Note: Descriptions are shown in the official language in which they were submitted.
Ca o c L3 5~ ~ 7 ~7
.
PREPARATION OF MOLl~CUI.ARLY ORII~NTE~D
CONTAINEL~S USING REI-IEAT PROCESS
BACKGROUND OF THE INVENTION
This invention relates to an improved ~ethod for heating molded
prffaforms to a temperature at which molecularly oriented containers can be
produced by subjecting said heated preforrrls to a therrr~oor~ning orienting
5 stfff~fp.
It is known to molecularly orient thermoplastics in systems
wherein such materials are being blow molded into hol3ow articles such as
containers. Such molecular orientation is highly desirable, when the thermo-
plastic is of such a nature that orientation can be developed therein, since
~0 it can represent an attractive route toward improving the strength properties
of the finished container. This feature is particularly important when the
~;~ formed containers are to be used for packaging pressuri~ed liquids such as
carbonated beverages and beer as well as other products which require low `~ `
permeability and high impact resistance as characteristics of the container.
A system is disclosed in Reilly et al, U.S. Patent 3, 754, 851 for
.. , ~ . ' ~ .~
blcffwing articles from molded preforms which are brought to orientation
temperature iD an intermediate conditioning step. In this approach heat is
removed from the preform during conditioning and such has become known
in the art as a "cool-down" process.~ It is likewise known to add heat to
20 preforms to bring them up to orientation temperature prior to finish forming
`f as tlrpically disclosed in Gilbert, U.S. Patent 3, 787, 170 and such technique
has become known in the art as a ~'reheat" process.
Although it has gcnerally befffen considercd less difficult to achieve
orientation on a hoating cycle (reheat procesfs) than on a cooling cycle (cool-
~ 25 down procf?ss), the reheat process i8 by no means a sim~fle procedure
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~ase L3$4 10~'78Z7
to ca~ry o7ut, particularly in a commercial operation. Somc factors which
aIfect the process are thc preform thickness, thickl~c~R variation~ within a
preform (partic7ularly significant in extrusion blown preforms), heating time
and thc thermal conductivity of thc preform material. Additionally compli-
5 cating the matter are problems associated with forming containers fromelongated tubular preorms having one end closed and made of thermoplastic
material. It is extremely difficult to heat such preforms with any degree
of uniformity because of the particularly low thermal conductivity of the
materials and also because of the difficulty of applying heat to the inside of
10 6aid preforms. Also, measuring the temperature of the preform both on its
inside surface and through its thickness is quite difficult thereby hampering
the ability to achieve thF conditions necessary to obtain containers having the
` desired properties.
In order to overcome some of the problems noted above, a variety
:, .
~`l 15 of processes and apparatus have been designed specifically or the reheat
process. For example, Steingiser, U.S. Patent 3,830,893 discloses a
~7 ~ ~ method for rapidly heating nitrile preforms to orientat1on temperature using
n~7icrowave energy; Seefluth, U.S. Patent 3,445, 096 discloses a process and
apparatus for heating tubular thermoplastic parisons to orientation temperature
20 by alternately passing the parisons between a heating zone and a constant
temperature zone maintained at a temperature just below the melting point
of the parisons to distribute heat evenly throughout; and Gilbert, U. S. Patent
3,715,109 who discloses apparatus for rapidly heating pFeforms to orientation
25 tempcrature by applying heat to said preforms both extcrnally and internally.~; :
Despite the attention given to the problem of reheating worlcpieces
to the ,desired orientation temperature as noted above, there still is the need
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C~IBC L354
8 ~'7
~or a simplificcl tcchniquc which will allow for the prcduction of rnolecularly
oricnted containcr3 using the reheat system and whlch i~ suitable for a
continuous commercial operation.
SIJMMARY OF THE INVENTION
Now, in accordance with this invention, there has been developed
,
an improved and simpliied method for eficiently reheating preforms to a ~'
'~ molecular orientation temperature in preparation for the ormation of
;~ . multiaxially oriented containers.
Accordingly, a principal object of this' invention is to provide
an improved method for preparing molecularly oriented containers using the
.
, ~' rehéat system,
~, Another object is to heat preforms made of an amorphous thermo-
'" plastic resin to a temperature range at which substantial molecular
,,1 ' orientation occurs using a two step reheating process.
~',, 15 ~other object of this invention is to prepare oriented containers
`' made' of high nitrile polymers by subjecting preforms made of such materials
'-' to a thermoforming orienting step while at a molecular orientation temperature
. j .
. ~ . .
f reached by first heating s~id preforms using external heating means to an
average outside temperature above the substantial molecular orientation
20 temperature range and cooling until the average outside temperature is within ,`
aid range thereby reducing the temperature gradient across said preform
thickness and bringing the entir'e preor ,m temperature within said range.
','',' ~Anothcr object o this invention is to provide a simpliied method '
for preparing oriented bottles on a continuous basis from high nitrile polymers
25 by axially stretching and exp~nding preforms o~ such polymers at an orienta-
tion temperaturc reached by a two step reheatin~ process,
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~al30 L354
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Othcr objccts of this invcntion will in part be Qbvious and will in
part ~ppear herein~fter.
These and other objects are accomplished by providing a method
o iorming a ~nolccularly oricnted container from a molded preform macle of
5 an amorphous thermoplastic resin and having a finished neck portion and a
body portion, which method includes subjecting the preforrn body to a thermo-
;- forming orienting step while iIl a temperature range at ~vhich substantial
~: molecular orientation occurs~ said orientation temperature being arrived
at by ~irst overheating said preform body using e~eternal heating means to an
10 average outside temperature greater than the su~stantial molecular orien-
`~ tation range thereby creating a t~mperature gradient across the thickness
~ of said preform body and then cooling said heated preform body until the
:.
average outside temperature is within said substantial molecular orientation
temperature range and the entire preforrn body temperature is within said
15 substantial molecular orientation temperature range and wherein said
'`! ,
- temperature gradient is significantly reduced.
,
BRIEF DESCRIPTION OF THE DRAWINGS
~- In describing the overall invention, reference will be made to the
accompanying drawings wherein: `
Fig. 1 i9 a perspective view with a portion broken away of a
typical molded prefor~n shape for use in.the present invention;
Fig. 2 is a schematic diagram illustrating the passage of
preforms through heating apparatus use~ul in carrying out the mcthod of
this invention;
~ .
t~ig. 3 i8 a schematic view showing one form of heating systen~
useful in the method of this invcntion;
Fig. 4 i8 a schematic diagram illustrating the oricnting and
containcr forming stcps of thc invention;
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Ca~c L354
.lIL~8'71~7
Fi~. 5 is a graph illu~tratin~ the r~aults in ternns of thc time-
tempcrature relationship of a typical run usin~ the reheating procedure of
this invcntion.
ETAILED Dl~SCRIPTION OF THIS INVENTION
In carrying out the method of this invention~ an elongated ~ubular
preform made oi an amorphous thermoplastic material nd having a general ~ -
configuration of the type shown in Fig. 1 is molecularly oriented for example
by axially stretching and radially expanding while at a ternperature at which
~;ubstantial molecular orientation occurs using a stretch blow mold station
of the type illustrated in Fig. 4.
Generally speaking molecular orientation cf an orientable thermo~
,
plastic preform Inay occur over a temperature range varying from just above
the glass transition temperature (that temperature or narrow temperatu~e
., .
range below which the polymer is in a glassy state) up to the melt temperatuFe
15 of the polymer. However, as a practical matter the formation of oriented
containers is success~ully carried out when the preform is at a much
narrower temperature range defined as the substantial molecular orientation
temperature range~ This is best illustrated by reference to Table I which
! .,
shows results obtained when preparing or attempting to prepare bottles over
. ,.
20 a wide temperature range. The birefringence stress values as noted in
the results sho~vn in Table I are used as an ind;cation of the relative
.. . .
orientation properties of thF prepared b~ttles. Such birefringence stress
values were determined from the measurements of birefringence for the
: 1 `
~; ~ prepared bottlcs and using the technique and formulas for stress as defi~ed ~ -
25 by D. C. Drucker in "Photoelastic Separation of Principal Stresses by
Oblique Incidcnce", Journal of Applied Mechanics, Sept. 1943, pp. A-1S6
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to A-160. Thc strcss-optical cocficient as used in this tcchniqu~ was
de~crmincd usîng a curvc of orientatiorl rclease stress (ORS) vs bire~ringcr~ce
~or the material with ORS arrived at by thc ASTM D 1504-70 mcthod.
As Table I indicatcs, when thc preform ternperature is slightly
S above the glass transition temperature i. e. 232F,, bulbs rather than
bottles were formed. When the preform temperature ~as increased to the
- 240 to 250 F. rallge, bottles were prepared having good orientation
properties, expressed as birefringence stress, however, they were formed
with low quality yields and s~ther disadvantageous characteristics. This
10 result was undoubtedly due to the difficulty to stretoh and process the preforms
in this temperature range. As the temperature is increased the processibility ~`
improves greatly and quality yields also improve, however, the orientation
properties begin to fall off. It thus becomes necessary to balance the needs
îor processibility and quality with orientation results and this is called the
15 temperature range at which substantial molecular orientation occurs.
; In other words the substantial molecular orientation temperature range as
used throughout the specification and claims is defined as the temperature
lange at which preLorms must be at to effectively and conveniently form
oriented containers having suitable orientation properties such as by axially
` 20 ~tretching and radially expanding said preforms. Thus, by forming oriented
containers while in the substantial molecular orientation temperature range,
,; .
proees~ and quality probIems related to the need for excessively high forces
to stretch the preform at lower temperatures or the rapid relaxation of
~tresses on stretching at higher temperatures are avoided. More
:",
`~ 25 particularly, the temperature range at which substantial molccular
:' :
orientation occurs for thermoplastic amorphous matcrials will vary from
about 20 tc- about 60 F~ and preferably Irom about 30 to about 55 F. above :
.. , ~
~- thc ~lasstrans;tion tcmpcraturc of said matcrial,
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Caso L35'1
~Q~37~ 7
T~BL,E I
Preparation of bottlcs by stretch/~lowing a preforln made o
acrylonitrilc/styrcnc (70/30 wt. ratio)h~inga g1ass tr~nsition tcmperature
of about 2 3 0 F .
. S ~reform Temper~ture Results
212 F. Stretch rod stopped on contact with prefoxn~
232 F. 8" bulbs formed - large areas of whitened
pc~lyme r
240-250 F. Poor bottles formed having stretch lines and
10 (outside/inside gradient) whitening
Low quality yi~ld
Bire~ringence stress 494/326 psi
; ~50-270 F. Quality yield approximately 50 percent
Birefringence stress 450/280 psi
260-275 F. Few quality defects
Birefringence stress 420/290 psi
- Convenient processability
290-310 F. Excellent processability
Birefringence stress 200/160 psi
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Th~3 method o this invcntion irlvolves thc tc~hnique wherein
amorphous thcrmoplastic preforms which have bcen ~ormed earlier and have
cooled down are reheated to thc temperature at which substantial molccular
orientation will occur. Reference to the graph of Fig. S will show how a
5 typical operation will be carried out. The graph shows the comp~terized
res~lts of a heat transfer study made on a simulated run using selected
preform material, size and shape and selected heating and cooling conditions.
The graph shows temperature ~s. time with 0 representir~g the outside
surface and I the inside surface of a preform having the shape as shown in
10 Fig. 1. As the preform is heated using external heating~ means, the outside
surface will be at a higher temperature (0) than the inside surface (temper-
ature I) and a temperature gradient across the thickness of the preform will
result ~n~te intermediate points between 0 and I). The temperature gradient
results from heat being applied externally as well as the low thermal
15 conductivity of thermoplastic materials. At the end of the heat up period,
shown by vertical line H, the temperature gradient across the preform will
..
be at its greatest but such gradient will be reduced and equalize itself some-
,:
- what during the ensuing cool down period. Lines Tl and T2 represent the
temperature range within which substantial molecular orientation occ~rs.
20 By heating the outside surfacc of the preform to a temperature above the
6ubstantial molecular orientation temperature range, a temperature gradient
To~TI results. Upon cooling the prefor~ until the outside temperature is
within said substantial molecular orientation temperature range, the
.
ternperature gradient is significantly reduced. Also the overall preform
25, or the entire preform body reaches a temperature equilibrium or distribution
which is within this range for a significant period of time. During thic
- ¢xtended period whcn the entire preorm body is at a temperature within the
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Ca~o L354 101~78~7
~ubstantial rnolccular orientation tcmpcraturc ran~c, molecularly oricnted
contalners can desirably bo formed using a stretch blow mold of the type
illustrated in Fig. 4. The term overall or entire preorm body as used
throughout the specification and claims means all or es~entially all of the
5 body portion of the preform.
As noted in the simulated run of Fig. 5, during cool down the
outside preform teniperature drops below the inside p~eform temperature
and remains that way for an extended period. Under certain conditions
the outside temperature may remain higher than the inside and select
10 conditions may even provide an equalization of temperature for an extended
: . .
period. The important feature of this reheat method is that the entire
preform body has a reasonably small temperature gradient or distribution
and is within a temperature range which coincides with the substantial
molecular orientation temperature range over an extended period of time
15Fig. 1 illustrates a typical elongated tubular preform 10 used to
prepare containers such as bottles in accordance with the method of this
inven~ion. Preform 10 comprises a body portion 12 and a ~inish or neck ~ -
portion 14 and has an open end 18 and a closed end 16. Outside surface 20
of said preform i9 directly exposed to the external heating means whereas
20 inside surface 22 is not exposed dlrectly to the ~xternal heating means and
becomes heated throug~ thermal conduction. Though the wall thickness and
.;
weight of the preform 10 may vary widely, it generally has relatively thick
walls along body 12 typically ranging from about 120 to about 260 mils, and
typically weighing from about 15 to about 110 grams. The preform 10 may
25 be ormed by conventional means such as injection or blow molding and will
., ~
generally comprise any amorphous thermoplastic material such a~ poly-
styrene, polyvinyl chloride and nitrile containin~ polymers. Particularly
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Ca~c L354
u~eful materials or prcparing containers u~ing th~ n~ethocl of this invention
arc nitrile polymcrs containing from about 55% to about 85% by weight of a
nitrile monomer unit, based on the total polymer weightJ wherein the weight
perccnt of nitrile monomcr is calculated as acrylonitrile. The nitrile
5 monomers include acrylonitrile, methacrylonitrile, ethacrylonitxiIe,
propacrylonitrile, glutaronitrile, methyleneglutaronitrile, furnaronitrile,
~- etc., as well as mixtures of these monomers. The preferred monomers
which are interpolymerized with the nitrile monomers include aromatic:
monomers such as styrene and alpha methlstyrene; lower alpha olefins
~0 containing 2 to 6 carbon atoms such as ethylene, propylene, butylene,
isobutylene, etc.; acrylic acid and methacrylic acid and the corresponding
acrylate and methacrylate esters containing 1 to 4 carbon atoms such as
` methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and the
corresponding methacrylates; vinyl esters such as vinyl acetate; alkyl
:
~ 15 vinyl ethers wherein the alkyl group contains from 1 to 4 carbon a~oms such
"
as ~nethyl vinyl ether, ethyl vinyl ether, etc., and mixtures of the foregoing.
Optionally, the high nitrile packaging materials may contain
from 0 to about 25% by weight of a synthetic or natural rubber component
~; such as polybutadiene, isoprene, neoprene, nitrile rubbers, acrylate rubbers,
20 natural rubbers, acrylonitrile-butadiene copolymers, ethylen~-propylene
copolymers, chlorinated xubbers, etc. ,~which is used to strengthen or
toughen the high nitrile packaging materials, This rubbery component may
, be incorporated into the polymeric packaging material by any of the methods
which are well kno~n to those fikilled in the art, e. g., direct polymerization
.~,j . .
`;~ 25 of monomers, grating the nitrile monomer onto the rubbery backbone,
.! . polyblend of a rubber graft polymer with a matrix polyme~, etc.
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Cafio L3$4
8'~'7
Tllc preferrcd nitrile E~olymcrs or those packa~ing applications
requiring exccllent oxy~cn and water vapor barrier proporties in the
packaging m~tcrials, arc those nitril~ polymers containing frorn about
55 to about 85% by weight, based on the total polymer wei6h~, of an
5' acrylonitrile and/or methacrylonitrile monomer (wherein the weight percent
c~ rnethacrylonitrile is calculated as acxylonitrile). When acrylonitrile
is used as the sole nitrile monomer the preferred range is ~rom about 60 to
about 83% by weight whereas with methacrylonitrile the preferred range is
~Erom about 70 to about 98% by weight of methacrylonitrile which corresponds
~- 10 to about 55 to about 78% by weight of nitrile monomer calsulated as
acrylonitrile. The pxeferred comonomers are styrene and alpha methyl
, ~
styrene, Also preferred are interpolymers such as acrylonitrile/meth-
acrylonitrile/styrene; acrylonitrile/styrene/methyl vinyl ether and
acrylonitrile/styrene/ethyl vinyl ether.
", 15 The heating of the cold preforms in accordance with the method,,: :
of this invention may ~be carried out by passing said preforms throug}~ a
' heating oven containing conventional external heating means such as radiant
~' heaters or forced hot air. Apparatus for carrying out the method is
illustrated in Fig; 2 where preforms 10 are shown passing through oven ` ~;
. , .
" 2,0 or enclosed unit 24. The preforms 10 are manually or automatically placed
~ neck down in holders 30 and conveyed in one or more passes through the
,,:, ~ s~ ^ ,
'^,1 oven 24 on an endless chain. In a manner not shown (except very generally ~;
in Fig. 3), the preform neck portion 14 (Fig. 1) is either placed within the
~, holdcr or othcrwise masked as it passes throu~h the oven 90 that only the ,
25 body portion 12 is exposed to the heatin~ means. Neck portion 14 has been
, ' , accurately inished and ormed to close tolerancc~ and is not intended to be
~urther modified Ol altered at thi~ time. The prcforms 10 are conveyed
. .
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'
C~ s o L3 5~
~ '713Z'7
~hrough unit 2~ entcring at inlet si(le 32 and discharging through exit 34.
Thc unit 24 iAS shown consists o~ two sections with 26 being the area where
the heating takes place and 28 bein~ the cool down area To get more
uniIorm hei~t distribution on the outside surface of the preforms, they may
S be rotated in a conventional manner such as by provid;ng means to rotate
the preform holders 30.
As the preforms lû pass through the heating section 26, the
t>utside surface is heated using external heating means ~mtil the average
; temperature is greater than the ten perature range at which substantial
10 molecular orientation occurs~ Heat may be applied using banks of infrared
heaters which surround the preform as illustrated by heaters 36, 38 and 40
- in Fig. 3. As a practical upper limit, the outside preform temperature will
.. .
not reach the point where sag, lean or distortion of the preform material
will occur or where foaming will result due to the presence of small amounts
; ;` 15 of moisture. More particularly the outside surface of the preform is heated
:, . .
; until it reaches a temperature of about 65 to about 100 F. greater than its
glass transition temperature (Tg) and preferably irom about 70 to about
90 F. greater than Tg. $ince the preforms are heated externally and also
. .
because of the low thermal conductivity of the amorphous thermoplastic
20 materials being used, the outside surface of the preform will be at an
. ; , . .
; average temperature significantly greater than that of the inside surface,
. ~ . .
i. e. a temperature gradient wiIl exist as shown at H in Fig. 5 as it leaves
the heating section 25, The heater temperatures are not particularly
;,
clltical and may be varied depending on such factors as the position within
25 the unit, the speed at which the preforms ar~ conveyed and the preform
`;. :
material. Temperature measuring means (not shown) may be provided to
measure the outside preform temperature ater it lcavcs the heating section
- and such information can be used to adjust and control the oven conditions
~o that thc deslred tompcratllre can be reached,
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Ca~c L35~
1a~'~3'~7
The l~cated prc~orm is thcn allowed to cool eithcr in air or by
pas8in~ throuE~h a second cnclosurc which may be joined with the heating
~ection 6uch as section 28 of Fig. 2, The temperature in this cool down
section is significantly lower tban the oven heating section and pref~rms
5 are slowly passed thl:rethrough until the outside average temperature drops
to within the substantial molecular orientation temperature range. At the
~ame time, as illustrat~d by Fig. 5, the temperature gradient across the
.
preform thickness is being signiflcantly reduced and the temperature or
temperature distribution of the entire preform body tends to equalize or
10 equilibrate within the substantial molecular orientation temperature range
: In this operatîon, the outside average temperature of the preform is
generally reduced to from about 20 to about 60 F. greater than Tg and
preferably from about 30 to about 55 F. greater than Tg. The temperature
. .
in this cool down section can vary widely depending on conditions such as ~
j 15 the speed at which the preforms are conveyed, the thickness of such preforms ;
and the material thereof. General1y this temperature will be varied from
oom or ambient temperature up to the molecular orientation ~emperature.
.
~ Besides reducin~ the temperature gradient and allowing for more
.. . .
uniform temperatures throughout the preform tbickness9 this two step
.;,, .
20 reheating procedure has another significànt advantage~ That is the ability
:: .
to compensate for unintentional thickness variations resulting in the preform ~;
during processing, partlcularly in blow molded preforn~s. Thus, in the
~1 extended heat up process thinner spots will overheat, but conversely in the
cool down process they will cool down faster thus allowing them to be lower
~",',!, 2S in temperature a3 desired but still within the substantial molecular orientation
tempcrature range when the overall operation is complete.
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The hcatcd and coolcd (lown preform 10 i9 formed into an
oricntcd container by enclosing it within partible sections 42 and 44 o
blow mold 46, as shown for example in Fig. 4, while the tcmperature is
within the substantial molecular orientation temperature range in order to
5 complete the operation by carrying out a thermoforming orienting step.
- The term thermoforming as used in the specification and claims is intended
to include all types of molding including blow molding as well as the axially
~tretching and radially expanding operation illustrated in the apparatus of
Fig. 4. As shown i~ Fig. 4, a ~tretching mechanism 48 is moved into place
10 over the end opening in the closed mold and xod member 50 is caused to
" ~ move downwardly within and against base 16 of each preform (shown in
., .
phantom in its initial position within the mold) to axially stretch the body
~` portion of the preforrn against the lower wall 52 of the mold 46, Simul-
. .
taneously therewith or irnmediately thereafter, an expanding medium
15 issuing from orifices 54 in rod 50 is admitted into the interior of the
preform to blow it outwardly against the cavity walls of the mold sections
to form the container whch, in the illustrated embodiment is a bottle 56.
The particular advantages of the method of this invention include
, .
., .
the ability to obtain oriented containers from preforms using the reheat
20 method in a simplified operation in high ~ield and quality and with improved
uniformity in thicknes6.
~ larious modifications and alteratio~s of the invention ~vill be
readily suggested to persons skilled in the art. For example, varying
conditions in the heating and cool down procedures can be obtained as
.
25 desired to allow for different materials and different thic:knesses e. g. higher
or lower heating and cooling temperatures and different rates of speed
, ~
through eithcr section. Additionally, temperaturc sensing and control
:1 . .
means may bc incorporated in thc operation to aid in reaching and mai~tainin~
- tho dcsired oondition~.
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Cawc L354
~'78Z7
Thc Iollowin~ cx~mplcs are ~ivcn to illu~itrate more clcarly the
p~inciples and pri~ctice o this invention and should not be construed as
limitations thercof.
`:
EXl~MPLE I ~ -
A series of 35 gram blow molded preforrns shaped as illustrated
in Fig. 1 and made of a polymer comprisiing a 70/30 mixture by weight of
polymerized acrylonitrile/sty~ene monomer and havin~ wall thickness of
a.bout 150 mils ~ 5 at an ambient temperature of about 75 F. were inserted ~-
. ' .~n holders mounted on a conveyor and passed through a heating oven which con-
10 tained two banks of infrared heaters on opposite sides, each bank being 35in~hes
` long and consisting of eight horizontal heater strips varying in temperature
from about 890 to about 1000 F. The ambient oven temperature as measured
by a thermometer on top of the unit was 365 F. and the preforms were
conveyed through said oven in a period o 2. 5 minutes. The temperature
.,, :. .
~ ij 15 of the preform was rnonitored at its outside surface (5 inches from the base
. . .
;~ of the neck) using a Williamson infrared recording instrun;sent as it left the
~ :.! o
- ~ ~ ovesl with average temperature being in the 300 to 310 F. range. The
preforms were then allowed to cool in air for about 2. 5 minutes until the
o ~ ~:
outside surface temperature of the preform was at 270 F. as recorded ;
20 by the Williamson instrument. The preform was then immediately removed
from its holder and enclosed within a blow mold in a manner illustrated
~n Fig. 4, axially stretched and expanded outwardly within the mold to form
a container in the form o a bottle. Over two-thirds of the bottles formed
had good material distribution and in no cases were holes or blow outs
.;
`; 25 found.
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Ca~G L354 ~ B~7
`
ISXAMPLI~ II
For the purposes of ~:omparison, another series of prcforms
having the same coniguration as thosc of Example I were passed through an
oven having the same characteristics as in Example I except the heatcr strips
S were at a temperature of from about 770 F. to about 890 F. and ambient
oven temperature was 335 F. The outside surface of ~h~ preforms were
.. measured at temperatures averaging about 270 F. shortly after leaving the
oven and were placed in a blow mold and stretched and expanded as described
isl Example I. Blow through holes were obtained in a significant number of
10 preforms t~ 20%) and less than half of the preforms were blown into bottles
. . having good material distribution.
.
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