CA1150651A - Multi-layer container and method of making same - Google Patents

Abstract

MULTI-LAYER CONTAINER
AND METHOD OF MAKING SAME
ABSTRACT
A rigid container is made 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 po-lymers so as to produce uninterrupted layers extending throughout the walls of the parison and to insure that the interior layers are completely encapsulated within the outer layers.

Description

~5~S~L

BACI~GROU~D OF THE INVENTION

Food p~oduct ri~id containers generally must be impermeable to oxygen. Most comr,on structural polymers for rigid ~ood containers are permeable to oxygen which invades 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 significant quantities of water. To be useful - for food packaging, particularly where extended shelf lifeis required, EVOH must be kept dr-y as by total encapsulation within polymers which have good moisture barrier properties.
Many foods are processed in the container in a ~; pressure cooker or retort~ Retort conditions commonly are 250F. at 30 psia steam pressure. ~ rigid container must survive retort conditions. It must not permanently distort during cooking or during cooling, and must not suEEer an alteration of the desirable properties of its components.
PolyoleEins, particularly blends or copolymers of poly-'' ~ 2 ~

365~
propylene and polyethylene, are well suited to manufacture of rigid containers and have adequate physical properties to sur-vive retorting. Polyolefins are relatively poor oxygen bar-riers, 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 poly-ethylene resin materials to improve adhesion between 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 four serious drawbacks when used to form multi-layer containers having a core ply of a moisture sensitive barrier 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 materials are adversely affected by mois-ture, exposure of the core ply at the container bottom renders the container susceptible to loss of barrier quality by intru-sion of moisture. The risk that the container exterior will encounter damp conditions in storage or transport is high and the resulting loss of barrier quality will 65~l degrade or spoil the food. Further, retort conditions are such that moisture from the steam will intrude into the barrieI layer through the exposed barrier at the bottom.
Second, extrusion blow molding necessarily produces scrap as a result of the pinch sealing procedure. Since the , scrap contains materials from each of the three layers, re-extrusion of the scrap i-s difficult and expensive.
Third, the pinch seal produces a bottom of non-uni-- form thickness and strength. The sealing takes place along a line between the abutting faces of the inner layer ma-terial. The seal line is bordered by regions of relatively i thick material. When stretched during blow molding, the bottom varies in thickness in the vicinity of the pinch seal. Because of the thickness variation due to the pinch seal, the stiffness 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-perature. This lack of even response causes unpredictable 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 barrieI layer at the seal, a line lacking barrier material will result. The area of the interruption .
- may be great enough to allow sufficient oxygen to enter to be a problem.
Because of these disadvantages, extrusion blow molding cannot produce an entirely satisfactory three layer rigid container having a core barrieI layer of a moisture .. , , , - - -~5~65~

sensitive polymer such as EVOH, particularly where the con-tainer is intended Eor retorting.

SUMM~RY OF THE PRESENT INVENTION

- ;~ The present invention is concerned with ~
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 layers of structural polymers such as polyolefins or a blend of polyolefins on either side of a core layer of a polymer having oxygen b~rrie~ properties such 3s EVOH.
Injection blow molding is a process whereby a pre-form or parison is formed by injection molding in a cavity.
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 injection mold and trans-ferred on the core pin to the blow molding cavity. The parison can be temperature conditioned before blow molding to achieve an optimum temperature or profile of tempera-tures. The core pin can be temperature controlled and the 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 as the parison is stretched during blow molding. Injection blow molding produces no scrap and requires no pinch;seal. ~
:

According to the present invention there is provided a method of making a multi-layer rigid article comprising the steps of: A) injection molding a parison in an injection mold cavity by: 1~ commencing 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, 2) subsequent to the commencement of the flow of the first and second polymer streams, commencing the flow of a third polymer stream between the first and second polymer streams, 3) continuing the flow of the first, second and third polymer streams concurrently, when the cavity is nearly filled, 4) terminating the flow of the first polymer stream, 5) subsequent-ly terminating the flow of the third polymer stream, and then 6) subsequently terminating the flow of the second polymer stream, B) transferring the injection molded parison to a blow molding cavity having the configuration of the article, C) in-flating the parison in the blow molding cavity to form the article.

- Sa -Polymer melts for the inside and outside surface layers and the core layer of the container walls are substan-tially simultaneously injected into a parison mold cavity through an injection nozzle having separate passages for each polymer melt arranged to lead to coaxial annular nozzle orifices surrounding the central orifice. Additional layers or layers interposed between the surface and core layers can also be in-jected simultaneously to produce a container wall having four or more layers.
The initiation, rate, and termination of flow for each layer can be independently and continuously controlled to provide control over the thickness of each layer and to insure that the core layer or layers are totally encapsulated between the surface layers. The injection molded parison is trans-ferred on the core pin to a blow 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 proper-ties such as impermeability, clarity, tensile strength, impact strength, and resistance to creep. The resulting product has a barrier layer or layers which extend without interruption throughout the container, yet are completely encapsulated within the material of the inside and outside surface layers.
Since the barrier layer is protected from moisture by the moisture barrier properties of the surface layers, the oxygen barrier quality is preserved.

5.~
DESCRIPTION OF A PREFERRED E~lBODIMENT
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:-Figure 1 is a schematic view in cross section of in-jection 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 appara-tus of the present invention;
Figure 4 is a schematic view illustrating the controlsystem for one of the injection rams;
Figure 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 the apparatus;
Figure 7 is a plot of ram position as a function 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 various 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 of the parison;

65~l i Figure 18 is a view in cross-secti~n of the finished container, Figure 19 is an enlarged view of a portion of a container wall having three layers, ; 5 Figure 20 is a plot of the oxygen permeability of a barrier material as a function of moisture content.
Figure 21 is an enlarged view of a portion of a container wall having five layers, and `:- The machine of the present invention injection ;. 10 molds a multi-layer parison from a plurality of polymers, -~ 1 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 contlolled to advance the ` 15 several polymer melts substantially simultaneously in the J die cavity unde~ non-turbulent flow conditions to preserve . the polymers as discrete layers in the parison. The fol-lowing detailed description explains how the foregoing is accomplished.
Figure 1 shows a portion of the injection blow molding machine (IBM) of the present invention. Two core ,.~
~i pins lOA, lOB are mounted on a transversely moveable plate - 40 on the axially moveable platen 42 of the machine. ~Core pin lOA is positioned in an injection mold 20 while core pin lOB is positioned in a blow mold 30B. When plate 40 is tra-versed to the left, core pin 10~ will be in blow mold 30A

~L~S~6~

and core pin lOB will be in the injection mol~ 20. A paIi-son is removed fLom tne mold by axial retreat of the move-able platen 42 and the plate 40 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 parison 60B. Parison 603 is inflated with air to assume the shape of 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 "~.i 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 for 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 is moved axially of the mold by a hydraulic press 44. Control cir-cuitry means for the press and blowing cycles are indica.ed at press control block 110. A microprocessor 100 is pro-grammed to control the servo hydraulics 120 which control the individual in~ection rams and to command the press con-, trol block 110.
Figure 3 shows one of the plural plasticators 82B
for melting and supplying molten polymer B to an injection -~15~651 ram 70B. The plasticator 82s 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 85s is openecl and the ram is retreated to the 5 left by hydraulic actuator 72. When the ram cylinder 71 is - s charged with molten resin, valve 85B is closed. Upon a con-~: trol signal from the microprocessor lOO, 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 complete 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 schematically the servo loop where the control signal from the microprocessor 100 (shown as voltage as a function of time) and a position signal from the displacement tranducer 76 are algebraically combined in an amplifier 78 and the resulting signal is used to control ::~
the hydraulic servo 120 for the hydraulic 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.

. . ~ : , ':

6~;1 Figure 6 is a flow chart of the system used to con-trol the machine. The injection blow molding machine is in-dicated as IBM on the chart. Upon initiati~n of the cycle, the program checks positions of valves, rams, etc. and iE
; 5 all are proper, recharges the ram cylinders 71 from the plasticators 82. The IBM control circuit 110 provides an "inject" signal to the microprocessor 100. Injection is caLried out according to the ram displacement-time schedule of the microprocessor and is terminated at the end of the schedule. 7~n "injection complete" signal is sent to the ~ I~M. The control 110 then causes the IsM to traverse to .5 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 s-hut down the machine.
Figure 7 is a plot of ram displacement as a func-tion of time for three rams. The positions of the rams are measured as the voltage analog output of the transducers 76 for each ram. The polymer for the inside surface layer is "~"; that for the core layer "C"; and that for the outside surface layer is "s". 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 slope indicates a retreat of the ram. The significance oE
Figure 7 is perhaps better understood by reference 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 2n at the rounded bottom of the parison. Figures 8-15 ale taken at different times in the cycle and those times are keyed to Figure 7.
Figure 8 IepLesents the conditions at the start o~
a cycle at time 0. The cavity 20 is empty. The entrance 52 - 5 of the cavity 20 initially contains only the polymers A and . .
for the inside and cutside surface layers. The rams for polymers A and B begin to advance to force those polymers into the cavity. At about 100 milliseconds into the cycle the ram for the core layer, polymer C, begins to advance.
Figure 9 shows that polymer C has joined the flow stream in the entrance and polymer C is about to enter the cavity.
Figure 10, taken at about 520 milliseconds, shows the flow .. .i 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 laminar, the velocity in the middle of the stream is higher than the velocities at the cavity walls. Therefore, initia . tion oE flow of polymer C is retarded enough (i.g., about 100 milliseconds) so that polymer C will reach the far end of the cavity just as the slower moving surface layers ~A
and B) reach the end. In this way, the far end of the parl-son, that which becomes the mouth end of the container, will ~ . .
-~' have all layers present in their 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 A is necked `'' ~ 12 ~5~6~

down in the entrance 52 as is shown in Figure 11 until it e~fectively is se~ered as shown in Figure 12. At 110 milli-seconds the ram for polymer C is stopped and the ram for po-lymer A is restarted. ~igules 13 and 14 show polymer A ad-vancing to pinch off polymer C in the entrance, thereby . pushing the last of polymer C into the cavity 20 with poly- -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-- 10 lation of polymer C and to return to the conditions a-t the start as shown in Figure 8. At the time of Figure 15 (1300 ; ¦ 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 ex~dation from the nozzle while the cavity is open. This exudation leads to premature , flow of polymers into the cavity during the next cycle which . can lead to smearing of polymer C on the surfaces of the container.
2Q 1500 milliseconds marks the end of the injection phase of 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 - 25 mold is opened by eetreating the hydraulic press 44 to with-draw the core pin 10 from 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 65i~

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 R, which forms the outside surface layer, is delivered by the ram 70B to an annular distribution channel 5~ which dis-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. Similarly, polymer C, which forms the core layer, is delivered by ram 70C to annular distribution ~ channel 54C and thence along conical passage 56C to annular :~ orifice 58C. Polymer ~, which forms the inside surface layer, is delivered by the ram 70A 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 finished container. The neck portion 62 remains virtually unchanged during blow molding. The parison is held by the chill~ed neck portion while the hot and soft parison is blown. Thus, the neck 62 including the - flange 64 is essentially formed in the in~ection mold. The ..!
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 .

~S~651 ~` the delay time in starting the ram for the core polymer.
The flange 54 will be employed in a double seam seal when a metal end is crimped, by well known techniques, onto the container mouth to close the filled container. Since the ~ 5 flange represents a significant area, it is important that - ~ the cole layer extend well into the flange. The programmed flows of the various polymers also ensure that the core layer is not exoosed at the sprue mark at the central ex-terior of the container.
Figure 19 is an enlargement of the container wall ~ within the circle of Figure 18. Layer A is the inside sur--~1 face layer formed from polymer A in the foregoing descrip-i~ tion. Layer B is the outside surface layer, forme~ from polymer B. Layer C is the core or barrier layer formed Erom polymer C. The thinnest layer is the relatively expensive barrieL 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-: ....................................................................... .
S l placement rates of the rams. A preferred wall structure is a layer of a blend of high density polyethylene and polypro-pylene on each face of a core barrier layer of ethylene vinyl alcohol copolymer (EVOH).
F'igure 20 shows how the oxygen barrier quality of EVOH decreases abruptly at high levels of moisture. Where the EVOH layer is thin, only a small quantity of water will cause a large increase in oxygen permeability. For this reason, the EVOH layer must adequately be protected against the intrusion of moisture.
, Polyolefins do not adhere well to EVOH. Adhesion can be improved by adding adhesion promotors to the polyolefin, the EVOH or both. Another approach is to provide an intermedi-ate layer of an adherent polymeric material which adheres to the polyolefin and the EVOH. Such materials include modified polyolefins sold under the name Plexar tTrade Mark) by the Chemplex Company of Rolling Meadows, Illinois. These comprise a blend of a polyolefin and a graft copolymer of high density polyethylene and an unsaturated fused ring carboxylic acid an-hydride. The polyolefin component of the blend can be poly-ethylene 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. Patent Nos. 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 name Admer (Trade Mark) by Mitsui Petrochemical Industries of Tokyo, Japan.
The use of interlayers on each side of the EVOH
oxygen barrier layer results in a five layer container. To -produce such a container, the three passage nozzle of Figure 16 is 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 .~ :
' ~

~5~

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. The two additional annular noz-~le 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 control1able ram for each layer. R 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 in Figure 21B wherein layers R and B are the inside and outside sur--~ face layers of polyolefin, layer C is the barrier layer ofEVOH, and two layers D are the interlayer material.

: EXAMPLE I
".
t 20 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 polypr~p ~ e~
; polyethylene block copolymer (Hercules Profax 7~1). The j, :
adhesive interlayers were ethylene vinyl acetate copolymer blended with a graft copolymer of high density 5~
polyethylene and a fused ring carboxylic acid anhydride (Plexar 1615-2 (Trade Mark)). The oxygen barrier was EVOH (Kuraray EVAL EP-F, tTrade Mark), available from Kuraray Co. Ltd., Osaka, ~apan). The layers were well aahered. The barrier ex-tended to the flange lip and was completely encapsulated.
EXAMPLE II
Five layer containers similar to those of Example 1 were made wherein the inside and outside surface layers were polypropylene (EXXON E612 (Trade Mark)); the interlayer material was Plexar III (Trade Mark), a blend of ethylene vinyl acetate copolymer and a graft copolymer; and the barrier was EVAL EP-F
(Trade Mark). The layers were well adhered. The barrier layer extended to the lip of the flange and was completely encapsulat-ed.
EXAMPLE 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 (EXXON E612 (Trade Mark)) and high density polyethylene (Chemplex 5701 (Trade Mark)); the interlayer material was Plexar III (Trade Mark); and the barrier layer was EVAL EP-F (Trade Mark). The layers were well ad-hered. The barrier layer extended to the lip of the flange and was completely encapsulated.

~ ~ `J

. . .

s~

EX~MPLE IV
~;' Five layer containers similar to those of Example I
were made wherein the inside and outside surface layers were a copolymer of propylene and ethylene (Hercules Profax 7631); the interlayer material was maleic anhydride grafted polyolefin (Mitsui Admer QB 530); and the barrier layer was EVAL EP-F. The layers were well adhered. The barrier layer extended to the lip of the flange and was completely , encapsulated.
¦ 10 In the making of the containers of Examples I-IV
. _ ~
the injection schedule began feeding the inside and outside surface layer polymer then the polymel for the adhesive interlayer was started and substantially simultaneously the barrier layer polymer was started. The flows of the adhe-sive interlayer polymer and the barrier layer polymer were ~, terminated before the outside surface layer polyme~ flow was terminated.

~`; ,1 .~
:~ ~

~, ''' :

a~

Claims (62)

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

1. A method of making a multi-layer rigid article comprising the steps of: A) injection molding a parison in an injection mold cavity by: 1) commencing the flow of a first polymer stream to become the inside surface layer of the pari-son and the flow of a second polymer stream to become the outside surface layer of the parison, 2) subsequent to the commencement of the flow of the first and second polymer streams, commencing the flow of a third polymer stream between the first and second polymer streams, 3) continuing the flow of the first, second and third polymer streams concurrently, when the cavity is nearly filled, 4) terminating the flow of the first polymer stream, 5) subsequently terminating the flow of the third polymer stream, and then 6) subsequently terminating the flow of the second polymer stream, B) transferring the injec-tion molded parison to a blow molding cavity having the config-uration of the article, C) inflating the parison in the blow molding cavity to form the article.

2. The method of claim 1 wherein a fourth polymer stream is introduced between the third and first polymer streams and a fifth polymer stream is introduced between the third and second polymer streams, the flow of the fourth and fifth polymer streams terminating before termination of the flow of the second polymer stream.

3. A method of making a multi-layer rigid container comprising the steps of:
A) infection molding a parison having an open end and a closed end in an injection mold cavity having a core pin and an entrance for polymer at the closed end of the parison by:
1) establishing in the entrance a flow of po-lymer comprising a central stream of a first polymer sur-rounded by an annular stream of a second polymer, 2) subsequently commencing an annular stream of a third polymer between the first and second polymer streams, 3) maintaining the flow of the three polymer streams until the cavity is nearly filled, 4) terminating the flow of the first polymer stream, 5) terminating the flow of the third polymer stream, 6) terminating the flow of the second polymer stream, B) transferring the parison to a blow mold cavity, C) inflat-ing the parison in the blow mold cavity to flow mold the pari-son into the finished container.

4. The method of claim 3 wherein following the ter-mination of flow of the third polymer, flow of the first poly-mer is recommenced and flow of the first polymer is terminated approximately simultaneously with the flow of the second polymer.

5. The method of making a multi-layer injection molded article comprising the steps of: 1) commencing the flow of a first polymer stream to become the inside surface layer of the article and the flow of a second polymer stream to become the outside surface layer of the article, 2) subsequent to the commencement of the flow of the first and second polymer streams, commencing the flow of a third polymer stream between the first and second polymer streams, 3) continuing the flow of the first, second and third polymer streams concurrently, 4) terminating the flow of the first polymer stream, 5) sub-sequently terminating the flow of the third polymer stream, and then 6) subsequently terminating the flow of the second polymer stream.

6. The method of claim 5 wherein a fourth polymer stream is introduced between the third and first polymer streams and a fifth polymer stream is introduced between the third and second polymer streams, the flow of the fourth and fifth poly-mer streams terminating before termination of the flow of the second polymer stream.

7. A method of forming a multi-layer plastic parison for an injection blow molded article comprising the steps of:
1) initially commencing the injection of a first inside sur-face layer; 2) commencing the injection of a second outside surface layer while continuing to inject the first layer;
3) then commencing the injection of a third core layer between the first and second layers while continuing to inject the first and second layers; 4) then terminating the injection of the first layer while continuing to inject the second and third layers; 5) then terminating the injection of the third layer;
6) then terminating the injection of the second layer.

8. An injection blow molded multi-layer rigid plastic container having a continuous core layer completely encap-sulated within outer layers.

9. An injection molded multi-layer plastic parison for a blow molded container, said parison having a continuous core layer completely encapsulated within outer layers.

10. The container of claim 8 wherein the inside surface layer is a polyolefin, the core layer is ethylene vinyl al-cohol copolymer having a layer of an adherent polymeric material on each face of the ethylene vinyl alcohol copolymer, and the outside surface layer is a polyolefin.

11. The container of claim 10 wherein the polyolefin layers are a blend of polyethylene and polypropylene and the layers of adherent polymeric material are a blend of ethylene vinyl acetate copolymer and a graft copolymer of polyethylene and an unsaturated fused ring carboxylic acid anhydride.

12. The container of claim 8 wherein the inside surface layer is a polyolefin, the core layer is ethylene vinyl al-cohol copolymer having a layer of maleic anhydride grafted polyolefin on each face of the ethylene vinyl alcohol copo-lymer, and the outside surface layer is a polyolefin.

13. The container of claim 12 wherein the polyolefin layers are a copolymer of propylene and ethylene.

14. The product of the process of claim 5.

15. The product of the process of claim 6.

16. The product of the process of claim 7.

17. The container of claim 10 wherein the polyolefin is polyethylene.

18. The container of claim 10 wherein the polyolefin is polypropylene.

19. The container of claim 10 wherein one surface layer is polypropylene and the other surface layer is polyethy-lene.

20. The container of claim 12 wherein the polyolefin is polypropylene.

21. The container of claim 10 wherein at least one of the surface layers is a blend of polyethylene and polypropylene.

22. The container of claim 10 wherein at least one of the surface layers is a copolymer of propylene and ethylene.

23. A method of making a multi-layer rigid article comprising the steps of A) injection molding a parison in an in-jection mold cavity by: 11 commencing the flow of a first poly-mer stream of moisture-protective material to become the inside surface layer of the parison and the flow of a second polymer stream of moisture-protective material to become the outside surface layer of the parison, 2) subsequent to the commence-ment of the flow of the first and second polymer streams, com-mencing the flow between the first and second polymer streams of a third polymer stream of moisture-sensitive, barrier layer material, 3) continuing the flow of the first, second and third polymer streams concurrently, when the cavity is nearly filled, 4) terminating the flow of the first polymer stream, 5) subse-quently terminating the flow of the third polymer stream, and then 6) subsequently terminating the flow of the second polymer stream, thereby to provide a parison having a continuous inner barrier layer completely encapsulated between the inside and outside surface layers, B) transferring the injection molded parison to a blow molding cavity having the configuration of the article, and C) inflating the parison in the blow molding cavity to form the article.

24. The method of claim 23 wherein a fourth polymer stream of adhesion-promoting material is introduced between the third and first polymer streams and a fifth polymer stream of adhesion-promoting material is introduced between the third and second polymer streams, the flow of the fourth and fifth polymer streams terminating before termination of the flow of the second polymer stream.

25. A method of making a multi-layer rigid container comprising the steps of: A) injection molding a parison having an open end and a closed end in an injection mold cavity having a core pin and an entrance for polymer at the closed end of the parison by: 1) establishing in the entrance a flow of polymer comprising a central stream of a first polymer of moisture-protective material surrounded by an annular stream of a second polymer of moisture-protective material, 2) subsequently com-mencing between the first and second polymer streams an annular stream of a third polymer of moisture-sensitive, barrier layer material, 3) maintaining the flow of the three polymer streams until the cavity is nearly filled, 4) terminating the flow of the first polymer stream, 5) terminating the flow of the third poly-mer stream, 6) terminating the flow of the second polymer stream, thereby to provide a parison having a continuous inner barrier layer completely encapsulated between the inside and outside sur-face layers, B) transferring the parison to a blow mold cavity, C) inflating the parison in the blow mold cavity to blow mold the parison into the finished container.

26. The method of claim 25 wherein following the termination of flow of the third polymer, flow of the first polymer is recommenced and flow of the first polymer is ter-minated approximately simultaneously with the flow of the second polymer.

27. The method of making a multi-layer injection molded article comprising the steps of: 1) commencing the flow of a first polymer stream of moisture-proof material to become the inside surface layer of the article and the flow of a second polymer stream of moisture-proof material to become the outside surface layer of the article, 2) subsequent to the commencement of the flow of the first and second polymer streams, commenc-ing between the first and second polymer streams the flow of a third polymer stream of moisture-sensitive, barrier layer mater-ial, 3) continuing the flow of the first, second and third polymer streams concurrently, 4) terminating the flow of the first poly-mer stream, 5) subsequently terminating the flow of the third polymer stream, and then 6) subsequently terminating the flow of the second polymer stream, thereby to provide an article hav-ing a continuous inner barrier layer completely encapsulated be-tween the inside and outside surface layer.

28. The method of claim 27 wherein a fourth polymer stream of adhesion-promoting material is introduced between the third and first polymer streams and a fifth polymer stream of adhesion-promoting material is introduced between the third and second polymer streams, the flow of the fourth and fifth polymer streams terminating before termination of the flow of the second polymer stream.

29. An injection blow molded multi-layer rigid plas-tic container, comprising a continuous, barrier layer completely encapsulated within protective outer layers.

30. The container of claim 29, wherein said barrier layer is moisture-sensitive and said outer layers are moisture-protective outer layers of moisture-protective material.

31. An injection molded multi-layer plastic parison for a blow molded container, said parison having a continuous barrier layer completely encapsulated within protective outer layers.

32. The container of claim 31, wherein said barrier layer is moisture-sensitive and said outer layers are moisture-protective.

33. A method of making a multi-layer rigid article comprising the steps of: A) injection molding, from a nozzle having an exit, a parison in an injection mold cavity by: 1) establishing in the nozzle prior to 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, 2) subsequently establish-ing in the nozzle prior to the exit of the flow of a third poly-mer stream between the first and second polymer streams, 3 continuing the flow of the first, second and third polymer streams concurrently, when the cavity is nearly filled, 4) terminating the flow of the first polymer stream, 5) subsequent-ly terminating the flow of the third polymer stream, and then 6) subsequently terminating the flow of the second polymer stream, B) transferring the injection molded parison to a blow molding cavity having the configuration of the article, and C) inflat-ing the parison in the blow molding cavity to form the article.

34. A method of making a multi-layer rigid article comprising the steps of: A) injection molding, from a nozzle having an exit, a parison in an injection mold cavity by: 1) establishing 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 layer of the pari--son, and the flow of a third polymer stream between the first and second polymer streams, when the cavity is nearly filled, 2) terminating the flow of the first polymer stream, 3) subse-quently terminating the flow of the third polymer stream, and then 4) subsequently terminating the flow of the second polymer stream, B) transferring the injection molded parison to a blow molding cavity having the configuration of the article, and C) inflating the parison in the blow molding cavity to form the article.

35. In a method of making a multi-layer injection molded rigid article using a nozzle having an exit, the steps comprising: 1) establishing in the exit the flow of a first polymer stream to become the inside surface layer of the article, the flow of a second polymer stream to become the outside sur-face layer of the article, and the flow of a third polymer stream between the first and second polymer streams, 2) terminating the flow of the first polymer stream, 3) subsequently terminat-ing the flow of the third polymer stream, and 4) subsequently terminating the flow of the second polymer stream.

36. In a method of making a multi-layer injection molded rigid article using a nozzle having an exit, the steps comprising: 1) establishing in the exit the flow of a central first polymer stream, the flow of an annular second polymer stream substantially surrounding the first stream, and the flow of an annular third polymer stream between the first and second polymer streams, 2) terminating the flow of the first polymer stream, 3) terminating the flow of the third polymer stream, and 4) terminating the flow of the second polymer stream.

37. The method of claim 1, 3 or 5, wherein the flows of the first and second polymer streams are established substan-tially simultaneously.

38. The method of claim 23 or 24, wherein the flows of the first and second polymer streams are established substan-tially simultaneously.

39. The method of claim 35 or 36, wherein the flows of the first and second streams are established before the flow of the third stream is established.

40. The method of claim 35 or 36, wherein the flows of the first and second streams are established before the flow of the third stream is established, and wherein the flows of the first and second streams are established substantially simul-taneously.

41. The method of claim 35 or 36, wherein the flows of the first and second streams are established before the flow of the third stream is established, and wherein the flow of one of said first and second streams is established before the flow of the other of said first and second streams is established.

42. The method of claim 1 or 2 wherein, there is included the step of controlling the relative thicknesses of the layers of the multi-layer article by independently controlling the relative flow rates of the polymer streams.

43. The method of claim 3 or 4 wherein there is in-cluded the steps of controlling the relative thicknesses of the layers of the multi-layer rigid container by independently con-trolling the relative flow rates of the polymer streams.

44. The method of claim 5 or 6 wherein there is in-cluded the step of controlling the relative thicknesses of the layers of the multi-layer injection molded article by indepen-dently controlling the relative flow rates of the polymer streams.

45. The method of claim 7 wherein there is included the step of controlling the relative thicknesses of the layers of the multi-layer plastic parison by independently controlling the relative flow rates of the layers.

46. The method of claim 33 wherein there is included the step of controlling the relative thicknesses of the layers of the article formed from the first, second and third polymer streams by independently controlling the relative flow rates of the streams.

47. The method of claim 34 wherein there is included the step of controlling the relative thicknesses of the layers of the article formed from the first, second and third polymer streams by independently controlling the relative flow rates of the streams.

48. The method of claim 35 or 37 wherein there is included the step of controlling the relative thicknesses of the layers of the article formed from the first, second and third polymer streams by independently controlling the relative flow rates of the streams.

49. The method of claim 1, 3 or 5, wherein the layer formed from the third polymer stream is thinner than the layer formed from the first polymer stream and is thinner than the layer formed from the second polymer stream.

50. The method of claim 1, 3 or 5, wherein the layer formed from the third polymer stream is the thinnest layer of the article.

51. The container of claim 8, wherein the layer is thinner than the encapsulating outer layers.

52. The parison of claim 9 wherein the core layer is thinner than the encapsulating outer layers.

53. The container of claim 29, wherein the barrier layer is thinner than the encapsulating outer layers.

54. The parison of claim 31, wherein the harrier layer is thinner than the encapsulating outer layers.

55. The container of claim 10 or 11 wherein the core layer is thinner than the combined thicknesses of the inside surface layer and of the layer of adherent material which is proximate to said surface layer.

56. A method of making a multi-layer injection molded article in an injection mold cavity having an entrance sprue comprising the steps of (1) providing at least three concentric streams of polymeric materials concurrently flowing through the sprue into the injection cavity, said flowing streams comprising a first stream to become the inside surface layer of the inject-ed article, a second stream to become the outside surface layer of the injected article, and at least one stream flowing be-tween said first and second streams to become a core layer in the injected article, and (2) independently and continuously control-ing the rate of flow of each of the flowing streams into the injection cavity to control the location and thickness of the flowing core layer stream relative to said flowing first and se-cond streams.

57. A method of making a multi-layer injection molded article in an injection mold cavity having an entrance sprue comprising the steps of (1) providing at least three concentric streams of polymeric materials concurrently flowing through the sprue into the injection cavity, said flowing streams comprising a first stream to become the inside surface layer of the in-jected article, a second stream to become the outside surface layer of the injected article, and at least one stream flowing between said first and second streams to become a core layer in the injected article, and (2) controlling the relative thick-nesses of the streams by independently and continuously control-ling the relative flow rates of the streams.

58. A method of making a multi-layer injection mold-ed article by use of a coinjection nozzle having an exit com-prising the steps of (1) flowing at least three concentric streams of polymeric material concurrently through the nozzle exit, said flowing streams comprising a first stream to become the inside surface layer of the injected article, a second stream to become the outside surface layer of the injected article, and at least one stream flowing between said first and second streams to become a core layer in the injected article, and (2) inde-pendently and continuously controlling the rate of flow of each of the streams through the nozzle exit to control the thickness of each of said layers of the article.

59. The method of claim 56, 57, or 58, wherein there are included the steps of terminating the flow of the first poly-mer stream, subsequently terminating the flow of the third poly-mer stream, and subsequently terminating the flow of the second polymer stream.

60. The method of claim 42, 43 or 44, wherein said core layer is thinner than said inside surface layer and is thinner than said outside surface layer.

61. The method of claim 42, 43, or 44, wherein said core layer is the thinnest layer of the article.

62. The method of claim 1, 3 or 5, wherein the first and second streams are of substantially the same polymeric material.