AU2001295835A1

AU2001295835A1 - Injection molding of multi-layer plastic articles

Info

Publication number: AU2001295835A1
Application number: AU2001295835A
Authority: AU
Inventors: Paul Swenson
Original assignee: Kortec Inc
Current assignee: Kortec Inc
Priority date: 2001-04-06
Filing date: 2001-10-26
Publication date: 2002-10-21

Description

Manufacture of Plastic Articles Field

The present invention relates to the co-extrusion of pluralities of flowing polymer plastic streams through nozzle extruders and the like into injection molding and similar apparatus for forming multi-layer plastic articles in which an interior core is encased by inner and outer layers of the article; and, more particularly, to the control of relative volumetric flow rates of the layers for attaining greater flexibility in the properties and relative thickness and positions of the layer sin the ultimate article. More specifically, the invention is especially, though not exclusively, useful with co-extrusion processes of the type described in my earlier United States patent No. 5,914,138, issued June 22, 1999 For Apparatus ForThrottle-Valving Control For The Co-Extrusion of Plastic Materials As Interior Core Streams Encased by Outer And Inner Streams For Molding And The Like.

Background of Invention A common problem in multilayer molding is the maintaining of a uniform penetration of the leading edge of the interior core layer, when that layer is not near the zero gradient of the velocity profile of the flowing polymer stream as it flows through a

hot runner nozzle and/ or into the mold cavity forming the molded article. Unlike the

prior art tapered leading edge flow of, for example, systems of the type disclosed in

United States Patents Nos.4,895,504 and 4,892, 699, my said earlier patent teaches the

combining of the different flow streams of materials to achieve a velocity profile of the

combined streams in the melt delivery system that is similar to the velocity profile of

the combined stream in the injection mold cavity, thereby insuring uniformity in a

resulting molded article.

This problem of maintaining uniform penetration of the leading edge of the

interior core layer when it is not close to the zero gradient of the velocity profile

becomes particularly severe when there is the requirement to form the multilayer article

with the core layer not centered on the midplane of the article.

In two-material, three -layer preform molding, for example, it may be desirable

to have a barrier or scavenger layer closer to either the inner sidewall or outer sidewall

of a blow-molded container article, in order to enhance the barrier property of the

container. In three-material, four-layer preform molding, this leading edge problem

also occurs, particularly when the volumetric flow rate of one of the interior core layers

is greater than that of the other interior core layer. Another common current problem also arises in using post-consumer recycled ^"

plastic (PCR) in a molded article that consists of layers of two other polymers. Current

art accomplishes this three-material combination by using apparatus and methods that

create a 5-layer article. With such 5-layer technology, however, the molding cycle times

are significantly longer than if the article had been molded of only one material. Such 5-

layer molded articles, moreover, suffer delamination of the layers if the second polymer

has low adhesion to the virgin skin layers and to the central PCR layer.

The present invention is directed to the solution of the above problems, and

limitations, among others, in such prior art systems through a later-described technique

for permitting changed or controlled variation of the relative volumetric flow rates of

the inner and outer layers after the flow of the interior core layer stream has started.

Objects of Invention

A principal object of the present invention, accordingly, is to provide a new and

improved method of and apparatus for molding multi-layer polymer plastic articles

having inner, outer and interior or core layers that shall not be subject to such problems

and limitations; but that, to the contrary, obviate such through the control of relative

volumetric flow rates of the inner and outer layers in such a way as to shift the position of the core and control also the relative thickness of the inner and outer layers of the

article.

Another object is to provide novel apparatus and methods to inject the leading

edge of the interior core layer on the zero gradient of the combined velocity profile

during the initial portion of the interior core layer flow, and then to change the relative

volumetric flow rates of the inner and outer layers to cause the later or subsequent

portion of the interior core flow to be offset from the zero gradient of the combined flow

velocity profile.

An additional object is to provide novel apparatus and methods to restrict either

the flow of the inner or of the outer layer volumetric flow rate in order to shift the

interior core layer trailing portion inside or outside the 50% streamline through the

nozzle and into the molded part.

Still a further object of the present invention is to provide a novel method and

apparatus to produce an article of three materials molded into four layers.

Another object is to provide in such apparatus, novel operation wherein the

leading edge of one of the interior core layers is injected on the zero gradient of the

velocity profile of the combined stream before the start of flow of the other interior core

layer. Other and further objects will be described hereinafter and are more fully -

delineated in the appended claims.

Summary

In summary, however, from one of its important aspects, the invention embraces

a method for co-extruding multiple plastic materials as for injecting through a gate

region into a mold cavity to produce a molded article, that comprises, co-extrusively

flowing streams of plastic materials with at least one interior stream that is to serve as

an interior core of a resulting molded plastic article within inner and outer streams of

plastic material that serve as covering wall plastic material layers for the core; forcing

the flowing streams to flow along concentric annular flow paths within and along a

longitudinally extending tubular extruder nozzle to the cavity gate region; adjusting

the flow streams initially to cause the core stream to start to flow at a region of

substantially zero gradient in the transverse flow velocity profile of the extrusion;

thereupon varying the relative volumetric flow ratio of the inner and outer layer

streams after the zero-gradient flow of the core layer has started in order to offset the

core layer flow from the zero-gradient and to shift the core layer closer to one of the

inner or outer annular flow boundaries, thereby to produce a molded article wherein

the major portion of the core layer is closer to one of the inner or outer article walls than the other. Preferred and best mode designs and configurations are later described in deta'i

Drawings

The invention will now be described in connection with the accompanying

drawings, Fig. 1 A of which is a schematic longitudinal section of the type of nozzle

described in my above-mentioned patent using a central longitudinal restrictor or

throttle pin to force concentric annular flow of the injected plastic thereabout within th

walls of the hollow extruder nozzle; and Fig. IB is a graph illustrating resulting flow

fraction and velocity profile curves across the annular channel within the nozzle of Fig

1 A for an inner flow-to-outer flow ratio of 50: 50 — the ordinate plotting the ratio of

velocity-to-average velocity as a function of the radius of the annulus between the innej

and outer nozzle wall, with the central solid line curve NP plotting said ratio and

showing zero gradient for the core stream CF (shaded vertical strip), and the curve

designated with a circle marker, plotting the flow IF between the radius and the throttle

pin T from the inner to the outer wall, and the curve marked with a triangle, plotting

the flow OF between the outer wall and the annular radius;

Fig. IC is a graph showing the relative timing and proportions of volumetric

flow rate of the combined inner and outer layer flows, the inner layer flow, and the

interior core layer flow, with Figs. ID and IE being similar to Fig.1 A, but showing ^; partially and completely filled conditions of the mold cavity fed from the throttled^"

nozzle for the conditions of Fig. IB;

Figs. 2, 2A, 2B and 2C correspond, respectively, to the showings of Figs. IB, IC,

ID and IE, but for an inner-to-outer flow ratio of 40:60;

Figs. 3, 3 A, 3B and 3C respectively correspond to Figs. 2, 2A, 2B and 2C, but for

an inner-to-outer flow ration of 60:40;

Figs. 4 and 5 are velocity profile graphs similar to Fig. 2, for respective ratios of

25: 75 and 75:25, with Figs.4A,B and C and Figs. 5A, B and C corresponding to Figs. 2A,

2B and 2C, respectively, but for such 25: 75 and 75:25 ratios, respectively;

Fig. 6 is a flow fraction and velocity profile similar to Figs. 1 A, 2, 3, and 5, but

embodying the methodology of the present invention, with an initial portion of the core

layer flow occurring for a 50: 50 ratio, and the major flow occurring with 80:20 ratio to

shift the core toward the outer wall, but without providing any leading-edge bias;

Figs. 6A, 6B and 6C are similar to respective Figs. 5A, 5B and 5C but describe the

operational conditions of the invention as reflected by Fig. 6;

Figs. 7, 7A, 7B and 7C correspond to respective Figs. 6, 6A, 6B and 6C,

illustrating the operation of the invention for the conditions converse to Fig. 6, wherein,

after the initial 50:50 flow ratio, the inner flow-to-outer flow ratio is decreased without shifting the initial core layer leading edge, the core layer being shifted towards the inner

layer;

Figs. 8 and 9 are graphs similar to Figs. 3A -6A for modifications wherein the

core is shifted back before the end of the flow, as shown in Figs. 8A, B, C and D for

original core shifts towards and away from the inner wall; and, in Figs. 9A, B, C and D,

for original core shifts away from and towards the inner wall, respectively;

Figs. 8E through 81 are respectively similar to Figs. 8 and 8A-8D, but are

designed for producing flat-shaped molded articles;

Figs. 9E through 91 similarly correspond to Figs. 9 and 9A-9D, but relate to

molding flat-shaped articles;

Figs. 10A-C are schematic top views of the inner, outer and core flow entry

channels and flow restrictor controls for varying the inner/ outer channel flow ratios for

the core shifting effects of the invention;

Figs. 11 A and B are similar views with flow restrictor controls disposed in the

most common channel feeding the respective outer and inner layers,

Figs. 12 A, B and C are schematic views of pin-type flow restriction elements;

Fig. 13 is a cross-section of a preferred nozzle - flow control apparatus for the

practice of the invention; Figs. 14 and 15 are enlarged cross - sections of varying flow control positions of

operation of the nozzle of Fig. 13;

Figs. 16A and B are similar to Figs. 10A-C, but are directed to feed channels for

three-material streams to each nozzle to form inner and outer annular covering layers.

Figs. 17 and 17 A-D ase 19 and 19 A-D illustrated the adaptation of the

techniques of the invention for producing three-material, four layered articles, and

illustrating graphs in Figs. 17 and 19 showing relative timing and proportions of

volumetric flow rate of combined inner and outer layer flow, the innermost interior

layer flow and the outermost interior layer flow of two different three-material, four

layer flow systems;

Figs. 18, 18A-D, Figs. 20, and 20A-D are views similar respectively to Figs. 17 and

17A-D and Figs. 19 and 19 A-D, but are directed to the molding of flat-shaped articles

rather than cylindrical-shaped containers and the like.

Figs. 21 A, 22D, 23D and 24D show various exemplary types of containers that may be

formed by the techniques of the invention from respective per-forms 21B-C-D, 22, 23

and 24; respective enlarged cross-sectional segments A, B and C of which are illustrated

in Figs. 22A-C, 23A-C and 24A-C. Preferred Embodiments Of The Invention

In my before-referenced prior co-extrusion patent, at least two-polymer plastic

materials are provided as a 3-layer combined flow stream; a first material L which

forms the ultimate outer and inner molded covering layers of the ultimate molded

product, article or part from the inner and outer flow stream layers (IL and OL),

injected as annular streams; and a second material (I) which forms the middle, inner or

interior core of the product formed from an injected concentric annular interior stream

(I A) encased within the inner and outer annular stream layers of the covering material.

The preferred apparatus employs a multiple-plastic stream co-extruder as for

injection molding cavities in which the extruder is internally provided therewithin and

therealong with a restrictor or throttle pin, rod or element that forces combined plastic

materials streams, formed with an interior core stream encased in outer and inner

stream layers, into corresponding concentric co-extensive annular flow stream layers

that are ultimately split transversely in opposite directions into a cavity gated to the

extruder, and with the core stream at a region of zero gradient in the transverse-flow

velocity profile within the extruder and cavity.

Referring to Fig. 1 A, a schematic cross-sectional view of a longitudinally

extending extruder nozzle N is shown provided with a central longitudinal throttle needle or pin acting as a flow restrictor T downstream of a combining section C,

providing uninterrupted continual annular flow within the extruder of the concentric

inner and outer annular stream layers IL and OL, with the encased interior annular core

stream IA, and into gate G. The combined streams A are then, as before stated, laterally

split and injected transversely in opposite directions into a molding cavity (CAV) —

shown for illustrative purposes of shape suitable for molding cylindrical containers

such as bottles or the like. As described in my said prior patent, other shaped cavity

molds may also be used for other products, as may a wide variety of plastic materials be

used, among them, for example, polyethylene, PET, and other plastic and polymer

compositions/as later more fully described.

As further taught in my prior patent, it is highly desirable in many applications

that, as shown in Fig. IB, the core layer flows substantially on the zero-gradient velocity

profile (O) in order to keep the leading edge of the core layer uniform 360-degrees

around a periphery of the annular flow, to insure, as the flow enters the cavity, that the

core layer is uniformly distributed in the cavity, with the highest point of the velocity

typically on the center line of the flow; and wherein 50 percent of the material is-on the

inside of the streamline and 50 percent is outside the streamline, and the zero gradient

occurs right on the 50-percent streamline. In Fig. IC, a graph is presented plotting as a function of time, the volumetric flov

rate of the combined inner and outer flow (top curve), the inner layer (IL) flow (dash-

line curve) and the interior core layer flow (bottom curve) encompassing the times A

and B, respectively representing a time after the start of the interior core layer flow, and

an intermediate time before the leading-edge of the core layer has left the extruder to

enter the mold cavity. Fig. ID is a longitudinal section similar to Fig.1 A for the

partially filled condition at time B, and Fig. IE shows the completely filled cavity,

demonstrating the distribution of the core layer extending most of the line length of the

flow in the cavity and having a uniform leading edge at a 180-degree section of the

cavity and with the core layer placed on the 50% streamline in the middle of the molded

article.

My earlier patent also provided for moving the throttle or restriction pin to vary

the percentage of the outer layer material in the inner annular flow layer vs. the outer

annular flow layer of the combined flow stream downstream of the combining area.

Changing the relative volumes of the outer layers shifts the position of the core

(interior) layer in the mold cavity to produce a part with controlled outer layer- ^•

thickness on both surfaces of the molded article or part. If the outer layer flow is biased

toward either the inner or outer annular flow layers, the outer layer thickness in the

molded part will be similarly biased on the corresponding surface molded from the biased annular layers. Material from the inner annular flow layer forms the surface

layer of the part molded by the cavity wall opposite the gate into the cavity and the

material from the outer annular flow layer forms the surface layer of the part molded

by the cavity wall adjacent to the gate.

The use of a movable throttle valve pin is typically appropriate in cases where it

is the advantageous to vary, during each injection, the relative percentage of the outer

layers material in the inner annular flow layer vs. the outer annular flow layer. For

cases where the relative thickness of the layer on both surfaces of the molded part can

remain in fixed proportion to each other, the embodiment uses a non-moving throttle valve pin.

A typical injection time-line for such three-layers molded articles is as follows:

Time, Action

Seconds

0 Close mold

0.1 Start injection of inner and outer layer material at substantially 50:50 ratio

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 Start injection of interior layer material on zero-gradient of velocity profile

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1-9

2.0 Finish interior layer injection on zero-gradient of velocity profile

>2.0 Finish injection of inner and outer layer material

It has now been discovered that if, instead of changing the relative percentages of

inner and outer annular layer volumes of materials to obtain unequal covering

thicknesses, as described in my earlier patent, one starts the flow process with the inner

layer-to-outer layer volume flow being equal (ratio of 1), this will start the initial

portion of the interior or core layer flow, along the desired zero-gradient velocity

profile; and then, during the continued flow, the ratio of inner-to-outer layer flow may

be changed to effect core layer shifting as later more fully described.

In accordance with the present invention, the core layer flow is thus started on

the zero-gradient velocity profile, with the inner layer in the combined flow and the

outer layer in the combined flow both having the same volumetric flow rate at the time

the core material layer is introduced. Shortly after so introducing the core layer to

create the leading-edge of the core layer, the invention enables the changing of the ratio

of inner layer-to-outer layer flow, advantageously to place the remaining portion —

preferably about 90 to 95 percent of the core layer that is flowing into the cavity— to be

shifted towards the outside boundary wall or towards the inside boundary wall^" of the

molded article. In this way, the advantages of knowledge of the zero-gradient velocity

profile is combined with the advantageous shifting of the position of the core layer to enhance the function of the molded article — the shifting of the volumetric flow of the

inner layer vs. the outer layer, causing the shift of position of the core layer.

As earlier described, Fig. IB shows operation with the type of nozzle described in

my above-referenced patent, employing a throttle pin adjustment such as to produce

substantially a 50: 50 inner flow (IF)-to-outer flow (OF) ratio, placing the leading-edge

of the interior layer flow IL on the zero gradient of the combined velocity profile, and

enabling the absence of any leading edge bias in the molded article due to flow velocity.

Fig. 2 is an operation showing similar to Fig. IB wherein the throttle pin

adjustment has been positioned to achieve an inner flow-to-outer flow ratio of 40: 60,

rather than the 50: 50 ratio of Fig. IB, placing the leading-edge of the interior layer IL

near the zero gradient of the combined velocity profile. This produces a small, but

acceptable leading edge bias in the molded article, as also explained in my earlier

patent.

Fig. 2A presents the same type of volumetric flow rate graph for the operation of

Fig. 2 as described in connection with Fig. IC for the operation of Fig. IB; and Figs. 2B

and 2C illustrate partially filled nozzle-cavity flow conditions at time B and for

complete cavity filling, respectively.

Fig. 3 illustrates similar operation but showing the ratio of inner flow-to-outer

flow as 60: 40, as opposed to Fig. 2. Again, as disclosed in my previous patent, the core layer (CF) remains close to the zero gradient, producing only a small but acceptable

leading edge bias, this time towards the outer wall. Thus, though shifting the core laye

either toward the inner wall or toward the outer wall approximately 10 percent of the

wall thickness, a reasonable and acceptable leading edge bias is still maintained. Figs.

3A, B and C, correspond respectively to Figs. 2A, B and C, above explained, but are

directed to the operation of Fig.3.

In Fig.4, however, a condition is shown for a flow ratio adjustment of 25: 5,

inner flow-to-outer flow, wherein the core layer flow CF is now well offset away from

the zero gradient of the combined velocity profile, resulting in a velocity distribution

bias of the core layer that produces a large leading edge bias that creates an

unacceptable molded article. In Figs. 4 A, B and C, corresponding to the type of

showings in respective Figs. 2A, B and C, the operation for the conditions of Fig. 4 are

similarly presented.

Fig. 5 shows the case where the inner-to-outer flow is 75:25, again illustrating the

bias created in the molded article; and Figs. 5A, B and C correspond to Figs. 2A, B and

C, respectively, but illustrate the conditions of Fig. 5, with a flow Δv (Fig. 5B) producing

a large bias Al (Fig. 5C).

As before stated, however, in accordance with the discovery underlying the

present invention, the core layer may indeed be shifted for useful purposes without having the resulting molded article suffer an unacceptable leading edge bias caused by

the velocity bias. The critical operational requirement for achieving this novel result is

graphically illustrated in Fig. 6, and involves, as earlier discussed, that necessity for

employing an initial throttle pin adjustment or other flow restrictor adjustment that

ensures that the initial portion of the core or interior layer flow occurs when the inner

flow (IF)-to-outer flow (OF) is in a substantially 50: 50 ratio to place the interior core

layer leading edge on the zero gradient of the combined velocity profile, as at region I

in Fig. 6. After that flow is well-established at I - - (of the order of a flow of a few,

preferably about 5, percent (+) of the core material that is to be flowed for the molding

of the article), then it has been found that a subsequent throttle pin adjustment or other

flow-restrictor adjustment at region II, as in the case of Fig. 6, increases the inner flow-

to-outer flow ratio, resulting in shifting the interior core layer leading edge. The

resulting molded article — in this case, having about an 80:20 ratio with the majority of

the core layer flow length III in the molded article extending closer to the outer wall —

will not produce a leading-edge bias caused by velocity bias, and will still enable the

production of the uniform leading edge on the molded article, but with the majority

(say 95%) of the core layer length shifted toward the outer wall, as for purposes earlier

and also hereinafter discussed. One of such purposes for positionable core layers is as barrier layers, where a

humidity sensitive barrier layer may be required within the molded article such as a

cylindrical bottle container or the like. There may be advantage to shifting the barrier

layer towards the outside walls of the container, away from the liquid content and thus

at a lower relative humidity environment that can enhance the performance of the

barrier layer and even require less volume of barrier material in order to provide the

same barrier effect to the contents. Another illustration is for use of oxygen scavenging

layers, the scavenging capacities of which may be increased by being in a higher relative

humidity and/ or being closer to the contents as opposed to being close to the outside

wall. A thicker container outer layer, moreover, would permit less oxygen permeation

than if the outer layer were thinner, slowing down oxygen transfer from the outside to

the scavenging layer. The scavenging capacity of a scavenging layer closer to the

contents would also remove residual oxygen left in the contents of the container during

the filling process.

While the invention is useful with all kinds of polymers, polyethylene

terephthalate (PET) is highly desirable for container skin materials; nylons and ethylene

vinyl alcohols are useful for barrier properties; scavenger materials include products

such as BP- Amoco " Amasorb", and compounds of heavy metals like cobalt with MXD6

nylon, or ethylene vinyl alcohol, wherein the cobalt makes the nylon or alcohol reactive to oxygen, as in chemical scavenging reaction therewith, rather than allowing oxygen

permeation through the materials; and combinations, such as the above, will provide

both barrier and scavenger properties. The incorporation of metal powders in the

polymer can provide electro-magnetic energy barrier layers, as well. Through the

technique of the invention, indeed, any desired position of the core layer and of the

relative thicknesses of the inner and outer layers of the article can readily now be

obtained through this novel control of relative volumetric flow rates of the inner and

outer layers above explained.

This is illustrated in the graph of Fig. 6 A, where the inner layer flow increase

(step S¹ in the dash-line curve) occurs after the start S of the core flow with 50: 50 inner

layer-outer layer flow to the left of S¹; at time A. As shown in the filled cavity of Fig. 6,

though nearly all the core length is shifted towards the outer wall, no leading-edge bias

exists in the article, and where the leading edge remains on the zero gradient.

The converse of the operation of Figs. 6 A, B and C, is shown in Figs. 7 A, B and

C, where, after the initial portion I of the interior core layer flow occurs during an inner

flow-to-outer flow ratio adjustment of substantially 50: 50,placing the core layerleading

edge on the zero gradient of the combined velocity profile, the throttle pin or other flow

restrictor is then adjusted to decrease the inner flow-to-outer flow ratio, again without

shifting the interior layer leading edge — this time resulting in a molded article with the bulk of the core layer shifted toward the inner wall in the same ratio of 80: 20, and agair

with no leading edge bias caused by velocity bias (Fig. 7C).

A typical injection time-line for systems of the invention such as those of Figs. 6

and 6A-C and 7 and 7A-C is as follows:

Time, Action

Seconds

0 Close mold

0.2

0.3

0.4

0.5

0.6

0.7

0.8 •

0.9

1.0 Start injection of interior layer material substantially on zero-gradient of velocity profile "*

1.1 Change ratio of inner layer: outer layer flow rates 1.2

1.3

1.4

1.5

1.6 .

1.7

1.8

1.9 2.0 Finish interior layer injection (trailing edge offset from zero-gradient of velocity profile)

>20 Finish injection of inner and outer layer material

The invention, moreover, provides not only for shifting the core layer to one side

or the other of the article, such as a hollow container, and for relatively varying the

thickness of the inner and outer layers, but also for enabling the shifting of the core

layer back into another position of the article. Examples of this are shown in Figs. 8A

8B, 8C and 8D for the operation graphically represented in Fig. 8 and in Figs 9A-9D for

the operation graphically represented in Fig. 9.

Turning first to Figs. 8 and 8 A-D, in accordance with this embodiment of the

invention, the flow starts at zero-gradient velocity profile (I in Fig. 8A~top curve in Fig.

8); shifting the core layer toward the inside wall (II-III in Fig. 8B) by decreasing the

inner layer flow (at Si in Fig. 8, between times A and B); and, near the end of the flow

(between times C and D), increasing the inner layer flow back to equality with the outer

layer flow (S₂ in Fig. 8) to shift the core layer (at IF in Fig. 8C) back to the zero-gradient

profile (at III' in Fig. 8C), thereby producing the shape shown in Fig. 8D.

A useful purpose for the operation of Fig. 8 resides in structural considerations,

wherein there may be a highly stressed portion of the molded article that can cause

mechanical failure, such as delamination of the article, with the barrier or core layer positioned closer to the inside wall. Secondly, it can be important to control the

thickness and shape of the terminal end of the core flow - -the last portion of the

molded article to freeze or solidify. Injection molding of the hot plastic into the cold

cavity causes the molded article to freeze or solidify from the inner surfaces toward the

interior layer, and it is advantageous to control the final flow of the material entering

the cavity along the 50-percent streamline.

Figs. 8 and 8B-D thus illustrate the shifting of the majority of the core flow

towards the inside boundary wall, with both the leading-edge and also the trailing or

terminal end on the zero gradient.

While the invention has heretofore been illustrated in connection with molding

bottle or cylindrical-shaped container applications, the techniques of the invention are

useful for molding other shaped articles or objects as well, including, as a further

illustration, flat-shaped molded articles. Figs. 8E-I illustrate such a flat-shaped molded

article application, with the views corresponding respectively to the above-described

Figs. 8 and 8A-8D for a hollow bottle or the like.

Similarly, in the embodiment of the invention shown in Figs. 9 and 9A-9D,"the

flow starts at zero-gradient velocity profile (I in Fig. 9A— top curve in the graph of Fig.

9); shifting the core layer toward the outside wall (II-III in Fig. 9B) by increasing the

inner layer flow (at Si¹ in Fig. 9, between times A and B); and, near the end of the flow (between times C and D), decreasing the inner layer flow back to equality with the outer

layer flow (S2¹ in Fig. 9) to shift the core layer (at IF in Fig. 9C) back to the zero-gradient

profile (at III' in Fig. 9C), thereby producing the shape shown in Fig. 9D.

Figs. 9-9B-D thus illustrate the shifting of the majority of the core flow towards

the outside wall, with both the leading-edge and also the trailing or terminal end on the

zero gradient.

A useful injection time-line for the systems of Figs. 8, 8A-D, 9 and 9A-D follows:

Time, Action seconds

0 Close mold

0.1 Start injection of inner and outer layer material at substantially ^'50:50 ratio

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 Start injection of interior layer material substantially on zero-gradient of velocity profile

1.1 Change ratio of inner layer: outer layer flow rates 1.2

1.3 1.4 1.5 1.6 1.7 1.8 1.9 Return ratio of inner: outer layer flow rates to substantially 50:50

2.0 Finish interior layer injection substantially on zero-gradient of velocity profile

>20 Finish injection of inner and outer layer material

Figs.10A-C are schematic views looking from the top of the nozzle N,

illustrating the entry flow channels or ports feeding the inner, outer and core or interior

layer flows (IE, OE, and CE, respectively) from their respective sources (Figs.10B and

C), and surrounding a central throttle pin entry point TE. This flow channel

arrangement is shown embodied in Figs. 10B and 10C with an array of four nozzles, fed

initially from an outer and inner layer source O/IS and a core or interior layer source

CS, respectively, in a balanced three-layer flow system. The outer and inner layer

plastic flow from the source O/IS is split at S¹ into two matched flow streams, and then

branched at B¹ to feed the entry channels for the outer layer OE and inner layer IE of

each of the upper and lower pairs of nozzles, in parallel. Similarly, the core layer source

CS branches to feed the core channels CE of the two pairs of nozzles and with balanced

feed.

Flow restrictor controls, such as well-known electrically, hydraulically or even

manually operated valves, are substantially illustrated in Fig. 10B at FR, placed in each

of the outer layer feed channels and synchronously operated to vary the relative ratio of

outer and inner layer flow at preselected times, for the previously described flow shifting purposes of the invention. Similarly, in Fig. IOC, the same controls can be

effected with the flow restrictor controls FR disposed in the inner layer feed channels

within each nozzle or in each final channel feeding material to the inner layer in each

nozzle. Thus, in the embodiments of Figs. 11 A and B, the flow restriction control is

shown inserted in the most common feed channel feeding the outer layer and the inner

layer, respectively, for changing such flow ratios.

Schematic views, showing a simple but effective way of operating pin-type flow

restrictors in a feed channel are shown in Figs. 12A, B and C for three different

positions. Fig.12A illustrates the least restricted position with the restrictor pin barely

inserted into the flow channel; and Figs. 12B and 12C illustrate more and most flow-

restricting positions, respectively. These may be effected, as before indicated, in the

most common channel of the runner system (Figs. 11A and B), or, if desired, in a least

common channel to the nozzle (Figs. 10B and C) and elsewhere, as desired. Again, as

earlier stated, the restrictor insertion and withdrawal control may be automatically

effected in well-known manner, electrically or hydraulically, for example, with timing

control of the position of each with respect to start or the end of the flow — all as^"

intended to be schematically represented at FR.

Turning, now, to specific practical designs for such nozzle channel flow and

restriction structures,, reference is made to Fig. 13 which illustrates a cross-section of a preferred hollow nozzle extruder construction of the form described in my said earlier

US patent 5, 914, 138 (Fig. 16 thereof), in which flow from a manifold is effected througl

a flat disc 3-layer flow combining area G-FD surrounding a central longitudinally

movable throttle valve pin T-T¹, and wherein annular flow is combined and gated into a

mold cavity .CAV. The flat disc structure FD comprises four flat discus surrounding the

throttle pin T and forming the inner flow channel wall C for the inner layer of the

combined flow stream. Flow channels Ci' , Of, f etc. are created between the three

mating planar surfaces of the discs FD, as also explained in said patent, uniformly to

disperse each flow layer to produce a uniform flow of the respective material flowing

from each channel into the area of combination C. In this manner, each layer of the

combined flow stream is uniformly annularly disposed as it flows from the combining

means through the extruding throttle nozzle and gate G into the cavity CAV. The

movable throttle valve pin T-T¹, under control of an upper adjusting restrictor-control

rod R, which is also, in a sense, part of the throttle pin structure as well, varies the

percentage of the outer layer material in the inner annular flow layer versus the outer

annular flow layer of the combined flow stream downstream of the combining area C.

As before explained, changing the relative volume of the outer layers shifts the position

of the core (interior) layer for the previously described purposes of the present invention. In the embodiment above Fig. 13, the restrictor rod R axially movable within the

nozzle inner housing E, is shown at R¹, just at the inner layer feed channel C '. This is a

neutral position with disc channels Ci', Of, etc. opened to balance inner layer flow with

respect to the outer layer flow for the purposes of the initial core layer flow in

accordance with the principles of the invention. In the enlarged views of Figs. 14 and

15,the throttle valve T has been adjusted by the rod R to an elevated position R", to

increase the inner flow rate with respect to the outer layer flow rate for the core shifting

control purposes of the invention — the least flow-restricted position; whereas, in Fig.

15, more restriction (most) is illustrated at R'".

A schematic feed channel diagram similar to Figs. 10A-C, but for the specific

annular layer flow of the nozzle of Figs. 13, 14 and 15 when used for 3-material polymer

plastic streams, is illustrated in Figs. 16A and 16B. The inner and outer stream is

divided within the nozzle to form the inner and outer annular covering layers. In this

case, the source O/IS of the inner and outer layer flows, is again branched into the

nozzle entry feed channels, but a first interior layer source CS branchfeeds the entry

channel CEι,and, as shown by the dash lines, a second interior layer source CS₂ branch-

feeds the entry channel CE2. The first interior layer stream (#1) is thus directed within

the nozzles N to form the interior annular layer adjacent the inner layer. The second interior layer stream (#2) is directed within the nozzle to form the interior annular layer

adjacent the outer layer.

As earlier mentioned, the techniques of the present invention are not restricted in

the numbers of materials and layers to be molded, though illustrating two-material,

three - layer pre-form molding examples; it having been previously noted that the

invention is also quite useful, for example, in three-material, four-layer pre-form

molding as well. Such an application is shown in Figs. 17 and 17A-D and Figs.19 and

19 A-D for molding hollow container articles or objects, and in Figs. 18 and 18 A-D and

Figs. 20 and 20A-D for flat-shaped articles, respectively.

In connection with the adaptation of the invention for molding of three materials

to form a four-layer object, typical applications would be for a plastic container

composed of two interior layers; one layer would usually be selected for its gas barrier

for gas scavenger properties, and the other interior layer would be selected for some

other property such as a structural layer or a recycled layer. The gas barrier and/ or gas

scavenger property still requires that the leading edge of this one of the two interior

layers be uniform in its penetration around the circumference of the molded object. This

uniform penetration can be achieved by starting the flow of this one interior layer

before starting the flow of the second interior layer, so that the leading edge of this first-

flowing interior layer starts on the zero gradient of the velocity profile. Subsequent initiation of the flow of the second interior layer offsets the later-flowing portions of the

first interior material from the zero gradient, but the uniform leading edge is

established by the initial flow of the first interior layer on the zero gradient.

In Fig. 17, the first-flowing interior layer CI (in this case the outermost interior

layer in the molded object) starts to flow at time SI. The second-flowing interior layer

C2 (in this case the innermost interior layer) starts flowing at time S2 which also

corresponds with the reduction of the flow rate of the combined inner and outer layer

flow. Fig. 17A shows the flow in the nozzle and partially-filled cavity at time A of Fig.

17; this time being between the time SI and S2. The first-flowing interior layer CI

leading edge is on the zero gradient of the combined flow velocity profile, thus assuring

its uniform penetration in the molded object. Fig. 17 B shows the partially filled cavity

at time B of Fig. 17. The leading edge of the first-flowing interior layer CI remains on

the zero gradient, while the later-flowing portions of the first-flowing interior layer are

moved off the zero gradient by the second-flowing interior layer C2, and are closer to

the wall of the extruder. Fig. 17C shows the position of the flows in the nozzle and

cavity at time C of Fig. 17. The second-flowing interior layer has ceased flowing-at time

S3, thereby allowing the final flow portion of the first-flowing interior layer to return to

the zero gradient just before its flow is terminated, S4. Fig. 17D shows the filled cavity

when the trailing edge of the first-flowing interior layer has been injected into the cavity by the continued flow of the combined inner and outer layer flow after time C, of Fig.

17. The filled cavity shows the first-flowing interior layer closer to the outer wall in the

portions of the filled cavity corresponding to the simultaneous flow of the second-

flowing interior layer.

Figs, 19, 19A, 19B, 19C, and 19D are similar to Figs. 17 and 17A-D in concept,

except that, in this example, the first-flowing interior layer CI is the innermost interior

layer and the second-flowing interior layer C2 is the outermost interior layer. All other

features are similar to the case of Figs. 17 and 17 A-D, but in the filled cavity, the first-

flowing interior layer is closer to the inside wall of the molded part in portions of the

cavity corresponding to the simultaneous flow of the second-flowing interior layer.

In both the embodiments of Figs. 17, 17A-D and 19 and 19 A-D, C2 is shown

terminating before the termination of CI in order to allow the final portion of CI to flow-

along the zero gradient of the velocity profile. It should be understood, however, that it

is within the scope of this invention that CI may also terminate before or

simultaneously with the termination of C2 if the desired properties of the molded object

are enhanced by such a termination sequence.

The operational graphs of Figs. 17 and 19 show a reduction in the flow rate of the

combined inner and outer layer flow at time S2, corresponding to the start of the flow of

the second-flowing interior layer. The thickness of each of the flowing layers is directly proportional to the volumetric flow rate of each layer relative to the total volumetric

flow rate of each layer relative to the total volumetric flow rate of all the layers during

the time when all layers are simultaneously flowing. The proximity of the innermost

interior layer and outermost interior layer to the respective inner and outer walls of the

molded article or object is changed by having the flow rate of the combined inner and

outer layer be greater or lesser during the time when all layers are simultaneously

flowing.

Such relative thickness and position of each of the interior layers is chosen to

enhance the properties of the final molded object. For example, if one of the interior

layers is a gas scavenger, the chosen position of the gas scavenger layer may typically

be the innermost interior layer CI of Figs. 19 and 19 A-D in order to reduce the

permeation rate of gas through the outer layers of the container into the scavenger, and

to increase the rate of gas scavenging from the contents of the container. Such a

position, indeed will extend the shelf life of the container contents if the purpose of the

scavenger layer is to absorb gas permeating from the atmosphere exterior to the

container. As another example, the position of outermost interior layer CI of Fig. 17

can enhance the performance of a humidity-sensitive gas barrier layer, such as the

before-mentioned EVOH or MXD6 nylon, by moving such barrier layer away from the

100% relative humidity of the contents of a beverage that is to fill the container to a position in the wall that is closer to the lower relative humidity of the atmosphere

surrounding the container.

A typical injection time-line for molding such three-material, four-layer articles

wherein the leading edge of the first interior layer is established substantially on the

zero-gradient of the velocity profile, and then a second interior layer is injected and its

injection is finished before the first interior layer injection is finished, as shown in Figs.

17, 17A-D and 19 and 19A-D, follows:

Time, Action seconds

0 Close mold

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.1 Start injection of second interior layer material and reduce combined flow- rate of inner and outer material

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Finish injection of second interior layer material

2.0 Finish injection of first interior layer material substantially on zero- gradient of velocity profile

>20 Finish injection of inner and outer layer material

As previously described, other-shaped objects or articles may also be molded by

the techniques of the invention, including the flat-shaped articles of earlier mentioned

Figs. 18 and 18A-D and 20 and 20A-D.

Exemplary articles, ports or products formable with the above-described

techniques of the present invention are shown in Figs. 21 A through 24C

Fig. 21A depicts a plastic molded cylindrical hollow container having an open

top and a closed bottom. Fig. 21B shows the cross-section of the container through its

axial center line (shown dashed), wherein the interior layer has a leading edge on the

centerline of the molded wall, this centerline corresponding to the zero-gradient of the

velocity profile during the flow of plastic into the mold cavity which formed the part —

for example as in the forming process of Figs. 7A-C. While the interior layer leading

edge substantially is on the part wall centerline, the other portions of the interior layer

are offset from the centerline toward the inner wall surface of the article.

Variants are illustrated in Figs. 21C and D; with the trailing edge of the interior

layer being substantially on the part centerline in Fig. 21 C, and with an additional

interior layer in Fig. 21D (see Fig. 19B, for example) having a leading edge that does not extend as far as the leading edge of the other interior layer and has a trailing edge that

terminates father from the gate than the other interior layer. What is not depicted, but

is possible, are molded articles wherein the leading edge of one interior layer extends

beyond the leading edge of the other interior layer, and wherein the trailing edges of

both interior layers terminate approximately at the same distance from the gate.

As another example, Fig. 22D illustrates a blow-molded hollow container

formed from the multilayer article of Fig. 22. Cross-sections of segments A, B and C of

Figs. 22 and 22D are show on enlarged scales in Figs. 22A, 22B and 22C, respectively.

Fig. 22 shows a molded preform having the leading edge of its interior layer on the wall

centerline and other portions of its interior layer offset from the centerline toward the

outer wall surface (as in Figs. 6A-C). In the wall section in the finish portion of the

article as illustrated wherein the leading edge of the interior layer is substantially on the

centerline of the wall, and another portion of the interior layer is offset from the

centerline toward the outer wall surface. The wall cross-section of a segment of the

container sidewall is shown in Fig. 22B wherein the interior layer is offset from the

centerline toward the outer wall surface; and Fig. 22 C shows the cross-section σf a

segment of the container base wherein the interior layer trailing edge terminates offset

from the article centerline. In the blow-molded container of Fig. 23 D, the molded pre-form of which is

depicted in Fig. 23, the trailing edge of the interior layer is substantially on the wall

centerline, as distinguished from the pre-form of Fig. 22. Figs. 23 A and 23B are similar

to before-discussed Figs. 22A and 22B, respectively, but with the variations of Fig. 23.

Fig. 23 C is the cross-section C of a segment of the base of the container of Fig.23 D

wherein the trailing edge of the interior layer terminates substantially on the wall

centerline.

Still another modification is presented in the cross-section of a four-layer molded

article and Fig. 24 that can be blow-molded into the container of Fig. 24 D (see Figs. 17-

19). The leading and trailing edges of one interior layer are substantially on the part

centerline and extend beyond the leading and trailing edges of the other interior layer

as shown, more specifically in Figs. 24 A and 24 B, respectively. What is not depicted,

but is possible, are four-layer molded articles for blow-molding wherein the leading

edge of the first interior layer extends beyond the leading of the second interior layer

and wherein the trailing edges of both interior layers terminate approximately the same

distance from the gate. An additional undepicted article is one wherein the trailmg

edge of the second interior layer extends beyond the trailing edge of the first interior

layer and wherein the leading edge of the first interior layer extends beyond the leading

edge of the second interior layer. The previously discussed layer distributions of Figs. 21B, 21C or 21D, moreover,

can also be molded into articles similar to pre-form of Fig. 22 for blow-molding into

containers similar to Fig. 22 D. Similarly, the layer distribution of Figs. 22, 23 and 24 car

also be molded into articles similar to Fig. 21. Additionally, any of these depicted layer

distributions can be molded into articles of other shapes, such as flat plates, (see Figs. 18

and 20), concave discs, lids and closures for containers, and other shapes limited only

by the imagination of one skilled in the art.

Other signs of flow control devices may also be employed, and other further

modifications will also occur to those skilled in this art, such being considered,

however, to fall within the spirit and scope of the invention as defined in the appended

claims.

Claims

What is claimed is:

1. A method for co-extruding multiple polymer plastic materials as for injecting

through a gate region into a mold cavity to produce a molded article, that

comprises, co-extrusively flowing streams of polymer plastic materials with at

least one interior stream that is to serve as an interior core of a resulting molded

plastic article within inner and outer streams of plastic material that serve as

covering wall plastic material layers for the core; forcing the flowing streams to

flow along concentric annular flow paths within and along a longitudinally

extending tubular extruder nozzle to the cavity gate region; adjusting the flow

streams initially to cause the core stream to start to flow at a region of

substantially zero gradient in the transverse flow velocity profile of the

extrusion; thereupon varying the relative volumetric flow ratio of the inner and

outer layer streams after the zero-gradient flow of the core layer has started, in

order to offset the core layer flow from the zero gradient and to shift the core

layer closer to one of the inner or outer annular flow boundaries, thereby to

produce a molded article wherein the major portion of the core layer is closer to

one of the inner or outer article walls than the other.

2. The method of claim 1 wherein the relative thickness of the inner or outer layers

is correspondingly varied substantially in said ratio.

3. The method of claim 1 wherein, prior to the termination of the extrusion, the

flow ratio of the inner and outer layers is varied to shift the terminal end of the

interior core stream back along substantially said zero gradient.

4. The method of claim 1 wherein the inner and outer stream ratio is varied after a

few percent of the core layer stream flow has initially flowed.

5. The method of claim 1 wherein the adjusting of the flow stream initially causes

the inner and outer streams to start to flow with substantially equal volumetric

flow rates.

6. The method of claim 1 wherein said forcing is effected by disposing a

longitudinal pin within and along the extruder to force the combined streams

into said concentric annular flow paths.

7. The method of claim 1 wherein the relative volumetric flow ratio of the inner and

outer streams is controlled by relatively restricting the respective flow channels

of the streams within the extruder.

8. The method of claim 7 wherein the timing of said relative flow restricting is

controlled to coincide with one or both of (1) a short time after the start o'f the

flow of the core stream, and (2) near the termination thereof.

9. The method of claim 7 wherein the timing of said relative flow restricting is

controlled intermediate the flow of the streams to the mold cavity.

10. The method of claim 7 wherein the relative flow restricting is effected by

inserting a flow restrictor into the inner or outer flow stream within the extruder.

11. The method of claim 7 wherein the inner, outer and core layer flow streams are

fed into respective entry channels in the extruder nozzle from respective material

sources, and the flow restrictor is inserted into one of either a source flow

channel, or near a nozzle entry channel.

12. The method of claim 11 wherein a plurality of similar nozzles are similarly

simultaneously fed from respective material sources, with flow restrictors

inserted near corresponding inner or outer layer entry flow channels in each

nozzle or in common feed channels from said sources.

13. The method of claim 1 wherein the inner and outer layer streams are fed from

the same plastic material source and the plastic core material stream from a

different source, and the annular co-extensive streams of the core material stream

encased by the inner and outer layer streams are combined near said gate region

and laterally injected in opposite transverse directions into the mold cavity.

14. The method of claim 13 wherein the molded article thereby formed is a hollow

plastic container in which the interior core layer encased by inner and outer

container walls is of material that serves as a barrier layer for such purposes as resisting the flow of gases through the container walls and/ or scavenging

oxygen.

15. The method of claim 1 wherein a three-material plastic article is to be molded

comprising inner and outer layers and two interior or core layer materials and

wherein the inner and outer layer material streams are divided within the nozzle

to form the inner and outer annular covering wall layers, one of the interior layer

streams being directed within the nozzle to form an interior annular layer

adjacent said inner layer, and the other interior stream being directed within the

nozzle to form an interior annular layer adjacent the outer layer.

16. A method for co-extruding multiple plastic materials as for injecting through a

gate region into a mold cavity to produce a molded article having an interior

core layer encased within inner and outer wall layers, that comprises, co-

extrusively flowing inner and outer layer streams of plastic material encasing an

interior core layer to inject the same though the gate region into the mold cavity;

initially starting the flow with a substantially 50:50 ratio of inner and outer layer

stream volumetric flows to cause the interior core stream to flow at a mid-plane

region of substantially zero gradient in the transverse flow velocity profile of the

extrusion; thereupon, for the major portion of the flow, varying the relative volumetric flow ratio of the inner and outer layer streams to offset the core layer

stream from the mid-plane and shif the core layer closer to one of the inner or

outer flow boundaries, thereby to produce a molded article wherein the major

portion of the core layer within the article is closer to the inner or outer article

wall.

17. The method claimed in claim 16 wherein said flow ratio is varied back to

substantially 50:50 near the terminal end of the flow into the cavity.

18. The method claimed in claim 16 wherein the ratio is varied after a few percent of

the core layer stream flow has initially flowed.

19. The method in claim 16 wherein the ratio is further varied during the continued

flow to the gate region, and into the mold.

20. The method of claim 19 wherein said ratio is varied back to substantially 50:50

near the terminal end of the flow to re-establish the interior core stream flow

back along substantially said zero gradient.

21. The method of claim 16 wherein the core layer stream material is selected for

barrier function characteristics such as at least one of gas permeation control,

gas-scavenging, and electromagnetic shielding.

22. Apparatus for co-extruding multiple plastic materials as for injecting through a

gate region into a mold cavity to produce a molded article having an interior core layer encased within inner and outer wall layers, the apparatus having, in

combination, a longitudinally extending extruder nozzle for receiving plastic

material from sources thereof and co-extrusively flowing the material as inner

and outer layer streams of plastic material encasing an interior core layer to inject

the same through the gate region into the mold cavity; flow control means for

stream volumetric flow rates to cause the interior core stream to flow at a mid-

plane region of substantially zero gradient in the transverse flow velocity profile

of the extrusion; means for thereupon, for the major portion of the flow,

adjusting the flow control means to change the relative volumetric flow ratio of

the inner and outer layer streams to offset the core layer stream from the mid-

plane and shift the core layer closer to one of the inner or outer flow boundaries,

thereby to produce a molded article in the cavity wherein the major portion of

the core layer within the article is closer to one of the inner or outer article wall.

23. The apparatus claimed in claim 22 wherein the flow control means is adjusted to

vary the flow ratio back to substantially 50:50 near the terminal end of th flow

into the cavity.

24. The apparatus claimed in claim 22 wherein the flow control means is operated to

change the ratio after a few percent of the core layer stream flow has initially

flowed.

25. The apparatus claimed in claim 22 wherein the flow control is adjusted to further

vary the ratio during the continued flow to the gate region.

26. The apparatus of claim 25 wherein the flow control means is adjusted to vary

said ratio back to substantially 50: 50 near the terminal end of the flow to re¬

establish the interior core stream flow back along substantially said zero

gradient.

27. The apparatus of claim 22 wherein the core layer stream material is selected for

barrier function characteristics such as at least one of humidity control, gas

permeation, gas scavenging and electromagnetic shielding.

28. Apparatus for co-extruding multiple plastic materials as for injecting through a

gate region into a mold cavity to produce a molded article, having, in

combination, a longitudinally extending tubular extrusion nozzle provided with

entry channels for receiving plastic materials from sources thereof and co=- -

extensively flowing the materials as inner and outer layer streams with one

interior strea that is to serve as an interior core of a resulting molded plastic

article within inner and outer streams of plastic material that serve as covering wall plastic material layers for the core; a longitudinal throttle means for forcing

the streams to flow along concentric annular flow paths within and along a

longitudinally extending tubular-extruder nozzle to the cavity gate region;

means for adjusting the flow streams initially to cause the core stream to start to

flow at a region of substantially zero gradient in the transverse flow velocity

profile of the extrusion; means operable thereupon for varying the relative

volumetric flow ratio of the inner and outer layer streams after the zero-gradient

flow of the core layer has started in order to offset the core layer flow from the

zero gradient and to shift the core layer closer to one of. the inner or outer flow-

boundaries, thereby to produce a molded article wherein the major portion of the

core layer is closer to one of the inner or outer article walls than the other.

29. The apparatus of claim 28 wherein the relative thickness of the inner or outer

layers is correspondingly varied substantially in said ratio.

30. The apparatus of claim 28 wherein, prior to the termination of said extrusion, the

adjusting means is controlled to vary the flow ratio of the inner and outer layers

to shift the terminal end of the interior core stream back along substantially said

zero gradient.

31. The apparatus of claim 28 wherein the adjusting means varies the inner and

outer stream ratio after a few percent of the core layer stream flow has initially

started.

32. The apparatus of claim 28 wherein the adjusting means initially causes the inner

and outer streams to start with substantially equal volumetric flow rates.

33. The apparatus of claim 28 wherein said adjusting means comprises an axial pin

or forcing the combined streams into said concentric annular flow paths.

34. The apparatus of claim 28 wherein the relative volumetric flow ratio of the inner

and outer streams is controlled by restrictors disposed in the respective flow

channels of the streams within the extruder.

35. The apparatus of claim 34 wherein means is provided for controlling the timing

of the relative restricting by the restrictors to coincide with one or both of shortly

after the start of the flow of the core stream, and near the termination of the core

stream flow.

36. The apparatus of claim 35 wherein means is provided for controlling the timing

of the relative flow restricting intermediate the flow of the streams to the-mold

cavity.

37. The apparatus of claim 35 wherein the relative flow restricting is effected by

means for inserting a flow restrictor into one of the inner or outer flow streams.

38. The apparatus of claim 28 wherein the inner, outer and core layer flow streams

are fed into respective entry channels in the nozzle from respective material

sources, and the flow restrictor is inserted into one of (1) a source flow channel or

(2) near a nozzle entry channel.

39. The apparatus of claim 28 wherein a plurality of similar nozzles is provided, the

nozzles of which are similarly simultaneously fed from respective material

sources, with flow restrictor means inserted in corresponding inner or outer

layer entry flow channels in each nozzle or in common feed channels from said

sources.

40. The apparatus of claim 28 wherein the inner and outer layer streams are fed from

the same plastic material source and the plastic core material stream from a

different source, and the annular co— extensive streams of the core material

stream encased by the inner and outer layer streams are combined near said gate

region and laterally injected in opposite transverse directions into the mold

cavity.

41. The apparatus of claim 40 wherein the molded article thereby formed is a hollow

plastic container in which the interior core layer is of material that serves as a

barrier layer for such purposes as resisting the flow of humidity and or gases through the container walls and/ or scavenging oxygen through chemical

combination therewith.

42. The apparatus of claim 28 wherein a 3-material plastic article is to be molded

comprising inner and outer layers and two interior or core layer materials, and

streams is directed within the nozzle to form an interior annular layer adjacent

said inner layer, and the other interior stream is directed within the nozzle to

form an interior annular layer adjacent the outer layer.

43. The method of claim 1 wherein a plurality of similar extruder nozzles is

provided similarly simultaneously fed from respective material sources, and

with flow restriction inserted in corresponding inner and outer layer entry flow

channels into each nozzle or in common feed channels from said sources.

44. The method of claim 1 wherein two interior streams are flowed within said inner

and outer streams, with the flow of one of the interior stream started before the

flow of the other interior stream and with its leading edge starting on said- zero-

gradient, and the subsequent initiation of the flow of said other interior stream

offsetting the later-flowing portions of said one interior stream flow from said

zero gradient, and with the completing of the injecting of the other interior stream before the completion of the injecting of said one interior stream through

said gate region and into said mold cavity, and finishing the injecting of said

interior stream on said zero gradient.

45. The method of claim 44 wherein the materials of the inner, outer and interior

streams constitute three molding materials forming a four-layer molded article.

46. The method of claim 45 wherein the relative thickness and position of each of the

interior streams is chosen to enhance the properties of the molded article.

47. The method of claim 46 wherein the innermost of the interior streams is of gas

scavenging material in order to reduce the permeation rate of gas through said

outer wall of the molded article, and to increase the rate of gas scavenging from

the contents of the article if the scavenger material is intended to absorb gas

permeating from the exterior of the article.

48. The method of claim 46 wherein the outermost of the interior streams is of

humidity sensitive gas barrier material in order to position such barrier at a

position within the molded article that is closer to the exterior atmosphere

surrounding the article.

49. The method of claim 44 wherein the article is one of a cylindrical-shaped hollow

container, such as a bottle, and a flat-shaped article.

50. The apparatus of claim 22 wherein said inner core layer comprises a pair of

interior core streams, with said adjusting means enabling one of the interior

streams to start flow before the other of the pair of interior streams and with its

leading edge starting on said zero gradient, and enabling the subsequent

initiation of the flow of said other interior stream offsetting the later-flowing

portions of said one interior stream through said gate region and into said mold

cavity, with the finishing of the injecting of said one interior stream lying on said

zero gradient.

51. The apparatus of claim 50 wherein the materials of the inner, outer and interior

streams constitute three molding materials forming a four-layer molded article.

52. The apparatus of claim 51 wherein the relative thickness and position of each of

the interior streams is chosen to enhance the properties of the molded article.

53. The apparatus of claim 52 wherein the innermost of the interior streams is of gas

scavenging material in order to reduce the permeation rate of gas through said

the contents of the article if the scavenger material is intended to absorb gas

permeating from the exterior of the article.

54. The apparatus of claim 52 wherein the outermost of the interior streams is of

humidity sensitive gas barrier material in order to position such barrier at a position within the molded article that is closer to the exterior atmosphere

surrounding the article.

55. The apparatus of claim 50 wherein the article is one of a cylindrical-shaped

hollow container, such as a bottle, and a flat-shaped article.

56. A molded plastic material article having an interior plastic core layer encased

within inner and outer plastic wall layers wherein the major portion of the core

layer within the article is closer to one of the inner or outer article walls.

57. The molded article of claim 56 wherein the article is hollow and bounded by the

core-encased inner and outer walls.

58. The molded article of claim 57 wherein the initial portion the core layer lies

substantially on the centerline of the core-encased inner and outer article walls.

59. The molded article of claim 58 wherein said initial portion constitutes a few

percent of the length of the core layer.

60. The molded article of claim 59 wherein the core layer near its terminal end again

lies substantially on said centerline.

61. The molded article of claim 59 wherein the core layer material is selected for

barrier function characteristics such as at least one of humidity control, gas

permeation, gas scavenging and electromagnetic shielding.

62. The molded article of claim 59 wherein the inner and outer walls and the core are

of three molding materials forming a four-layer molded article.

63. A pre-form for a hollow molded plastic material article having an interior plastic

core layer encased within inner and outer plastic wall layers wherein the major

portion of the core layer within the pre-form is closer to one of the inner and

outer article walls.

64. The pre-form of claim 63 wherein the initial portion of the core layer lies

65. The pre-form of claim 64 wherein said initial portion constitutes a few percent of

the length of the core layer.

66. The pre-form of claim 65 wherein the core layer near its terminal end again lies

substantially on said centerline.

67. The pre-form of claim 65 wherein the core layer material is selected for barrier

function characteristics such as at leastone of humidity control, gas permeation,

gas scavenging and electromagnetic shielding.