Patent Description:
A molding apparatus 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 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 material simultaneously with an annular stream of an internal layer material sandwiched between the inner and outer streams. The surface layer material may for example be polyethylene terephthalate (PET), and the internal layer material may for example comprise a barrier material (e.g. an oxygen scavenger material) suitable for protecting subsequent contents of the molded article from outside 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 maximize a degree of control over the placement within the molded article of the internal layer material and to make the edges the internal layer material as well-defined or "crisp" as possible within the encapsulating surface material. Inaccurately placed, poorly defined, uneven, or thin leading or trailing edges of internal layer material may be undesirable, e.g. for aesthetic reasons or for reasons of cost. In respect of the latter, it may be cost-effective to limit the use of internal layer material as much as possible, since the internal layer material may be more expensive that the surface layer material.

<CIT> and <CIT> both describe multilayer molding systems in which an internal layer is supplied during only part of the injection process.

According to one aspect of the present disclosure, there is provided a method of coinjection molding a multilayer article having a multi-segment internal layer, comprising: injecting a surface layer material into a mold cavity from at least one of an inner outlet and an outer outlet of a multi-channel nozzle; and intermittently injecting an internal layer material into the mold cavity from an intermediate outlet of the multi-channel nozzle, the intermediate outlet being between the inner and outer outlets of the multi-channel nozzle, wherein the intermittent injecting of the internal layer material is controlled, at least in part, by intermittent opening and closing of the intermediate outlet, wherein the intermittent injecting of the internal layer material comprises: closing the intermediate outlet; pre-compressing the internal layer material upstream of the closed intermediate outlet; and then forming each of a plurality of internal layer segments of the multilayer article by: opening the intermediate outlet of the multi-channel nozzle to release a stream of internal layer material; and then closing the intermediate outlet of the multi-channel nozzle to terminate the stream of the internal layer material.

The method may further comprise, for each of the plurality of internal layer segments of the multilayer article: upon the opening the intermediate outlet, activating an upstream injection unit to commence injection of the internal layer material from the intermediate outlet; and upon the closing the intermediate outlet, deactivating the upstream injection unit.

In some embodiments, a first one of the plurality of internal layer segments has a first axial extent and a second one of the plurality of internal layer segments has a second axial extent less than the first axial extent. In such embodiments, the forming of the first and second internal layer segments may comprise releasing the internal layer material from the intermediate outlet for first and second durations respectively, wherein the first duration is longer than the second duration.

In some embodiments, a first one of the plurality of internal layer segments has a first thickness and a second one of the plurality of internal layer segments has a second thickness less than the first thickness. In such embodiments, the opening of the intermediate outlet may comprise, for the forming of the first internal layer segment of the first thickness, fully opening the intermediate outlet, and for the forming of the second internal layer segment of the second thickness, only partially opening the intermediate outlet.

In some embodiments, the injecting of the surface layer material into the mold cavity comprises: before the intermittent injecting of the internal layer material, injecting the surface layer material into the mold cavity from both of the inner outlet and the outer outlet of the multi-channel nozzle; and during the intermittent injecting of the internal layer material, injecting the surface layer material into the mold cavity from only the outer outlet of the multi-channel nozzle with the inner outlet in a closed state.

In some embodiments, the multi-channel nozzle comprises a reciprocable valve stem, each of the intermediate and outer outlets comprises an inwardly facing annular outlet, and the intermittent opening and closing of the intermediate outlet comprises reciprocating the valve stem between a first position in which the valve stem does not block either of the intermediate or outer outlets and a second position in which the valve stem blocks the intermediate outlet but does not block the outer outlet.

In another aspect of the present disclosure, there is provided an apparatus for coinjection molding a multilayer article having a segmented internal layer, the apparatus comprising: a mold cavity defined within a mold; a multi-channel coinjection nozzle having inner and outer outlets, each of the inner and outer outlets for injecting a surface layer material into the mold cavity, and an intermediate outlet between the inner and outer outlets for injecting an internal layer material into the mold cavity; and a controller configured to cause the apparatus to: inject the surface layer material into the mold cavity from at least one of the inner outlet and the outer outlet of the multi-channel coinjection nozzle; and intermittently inject the internal layer material into the mold cavity from the intermediate outlet at least in part by intermittently opening and closing the intermediate outlet, each discrete injection of the internal layer material for forming a respective one of a plurality of discrete internal layer segments of the multilayer article, wherein the controller is configured to control the apparatus to intermittently inject the internal layer material by: closing the intermediate outlet; pre-compressing the internal layer material upstream of the closed intermediate outlet; and then forming each of a plurality of internal layer segments of the multilayer article by: opening the intermediate outlet of the multi-channel nozzle to release a stream of internal layer material; and then closing the intermediate outlet of the multi-channel nozzle to terminate the stream of the internal layer material. In such embodiments, the controller may be configured to further control the apparatus to, for each of the multiple internal layer segments of the multilayer article: upon the opening the intermediate outlet, activate an upstream injection unit to commence injection of the internal layer material from the intermediate outlet; and upon the closing the intermediate outlet, deactivate the upstream injection unit.

In some embodiments, a first one of the plurality of internal layer segments has a first axial extent, a second one of the plurality of internal layer segments has a second axial extent less than the first axial extent, and the forming of the first and second internal layer segments comprises releasing the internal layer material from the intermediate outlet for first and second durations respectively, wherein the first duration is longer than the second duration.

In some embodiments, a first one of the plurality of internal layer segments has a first thickness, a second one of the plurality of internal layer segments has a second thickness less than the first thickness, and the controller is configured to, for the first internal layer segment of the first thickness, fully open the intermediate outlet, and for the second internal layer segment of the second thickness, only partially open the intermediate outlet.

In some embodiments, the controller is configured to control the injecting of the surface layer material into the mold cavity by: before the intermittent injecting of the internal layer material, injecting the surface layer material into the mold cavity from both of the inner outlet and the outer outlet of the multi-channel nozzle; and during the intermittent injecting of the internal layer material, injecting the surface layer material into the mold cavity from only the outer outlet of the multi-channel nozzle with the inner outlet in a closed state.

In some embodiments, the multi-channel nozzle comprises a reciprocable valve stem, each of the intermediate and outer outlets comprises an inwardly facing annular outlet, and the intermittently opening and closing of the intermediate outlet comprises reciprocating the valve stem between a first position in which the valve stem does not block either of the intermediate or outer outlets and a second position in which the valve stem blocks the intermediate outlet but does not block the outer outlet.

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" or "above" 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 use.

<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 example 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>. The first injection unit <NUM> is for plasticizing (melting) and injecting a surface layer material, which may for example be PET. The second injection unit <NUM> is for plasticizing and injecting an internal layer material, which may for example be a barrier or oxygen-scavenging material, or a PET material with a colorant additive. Both the surface and internal layer materials may be considered as forms of molding material. As will be appreciated, the different materials will be used to form different layers of the preform <NUM>, respectively. Each injection unit may for example utilize a reciprocating screw or plunger for injecting molding material into mold cavities.

A controller <NUM> 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. Control instructions may be entered by a human operator via human-machine interface (HMI), which may for example be a multi-function touchscreen <NUM> that forms part of, or is coupled to, the controller <NUM>. The controller <NUM> may for example be a Beckhoff® model CP22xx Panel PC with Intel® Core™ i processor, or another model of industrial PC.

A hot runner (not shown) 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.

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 segments <NUM>, <NUM>, and <NUM> which are comprised of the internal layer material <NUM>. The segments <NUM>, <NUM>, and <NUM> of internal layer material <NUM> are entirely encapsulated by the surface layer material <NUM> in the present embodiment. Each of the segments <NUM>, <NUM> and <NUM> of the illustrated embodiment is substantially annular, with segment <NUM> being flared, i.e. wider at the bottom of <FIG> than at the top, by virtue of the flaring of the preform body <NUM> immediately adjacent to neck finish <NUM> (i.e. immediately above neck finish <NUM> in <FIG>). In some embodiments, the placement and number of the segments is dictated primarily by aesthetic considerations.

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 mold 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 nozzle <NUM> of the hot runner. <FIG> depicts a portion of the hot runner 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>.

Valve stem <NUM> is used to control the flow of molding material into the molding 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 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.

As will be described, the controller <NUM> moves the valve stem <NUM> between the various positions shown in <FIG> in a particular sequence during an injection molding cycle to facilitate injection molding of the preform <NUM> of <FIG> with its encapsulated internal layer segments <NUM>, <NUM>, and <NUM>.

Operation <NUM> of the molding machine <NUM> for coinjection of a multilayer molded article with a segmented internal layer 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> and <FIG>. <FIG> depicts a graph <NUM> showing the positions of three moving components of the molding machine <NUM> over the course of a single injection molding cycle: the valve stem <NUM>, the injection unit <NUM>, and injection unit <NUM>. For the latter two components, the term "position" refers to the position of the driving element used to drive melted molding material, such as a plunger of a shooting pot or a reciprocating screw within an extruder. <FIG> depicts a graph <NUM> showing the velocity of the surface layer material and of the internal layer material over the course of a single injection molding cycle. Reference will also be made to <FIG>, which schematically depict, in longitudinal cross section, the nozzle <NUM> of <FIG> and an associated mold cavity <NUM> at various stages of formation of a preform <NUM> during a single injection molding cycle.

Referring to <FIG>, at time T0, which represents 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, at time T0, the distal end of intermediate channel <NUM>, immediately upstream of intermediate outlet <NUM>, contains a small amount of surface layer material <NUM>. This is despite the fact that the intermediate channel <NUM> is intended to flow internal layer material <NUM> from injection unit <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>, the positions of the valve stem <NUM>, first injection unit <NUM> for injecting surface layer material <NUM>, and second injection unit <NUM> for injecting internal layer material <NUM>, are depicted by plots <NUM>, <NUM>, and <NUM> respectively. At time T0, the valve stem <NUM> is at Position <NUM>, consistently with <FIG> (described above). Moreover, at time T0, each of the injection units <NUM> and <NUM> is in a ready position for injecting a shot of its respective molding material. In graph <NUM>, the plot <NUM> for injection unit <NUM> is located below the plot <NUM> for injection unit <NUM>. These relative locations reflect the generally smaller amount of internal layer material injected in a single molding cycle by the former compared to the amount of surface layer material injected by the latter in the present embodiment. For clarity, plots <NUM> and <NUM> of <FIG> share a common scale on the vertical "position" axis, whereas plot <NUM> does not share a common scale with either of plots <NUM> or <NUM> in the illustrated embodiment. In the graph of <FIG>, a downward trend of plot <NUM> or <NUM> over time indicates positive movement of the respective driving element, i.e. injection of the respective molding material, whereas an upward trend indicates negative (reverse) movement thereof.

Referring to <FIG>, at time T0, the velocity of each of the surface layer material and the internal layer material is zero, i.e. the driving elements of the respective injection units are stationary and no molding material flows within the nozzle <NUM>. For clarity, the present disclosure refers interchangeably to the velocity of an injection unit and the velocity of the (corresponding) molding material.

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> is commenced. The surface layer material <NUM> is injected via both the inner and outer outlets <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 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.

Referring again to graph <NUM> of <FIG>, it will be appreciated that operation <NUM> of <FIG> commences just after time T0 and continues to time T3. Once both of the inner and outer outlets <NUM> and <NUM> have been opened by retraction of valve stem <NUM> to Position <NUM>, Injection of the surface layer material <NUM> commences at time T2. Injection of surface layer material by unit <NUM> is represented by the downward trend of the plot <NUM> in <FIG>. It will be appreciated that, in plots <NUM> and <NUM> of <FIG>, the lower the position on the vertical axis, the greater the amount of injected molding material. Referring to <FIG>, the velocity of the surface layer material <NUM>, represented by plot <NUM>, increases at time T2. It will be appreciated that, although the increase is depicted in plot <NUM> as occurring instantaneously (for simplicity and for consistency with <FIG>), the increase may actually occur over a short time interval. The same is true for other changes in velocity of the surface layer material <NUM> depicted in <FIG>. No internal layer material injection is performed at this stage, as reflected by the zero velocity of plot <NUM> in <FIG>, and the zero slope of the plot <NUM> representing the position of injection unit <NUM> in <FIG>, through time T4.

The state of the nozzle <NUM> and mold cavity <NUM> during operation <NUM> of <FIG> are schematically 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 "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> in the previous injection molding cycle, using a mechanism that will be described below.

Referring back to <FIG>, in a subsequent operation <NUM>, controller <NUM> causes valve stem <NUM> to move from Position <NUM> to Position <NUM> as shown in <FIG>. Operation <NUM> occurs from time T4 to just before time T5 (see <FIG> and <FIG>). In Position <NUM>, the valve stem <NUM> physically blocks (i.e. has closed) both the inner outlet <NUM> and the intermediate outlet <NUM>. Closure of inner outlet <NUM> ceases the flow of surface layer material <NUM> from inner channel <NUM>. However, the surface layer material <NUM> continues to flow from the still-open outer outlet <NUM>. In fact, the flow rate of material <NUM> from outer outlet <NUM> will increase upon the closure of inner outlet <NUM> because the overall the volumetric flow rate of material <NUM> flowing into the cavity (i.e. speed of injection unit <NUM>) remains unchanged. This is in view of the constant velocity of the driving element of injection unit <NUM> during operation <NUM>.

Operation <NUM> additionally comprises pre-compressing the internal layer material <NUM> in nozzle <NUM>. In the present embodiment, pre-compression is performed by the injection unit <NUM>, under control of controller <NUM>, after the intermediate outlet <NUM> has been closed.

The rationale for pre-compressing the internal layer material <NUM> is primarily twofold. Firstly, the inventor has noted that pre-compression combined with a physical unblocking of the intermediate outlet <NUM> results in a well-defined leading edge of the internal layer material <NUM>, which may be desirable for the internal layer as earlier noted. Secondly, the lag time between instructing internal layer material flow and actual flow may be shorter with pre-compression and physical unblocking than it might otherwise be, e.g. if the injection unit <NUM> were solely responsible for initiating flow. In the latter case, lag time between instructing flow and actual flow may result from various factors, such as melt compressibility, bends and/or constrictions in the hot runner manifold between the injection unit <NUM> and nozzle <NUM>, and other reasons. By performing pre-compression in parallel with the initial injection of surface layer material in operation <NUM>, the benefit of a reduced lag time may be enjoyed without the penalty of added delay, e.g. as might result if pre-compression were performed before the commencement of molding material injection. Pre-compression of the internal layer material <NUM> may also decrease the duration of injection of the internal layer material, which may facilitate shorter mold cycle times. In some embodiments, there may be some pre-compression of the surface layer material in addition to the internal layer material, e.g. to minimize cycle times.

In <FIG>, pre-compression of the internal layer material is represented by the downward trend (negative slope) of the plot <NUM> representing the position of injection unit <NUM> between times T4 and T5 while the intermediate outlet <NUM> is closed (i.e. with valve stem <NUM> in Position <NUM>).

In a subsequent operation <NUM> (<FIG>), controller <NUM> opens intermediate outlet <NUM> by causing valve stem <NUM> to move from Position <NUM> to Position <NUM> as shown in <FIG>. Operation <NUM> occurs from time T5 to just before time T6 (see <FIG> and <FIG>). Opening the intermediate outlet <NUM> (<FIG>) releases a stream of the pre-compressed internal layer material <NUM> into mold cavity <NUM>, with a well-defined leading edge, and thereby initiates injection of an internal layer segment. 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 outlet <NUM>.

Although not expressly depicted in <FIG> (or any subsequently referenced drawings), when the valve stem <NUM> is in Position <NUM> as shown in <FIG>, the internal layer material <NUM> entering mold cavity <NUM> may be biased somewhat closer to the core <NUM> side of mold cavity <NUM> than to the cavity side <NUM> within the cross-sectional widthwise extent of the preform wall. The reason is that inner outlet <NUM> remains closed, preventing any surface layer material <NUM> from flowing centrally into combination area <NUM> and through the middle of gate area <NUM> into mold cavity <NUM>. Nevertheless, the internal layer material <NUM> entering mold cavity <NUM> remains encapsulated by the surface layer material <NUM> of the preform wall. The reason is that at least some surface layer material <NUM> from the initial injection of operation <NUM> has by then coated and adhered to the core <NUM> side of the cavity <NUM>. The degree of bias may impact upon the aesthetic appearance of the molded container into which the preform may be subsequently blow-molded, and may accordingly be chosen on an application-specific basis.

Referring again to <FIG>, it can be seen from the negative slope of plot <NUM> that the driving element of injection unit <NUM> advances linearly between time T5 and T6, corresponding with the injection of internal layer material <NUM> into the mold cavity at a steady rate during this interval. In <FIG>, it can be seen that the velocity of the driving element during injection operation <NUM> is greater than the velocity of the driving element during the pre-compression time interval T4 to T5.

In a subsequent operation <NUM> (<FIG>), controller <NUM> causes valve stem <NUM> to move from Position <NUM> back to Position <NUM> as shown in <FIG>. This action closes the intermediate outlet <NUM> and thereby terminates the stream of internal layer material <NUM>, which in turn completes injection of the current internal layer segment. Some minor "tailing" (thinning or tapering) of the trailing edge of the segment, which is not expressly depicted in <FIG> but is shown in <FIG>, may occur, depending upon factors such as the speed at which the valve stem <NUM> is moved during closure of outlet <NUM> and the viscosity of the material <NUM>. Surface layer material <NUM> to continue to flow from outer outlet <NUM>, which remains open. Operation <NUM> occurs from time T6 to just before time T7 (see <FIG> and <FIG>). In <FIG>, it can be seen that the velocity of the internal layer material <NUM> during time interval T6 to T7 is zero.

The inventor has determined that physically interrupting (mechanically blocking) the trailing edge of the internal layer material results in a generally well-defined trailing edge, with the exception that some minor tailing (i.e. a relatively short taper on the trailing edge) may occur. In contrast, the inventor has determined that merely stopping injection at the injection unit <NUM>, without closing the intermediate outlet <NUM>, tends to leave a long, tapered edge of internal layer material. Such a long, tapered edge may be unsatisfactory, e.g., because it differs in appearance from the generally blunt, rounded leading edge of the segment (see <FIG>) or may bridge adjacent internal layer segments. Bridging may be undesirable for aesthetic reasons, e.g. if the intended effect is for each segment to be distinct.

It will be appreciated that operations <NUM> and <NUM> of <FIG> collectively result in the formation of the first internal layer segment <NUM> (see <FIG>). Because surface layer material <NUM> continues to flow into the mold cavity <NUM> from outer outlet <NUM>, the newly formed annular segment <NUM> is effectively pushed or urged axially about the core <NUM> towards the distal end of the mold cavity <NUM> (downwardly in <FIG>).

Referring again to <FIG>, it can be seen that, between time T6 and time T7, injection unit <NUM> suspends injection of internal layer material when the intermediate outlet <NUM> has closed. As such, the velocity of the internal layer material <NUM> between time T6 and time T7 is shown to be zero in <FIG>. As will become apparent, injection by unit <NUM> shall be recommenced when the intermediate outlet <NUM> reopens for injection of each subsequent internal layer segment.

Referring back to <FIG>, with formation of the first internal layer segment <NUM> having been completed, operations <NUM> and <NUM> are subsequently repeated, in sequence, once for each additional internal layer segment <NUM>, <NUM> of preform <NUM> (see <FIG>). Referring to <FIG> and <FIG>, the first repeat of operations <NUM> and <NUM> for forming the next internal layer segment <NUM> occurs between time T7 and just before time T8 and between time T8 and just before T9, respectively. The second repeat of operations <NUM> and <NUM> for forming the last internal layer segment <NUM> occurs between time T9 to just before T10 and between time T10 and just before T11, respectively. <FIG> and <FIG> depict the outcome of the first repeat of operations <NUM> and <NUM> respectively, whereas <FIG> and <FIG> depict the outcome of second repeat of operations <NUM> and <NUM> respectively. As shown in <FIG>, when the intermediate outlet <NUM> is closed, injection unit <NUM> suspends injection of internal layer material, between time T8 and time T9 and again between time T10 and time T11.

It is noted that, at or near time T11, controller <NUM> causes injection unit <NUM> to reduce the rate of surface layer material injection (see <FIG>). This is done because, by time T11, the mold cavity <NUM> has been nearly filled with molding material. A slower rate of surface layer material injection continues past time T14, with the rationale of filling any gaps that may form in the mold cavity <NUM> as the molded article (preform <NUM>) cools, shrinks, and hardens over time. Referring to <FIG>, it can be seen that the velocity of the surface layer material injection begins to slow at or near time T11. Although not expressly depicted, the velocity may change at irregular intervals during this "hold phase," in response to irregular contractions of the preform <NUM> within the mold as it cools, e.g. if the injection unit <NUM> is operated on a pressure control versus velocity control basis.

At operation <NUM> (<FIG>), the controller <NUM> reopens the intermediate outlet <NUM> by moving the valve stem <NUM> from Position <NUM> to Position <NUM>. Operation <NUM> occurs from time T11 to just before time T12 in <FIG> and <FIG>. As illustrated in the schematic diagram of <FIG>, with the intermediate outlet <NUM> open and with surface layer material <NUM> still flowing (albeit slowly) from outer outlet <NUM>, the controller <NUM> causes the internal layer material injection unit <NUM> to pull back slightly. In <FIG>, the pullback is evidenced by the segment of the plot <NUM> between times T11 and T12 having an upward trend (positive slope), i.e. showing reverse movement of the driving element of injection unit <NUM>. In <FIG>, the pullback is evidenced by the negative velocity of the internal layer material (plot <NUM>) between times T11 and T12, i.e. by movement of the internal layer material <NUM> in the upstream rather than downstream direction within intermediate channel <NUM>. The pullback has the effect of drawing a small amount of surface layer material <NUM> into the distal end of intermediate channel <NUM>, which is done for the reasons mentioned hereinabove.

In the present embodiment, the controller <NUM> causes the internal layer material injection unit <NUM> to hold its position steady between times T12 and T13. This is done to give internal layer material time to flow into the intermediate channel <NUM>. The reverse movement of the driving element between times T13 and T14 is for the purpose of drawing a new shot of internal layer material, from an upstream source, into injection unit <NUM> for the next molding cycle. In the present embodiment, a valve at or near the outlet of the injection unit <NUM> (not depicted) is closed before time T13 to facilitate this refilling of injection unit <NUM>, particularly in view of the open state of the intermediate outlet <NUM> at that time (valve stem at position <NUM>). The rationale for holding the outer outlet <NUM> open from time T12 to just before time T15 is top permit "packing" of the mold cavity with additional surface layer material, as the freshly molded preform cools and shrinks within the mold.

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 its state as shown in <FIG>.

In some embodiments, the injection unit <NUM> may adjust the pressure of the internal layer material <NUM> to different levels at different stages of the molding cycle. Such operation would entail at least one pressure-sensing transducer and may for example be controlled by suitable programming of controller <NUM>.

In one example, the pressure of the internal layer material <NUM> may be increased to a higher level during the injection operation <NUM> and decreased to a lower level during subsequent operation <NUM> (<FIG>). A possible rationale for these distinct pressure settings may be energy conservation or reducing a risk of internal layer material leaks at the intermediate outlet <NUM> of <FIG>, as components of the nozzle <NUM> wear over time.

In other embodiments, the controller <NUM> may be programmed to keep the pressure of the internal layer material <NUM> in injection unit <NUM> at a predetermined level even as segments are being formed during operations <NUM> and <NUM>. <FIG> and <FIG> illustrate the operation <NUM> (<FIG>) of such an embodiment. For the purposes of <FIG> and <FIG>, it is presumed that the same molding machine hardware is being used to mold preforms <NUM>, albeit using pressure-based control for injection unit <NUM>.

<FIG> depicts a graph <NUM>, similar to graph <NUM> of <FIG>, showing the positions of the valve stem <NUM>, the injection unit <NUM>, and injection unit <NUM> of molding machine <NUM> over the course of a single injection molding cycle. <FIG> depicts a graph <NUM>, similar to graph <NUM> of <FIG>, showing the velocity of the surface layer material and of the internal layer material over the course of that injection molding cycle. For clarity, the conventions used in <FIG> and <FIG> and the associated description above are maintained in <FIG> and <FIG> and the following description.

Referring to <FIG>, the present embodiment preforms the first operation <NUM> in the same manner as the above-described embodiment (see <FIG> and <FIG>).

In operation <NUM> (<FIG>), controller <NUM> causes valve stem <NUM> to move from Position <NUM> to Position <NUM> to close both the inner outlet <NUM> and the intermediate outlet <NUM>, in the same way as was described above. However, the manner in which the driving element of injection unit <NUM> is controlled in order to pre-compress the internal layer material <NUM> in nozzle <NUM> is different from that of the previously described embodiment. In particular, rather than causing the driving element to advance linearly, the controller <NUM> causes the driving element of injection unit <NUM> to advance non-linearly in a suitable manner for achieving and maintaining a predetermined target pressure of the internal layer material <NUM>.

In particular, immediately after time T4 of the depicted example, the driving element velocity increases non-linearly, first slowly and then progressively more quickly, until the desired pre-compression pressure is reached approximately midway between times T4 and T5. Thereafter, the velocity of the driving element is reduced to zero, quickly at the outset and then progressively more slowly, in a converse manner to the velocity increase. The non-linear velocity increase and decrease are shown in plot <NUM> of <FIG> between times T4 and T5.

In the subsequent operation <NUM> (<FIG>), which occurs from occurs from time T5 to just before time T6 of <FIG> and <FIG>, controller <NUM> opens intermediate outlet <NUM> to initiate formation of an internal layer segment. This action releases the pre-compressed internal layer material <NUM> into the molding cavity <NUM> via the gate area <NUM> of the nozzle <NUM>, as shown in <FIG>. The release of internal layer material <NUM> into cavity <NUM> results in a pressure drop of the material <NUM> in injection unit <NUM> shortly after time T5. Sensing this drop, the controller <NUM> advances the driving element of injection unit <NUM> with a view to restoring the target pressure. The velocity of the driving element increases non-linearly as during pre-compression operation <NUM>. However, in operation <NUM>, the velocity increase occurs more quickly, and the maximum velocity is greater, than during the preceding operation, in order to compensate for the outflow of internal layer material <NUM>. Once the target pressure is reached, the velocity decreases in a converse, non-linear manner, as shown in plot <NUM> of <FIG>.

The subsequent operation <NUM> is performed in substantially the same way as in the earlier-described embodiment.

With formation of a first internal layer segment <NUM> having been completed, operations <NUM> and <NUM> are subsequently repeated, in sequence, once for each additional internal layer segment <NUM>, <NUM> of preform <NUM> (see <FIG>). Referring to <FIG> and <FIG>, the first repeat of operations <NUM> and <NUM> for forming the next internal layer segment <NUM> occurs between time T7 and just before time T8 and between time T8 and just before T9, respectively. The second repeat of operations <NUM> and <NUM> for forming the last internal layer segment <NUM> occurs between time T9 to just before T10 and between time T10 and just before T11, respectively.

At operation <NUM> (<FIG>), the controller <NUM> reopens the intermediate outlet <NUM> by moving the valve stem <NUM> from Position <NUM> to Position <NUM>. Operation <NUM> occurs from time T11 to just before time T12 in <FIG> and <FIG>. As illustrated in the schematic diagram of <FIG>, with the intermediate outlet <NUM> open and with surface layer material <NUM> still flowing from outer outlet <NUM>, the controller <NUM> causes the internal layer material injection unit <NUM> to pull back slightly. In <FIG>, the pullback is evidenced by the segment of the plot <NUM> between times T11 and T12 having an upward trend (positive slope), i.e. showing reverse, non-linear movement of the driving element of injection unit <NUM>. In <FIG>, the pullback is evidenced by the negative velocity of the internal layer material (plot <NUM>), which changes non-linearly between times T11 and T12 as depicted. In the result, a small amount of surface layer material <NUM> is drawn into the distal end of intermediate channel <NUM>.

In the present embodiment, the controller <NUM> causes the internal layer material injection unit <NUM> to hold its position steady between times T12 and T13. This is done to give internal layer material time to flow into the intermediate channel <NUM>. The reverse movement of the driving element between times T13 and T14 is for the purpose of drawing in a new shot of internal layer material, from an upstream source, into injection unit <NUM> for the next molding cycle.

As the freshly molded preform <NUM> cools, hardens, and shrinks over time, gaps may form within the mold cavity <NUM>. The filling of any such gaps with additional surface layer material <NUM> from outer outlet <NUM> may result in a decrease in pressure of that material in the upstream injection unit <NUM>. If the pressure falls below a threshold, the controller <NUM> will automatically activate the driving element of injection unit <NUM> to restore and/or maintain the target pressure. In view of the possibly irregular timing of the gap formation during this interval, the surface layer injection unit <NUM> may have an irregular velocity profile after time T14, as shown in <FIG>.

It will be appreciated that operation of the example embodiments of molding machine <NUM> described above represents a balancing of various, in some cases competing, interests, such as minimizing molding cycle time and promoting well-defined internal layer material segments.

More specifically, to minimize cycle time, physical blocking of internal layer material flow is used to terminate segments <NUM>, <NUM>, and <NUM> (operation <NUM>). It has been found that the time required to terminate the flow of internal layer material by physical blocking is less than the time required to achieve the same result using pullback at the injection unit <NUM>. Similarly, pre-compression of the internal layer material in parallel with an initial injection of only surface layer material (operation <NUM>) may facilitate faster internal layer material flow when the intermediate outlet <NUM> is opened than if no such pre-compression were performed. The initial injection of the surface layer material <NUM> through inner outlet <NUM> and outer outlet <NUM> in operation <NUM> may also permit faster material flow in comparison to using only the outer outlet <NUM> during this stage.

Moreover, the combination of pre-compression (operation <NUM>) and mechanical opening of intermediate outlet <NUM> (operation <NUM>) to initiate each internal layer segment has been found to promote a well-defined leading edge of at least internal layer segments <NUM> and <NUM>. It is noted that the leading edge of the first segment <NUM> of a molding cycle may be somewhat less well-defined, e.g. may be "wavy" circumferentially. If present, the less well-defined leading edge of the first segment <NUM> may be attributable to an inconsistent amount of surface layer material <NUM> pulled back into the distal end of the annular intermediate channel <NUM> at the conclusion of the previous molding cycle (see <FIG>).

Conversely, the use of mechanical closure (physical blocking) of the intermediate outlet <NUM> to terminate each segment has been found to yield a well-defined trailing edge of internal layer material <NUM>, e.g. in the sense that each segment has limited circumferential waviness and/or a reasonably short taper with minimal risk of bridging to the following segment.

Still other aspects of the machine operation described above promote long-term reliability. For example, operation <NUM> (<FIG>) for pulling back the surface layer material into the distal end of the intermediate channel <NUM> permits use of nozzle <NUM> even when the valve stem <NUM> or intermediate outlet <NUM> begin to wear. In particular, even if the seal between these features becomes imperfect over time due to wear, whatever material may leak out between them in operations <NUM> or <NUM> will be surface layer material <NUM> rather than intermediate layer material <NUM>, so the neck finish region or intra-segment areas of the molded article <NUM> will not be unduly comprised with the latter material.

Various alternative embodiments are contemplated.

In alternative embodiments, the nozzle <NUM> may be controlled to produce molded articles having a number, axial length, thickness, and/or placement of internal layer segments that is/are different from what is shown in <FIG> above. <FIG> depict a number of example alternative preform designs.

Referring first to <FIG>, a first alternative preform <NUM> comprises eleven internal layer segments <NUM> of substantially uniform thickness and relatively short axial extent. To create such a preform <NUM>, the valve stem <NUM> may be made to reciprocate between Positions <NUM> and <NUM> in operations <NUM> and <NUM> more quickly than for preform <NUM> by suitable programming of controller <NUM>.

Referring next to <FIG>, the nozzle <NUM> may be alternatively controlled to mold a second alternative preform <NUM> comprising internal layer segments of different lengths (i.e. axial extents). For example, the preform <NUM> comprises two internal layer segments <NUM>, one at each end of the preform <NUM>, each having substantially the same axial extent L1. The preform <NUM> further comprises three internal layer segments <NUM>, each having a second axial extent L2 smaller than the first. The axial extent of each internal layer segment may for example be set by programming the controller <NUM> to effect a suitable duration of releasing the internal layer material stream (i.e. the time interval between the opening and the subsequent closing of the intermediate outlet <NUM>) in operations <NUM> and <NUM>, with longer durations generally resulting in segments of longer axial extents. In the example preform <NUM> of <FIG>, all of the segments <NUM>, <NUM> have a substantially uniform thickness, but this is not expressly required.

Some alternative preform designs comprise multiple thicknesses of internal layer segments, e.g. for aesthetic reasons. In <FIG>, preform <NUM> defines a first type of segment <NUM> of a first thickness T1 and a second type of segment <NUM> of a second thickness T2 smaller than the first. In preform <NUM>, there are two instances of segment <NUM>, one on either side of a single instance of segment <NUM>. In <FIG>, the situation is reversed: preform <NUM> defines two internal layer segments <NUM> of a first thickness T2 and a third segment <NUM> of a second thickness T1 greater than the first, disposed therebetween.

To control the thickness of each internal layer segment during coinjection, the controller <NUM> may open the intermediate outlet <NUM> to different extents (<FIG>). For example, in one alternative embodiment, a new stop may be defined approximately midway (vertically in <FIG>) between stops <NUM> and <NUM>. When the end <NUM> of valve stem <NUM> is positioned at the new stop, the intermediate outlet <NUM> will be only partially open. Injection by unit <NUM> will cause internal layer material <NUM> to be discharged from the partially open intermediate outlet <NUM> in a thinner stream than when the intermediate outlet <NUM> is fully open as earlier described in conjunction with operation <NUM>. In general, each stage of the back and forth movement of the valve stem <NUM> can be performed using different speeds, positioning, and/or timing to control internal material segment placement, thickness, and/or length within the molded article.

It will be appreciated that, in the pullback operation <NUM> (<FIG>), the valve stem <NUM> could be positioned at Position <NUM> rather than Position <NUM>. The latter position may however be considered preferable for reasons of energy conservation and/or injection molding cycle speed. The reason is that the distance of travel between Position <NUM> and each of the preceding Position <NUM> of operation <NUM> and the succeeding Position <NUM> of operation <NUM> is smaller than it would have been if operation <NUM> were performed with the valve stem <NUM> at Position <NUM>.

It will also be appreciated that the pullback performed in operation <NUM> of <FIG> is not mandatory in all embodiments. For example, in some embodiments, the initial injection of only surface layer material <NUM> in operation <NUM> may be effected using only the outer channel <NUM>, with the valve stem <NUM> in Position <NUM> (<FIG>). In that case, the risk of internal layer material <NUM> bleeding from intermediate outlet <NUM> during the initial injection of surface layer material may be limited or avoided by fact that the outlet <NUM> is closed by the valve stem <NUM>. Indeed, because such mechanical closure of intermediate outlet <NUM> is possible using valve stem <NUM> and is indeed performed in operation <NUM>, it may be considered counterintuitive to utilize pullback in operation <NUM> in the same embodiment. To the extent that pullback is not performed in operation <NUM> in favor of mechanical closure of intermediate outlet <NUM> in operation <NUM>, pre-compression of the internal layer material <NUM> could be commenced earlier than described above, e.g. in operation <NUM> rather than operation <NUM>.

Fundamentally, alternative embodiments of nozzle <NUM> could be designed to mechanically open and close the inner, intermediate, and/or outer outlets in ways other than by reciprocation of a cylindrical valve stem in relation to those outlets. For example, one or more of the outlets could be implemented as a segmented annulus, with valve stem having corresponding flutes defined therein. In such implementations, an outlet could be opened by rotating the valve stem to bring the flutes into alignment with the open sections of the annulus and closed by rotating the valve stem to bring the flutes out of alignment with the open sections.

Claim 1:
A method (<NUM>) of coinjection molding a multilayer article (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a multi-segment internal layer, comprising:
injecting (<NUM>) a surface layer material (<NUM>) into a mold cavity (<NUM>) from at least one of an inner outlet (<NUM>) and an outer outlet (<NUM>) of a multi-channel nozzle (<NUM>); and
intermittently injecting (<NUM>, <NUM>) an internal layer material (<NUM>) into the mold cavity from an intermediate outlet (<NUM>) of the multi-channel nozzle, the intermediate outlet being between the inner and outer outlets of the multi-channel nozzle,
wherein the intermittent injecting of the internal layer material is controlled, at least in part, by intermittent opening and closing of the intermediate outlet;
characterised in that
the intermittent injecting of the internal layer material comprises: closing the intermediate outlet;
pre-compressing (<NUM>) the internal layer material upstream of the closed intermediate outlet; and then
forming each of a plurality of internal layer segments (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) of the multilayer article by:
opening (<NUM>) the intermediate outlet of the multi-channel nozzle to release a stream of internal layer material; and then
closing (<NUM>) the intermediate outlet of the multi-channel nozzle to terminate the stream of the internal layer material.