CA1294100C - Bubble forming and stabilizing device for use in a continuous extrusion process for making a blown film - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention discloses a new bubble forming and stabilizing device for use in a continuous extrusion process for making a blown film and a process for using same. The apparatus comprises a bowl shaped mandrel mounted subsequent to a die, the mandrel has an undersurface extending substantially parallel to and spaced from the path of travel of the blown film from the die and the undersurface is contoured to guide a stream of cooling air along its surface between the undersurface and the blown film as the blown film emerges from the die. The apparatus allows for increased production rates and improved physical properties of the forming bubble by creating more efficient heat transfer from the forming bubble to the cooling air stream. The device also provides support for the molten bubble during its most unstable state.

Description

3~ I
.

~.
1. ~ield Of The Invention This invention relat~s to ~ new apparatu~ -used a~ a bubble ~orming and ~tabilizing device in a continuous extru~ion process for making a blown film and a process for uslng same. B10WA films may be made from any one of ~everal proce~ses and one ~uch proces3 is commonly reerred to as a blown continuous extru~ion process. The invention discloses an int~rnal air de~lector and bubble forming and stabilizing mandrel for u~e in internally coo}ing and ~abilizing a bubble of blown film during the extrusion proce~s. The device allows for increased production rates, improved stabilization and improved physical properties o~ the forming bubble by effectivel~ ~orming the bu~ble over an in~ernal mandrel enabling a high velocity cooling air strea~ to be directed between the unde~r and ou~er surface~ of ~he mandrel and the innee 3ur~ace o~ the ~orming bu~ble u~ually ~ormed o ~ ~olymer~ The inve~tion en3bles more e~lclent heat trans~er ~rom the extru~ion polymer to the cooling air ~trea~ cau~ing the molten polymer to drop in temperature more qulckly ln the blowing proces~ which ~ubsequently al~o improve~
the s~ability of ~he process and further allows even high~r internal and external air veloc~ti2~ to be 1 introduced which in turn allow~ for lncrea~ed productivi~y and ~proved product quality due to improved stability. The device al90 provides upport for the molten polymer during its mo~t unstable ~t~te ~ ~ "551E51g'L5~ 13L_~ LL~5_~5~
The devic~ of the present inventlon is particularly sui~able for use in a con~inuou~ process for the production of blown fil~ In many cases~ the blown film will be foemed from a polymer resin although other materials may be used to produce a blown bubble. For ease of reference, and no~ for limi~ation purpose, the following des~rip~ion will be made wi~h reference ~o a bubble formed from a polymezO In a typical proces~, a hot polymer melt i5 ~ed to a die lS f~om whlch it is extruded ln the for~ of a tu~e which is nipped at a de~i~ed point after cooling to form ~
bubbl~. The extruded polymer is generally exp~n~ed by using internal air pres~ure to blow the polymer int~ ~
bubblc and the bubble ~hould be o uni~orm and con~tant thickness ~ubsequent to the ~ro~t line. ~oweve~, the tube which emeege3 fro~ the di~ itself i~ gener~lly unstable due to low melt trensth untll ~ts temperature is reduced ~uPficiently to improve the melt ~trength and eventually ~olidify ~he polymer, th~t is, a~ i~s frost line.

1 To increase the rate at which the molt~n bubble reaches the point o~ ~olldlfying at the fro~S
line, the temperature oE the ~orming bubble is reduced as quickly as possible while still ~aintaining the deslred stabilityO This may be done ln several ways.
One of several known ~ethod~ is by using an external air ring which directs cooling air on~o ~he ou~er surface of the forming ~ubble as it emerges from the die. Additional cooling can also be achi~ved by cooling the inside of the bubble such as is disclosed in United State~ patent number 4,236,884 granted on December 2, 1980 to Gloucester Engineering Co., Inc.
The amount of cooling is yenerally limited by the temperature of the cooling air, the ~elt strength of ~he ex~rusion polymer, ~he blow-up ratio of the bubbl~
size to ~he die size and the volume and velocity o~
cooling air that can b~ introduc~a to the i~ner an~
outer ~urEaces o~ the ~orming bubble without de3troying the ~tabllity o~ the iSorlning bubble. The~e limitations directly a~fect ~he production line speed and the product quality through the extru~ion proce~.
Various devic~s have been proposed which a~tempt ~o reduce ~he temperature of the air withln ~he forming bubble to improve the extrusion ra~ whi ch $n turn reduces production costs~

1 Cooling of the formlng bubble can be achieved by cooling Erom ~he in3ide of the ~ormlng b~bble or b~
outside cooling o~ the bubble, or by both. An exampl~
o~ the ex~erior c401ing i8 ~hown in Uni~d States patent 4,25g,947 granted to Robert J. Cole, the inventor heeein. In this patent, there is disclosed a dual lip air ring wherein the exterior air is blown radially outwardly away from the forming bubble emerging from the die. The resulting v~nturi effect and low pressure zone causes the for~ing bubble to draw away ro~ the medial line as it emerges from the d~e and allows a non-impinging~ relatively high velocity air stream ~o be introduced to the exterior wall of the forming bubble, cooling it faster than direct impingement coolingO By cooling the for~ing bubble faster while maintaining the s~abili~y of th~ bubble, it is po~sible ~o lncrea~e the rate o~ extru~ion o~ the bubble and Maintain good quali~y thuR reducing pro~uction ~:lme and co~ts.
Additional aooling can al80 be achie~ed ~ro~
the inslde of the bubble. A8 shown in Unit~d States patent number 4,236,884~ there is proposed a device which exchangQs ~he hot interioE air w~thin ~he ~orming bubble with cooler air via por~s located within the die mandrel ltself. Air is supplied to a series of o~

1 internal nozzles whlch blow the air radially outwardly at ~he internal ~urface o~ ~he forming bubble.
These and other processes of the prior art have clear limitations due to ~he effect of ~he impingement of ~he air and the low melt ~trength of the polymer during the blow~ng proces~. Further, as the forming bubble itself i8 increa~ed in size with relation to the die size, the radial distance between the internal air nozzles ana the wall of the Porming bubble will also increase which has the undesired effect of reducing the efficiency of the cooling process.
SUMMARY OF ~HE INVENTION
Accordingly, lt is an obj~ct of the present invention to at least partially overco~e ~hese disadvantages by providing an apparatus suitabl~ for use in a continuous blown film proces~ which allows for more e~ficient cooling of ~he forming bubble as it emerges from the die.
~t 18 a ~urther ob~ect oP the pre~ent lnvention ~o prvvide an app~ratus ~uitable ~or use ln a Gontinuous blown 11m proce~s which provides a method of bett~r supportlng and ~tabilizing ~he fvrming bubbl~
during the blowing procegs while ~he mol~en polymer i~
in lts mo3t sensi~ive and un~table ~tate.

~ 6 --1 It is yet ~ further ob~ect of the p~e~en~
invention to peovide an apparatu~ suitable for u~e in a continuous blown ~ilm proce~ which results in improved product thickness uniformi~y and which reduce~ wldth variations of the resultant product thereby resulting in an improved product sheet flatness.
A still further objec~ of the present invention is to provide an apparatus for use in a continuous blown fllm process which result~ in a faster quenching of the molten polymer rela~ive to the distance or time of the polymer from the di~ to ~he f~ost linet ~hereby resul~ing in improved clarity and less haze of the resultan~ product.
It is yet a still further ob~ect o~ the present invention to provide an apparatus foc use in a continuous blown film proce~ which allows for control of the stock of the bubble and the t~perature of the polymer at the point of blowing thu~.al~owlng ~or improved control o the orlentation o~ the fo~ming bubble and its physical properti~.
To this end, in one of lts aspects, the invention provide~ an apparatus for use in a continuou~
extrusion proce~s for making a blown ~ilm which comprise~ a bowl-~haped mandrel mounted subsequent to a die suitable for forming a blown film, wherein said - 7 ~

mandrel has an undersu~face extending substantially parallel to and spaced rom the path o~ ~ravel of the blown ilm rom said die, said undersur~ace conto~red to guide a s~ream o~ cooling air along lts surface between said undersurface and said blown fllm as said blown film emerges from said die.
Other objects and adv~ntages of the present invention will appear from the following description taken together with the accompanying drawings.
BRIEF DESCRIPTION OF THB DRAWINGS
FIGURE 1 is a schematic representation of an apparatus for a typical blown film proce~s embodying the present invention.
FIGURE 2 is a sectional view through one-half of the internal supply air deflector and bubble forming mandrel of the present invention.
FIGURE 3 is a schematic rep~esentation of an apparatus for a ~ypical blown fllm proce~s embodying the present invention wherein the moveable poc~ion of the mandrel is ~eparated fro~ the ~tationary por~ion, to allow or ~tar~-up of the proce~.
FIGURE 4 is ~ schema~ic representation of an apparatus for a typical blown filrn process using a second embodiment of the present invention.
2S DESCRIPTION O~ THE PREF~RR~D ~MBODIM~NT
- ~eferring now to figure 1~ there is shown a schematic representation of an apparatus for typical blown ~ilm process embodying the present lnvention.

_ 8 ~

l The polymer 2 1~ ~ed from a supply 4 to a dle 6 wherein the polyme~ 2 i5 converted ~o a tubular Elow surround1ng a mandrel in the die 6. ~he polymer 2 emerges from the die 6 in a t~bular form and is blown S into a continuou~, ~ubular film 8 which may or may no~
be stabilized by an external s~abilizer calibration cage 10. Following stabilization and calibration by the stabilizer cage 10, the film 8 ic nipped by nip rollers 12 and collected, at a desired stage downstream of the nip rollers. Films currently made may vary in thickness from 10 microns to up to l.Omm in thickness, but not limited thereto.
As the f ilm 8 leaves the die 6 at point gap 15, the polymer is very hot and must be cooled rapidly. In most applications, the poly~er ~us~ be stabilized by good aerodynamic principle~ until the desired s~ock temperature is achievedO The longer the cooling ~akes, the longer the polymer is in a condition wherein it i5 unstable thus m~king the ex~ru~ion proce~s more dief1cult to control. Thu~, it i~ i~portant to ~uickly cool or control the molten polymer as quickly as i5 po~sible to maintain the integrity of the resulting ~llm. For example, if an attempt i~ made to cool the forming bubble more quickly by increasing the velocity of the cooling air, the bubble may well become unstable 1 and may collaps~ due to the pressure of the impinging air or pressure of the alr rela~ive to ~he weak melt strength of the forming bubble. Thu~, ~t i~ important to balance rapid cooling with the integrity of the bubble during the blowlng and cooling proce~.
In order to effect such cooling, figure 1 shows the use of a dual lip air ring 16. This device is fully di~closed in United Sta~es patent 4,259,047 issued on March 31, 1981 to ~obert J. Cole, th~ present ~o in~entor. This air ring 16 is used with a die ln a blown film process to apply cooling air to the exterior surface of an extruded tube of film-forming material pa~sing ~hrough the air ring 16. Air 18 is supplied from a supply 20 and is discharged fro~ a first lS downsteeam gap 22 in air ring 16 radially outwardly from the path of movement oP the fil~ 8 in the un~xpanded state so as to create a vacuum force which urges the tube outwardly by vacuum ~orces and cau~e~
cooling air to flow along th~ ~ur~ace. A ~econ~
upstr~m gap 24 dQllvers a tubular strea~ a~ a bound~ry layer of air that precool~ the film 8 and lubr~cate~
the sur~ace of the external ds~lec~r dye or forming cone 25 and prevent~ ~he or~in~ bubbl~ from ~ticking to ~he ~tructure be~ween the upstream gap 22 and ~he down~tream gap 24.

- 10- ~2~

l The present lnvenSion relates to the u~e of an internal supply air de1ectoc~ bubble ~orming and stabilizing mandrel ganerally lndicated a~ 14, This devlce 14 is a bowl shaped mandr~l which surr4und~ a S central air exhaust stack 26 and affixed ~o an elevator device 54D As will be explained hereinafte~, the internal hot air is exhausted through the air exhaus~
stac~ 26 ~o exhaust port ~8. Cool air is supplied through supply manifold 30. The supply and exhaus~ of air through the manifold system and bubble gize senso~
system (not shown) may be carefully controlled by means of blowers 32, 34 and control dampers 36~ 38. The blowers 32, 34 may or may not be variable speed blowers.
lS Figure 2 i5 a 5ectional view through one half of the internal ~supply ~ir~ deflector and bubble forming and stabillzing mandrel 14, Tbe mandr81 14 has a continuous undersurface 40 along which relatively high velocity cooling air 42 i9 supplied and at~ached.
The cooling aLr 42 is Ped Prom the conduit 44 radially outwardly and along fixed f;rst surfac~ 46 to second surface 48. This cooling air 42 attaches itself to the second surface 48 anfl pulls the stock of the forming bubble 8 along the same path from the extrusion die 6. The forming bubble 8 attach~s itself to the air 1 8tream ~2 becau~e of th~ vacuum e~ct caused by the low pressure zone o high velocity ai~ along the ~econd ~urface 48. The stream of cooling air 42 b~come~
itself ~he lubrlca~ion over the mandrel ~urface for the s formlng bubble ~ emerging from the die 6. Since there i~ not any impingement of the air onto ~he molten polymer of the forming bubble, it is poss~ble to u~e even higher velocities of cooling air along ~he inner bubble sur~ace which serves to cool the melt much more rapidly than any o~ the prior art devices~ At the same ~ime, improved stabilization of ~he forming bubble is achieved due to the vacuum forming ef~ect on ~he melt. The transfer of heat fro~ the melt to the cooling air is markedly improvea thu~ increasing the efficiency of ~he overa.Zl sy~te~.
The bowl shaped mandrel 14 is rotatably secured to the die 6 ~o tha~ lf and when the die 6 ro~ate6 during ~he blowing process, the m~ndrel 14 will rotate in con~unc~ion therewith~ ~uring the blowlng proae~ someti~e advantag~ou~ ~o rotata ~he dle 6 to move any lmperfections in thiGkn0s~ variation, back and ~orth acro~ ~he winding roll. In ord~r ~o malntain the de~ired ~f~ect without ~estroyi ng the integrity of the forming bubbls, the ~andrel 14 rotates in concert with ~he ~i~. This may be accomplished by }~
~ 12 --ary suitable mean~, such a~ a~fixing the mandrel to the die it~elf.
The bowl shaped mandrel 14 consists of a ir~t portion SO fixed to the die and an axially moveable portion 52, which is moveable away from th~
first portion 52 as shown in figure 3 for ~he purpose of start-up and inding the optlmum gap between the lnteenal mandrel and the external air ring deflector cone. The fir~t portion 50 is affixed to the die 6 itself and can only rotate as the die rotate~ a~
explained hereinbefore. No movement away or towards the die will occur. The axially moveable portion 52 is attached ~o an elevating device 54 which allows axlally moveable portion 52 to be moved away frora or towards ~5 ~he first portion 50. Thi~ may be done in any desired : way. One example as shown in figure 3 is to a~tach ~he upper sur~ace o~ the axia}ly moveabl~ poe~lon 52 to a pair of plston rod~ 5fi which ln turn cooperate with piston3 58. ~s the thread drive rod 60 i8 rota~ed by the air motor elevating device 57~ thi~ in turn rai~e~
rods 56 which in turn raise~ the axially moveabl~
portion 52 away from th~ flrst portion 50.
When ~he axially moveable portion 52 is lowered and m~she~ wi~h ~ir~t portion 50, the pin 6~
fits within openin~ 64 to orientate the portions in the ~ 13 ~ 3~

correct alignment and drive tlle mand~el 52. A3 shown ln flgure 3, the leadlng edge 66 of the undersids cut-away poction of the axially moveable portlon 52 engages outer wall 6~ of first portion 50. Thu.~, in the rontiguous position as shown in figure l, axially moveable portion 52 is correctly aligned with first portion 50.
Thus, when the axially moveable portion 52 ls engaged with first portion 50, the entire bowl will rotate as a unit when ~he die is rotated.
One example of a means to affix the mandrel 14 to the die 6 is shown in figure l and 3. In this case, first portion 50 is connected to a spoke 51.
Spoke 51 is connected at its opposite end ~o connector : 15 53 which is secured in the die 6. Thus, when die 6 rotates, thi~ rotates spoke 51 which rotates portion 51 of the mandrel 1 l. While only one spoke Sl i shown in f igures 1 and 3, i~ is pee~erably ~o have a number of such spokes Sl to seeurely af~ix porkion 50 to die 6.
In orde~ ~or the die 6 to rotate ahout the aha~t 26, a sleeve heariTlg S5 cover3 sha~ 26 at the plac0 of rotation o~ the mandrel.
It is important that axlally moveable portion 52 i8 able to move away from first portion 50 during the star~ up phase of ~he blown film prvcess. It has - 14 ~ 3~

been found that during the start up phase, a gap o about 12 inches $s nece~sary for the cperator to place his hands to pull the forming bubble up around the mandrel during the ini~lal s~art-up s~ge, The bowl-shaped mandrel may be made o~ any desired slze and is not limited to any particular dimensions. The mandrel may be made of any desired material in this case, made of ca~t aluminum. I~ is also possible that the bowl-shaped mandrel may be designed to create specific properties in the finished product, by altering the exact shape and slze of the mandrel and elevation from the extrusion point 15.
Air 42 is of a high velocity and it i~
thought that it is attracted to and attaches ~tself ~o : 15 the unde,rcurfaces 46, 48 of ~he mandrel its~lf. ~ased on an understanding of current aerodyna~ic theory it is understood that this high veloci~y air will not wander away from these surfaces but lts path literally conforms to the contour of the ~andrel but when leavlng the ~andrel, attaches it~elf to the inner ~ur~ace o~
the ~ormlng bubble. Since the alr i~ of high veloclty, lt create~ a low pre~sure area or zone which attract~
the forming bubble thereto and pulls lt along as the air travels over its path.

¢

- 15 ~ f~

1 It has been found by the present lnventor that substantial improvements in the coollng processe~
and other benef~ts are achieved by using the apparatus of the present lnvention~ For example, improvement ln the cooling rates of not le~s than 15~ over prior art processes have been noted and expected up to 50% with further refinements. It is also lmportant that with low melt stcength polymers, the gains are potentially greater since more failure of the bubble stability occurs with impinging air of the prior art. Many of ~he new resins used for blown films have very low melt strengths thus making it even more important to improve and maintain the integrity of the for~ing bubble during the cooling stage.

The velocity of the cooling air along the inner surface of the forming bubble using the apparatus of the present invention has been increased considerably over that oP currently use~ velocities. The temperature of the cooling air has not provecl critical a~ tn the prior art but it is belLeved better utillzation of cooler ai.r is achLeved. The significant advances in heat transfer and other notable gains are not completely understood but some are known to relate to the successful i.ntroduction of high velocity air along the inner surface of the molten bubble in its most sensitive ~ ?d~

1 state, as well a~ to a good scrubbing ac~ion achieved along thi~ ~ame surface br~aking up ~he boundary layer of air, with the present apparaku~.
The prior art devices generally blow cooling S air radially outwardly at the inner wall of the ~orming bubblel and do not provide means to ~tabilize ~he ~orming bubble. Thu~, the melt strength of the forming bubble in the molten s~ate limits the v~locity of the cooling air. Since there i~ also no direct implngem~nt of cooling air on the bubble, the previous restriction based on the melt streng~h has been effectively removed thus allowing for higher velocities to be used resulting in more effective cooling. Since this air travels in the same direction as the direction o~
lS travel o~ the forming bubble, it ~ignificantly aids in more rapid cooling. It is al~o believed that the vacuum crea~d by ~he low pre~sure zones contribute~
signlficantly to the stabilization of th~ ormin~
bubble .
It is ~l~o ~igni~lc~n~; khat the cooling air 42 acts on the ~orming bubble 8 clos~r to the die 6 80 that cooling i~ e~fec~ed ea~lier. It i~ al~o ~ignifican~ to understand that ~ince the cooling of forming bubble 8 i~ achieved much fa~ter than with 2S prior art device~ it allows, a~ a dir~c~ resuï~ of improved melt ~trength, increased ~ir veloc1t1e~ to be used with such othet features as the external dual lip alr ring. Since initial cooling is much faster, the limitation of the melt s~rength of the orming bubble vis-a-yis the velocitles of the air in the air ring i~
significantly reduced, thus allowing higher velocities to be used from the exteenal air ring thu~ further increasing the rate o cooling. This synergistic effect is most notable with polymers of low melt strengthO Also, due to the internal support of the mandrel backing the melt agai~st a fixed form or surface allows for higher velocities of external air ~ooling without collapsing ~he bubble in its mol~en : state.
In anothsr embodiment of the present invention, when it is desired to produce a bubble having a long stock, commonly referred to as a wine glass shaped bubble or a long stock bubble, the man~rel 1~ is ~aised to the desired dis~ance Prom the die 6.
In thi~ embodiment~ the molten poly~er emerges from the die and ri8CS as ~he stock wi~h a small diameter untll the stock of the pol~mer has sufPiciently reduce~ its temperature to a desired temperature at which time, the bubble will be blown in the same manner as explained hereinbefore.

10~3 1 In this embodlment, the ext~rnal air ring 16 ha~ an elevator device aflxed thereto and the air ring 16 would be elevated ~o a position immediately below the mandrel 14 allowing an approprlate gap between the undersurfacP 40 of the mandrel 14 and the deflector lip of ~he air ~ing 16 as disclosed bereinbe~ore. The relationship between the mand~el 14 and the air ring 16 in this embodiment would be inden~ical to that shown ~n figure 1, but elevated from the dle 60 This embodiment allows for a change in the orientation of the polym~r which affects the mechanical properties of the polymer such an elongation ~nd tear resi~tance in the machine direction vis-a-vis the transverse direction.
It is also possible wi~h a further embodiment of the invention, to f~rther i~prove the process by introducing and exchanglng as much cooler air volum~ a3 pos~ible a~ quickly as pos~ible to reduce the internal bubbl~ temperature for ~u~ther cooling affect. In order to increase this cooling, i~ is preferred to exchange the to~al volu~e o air wi~hin the bubble al3 many 'cimes per minute a~ can be achievedO Thl~ can be done l:y erea~ing a æupply air annular flow channel currounding the exhau t sltack to channel air past ~he elevating bowl mandrel and in~roduce the air radially ~ 19 ~ 3~

1 outwardly through one or ~ore ori~ic~ at a po1nt pa~t the bowl ~andrel. This may be below Ot pa~t the f~o3t line or both. In this case, the ~andrel would slide up and down th~ outer diameter o thig add~tional annular s supply air channel on a ~leeve bearing cimilar to the d0~1gn described hereinbefore.
Th~ embod~ment i~ 111u~tra~ed by Flgu~ 4 o~
the appended dra~ing~ In Figure 4, annular hole~ 100 are provided extending through ~he first portion 50 of the bowl shaped mandrel 14. Annular hole~ 102 ~re : provided through axially movable portion 527 A flow ; control valve 104 is rotatably mounted on the top surface of the portion 52 via screw 106. Flow control valve 104 ha~ holes 108 which corce~pond in number and size to holes 102 in portion 52.
A diffuse~ ~pteferably a perforated ~creen) 110 ls ~ount~d on brackets 11~ which ~re ~lxed to po~tlon 52. The top of ~he ~cceen 110 i~ mounted on arms 114 o~ the elevatiny device 54 A~ explainad herelnbe~ore, coollng ai~ i~
introduced along the undec~ide o~ the mandrel 14 to break up ~he boundary dir 30 ~ha~ ~h~ cooler air will cool the bubble more effec~ively. Thi~ cooling alr sorub~ the surface of the melt to increa~e the ovsrall ~5 - 20 ~ 3~

efficiency o~ the proce~, However, the amoun~c of ~ie which can be lntroduced i~ limlted by the melt strength of the bubble. The velocity of the air and th~
turbulence thu~ created i~ thus restric~ed by ~his melt ~reng~h~, The inventor has found that if more cooling air were introduced to the ~ nside of ~he buhble as the limit of the v~locity of the ex~e~ior eeoling air i5 reached, thl~ will also increase the cooling of the bubble. In this embodiment~ cool air is fed up under the mandr~l 14 and then through the annular hole~ 100, hole 102 and holes 108. This cooling air move~
upwardly and out through ehe di~user 110 as shown by arrow~ 116. ~y feeding ~hi~ cooling air radially 15: outwardly at a higher level, a me~n~ has been ~ound to provide add~tional cooling air to the bubble to increase the exahange oP hot alr thus promoting ~urther cool ing, rrl~e ~low control device 10~ i~ rotatabl~
~o pre~erably by a motor ~not ~hown) to align the holes 102 with ~he hole~ 108 and to controï the amount o~ alr pa~sing througll the~e holes~. The ~crew 106 ls firs~
unlocked, the v~lve turned as de~ired and then tbe screw i~ lock~d in place. P~e~erably, the flow con~rol - 21 ~ 3(~

valve 1~ an aluminum plate. The dlf Puser 110 may ~ oP
any suitable material and i8 preferably a ~teel scr~en having an open area of about 40%.
By using this embodiment, the total volume of air within the bubble may be e~changed more generally and thus, cools ~he bubble even further, without destroying the integrity of the bubblel The presant invention has been de~cribed ana:
illu~tr~t~d with respect-to ~ ~erti~ally al~gned ~pparatus and process wherein the bubble is formed il~ a vertical direction. This ha~ been done for illustrative purpo~es only and it is equally applicable to a line il~ any other orientation.
While th~ present invention ha~ been lS ~xplained with reference to a bubble ~ormed rom a p~:>lymer ~esin, it i~ to b~ undQr~os:~d that it i~
equally applicable to forming bubble~ o~ other mate~ uch a5 varlou3 type~ o rubber~, tha invention i8 appliaable ~or u~e in arly continuous blown ~ilm materi~l.
While the inven~ion di~clo5es ~nd de~crib~ a preerr~d embodlment of the inverltlorl, it i~ undex~tood ~h~ inven~ion i5 not so restricte~.

Claims (15)

1. An apparatus for use in a continuous extrusion process for making a blown film, comprising:
a bowl-shaped mandrel mounted subsequent to and rotatably in concert with a die suitable for forming a blown film, said mandrel including a first portion fixed to said die and an axially movable portion seating with said first portion and adapted to be moved away from or towards said first portion, wherein said mandrel has a continuous undersurface extending substantially parallel to and spaced from the path of travel of the blown film from said die, said undersurface contoured to guide a stream of cooling air along its surface between said undersurface and said blown film as said blown film emerges from said die.

2, An apparatus as claimed in claim 1 wherein said apparatus is mounted on a central air exhaust stack.

3. An apparatus as claimed in claim 1 wherein said undersurface is adapted to direct said stream of cooling air radially outwardly and in the direction of travel of said blown film.

4. An apparatus as claimed in claim 1 wherein said apparatus is made of cast aluminum

5. An apparatus as claimed in claim 1 wherein said axially moveable portion is affixed to an elevating device which is adapted to move said axially moveable portion away from or towards said first portion.

6. An apparatus as claimed in claim 1 wherein said mandrel is mounted on a rotatable sleeve bearing mounted on a central exhaust stack such that said mandrel will rotate about said central exhaust stack in concert with the rotation of said die.

7. An apparatus as claimed in claim 6 wherein said mandrel is connected to one or more spokes and said one or more spokes are connected to a connector mounted in said die such that when said die rotates, said mandrel rotates in concert therewith.

8. An apparatus as claimed in claim 1 for making a blown film having a long stock, wherein said mandrel is mounted at a substantial distance from said die.

9. An apparatus as claimed in claim 8 wherein said mandrel is mounted on an elevating device to elevate said mandrel to a substantial distance from said die.

10. An apparatus as claimed in claim 2 wherein a supply air annular flow channel surrounds said central air exhaust stack for channeling cooling air, to the interior of the forming bubble past said mandrel.

11. An apparatus as claimed in claim 10 wherein said supply air annual flow channel is a plurality of orifices to supply said cooling air to the interior of said forming bubble.

12. An apparatus as claimed in claim 10 wherein said supply air annual flow channel comprises a plurality of orifices extending through said mandrel and a diffuser mounted about said mandrel to diffuse said cooling air towards said forming bubble.

13. An apparatus as claimed in claim 12 further including a flow control valve for controlling the amount of cooling air passing through said control flow channels.

14. An apparatus as claimed in claim 13 wherein said flow control valve is an aluminum plate rotatably mounted on the top of said mandrel, said plate having a plurality of orifices therethrough.

15. An apparatus as claimed in claim 12 wherein said diffuser is a perforated steel screen having an open area of about 40%.