Patent Description:
A molding machine may channel a flow of melted molding material, such as melted plastic or resin, through a distribution network, such as a hot runner, for dispensing into a mold through a nozzle. Dispensing of the melted molding material may occur during injection molding for example. Melted molding material may be dispensed from a nozzle in a substantially annular or cylindrical flow. For example, an annular or cylindrical flow may be dispensed or injected into a mold cavity during injection molding of an article having a generally tubular shape, such as a preform suitable for subsequent blow-molding to form a container such as a plastic beverage bottle for example. The flow may be, or may become, annular as it enters the gate of the mold cavity and may spread to surround a core insert component of the mold cavity.

A multi-channel coinjection nozzle having multiple channels for simultaneously dispensing multiple respective layers of material may be used to form multilayer molded articles. For example, a coinjection nozzle may dispense annular inner and outer melt streams of a surface layer (or "skin layer") material simultaneously with an annular stream of an internal layer (or "core layer") material sandwiched between the inner and outer streams, see for example document <CIT>.

The surface layer material may for example be polyethylene terephthalate (PET). The internal layer material may for example comprise nylon or a barrier material (e.g. an oxygen scavenger material) suitable for protecting subsequent contents of the molded article from external contamination (e.g. oxidation).

It may be desirable to incorporate an internal layer into only certain areas of a molded article, such as only in the body area (side wall) of a preform, and not in other areas, such as the closed base area or neck finish area of a preform. Moreover, it may be desirable to fully encapsulate the internal layer material within the surface layer material. For example, molded articles ultimately intended to contain a food or beverage may have an internal layer that is made from a non-food grade material, e.g. a material made from recycled plastic. If the internal layer were inadvertently exposed to an interior surface of the container, consumer safety may be compromised due to impurities in the non-food grade material.

It is normally undesirable for a surface layer of a multilayer molded article to delaminate and separate either from the molded article or from a container blow-molded therefrom. Such delamination and separation may be considered aesthetically unappealing. Moreover, if present on an interior side of a container wall, delamination and separation may compromise consumer safety, e.g. in the event that pieces of delaminated material break away into a contained food or beverage.

According to one aspect of the present disclosure, there is provided an injection molding machine for molding a multilayer article, comprising: a coinjection nozzle having a surface layer material channel and an internal layer material channel; a surface layer material injection unit; an internal layer material injection unit; a mold cavity; and a controller operable to: cause the surface layer material injection unit to commence injecting a surface layer material into the mold cavity via the surface layer material channel; then cause the internal layer material injection unit to commence injecting an internal layer material into the mold cavity via the internal layer material channel; then, during application by the surface layer material injection unit of a hold pressure upon the surface layer material in the surface layer material channel and with the surface layer material injection unit and the internal layer material injection unit in fluid communication with one another via the surface layer material channel and internal layer material channel, cause a pullback stroke to occur at the internal layer material injection unit for reducing a pressure of the internal layer material; then, after a delay interval, detect at least one physical parameter indicative of a post-pullback pressure of the internal layer material at the internal layer material injection unit; and generate an indicator of pullback effectiveness based on a relationship of the post-pullback pressure indicated by the at least one physical parameter and a threshold pressure.

In another aspect of the present disclosure, there is provided a method of molding a multilayer article, comprising: providing a mold cavity, a surface layer material injection unit, an internal layer material injection unit, and a coinjection nozzle having a surface layer material channel and an internal layer material channel; causing the surface layer material injection unit to commence injecting a surface layer material into the mold cavity via the surface layer material channel; then causing the internal layer material injection unit to commence injecting an internal layer material into the mold cavity the internal layer material channel; then, during application by the surface layer material injection unit of a hold pressure upon the surface layer material in the surface layer material channel and with the surface layer material injection unit and the internal layer material injection unit in fluid communication with one another via the surface layer material channel and internal layer material channel, causing a pullback stroke to occur at the internal layer material injection unit for reducing a pressure of the internal layer material; then, after a delay interval, detecting at least one physical parameter indicative of a post-pullback pressure of the internal layer material at the internal layer material injection unit; and generating an indicator of pullback effectiveness based on a relationship of the post-pullback pressure indicated by the at least one physical parameter and a threshold pressure.

In a further aspect of the present disclosure, there is provided a tangible medium storing computer-readable program code that, upon execution by a controller of a molding machine having a mold cavity, a surface layer material injection unit, an internal layer material injection unit, and a coinjection nozzle having a surface layer material channel and an internal layer material channel, cause the controller to: cause the surface layer material injection unit to commence injecting a surface layer material into the mold cavity via the surface layer material channel; then cause the internal layer material injection unit to commence injecting an internal layer material into the mold cavity the internal layer material channel; then, during application by the surface layer material injection unit of a hold pressure upon the surface layer material in the surface layer material channel and with the surface layer material injection unit and the internal layer material injection unit in fluid communication with one another via the surface layer material channel and internal layer material channel, cause a pullback stroke to occur at the internal layer material injection unit for reducing a pressure of the internal layer material; then, after a delay interval, detect at least one physical parameter indicative of a post-pullback pressure of the internal layer material at the internal layer material injection unit; and generate an indicator of pullback effectiveness based on a relationship of the post-pullback pressure indicated by the at least one physical parameter and a threshold pressure.

Other features will become apparent from the drawings in conjunction with the following description.

The non-limiting embodiments will be more fully appreciated by reference to the accompanying drawings, in which:.

The drawings are not necessarily to scale and may be illustrated by phantom lines, diagrammatic representations and fragmentary views. In certain instances, details that are not necessary for an understanding of the embodiments or that render other details difficult to perceive may have been omitted.

In this document, any use of the term "exemplary" should be understood to mean "an example of" and not necessarily to mean that the example is preferable or optimal in some way. Terms such as "downwardly," "right," and "left" may be used to describe features of some embodiments in this description but should not be understood to necessarily connote an orientation of the embodiments during manufacture or use. The term "monitoring" as used herein may mean "periodically determining" and does not necessarily mean "continuously monitoring.

<FIG> depicts an injection molding machine <NUM> in perspective view. The exemplary injection molding machine <NUM> is for molding multilayer articles, specifically preforms, such as the example preform <NUM> of <FIG> (described below).

The injection molding machine <NUM> depicted in <FIG> comprises an enclosure <NUM> housing a clamp unit, a fixed platen, a movable platen, and a mold mounted therebetween, none of which are visible in <FIG>. The injection molding machine <NUM> further comprises first and second injection units <NUM> and <NUM>, which are for plasticizing (melting) and injecting a surface layer material and an internal layer material respectively (both being forms of molding material) and which may accordingly be referred to herein as the surface layer material injection unit <NUM> and the internal layer material injection unit <NUM> respectively. The surface layer material may for example be PET. The internal layer material may for example be nylon, a barrier or oxygen-scavenging material, or a PET material with a colorant additive. In the present example, each of the injection units <NUM> and <NUM> comprises an extruder that uses a reciprocating screw as a driving element to inject molding material into mold cavities via a hot runner. The internal layer material injection unit <NUM> of the present embodiment is depicted in greater detail in <FIG>, described below.

The controller <NUM> of <FIG> controls the operation of injection molding machine <NUM> based on human operator input or based on a preset control sequence, among other functions. In the present embodiment, the controller <NUM> comprises at least one processor in communication with volatile or non-volatile memory storing computer-readable program code stored on a tangible medium, e.g., ROM, optical disk, USB drive, or magnetic storage medium. In some embodiments, the computer-readable program code may be transmitted to the memory via a modem or communications adapter communicatively coupled to a network, e.g. a wide area network such as the Internet. The controller <NUM> may for example be an industrial PC, e.g. a Beckhoff® model CP22xx Panel PC with Intel® Core™ i processor. Control instructions may be entered by a human operator via human-machine interface (HMI) <NUM>, which may for example be a multi-function touchscreen that forms part of, or is coupled to, the controller <NUM>. The HMI <NUM> may display various graphical user interface (GUI) screens used for controlling or monitoring aspects of the molding process pertaining to pullback at internal layer material injection unit <NUM>, as will be described.

A hot runner within enclosure <NUM> defines a network of channels for conveying molten surface layer material and molten internal layer material from injection units <NUM> and <NUM> respectively to each of a plurality of multi-channel nozzles, described below. Each nozzle is positioned near an associated mold cavity defined in the mold. Each mold cavity is a negative shape (space) in the shape of the article to be molded, which in this example is preform <NUM> of <FIG>. The number of mold cavities that can be simultaneously filled by molding machine <NUM> is typically greater than one and may vary between embodiments.

<FIG> schematically depicts the internal layer material injection unit <NUM> of <FIG> in isolation from the other components of injection molding machine <NUM>. Injection unit <NUM> comprises a helical reciprocating screw <NUM> (a form of driving element) housed in an extruder barrel <NUM>. The barrel <NUM> can be selectively heated and has an inlet (not expressly depicted) for receiving internal layer material <NUM>, e.g. in pellet form. The screw <NUM> is rotatable within the heated barrel <NUM> to mix and plasticize internal layer material. An outlet nozzle valve <NUM> can be selectively opened or closed by controller <NUM> (<FIG>) to selectively establish fluid communication between the internal layer material injection unit <NUM> and the downstream hot runner. In <FIG>, the valve <NUM> is in the open position.

The injection unit <NUM> of <FIG> also comprises, or is otherwise associated with, an injection actuator <NUM>. The injection actuator <NUM> (or simply "actuator <NUM>") is configured to reciprocate the screw <NUM> longitudinally within the barrel <NUM> to effect injection and recovery phases of operation of internal layer material injection unit <NUM>. In the present embodiment, the actuator <NUM> comprises a piston <NUM> housed in a hydraulic cylinder <NUM>. The piston <NUM> is attached to a rod <NUM> that drives screw <NUM>. The rod <NUM> may be an extension of a central shaft <NUM> of screw <NUM>.

The depicted actuator <NUM> is controlled by controller <NUM>. To commence injection of melted internal layer material <NUM>, the controller <NUM> may cause a "bore-side" pressure PB acting upon on face <NUM> of piston <NUM> to exceed the sum of the "rod-side" pressure PR on the opposite side of the piston <NUM> (where PR may be zero or ambient pressure) and a plastic pressure PP of melt pushing back upstream on the tip <NUM> of screw <NUM>. A pair of pressure sensors <NUM> and <NUM> are configured (e.g. positioned and communicatively coupled with controller <NUM>) to dynamically sense the bore-side pressure PB and rod-side pressure PR respectively and relay that information to the controller <NUM>.

An example preform <NUM> produced by the injection molding machine <NUM> of <FIG> is shown in <FIG> in perspective view and in <FIG> in longitudinal cross section. As illustrated, the preform <NUM> has an elongate body <NUM>, a hemispheric closed base <NUM>, and a neck finish <NUM>. The neck finish <NUM> of this example preform includes various external features including threads <NUM> for accepting and retaining a closure such as a threaded cap, an anti-pilfer bead <NUM>, and a support ledge <NUM>.

As best seen in <FIG>, the preform <NUM> is made primarily from the surface layer material <NUM>, with the exception of cylindrical internal segment <NUM>, which is comprised of the internal layer material <NUM>. The internal segment <NUM> is entirely encapsulated by the surface layer material <NUM> in the depicted embodiment. The orientation of the preform <NUM> in <FIG> is inverted, i.e. the open end <NUM> opposite base <NUM> points downwardly. This is not necessarily the orientation in which preforms are molded in practice by molding machine <NUM> or alternative machine embodiments.

The preform <NUM> of <FIG> is formed from molten surface layer material <NUM> and molten internal layer material <NUM> injected into a mold cavity by an associated multi-channel coinjection nozzle <NUM> of the hot runner. <FIG> depicts a portion of the coinjection nozzle <NUM> in longitudinal cross section. The depicted portion of nozzle <NUM> is the downstream-most end of the nozzle, including the nozzle tip <NUM> from which melt is discharged into the mold cavity.

In the present embodiment, nozzle <NUM> is an assembly formed from three nested components: an innermost nozzle insert <NUM>, an intermediary nozzle insert <NUM>, and an outermost nozzle insert <NUM>. In alternative embodiments, the nozzle may be formed in other ways, e.g. as a unitary component made using additive manufacturing techniques, such as direct metal laser sintering (DMLS). The example nozzle <NUM> has a substantially cylindrical shape, as does each of its component nozzle inserts <NUM>, <NUM>, and <NUM>, but this is not a requirement.

Nozzle <NUM> of <FIG> defines three channels for conveying melt.

A first, centrally disposed channel <NUM> defined by the innermost nozzle insert <NUM> provides a passage for conveying melted surface layer material, received from the first injection unit <NUM>, axially towards nozzle tip <NUM>. Channel <NUM> also accommodates an axially reciprocable valve stem <NUM> that is used for controlling the flow of both types of melt (i.e. surface layer material and internal layer material) in the present embodiment, as will be described. Specifically, the channel <NUM> and valve stem <NUM> collectively define an annular passage through which surface layer material is flowable until the melt clears the end of valve stem <NUM> (when the valve stem <NUM> is in the fully retracted position of <FIG>) and exits outlet <NUM> as a substantially cylindrical flow. Upon exiting outlet <NUM>, the melt enters nozzle combination area <NUM> for combination with one or more other melt streams, as will be described. Channel <NUM> may be referred to as inner channel <NUM>, and outlet <NUM> may accordingly be referred to as the inner outlet <NUM>.

A second, substantially annular channel <NUM> is defined between the innermost nozzle insert <NUM> and the intermediary nozzle insert <NUM>. The second channel <NUM> conveys melted internal layer material received from the second injection unit <NUM> axially towards an inwardly facing annular outlet <NUM>. Upon exiting the annular outlet <NUM>, the annular melt stream flows into nozzle combination area <NUM> for combination with one or more other melt streams. Channel <NUM> may be referred to as the intermediate channel <NUM>, and outlet <NUM> may accordingly be referred to as the intermediate outlet <NUM>.

A third, substantially annular channel <NUM> is defined between the intermediary nozzle insert <NUM> and the outermost nozzle insert <NUM>. The third channel <NUM> conveys surface layer material received from the first injection unit <NUM> to inwardly facing annular outlet <NUM>. Upon exiting outlet <NUM>, the discharged melt enters nozzle combination area <NUM>, where it may be combined with one or more other melt streams. Channel <NUM> may be referred to as the outer channel <NUM>, and outlet <NUM> may accordingly be referred to as the outer outlet <NUM>. In the present embodiment, the outer channel <NUM> is substantially concentric with each of the intermediate channel <NUM> and the inner channel <NUM>.

It will be appreciated that, by virtue of the above-described nozzle structures, the inner, intermediate, and outer channels <NUM>, <NUM>, and <NUM> all supply or feed respective streams of molding material to the combination area <NUM>, which may accordingly be referred to a "material combination area. " By virtue of the material that they convey, the inner and outer channels <NUM>, <NUM> may alternatively be referred to as surface layer material channels. Similarly, the intermediate channel <NUM> may alternatively be referred to as an internal layer material channel.

Valve stem <NUM> is used to control the flow of molding material into the combination area <NUM> and thus the mold cavity associated with nozzle <NUM>. The valve stem <NUM> is controlled by controller <NUM> by way of an actuator (not depicted) that reciprocates the valve stem <NUM> between at least a subset of four positions or stops.

The first valve stem position is the fully opened position depicted in <FIG>, in which the distal end <NUM> of the valve stem is positioned at axial "Stop <NUM>. " In this position, the valve stem <NUM> does not impede the flow of molding material from any of the inner outlet <NUM>, intermediate outlet <NUM>, or outer outlet <NUM>. This valve stem position is referred to herein as Position <NUM>, with the number <NUM> representing the number of open (unblocked) nozzle outlets (i.e. outlets <NUM>, <NUM>, and <NUM>).

The second position is a mostly open position in which the end <NUM> of valve stem <NUM> is advanced (downwardly in <FIG>) to the axial position marked as "Stop <NUM>. " When the valve stem <NUM> is in this position, it blocks (closes) inner outlet <NUM> and thereby prevents surface layer material from flowing therefrom. Intermediate outlet <NUM> and outer outlet <NUM> remain open. This valve stem position is referred to herein as Position <NUM>, with the number <NUM> representing the number of open nozzle outlets (i.e. outlets <NUM> and <NUM>).

The third position is a mostly closed position in which the end <NUM> of valve stem <NUM> is advanced to the axial position marked as "Stop <NUM>" in <FIG>. When the valve stem <NUM> is in this position, it blocks both of inner outlet <NUM> and intermediate outlet <NUM> and thereby prevents surface layer material and internal layer material, respectively, from flowing therefrom. Outer outlet <NUM> remains unblocked, permitting surface layer material from injection unit <NUM> to flow into combination area <NUM>. This valve stem position is referred to as Position <NUM>, reflecting the single nozzle outlet (outlet <NUM>) that is open in this position.

Finally, the fourth position is a fully closed position in which the end <NUM> of valve stem <NUM> is advanced to the axial position marked as "Stop <NUM>" in <FIG> within gate area <NUM>. When the valve stem <NUM> is in this position, it blocks each of the inner outlet <NUM>, intermediate outlet <NUM>, and outer outlet <NUM>, thereby preventing molding material from flowing from any of those outlets. This valve stem position may be referred to as Position <NUM>, with the number <NUM> reflecting the number of open nozzle outlets (i.e. none).

In order to effectively block the flow of melt from outlets <NUM>, <NUM>, and/or <NUM>, the clearance between the valve stem <NUM> and each of these outlets may for example be on the order of microns. The clearance may vary between embodiments based on, e.g., the viscosity of the melted molding materials in the respective channels <NUM>, <NUM>, and <NUM>, the pressure of the melt within nozzle <NUM> immediately upstream of the valve stem <NUM>, and other factors.

Operation <NUM> of the molding machine <NUM> for coinjection of a multilayer molded article with an internal layer segment <NUM> during a single injection molding cycle is depicted in <FIG> in the form of a flowchart. Operation <NUM> will be described in conjunction with <FIG>, which schematically depict, in longitudinal cross section, a portion of the nozzle <NUM> of <FIG> and at least part of an associated mold cavity <NUM> at various stages of formation of a preform <NUM> during a single injection molding cycle.

Referring to <FIG>, at the beginning of an injection molding cycle, the valve stem <NUM> of nozzle <NUM> is in Position <NUM>, i.e. the fully closed position. In that position, the valve stem <NUM> blocks (i.e. closes) the inner outlet <NUM>, intermediate outlet <NUM>, and outer outlet <NUM>, thereby preventing any surface layer material <NUM> or any internal layer material <NUM> from flowing. The mold cavity <NUM> (shown only in part in <FIG>) associated with the nozzle <NUM>, which defines a negative space in the shape of preform <NUM>, is initially empty, with any preform from a previous molding cycle having been ejected.

In the embodiment illustrated in <FIG>, it can be seen that the distal end of intermediate channel <NUM>, immediately upstream of intermediate outlet <NUM>, initially contains a small amount of surface layer material <NUM>. This is despite the fact that the intermediate channel <NUM> is intended to convey internal layer material <NUM> from injection unit <NUM> towards mold cavity <NUM>. The manner in which the distal end of channel <NUM> is filled with surface layer material <NUM> at the end of the previous molding cycle and the rationale for doing so are described below.

Referring to <FIG>, in a first operation <NUM>, the valve stem <NUM> is moved from Position <NUM> (the fully closed position) to Position <NUM> (the fully open position), and injection of the surface layer material <NUM> by injection unit <NUM> (<FIG>) is commenced. The surface layer material <NUM> is injected via both the inner and outer channels <NUM> and <NUM>, in order to maximize the rate of flow and in turn minimize the duration of injection of operation <NUM>. Notably, the other injection unit <NUM> is not yet activated in operation <NUM>, i.e. no internal layer material is yet made to flow from the intermediate outlet <NUM>. The initial flow of molding material is limited to only surface layer material <NUM> because it will ultimately occupy the neck finish area <NUM> of the preform <NUM>, which should be kept free of any internal layer material in the present embodiment.

The state of the nozzle <NUM> and mold cavity <NUM> during operation <NUM> of <FIG> are depicted in <FIG>. As illustrated, surface layer material <NUM> from both of the inner and outer channels <NUM> and <NUM> flows into mold cavity <NUM> via gate area <NUM>. It will be appreciated that the stream of surface layer material <NUM> from the inner channel <NUM> flowing past intermediate outlet <NUM> may have a tendency to entrain or "drag" some of the material from outlet <NUM> along with it. Advantageously, to the extent that this does occur, the dragged material will also be surface layer material <NUM>, in view of the small amount of surface layer material <NUM> occupying the distal end of channel <NUM>. As such, the initial flow of surface layer material <NUM> during the current molding cycle is kept free from contamination by any internal layer material <NUM>. It is for this reason that the distal end of intermediate channel <NUM> was filled with small amount of surface layer material <NUM> at the end of the previous injection molding cycle, using a mechanism that will be described below.

In a subsequent operation <NUM> (<FIG>), controller <NUM> causes valve stem <NUM> to move to Position <NUM>, as shown in <FIG>. In addition, controller <NUM> triggers injection by injection unit 106of internal layer material <NUM> into mold cavity <NUM> from the intermediate outlet <NUM> of nozzle <NUM>, i.e. initiates injection of internal layer segment <NUM> (<FIG>). Referring to <FIG>, the triggering entails increasing the bore-side pressure PB of injection actuator <NUM> sufficiently to cause translation of the piston <NUM> and screw <NUM> in a downstream direction (i.e. to the right in <FIG>). Referring to <FIG>, the internal layer material <NUM> entering the mold cavity <NUM> flows along with the surface layer material <NUM>, which continues to be injected from outer channel <NUM>.

In a subsequent operation <NUM> (<FIG>), injection of internal layer material <NUM> from outlet <NUM> is terminated and the formation of the internal layer segment <NUM> is accordingly completed. Some minor "tailing" (thinning or tapering) of the trailing edge of the segment <NUM>, which is not expressly depicted in <FIG> but is shown in <FIG>, may occur. Surface layer material <NUM> continues to flow from outer outlet <NUM>, which remains open. It will be appreciated that operations <NUM> and <NUM> of <FIG> collectively result in the formation of the internal layer segment <NUM> of <FIG>.

With formation of the internal layer segment <NUM> having been completed, controller <NUM> causes injection unit <NUM> to reduce the rate of surface layer material injection. This is done because, by this time, the mold cavity <NUM> has been nearly filled with molding material. The rationale for continuing to supply surface layer material injection is to fill any gaps that may form in the mold cavity <NUM> as the molded article (preform <NUM>) cools, shrinks, and hardens over time.

With the intermediate outlet <NUM> open and with the surface layer material injection unit <NUM> in a "hold phase" in which surface layer material <NUM> is still under positive pressure and flowing (albeit slowly) from outer outlet <NUM>, the controller <NUM> causes the internal layer material injection unit <NUM> to pull back slightly (operation <NUM>, <FIG>). The pullback has the effect of reducing a pressure of the internal layer material <NUM> within the extruder barrel <NUM> and the intermediate channel <NUM>. The reduced pressure in turn allows a small amount of pressurized surface layer material <NUM> to flow into the distal end of intermediate channel <NUM>. It will be appreciated that the direction of this flow is upstream, i.e. opposite to the normal direction of flow of intermediate layer material <NUM> through channel <NUM> during the injection phase (operation <NUM> of <FIG>, described above). For this reason, the filling of the distal end the channel <NUM> with surface layer material <NUM> in operation <NUM> may be referred to as "backfilling. " Backfilling is done for the reasons mentioned hereinabove.

Finally, in operation <NUM> (<FIG>), the controller <NUM> causes valve stem <NUM> to return to its original, fully closed position, i.e. Position <NUM>. This closure has the effect of trapping a small amount of surface layer material in the distal end of the intermediate channel <NUM>, in preparation for the next molding cycle. In the result, the state of the nozzle <NUM> at the conclusion of operation <NUM> will be the same as its initial state of <FIG>.

It will be appreciated that operation <NUM> of <FIG> could be implemented differently in alternative embodiments of the molding machine. For example, in operation <NUM>, the stem <NUM> could be kept in position <NUM> rather than moved to position <NUM>, with surface layer material <NUM> being injected from both the inner and outer outlets <NUM>, <NUM> of the nozzle <NUM>, rather than just the outer outlet <NUM>. In operation <NUM>, the valve stem could be position <NUM> rather than position <NUM>, so that surface material <NUM> for backfilling is supplied from not just the outer outlet <NUM> but also the inner outlet <NUM>. Aspects of operation <NUM> may also differ somewhat from what is shown in <FIG> based on the design of the coinjection nozzle of the molding machine. For example, in some embodiments, the coinjection nozzle has an annulus of clearance between the valve stem and each of the intermediate outlet and the outer outlet. Such embodiments can still achieve backfilling of the distal end of their intermediate channels, even if their valve stems cannot mechanically block the intermediate or outer outlets or mechanically trap surface layer material <NUM> at the distal end of the intermediate channel as described in operation <NUM>.

The inventors have observed that some containers blow-molded from multilayer preforms made by molding machine <NUM>, or by similar injection molding equipment using similar techniques, can delaminate and separate during use. In particular, a thin layer of molding material has been observed to stand away or break away from either or both of the interior surface and exterior surface of blow-molded bottles. Three examples of such defects are shown in <FIG>.

<FIG> is a perspective view showing a portion of a plastic bottle <NUM> that has been blow-molded from a preform <NUM>. In <FIG>, the bottle <NUM> is shown to be partly filled with a consumable beverage <NUM>, such as water. A delaminated portion <NUM> of molding material that has detached from an area <NUM> on an interior surface of the bottle wall can be seen stuck to (hanging on) the interior bottle surface. In this example, the delaminated portion <NUM> is a detached thin film having an irregular shape. The delaminated portion <NUM> may be considered aesthetically unappealing and could constitute a choking hazard in the event of its inadvertent ingestion by a consumer. Moreover, if the delaminated portion <NUM> comprises a non-food grade material (e.g. a recycled internal layer material containing impurities), the delaminated portion <NUM> may contaminate the liquid <NUM> to the possible detriment of consumer safety.

<FIG> is a perspective view of a cutaway base portion of another plastic bottle <NUM> having a delaminated portion <NUM> comprising a thin film that has detached from an area <NUM> of the interior surface of the bottle <NUM>. In this example, the delaminated portion <NUM> has a distorted cup shape and remains partially attached to the bottle <NUM> at a central gate portion <NUM> of the bottle base. The delaminated portion <NUM> suffers from at least some of the disadvantages noted above.

<FIG> is a perspective view of an underside of the plastic bottle <NUM> of <FIG> showing yet another delaminated portion <NUM>, which in this case is located on an exterior surface of the bottle <NUM>. Part of the delaminated portion <NUM> has separated and broken away from the bottle <NUM>. As with the delaminated portions in <FIG> and <FIG>, the delaminated portion <NUM> of <FIG> may be considered aesthetically unappealing. Moreover, any pieces of the delaminated material that have broken away from the bottle <NUM> may create plastic or micro-plastic pollution that may be harmful to the environment.

The inventors have determined that the delaminated portions <NUM>, <NUM> and <NUM> in these examples are comprised of an internal layer molding material. The inventors believe that a previously unrecognized problem with the operation of injection molding machine <NUM> has resulted in an undesired film of internal layer material on the surface of the bottles <NUM>, <NUM>. More specifically, the inventors believe that, despite the "pullback" operation <NUM> (<FIG>) at the conclusion of the injection phase of preform molding, backfilling of the intermediate channel <NUM> of the hot runner nozzle <NUM> that molded the preform was at least partially unsuccessful. It is suspected that this may have occurred for reasons such as: an unexpectedly high viscosity of surface layer material <NUM> causing slower than anticipated material flow rates; an anomalous constriction in the intermediate channel <NUM> upstream of the distal end to be backfilled; a premature deactivation of the surface layer material injection unit <NUM> during application of a "hold" or packing pressure to the surface layer material <NUM>; a premature closing of outlet nozzle valve <NUM>; or a combination of these. The foregoing list is not necessarily exhaustive. Regardless of the reason(s) for the defects, it is believed that at least some internal layer material <NUM> from the distal end of intermediate channel <NUM> is being entrained into the gate area <NUM> during the subsequent injection molding cycle and is forming the superfluous surface layer film.

<FIG> depict operation of molding machine <NUM> that could result in a superfluous film or skin of internal layer material <NUM> on a molded preform. Referring to <FIG>, portions of the hot runner nozzle <NUM> and mold cavity <NUM> are depicted longitudinal cross section at different points in time at the beginning of an injection molding cycle. As in <FIG>, the valve stem <NUM> of <FIG> is in Position <NUM>, i.e. the fully closed position, and the mold cavity <NUM> (shown only in part) is empty. However, <FIG> differs from <FIG> in that the distal end of intermediate channel <NUM> of <FIG> contains only intermediate layer material <NUM>. In other words, <FIG> shows the state of nozzle <NUM> when the pullback operation <NUM> of <FIG> of the previous molding cycle has failed to achieve the intended result of backfilling the distal end of intermediate channel <NUM> with a small amount of surface layer material <NUM>, as in <FIG>.

Turning to <FIG>, the state of the nozzle <NUM> and mold cavity <NUM> during operation <NUM> of <FIG> is depicted. In this operation, the valve stem <NUM> is moved from Position <NUM> (the fully closed position) to Position <NUM> (the fully open position), and injection of the surface layer material <NUM> by injection unit <NUM> via both the inner and outer channels <NUM> and <NUM> is commenced. Notably, the stream of surface layer material <NUM> from the inner channel <NUM> flowing past intermediate outlet <NUM> has entrained or "dragged" some of the internal layer material <NUM> from outlet <NUM> along with it. More specifically, a globule <NUM> of entrained internal layer material <NUM> has broken free in this example and has been carried through the material combination area <NUM> towards mold cavity <NUM>. It will be appreciated that this globule <NUM> of intermediate layer material <NUM> may be considered as a contaminant to the initial flow of molding material, which was intended to be exclusively surface layer material <NUM>.

<FIG> schematically depict a portion of mold cavity <NUM> corresponding to the curved closed end <NUM> of the preform <NUM> in longitudinal cross section at four sequential points in time during operation <NUM> of <FIG>. <FIG> show the manner in which the "fountain flow" effect can transform an entrained globule <NUM> of internal molding material <NUM> into a thin film on the internal and external surfaces of the molded preform.

<FIG> shows the mold cavity <NUM> at a point in time later than what is shown in <FIG>. As illustrated, the globule <NUM> of internal layer material <NUM> has advanced to the leading edge of the advancing flow of surface layer material <NUM> by virtue of fountain flow, described below.

<FIG> shows the mold cavity <NUM> at a point in time later than what is shown in <FIG>. The molding material in the center of the mold cavity (i.e. channel) flows faster than the molding material at the perimeter of the mold cavity. Upon reaching the leading edge of the flow, the fastest-flowing central stream of molding material spreads out laterally, or "fountains," to the mold cavity walls. This so-called "fountain flow" is denoted in <FIG> by dashed arrows FF. In the result, the internal layer material <NUM> at the leading edge of the melt flow spreads out laterally, at which time it comes into contact with the cavity surface <NUM> and the core surface <NUM> of the mold cavity <NUM>.

Because the cavity and core surfaces <NUM> and <NUM> of the mold cavity <NUM> are cold in comparison to the melted molding material flowing thereinto, whatever molding material first touches those surfaces tends to immediately cool and adhere thereto. In this case, it is the internal layer material <NUM> fountaining to the cavity walls that is the first to touch those surfaces and adhere thereto. For that reason, a film of the internal layer material <NUM> begins to form on the interior and exterior surfaces of the preform <NUM> taking shape within mold cavity <NUM>.

In <FIG>, molding material has flowed further into mold cavity <NUM>. The globule <NUM> of internal layer material <NUM> has significantly flattened in the longitudinal dimension and continues to spread out laterally, adding to the thin film of internal layer material <NUM> forming on the mold cavity walls.

In <FIG>, the flow of molding material has advanced still further into the mold cavity <NUM>. At this stage, most of the internal layer material <NUM> comprises a thin film or "skin" along the mold cavity walls. A substantial portion of the film in this example is located near the gate area of the preform, i.e. along the curved portion <NUM> of the cavity surface and along the curved portion <NUM> of the core surface of mold cavity <NUM>.

The precise location and thickness of the superfluous film of internal layer material <NUM> may vary between embodiments and even between injection molding cycles of a given embodiment, depending upon how much internal layer material <NUM> has been entrained (see <FIG>) and how the entrained material <NUM> is carried into mold cavity <NUM>. In some cases, the film may form primarily or exclusively on the external surface of the preform, i.e. on the cavity side of mold cavity. In other cases, the film may form primarily or exclusively on the internal surface of the preform, i.e. on the core side of mold cavity. The film may be localized to only some portions of a preform and may take on unpredictable shapes. In view of these variables, it may be difficult to detect the presence of the film based on visual inspection alone, particularly when the color of the surface layer material and the color of the internal layer material are similar or identical.

Regardless of the exact location of the superfluous film on the molded preform, subsequent blow molding of the preform into a container (e.g. bottle) may cause the film to delaminate and separate, in whole or in part, from the remainder of the container. Such delamination and separation may be particularly likely when the internal layer material <NUM> and the surface layer material <NUM> do not bond well with one another, e.g. as in the case of nylon and PET. In the result, the problems described hereinabove in relation to <FIG> may occur. Moreover, because the blow-molding of preforms into containers may occur at a later date and possibly at a different location from the injection molding of the preforms, there is some risk that many batches of defective preforms may be produced before the problem is detected.

<FIG> is a perspective view of an injection molding machine <NUM>' having a reduced risk of producing defective multilayer molded articles of the type described above. The injection molding machine <NUM>' is in many respects similar to the injection molding machine <NUM> of <FIG>. For example, the machine <NUM>' is designed to mold the same type of multilayer articles, specifically preform <NUM> of <FIG>. Some components of molding machine <NUM>' may be identical to those of the above-described molding machine <NUM>. These include the enclosure <NUM> and at least some of the housed subcomponents (i.e. a clamp unit, a fixed platen, a movable platen, and a mold mounted therebetween, none of which are expressly depicted in <FIG>), the surface layer material injection unit <NUM>, and the internal layer material injection unit <NUM>. Each of these components of injection molding machine <NUM>' is referenced using the same numerals as were used above to reflect the fact that the components may be identical to their counterparts of machine <NUM>.

Other components of injection molding machine <NUM>' are configured to operate differently than their counterparts of molding machine <NUM> with a view to reducing the risk of molding defective preforms of the type described above. In this embodiment, these components include controller <NUM>' and HMI <NUM>'. By convention, these components are denoted herein by a variation of the reference numerals that were used to identify their counterparts in molding machine <NUM>, namely the same reference numeral but with an appended apostrophe ("prime") (') symbol.

<FIG> depicts, in the form of a flowchart, operation <NUM> of the controller <NUM>' of the injection molding machine <NUM>' of <FIG> for facilitating the molding of a multilayer article with a reduced risk of defects of the type described above. Operation <NUM> will be described below in conjunction with <FIG>. <FIG> is a graph showing the positions of the output nozzle <NUM> and driving element (reciprocating screw <NUM>) of the internal layer material injection unit <NUM> of <FIG> over a single injection molding cycle (plots <NUM> and <NUM> respectively). <FIG> also depicts the bore-side pressure PB and rod-side pressure PR at injection actuator <NUM> of injection unit <NUM> by which the screw <NUM> is made to reciprocate (plots <NUM> and <NUM> respectively). <FIG> schematically depicts a portion of the injection molding machine <NUM>' during a pullback operation. <FIG> shows an example graphical user interface (GUI) <NUM> that may be displayed on the human-machine interface (HMI) <NUM>' of <FIG> for configuring control parameters and monitoring status of a pullback and/or backfilling operation at molding machine <NUM>'.

In overview, the injection molding machine <NUM>' of <FIG> differs from injection molding machine <NUM> at least in that machine <NUM>' is configured to detect at least one physical parameter indicative of a pressure of the internal layer material <NUM> at the internal layer material injection unit <NUM> after a pullback stroke has been effected (referred to herein as the "post-pullback pressure"). The inventors have determined that a lower-than-anticipated post-pullback pressure can indicate inadequate backfilling of the distal end of the internal layer material channel <NUM> with surface layer material, and thus a higher than normal risk of defective preforms having a superfluous internal layer material film. Accordingly, when the post-pullback pressure is found to be below a minimum threshold pressure, an indicator can be generated at the HMI <NUM>' to apprise an operator of this risk.

In response to the indicator, the operator may manually take remedial action to increase the likelihood of effective backfilling. The remedial action may include one or more of: increasing a pullback dwell time; increasing a pullback volume (stroke length) at the internal layer material injection unit <NUM>; increasing a surface layer material injection pressure and/or hold time; increasing a speed of the pullback stroke at the internal layer material injection unit <NUM>; increasing a speed at which a secondary channel for surface layer material <NUM> at nozzle <NUM> is opened at the commencement of pullback (this remedial action presuming that the embodiment in question has such a secondary channel, which is not necessarily present in all embodiments); or a combination of these. The controller <NUM>' may alternatively be operable to automatically take the remedial action(s) or a subset thereof. As a result, machine <NUM>' may produce fewer batches of defective articles than machine <NUM>. Moreover, reliance upon human visual inspection for detecting such defects may be diminished.

It is presumed that, at the commencement of operation <NUM> of <FIG>, injection molding machine <NUM>' is ready to commence an injection molding cycle as described above in connection with <FIG>. The reciprocating screw <NUM> of the internal layer material injection unit <NUM> is accordingly in a charged position, ready to inject a shot of plasticized internal layer material <NUM>, as depicted in <FIG> (see e.g. plot <NUM>, time T0).

Initially, the controller <NUM>' (<FIG>) causes the surface layer material injection unit <NUM> to commence injection of surface layer material <NUM> into the mold cavity <NUM> via surface layer material channel <NUM> of coinjection nozzle <NUM> (operation <NUM>, <FIG>). Operation <NUM> may for example entail issuance from controller <NUM>' to the surface layer material injection unit <NUM> of suitable commands and/or control signals for opening output nozzle valve <NUM> and causing the injection actuator associated with unit <NUM> to commence injection. The injection of surface layer material <NUM>, which is not expressly depicted in <FIG>, may be performed according to operation <NUM> of <FIG>, described above, and may have the result depicted in <FIG>, described above. Injection may continue for some period of time before subsequent operation <NUM> (described below) is performed.

With injection of surface layer material <NUM> by surface layer material injection unit <NUM> ongoing, the controller <NUM>' next causes the internal layer material injection unit <NUM> to commence injection of internal layer material <NUM> into the mold cavity <NUM> via internal layer material channel <NUM> of the coinjection nozzle <NUM> (operation <NUM>, <FIG>). Analogously to operation <NUM>, operation <NUM> may entail issuance from controller <NUM>' to the internal layer material injection unit <NUM> of suitable commands and/or control signals for opening output nozzle valve <NUM> and causing the actuator <NUM> to commence injection.

In the example embodiment of <FIG>, it can be seen that the output nozzle valve <NUM> of internal layer material injection unit <NUM> opens just after time T0 (see plot <NUM>, representing a control signal generated by controller <NUM>' to control a position of valve <NUM>). After a delay, injection of the internal layer material <NUM> commences at time T1 (<FIG>). The delay ensures sufficient time for the surface layer material injection unit <NUM> to initially inject enough surface layer material <NUM> into the mold cavity <NUM> for the neck finish <NUM> (<FIG>) to be comprised only or primarily of surface layer material <NUM>.

In the present embodiment, the injection actuator <NUM> (<FIG>) commences injection by increasing the bore-side pressure PB sufficiently to begin driving the reciprocating screw <NUM> forward (see <FIG>, plot <NUM>, just before time T1; for clarity, injection by screw <NUM> is depicted in <FIG> as a downward trend of plot <NUM> over time). Injection of internal layer material <NUM> continues throughout coinjection phase <NUM>, i.e. from time T1 to time T2 (<FIG>). For clarity, the bore-side pressure PB begins to drop before the coinjection phase <NUM> concludes in the illustrated embodiment because the rate of injection slows towards the end of that phase. The coinjection operation <NUM> may be initiated and concluded according to operations <NUM> and <NUM> respectively of <FIG>, described above, and may have a result similar to what is depicted in <FIG>, described above.

At the conclusion of the coinjection phase <NUM> (<FIG>), the rate at which surface layer material <NUM> is injected into the mold cavity <NUM> via channel <NUM> is significantly slowed (not expressly shown). The reason is that, by this time, the mold cavity <NUM> has been nearly filled with molding material. In particular, the surface layer material injection unit <NUM> may enter a "hold phase" of operation. In that phase of operation, the surface layer material injection unit <NUM> applies sufficient "packing pressure" or "hold pressure" for surface layer material <NUM> to fill any gaps arising within the mold cavity <NUM> as the molded article (preform <NUM>) cools, shrinks, and hardens over time.

It will be appreciated that, at this stage, nozzle output valves <NUM>, <NUM> of injection units <NUM>, <NUM> respectively are still both in an open state (see <FIG>). As a result, the surface and internal layer material injection units <NUM> and <NUM> are in fluid communication with one another via the surface and internal layer material channels <NUM>, <NUM> of nozzle <NUM> of hot runner <NUM>. In other words, a fluid communication path may be considered to exist between the surface and internal layer material injection units <NUM> and <NUM> via the hot runner <NUM>, channels <NUM>, <NUM>, and the material combination area <NUM> of the nozzle <NUM>.

Next, as the surface layer material injection unit <NUM> continues to apply a hold pressure upon the surface layer material in the surface layer material channel <NUM>, and with the surface layer material injection unit <NUM> and the internal layer material injection unit <NUM> in fluid communication with one another as described above, the controller <NUM>' causes a pullback stroke to occur at the internal layer material injection unit <NUM> (operation <NUM>, <FIG>). The purpose of the pullback stroke is to reduce the pressure of the internal layer material <NUM> in the internal layer material injection unit <NUM> and downstream thereof. This is done to permit pressurized surface layer material <NUM> from the surface layer material channel <NUM> of nozzle <NUM> to backfill the distal end of the internal layer material channel <NUM>, as earlier described in conjunction with <FIG>. The effect of the pullback in operation <NUM> of the present embodiment of injection molding machine <NUM>' is depicted in <FIG>.

<FIG> schematically depicts a portion of injection molding machine <NUM>' comprising injection units <NUM>, <NUM>, hot runner <NUM>, part of a single coinjection nozzle <NUM>, and part of an associated mold cavity <NUM>. <FIG> illustrates the manner in which molding material flows through the illustrated components during operation <NUM> of <FIG>.

In the present embodiment, the pullback of reciprocating screw <NUM> at internal layer material injection unit <NUM> is commenced by reducing the bore-side pressure PB of injection actuator <NUM> sufficiently to initiate pullback (<FIG>). In the depicted embodiment, pullback commences at time T2 and ends at time T3. That interval is referred to as pullback phase <NUM> (<FIG>). During that phase, the reciprocating screw <NUM> moves in the reverse direction (i.e. left in <FIG>) over a pullback stroke length denoted LPB (<FIG>). The pullback stroke defines a pullback volume VPB equal to the pullback stroke length LPB multiplied by the transversely projected area of the head <NUM> of screw <NUM>. As illustrated in <FIG>, the bore-side pressure PB may be greater than the rod-side pressure PR at the commencement of pullback (time T2). This is in view of significant plastic pressure pushing back on the tip <NUM> of screw <NUM> at that time.

At the conclusion of the pullback phase <NUM> (<FIG>), the injection molding machine <NUM>' of the present embodiment holds the reciprocating screw <NUM> in a pulled-back position for a period of time referred to as the pullback dwell time or pullback dwell phase <NUM> (time T3 to time T4 of <FIG>). This interval provides time for the plasticized molding materials <NUM> and <NUM> within nozzle <NUM> to react to the reduced pressure of the internal layer material <NUM> at internal layer material injection unit <NUM>. In particular, the pullback dwell phase <NUM> is intended to allow surface layer material <NUM> from outer channel <NUM> (and, in some embodiments, inner channel <NUM>, presuming that inner outlet <NUM> is open at the relevant time), to backfill the distal end of the internal layer material channel <NUM>, e.g. as earlier described in connection with <FIG>.

It will be appreciated that, if backfilling is successful, e.g. as denoted by arrows <NUM> in <FIG>, then the pressure of the internal layer material at the internal layer material injection unit <NUM> should increase during the pullback dwell phase <NUM> by virtue of material flowing upstream within channel <NUM>. Conversely, if backfilling is unsuccessful, then the pressure of the internal layer material <NUM> at the internal layer material injection unit <NUM> will not increase by the same extent, or possibly at all, during the pullback dwell phase <NUM>. As earlier mentioned, possible reasons for unsuccessful backfilling may include: an unexpectedly high viscosity of the surface layer material <NUM>; an anomalous constriction in the intermediate channel <NUM> upstream of the distal end to be backfilled; a premature deactivation of the surface layer material injection unit <NUM> that is applying the "hold pressure" to the surface layer material <NUM>; a premature closing of outlet nozzle valve <NUM>; or a combination of these.

To ascertain an effectiveness of the backfilling operation (or, more generally, of the pullback operation), controller <NUM>' triggers the detection of at least one physical parameter indicative of the post-pullback pressure PPB of the internal layer material <NUM> in the internal layer material injection unit <NUM>. In the present embodiment, this operation is performed just prior to the end of the pullback dwell phase <NUM>, after a post-pullback delay interval has elapsed (operation <NUM>, <FIG>). In the present embodiment, the detection is performed with the surface and internal layer material injection units <NUM> and <NUM> still in fluid communication with one another and with the hold pressure still being applied by the surface layer material injection unit <NUM>.

In some embodiments, the detected physical parameter is the post-pullback pressure PPB itself. This may for example be done when the injection unit incorporates a sensor suitable for directly measuring the post-pullback pressure PPB, such as a transducer located within the extruder barrel downstream of the driving element for example.

Because the present embodiment lacks such a sensor, the post-pullback pressure PPB is computed based on two detected physical parameters, namely the bore-side pressure PB and the rod-side pressure PR at the injection actuator <NUM>, as follows. After the pullback stroke has been completed and the delay interval has elapsed, the PB and PR values are dynamically detected using sensors <NUM> and <NUM> respectively with the screw <NUM> in a stationary position. Detection is performed just prior to the closure of the internal layer material injection unit <NUM> output nozzle valve <NUM>, i.e. just before time T4 in <FIG> of the present embodiment. Using these values, the post-pullback pressure PPB is computed according to the equation PPB = (PB*AB - PR*AR) / ADE, where:.

It will be appreciated that each of the above-referenced projected areas AB, AR, and ADE is projected onto a plane that is transverse to the dimension of reciprocation of the screw <NUM>.

Thereafter, the controller <NUM>' generates an indicator of pullback effectiveness based on a relationship of the post-pullback pressure PPB indicated by the at least one physical parameter and a threshold pressure PT (operation <NUM>, <FIG>). In the present embodiment, the threshold pressure PT is an empirically predetermined minimum threshold, and the indicator is either a positive indicator or a negative indicator. A positive indicator is generated when the pullback pressure PPB is at least as large as the minimum threshold pressure PT, indicating that backfilling of the distal end of intermediate channel <NUM> was likely successful. A negative indicator is generated when the pullback pressure PPB is below the minimum threshold pressure PT, indicating that the backfilling is at risk of having been partly or wholly unsuccessful.

In the present embodiment, the indicator generated in operation <NUM> is displayed by way of a GUI displayed at HMI <NUM>' (<FIG>). An example GUI <NUM> by which the indicator could be displayed is depicted in <FIG>. As illustrated, GUI <NUM> comprises multiple panels, each displaying a set of GUI constructs for controlling or monitoring associated machine parameters.

A first GUI panel <NUM> includes GUI controls (e.g. editable textbox fields) for configuring operational parameters of the internal layer material injection unit <NUM> at machine <NUM>'. These controls include: a pullback dwell time field <NUM> for setting a duration of the pullback dwell phase <NUM> (<FIG>); a pullback volume field <NUM> for setting a pullback volume, expressed here as a percentage of a total volume of mold cavity <NUM>; and a pullback speed field <NUM> for setting a pullback speed, expressed here as a percentage of maximum pullback speed.

A second GUI panel <NUM> includes GUI controls (e.g. editable textbox fields) for configuring operational parameters of the surface layer material injection unit <NUM> of machine <NUM>'. The controls include a hold time field <NUM> for setting a duration of the hold phase and hold pressure fields <NUM> and <NUM> for setting starting and ending surface layer material pressure levels during the hold phase. In the present embodiment, the starting and ending hold pressures are expressed as percentages of a maximum hold pressure that the surface layer material injection unit <NUM> is capable of applying. Alternative embodiments could express these values in other ways, e.g. in absolute units such as pounds per square inch.

A third GUI panel <NUM> includes GUI constructs for monitoring the effectiveness of the pullback operation <NUM> of <FIG>. The example GUI constructs include: a threshold post-pullback pressure textbox field <NUM> for specifying a threshold post-pullback pressure PT; a "current" post-pullback pressure output <NUM> showing the most recently detected post-pullback pressure value PPB; and a pullback effectiveness indicator <NUM> for providing an indication of the effectiveness of the pullback performed in operation <NUM> of <FIG>. In the illustrated embodiment, the threshold pressure and the current pullback pressure output are expressed as percentages of a maximum hold pressure that the surface layer material injection unit <NUM> is capable of applying. Alternative embodiments could express these values in other ways, e.g. in absolute units such as pounds per square inch.

The GUI <NUM> may comprise other GUI panels or constructs, which are omitted from <FIG> for brevity.

In the present embodiment, the minimum threshold pressure specified in field <NUM> is empirically determined. For example, an operator of injection molding machine <NUM>' may initially closely inspect preforms produced by the machine <NUM>' for evidence of any superfluous internal layer material film as described above. If any such defects are found, then the control parameters within panels <NUM> and <NUM> may be selectively configured until the defect is no longer evident in subsequent shots (batches).

For example, in one embodiment, the control parameters may be adjusted as follows. If any of the relevant defects are found, the first reconfiguration of machine <NUM>' may be to increase the pullback dwell time (i.e. the post-pullback delay interval referenced in operation <NUM>, <FIG>) via field <NUM> of <FIG>. The rationale for this reconfiguration is to provide more time for proper backfilling to occur. For example, this may be sufficient to compensate for a more-viscous-than-anticipated, and therefore slower moving, surface layer molding material <NUM>. In many cases, increasing the pullback dwell time may be considered the best way in which to address any possible defects resulting from incomplete or improper backfilling and should thus be tried first. Operators may consider this remedial action counterintuitive due to an engrained prevailing belief that pullback dwell time should always remain fixed.

Once the machine <NUM>' has been so reconfigured, then another shot or batch of articles may be produced and the articles inspected. If inspection of the articles reveals that the increased pullback dwell time has not fully eliminated the relevant defect(s), then another machine reconfiguration may be performed. In particular, a pullback volume may be increased via appropriate configuration of the pullback volume field <NUM> (<FIG>), which will result in appropriate adjustment of pullback stroke length LPB. The rationale for increasing pullback volume is to lower the pressure at the internal layer material injection unit <NUM> to promote better backfilling. This may be considered as the next best approach for remedying the defect(s) after increased pullback dwell time.

Another batch of articles may then be molded with the increased pullback volume setting in effect. If inspection of this batch of molded articles again reveals that one or more of the relevant defect(s) remain(s), then a further machine reconfiguration may be performed. At this stage, either or both of the hold time and hold pressure of the surface layer material injection unit <NUM> may be increased via fields <NUM>, <NUM>, and/or <NUM> (<FIG>). The rationale for this reconfiguration is to increase the pressure of the surface layer material <NUM> at layer material injection unit <NUM>, or a duration of maintaining that pressure at unit <NUM>, to promote improved backfilling. These may be considered as the next best option for reconfiguring machine <NUM>' after increasing pullback dwell time and pullback volume.

Another batch of articles may then be produced with the reconfigured settings in effect. If any defect(s) remain(s), then the machine <NUM>' may be reconfigured by increasing a pullback speed at the internal layer material injection unit <NUM> via GUI field <NUM> (<FIG>). The rationale for this reconfiguration is to more quickly lower the pullback pressure at the internal layer material injection unit <NUM> with a view to initiating backfilling more quickly.

If the machine <NUM>' produces a shot of molded articles without the relevant defects after any of the foregoing reconfiguration steps, then further reconfiguration may be unnecessary. At that time, a post-pullback pressure value from the most recent molding cycle may be read from the most recent post-pullback pressure field <NUM> of GUI <NUM> (<FIG>). That value may serve as the empirically determined baseline for setting the minimum threshold pressure value via field <NUM>.

For example, if field <NUM> were to indicate that the pullback pressure at the conclusion of the pullback dwell phase <NUM> is <NUM>%, that percentage value may be used as a baseline. The minimum pullback pressure threshold PT may then be set to a value slightly higher than the baseline value (e.g. <NUM>%). The slightly higher value may be considered to provide a "buffer" by which remedial action is triggered before any defective articles are likely to have been molded. In other words, remedial action may be triggered in this example when the most recently detected post-pullback pressure value drops below <NUM>% even if the pressure remains above <NUM>%. This may lower a risk of defective articles more readily than if the most recently detected post-pullback pressure value from field <NUM> were itself used as the threshold value in field <NUM>.

Referring to <FIG>, when the most recently detected post-pullback pressure (field <NUM>, <FIG>) is at least as large as the minimum pressure threshold PT (field <NUM>, <FIG>), then the pullback effectiveness indicator <NUM> that is generated in operation <NUM> is a positive indicator. In the embodiment depicted in <FIG>, the positive indicator is a textual "OK" symbol <NUM>. Other positive indicators that might be used in conjunction with, or alternatively to, that indicator may include other visual indicators, audible warnings, or haptic feedback for example.

If the most recently detected post-pullback pressure value (field <NUM>, <FIG>) were lower than the minimum threshold pressure PT (field <NUM>, <FIG>), then a negative indicator of pullback operation effectiveness would be generated in operation <NUM> (<FIG>). In the present embodiment, the negative indicator takes the form a textual "Warning" symbol <NUM> (ghosted in <FIG>) that becomes highlighted or visually noticeable. Other negative indicators that might be used in conjunction with, or alternatively to, that indicator may include other visual indicators, audible warnings, or haptic feedback for example. These indicators may be designed to be particularly noticeable to a human operator as they may indicate a possible fault warranting quick action.

In some embodiments, additional remedial measures may be available for attempting to improve backfill effectiveness. One such remedial measure, alluded to hereinabove, is to increase a speed at which a secondary surface layer material channel of a coinjection nozzle is opened at a commencement of the pullback at internal layer material injection unit <NUM>. For example, in nozzle <NUM> of <FIG>, channel <NUM> may be considered as a primary channel for surface layer material <NUM>, and inner channel <NUM> may be considered as a secondary channel. A faster rate of opening the secondary channel <NUM> (e.g. by quicker opening of a mechanical closure, such as quicker retraction of valve stem <NUM>) may more quickly facilitate the flow of a greater volume of surface layer material <NUM> into the material combination area <NUM> of the coinjection nozzle compared to the volume of flow from only a single, primary channel for surface layer material <NUM>. This action may alternatively be considered as opening a secondary surface layer material channel at a commencement of pullback or as increasing a speed of opening of a secondary surface layer material channel at a commencement of pullback.

In some embodiments, the controller <NUM>' is operable to automatically trigger at least one remedial action for increasing pullback operation effectiveness when the post-pullback pressure indicated by the at least one physical parameter detected in operation <NUM> (<FIG>) is below the minimum threshold PT. The remedial action(s) may be one or more of the remedial actions described above in the context of setting the minimum pullback pressure threshold, i.e.: (a) increasing a pullback dwell time (post-pullback delay interval) at the internal layer material injection unit <NUM>; (b) increasing a length of the pullback stroke, and thus the pullback volume, at the internal layer material injection unit <NUM>; (c) increasing either or both of a pressure of the surface layer material <NUM> at the surface layer material injection unit <NUM> and a hold time of the surface layer material <NUM> by the surface layer material injection unit <NUM>; (d) increasing a speed of the pullback stroke at the internal layer material injection unit <NUM>; and (e) increasing a speed at which a secondary channel for surface layer material <NUM> within nozzle <NUM> (if present) is opened. When two or more of the remedial actions (a) to (e) are triggered, they may be triggered in the sequence (a) to (e), as described above in the context of setting the minimum pullback pressure threshold. In alternative embodiments, the remedial actions may be effected out of sequence.

After automatically effecting one of the remedial actions, the controller <NUM>' may automatically trigger another molding cycle and then automatically check the latest post-pullback pressure value (field <NUM>, <FIG>) to determine whether pullback effectiveness has sufficiently improved. The controller <NUM>' may automatically cease taking remedial action once the current pullback pressure reaches or exceeds the predetermined threshold defined via field <NUM> (<FIG>). Visual inspection of the molded articles may become unnecessary, and injection molding machine downtime may accordingly be reduced or avoided.

Various alternative embodiments are contemplated.

The example coinjection nozzle <NUM> of <FIG> and <FIG> has two surface layer material channels <NUM> and <NUM>. In some embodiments, the coinjection nozzle may have only a single surface layer material channel.

The shape and relative positions of the surface layer material channel(s) and the internal layer material channel may vary between embodiments.

In some embodiments, the physical parameter(s) indicative of post-pullback pressure of the internal layer material that is detected in operation <NUM> (<FIG>) may be a force exerted by the internal layer material <NUM> on the downstream-most end of the driving element <NUM> (e.g. the tip <NUM> of the screw) of internal layer material injection unit <NUM>. For example, a force sensor for that purpose could be mounted on the tip of a non-hydraulically actuated reciprocating screw of the internal layer material injection unit. The timing of detecting the physical parameter (force) may be similar to the timing for detecting rod-side and bore-side pressures in the above-described embodiment, i.e. it may be done after a post-pullback delay interval has elapsed. The force may be detected while the surface layer material injection unit and internal layer material injection unit are in fluid communication with one another. The indicator of pullback effectiveness may be generated in operation <NUM> (<FIG>) based on a relationship of the detected force and a minimum threshold force (which may correspond with the minimum threshold pressure PT described above). For example, a negative indicator, indicating pullback and/or backfill ineffectiveness, may be generated when the detected force is below the minimum threshold force.

Conversely, a positive indicator, indicating pullback and/or backfill effectiveness, may be generated when the detected force is at least as large as the minimum threshold force.

In some embodiments, the value that is monitored for assessing pullback effectiveness may not be restricted to a post-pullback pressure PPB of the internal layer material at the internal layer material injection unit. For example, the monitored value may be the post-pullback pressure PPB multiplied by one or more of the parameters that is being used to remedially adjust the post-pullback pressure (e.g. the operative pullback volume VPB). In such embodiments, the minimum threshold value may be expressed in similar units, e.g. not purely as a minimum post-pullback pressure PT but rather as the minimum post-pullback pressure PT multiplied by a baseline pullback volume VB. If the product of PPB * VPB is determined to be below the threshold value PT * VB, then this may indicate a higher risk of defects as described above. The rationale for such an approach may be to conveniently monitor, as a combined value, not only the post-pullback pressure at the internal layer material injection unit but also one or more important system parameters whose deviation from expected settings could indicate a potential problem with backfilling.

In operation <NUM> (<FIG>) of the above-described embodiment, the controller <NUM>' causes a pullback of the reciprocating screw <NUM> of internal layer material injection unit <NUM> to actively occur, in the sense that the injection actuator <NUM> actively pulls back the screw. In some embodiments, the pullback may be a passive versus active pullback. In a passive pullback, plastic pressure of the internal layer material <NUM> downstream of the screw <NUM> is used to "push" the screw <NUM> back. Such a passive pullback may for example be caused to occur through appropriate opening of valves at the injection actuator <NUM> so that the bore-side pressure PB is lowered sufficiently for the desired pullback to result.

It will be appreciated that the GUI <NUM> illustrated in <FIG> may vary between embodiments. For example, alternative GUIs may differently arrange the displayed user interface constructs, e.g. across multiple screens, menus, or frames.

In the embodiments described hereinabove, the detecting of a physical parameter indicative of post-pullback pressure in operation <NUM> is performed with the surface layer material injection unit <NUM> and the internal layer material injection unit <NUM> in fluid communication with one another (i.e. before either of valves <NUM> or <NUM> of <FIG> is closed). In some embodiments, the detecting may occur immediately after one of the valves, e.g. valve <NUM>, is closed, presuming that the value of the detected parameter will briefly persist after the fluid communication has been severed. However, the reliability of such embodiments may be lower than in embodiments in which the detecting is performed before fluid communication between the surface layer material injection unit <NUM> and the internal layer material injection unit <NUM> is severed.

The above-described molding machines <NUM> and <NUM>' are both for molding multilayer articles that are preforms. In alternative embodiments, the molding machine may be intended for molding other types of multilayer articles, e.g. other types of containers or closures such as lids.

Claim 1:
An injection molding machine (<NUM>') for molding a multilayer article (<NUM>), comprising:
a coinjection nozzle (<NUM>) having a surface layer material channel (<NUM>, <NUM>) and an internal layer material channel (<NUM>);
a surface layer material injection unit (<NUM>);
an internal layer material injection unit (<NUM>);
a mold cavity (<NUM>); and
a controller (<NUM>') operable to:
cause the surface layer material injection unit to commence injecting a surface layer material (<NUM>) into the mold cavity (<NUM>) via the surface layer material channel; then
cause the internal layer material injection unit to commence injecting an internal layer material (<NUM>) into the mold cavity via the internal layer material channel; then
during application by the surface layer material injection unit of a hold pressure upon the surface layer material in the surface layer material channel and with the surface layer material injection unit and the internal layer material injection unit in fluid communication with one another via the surface layer material channel and internal layer material channel, cause a pullback stroke to occur at the internal layer material injection unit for reducing a pressure of the internal layer material; then
after a delay interval, detect at least one physical parameter indicative of a post-pullback pressure of the internal layer material at the internal layer material injection unit; and
generate an indicator of pullback effectiveness based on a relationship of the post-pullback pressure indicated by the at least one physical parameter and a threshold pressure (PT).