CA1155263A - Apparatus for making a multi-layer injection blow molded container - Google Patents

Abstract

8026.1 APPARATUS FOR MAKING A MULTI-LAYER
INJECTION BLOW MOLDED CONTAINER
ABSTRACT
Apparatus for making a rigid container by injection molding a parison having plural layers of polymers. The parison is blow molded to the final shape of the container.
Control during injection is exercised over each of the plural polymers so as to produce uninterrupted layers ex-tending throughout the walls of the parison and to insure that the interior layers are completely encapsulated within the outer layers.

Description

1~55~63 BACKGROUND OF THE INVENTION
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Food product rigid containers generally must be j impermeable to oxygen. Most common structural polymers for .~
;~ rigid food containers ar~ permeable to oxygen which invades . ..~
`~ 5 ~ the food product causing`degradation or spoilage. Those po-lymers which~are sufficiently impermeable to oxygen general-ly are not suitable alone for rigid containers for foods be-` cause they do~not possess adequate structural properties, -~ are moisture sensitive, or are not approved for or are of questionable safety when used in contact with foods. Ethy-lene vinyl alcohol copolymer ~EVOH) is a transparent extru-sible material possessing high impermeability to oxygen when dry, many times less permeable than acrylonitrile copolymers, but is very moisture sensitive. The oxygen barrier properties of EVOH are markedly diminished in the presence of signiflcant quantities of water. To be useful :; for food packaging, particularly where extended shelf life is required, EVO~ must be kept dry as by total encapsulation 1~ within polymers which hav-e good moisture barrier properties.
Many foods are processed in the container in a ~ pressure cooker or retort. Retort conditions commonly are ;i 250~. at 30 psia steam pressure. A riyid container must survive retort conditions. It must not permanently distort during cooking or during cooling, and must not suEfer an alteration of the desirable properties of its components.
, PolyoleElns, particularly blends or copolymers oE

.
-:
~, ~ ~ 55~63 polypropylene and polyethylene, are well suited to manufacture of rigid containers and have adequate physical properties to survive retorting. Polyole~ins are relatively poor oxygen barriers, but are relatively good moisture barriers. The use of polyolefins with a central core of an oxygen barrier polymer is a desired goal of the food packaging industry.
Nohara et al. U.S. Patent No. 3,882,259, issued May 1975, discloses a three ply plastic bottle having a core of EVOH blended with Surlyn A brand ionomer resin and outer plies of polyethylene blended with Surlyn A (trade mark).
The Surlyn A (trade mark) ionomer is added to both the EVOH
and the polyethylene resin materials to improve adhesion be-tween layers. The bottle is to be made by extrusion blow molding whereby the three layers are simultaneously extruded to produce a three ply tube. While still hot from extrusion, the tube is pinched together at the bottom to form a seal and inflated in a blow mold having the shape of the desired bottle.
Extrusion blow molding has our serious drawbacks when used ko orm multi-layer containers having a core ply o a moisture sensitive harrier material such as EVOH.
First, the pinch seal at the bottom leaves the core ply of EVOH exposed on the bottle exterior. Since EVOH and certain other barrier matexials are adversely affected by moisture, exposure of the core ply at the container bottom renders the container susceptible to loss of barrier quality by intrusion of moisture. The risk that the container ex-terior will encounter damp conditions in storage or trans-. , ~ - 3 -~ 1552~3 .
,- , .

i port is high and the resulting loss of barrier quality will degrade or spoil the food. Further, retort conditions are such that moisture from the stea~ will intrude into the barrier layer through the exposed barrier at the bottom.
~:, 5 Second, extrusion blow molding necessarily produces scrap as a result of the pinch sealing pr~cedure. Since the ''`' .-'1 ~l scrap contains materials from each of the three layers, re-extrusion of the scrap is difficult and expensive.
Third r the pinch seal produces a bottom of non-uni-form thickness and strength. The sealing takes place along .
i~ a line between the abutting faces of the inner layer ma-~ terial. The seal line is bordered by reglons of relatively i ~ thick material. When stretched during blow molding, the :,~
~ bottom varies in thickness in the vicinity of the pinch . ~. . .
, 15 9eal. BecaLlse of the thickness variation due to the pinch ..;ii' seal, the stifEness of the bottom is not uniform along all diameters. Consequently, the bottom does not evenly respond to expansion and contraction as the product changes in tem- !
,::., . I
perature. This lack of even response causes unpredictable ~: 20 performance of the container when retorted.
Fourth, the pinch seal may create an interruption in the barrier layer. If the inside surface layer is inter-posed between the barrier layer at the seal, a line lacking .. .,; .~
barrier material will result. The area of the interruption . .
;- ; 25 may be great enough to allow sufficient oxygen to enter to ~ be a problem.
- Because of these disadvantages, extrus;on blow , r ~ molding cannot produce an entirely satisfacto-ry three layer :. ~....................... .

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~; -~ 1~526~

;~ rigid container having a core barrier layer of a moisture sensitive polymer such as EVOH, particularly where the con-tainer is intended for retorting.

SUMM~RY OF THE PRESENT INVENTION

' ; 5 The present invention is concerned with apparatus for making a plastic container by injection molding or by an injection blow molding technique which produces a container whose walls are multiple plies of different polymers. In particular, the container walls comprise inner and outer L
`'4- i 10 layers of structural polymers such as polyolefins or a blend i of polyoleins on either side of a core layer of a polymer having oxygen barrier properties such as EVOH.
Injection blow molding is a process whereby a pre-form or parison is formed by injection molding in a cavity.
15 The parison is transferred to a blow mold cavity and blown to the shape of the desired container. The parison can be retained on the core pin of the in~ection mold and trans-ferred on the core pin to the blow molding cavity. The parison can be temperature conditioned before blow molding 20 to achieve an optimum temperature or profile of tempera-tures. The core pin can be temperature controlled and the ....
1 exterior of the parison can be temperature conditioned by contact with air or other fluid such that blow molding occurs at optimal conditions. Orientation can be achieved ~;, 25 as the parison is stretched during blow molding. Injection blow molding produces no scrap and requires no pinch seal.
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1 11 5.~2~3 :., According to the present invention, poiymer melts ;3 for the inside and outside surface layers and the core layer of the container walls are substantially simultaneously in-jected into a parison mold cavity through an in~ection noz-~le having separate passages for each polymer melt arranged ``^! to lead to coaxial annular nozzle orifices surrounding thecentral orificè. ~dditional layers or layers interposed between the surface and core layers can also be injected simultaneously to produce a container wall having four or more layers.
The initiation, rate, and termination of flow for each layer are independently and continously controlled to ,~
provide control over the thickness of each layer and to insure that the core layer or layers are totally encapsu-lated between the surface layers. The injection molded pari-son is transEerred on the core pin to a blaw mold cavity having the shape of the container and is then blow molded into the finished container. Temperature conditioning of the parison just prior to blowing can result in biaxial orientation of the various polymers to achieve desirable . , improvements in physical properties such as impermeability, clarity, tensile strength, impact strengthj and resistance to creep. The resulting product has a barrier layer or . . . .
; ~ layers whlch extend without interruption throughout the - 25 container, yet are completely encapsulated within the ma- ;
terial of the inside and outside surface layers. Since the barrier layer is protected from moistur-e by the moisture barrier properties of the surEace layers, the oxygen barrier quality is preserved.

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n DESCRIPTION OF i~ PREFERRED EMBODIMENT
. _ , . . . _ . . . _ . . _ DRAWI NGS

In the drawings:
-. Figure 1 is a schematic view in cross-section of . -5 injectlon blow molding apparatus, Figure 2 is a schematic view of the apparatus of -~- the present invention, ; Figure 3 is a simplified view of the injection ,.... ~
:; apparatus of the present invention~
~ !
Figure 4 is a schematic .view illustrating the control system for one of ~the injection rams, Fi~ure 5 is a plot of the position of one of the ' . injection rams as a function of time, Figure 6 is a flow chart for the control system for :~ 15 the apparatus, ,. -Figare 7 is a plot of ram position as a functi~on of . time for three rams, Figures 8-15 are views in cross-section taken ~: through the nozzle and cavity:showing the confluence of flow of the various layers at varlous times during the injection . ,~
cycle, ; Figure 16 is a view in cross-section of the injection nozzle, Figure 17 is a view in cross-section oE the : 25 parison, ~ 155~63 Figure 18 is a view in cross-section of the finished container, Figure 19 is an enlarged view of a portion of a cont~iner wall having three layers, Figure 20 is a plot of the oxygen permeability of a barrier material as a function of moisture content, and Figure 21 is an enlarged view of a portion of a container wall having five layers.
The machine of the present invention injection molds a multi-layer parison from a plurality of polymers, each separately plasticated and fed to separate injection rams. The rams each force a shot of polymer to appropriate nozzle passages which lead to the entrance to the injection mold cavity Conditions are controlled to advance the several polymer rnelts substantially slmultaneous:ly in the die cavity under non-turbulent Elow conclitions to preserve the polymers as discrete layers in the parison. The fol-, lowing detailed description explains how the foregoing is - accomplished.
Figure l shows a portion of the injection blow molding machine ~IBM) of the present invention. Two core pins lOA, lOB are mounted on a transversely moveable plate 40 on the axially moveable pIaten 42 of the machine. Core `~ pin lOA is positioned in an in~ection mold 20 while core pin 10B is positioned in a blow mold 30B. When plate 40 is tra-versed to the left, core pin lOA will be in blow mold 30A
and core pin 10B will be in the injection mold 20. A pari-son is removed from the mold by axial retreat of the move-' ' able platen 42 and the plate ~0 with core pins 10 is tra-- versed either left or right to the available blow mold.
Figure 1 shows blow mold 30A ready to receive the parison .~ - and shows blow mold 30B containing a parlson 60B. Parison 60B is inflated with air to assume the shape Oe blow molding ., cavity 30B while parison 60A is being injected in cavity 20.
The blow molds open as the platen retreats to eject the fi-nished container. The plate 40 shuttles back and forth each cycle so that a container is blown simultaneously each time : 10 a parison is injected.
Figure 2 shows the general layout of the injection ;
:-~ blow molding machine and indicates the control means. Plas-ticators 82A, 82B, 82C feed three rams 70A, 70B, 70C or - three polymer melts which are fed to a manifold block 75 which contains separate passages leading to a multi-passage nozzle 50 for the injection mold 20. The platen 42 i.s moved i axially of the mold by a hydraulic press 44. Control cir-cuitry means for the press and blowing cycles are indicated at press control block llO. A microprocessor lO0 is pro-grammed to control the servo hydraulics 120 which controlthe individual injection rams and to command the press control block llO.
~- Figure 3 shows one of the plural plasticators 82B
. j .
for melting and suppIying molten polymer B to an injection ram 70B. The plasticator 82B is a conventional reciprocat-ing screw device which forces molten polymer into the cylin-der 71 of the ram when manifold valve 84B is closed and ma-nifold valve 85B is opened and the ram is retreated to the ~ ~.52~3 left by hydraulic actuatur 72. When the ram cylinder 71 is charged with molten resln, valve 85B is closed. Upon a con-trol signal from the microprocessor lO0, valve 84B is opened and the servo control 120 for the ram causes the ram to ad-vance to the right, according to a displacement-time sche-~, dule stored in the microprocessor program. A displacement transducer 76 provides an analog signal proportional to ram displacement to eomplete a feed-back loop for the servo 120.
Polymer B forced according to the program flows past valve 84B through the manifold passages to the injection nozzle, through the nozzle passages and into the injection mold ca-vity where polymer B becomes the outside layer of a parison 60.
Figure 4 shows schematieally the servo loop where the eontrol signal from the mieroproeessor 100 (shown as voltage as a funetion of time) and a position signal from the displacement tranducer 76 are algebraically cornbined in an amplifier 78 and the resulting signal is used to control the hydraulic servo 120 for the hydraulie actuator 72. A
typical ram position control signal is shown in Figure 5.
Since displacement is measured by transducer 76, the plot is in voltage as a function of time.
~igure 6 is a flow chart of the system used to con-, ...... i ~
trol the machine. The injection blow molding machine is in-dieated as IBM on the ehart. Upon initiation of the cycle, the program checks positions of valves, rams, etc. and if all are proper, recharges the ram cylinder~ 71 from the plasticators 82. The IBM control circuit llO provides an 1 1~52~3 .. . .
"inject" signal to the microprocessor 100. Injection is carried out according to the ram displace~ent-time schedule of the microprocessor and is terminated at the end of the schedule. An "injection complete" signal is sent to the IBM. The control 110 then causes the I~M to traverse to ;~ place the parison in the blow mold and to procede with the blow molding phase. The machine continues to cycle through this sequence. Keyboard 115 may be used to change the dis-placement-time schedule or to shut down the machine.
-~' 10 Figure 7 is a plot of ra~ displacement as a func-- ~ tion of time for three rams. The positions of the rams are ~, measured as the voltage analog output oE the transducers 76 for each ram. The polymer Eor the inside surface layer is "A"; that for the core layer "C"; and that for the outside surface layer is "B". In this figure an upward slope indi-cates a forward motion of the ram to deliver polymer, a horizontal slope indicates a stopped ram, and a downward ~t slope indicates a retreat of the ram. The significance of Figure 7 is perhaps better understood by referencé to Fi gures 8-15, which show the flow of the polymers at the exit of the nozzle 50 and the entrance 52 of the injection mold cavity 20 at the rounded bottom of the parison. Figures ~'i 1 8-15 are taken at different times in the cycle and those ,, , times are keyed to Figure 7.
. - . .j .
Figure 8 represents the conditions at the start of a cycle at time 0. The cavity 20 is empty. The entrance 52 of the cavity 20 initially contains only the polymers A and B for the inside and outside surface layers. The rams for 1 ~52~3 ., ~
' polymers A and B begin to advance to force those polymers ; into the cavity. At about 100 milllseconcls into the cycle the ram for the COI e layer, polymer- C, begins to advance.
Fig~re 9 shows that polymer C has joined the flow stream in -~ 5 the entrance and polymer C is about to en~er the cavity.
~`~ Figure 10, taken at about 520 milliseconds, shows the flow -~ of the three polymers as the cavity continues to be filled.
` All three polymer layers must extend throughout the entire length of the parison. Since the flow in the mold cavity is ---. 10 laminar, the velocity in the middle of the stream is higher , than the velocities at the cavity walls. Therefore, initia-:i .'.. ,!~' tion of flow of polymer C is retarded enough ~e.g., about ; 100 milliseconds) so that polymer C will reach the far end of the cavity just as the slower moving SUI face layers (A
lS and B) reach the end. In this way, the far end of the pari-son, that which becomes the mouth end of the container, will ;~; have all layers present in thelr proper positions.
,;~ At about 1000 milliseconds into the injection - cycle,~the ram for polymer A (the inside surface layer) is . -stopped and the ram for polymer C (the core layer) can be . ., accelerated slightly to achieve the desired thickness of ma-terial in the bottom of the container. Polymer ~ is necked .... ~ .
down in the entrance 52 as lS shown in Figure 11 until it effectively is severed as shown in Figure 12. At 1100 milliseconds the ram for polymer C is stopped and the ram for polymer A is restarted. Figures 13 and 14 show po:lymer A advancing to pinch off polymer C in the entrancer thereby pushing the last of polymer C into the cavity 20 with poly-: ,1 .
~v3~ ~ I

1 1552~3 mer A to bury or encapsulate to isolate polymer C from expo-sure at the surface of the parison. Figure 15 shows polymer A knit to polymer B at the entrance to complete the encapsu-lation of polymer C and to return to the conditions at the start as shown in Figure 8. At the time of Figure 15 (1300 ,1 milliseconds) all three rams are retreated to depressurize the cavity to prevent expansion of the parison when the ca-vity is opened and to depressurize the polymers remaining in the nozzle and entrance to prevent exudation from the nozzle , . . .
:` 10 while the cavity is open. This exudation leads to premature -~j flow of polymers into the cavity during the next cycle which ~ can lead to smearing of polymer C on the surfaces of the , . ~
container.
1500 milliseconds marks the end of the injectiorl -~ 15 phase oE the machine cycle for this example. Subsequent to the end of the injection phase of the cycle, manifold valves ;J 84, 85 are actuated and the ram cylinders 71 are recharged with their polymers by the plasticators 82. The injection mold is opened by retreating the hydrauiic press 44 to wi-th-draw the core pin I0 Erom the cavity 20. The parison just formed is transferred to one of the blow mold cavities 30A, . ,.~, ~ .
30B and the container which was blow molded simultaneously ,~ with the injection cycle is ejected from the blow mold in ~, .
- which it was finished.
Figure 16 shows a nozzle 50 appropriate for injec-tion of a parison having a three layer wall. Polymer B, which forms the outside surface layer, is delivered by the ram 70B to an annular distribution channel 54B which dis ,~
-~
~,~0~

1 1~5263 J tributes the polymer circumferentially of the nozzle struc-ture. Polymer B advances along a conical passage 56B to an annular orifice 58B at the exit of the nozzle which leads to the injection cavity. Simila-rly, polymer C, which forms the j 5 core layer, lS delivered by ram 70C to annular distribution J channel 54C and thence along conical passag* 56C to annular orifice 58C. Polymer ~,~which forms thé inside surface layer, is delivered by the ram 70~ to a passage 56A which exits at~the center of the concentric flows issuing from orifices 58B and 58C. A nozzle shut off valve 59 can be . :
moved axially to arrest flow of polymer A.
Figures 17 and 18 compare the parison 60 as injec-tion molded with the inished container. The neck portion 62 remains virtually unchanged during blow molcling. The parison is held by the chilled neck portion while the hot - and soft parison is blown. Thus, the neck ~2 including the flange 64 is essentially forrned in the injection mold. The ~`1 remainder of~the parison walls are thinned as the parison is stretched during blow molding.
Figure 18 shows that the core layer C extends throughout the flange 64, but does not penetrate the flange edge. This is accomplished in large part by selection of :i the delay time in starting the ram for the core polymer.
! The flange 64 will be employed in a double seam seal whel a ' 25 metal end is crimped, by well known techniques, onto the containe~ mouth to close the filled container. Since the flange represents a significant area, it is important that the core layer extend well into the flange. The programmed ~ .

2 6 3 flows of the vaI-ious polymeLs also ensure that the core layer is not exposed at the sprue mark at the central ex-terior of the container.
Figure 19 is an enlargement of the container wall ~ 5 within the circle of Figure 1~. Layer A is the inside sur-`:~ face layer formed from polymer ~ in the foregoing descrip-tion. Layer B is the outside surface layer, formed from polymer B. Layer C lS the core or barrier layer formed from -~ polymer C. The thinnest layer is the relatively expensive~ 10 barrier polymer C. The relative thickness of the three :~ layers is controlled by controlling the relative flow rates ~. ., of the three polymers by microprocessor control of the dis-placement rates of the rams. A preferred wall structure is a layer of a blend of high density polyethylene and polypro-pylene on each Eace of a core barrier layer of ethy]ene vinyl alcohol copolymer (EVOH).
1 Figure 20 shows how the oxygell barrier quality of 11 EVOH decreases abruptly at high levels of moisture. Where the EVOH layer is thin, only a small quantity of watet ~
cause a large increase in oxygen permeability. For this reason, the EVOH layer must adequately be protected against the intrusion of moisture.
l Polyolefins do not adhere well to EVOH. Adhesion can be improved by adding adhesion promotors to the polyole-fin, the EVOH or both. Another approach is to provide an intermediate layer of an adherent polymeric material which adheres to the polyolefin will cause a large increase in . oxygen permeability. For this reason, the EVOH layer must ,; ., adequately be protected against the intLusion of moisture.

I 1~52B3 Polyolefins do not adhere well to EVO~l. Adhesion can be improved by adding adhesion promotors to the polyole-fin, the EVO~ or both. Another approach is to provide an intermediate layer of another material which adheres to the polyolefin and the EVOH. Such materials include modified polyolefins sold under the trade mark Plexar by the Chemplex Company of Rolling Meadows, Illinois. These comprise a blend of a polyolefin and a graft copolymer of high density poly-ethylene and an unsaturated fused ring carboxylic acid anhydride.
The polyolefin component of the blend can be polyethylene or preferably is an olefin copolymer such as ethylene vinyl acetate. Schroeder U.S. Patent No. 4,254,169 issued March

3, 1981 teaches the use of these materials to bond to EVOH.
The materials themselves are disclosed in U.S. patents 4,087,587 and 4,087,588. We have found these modified polyolefins to be suitable as interlayers to improve adhesion between the polyolefin surface layers and the EVOH core layer.
Another suitable material for use as an interlayer to improve adhesion between the EVOH polyolefins are maleic anhydride grafted polyolefins sold under the trade mark Admer by Mitsui Petrochemical Industries of Tokyo, Japan.
The use of interlayers on each side of the EVOH ~ i oxygen barrier layer results in a five layer container. To produce such a container, the three passage nozzle of Figure 16 i5 replaced with a five passage nozzle of similar construction.
Where the inside and outside surface layers are of the same polymer one ram can be used for both those layers. The flow from that ram is divided and proportioned with part supplying the central axial passageway to form the inside surface layer and the balance supplying the outermost nozzle annular orifice.
The two additional nozzle orifices are located just inside and just outside the nozzle orifice for the EVOH barrier layer.

1 155~
The two additional annular nozzle orifices can be supplied with the interlayer polymer from a single ram, the flow being divided and proportioned. Thus, a three ram machine can produce a five layer parison. Greater control can be exercised over the polymer flows by using a machine with an independently control-lable ram for each layer. A nozzle shut off valve can be employed to selectively control the polymer flows. The three layers of interlayer polymer and the barrier polymer can be treated as a single core layer. A five layer wall is shown lQ in Figure 21B wherein layers A and B are the inside and out-side surface layers of polyolefin, layex C is the barrier layer of EVOH, and two layers D are the interlayer material.
Example 1 Five layer containers having a capacity of about 5 1/2 ounces, of 202 x 307 size, weighing about llg were made using a five orifice nozzle on a three ram machine. The inside and outside surface layers were polypropylene-polyethy~
lene block copolymer (supplied under the trade mark Hercules Profax 7631). The adhesive interlayers were ethylene vinyl acetate copolymer blended with a graft copolymer of high density polyethylene and a fused ring carboxylic acid anhydride (supplied under the trade mark Plexar 1615-2). The oxygen barrier was EVOH (supplied under the trademark Kuraray EVAL
EP-F, available from Kuraray Co. Ltd., Osaka, Japan). The layers were well adhered. The barrier extended to the flange lip and was completely encapsulated.
EXample II
Five layer containers simiLar to those of Example I
were made wherein the inside and outside surface layers were polypropylene (supplied under the trademark EXXON E612); the interlayer material was Plexar III, a blend of ethylene vinyl acetate copolymer and a graft copolymer; and the barrier ; - 17 - !

~ ~.S~63 was EVAL EP-F. The layers were well adhered. The barrier layer extended to the lip of the flange and was completely encap-sulated.
E'x;amp'l'e III
Five layer containers similar to those of Example I
were made wherein the inside and outside surface layers were a 50-50 blend of polypropylene ~supplied under the trade mark BXXON E612) and a high density polyethylene (supplied under the trade mark Chemplex 5701); the interlayer material was Plexar III; and the barrier layer was EVAL EP-F. The layers were well adheredO The barrier layer extended to the lip of the flange and was completely encapsulated.
Example IV
Five layer containers similar to~those of Example I
were made, wherein the 1nside and outside surface layers were ~ ~
a copolymer of propylene and ethylene (supplied under the '' trade mark Hercules Profac 7631); the interlayer material was maleic anhydride grafted polyolefin (~upplied under the trade maxk Mitsui Admer QB 530); khe barrier layer was EVAL
EP-F. The layers were well adhered. The barrier layer exten~-ed to the lip of the flange and was completely encapsulated.
In the making of the containers of Examples I-IV
the injection schedule began feeding the inside and outside surface layer polymer then the polymer for the adhesive interlayer was started and substantially simultaneously the barrier layer polymer was started. The flows of the adhesive interlayer polymer and the barrier layer polymer were terminated before the outside surface layer polymer flow was terminated.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for making a multi-layer rigid article comprising: A) an injection mold and a core pin which together define a cavity for molding a parison, the cavity having an en-trance at the bottom of the parison, 1) an injection nozzle hav-ing an exit communicative with the entrance, 2) means for inde-pendently commencing in the exit the flow of a first polymer stream to become the inside surface layer of the parison and the flow of a second polymer stream to become the outside surface layer of the parison, and the flow of a third polymer stream be-tween the first and second polymer streams, 3) means for inde-pendently controlling the rates of flow of the polymer streams, 4) means for independently terminating the flows of the polymer streams, 5) means associated with the independent means for co-ordinating the commencement, rate and termination of flow of the three polymer streams during each injection cycle, B) means for transferring the injection molded parison to a blow molding cavity having the configuration of the article, C) means for in flating the parison in the blow molding cavity to form the article.

2. The apparatus of claim 1 including means for in-troducing a fourth polymer stream between the third and first polymer streams and means for introducing a fifth polymer stream between the third and second polymer streams, and means for con-trolling and for terminating the flows of the fourth and fifth polymer streams.

3. Apparatus for making a multi-layer rigid contain-er comprising: A) an injection mold and a core pin which to-gether define a cavity for molding a parison, having a closed end, the cavity having an entrance for polymer at the closed end of the parison, 1) an injection nozzle having an exit communi-cative with the entrance, 2) means for establishing in the en-trance a flow of polymer comprising a central stream of a first polymer surrounded by an annular stream of a second polymer, 3) means for establishing an annular stream of a third polymer between the first and second polymer streams, 4) means for in-dependently controlling the flow of the three polymer streams until the cavity is nearly filled, 5) means for independently terminating the flow of the polymer streams, 6) means associat-ed with the establishing means and with the independent means for coordinating the establishment, control and termination of the three streams during each injection cycle, B) means for transferring the parison to a blow mold cavity, C) means for inflating the parison in the blow mold cavity to blow mold the parison into the finished container.

4. Apparatus for making a multi-layer injection molded article comprising: 1) an injection nozzle having an exit, 2) means for independently commencing in the exit the flow of a first polymer stream to become one surface layer of the article, the flow of a second polymer stream to become the other surface layer of the article, and the flow of a third poly-mer stream between the first and second polymer streams, 3) means for independently controlling the flow of the polymer streams, 4) means for independently terminating the flow of the polymer streams, and 5) means associated with the independent means for coordinating the commencement, control and termination of flow of the three polymer streams during each injection cycle.

5. Apparatus for forming a multi-layer plastic pari-son for an injection blow molded article comprising: 1) an in-jection nozzle having an exit, 2) means for commencing in the exit the injection of a first inside surface layer, 3) means for commencing in the exit the injection of a second outside surface layer, 4) means for commencing in the exit the injection of a third core layer, 5) means for independently terminating in the exit the injection of the first, second and third layers, and 6) means associated with the commencing means and the termina-ting means for coordinating the commencements and terminations of the first, second and third layers during each injection cycle.

6. Apparatus for injection blow molding a multi-layer rigid container comprising: an injection mold for a parison, two core pins mounted on a plate which transverses to register either pin with the injection mold, two blow molds for blow molding the parisons into the container, the blow molds being located to register one blow mold with one core pin when the other core pin is registered with the injection mold, an injec-tion nozzle in communication with the injection mold at the bot-tom of the parison, the nozzle having a plurality of three con-centric orifices for three polymer streams, a plurality of poly-mer injection means associated with the nozzle orifices, con-trol means to independently control the flow of each of the polymer streams as a function of time, and means associated with the independent control menas for coordinating the flow of each of the polymer streams as a function of time during each injec-tion cycle.

7. The apparatus of claim 6 wherein the plurality of injection means comprises a plurality of injection rams and a plurality of plasticators for supplying molten polymer to the injection rams, and wherein the control means control the dis-placement of the injection rams.

8. Apparatus for injection molding a multi-layer con-tainer comprising: at least three plasticators for independently melting polymers for the different layers, at least three servo controlled hydraulically actuated injection rams associated with the plasticators, an injection nozzle having three polymer ori-fices, each for a polymer stream and each associated with a ram, a linear transducer for each ram for producing an electri-cal signal related to the linear displacement of the ram, means to generate a time-displacement schedule signal for each ram, means to control the servo hydraulic actuator for each ram in accordance with the algebraic sum of the two signals, and means associated with the control means for coordinating the control of each servo hydraulic actuator for each ram during each in-jection cycle.

9. Apparatus for injection molding a multi-layer con-tainer comprising: at least three plasticators for independent-ly melting polymers for the different layers, at least three servo controlled hydraulically actuated injection rams associat-ed with the plasticators, an injection nozzle having three poly-mer orifices, each for a polymer stream and each associated with a ram, a linear transducer for each ram for producing an elec-trical signal related to the linear displacement of the ram, means to generate a time-displacement schedule signal for each ram, and to coordinate said time displacement schedules for the rams each cycle, means to control the servo hydraulic actuator for each ram in accordance with the algebraic sum of the two signals.

10. Apparatus for injection molding a multi-layer container comprising: at least three plasticators for indepen-dently melting polymers for the different layers, at least three servo controlled hydraulically actuated injection rams associated with the plasticators, an injection nozzle having three polymer orifices, each for a polymer stream and each as-sociated with a ram, a linear transducer for each ram for pro-ducing an electrical signal related to the linear displacement of the ram, means to generate a time-displacement schedule signal for each ram, means to control the servo hydraulic actuator for each ram in accordance with the algebraic sum of the two sig-nals, and, means for coordinating the operation of said time-displacement schedules for each ram during each injection cycle.