Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to a method o blow molding
molecularl~ oriented bottles and more particularly to improve-
ments in a temperature-conditioning phase of such process.
U.S~ Pat. No. 3,754,851 describes a system for
making molecularly oriented articles by blow molding a pre-
form from an extruded tubular parison of thermoplastic material,
temperature-conditioning the preform in a chamber downstream
of the preform mold to bring the greater part of it to within
the molecular orientation temperature range followed by re-
1~ molding into the oriented article in a further downstream sta-
tion. Assignee's above patent describes an apparatus for
accomplishing the temperature-conditioning step, and also recog-
nizes the desirability of maintaining a temperature gradient
in planar circumferential sections of the material of ~he blow
molded body.
When the molded article formed in this wa~ is a bot-
tle for pressurized applications, it is knwon that the lower por-
tion, particularly in and around the base area, is most critical
from the standpoint of successful performance. More specifically,
the region of the ~uncture of the sidewall and base (chime) is
guite prone to impact during handling and use and also is where
stress from the pressure of the contents is greatest. Accord-
ingly, for these and other reasons such area must be rather
carefully formed if the container is to function satis-
factorily. If the lower sidewall-base area is too thin, not
only is impact resistance and pressure retention capability
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diminished, but the material will tend to creep (enlarge in
~olume) there. If circumferential wall di~tribution i~ uneven,
creep will be uneven and the ~illed bottle will lean or vary
excessi~ely ~rom a truly vertical po~ition when seated on a
flat surface. If a raised9 pressure-resist;ant base is present,
it has a tendency to diaphragm outwardly under pressure.
On the other hand9 the material forming the reduced
diameter upper portion of the bottle between the base of the
finish and the portion below it o~ sub~tantially greater cross
section does not undergo much expansion at all during final
~orming. Consequently, thickness in this area of the bottle
iæ not reduced very much in comparison with that extant in
the part of the pre~orm which is to form such upper portion,
though it very well could be without much affecting container
performance. This is so because, from a pressure-resistant
standpoint, hoop stress generated by the contents is relatively
low in such reduced diameter area and, furthermore, because
of its location in the bottle, such area is not too prone to
be impacted under normal conditions of handling and use.
Accordingly9 during final blowing of the bottle it would be
advantageous, from the standpoint o~ conser~ing material, to
haYe more plastic in the portion of the preform which will
form the lower portion of the bottle than in the part which
i8 to form the reduced diameter neck~
.
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The present lnventio~ relates to a
cool-down prooess for forming a molecularly orlented bottle
which includes the steps of blow molding thermoplastic material
into a tubular pre~orm having a body and a finish portion
adjacent an open end~ extraoting heat from said preform in a
~emperature-conditioni~g chamber ~o bring the temp~rature of
the t~ermoplastic material to within it~ molecular orientation
temperature range, and then distending said preform longitud-
inally and circumfere~tially to form said molecularly ôrie~ted
bottle, by providing the improvement whereby thermoplastic
material distribution in the bottle is improved which comprises 9
i~ oQmbiaation, the step of af~irmatively applying heat into
a vertical region of the body adjacent the finish while continuing
to extraet heat from the remainder of the body in the chamber
, . .
15~: to establi~h a temperature gradient along the length of the
body of about 1.5 to 11C prior to distending, such body w1th
he temperature gradient extant therein being within the
molecular orie~tation temperature range of the thermopla~tic
. . material9
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BRIEF DESCRIPTION OF THE DRAWINGS
In describing the overall invention, reference
will be made to the accompanying drawinqs wherein:
Pig. 1 is a schematic, vertical end view
illustrating the process improvement step of the present
invention;
Fig. 2 is a vertical, sectional view schematically
illustrating the condition of the preform of Fig. 1 after a
su~sequent step in the process and prior to final blowing; and
Fig. 3 is a sectional view of the bottle formed
from the preform of Fig. 2.
With respect to an environment in which the
present invention is operable, reference is here made to
copending Canadian application No. 214,217 filed November 20,
1974, and more particularly to page 7, line 15 through page
12, line 9 and Figs. 1-11.
Referring now to the present drawings, there is
shown in Fig. 1, heat transfer units, generally indicated as
12, which comprise a series of spaced, closely adjacent up-
right panels 38 extending lengthwise of the plane of Fig. 1,
only two being shown for illustrative purposes. Inter-
connected, vertically adjacent flow channels 40 are formed
in each panel 38,: extend generally parallel to the length
thereof, and contain a heat transfer medium 41, such as oil
at elevated temperature~ flowing therethrough from a conven-
tional source, not shown. Opposing vertical surfaces 11 of
each pair of adjacent panels 38 and the floor member support-
ing them delimit a heated, atmospheric path 39 through which
a preform 50 is conveyed according to the invention while
suspended beneath a step 60 thereon.
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Mechani~m 51 for supporting and preferably rotating
preforms 50 includes a socket 56, having a collar 58 ~upporting
ætep 60 of the pre~orm, and which is force--~itted within a bore
of pinion 64 which cooperates with worm sections ~not shown)
on through-shaft 74 to turn each preform 50 about its verti-
cal axis 122 as mechanism housing 54 ad~ances through.the
trans~er chamber (not shown) containing panels ~8.
In accordance with the in~ention~ a vertically n~rrow,
strip type electrically actuated, resistance heater 10 is
`~ 10 above and extends perpendicular to each side 11 of a panel
~ 38 though it could be secured directly to the upper portion . o~ each side 11. In the embodiment shown, a pair of heaters
10 are set in hanger~ 14 spaced along the length of a panel
38 which in turn are mounted to a suitable support 17 on the
top face of such panel. Each heater 10 is preferably indivi-
~; dually controlled via suitable conventional circuitry to
regulate the temperature of the radiating outer surface thereof.
I~ operation, molded, elon~ated preforms 50 arepro~ided to the apparatus shown, each preform hav.ing a contour
generally sgmmetrical about lengthwise axis 122 and preferably
having one closed end 243 with a spherical radius and a finish
portion 242 at its other end, which finish portion in the
illustrated embodiment include~ spiral threads (~igo 1) and
step 60 immediately below such threads. Though preform~ 50
may smoothly and gradually taper in thickness, they are
preferably substantially uni~orm in wall thickness along their
: length below finish portion 242, such variations in thick-
ness as e~i~ting being in the circumferential direction
and occuring as a result of uneveness developed in the ex-
trusion ori~ice w~ere the inltial tubular shape wa~ formed
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from whioh each preform 50 was blown. Pre~orms 50 will
ha~e ~ust been di~charged at ele~ated temperature from a
blow molding station a few minutes before going through the
pr~sent proces~, and it is desired ~o bring the thermoplastio
material con~tituting the body portion beneath ~inish 242 to
within a temperature range at which substantial molecular orien-
tation can be de~eloped on stretching. Such range may be defined
as that from the glass transition temperatura of the polymer
forming the thermoplastic mate~ial at the lower end of the
range up to a temperature at which melt flow of the polymer can
occur. Such range i~ pre~erable from about 14 to 56C above
the glass transition temperature of the polymer to avoid, on
one hand, the need for excessively high stretching forces
at low temperatures and, on the other hand, to avoid rapid
relaxation of stresses de~eloped on stretching at high tem-
perature~.
Preforms 50 are inserted either manually or automa-
tically into housing 54 at an upstream loading station and
discharged in the same manner. During traversal of path 39
such body portion below ~ertical reglon 16 is at an ~verage
wall temperature greater than that of the surrounding air in
path 39 and heat is therefore con~ectively extracted there-
from a~ schematically illustrated ~y arrows 1~, to medium
41`in panels 38, which is being controlled via an external
heat exchanger,not shown, at a temperature greater than that
of the air but less than that of the outer surface of the
preform body. ~he temperat~re of such air in path 39 as
heated by panels 38 can vary within wide limit~ depending on
the temperature of the thermoplastic material a~d the breadth
~0 and level of its molecular orientation temperature xange,
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~ith a preferred air range being about 37 to 110C. Heat-
ing the panels while neverthele~s extractlng heat from the
plastic minimize~ the temperature di~feren-tial between the
two and helps control and 910w the rate of heat loss and
avoid over-cooling to below the molecular orientation tem-
perature range, which otherwise might occur without such
heated panels.
. Aæ the suspen~ed preforms 50 traverse path 39
adjacent the exit end of the heat transfer chamber and con- ~
tinue to lose heat to panels 38 along the lower portion of the
length, the upper portion of the body below finish 242 passes
in front of heaters 10 which function to a~firmati~ely transfer
heat, substantially ~ia radiation in the direction of arrows
15, into region 16 such that at the end of path 39 prior to
15~ further remolding, a temperature gradient of about 105 to 11C
exi~ts along the length of the body below the cool ~inish
242. Vertical region 16 constituting about 25 to 40~0 of the
length below finish portion 242 may be either higher or lower
than the temperature of the remainder of the body, and the a~erage
temperature of the body with such gradient extant therein is
nevertheless still within the molecular orientation temperature
ran~e o~ the plastic, ~ince sagging ln the affixmati~ely heated
region 16 from the weigh~ of the preformg as well as exce~
thinning durtng remolding i8 to be a~oided.
~he a~orementioned temperature di~fexence i9 preferably
obtained via heat transfer into the pla~tic in region 16 which
t~nd~ ~o cool faster than the lower portion ~ince the upper end
o~ the preform i9 above the heating panels where a~bient air
temperature i~ not controlled. Adding heat ha~ been ~ound to
result in clo~er temperature contrvl as opposed to conv~ctively
cooling ln ~ zoning manner along the full preform length~ which
is di~ficult to control to obtain the intended gradientO
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The magnitude of the temperatures of preform 50 along the
length are influenced by a large number of factors such as
the nature and thickness of the thermoplastic material~ the
molecular orientation temperature range thereof, the amount
o~ molecular orientation de~i~ed in the finished articlet
the surface contour and overall dimension~ of the bottle,
the time which will elapse between the exit of the heat trans-
fer cham~er and the actual subsequent remolding, and so forth.
~or high nitrile thermoplastic materials wherein the major
constituent of the polymer ~at least 55 weight .ercent) is
a polymerized nitrile-group-containing monomer such as acryl-
onitrile 9 methacrylonitrile and mixtures thereof, good results
have been obtained when the outer surface temperature of ~er-
tical region 16 i~ about 141 ~o 155C, ~hat o~ the outer
sur~ace of the rest of the body below region 16 is less than
that of the latter and about 132 to 146C and the surface
temperature of heater~ 10 is about 137 to 316C.
Immediately thereafter the temperature-conditioned
preform 50 is supported within a con~e~tional, closed blow
mold, not shown, for subse~uent distending in the longitud-
inal and circumferential directions. In connection with the
~ormer, a telescoping stretch rod is preferably introduced
through open end 62 against the inner sur~ace Qf closed end
243 ~nd then further ad~anced to longitudinally ~tretch the
~: 25 temperature-conditioned preform, preferably against the in-
side of the base of the blow mold, into the configuration~ : depicted in ~ig. 2, thereby deYeloping ~ubstantlal a~ial
molecular orientation i~ the thermoplastic materialO As
~hown in Fig. 2, after such longitudinal ~tretohi~g, prior
~0 vertical region 16 of the preform (Fig. 1) ha~ been elongated
,
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and pre~erentially stretched into a substantially thinned-
ou~ portio~ 17 in comparison with the thickness ln the re-
mainder of the pre~orm. Dotted line 18 represents the app-
roximate inner ~urface o~ area 17 o~ a preform 50 after
longitudinal stretching without the temperature gradient,
.
supra, therein.
Following such longitudi~al stretching, blow air i~ con-
~- ventional~y inje~ted into the interior of the preform through
~ a~pa~sage in the stretch rod to expand the material outwardly
toward and again~t the wall~ o~ the cavity of the blow mold
corresponding in contour to the configuration of bottle 20 in
~ig. 5. Wall portion 21 o~ bottle 20 has been formed from and
is substantially equi~alent in length to area 17 of the longi-
tudinally stretched preform in ~ig. 2, portion 21 forming the
~-15 reduced diameter upper sectio~ of the vertically symmetrical,
cylindrical bottle di~cussed previously where impact, burst
; and creep resistance is not as critical as in the remaining
, ~,
lower portion thereof. As can be seen from the relative
thicknesses along the length of the bottle wall in ~ig. 3,
portion 21 approaches the thickness of the lower portion o~
the bottle body, whereas it would have greater thickness as
; per dotted line 19 representing the inner sur~ace thereof if
blown from a preform in wh1ch the temperature gradient had not
~ been previou~ly generated. Thus, as a result of such tempera-
ture gradient, material ha3 been selectively moved out of area
21 of bottle 20 down into the larger diameter body, a~d sp0ci-
-~ fically into the rounded chime area and ba~e o~ bottle 20~
I~ in examining such thicknesses, it is determined that ~nother
d~tribution pattern is desired, this may be easily obtained
,
3Q~ ~by merely varyin~ the settings of the ~trip heaters, to vary
the a~oreme~tioned temperature profile. In thi~ co~nection,
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it has been found that if the top/bottom, high/low temperature
gradient is excessive, too much material may be drawn out of the
upper portion oE the preform down into the base area.of the bottle
resulting in the development of double thickness folds in area
23 (Fig. 3) between the larye diameter chi~e and vertical bottle
axis, and it may even be necessary under certain conditions to
reverse the gradient and run the bottom portion of the preform
body at a greater temperature than region 16, the gradient
nevertheless still lying within the aforementioned l.5 to 11C
range.
EXAMPLE
Blow molded preforms configured as previously des-
cribed herein and formed of a thermoplastic material comprising
a 70/30 weight percent polymer of polymerized acrylo~trile/
styrene were passed through the apparatus of Fig. 1. At the
end of path 39, the outer surface temperature of the preform
3.96 cm below the base of the finish as indicated on a conven-
tional infra-red temperature measuring instrument, was 143C,
whereas that 12 cm below such finish (the total length below
the finish being 14.6 cm) was 141C, such elevated temperature
at the upper end having been obtained by setting the heaters at
171C. After removal from the conditioning apparatus, preforms
having such a gradient therein were then immedia~ely axially
stretched and blown as aescribed herein into bottles configured
: 25 as in Fig. 3.
The following performance tests.were conducted
on such bottles:
Lean - Each bottle was filled with a carbonated
cola beverage at 3.8 volumes C02, capped and placed in an
: 30 oven at 38C for 24 hours, removed and allowad to return
to room temperature. The unopened bottles were placed on a
flat, level surface and a dial gauge positioned adjacent
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~ )655~i3
`each one, such gauge ha~ing a ~eeler resting agalnst the
bottle surface immediately beneath the fi~ish designed to
deflect with any deviat~on of such ~urface ~rom ~ertioal,
and to indicate the magnitude of such deflection ~ia a pointer
on a face calibrated in cm. Each bottle was then ro-
tated ~60 and the total difference between minimum and max-
imum pointer readings measured, the spec:ification being nogreater than 1l1 cm. Impact Resistance - ~illed and capped bottles at
room temperature were ~ropped once from a heigh~ o~ O.91m
at a 30 degree angle ~o the vertical onto a flat ~teel plate
. and the number passing noted.
~ urst Pressure - Bottles filled with tap water were
clamped in place in an Americal Glass Research Incremental
Pressure ~ester and the internal pre~sure gradually increased
. until each bottle failed. Pressure at ~ailure wa~ noted,
the specification on minimum pressure rete~tion bei~g 11 Xg/cm2
Results were a~ ~ollows:
Passin~
.
~ean 90
Impaot 80
Burst 100
~ONTRO~
~ ~he foregoing temperature-co~ditioning, stretchin~
: ~ 25 and blow molding operatio~ was repeated exoept that strip heaters
were no~ used in the heat transfer chamber a~d there~ore no pur
: po3ely developed temperature gradient existed along the length
of ~he preforms.
~he bottle~ formed were vLsually examined and were
~udged to be ~o paper th~n at the lower end of the body in the
base and chlme area ~n compariso~ with those of the ~oregoing
.
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Case ~352
Example~ that it was postulated that 0~ would pass the fore-
going lean, burst and impact tests.
The above description and particularly the drawing
i~ set forth for purposes of illustration onl~ and is not to
be taken in a limited sense. ~arious modifications and alter
ations will be readily suggested to persons skilled in the art.
It is intended, therefore, that the foregoing be considered
as e~emplary only and that the scope o~ the invention be as-
certained from the following claims.
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