CA2080143A1 - Blow molding apparatus and method with parison uniformity and alignment control - Google Patents

Abstract

ABSTRACT
A blow molding apparatus and method in which a substantially stress reduced parison is formed by extrusion means which provides for a substantially uniform process condition history around the periphery of the parison and in which means are provided for enhancing the structural rigidity of the parison to prevent sagging and buckling of the parison and maintain alignment thereof with the longitudinal axis of the extrusion die as the parison is elongated from the die, and for further maintaining alignment of the parison with the axis during the blow molding operation to form a stress reduced container having a substantially uniform wall thickness. In one embodiment, the structural rigidity of the parison is enhanced by cooling the outer surface thereof to form a thin outer surface region of higher viscosity material on the heated parison.

Description

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B~OW NOLDING APPAR~TIlS AND ME~OD WIT~
PARI~O~ tJNIFoR~I~r AND ~IGN~N~ CON~OL

F i-ld .~f th~
Th~ pr~sent in~tion relat~s tc~ blow ~oldlng :
appara~cu~ and m~thod~ for for~Ln53 ~ubular.a~rticles and ~ontalner~ fro~ plasti~ and ~ ilar d~fonn~le mat~ri~l~, which ~r~ first formad ~Lnto ~ c~xsor S tub~lar pari~on ~h~p~ and the~ blo~ mols~d lnto a 8elect~d con~a~n~r conflguratlo~ and ~o improved conltainers fo~eld from said ap~par~u~ and utlli~ing ~uch method~ .
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Parl~on~, tubular extru810n8 oi~ pla~tic re~in whlch ar~ ~ubseqtlently blow molded to fo~ bottle~ or other container~ or artle:le~, are ~ormed ~n ~he~ prior art by variou~ apparatus some in~:ludins~ extru~ion head~ which ea~trud0 ~ucc:~s~iv~ layer~ of pl~sti~ re~in onto mandrel. A typical multll~yer parison extru~iLon head ha~ separate inlets for receiving he~ted ~nd plasticlz~d resin from lnd~vidual ~crew ~ ruder~ and has ~epar~te channel~ for d1 s~ril~u~ing and ea:pr~3s~Lng tha re~l?ectlve plastiG rexin~ in 8ucce58ive layer~ on the mandrel.
Each channel include~ an annular equal:L~atlon and :~ : ,'`" " ' ' , 2~

distribution chamber surrounding and spaced from the mandrel for receiving the plastic resin from the corresponding inlet. From the equalization chamber the plastic resin i~ fed though a frustoconical transfer passage downward and inward to a tubular extruRion channel formed around the mandxel. This annular extru~ion channel exits through an inwardly or outwardly flaring annular die which includes a conical core member which may be moved longitudinally relative to the outer member of the die to vary the thickness of the wall of the extruded tubular article.
One.particularly u~eful and successful e~trusion head for fo~ming tubular articles such as parisons i8 disclo~ed in U.S. Patent No. 4r79~5!~ Thi~ head includes ona or more individual annular extrusion module~ surrounding re peetive ~uccessi~e portions of a stepped.or tapered mandrel to form the annular extrusion channel which receives one or more successively extruded plastic resin layers from the modules. Each module has a pair of members with mating surfaces.wherein the equalization and distribution chamber and th~
frustoconical transfer passage are formed. Haring the head formed from individual coaxially ~paced extrusion modules enable3 the head to be readily a~s~mbled and 2$ disassembled as well as enabling the a~sembly o an extrusion head with ~arying numbers of modules so that a module can be used in one asqembled head to extrude a single layer tubular article or can be used in a differently assembled head to extrude any layer of a multilayer article. The module~ forming an extrusion head can be positioned in any desired order.
Furthermore, the die module~ are separated from each other by annular air spaces. Concentric tubular necks or collars extend from each module into engagement with 3S an adjacen~ module to define the separation distance or the width of the air spaces between module~. These air spaces prevent heat transfer from a high temperature 08CTo5349 3 ~ ~8~3 module to an ad~acent low temperature module. Low temperature re~in~ can be degraded if heated to the higher temperature. This patent further discloses polymer inlet pressures at the extrusion head of 4,000 S to 6,000 psi (27,000 to 41,000 KPa) for polycarbonate, 2,500 to 4,000 psi (17,000 to 28,000 XPa) for polypropylene, and 2,000 to 3,000 psi (13,000 to 21,000 KPa) for tie resin~ and barrier re~ins.
U.S. Patent~ No. 3,~49,143, No. 4,111,630 and No.

4,182,603 di~close tubular extrusion dies for blow molding of multi-ply films and having nested fru~toconical, hemispherical and cylindrical die members forming polymer distribution chambers wherein 6piral and helical grooves are formed on the outer surfaces of inner members. These grooves progres~ from points near or at the inlets toward the outlets with decreasing depth so that the polymer flow is gradually forced oùt of the grooves and into the fru,stoconical, hemispherical or tubular space between die me~bèrs to evenly distribute the polymer around the chamber. These nested arrangements have several defic.iencie6 such as limiting any temperature differential between the different layers being extrudQd, xequiring laryer haad~ for extruding greater numbers of layers, and having long conical pa~ages from the end of the groove or grooves to the annular outlet.
Generally the prior art tubular extru~ion apparatus requires a xestrictive frustoconical transfer pa~sage from the di~tribution chamber to the annular outlet from which the tubular article is extruded. This restrictive passage provides a relatively large pre~sure drop, i.e., greater than 50% of the total pressure drop from the extrusion head inlet through the di6tribution region or chamber and the restrictive pa~age to the outlet, in order to assist in even distribution of the polymer in the distribution chamber. In the absence of the restrictive outlet passage with ~he relatively large 08CTo5349 2 ~ 4 3 pres~ure drop, the polymer tends to flow at a greater rate alony the shortest path between the inlet to the di~txibution chamber and the closest region of the annular outlet producing unevenness in the thickness of the tubular article about its circumference.
While the prior art apparatus i~ generally efficient and ~ucces~ful in the extrusion of tubular articles such as multilayer parisons, blown film~, wire coatings, etc., there i~ room for impro~ement. In addition to the pressure differential problem~ discussed above, the stresses caused by temperature diferentials need to be reduced. For instance, polymer melt in prior art extru~ion head~ flow from the inlet s~de of an equalization and distribution chamber to the opposite side. As a result, resins processed In prior art extrusion head~ are subjected to temperàture differentials, as well as subjected to the above-described pressure differential~, a~ the resin is processed through the inlet, the distribution means, and outlet. As a result of these processing differentials, the resin extrudate will deposi1; in a non-homogeneous distribution, thereby creating actual and latent internal stxes~e~ in the e~txuded parison. Then when the pari~on i8 formed into a final shape oP a bo~tle or similar article, ~uch internal stresses will be carried forward, ~nd perhaps in some instances even exacerbated, in the final product. For in~tance, if the bottle or like article is to be reused and subjected to high temperature cleaning or the like and/or hot filled or filled under pressure, e.g., with carbonated beverage, the article may explode as a result of such internal stresses. Given that prior extrusion apparatus are likely unable to alleviate these stresses there is a need to further improve extrusion heads. This i~
especially so in light of environmental demands which require reuse of containers rather than their disposal in landfills or the like.

5 ~ D 8;~ 3 Accordingly an object of the present invention is to con~truct a new and improved polymer e~trusion head and process for tubular extrusions which minimize processing differentials that occur in prior art extrusion heads and processe~ and thereby resulting in a more homogenous di~tribution of polymer as it i~ extruded.
It is also an object of the invention to provide a container having superior properties as a result of the improved polymer distribution described abovel and to thereby provide a container having sufficient properties to be effec~ively and ~afely reused or reclaimed, while utilizing a minimum amount of polymer for attaining ~he ~ame.
Another problem encountered wlth prior art apparatus and method3 of pari~on formation and blow molding stems from the tendency of the pari~on to "sag" as it extends and elongates from the annular aperture of the extrusion die and to la~er 'ibuckle" when it i~ captured in the mold. In the prior art apparatus and method~, when the parison exits from the die and is elongated from the exit, it tend3 to sag along the direction of the axis thereof such that some portions of thP pari~on are thinner than others, thereby cau~ing a non-uniform wall thickne8~ di~ribution in the axial direc~ion.
In addition, when the parison is cut and captured in the blow molding cavity at both ends by the blow mold, portions of the parison tend to "buckle" or warp and go off center in the mold cavity. When the parison is blow molded to the final container shape, these laterally displaced portions of the parison wall are stretched by different distances in order to reach the cavity wall and difference~ in the thickness of the containar wall result. That is, the sid2waya buckling of the parison along it~ length and away from its nominally straight axi3 cau~e~ a change of the "blow ratio" for different portions of the parison, which results in ~ubstantial circumferential variation~ in the thickness of the ,.................. .

2iD3g~1 ~ 3 container when the blow molding operation is performed.
The~e circumferential variations in wall thickness caused by buckling are in addition ~o those wall thickness varia~ions in the axial direction which are cau~ed by sag a~ d~scribed above.
~s a result, some portions of the wall of the container are substantially thinner than others and present weak spots in the structural integrity of the container. These weak spots limit the ability of the container to withstand high pres~ure and otherwise generally cause deterioration in the ability of the container to withstand stresses under conditions encountered in use, such a~ in single u~e or throw away applications where the container is hot filled or filled under pressur~; su~h as with a carbonated beverage, as well as in-c~rta~n other single u6e or throw away applications,~and also in functloning a~ a refillable co~tainer. Therefore, even when more homogeneo~sly formed parisons are producedt as are di~cus~ed above in connection with the above-mentioned ob~ects of ~he present invention, ~uch sagging and huckling of the parison still cause variations in the container wall thickness with the attendant problems as discussed a~ove.
In an attempt to ~ddress ~uch v~riation~ in wall thickne~ of the finished container, the overall thickness of the walls of such container~ has been increased in an effort to maintain the thinnest portions of the wall-at a thickness level sufficient to meet worst case conditions. However, this re~uire~
substantially thicker parisons, which are more difficult and more costly to extrude, and introduces other complications as well, such as further difficulties in the blow molding portion of the proce~s, which otherwi~e compromise the quality and structural integrity of the finished product. In addition, the finished container 08CTo5349 7 2;~8~1~3 is substantially heavier and bulkier as a result of the increase in the wall thickness.
It is therefore another object of this invention to provide an improved blow molding apparatus and method in which such sagging and/or buc]cling of the parison are greatly reduced and nearly eliminated, as a practical matter, as a source of variations in the thickness of the walls of the finished blow molded container.
Other objects and advantages of the present invention will become apparent and the invsntion will be more fully understood from the detailed de~cription which follows, taken in connection with the accompanying drawing~.
UMNARY OF T~E IMVE~TION
The present invention pro~ides a parison extrusion and blow molding appar~tus an~ method which achieves the above de cribed objects and which provides an improved blow molded container which is superior to prior art blow molded containers for various single use and throw away applications, such as, for example, where the container is hot filled or filled under pressure, and which is also capable of use as a refillable container.
In accordance with one embod;Lment of the invention, a homogeneou~ parison of substantially ~miform thickness 25 is formed (although the thickne~s thereof in the axial direction may be purposely varied at the point of extruRion to accommodate different blow ratios along the axi~ of the parison), and a thin, outer surface region of the pari~on is cooled as it emerge6 from the extrusion die by an amount sufficient to cau~e a substantial increase in the viscosity of the cooled outer surface region, thereby increasinq the stiffness or rigidity of the outer surface region and enhancing the hot melt strength of the parison. This prevents substantial deformations, such as sagging or buckling, in the shape of the parison as it is extruded from the die and a it is elongated downstream thereof.

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08CTo5349 8 2 ~
Only a relatively thin, outer 3urface region of the parison i8 S0 cooled and the amount of heat extracted from the bulk of the hot parison is therefore quite small in comparison to the total amount of heat stored S in the thermal mass of the hot parison. That i5, the depth of the cooling extends only in a relatively thin outer surface region of the parison. However, the depth of the cooled ~urface region can vary depending upon the time the surface of the parison is exposed to the cooling gas and also d~p~nding upon the temperature of ~he cooling ga~ and the flow rate ~hereof. The depth of the cooled surface region can al80 vary along the length of the parison as will later be pointed out in further detail.
lS After completion of the extrusion stepr the cooling is discontinued prior to the blo~ molding operation and the temperature of the outer region i8 allowed to increase to approach the bulk temperature of the parison. The time interval betwe~n the discontinu~nee of the cooling of the outer suxface region ~nd ~he performance of the blow molding operation i3 selected to be sufficient to allow the temperature of the outer region to increase to approach 1:he bulk temperature of the parisonO The amount by which the cooled region is allowed to increase in tempera~ure in order to exhibit suitable properties for blow molding will depend in each case upon the particular materials used and the process conditinns which are selected.
The final temperature of the outer surface region of the parison iE typically reduced only slightly from the bulk temperature of the parison as a result of the heat absorbed in reheating the cooled outer region. The overall viscosity o~ the composite parison is therefore returned to within the optimum range for blow molding and the subsequent performance of the blow molding operation i8 not compromised in any way.

08C~05349 2~8~
The container thu~ formed in the final blow molding operation i therefore exhibits substantially reduced residual stresses and local variations in wall thickness and has greatly enhanced structural properties such that it has superior properties applicable to single use and/or throw away applications, ~uch as, for example where tha container is hot fllled or filled under pressure, a~ well a~ other singl~ use and throw away applications, and also is capable of use as a refillable container.
The invention will be better understood and other objects and advantage~ thereof will become apparent from the following detailed descriptiQn taken in connection with the accompanying drawing~.
~RIE DESCRIPTION OF THE DRAWIN~GS
Fig. 1 i3 a section view of an sxtru~ion head for a extruding a multilayer parison :in accordance with one a~pect of the inv~ntion~
Fig. 2 i~ a bottom view of an upper membex of on~
extrusion module in the hsad of Fig. 1.
Fig. 3 is a sectional view, taken at line 3-3 of Fig.
2, of an extrusion module removed from the head of Flg.
1. ' .. .
Fig. 4 i -a sectional view, taken at line 4~4 of Fig.
2, of a por~ion broken away f rom the module of Fig . 3 .
Fig. 5 is an elevational view, partially in section, of a broken away portion of an upper me~ber of the module of Fig. 3 with the section taken at line 5,6 -5,6 of Fig. 2.
Fig. 6 is an eleva-tional sectional view of a broken away portion of a lower member of the module of Fig. 3 with the ~ection taken at line 5~6 - 5,6 of Fig. 2.
Fig. 7 is a diagrammatic view of a parison extrusion apparatu~ including the extrusion head of Fig. 1.
Fig. 8 i~ a view similar to Fig. 2 showing a variation of the spiral channel in the upper member of the extrusion module.

lo 2~ 3 Fig. 9 i~ a view ~imilar to Figs. 2 and 6 3howing another ~ariation of the spiral channel in the upper member of the extru~ion module.
Fig. 10 is a schematic illustration of a container blow molding process and apparatus which can incorporate an extru~ion head according to this invention.
Fig. 11 is a partial view in cross section of an annular die accordin~ to the invention.
Fig. 12A is a cross-sectional side view 3howing parison sag upon exit from an extrusion die a~-the parison extends and freely hangs from the die, illustrating a problem with prior art app~r~tus and methods;
Fig. 12~ is a cros~-sectional eide Yi~W 3howing the buckling of a parison during clamping in the mold and prior to blow molding into a container, illu~trating another problem with prior art apparatu~ and methods;
Fig. 13 is a top cross seckional view of a 6ection of the parison shown in Fig. 12B;
Fig. 14 is a partial section,l view of a container formed in accordance with prior art blow molding methods;
Fig. 15 is a side sectional ~vie~ of a porti~n of apparatus embodying the present in~ention and illustrating the cooling of thA surface of a parison as it exits an extrusion die;
Fig. 1~ is a cross sectional view in further detail of the apparatus of Eig. 15 J and ~ig. 17 i5 a fragmentary view of a portion of the apparatu~ of Fig. 16 illustrating passage shapes for r~ducing and controlling the circumferential motion of the cooling gas flow.

DESCRIPTION OF THE PREFERRED EMBODIMENT
~s shown in Fig. 7, one embodiment of an extrusion head, indicated generally at 10~ in accordance with one aspect of the invention include3 one or more extrusion modules such as a plurality of extrusion modules indicated generally at 14, 16, 18 and 20 which receive streams of different polymer materials from respective conventional screw extruders 24, 26, 28, and 30 for forming a multilayer parison 32 which is then e~truded into a container blow mold as illustrated in Fig. 10.
As shown in Fig. l, the modules 14, 16, 18 and 20 are coaxially mounted in spaced relationship along the axis 22 of the modules so as to form air spaces 88 including frustoconica~ air spaces 90 thermally- isolating each module in th~ head to enable improved extrusion temperature control of each layer being extruded.
In the illu-~trated parison head, the module~ 14, 16, 18 and 20 coaxially extend over ~pa~ed-seotions of a tapered stepped mandrel 34 so a~ to extrude their re~pective layers into a tubular-extrusion channel 35 defined between the inner surfaces of the modules and the outer eurface of the mandrel.
The.modules 14, 16, 18 and 20 have sub~tantially similar con3~ructions. As shown in Fig. 3 for the module 18, each of the modules includes upper and lower members 40 and 42 which mate tc~gether and include a plastic material inlet 46 openi.ng.on the periphery of the module, an annular outlet 48 opening at the inner surface of the module, and one or more ~piral channel~
~uch as a pair o spiral channels 50 and 51, Figs. 2 and 3, extending from bifurcated inle~ channels 52 and 53 to a position adjacent to the outlet 48. The inlet 46 is formsd by machining the mating surfaces of the member~
or by boring along the parting line between the outer portions of the membPrs. Alternatively, the inlet 46 can be foxmed by boring in one of the member~ 40 or 42 similar to that shown in U.s. Patent 4,798,526. The inlet bifurcated channels 52 and 53 are machined in opposite direc~ions through ninety degree arcs in the mating surface~ of the outer flange portions of the member~ 40 and 42. The mating flat or land surface~ of O~CT05349 the flange portions of the members 40 and 42 sealingly engage each othex to close the channels 52 and 53.
Centex portions 54 and 56 of the members 40 and 42 are generally frustoconical with apexes extending downstream. As shown in ~ig. 6, the inside surface of the center portion 56 has a cylindrical ring portion 58 and three successive frustoconical portion~ 60, 61 and 62 which extend inward from the ring portion 58 to the cylindrical surface 63 of a bore which define~ a portion of the outer wall of the tubular extru~ion channel 36, Fig. 1. Th~ slant angle of the surface 61, i.~., the angle of the surface 61 relative to the axi~ 22, i8 lesg than the slant angle of the surface~ 60 an~ 62 so that ~he t~ickne~ of an annular frustoconical space or lS passage 64, Fig. 4, betwee~ th~ portions 54 and 56 gradually increases ovex th0 region of the spiral channels 50 and 51, as illustrated by the short and long dashed line 70 which has the same angle as ~urfaces 60 and 62. A~ shown in Fig. 5, the outside surface of the ~0 inner frustoconical portion 54 has a cylindrical ring portion 65 seaIingly engaging the surface 58, a first frustoconical surface portion 66 extending inward from the ring portion 65 to the first convolution of the spiral channels 50 and 51, and a-second frustoconical ~urface portion 67 extending inward from the outermost ~piral convolution formed by channels-50 a~ 51 to the apex of the frustoconical portion 54 where a cylindrical surface 68 of above, Fig. 4, defines a portion oi the outer ~all of the tubular extrusion channel 36. The bores defining cylindrical surfaces 63 and 68 are coaxial. Edges 71, Fig. 2, between the first and second frustoconical surfaces 66 and 67 are formed in the land areas between the first convolutions of the spiral channels 50 and 51. The first frustoconical surface poxtion 66 has a slant angle equal to surface 60 so that surface portion 66 sealingly engages the surface portion 60. ~he second frustoconical surface portion 67 also has the ~ame slant angle as surfaces 60 and 66 but has a reduced diameter, as illustrated by the long and short da~hed line 69 which is an extension of the surface 66, so as to introduce an initial frustoconical space or thickness between ~he surface 61 and the land areas separating the ~piral channels 50 and 51-to begin the frus~-oconical passage 64. At its inner end the frustoconic~l passage 64 defines the outlet 48.
Referring to Fig. 2, the inlet channel~-52 and 53 have extensio~s 72 and 73 machined in the surfaces 65 and 66 o the inner center portio~ 54 to open into the origin3 of the respective spiral channels 50 and 51.
thes~ orlgins are on opposite sides, 18~ ~part. The spiral channels 50 and 51 are formed by machining the frustoconical ~urface 67 of the inner frustoconical portion 54 and ~ach extend clockwis~ for approximately one and one-half convolutions about the frustoconical-portion 54`. The cross-sectional area of each channel 50 and 51 gradually decrease~ from its origin to it~
endpoint so that the polymer forced into each channel at it~ origin is gxadually dispersad into the increasing width of the frustoconical pass2lge 64 to distri~ute the polymer evenly about the frustoconical portion 54. The pitch of the spiral channels, i.e., the spacing between adjacent convolutions, is constant and the depth of the ~pixal channels relative to surace 67 changes li.nearly so as to facilitate the machining of the channels.
The length of the spiral channels must together circumscribe or extend symmetrically around the longitudinal axi~ of the extrusion module ox modules, i.e., extend sub~tantially 360 around the axis of the bore which the matin~ inner and outer portions create to fonm extrusion channel 36, so as to subject all of the polymer flowing from the inlet to the outlet to 35 substantially the same process conditions.
"Circumscribe," as used herein, iR meant to include circular a~ well as non~circular paths. Such channels 2~ 3 provide a means whereby the polymer is distributed at the annular extrusion outlet with properties which are substantially s~mmetrical around the axi~ of the extrusion module or modules for all resin which is distributed through the outlet.
In the modification shown in Fig. a, channels 93 and 94 extend in opposite directions each through a minimum of 180 along spiral paths so that the channels 93 and 94 together extend completely around the inner fruztoconical portion. The number~ of spira~-channel~
and their direction can va~y. Th0 mo~i~icatinn of Fig.
9 illustrates a single spiral channel 96 wh~ch makes more than three full convolutions around the inner ~rustoconical portion.
Ref~rring back ts Fig. 3, the outsidQ surface 76 of the lower-portion of the lower frustoconical portion 56 ha~ a slant angle which i5 le~s than the ~lant angle-of the inside surface 78 of the upper frustoconical portion S4 so that the width 82 of the inside surface of the module 18 along the axis 22 i~ gr~ater than the width 86 of the outer portion~ of ths module 18. The difference between the widths 82 and 86 i~ selected to provide the desir~d ~pacing 88, Fig. 1, b~twe~n ad~acent modules.
The low~r edge of the apex of e~ch hlgher module 14, 16 and 18 ~ngage~ the upper side of the next lowex module 16, 18 and 20 to define the spacing 88 between module~.
Spacer~ 84 fonmed on the bottom of the flanges of the lower members 42 abut the adjacent module~ to assist in maintaining even spacing between the flange~ or outer portion~ of the modules around their circumference.
These spacers 84 are broken by the variou~ boxe6 into the flange ~o ~ to permit air flow into and out of the ~paces 88. The frustoconical air ~pace por~ion~ 90 of the spaces 88 e~tend to the points of engagement between module~.
~olts 98, Figs. 1 and 2, Becure the upp~r and lower member8 40 and 42 of the extru~ion modules 14, 16, 18 ~ ~ 8 O 1 4 3 and 20 together~ Guide pinz g9, Figs. 2 and 4, provide for proper alignment of the member6 40 and 42 during a~semb~y. Threaded bor~s 101, Fig. 6, in the members 42 are aligned with rec~sse~ 103, ~igs. 2 and 5, in the members 40 ~o that conventional ~acking bolts (not shown) can be screwed into the bores 101 to engage the recesse~ and foree the members 40 and 42 apart during disassembly.
As shown in Fig. 1, the modules 14, 16, 18 and 20 are held in the extrusion head 10 by upper and lower clamp members 100 and 102 and by bolts 104, ~ee al~o Fig. 2, which exten~ through bore~ in the clamp members and the e~tru~ion module~. The lower ~urface 106 of the upper clamp member 100 ha~ a convex frustoconical configuration ~imilar to the lower ~urface of the extru~ion modules 14, 16, 18 and 20, and the upper surface 108 of the low~r ~lamp ~nember 102 ha~ ~ concave frustoconical configuration ~im:ilar to the upper surface of th~ extru~ion modules. This enable~ extxusion module~ to be interchanged in position as well as the clamp member~ to be used to hold a single extrusion module or any number of modulQs.
The mandrel 34 i~ tubular and extend~ through the upper ~lamp member and a mounting plate 110 fastened by bolts 112 to the upper clamp ~ember 100. Bolts 113 ~ecure the mountîng plate 11~ to conventional blow molding and ~upporting structures (not shown). A
thread~d nut 114 secures the upper end of the mandrel which ha~ A tapered fit in the clamp member 100. The mandrel 34 is tapered downward with by a plurality of successive steps 118, 120, 122 and 124 which begin at each corresponding outlet of the modules 14, 16, 18 and 20 to provide for the extrusion of the successive polymer lay~r~ on the mandrel. The diameters of each ~tep are ~elected in accordance with the desired thickness of the corresponding layer being extruded.

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Generally different mandxels are required for different arrangements of e~trusion modules.
Alternatively, the mandrel can have a constant diameter through the extrusion modules and the inner diameters of the extrusion module can be stepped. This limits the interchangeability of the module~, but blank modules can be manufactured with the inner diameters machined later after the extru~ion head configuration is determined.
Annular upper and lower die~ ~28 and 130 are mounted by a die clamp 132 and bolt~ 136 and 138 on the bottom of the module clamp member 102. The lower die 130 is threaded to the upper die 128. Positioned within the dies is a die core 140 which is thread~d onto the lower end of a shaft 142 slidably extending through the lumen of the mandrel 34. The die 128 ha~ its die opening tapered or stepped down in diameter at 144 in correspondence to the tapered terminal end of the mandrel 34 50 that a constant cxos~-sectional area of the extrusion passage is mainta:ined. This reduced diameter extends along a section 146 of constant diameter through the upper port.ion of the lower die 130 with the-bottom portion 148 o the lower die flaring out to the desired diameter of the article or parison. Ths bottom porti-on 150 of the die core 140 flare~ outwardly at an angle slightly greater than the angle of the die portion 148 so that the e~it thickness of ~he annular extru~ion channel is less than the upp2r portion of the extrusion channel to insure that the layeræ of plastic polymer are firmly bonded together and that ~he cross-sectional area of the extrusion passage is maintained.
In order to a~sure that the polymer-layers are preferably radially co~pres~ed to some degree upon being extruded from the dier the cro6s-sectional area of the annular channel at the exit from the bottom of the die portions 148 and 150 is slightly less than the cro~s-sectional area at the entrance portion of the channel.

~ 0 8 01~ 3 In other words, the extruded multi-layer polymer structure i6 preferably compressed slightly by reason of the reduction in the cross-sectional rea of the flow passage formed by the channel formed by the elements 148 and 150 in the direction of the exit therefrom. This assures compression of the multi-layer structure as it exits from the die and provides firm bonding and enhanced stxuctural integrity of the extruded multi-layer parison.
As illustrated in Fi~. 11 the bottom portion 150 of the die core 1~0 can alternatively flare inwardly at an angle greater than the angle of the die portion 14%. As a result the die i8 inwardly tapered, but ha~ an expanding extrusion channel annulus. In the-embodiment of Fig. 11, the ~ame contraction in cro~s-sectional area of the annular flow passage iB preferably provided in order to compre~s the extruded multi-layeF ~tructure as it exits tha die. Depending upon ths properties desired, the cross-sectional area of the annular flow passage can either be contracting, as illustrated, or it can be expanding in the direction of the exit.
A center longitudinal bore 152 is formed through the die core 140 and the shaft 142 for pa~Bing ga8 into the pari~on ~ein~ extruded to p~vent collapse of the parison.
The extrudate exits ~he above-described die into a container blow mold according to conventional technigues. As illu~trated in Fig. 10 parison 32 exit~
into a container blow mold 200. Container blvw mold 200 can be a conventional split mold which i~ divided into halves 200a and 200b along its ~ongitudinal axis and ha~
a shape selected for the particular container desired.
The extruded parison 32 is then processed according to conventional blow molding technique~. See, for example, ~Blow Molding", Modern Plastics, Octo~er 1991, pp. 222-224.

~ ~ 8 ~ ~ ~ 3 For exampler after parison 32 e~its into container blow mold 200 halves 200a and 200b of the mold come together, thereby pinching the bottom of pari~on 32 to form a seal. The sealed bottom of the parison will become the bottom of the finis~ed container. Shortly after the bottom of the parison is pinched, a conventional cutting blade (not shown) severs the parison from the extrudate exiting the annular die 130.
The container blow mold 200 is then removed from under annular die 130 and replaced with another mold 300 to repeat the process de~cribed above. This particular process is known as a single-~tation shuttle process.
After the container blow mold is remo~ed from under extrusion head 10, container blow mold 20~ i~ shuttled to calibration station 310. A ~low pin 311 i8 then inserted into container blow mold 200 and parison 32 to inflate the parison into a container schematically illu~trated as 312 in figure 10. Container blow mold 200 i8 not illustrated at calibration st~tion 310 in orde.r 2Q to better illuskate container 3.l2. The blown container 312 is then separated from mold 200 and trimmed using standard techniques.
As shown in Fig. 7, the illustrated parison extrusion apparatus includes a convention~l control 160 which controls the vertical position of the ~haft 142 in the mandrel 34. Parisons being extruded are often varied in thickness from the ~ottom to the top; i.e., bottle bottom portions having inverted bottoms need thicker walls at the bottom to prevent bulging of the bottoms from the pressure of the bottle contents such as a carbonated beverage. AdditionAlly the control 160 can vary the extrusion pressures of the extruders 24, 26, 28 and 30 to vary the thickness of each layer bein~
extruded relative to the other layers in a conventional manner. The~ variations are deliberately introduced and are not the result of parison sag or buckling.
Thu8, the term "variations" in the wall thickne~s as 19 `
u~ed to describe and refer to the present invention are in~ended to refer to those ~ariations in the wall ~hickness which occur a~ a result of unwanted parison deformations and dis~ortions, such as sag and/or buckling.
Referring back to Fig. 1, electrical heater coils 164, 166, 168, 170, 172, 174, 175 and 176 are mounted on the extrusion modules 14, 16, 18 and 20, ~he clamp members 100 and 102 and the lower die member 130, respectively, for initially heating the corre~ponding members to their desired operating temperatures as well as maintaining a proper temperature during operation.
Thermocouple sensing elements 180, 182, 184, 186, 188 and l90 provide temperature signals of the extxusion modules 14, 16, 18 and 20, the lower clamp 102, and the die member 130 to conventional contxol circuitry (not shown) operating the hea~er coils.
In an example of a paxison suitable for blow molding to form a bo~tle, the parison is formed by extruding inner and outer layers of polycarbonate, and intermedi~te layers of amorphous polyamide and regrind through multiple extrusion modules. However, there may be instances where a single material ha~ properties which m~et1ali of the requirements of a particular con~ainer application. In ~hose ins~ance~, pari~ons having only one layer are needed. Accordingly, those single-layered parisons can also be prepared into single-layered containers according to the invention wherein only one extrusion module would be used.
The described embodiment has ~everal advantages over the prior axt extrusion apparatus. The spiral channel or channels forming together at least one full convolution gradually opening into the frustoconical passage 64 results in pressure differential~ in the channel or channels being cancelled by pressure differentials in the thinner upper portions of the frustoconical pa~Eage 64. This eliminates the need for an annular pressure equalization and distribution chamber which is gQnerally required in prior art tubular article extrusion apparatus. Such equalization and distribution chambers still have some unequal pressure, i.e., thers must be a pressure differential to produce plastic pol~mer flow from one side to the other side of the annular chamber. The uneven pressure around the annular outlet produces uneven thicknesses in the layers being formad in the parison. Thus the embodiments of lQ Figs. 1~9 produce superior circumferential l~yer thickness uniformity.
Furthermore a generally restrictive frustoconical transfer pas~age extends from the prtor art equalization and distribution chamber to the annular outlet in order to minimize the pre3sure differential in th~
equalization and distribution chamber. This prior art restrictive transfer passage result~ in a requirement for a substantially higher melt pressure compared to the present embodiment which relies upon at least one convolution formed by a channel or by the combined length of two or more channels of decreasing cross section opening into the gradua:L increasing thickness of the frustoconical pa~sage 64 to minimize circumferential pressure differentials at the outlet 48. The sLze of the spiral channel or chann~l~ and the thicknes~ o f the passage 64 are selected to produce sub~tantially les~
pre~sure drop between the inlet 46 and outlet 48 compared to the priox art.
Still iurther the elimination of the prior art equalization chamber with its opening into a restrictive rustoconical txansfer passage reduces shear on the plastlc pol~mer that is produced by such opening.
Substantially less shear results from the present gradual opening of the spiral channel or channels through one or more spiral convolutions in the frustoconical passage 64. This results in increased strength in the article being produced.

Circum~erential polymer extru3ion temperatuxe~ tend to be more uniform in extrusion heads according to the invention, and substantially more uniform in the embodiments having two or more spiral distribution channel con~olution~. As discus~ed earlier, since polymer melt in the prior art flows from the inlet ~ide of the equalization and distribution chamber to the oppo~ite side, a temperature differential can be produced where the inlet polymer melt temperature differs from the average temperature of the distribution module. As a result, the actual and la~ent internal stresses discu~sed above occur. However, in extru~ion heads according to thi~ invention all portions of the polymer material flowing from the inlet to the annular extru~ion channel are exposed to substantially the same proce~s con~itions, e.g., temperature, pEe~ure, shear, etc., along the channel mean~ from the inlet t~ the annular ~xtrus on channel. Therefore, all of the polymer arriving at the annular extru~ion channel has substantially tha same process hi6tory, that is a substantally identical prior expo~ure to such proces~
con~itions, and i~ therefore substant ally uniform in its propertien around the periphery of the extru6ion channel a8 it is extxuded therefrom. Thus, the tendency for circum~erential temperature diffexentials and the occurrence of non-ho~ogeneiti~s are reduced.
Reducing the occurrence~ of non-homogeneities allow~
one to-produce parisons and bottles which are believed to be superiox ~o those in the art. A~ indicat~d earlier, redu~ing non-homogenous distribution of resin which result from pressure and temperature differential~, as well as other processin~
differential3, xeduces the number of actual and latent internal stresse~ in any parison, bottle or liXe article prepared ~rom the resin. Accordingly, the resulting bottle or like article will po~e3~ suparior ability to maintain its integrity under exter~al stresses.

08CTo53~ 8 ~ ~ ~ 3 The texm ~'properties" as used herein refer to those properties which are the result of process conditions applied to the resin during the flow from the inlet to the outlet. These include such parameters as process temperatures, pressures, shear condition~ and other process condition to which the polymer is exposed along the path of flow from the inlet to the annular extrusion outlet. The flow path is arr~nged s~mmetrically around the periphery of the axis of the module(~) so that all of the po~ymer is exposed to substantially the same proce~s con~itions during it~ fl~ow from the inlet to the extrusion outlet, with the rQsult that it arrives at the extrusion outlet with substantially symmetrical and homogenous properties around the full periphery of the extrusion outlet.
The present embodiment also ha~ the capability of providing greater temperature isolation between adjacent modules with a relatively simple and inexpQnsive structur~. This allow~ independent contr~1 of the temperatures of the modules so that the temperatures of the individual modules can be controlled to b~ either the same or different from each other. The prior art included abutting collars ~or spacing module~, but the collar~ ha~ substantial thickne~3s to tEansfer hea~
between module3. The present e~bodiment by including fru~tocon~cal air ~paces 90 provides improved temperature isolatio~ hetwe~n extrusion module~.
While the de6cribed embodiment ic directed to manufacture of parisons used for blow molding bottles, the disclosed modular extrusion head iB ~uitable for the manufacture of many other tubular articles such as film which i5 formed by slitting a tubular form with or without blowing of the tubular form; pipe or other elongated profile article which may or may not be filled with foam su~h as through bore 152; glass mat reinforced sheet wherein polymer is extruded from one or more annular extru~ion heads with rect~ngular center boxes ~0 8 01~ 3 onto a glass fiber mat; pultruded sheet, rod or profile article; and wire coatings. For certain applications ~uch a~ forming wire coating~ or extruding coatings on other elongated materials, the extru~ion head may not need a mandrel; rather the ob~ect on which the coatings are being extruded takes the pla~e of the mandrel. The term "container" is used herein to include all of the above described article~.
The container of the present invention i5 remarkably superior to those formed by prior art method in that it iR relatively free from residual internal stre~ses otherwise carried forward from the parison by rea30n of the fact that the polymers of which such prior art parisons wer formed were subjected to non-uniform proces~ing conditions in the extrusion head. These non-uniform conditions resulted from the fact that flow paths from the inlets of such prior art e~trusion apparatus were non-s~mmetrical in flow pattern from the inlets to the annular extrusion channel. In the apparatus and method of the present invention, such flow paths extend symmetrically about the axis of each module such that all of the polymer flowing from the inlet to the extrusion channel is subjected to substantially the same process conditions, whereby the properties of the polymer are substantially the ~ame and homo~ene~us around the full periphery of the annular extrusion channel at the point of extrusion from the channel.
The parison thus formed is therefore exhibits substantially reduced residual internal stresses relative to what would otherwise occur as a result of such non-uniformities and non-homogeneities. After the stress reduced parison is formed, however~ ~tructural stres~es and discsntinuities can still be ~ormed in the finished container in the sub~equently performed blow molding operations. Such problems, which will be discus~ed further below, can be caused, for example, by 08CTo5349 ~3~43 ~4 deforma~ions such as ~a~ and/or buckling of the heated parison before the blow molding operation i8 performed.
Referring now to Fig. 12A, there i5 shown a parison lS0 formed in accordance with prior art methods which has undergone ~sagging" along the axis thereof as it has emerged from a~ extrusion die 162 and has been elongated to hang free therefrom. As illustrated, the sagging of the parison 160 as it hangs free from the die 162 has resulted in thinner wall sections 160a and thicker wall sections 160b. These cause unwanted variations in the w~ll thickne~s of the finished container or other blow molded article.
Referring now to Fig. 12B, there is ~hown a cross-sectional view of a pariaon 160 which has been extended from an extrusion di~ 162 and formed in accordance with priox art methods, and which has been cut o:Ef at 160c by a hot knife and captured in a blow mold 166. The parison 160 is shown as being deflected or ~buckled~
from the longitudinal axis 164 of the die 162. The amount of the buckling shown in Fig. 12B i~, of course, exaggerated for purposes of clei~r illustration and in order to explain the problems which are caused thereby.
The parison 160 is shown positioned with the longitudinal axi~ theraof (that i~, the longitudinal 25 axi~ of the extrusion die 162) centrally aligned with the cylindrical inner ~urface 166 of the blow molding apparatus, such as that shown in Fig. 10. Because of the buckling of the parison in the elongated portion thereof extending from ~he extrusion die 162, the portion of the parison extending further away from the die are deflec~ed sideways laterally from the longitudinal axis 164. At the plan~ C-C, the parison 160 i~ buckled such that the distance A from one side thereof to the inner wall 166 of the blow molding wall 35 i8 substantially less than the distance B from the o~her ~ide of the parison to such inner surface 166. As a re~ult, when the paxi~on 160 ia blow molded, one portion 08CTo5349 of the parl~on along the section C C i~ stretched by the distance A and the portion at the opposite side i~
stretched by the substantially greater distance B. The wall of the blow molded con~ainer stretched over ~he greater distance B is therefore thinner than the wall portion ~tretched over the short~x di~tance A.
This effect i6 illustrated in Fig. 13, in which, along the section of plane C-C t the wall portion 168 of the container ~tretched over the greater distance B is sub~tantially thinner than the wall portion which ha~
been stretched over the shorter di~tance A. This is the result of the ~'blow ratio" along the distance B being substantially greater than the blow ration along the distance A. The "blow ratio" i~ the ratio of the new diameter of the container after blow molding divided by the original diameter of the parison. The blow ratio over the distance A is much smaller then elsewhere around the periphery of the par:ison at the plane C-C.
Therefore, the thickne~s of the wall of the finished container i8 the thinnest at the distance B and increases as a function of the blow ratio around the periphery to the distance A, as shown in Fig. 13.
Fig. 14 show~ a section of the fini~hed container in which the wall portion 168 is substantially thinner than the wall portion 170. Other forms of discontinui~ies in the thickn~s~es of prior art blow molded containers also occur, such as the ~o-called ~football~ shaped region 172, which is the result of a localized buckling of the pari~on before blow molding. Highly localized thickne~s discontinuitie~ such as region 172 ar~ particularly trouble~ome because they repre~ent local weaknesses in the wall of the container which are highly ~ubject to rupture in u~e, particularly when use as a refillable container i ~ttempted.
The present invention avoid~ the occurrence of substantially different blow ratios around the periphery of the blow molded container. Shown in Fig. 15 is one o~cTO5349 embodiment of an apparatus and method of the pre~ent invention for increasing the structural rigidity of a parison 173 as it is elongated from the extru~ion die 162. Positioned adjacent the exit of the extru3ion die 162 is an air ring 174 which includes an annular discharge aperture 176 through which a cooling ga~ 178, in thi~ case air, i6 directed again~t the exterior surface 180 of the pari60n 173 as it QXitS the extrusion channel of the die 162. The cooling ga~ 178 iB directed against the pari~on outer surface 180 with an axial velocity component and preferably al~o at least a slight peripheral velocity component such that the cooling ga~
flow forms a spiral pattern around the exterior of the parison a~ shown in Fig. 15. The annular discharge aperture 176 of the air ring 174 is positioned ~ust ad~acent tho annular outlet 2xtrusion channel of the extru6ion die 162 such that the cooling gas 178 i~
directed against the outer surface 180 of the parison almost immediately downstream of the outlet channel of the die 162.
While the term "air ring" i~ used to describe the device 174, it is to be understood that this term is used in a generic sense and that the device 174 can accommodate any cooling gas or any mixture of gases and fluid~ or vapors thereof which are capable of performing the cooling function as described herein. Similarly, the term "ga~ means any cooling fluid suitable for the purpose~ se~ forth.
The temperatur~ of the cooling gas 178 and the direction and velocity of the flow thereof are selected such that a thin outer surface region 182 of cooled material of the parison is formed a~ the outer surface of the pari~on. The parameters of the cooling gas flow must be selected 3uch that the thin, coolsd surface region 182 remains intact and of the proper thicknes~
along the length of the parison as i~ i6 form~d. The ~ooling gas may be turned on and off a~ the parison , 08CT0534s 2 ~ 3 emerges from the die and the thickne~s of the cooled surf ace region may thus be varied along the length of the parison to suit the properties of the materials and the process conditions being u~ed.
When the parison has been fully formed to the proper length, the f low of cooling ga6 i~ di continued. At thi~ point, the parison is still s~ruc~urally rigid by raason of the thin outer surface region 18 2 of lower temperature, high viscosity materîal. Af ter the f low of cooling gas i~ di~continued, the blow molding operation i~ performed in the manner already described, in this ca~e with the parison still properly aligned with the longitudinal a~cis o$ the extrusion die.
The outer cooled region 182 i~ pX8 erably sufficiently thin in relation to the bulk and thermal mass of the remainder of the parison such that, when the cooling is discontinued, there will remain enough heat stored in the remaind~r of th~ parison, i.e., the non-cooled portion, that heat transfer from the still hot portion to the initially cooled outer region 182 will reheat the outer surface region to a temperature which is compatible with the blow molding operatiom.
Typically, thi~ temperature is believed to be only slightly below the original temperature before cooling.
This assure~ that the parison will ba at tho proper temperature level throughout it~ bulk when the blow molding operation is performed.
The cooling can be maintained alo~g the full length of the parison at a rate which, at each point along the length, maintains the desired reduced temperature of the outer region 182, thereby maintaining the enhanced structural properties thereof contributed by the high vi~cosity outer layer. Cooling can also be varied along the length of the parison to attain the same resul~ in certain applications depending upon the properties of the materials used and the proces~ conditions employed.
The flow of coolin~ gas is preferably directed away from 08CTo5349 28 2 ~3 ~1 ~ 3 the exit of the extrusion die and toward the free end of the parison. ~f too much cooling is effected, that is, if the cooling rate is too high or maintained for too long a time, the cooled outer region will be too thick in relation to the remainder of the parison and there will remain insufficient stored heat in the remainder of the parison to bring the cooled region back up to the proper temperature for accommodating the proper performance of the blow molding operation. On the other hand, if the cooling rate i~ too low, the thickness of the outer region 182 will be insufficient to provide the desired structural rigidity and buckling of the parison will occur. The flow of cooling ga3 may in any event, however, be selectively turned on and off a~ needed as the parison i~ extruded ~rom the die.
A~ noted abovo, the flow direction of the cooling gas i~ generally away from the exit of the extrusion die and toward the free end of the parison. The reason for this is that a higher cooling rate i~; preferred at the point where the pari~on exit~ the extrusion die because the outer surface region has not yet been formed at this point and the higher cooling ra1:e is desired to cause rapid formation thereof. Once i.ormed, the thin cooled outer xegion 182 can be maintained along the length of the pari~on by a lower cooling rate or varied along the length of the parison by controlling the cooling rate or turning the cooling on and off entirely along different portion~ of the parison length.
As also noted above, it is also desirable that the cooling gas have at least some peripheral velocity component around the ou~er surface of the parison. Thi~
assures homogeneous cooling around the periphery of the parison. Thu~, the preferred flow pattern i8 a radially inward flow of the cooling gas against the outer ~urface of the parison with an angular velocity component along the axis of the parison and a peripheral velocity component around the periphery of the parison.

. "
.,. ,~ , .
.

~9 The timing of the interval between the discoQt~
of the cooling and the performance of the blow molding operation i~ also controlled in accordance with the present invention. This time interval is selected to allow a sufficient time for the cooled outer region 182 to become reheated to some extent (depending upon the article bein~ produced and the material~ and process conditions 3elected) by heat tran~fer from the remainder of the heated parison such that the outer region is heated back up to a temperature within the desired range for the blow molding operation. If this interval is too short, the temperature of the outer region may still be too low and its ~iscosity too low for proper performance of the blow molding operation. If this interval is too long, the pari~on will continue to lose heat and the entire body thereof may drop ~elow the optimum range for blow moldiny.
For the performance of the b:Low molding operation, the parison i~ usually cut off at the exit point from the e~trusion die to allow the blow molding steps to be carried out as shown in Fig. 10. At this point, the parison has suf~icient structural rigidity to maintain its alignment with its longitud:Lnal axis a~ established during the formation of the parison. The dwell time between the completion of the parison formation and the commencement of blow molding to the finished container ~hape is typically about 5 to 8 seconds, but can be longer or shorter depending upon the product being produced. During this time, the cooled outer surface region of the parison is typically reheated in the manner already explained to bring the outer region to the proper temperature for the blow molding operation.
Although the parison is moved away from the exit of the extrusion die, the alignment with the longitudinal axi~
thereof is maintained during this period by the structural rigidity e~tablished by the cooled outer ~urfaca region. Thu~, the "longitudinal axis" of the 08CT~5349 30 2~8 0 parison, as referred to herein, means the longitudinal ~
axis es~ablished during the formation of the parison, which is initially the longitudinal axis of the extrusi.on die.
Control of all of the above parameker~ is a function in each case of the properties and dimensions of the particular parison which is formed in the parison ~orming step of the process. In addition to the dimensions of the parison, parameters such as the initial temperature of the heated parison, the thermal mass thereof, the specific heat and the heat transfer properties thereof are taken into account in determining the exact cooling parameters selected. By following the teachings set forth herein, those ~killed in the art will readily be able to choose the proper parameters to attain the improved results provided by the present invention.
While it has been found that ~atisfactory cooling properties can be attained in m~st instances by a single stage of cooling, that is, by a single air ring 174 with one annular outlet aperture 176, additional stages of cooling along the length of the parison may be used if the same are deemed necessary or desirable to attain the desired structural properties of the parison. ~n important feature of this embodiment i~ that the thin outer surface region be fo~med by cooling of the outer surface of the parison, that it have sufficiently increased viscosity to provide the additional structure rigidity to pre~ent buckling, tha~ it extend along the lenyth of the parison either continuou~ly or in a varied pattern produced by varying the cooling along the length or by turning the cooling on and off entirely along selected portions of the length, and that it be ~ufficiently thin so that, when cooling is discon~inued, 3~ the outer suxface region will be reheated to a desired extent by heat flow from the remainder of the parison to :., ;

08CTo5349 31 '~ 3 a temperature within the desired range for performing the blow molding operation.
Referring now to Figs. 16 and 17, the structure of a preferred embodiment of the air ring 174 will be described. Fig. 16 is a side view of an ai.r ring apparatus 174 embodying one aspect of the present invention. The air ring apparatus 174 includes a body portion l90 having therein a gas flow passage 191 extendLng internally from one or more connection ports 192, connected to a source 193 of cooling gas, to an annular flow passage 194 which extends into an annular discharge aperture 176. An adjustable flow device 193a is connected between the source 193 and flow pa~sage 191 to provide for control of the flow of the cooling ga~
from the source. The air ring apparatus 174 is positioned adjacent the annulax exit o the extrusion die 162 as ~hown in Fig. 15.
Formed in the body of the air ring is a series of annular chambers 196 vertically displac~d one above the other and connected via ports 198. The ports 198 are located at discrete positions alround the peripheries of the annular chambers 196 and se!rve to provided vertical flow connections between the passages at these discrete locations. The ports 198 are positioned around the periphery such that, while directing the flow between the vertically spaced chambers 196, some portion of the peripheral velocity component of the cooling gas flow i~
preserved. Thus, the cooling gas exiting at the annular discharge aperture 176 contains a peripheral velocity component which assures some swirl of the cooling gas around the paris~n as it flow~ along the axis of the parison. The location of the ports 198 around the periphery of the annular passages 196 i8 shown in the fragmentary view of Fig. 17.
The cross section view of Fig. 17 is taken along the plane A A of Fig. 16 between the upper and middle of th~
chambers 196 and shows the ports 198a, which extend 08CTo5349 ~8~

between th~ upper and middle of the chamber~ 196 r peripherally displaced from the ports 198b, which connect the middle and lower chambers. Thus, the cooliny gas flows from the upper chamber into the middle chamber through the ports 198a and then through the ports 198b from the middle chamber into the lower ch~mber. Some peripheral component of velocity ie ~herefore r~quired for flow between ad~acent chambers of the chambers 196.
The bottom chamber of the annular chamber~ 196 is connected to an annular flow duct 200 which connect~ the bottom annular chamber to the annular discharge aperture 176. Thus, the cooling gas flows from the source 193 through the annular chambers 196, connected by the ports 198, and through the annular duct 200 to the annular discharge aperture 176, from which the cooling gas is directed against the outer surface 180 of the parison 173.
Cooling gas flow along the outer surface of the parison may also be induced by suctiun through the annular aperture 176. However, the preferred embodiment is that illustrated in Fig. 15 with the cooling gas flowing out of the aperture 176 and along the parison toward the fres end thereof.
The body of the air ring 174 is preferably cooled to maintain the proper temperature. In the embodiment 3hown, cooling is effected by circulating a cooling fluid such as cold water through passages 202 (shown in Fig. 16). The passages 202 are connected to a source of cooling water through an inlet pipe 204 and an outlet pipe 206 as shown in Fig. 17.
Some of the parameters which have been applied to a repre~entative emodiment of the pre~ent invention will now be set forth.
For the blow molding of typical plastic materials such as polycarbonates, nylons, ABS, styrenes~
polyvinylchlorides, polyolefins and the like, good 33 2~
result3 are obtained if the temperature of the air rin~
is maintained at about 50 F. This i6 accomplished by circulating water at the 50 F temperature through the cooling passages 202 shown in Fig. 16.
The cooling gas utilized was compressed air from a compressed air source 193 (Fig. 16). The compressed air source 193 was maintained at a pressure of about 20 psig at a normal indoor ambient temperature of about 70 F.
The flow rate of cooling air to the air ring was 1~ regulated between 0.5 and 1.5 cubic feet per minute through two inlet ports 192 as illustrated in Fig. 16.
For a three layer structure consisting of an ou~er layer of p~lycarbonate material, a middle layer of nylon material and an inner layer of poly~arbonate material, the following Table I shows a compari30n of iini~hed container wall thicknes6es mea~ured at 6elected points around the p~riphery for blow molded containers formed under identical condition~ except that one ~et of containers (listed under ~'With Air Ring~ column) was formed in accordance with the present invention.

Table I
~Thicknesse~ in Mils) Wall Location~ith Air RinqWithout Air Rin~

Above label panel43.5 38.8 Upper label panel47.2 33.6 Central label panel 44.5 46.0 Below label panel45.8 48.1 Total Variation 3.7 14.5 Bottle Weight 162.6 grams 161.1 grams It will be noted that the container6 formed in accordance with the present invention showed a total ,,: ,, , ,, : ~., 34 2~ 3 variation in wall thickness of 3.7 mils around the periphery, whereas those made with prior art techniques ~howed a variation in wall thickness of 14.5 mils, about four time3 greater ~ariation in wall thickn~s than the cont~iner~ made in accordance with the present invention. While the variations in wall thickness produced by prior art apparatus and methods w~re h~retofore unavoidable and thu~ were accepted as applied to ~ingle use containers, that i6, ~ontainer~ which are discarded after a ~ingle use, these variations are not acceptable for use in refillable containers for the reasons given above. In addition, the presence of such ~ariations in prior axt blow molded containers for single use and/or throw away applications resulted in significarlt di~advantages such as excess wall thickne~ses and accompanying excess weight, substantial variations in wall thicknes~ and the pre~ence of internal ~tresses and stress concentration~, all of which were unavoidable in such prior art blow molded containers. The present invention therefore pxovides a truly remarkable and important i:mprovement, which makes possible the blow molding production of greatly improved blow moldad containers for singl~e use and throw away applications as well as for use as refillable plastic 2~ ~ontainers. The present invention also provides a reduced container weight for ~he same minimum tar~et wall thickness, an advantage applicable as well to all applications, including single use and throw away application~ and refillable applications, thereby 3 0 yielding an even f urther advantage over the prior art.
The same advantages are realized whether the container is formed from a single layer or from a plurality of layers in accordance with the present invention. In eithex case r the finished container exhibits sub~tantia1ly reduced residual internal stresses which would otherwise be present from the formation of the parison. The finished container of thi~

~8~
invention thus provides important advantages for single use and throw away applications, such as, for example, applications in which the conatainer is hot filled or filled under pressure/ as well as in other single use and throw away applications, and can also as well be effectively and safely reused and/or reclaimed.
The above described embodiment is only illustrative of the disclosed embodiment and many other embodiments, varia~ions, modifications, and changes in detail can be devised without departin~ from the scope and spirit o the invention as defined in the following claims.

Claims (21)

1. A blow molding apparatus for forming blow molded containers comprising:
one or more annular extrusion modules disposed along a longitudinal axis of the module or modules;
means for holding the annular extrusion module or modules along the axis;
the extrusion module or modules each having a polymer inlet, a bore having an inner cylindrical surface, and an annular extrusion outlet opening into the inner cylindrical surface;
each of said module or modules having channel means for receiving and distributing polymer extending from the inlet to the outlet and defining a flow path for the polymer to flow from the inlet to the annular extrusion outlet through which the polymer is extruded in annular form to form a heated parison, said channel means extending symmetrically around the longitudinal axis of said extrusion module or modules in a manner so as to subject all of the polymer flowing from said inlet to said extrusion outlet to substantially the same process conditions along said flow path whereby the polymer is distributed at the annular extrusion outlet with properties which are substantially symmetrical around the axis for all resin distributed through said outlet;
means for enhancing the structural rigidity of the heated parison as it exits and is elongated from said annular extrusion outlet for resisting sagging and buckling of the parison and for maintaining the substantial alignment of the parison with the longitudinal axis thereof before the blow molding thereof into a finished container; and molding means for blow molding said parison while the alignment of the parison along its longitudinal axis is so maintained.

2. A blow molding apparatus as set forth in claim 1 in which said means for enhancing the structural rigidity of the heated parison comprises cooling means positioned adjacent the exit of said annular extrusion outlet for cooling the outer surface of said parison as it is elongated from said exit; and control means for controlling said cooling means to control the rate of cooling and the time interval over which the cooling is applied by said cooling means to form on said parison a relatively thin cooled outer surface region of material having an increased viscosity, thereby to increase the structural rigidity of said parison for resisting sagging and buckling;
said control means including means for discontinuing the cooling applied by said cooling means upon the expiration of a selected time interval prior to operation of said molding means.

3. A blow molding apparatus as set forth in claim 2 in which said cooling means comprises means for directing a cooling gas at the outer surf ace of said parison.

4. A blow molding apparatus as set forth in claim 3 in which said cooling gas directing means comprises means for directing the cooling gas flow in a direction having a component of velocity along the longitudinal axis of the parison.

5. A blow molding apparatus as set forth in claim 4 in which said cooling gas directing means further includes means for directing the cooling gas in a direction tangential to the surface of the parison whereby the cooling gas flows with an axial component of velocity and a peripheral component of velocity around the parison.

6. A blow molding apparatus for forming blow molded containers comprising:
extrusion means for extruding a heated parison from an extrusion die;

cooling means positioned adjacent the exit of said extrusion die for cooling the outer surface of said heated parison as it is elongated said exit of said extrusion die;
control means for controlling said cooling means to control the rate of cooling and the time interval over which the cooling is applied by said cooling means to form a relatively thin cooled outer surface region on said parison of material having an increased viscosity, thereby to increase the structural rigidity of said parison for resisting sagging and buckling;
said control means including means fox discontinuing the cooling applied by said cooling means upon the expiration of a selected time interval; and blow molding means for blow molding said parison into a container after the cooling is discontinued by said control means.

7. A blow molding apparatus as set forth in claim 6 in which said cooling means comprises means for directing a cooling gas at the outer surface of said parison.

8. A blow molding apparatus as set forth in claim 7 in which said cooling gas directing means comprises means for directing the cooling gas flow in a direction having a component of velocity along the longitudinal axis of the parison.

9. A blow molding apparatus as set forth in claim 8 in which said cooling gas directing means further includes means for directing the cooling gas in a direction tangential to the surface of the parison whereby the cooling gas flows with an axial component of velocity and a peripheral component of velocity around the parison.

10. A method of forming a blow molded container comprising:
disposing and securing an extrusion module or modules along a longitudinal axis, said extrusion module or modules each having a resin inlet, a bore having an inner cylindrical surface, and an annular extrusion outlet opening into said inner cylindrical surface;
each of said module or modules having channel means for receiving and distributing resin extending from the inlet to the outlet and defining a flow path for the polymer to flow from the inlet to the annular extrusion outlet through which the polymer is extruded in annular form, said channel means extending symmetrically around the longitudinal axis of said extrusion module or modules in a manner so as to subject all of the polymer flowing from said inlet to said outlet to substantially the same process conditions along said flow path whereby the polymer is distributed at the annular outlet with properties which are substantially symmetrical around the axis for all resin distributed through the outlet;
introducing a polymer material into said inlet and flowing said polymer through the module or modules from the inlet and through said flow path to said extrusion outlet so that the flowing polymer material substantially circumscribes the axis and arrives at the extrusion outlet with properties which are substantially symmetrical around the axis for all polymer flowing through the module or modules;
extruding the polymer material through said extrusion outlet;
forming a heated parison from the polymer material as it exits an exit extrusion channel;
enhancing the structural rigidity of the heated parison which exits and is elongated from said exit extrusion channel to resist sagging and buckling of the parison and maintaining substantial alignment of the parison with the longitudinal axis of said exit annular extrusion channel; and blow molding a container from the parison so formed while said substantial alignment with the longitudinal axis is so maintained, whereby said container is formed with a wall of substantially uniform thickness and is substantially free of internal stresses which otherwise result from variations in the properties of the extruded polymer around the periphery of said parison.

11. A method of forming a blow molded container as set forth in claim 10 in which the enhancing of the structural rigidity of said heated parison comprises cooling the outer surface of said parison after it exits said exit extrusion channel to form on said parison a relatively thin cooled outer surface region of material having an increased viscosity, thereby to increase the structural rigidity of said parison for resisting sagging and buckling.

12. A method of forming a blow molded container as set forth in claim 11 in which the cooling of the outer surface of the parison includes directing a cooling gas at the outer surface of said parison.

13. A method of forming a blow molded container as set forth in claim 12 in which the cooling gas is directed at the outer surface of the parison with a component of velocity along the axis of the parison.

14. A method of forming a blow molded container as set forth in claim 13 in which the cooling gas is also directed at the outer surface of the parison with a velocity component tangential to said surface of the parison whereby the cooling gas flows with an axial component of velocity and a peripheral component of velocity around the parison.

15. A method of forming a blow molded container comprising:
extruding a heated parison from an annular extrusion channel of an extrusion die;
cooling the outer surface of said parison which exits said annular extrusion channel to form on said parison relatively thin cooled outer surface region of material having an increased viscosity, thereby to increase the structural rigidity of said parison for resisting sagging and buckling; and blow molding the parison after the thin cooled outer surface region is formed thereon to form a blow molded container.

16. A method of forming a blow molded container as set forth in claim 15 in which said blow molding is performed after discontinuing the cooling of the parison and after at least some reheating of the outer surface region occurs by heat transfer from the remaining portions of the heated parison, whereby the temperature of the outer layer is increased from the cooled state and the viscosity thereof is reduced for the blow molding of the container.

17. A method of forming a blow molded container as set forth in claim 15 in which the cooling of the outer surface of the parison includes directing a cooling gas at the outer surface of said parison.

18. A method of forming a blow molded container as set forth in claim 17 including directing the cooling gas flow in a direction having a component of velocity along the longitudinal axis of the parison.

19. A method of forming a blow molded container as set forth in claim 18 including further directing the cooling gas in a direction tangential to the surface of the parison whereby the cooling gas flows with an axial component of velocity and a peripheral component of velocity around the parison.

20. A blow molded container formed by the method set forth in any of claims 10 through 19.

21. The invention as defined in any of the preceding claims including any further features of novelty disclosed.