material~ and
having inner, middle and outer portions, and characterized in -.
that in an axial zone of said sidewall, the percentage variation
of the circumferential orientation release stress (ORS), as
:
defined below, or the percentage variation of the circumferential
orientation as indicated by the ORS, from the inner portion to the
outer portion is less than about 4% per mil of wall thickness, tho
percentage variation being determined by multiplying 100 by a
fraction in
~,
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which the numerator is the difference between ORS at the inner
and outer portions and the denominator is the average ORS of the
inner, middle and outer portions.
Containers according to the invention are also charac- !
terized in most instances in that the maximum circumferential
orientation release stress, or the orientation as indicated by
the ORS, in an axial zone of the sidewall along each line defined
by the intersection of a plane normal to the axis of the tubular
sidewall and a plane including said axis is less than about twice
10 the minimum ORS, or orientation as indicated by the ORS, along that
line. Further, the ORS, or orientation as indicated by the ORS,
in the inner portion of the wall, along such a line is usually
from about 7~ to about 125 percent of the ORS, or orientation
. as indicated by the ORS, in the middle portion.
According to the present invention there is provided
a method for making a self-supporting biaxially oriented con-
tainer having a substantially uniform high degree of orientation ..
radially of the sidewall of the container comprising the steps
of forming a parison having a tubular sidewall with inner and
outer surfaces from a glassy, essentially non-crystalline thermo-
plastic polymeric material which is capable of being biaxially
oriented during blow molding, temperature conditioning the pari- ..
son to establish between the inner and outer surfaces of the
sidewall of the parison outwardly radially decreasing tempera-
tures within the orientation temperature range of the polymeric.
material, the decreasing temperatures being related to the
radially outwardly decreasing degree of blow molding induced
stretch so as to achieve substantial radial uniformity of orien- . .
tation and blow molding the temperature conditioned parison to
stretch the polymeric material of the parison to the container 3
shape and to biaxially orient the material.
Thus in accordance with the invention, an improvement
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is provided in methods for stretching containers which methods
involve stretching one surface of the container to a proportion;
ately greater extent than a second surface spaced apart from the
first. The improvement comprises heat-treating the container
to establish a temperature gradient between the surfaces such .
that the first surface is hotter than the second, both tempera-
tures being within the molecular orientation range of the poly-
meric material involved, and stretching the container while main-
taining that gradient.
Specifically, in connection with forming a container
from a closed-end tube, the invention envisions heat-treating : :
an axial zone of the tube to establish a temperature gradient : -
: across the thickness of the sidewall in the zone such that the
inner surface is brought to a higher temperature than the outer
surface, blow-molding the tube to form the container and main-
taining the temperature of the inner surface greater than the :~
temperature of the outer surface during at least a portion of ~ :
said molding. ~-~
Preferably, in accordance with the invention, and ~ `
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particularly when the container is a bottle, the temperature
gradient in the zone in Farenheit degrees is in the range from
about
25([SR(i)/SR(o)]
to about
150 ( 1SR(i)/SR(o) ]
- and preferably is
75-125(ISR(i)/SR(o)] - 1),
and most preferably is
lOO(ISR(i)/SR(o)] - 1). ¦ -
In the above formulae, SR(i) is the ratio of the inner
diameter of the bottle in said zone to the inner diameter of
that portion of the tube from which the zone was formed and
SR(o) is the ratio of the outer diameter of the bottle in said
zone to the corresponding outer diameter of the tube.
BRIEF DESCRIPTION OF THE DRAWINGS
; Figure 1 is a central vertical sectional view of an
injection molded parison to be heat treated prior to blow-molding
into a bottle.
Figure 2 is a partial central vertical sectional view
- and partial elevational view of a bottle blow-molded from the `
parison of Figure 1. ;
Figure 3 is a central, vertical, sectional view of an
~ electrical, contact heating apparatus for establishing a temper-
` ature gradient in the parison of Figure 1 prior to blow-molding.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is preferably utilized in the
production of a molecularly oriented bottle by blow-molding from
a thermoplastic parison. It has been found that the temperature
gradient to be established in the parison in order to produce a
more uniformly oriented blown bottle is affected by the relative
amounts of stretch of the inner and outer ~urfaces of thc parison
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in the blowing operation, by the stretching rate and by the
average temperature of thermoplastic material during the blowing
operation. The temperature gradient is greater for a larger
relative amount of stretch, a lower stretching rate and a higher
blowing temperature.
The amount of stretch of the inner surface of the
parison during the process of forming the parison into a blow-
molded article may be expressed in terms of an "inside stretch
ratio", SR(i), which is the ratio of the inside diameter of the -
blown article at any given axial location to the inside diameter
of that portion of the parison which was formed into the article -
.. :
at the axial location where the article's diameter was measured.
The amount of stretch of the outer surface of the parison may -
similarly be expressed in terms of an "outside stretch ratio",
j , .
SR(o~. In the case of a non-circular cross-sectional shape of
the parison or the blown-article, the effective diameters may -
be used to obtain the respective stretch ratios. --
The effect of the relative amounts of stretch of the
inner and outer surfaces of the parison is illustrated by refer-
ence to the parison 11 shown in Figùre 1 and the bottle 13 blown
therefrom as shown in Figure 2. When parison 11 is blow-molded
into bottle 13, the inside of the parison is stretched, for
example, from a diameter of 0.525 inch at point A, 3.56 inches
` from the top of tho parison, to become the inside of the bottle
'~ wall at point A', 4.7 inches from the top of the bottle, at a
i diameter of 2.1~4 inches, with a resultant SR(i) of 4.17. At
the 8ame time, the outside of parison 11 is stretched at point B
from a diameter of 0.787 inch to a diameter of 2.24 inches at
point B' on the outside of bottle 13, with a resultant SR(o) of
2.85. The extent to which SR(i) is greater than SR(o) is a
measure of the relative amounts of stretch of the inner and outer
surfaces of the parison.
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If, during the blowing operation, there is a uniform
temperature across the thickness of the sidewall of the parison,
the inside portion of the blown article's sidewall will be sub- :
stantially more highly oriented than the outside because, relative
to the outside portion, the inside is stretched to a greater
extent.
The parison is heat treated in accordance with the
; present invention to compensate for the relative difference in
; amounts of stretch of the parison side~lall from the inner to the
outer portions thereof.. Since less orientation occurs, for a
given amount of stretch, at a higher stretching temperature, a :
temperature gradient is imparted to the parison sidewall parison
to the blowing operation, with the temperature of the inner
surface being greater than that of the outer surface.
It has been found that, in order to produce a blown `.
;: bottle in which the maximum circumferential ORS at any axial :
location in the bottle sidewall is less than about twice the
minimum ORS at that location, the temperature gradient across ~:
the parison sidewall in Farenheit degrees at the corresponding
axial location in the parison, should be from about:
25(1SR(i)/SR(o)]
to about:
150([SR(i)/SR(o)] - 1)
A preferred range of the temperature gradient in
Farenheit degrees is from about:
75([SR(i)/SR(o)] - 1)
' to about:
125([SR(i)/SR(o)] - l)
For the parison and bottle of the type illustrated in
Figures l and 2, the most preferred temperature gradient, in
Farenheit degrees, in an axial zone of the parison i8 determined
according to the formula: 100([SR(i)/SR(o)]) - l).
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It has been found that when the maximum circumferen-
tial O~S, in an axial zone of the bottle siaewall and along each
line defined by the intersection of a plane normal to the axis
of the bottle and a plane including said axis, is less than about
twice the minimum circumferential ORS along said line, the cir-
cumferential orientation of the polymeric material from which
the bottle is formed is substantially more uniform, throughout `;
the thickness of the side~4all, than the orientation o~tained in
a bottle that is blown from a parison in which there is an ~-
essentially isothermal temperature profile in the sidewall
thereof. Preferably, for greater uniformity of orientation, the
maximum ORS is less than about 1.5 times as large as the minimum
ORS, and, in the most preferred case, the ORS is substantially
uniform across the bottle's sidewall. The improved, more
uniform, orientation distribution in the bottle's sidewall enables
the optimum circumferential orientation to be achieved over a
substantial portion of the sidewall'~ thickness.
The orientation release stress (ORS~ of a polymeric -
material has been found to be a useful measure of the relative
degree of molecular orientation of one portion of the thickness
of an article's sidewall with respect to orientation of another
portion.
For purposes of this specification, the orientation
release stress is determined according to an adaption of ASTM
Test D 1504. In this method, bottles are first conditioned at
:
72 degrees F. ~+ 5 degrees F.) at 50% relative humidity (+ 1~%)
for about 6 hours. The bottle specimens are prepared as follows:
The tops and bottoms of a given bottle are removed by
cutting with a band saw. Annular rings of approximately 1/8
inch width and approximately 20 to 30 mils thick in Zone 4 ~see
Figure 2) are cutt off with a lathe in seauence from the result-
ing cylindrical section of the bottle wall. After the edges of
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each annulus are filed to remove flash material, the maximum and
minimumthicknesesof each are measured in the region to be
analyzed.
To obtain "inside" specimens which will provide informa-
tion of the a~erage circumferential direction orientation near
the inner surface of the bottle wall, an annulus is slipped over
a mandrel mounted on a lathe and material is removed from the
- outside surface in 2.5 mil steps, thereby resulting in an annulus
thickness of about 10 mils. The lathe is operated at a lineal
speed of 250 feet per minute at the cutting tool. The last few
mils of material are always removed on a milling machine accord- -
ing to the procedure described below. ` ~-
d ~o obtain "outside" specimens from which the average
~ circumferential direction orientation near the outer surface of
::
the bottle wall can be determined, an annulus is slipped into a
coilet mounted on the lathe and the material is removed from the
inside surface in 2.5 mil steps, to give an annulus thickness
of about 10 mils. An additional few mils of material are then
removed on a milling machine.
To obtain "middle" specimens which provide a measure
~ of the average circumferential direction orientation midway ~ -
`~ through the thickness of the bottle sidewall, material is first
removed from the inside of an annulus as set forth above to give ;
~ a thickness of 15 to 20 mils. An almost equal amount of material
`~ is then removed from the outside of the annulus as set forth
~` above to give `'middle" specimens approximately 10 mils thick.
`~ The final step in sample preparation is milling of the
i annuli to assure reasonably uniform cross-sections. This is
- accomplished by cutting each of these annuli so that the result-
ing three 8trips can be mounted via double-faced masking tape
``' onto an aluminum block previously locked onto the table of the
milling machine and ~faced off" to assure parallel positioning
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of the samples to be milled. The milling operation is performed
on the specimens by removing only about 1 mil of material per
pass until 1 mil from the re~uired 6 to 7 mil thickness,
followed by 1/3 mil steps so that the desired thickness is
achieved. The slowest machine cross head speed, 9/16 inch per
.,
minute, is used in conjunction with a two-fluted end mill 3/4
inch in diameter, rotating at 1150 r.p.m. The three specimens
are then stripped from the mounting plate, cut into minimum one
inch lengths and the maximum and minimum thickness measured
with a micrometer. These specimens are now ready for the actual
measurement of ORS according to ASTM Test D 1504. In the
modified procedure employed herein, samples are immersed in a
133 degree C. silicone oil bath.
The present invention is particularly applicable to
the production of plastic bottles containing fluids under a high
internal pressure, such as, for example, beer, carbonated
beverages and aerosol container products. Such bottles reguire
that the polymeric material from which the bottle is formed have
a low permeability to gases such as carbon dioxide.
.
Suitable polymers for these purposes are prepared ~y
polymerizing a major portion of an olefinically unsaturated
nitrile, such as acrylonitrile, and a minor portlon of an ~
~- ester of an olefinically unsaturated carboxylic acid, such as
ethyl acrylate, in the presence of a rubber containing a major
proportion of a conjugaeed diene monomer, such as butadiene, and
a minor proporti~on of olefinically unsaturated nitrile, such as
acrylonitrile.
The conjugated ~iene monomers u~eful in the preparation
of such polymers include 1,3-butadiene, isoprene, chloroprene,
bromoprene, cyanoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-
?
butadiene, 2,3-diethyl-1,3-butadiene and the iike.
The olefinically unsaturated nitriles u~eful in the
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preparation of such polymers are the alpha,beta-olefinically
unsaturated mononitriles having the structure
CH2 - C - CN
R
wherein R is hydrogen, a lower alkyl group having from 1 to 4
carbon atoms, or a halogen. Such compounds include acrylonitrile
alpha-chloroacrylonitrile, alpha-fluoroacrylonitrile, metha-
crylonitrile, ethacrylonitrile, and the like.
: 10 The esters of olefinically unsaturated carboxylic
acid useful in the preparation of such polymers are preferably
the lower alkyl esters of alpha,beta-olefinically unsaturated
carboxylic acids and more preferred are the esters having the
structure
~- 2 2
.,
', Rl `~
wherein Rl is hydrogen, an alkyl group having from 1 to 4 carbon ~ ~
atoms, or a nalogen and R2 is an alkyl group having fro~ 1 to 6 -
carbon atoms. Compounds of this type include methyl acrylate,
ethyl acrylate, the propyl acrylates, the butyl acrylates,
the pentyl acrylates, and the hex~l acrylates, methyl metha-
~ crylate, lethyl methacrylate, the propyl methacrylates, thebutyl methacrylates, the pentyl methacrylates, and the hexyl
methacrylates, methyl alphachloroacrylate, ethyl alpha-chloro-
acrylate and the like. ---
The more preferred polymers are derived from (A) about
60 to 90 parts by weight of an alpha,beta-olefinically unsatur-
ated mononitrile having the structure CH2-C(-Rl)-CN where -Rl
is selected from the group consisting of hydrogen, halogen, and
the lower alkyl groups, (B) about 40 to 10 parts by weight of
an ester of an olefinically unsaturated carboxylic acid having
the structure CH2=C(-Rl)-C(O)-O-R2 where -Rl is as defined
--10--
.
. . ~ , ~ . I . . . .
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above and -R2 is an alkyl group having from 1 to 6 carbon atoms,
(A) and (B) together comprising 100 parts by weight, polymerized
in the presence of (C) about 1 to 20 parts by weight of a nitrile
rubber containing about 60 to 80 per cent by weight of moieties
derived from a conjugated diene monomer and about 40 to 20 per
cent by weight of moieties derived from a mononitrile having said
CH2=C(-Rl)-CN structure.
The most preferred polymers are derived from about
60 to 90 parts by weight of acrylonitrile or methacrylonitrile
~ 10 and about 40 to 10 parts by weight of an ester selected from the
; group consisting of methyl acrylate, ethyl acrylate and methyl
methacrylate, polymerized in the presence of about 1 to 20
' additional parts by weight of a nitrile rubber containing about
60 to 80 per cent by weight butadiene or isoprene moieties and
about 40 to 20 per cent by weight of acrylonitrile or metha-
crylonitrile moieties.
More specifically, the most preferred polymers are ~`
derived from about ?3 to 77 parts by weight acrylonitrile and
27 to 23 parts by weight methyl acrylate, polymerized in the
presence of 8 to 10 additional parts by weight of a nitrile
rubber containing about 70 per cent by weight butadiene moieties
and about 30 per cent ~y weight acrylonitrile moieties.
Further examples of such polymers may be found in U.S.
Patent 3,426,102.
Preferred embodiments of the instant invention are
described below, in the following examples, in conjunction with
` the parison and bottle illustrated in Figures 1 and 2 wherein `
the invention is utilized in heat treating a parison to be blow-
molded into a bottle suitable for containing beer or a carbonated
beverage.
Example 1
Parison 11, shown in Figure 1, to be blown into the
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bottle 13 having a sidewall 15, shown in Figure 2, is formed by
injection molding a thermoplastic polymer derived from 75 parts
by weight acrylontrile and 25 parts b~ weight methyl acrylate
polymeri~ed in the presence of 9 additional parts by weight of
a nitrile rubber containing about 70 per cent by weight 1,3-
butadiene and about 30 per cent by weight acrylonitrile. As is
well known to the art, injection molding is a techni~ue used to
form a closed-end tube, commonly referred to as a "parison",
having a particular material distribution, such as is shown in
Figure 1, but any other of the conventional parison forming
techniques may be employed.
Parison 11 is then subjected to a heat treatment
wherein a temperature gradient according to the present invention
is established therein, whereby the temperature of its inner
surface 17 is higher than that of its outer surface 19, both
temperatures being within the molecular orientation temperature
range of the polymer. During at least a portion of the blow- -
molding of parison 11 into bottle 13, the temperature of the
inner surface of the parison is greater than that of its outer ~ -
surface.
The contact heating apparatus of Fig. 3 which may be ~-
employed in heat-treating the parison 11 to form the temperature ;~
gradient comprises a metal blowing core pin 31 and in direct ;
contact therewith lie three electrically-activated ceramic
heaters 35, 37 and 39, and two electrically-activated metal
` cartridge heaters 41 and 43. Five thermistors 45, shown on the
exterior of the core pin 31, are utilized to measure and control
the temperature in each of the five core pin heating zones.
Appropriate lead wires are employed for each thermistor and eac~
heating unit in the core pin 31, which also include apertures
47 for releasing a high pressure fluid such as, for example, air
in the 8ubsequent blow-mol~ing operation.
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Surrounding the outer shell 33 is electrical insula-
; tion 49 around which are wrapped five band heaters 51. Electric-
al leads are shown leading from each of the band heaters to a
source (not shown) of electrical power.
By suitably choosing the temperature of the core pin
heating zone and the shell at any one or more of the five axial
locations, the portion of the sidewall of parison 11 at each
correlative zone can be given a predetermined radial temperature
gradient. The temperature gradient may be the same in each of
the zones, or it may vary from zone to zone, depending upon the
variation, from one zone to another, of parison sidewall thick- ~-
.. . .
ness, of the relative amount of stretch of the sidewall surfaces,
of the stretching rate and of the average sidewall temperature.
For example, in the parison illustrated in Figure 1,
the sidewall temperature gradient varies from zone to zone. The
` outer surface temperature at the time when each zone begins to
~, inflate is about: 180 degrees F. in zone 1; 180 degrees F.in zone
, 2; 175 degrees F. in zone 3; 175 degrees F. in zone 4; and 175 ;
degrees F. in zone 5. The inner surface temperature at that
time, in each zone, is about: 190 degrees F. in zone 1; 195 `~
degrees F. in zone 2; 205 degrees F. in zone 3; 220 degrees F.
in zone 4; and 225 degrees F. in zone 5.
The parison 11 is blow-molded with an increasing ~
pressure which reaches about 250 p.s.i. in about 15 seconds to ;
produce a bottle 13 whose sidewall 15 has a circumferential ORS -
varying between 1000 and 1500 p.s.i., the greater stress being
on the inside.
The following examples illustrate that the use of a
temperature gradient in the parison in accordanc~ with the
present invention is effective to give an ORS distribution in a
bottle sidewall that is more uniform than when the same pari-son
is blown isothermally into a bottle.
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Example 2
Parisons according to Figure 1 were injection moldedfrom the polymer described in Example 1 and were found to
exhibit the following axial orientation release stress (ORS)
distribution in Zone 4 prior to blowing:
ORS
Inside of parison 9 p.s.i.
Niddle of parison O p.s.i.
Outside of parison 13 p.s.i.
These parisons, which may be considered to be sub-
stantially unoriented, were then mounted on a blow-molding core
pin with five, axial, heating zones and placed within a heating
shell having five correspondlng heating zones, as described ~ -
above and as shown in Figure 3 to heat treat the parison prior
to blowing. Axial heating zone 1 extended from the open end of
the parison to about 1.25 inches from that end, measured along
the longitudinal axis of the parison; zone 2 e~tended from about
1.25 inches to about 2.3 inches from that end; zone 3 extended ~ ~-
from about 2.3 inches to about 3.3 inches from that end; zone 4
from about 3.3 inches to about 4.3 inches from that end; and
zone 5, from about 4.3 inches from the open end to the closed
end of the parison.
~.
The parisons of Group A were heat treated to produce a
different radial temperature gradient in each heating zone. -~
The parisons of Group B were heat treated to be isothermal in a
radial direction in each zone.
Table I gives the zonal temperatures of the pin and
j shell employed to heat-treat the parisons. The temperature of
- the inner and outer surfaces of the parison immediately after -
the parisons left the heating shell were substantially as shown
in Table I.
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TABLE I
PIN TEMP . /SHELL TEMP . ( F . )
(Top) (Bottom) Gradient
Parison Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 in Zone 4
1 180/165 190/160 204/160 230/160 237/160 70F.
2 180/165 190/160 204/160 230/160 237/160 70F.
3 180/180 185/185 190/190 200/200 200/200
B 4 180/180 185/185 190/190 200/200 200/200 ---
180/180 185/185 190/190 200/200 200/200 ---
The pin temperatures of Table I, in the respective
zones, were measured at the distances from the open end of the
parison and at the parison diameters and sidewall thicknesses
~ stated in Table II; the shell temperatures of Table I were
`', measured at the distances frqm the open end of the parison
: stated in Table II.
TABLE I I
Pin Outer Sidewall Shell .
Temperature Diameter Thickness Temperature
Zone 1 0.5 inch 0.88 inch 0.045 inch 0.80 inch
Zone 2 1.5 inches 0.86 inch 0.047 inch 1.8 inches
Zone 3 2.5 inches 0.82 inch 0.072 inch 2.9 inches
Zone 4 3.8 inches 0.78 inch 0.150 inch 4.0 inches
Zone 5 4.9 inches 0.77 inch 0.194 inch 5.0 inches -
These 5 parisons were then blown into the bottle of
Figure 2. The average sidewall thickness in zone 4 of the bottles
' blown from the parisons of Group A was 22 mils; the bottles blown
from the Group B parisons had an average sidewall thickness of
2~ mils in zone 4.
The parisons of Group A were blown into a polymethyl-
methacrylate mold with an increasing pressure which reached ~O
p.8.i. in about 18 seconds; the parisons of Group B, were banffn
with an increasing pressure which reached 150 p.~.i. in about
20-25 seconds.
.
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Inflation of each parison began approximately 6
seconds after the parison was removed from the heating shell and
occurred at that part of zones 1 and 2 where the sidewall thick-
ness was a minimum. Inflation began in zone 3 at about 9 seconds
after removal from the heating shell; in zone 4, at about 11
seconds after removal; and in zone 5, at about 15.5 seconds
removal. The inner surface of the portions of the parison corr-
esponding to zones 1-4 remained in contact with the heating pin
until inflation occurred. The surface portion in zone 5 broke
contact at about 11 seconds after removal due to axial elonga-
tion occurring during inflation of zones 1-4.
The first row of Table III gives the inside and out-
side surface temperatures of the Group A parisons, at each axial
zone thereof as determined at the locations stated in Table II,
approximately six seconds after the parison was removed from the
heating shell. The second row of Table III gives the correspond-
ing temperatures at the respective times when inflation commenced
in each zone.
TABLE III
INSIDE/OUTSIDE TEMP. (F.)
Gradient
Parison Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 in Zone 4
Al & A2 180/172 190/176 204/176 230/172 237/170 58F.
Al & A2 180/172 190/1?6 204/179 230/176 227/175 54F.
` Orientation release stresses (ORS) for the "insiden, --
nmiddle" and "outside" portions of the bottle sidewall at Zone
4 were as stated in Table IV.
.
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TABLE IV
Bottle From ORS (p. 8 . i . )
Parison
IndicatedSpecimen Inside Middle Outside
1 a 1078 1318 578
'! A b 984 1246 689
2 a 951 1058 588
b 968 996 598
Avg. 995 1156 613
3 a 2293 1408 572 ;-
b 1941 1066 584
B 4 a 1616 707 365
- b 1061 772 345
a 1342 1274 598
b 1387 1246 630
Avg. 1607 1079 516
As seen above, the bottles of Group A, which were
blown from parisons having the radial temperature gradients of
Table III, exhibited less variation in circumferential orienta-
tion across the sidewall in Zone 4 than did the isothermally
blown bottles of Group B. In the case of the inside, middle
and outside sidewall portions of the Group A (temperature grad-
ient) bottles taken as a whole, the maximum circumferential
orientation release stress (Zone 4) was no more than about twice
as large as the smallest orientation release stress, whereas in
the case of the bottles of Group B (isothermalj, taken as a
whole, the maximum orientation release stress (Zone 4) was
. greater than three times the minimum. A comparable reduction in
the variation of orientation i8 effected in the other axial 20nes
of the sidewall of the bottle~
Considering 7 mils to be the average thickness of each
of the ~inside", "middle" and "outside" portions of the bottle
sidewall that were utilized to obtain the ORS data of Table II,
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a "percentage full width ORS gradient" from the "inside" portion
to the "outside" portion can be determined from the ORS data of
Table II bv (1) subtractin~ the "outside" ORS from the "inside"
ORS, by (2) dividing the difference by the product of (a) the
radial distance from the center-line of the "inside" portion to
the center-line of the "outside" portion times (b) the average
of the "inside", "middle" and "outside'i orientation release
stresses, and (3) by multiplying the quotient by one-hundred.
The resultant "percentage full width ORS gradients", in percent
per mil, are qiven in Table V, together with the respective
center-line to centèr-line distance, in mils, for each specimen.
TABLE V
Bottle From Center-Line Percentage
Parison Specimen Distance ORS Gradient `
Al a 16.4 3.08
b 16.3 1.86
A2 a 15.2 2.76
b 15.25 2.84
Average 2.64
B3 a 19.9 6.07
b 19.9 5.70
B4 a 21.7 6.43
b 21.75 4.53
B5 a 20.7 3.35
b 20.8 3.35 ~ -
Average 4.91
t The data of Table V illustrate that the bottles of
Group A, blown from parisons that were heat-treated to have a
radial temperature gradient in accordance with the present
invention, have a substantially greater uniformity of circum-
ferential orientation in their sidewalls than do the bottles of
Group B, blown from radially isothermàl parisons.
Bottles made from parison8 have the temperature gradient
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of the present invention have in their sidewalls a "percentage
full width ORS gradient" of less than about 4 percent per mil of
sidewall thickness, and preferably less than about 3 percent per
mil.
In the above examples, the parisons were substantially
unoriented in the axial and circumferential direction prior to
being heated for the blowing operation. Depending upon the
process used to form it, the parison may itself have a given
amount of axial of such orientation upon the ORS distribution
in the bottle sidewall is illus~rated in the following example:
; Example 3
The parisons of Figure 1 are injection molded from the
same polymer set forth above and their sidewalls in Zone 4
exhibit the following axial orientation release stress (p.s.i.):
Parison ~nside Middle Outside
6 61 0 36
7 61 0 36
8 89 0 43
; 9 ~9 0 43
Tbese parisons are then heat-treated similarly to the
parisons of Group A to produce radial temperature gradients in
the sidewalls thereof in accordance with the present invention.
Table VI gives the zonal temperatures of the pin and
shell employed to heat-treat the parisons. The temperatures
were measured at the locations stated above in Table II, and
the parison dimensions were as stated therein.
TABLE VI
PIN TEMP./SHELL TXMP. (F.
Parison Zone 1Zone 2 Zone 3 Zone 4Zone 5 Grad ent
6 200/162 200/157 205~157 212/163 210/158 49F.
7 20i/167 204/162 217/161 218/168 --/165 50F.
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8 196/167 193/163 206/162 222/170 --/167 52F.
9 196/167 193/163 206/162 222/170 --/167 52F.
These four parisons were then blown into the bottle
of Figure 2 with an increasing pressure that reached 180 p.s.i.
in about 20 seconds. The average sidewall thickness in zone 4
of the bottles was 22 mils.
The chronology of the sequential, axial inflation and
the residence times on the heating pin of the zonal portions ?
of the parison after removal of the heating shell were the same
as in Example 2.
The first three rows of Table VII give the inside and
c outside surface temperatures of parisons 6-9, at each axial
zone thereof as determined at the locations stated in Table II,
; approximately six seconds after the parison was removed from the
heating shell. The second three rows of Table VII give the ` ?
' corresponding temperatures at the respective times when infla-
, tion commenced in each zone.
TABLE VII
INSIDE/OUTSIDE TEMP. (F.)
Gradient ~
Parison Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 in Zone 4 - -
6 200/182 200/I83 205/174 212/171 210/164 41F.
; 7 207/189 204/185 217/181 218/175 220/173 43F.
8 & 9 196/183 193/179 206/176 222jl78 220/173 44F.
6 200/185 200/183 205/178 212/173 203/167 39F.
7 207/189 204/185 217/185 218/177 213/176 41F.
8 & 9 196/183 193/179 206/186 222/180 213/176 42F.
Orientation release stresses (p.s.i.) for the ~inside~
"middle" and "outside" portions of the bottle sidewall at Zone
.::
were as stated in T~ble VIII.
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TABLE VIII
Bottle From ORS (p. 8. i. )
Parison Specimen Inside Middle Outside
6 a 1207 1278 808
b 1015 1072 690
7 a 936 1061 545
b 1255 1144 570
8 a 890 1127 598
b 1077 1132 595
9 a 876 973 531
b 1015 1049 584
Avg. 1034 1105 615
From the data of Table VIII, taken as a whole, ror
bottles fro~. p~risons 6-9, it can be seen that with respect to
the "inside", "middle" and "outside" portions of the bottles'
sidewalls, the maximum circumferential orientation release stress
was no more than about twice as large as the smallest orientation
release stress therein.
From the data of Table VIII, the "percentage full
`, width ORS gradient" for each specimen can be determined in the -
~ame manner as in Example 2. The resultant gradients, in percent
`~ per mil, are presented in Table IX, together with the respective -~ -
` center-line to center-line distance, in mils, for each specimen.
.,. , :
TABLE IX
Bottle From Center-Line Percentage
Parison Specimen Distance ORS Gradient
i 6 a 15.0 2.42
b 14.2 2.47
7 a 15.1 3.06
b 15.2 2.47
8 a 15.2 2.20 ~ ;
b 15.4 3.35
9 a 15.0 2.91
b 15.0 3.26
Average 3.03
The data of Table IX illustrate that parisons which
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themselves possess a ~iven a~ount of axial orientation in the
sidewall prior to blowin~ m~ be heat-treated in accordance with
` the present invention to impart a temperature gradient to the
sidewall thereof whereby the sidewalls of the bottles blown
therefrom have substantially the same full width ORS gradient as
to bottles made from essentially unoriented parisons.
Blow-molded articles made from parisons heat-treated
according to the present invention have a substantially more
uniform circumferential orientation from the inner to the middle
10 portions of the sidewall thereof than do articles made from radi-
ally isothermal parisons. In an axial zone of the sidewall, the
circumferential ORS in the inner portion of the sidewall is be-
~ tween about 75 and about 125 percent of the ORS in the middle
`` portion thereof, and, preferably, is between about 90 and 110
;~ percent of the ORS in said middle portion.
3 The instant invention is applicable for any bottle
æidewall thickness, but is-especially useful for thicknesses
between 5 and 60 mils, and particularly between 15 and 35 mils.
The invention is aiso applicable for any parison which at its
20 thickest part, exclusive of closure finish, is between 100 and
300 mils thick.
Bottles blow-molded by the method of this invention can
be produced from any glossy,~essentially non-crystalline, thermo-
plastics which can be biaxially oriented. Examples of such ~-
materials are polyvinyl chloride, polystyrene, acrylonitrile
copolymers and methacrylonitrile copolymers.
The molecular orientation temperature range of an -
essentially non-crystalline thermoplastic polymer useful in the
practice of the pre~ent invention is that temperature range
30 above the glass transition temperature, and below the softening
temperature, in which the polymer is rubbery or leathery. The
highest degree of molecular orientation is obtained by stretching
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the polymer when it is in the leathery state, viz. where it~
behavior is retarded, highly elastic, which is evidenced when
the polymer is subjected to a stress and undergoes a small,
instantaneous strain and then a much larger strain over a rela-
tivelv long period of time. The orientation temperature range
of the polymer described in Example 1 is from about 170F to
about 275F.
: It is thought that the invention and many of its attend-
ant advantages will be understood from the foregoing description;
and it will be apparent that various changes may be made in the
form, construction and arrangement of the parts of the article
and that changes may be made in the steps of the method described -
and their order of accomplishment without departing from the
spirit and scope of the invention or sacrificing its material
advantages.
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