Machine and method for injection moulding multilayer articles with a high proportion of inner layer material

Abstract

In one aspect, a method of co-injection molding a multi-layer article using a co-injection nozzle having an inner outlet, an outer outlet, and an intermediate outlet between the inner and outer outlets is provided. A skin layer material stream is injected from the intermediate outlet into a mold cavity. As injection proceeds, two inner layer material streams are injected from the inner and outer outlets of the co-injection nozzle, respectively. The two streams sandwich the stream of skin layer material and flow behind the melt front of the skin layer material. The sandwiched stream of skin layer material continues to supply skin layer material to the melt front at least until the melt front approaches a distal end of the mold cavity. The resulting article is substantially or completely encapsulated by an outer layer of skin layer material and contains a high proportion of inner layer material.

Description

Technical Field

[0001] This invention relates to a machine and method for injection molding multilayer articles having a high proportion of inner layer material, and the resulting injection-molded multilayer articles. Background Technology

[0002] Injection molding machines guide a flow of molten molding material (such as molten plastic or resin) through a distribution network (such as a hot runner) for dispensing into a mold via nozzles. The molten molding material can be dispensed or injected into the mold cavity to mold articles with a generally tubular shape, such as preforms suitable for subsequent blow molding into containers (such as plastic beverage bottles). The injected molding material flow can enter the gate of the mold cavity and can flow in a cylindrical shape around the insert-type components of the mold.

[0003] Such multilayer molded articles can be formed using a multi-channel co-injection nozzle having multiple outlets for simultaneously dispensing multiple respective material layers. For example, co-injection nozzles are known to simultaneously dispense internal and external melt flows of a surface layer (or “surface layer”) material, as well as a flow of inner layer (or “core layer”) material sandwiched between the internal and external flows. The surface layer material may, for example, be polyethylene terephthalate (PET), possibly with added colorants. The inner 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). In another example, the inner layer material may be recycled PET.

[0004] It may be necessary to encapsulate the inner layer material within the surface layer material of the resulting molded article. For example, a molded article ultimately used to contain food or beverages may have an inner layer made of a non-food grade material, such as a material made from recycled plastic. Exposure of the inner layer on the inner surface of the container may undesirably expose the contained food or beverage to impurities in the non-food grade material. Exposure of the inner layer on the outer surface of the container may adversely affect the appearance of the container.

[0005] For various reasons, it may be desirable to maximize the proportion of inner layer material in multilayer articles. One reason might be to minimize material costs, such as when the inner layer material is cheaper than the surface layer material. Another reason might be to conserve natural resources, such as when the inner layer material is recycled plastic while the surface layer material is virgin plastic. However, multilayer articles manufactured using conventional co-injection molding techniques often contain only a limited proportion of inner layer material. Summary of the Invention

[0006] According to one aspect of the invention, an injection molding machine for molding multilayer articles is provided, the molding machine comprising: a co-injection nozzle having an internal channel, an external channel, and an intermediate channel terminating at an internal outlet, an external outlet, and an intermediate outlet, the intermediate outlet being between these internal and external outlets; a surface layer material injection unit; an inner layer material injection unit; and a hot runner defining: a first passage for conveying surface layer material from the surface layer material injection unit to the intermediate channel of the co-injection nozzle; and a second passage for conveying inner layer material from the inner layer material injection unit to the internal and external channels of the co-injection nozzle.

[0007] In some embodiments, the injection molding machine further includes a mold cavity associated with a co-injection nozzle; and a controller operable to: cause a surface layer material injection unit to begin injecting a surface layer material flow from the intermediate outlet of the co-injection nozzle into the mold cavity; and then, as the injection of the surface layer material flow from the intermediate outlet proceeds, cause an inner layer material injection unit to inject two corresponding inner layer material flows from the inner and outer outlets of the co-injection nozzle into the mold cavity, the two inner layer material flows sandwiching the surface layer material flow and flowing after the melt front of the surface layer material, such that the sandwiched flow of surface layer material continues to supply surface layer material to the melt front, at least until the melt front approaches the far end of the mold cavity.

[0008] In some embodiments, for example, the controller is operable to cause the inner layer material injection unit to inject at least 50% by volume of the inner layer material of the multilayer article. This amount may be about 54% by volume of the multilayer article. In other non-limiting embodiments, the volume of the inner layer material is less than 50%, and as low as 3%.

[0009] In some embodiments, the controller may also be operable to, at the end of the molding cycle: cause the surface layer material injection unit to apply a holding pressure on the surface layer material; and cause a pull-back stroke at the inner layer material injection unit to reduce the pressure of the inner layer material in the inner and outer channels of the co-injection nozzle, such pressure reduction being sufficient to allow the pressurized surface layer material to flow upstream to each of the distal ends of the inner channel and the distal ends of the outer channel.

[0010] According to another aspect of the invention, a method for molding a multilayer article is provided, the method comprising: providing a co-injection nozzle having an inner outlet, an outer outlet, and an intermediate outlet between the inner outlet and the outer outlet; injecting a surface layer material flow into a mold cavity starting from the intermediate outlet of the co-injection nozzle; and then, as the injection of the surface layer material flow from the intermediate outlet proceeds, injecting two corresponding inner layer material flows from the inner outlet and the outer outlet of the co-injection nozzle into the mold cavity, the two inner layer material flows sandwiching the surface layer material flow and flowing after the melt front of the surface layer material, such that the sandwiched flow of surface layer material continues to supply surface layer material to the melt front, at least until the melt front approaches the far end of the mold cavity.

[0011] In some embodiments, the injection is performed on an amount of inner layer material that is at least 50% by volume of the multilayer article. This amount may be about 54% by volume of the multilayer article. In other non-limiting embodiments, the volume of the inner layer material is less than 50%, and as low as 3%.

[0012] According to another aspect of the invention, a tangible medium storing computer-readable program code is provided, which, when executed by a controller of an injection molding machine having a surface layer material injection unit, an inner layer material injection unit, and a co-injection nozzle having an inner outlet, an outer outlet, and an intermediate outlet between the inner and outer outlets, causes the controller to: cause the surface layer material injection unit to begin injecting a surface layer material flow from the intermediate outlet of the co-injection nozzle into the mold cavity; and then, as the injection of the surface layer material flow from the intermediate outlet proceeds, cause the inner layer material injection unit to begin injecting two corresponding inner layer material flows from the inner and outer outlets of the co-injection nozzle into the mold cavity, these two corresponding inner layer material flows sandwiching the surface layer material flow and flowing after the melt front of the surface layer material, such that the sandwiched flow of surface layer material continues to supply surface layer material to the melt front, at least until the melt front approaches the far end of the mold cavity.

[0013] In some embodiments, the computer-readable program code further causes the controller to: maintain pressure applied to the surface layer material supplied to the intermediate outlet of the co-injection nozzle; and to sufficiently reduce the pressure of the inner layer material supplied to the inner outlet and the outer outlet of the co-injection nozzle to allow the pressurized surface layer material to flow upstream into each of the inner outlet and the outer outlet.

[0014] According to another aspect of the invention, a co-injection molded multilayer container preform is provided, the multilayer container preform comprising: a tubular body; a base at a closed end of the tubular body; and a neck opening defining a top sealing surface at an open end of the tubular body, wherein the tubular body comprises: an intermediate layer of surface layer material; an inner layer and an outer layer of inner layer material sandwiching the intermediate layer of surface layer material between them; and an inner surface layer and an outer surface layer of surface layer material adjacent to the inner and outer layers of inner layer material, respectively, and wherein the intermediate layer of surface layer material extends through the neck opening to form the top sealing surface.

[0015] In some embodiments, the inner and outer layers of the inner layer material extend into the base, and in the base, the inner and outer layers of the inner layer material together define at least 20% of the base thickness.

[0016] In some embodiments, the volume percentage of the inner layer material in the co-injection molded multilayer container preform is at least 50%. The volume percentage of the inner layer material may be about 54%. In other non-limiting embodiments, the volume percentage of the inner layer material is less than 50%, and as low as 3%.

[0017] In some embodiments, the thickness of the outer inner layer of the inner layer material and the thickness of the inner inner layer of the inner layer material together define at least 50% of the total wall thickness of the tubular body of the co-injection molded multilayer container preform.

[0018] According to another aspect of the invention, a co-injection molded multilayer container preform is provided, the multilayer container preform comprising: a tubular body; a base at a closed end of the tubular body; and a neck at an open end of the tubular body, wherein the wall of the tubular body has five layers, the five layers being an outer surface layer of a surface layer material adjacent to an outer inner layer of an inner layer material, an outer inner layer of an inner layer material adjacent to an intermediate layer of the surface layer material, an intermediate layer adjacent to an inner inner layer of the inner layer material, and an inner surface layer of the inner layer material adjacent to an inner surface layer of the surface layer material.

[0019] In some embodiments, the volume percentage of the inner layer material in a co-injection molded multilayer container preform is at least 50%. The volume percentage of the inner layer material in a co-injection molded multilayer container preform may be approximately 54%.

[0020] In some embodiments, the thickness of the outer inner layer of the inner layer material and the thickness of the inner inner layer of the inner layer material together define at least 50% of the total wall thickness of the tubular body of the co-injection molded multilayer container preform.

[0021] In some embodiments, the five layers extend into the neck of the preform, and the five layers are the outer surface layer of the surface layer material adjacent to the outer inner layer of the inner layer material, the outer inner layer of the inner layer material adjacent to the middle layer of the surface layer material, the middle layer adjacent to the inner inner layer of the inner layer material, and the inner inner layer of the inner layer material adjacent to the inner surface layer of the surface layer material.

[0022] According to another aspect of the invention, a co-injection molded multilayer article is provided, comprising: a body; a base at a closed end of the body; and a neck defining an annular edge surface at an open end of the body, wherein the body comprises: an intermediate layer of surface layer material; an inner layer and an outer layer of inner layer material sandwiching the intermediate layer of surface layer material between them; and an inner surface layer and an outer surface layer of surface layer material adjacent to the inner and outer layers of inner layer material, respectively, and wherein the intermediate layer of surface layer material extends through the neck to form the annular edge surface.

[0023] In some embodiments, the volume proportion of the inner layer material in a co-injection molded multilayer article is at least 50%.

[0024] Other features will become clear from the accompanying drawings in conjunction with the following description. Attached Figure Description

[0025] The non-limiting embodiments will be more fully understood with reference to the accompanying drawings, in which:

[0026] Figure 1 This is a perspective view of a conventional injection molding machine used for molding multi-layer preforms;

[0027] Figure 2 It is by Figure 1 A perspective view of a multi-layer preform molded by an injection molding machine;

[0028] Figure 3 yes Figure 2 The longitudinal cross-section of the precast component;

[0029] Figure 4 It is used for injection molding materials to form Figure 2 and Figure 3 The longitudinal cross-section of a portion of the hot runner of the precast component and the injection nozzle;

[0030] Figure 4A More detailed schematic description Figure 1 Part of an injection molding machine;

[0031] Figure 5 yes Figure 1 The flowchart illustrates the operation of a molding machine used to form molded products during a single molding cycle according to conventional processes. Figure 2 and Figure 3 Precast components;

[0032] Figure 6 , Figure 7 , Figure 8 , Figure 9 and Figure 10 yes Figure 4 At least a portion of the nozzle and the associated mold cavity in Figure 5 A schematic diagram showing the various stages of the operation in a longitudinal cross-section;

[0033] Figure 11A It is based on Figure 5 The longitudinal cross-section of the multi-layer preform of the sample manufactured according to the operation flowchart;

[0034] Figure 11B It is based on Figure 5 The longitudinal cross-section of the base region of another sample multilayer preform manufactured according to the operation flowchart;

[0035] Figure 12 This is a perspective view of an injection molding machine used for injection molding multilayer articles with a high proportion of inner layer material.

[0036] Figure 13 More detailed schematic description Figure 12 Part of an injection molding machine;

[0037] Figure 14 Is using Figure 12 Flowchart of the operation of injection molding of multi-layer products with a high proportion of inner layer material using a molding machine;

[0038] Figure 15 , Figure 16 and Figure 17 yes Figure 4 At least a portion of the nozzle and the associated mold cavity are in Figure 14 A schematic diagram of the longitudinal cross-sections of each stage of the operation; and

[0039] Figure 18 and Figure 19 It is based on Figure 14 The process flow diagram shows the longitudinal cross-sectional view of the multi-layer preform of the sample manufactured.

[0040] The accompanying drawings are not necessarily drawn to scale and may be illustrated using dashed lines, graphical representations, and fragmentary diagrams. In some cases, details that are unnecessary for understanding these embodiments or that would make other details difficult to perceive have been omitted. Detailed Implementation

[0041] In this document, any use of the term "exemplary" should be understood as meaning "an example of..." and not necessarily indicating that the example is preferred or optimal in some way. Terms such as "downward" and "rightward" may be used to describe features of some embodiments in this specification, but should not be construed as necessarily implying the orientation of the embodiments during manufacture or use. References to a "high proportion" of inner layer material in a multilayer injection-molded article do not necessarily indicate any absolute lower limit of the amount of inner layer material relative to the total amount of material in the article.

[0042] Figure 1 A conventional injection molding machine 100 is depicted in perspective. The exemplary injection molding machine 100 is used for molding multilayer articles, specifically preforms, such as... Figure 2 and Figure 3 Example prefabricated component 200 (described below).

[0043] Figure 1 The injection molding machine 100 depicted includes a housing 102 that houses a fixture unit, a fixed pressure plate, a movable pressure plate, and a mold mounted therebetween. Figure 1 (Neither visible in the image). The injection molding machine 100 also includes a first injection unit 104 and a second injection unit 106, which are used for plasticizing (melting) and injecting surface layer material and inner layer material (both in the form of molding materials), respectively, and are referred to herein as surface layer material injection unit 104 and inner layer material injection unit 106, respectively. The surface layer material may be, for example, PET. The inner layer material may be, for example, nylon, barrier or oxygen scavenging material, or PET material with colorant additives.

[0044] Figure 1 The controller 108 controls the operation of the injection molding machine 100, particularly based on human operator input or based on preset control sequences. In this embodiment, the controller 108 includes at least one processor communicating with volatile or non-volatile memory storing computer-readable program code stored on a tangible medium (e.g., ROM, optical disc, USB drive, or magnetic storage medium). In some embodiments, the computer-readable program code may be transferred to the memory via a modem or communication adapter communicatively connected to a network (e.g., a wide area network such as the Internet). The controller 108 may be, for example, an industrial PC, such as having... Core TM i processor Model CP22xx Panel PC. Control commands can be input by the operator via a human-machine interface (HMI) 109, which may be, for example, part of the controller 108 or a multi-function touchscreen coupled to the controller 108. The HMI 109 can display various graphical user interface (GUI) screens for controlling or monitoring aspects of the molding process.

[0045] Hot runner 388 inside the outer casing 102 Figure 1 (Not shown) Defines a pathway network for conveying molten surface layer material and molten inner layer material from injection units 104 and 106 to each of the plurality of multi-channel nozzles described below. Each nozzle is located near an associated mold cavity defined in the mold. Each mold cavity is a negative space of the shape of the article to be molded, which in this example is Figure 2 and Figure 3 The preform 200. The number of mold cavities that can be filled simultaneously by the molding machine 100 is typically greater than one and can vary between embodiments.

[0046] pass Figure 1 The exemplary container preform 200 produced by the injection molding machine 100 in Figure 2 Shown in perspective and in Figure 3 The figure is shown in a longitudinal cross-section. As shown, the preform 200 has an elongated tubular body 202, a dome-shaped closure base 204, and a neck opening 206. The neck opening 206 of this example preform includes various external features, including threads 208 for receiving and retaining a closure (e.g., a threaded cap), lock beads 210, and support lugs 212. As will be understood, the neck opening region defines the neck of the molded article at or near the opening of the molded article.

[0047] like Figure 3 As best seen in the image, preform 200 is primarily made of surface layer material 455, except for the internal segment 224, which is composed of inner layer material 466. In this embodiment, the internal segment 224 is completely encapsulated by surface layer material 455. Figure 2 and Figure 3 The orientation of the preform 200 is inverted, meaning that the open end 226 opposite to the base 204 points downwards. This is not necessarily the orientation of the preform in practice when it is molded by the molding machine 100 or an alternative machine embodiment.

[0048] It should be understood that the inner layer material 466 and the surface layer material 455 within the article 200 are distributed in... Figure 3 The diagram is schematically depicted. The actual distribution of materials 455 and 466 within article 200 may differ. The sample distribution in the manufactured prototype article is shown in Figure 11, as described below.

[0049] Figure 2and Figure 3 The preform 200 is formed by molten surface layer material 455 and molten inner layer material 466 injected into the mold cavity through an associated multi-channel co-injection nozzle 400 via a hot runner. Figure 4 A portion of the co-injection nozzle 400 is depicted in longitudinal cross-section. The depicted portion of the nozzle 400 is the most downstream end of the nozzle, including the nozzle tip 402 from which the melt is discharged into the mold cavity.

[0050] In this embodiment, the nozzle 400 is a component formed by three nested parts: the innermost nozzle insert 404, the middle nozzle insert 406, and the outermost nozzle insert 408. In alternative embodiments, the nozzle may be formed in other ways, for example, as a monolithic component made using an additive manufacturing technique such as direct metal laser sintering (DMLS). The exemplary nozzle 400 has a substantially cylindrical shape, as do each of its components, nozzle inserts 404, 406, and 408, but this is not required.

[0051] Figure 4 The nozzle 400 defines three channels for conveying the melt.

[0052] A channel 424, defined by the innermost nozzle insert 404, provides a passage for axially conveying the melt surface layer material received from the first injection unit 104 toward the nozzle tip 402. The channel 424 also accommodates a valve stem 432 capable of axial reciprocating motion. The channel 424 and valve stem 432 together define an annular channel through which the surface layer material can flow until the melt passes the end of the valve stem 432 (when the valve stem 432 is in position). Figure 4 When fully retracted, the melt exits outlet 444 as a substantially cylindrical flow. Upon exiting outlet 444, the melt enters nozzle combination region 429 to combine with one or more other melt flows, as will be described below. Channel 424 may be referred to as internal channel 424, and outlet 444 may therefore be referred to as internal outlet 444.

[0053] Second, a substantially annular channel 426 is defined between the innermost nozzle insert 404 and the intermediate nozzle insert 406. The second channel 426 axially conveys the molten inner layer material received from the second injection unit 106 toward the inward-facing annular outlet 446. Upon exiting the annular outlet 446, the annular melt flow flows into the nozzle combination region 429 to combine with one or more other melt flows. Channel 426 may be referred to as intermediate channel 426, and outlet 446 may be correspondingly referred to as intermediate outlet 446.

[0054] Third, a substantially annular channel 428 is defined between the intermediate nozzle insert 406 and the outermost nozzle insert 408. The third channel 428 conveys the surface layer material received from the first injection unit 104 to an inward-facing annular outlet 448. Upon exiting outlet 448, the discharged melt enters the nozzle combination region 429, where it can be combined with one or more other melt flows. Channel 428 may be referred to as outer channel 428, and outlet 448 may therefore be referred to as outer outlet 448. In this embodiment, outer channel 428 is substantially concentric with each of the intermediate channel 426 and inner channel 424.

[0055] It should be understood that, with the aid of the above-described nozzle structure, the internal, intermediate, and external channels 424, 426, and 428 all supply or feed the corresponding flow of molding material to the assembly region 429, which may therefore be referred to as the "material assembly region".

[0056] The valve stem 432 can be used to control the flow of molding material into the assembly area 429 and thus into the mold cavity associated with the nozzle 400. The valve stem 432 is controlled by the controller 108 via an actuator (not shown) that causes the valve stem 432 to reciprocate between at least a subset of four positions or stops.

[0057] The first valve stem position is Figure 4 The fully open position is depicted, with the distal end 433 of the valve stem located at the axial "stop 3". In this position, the valve stem 432 does not obstruct the flow of molding material from any of the internal outlet 444, intermediate outlet 446, or external outlet 448. This valve stem position is referred to herein as position 3, where the number 3 indicates the number of open (unblocked) nozzle outlets (i.e., outlets 444, 446, and 448).

[0058] The second position is the main open position, in which the end 433 of the valve stem 432 advances (in... Figure 4 From the center downwards, to the axial position marked "Stop 2". When the valve stem 432 is in this position, it blocks (closes) the internal outlet 444, thereby preventing the surface layer material from flowing out. The intermediate outlet 446 and the external outlet 448 remain open. This valve stem position is referred to herein as position 2, and the number 2 indicates the number of open nozzle outlets (i.e., outlets 446 and 448).

[0059] The third position is the mostly closed position, in which the end 433 of the valve stem 432 advances to... Figure 4The axial position is marked "Stop 1". When the valve stem 432 is in this position, it blocks the inner outlet 444 and the intermediate outlet 446, thereby preventing the surface layer material and the inner layer material from flowing out, respectively. The outer outlet 448 remains unblocked, allowing the surface layer material to flow from the injection unit 104 into the combination area 429. This valve stem position is referred to as position 1, reflecting the single nozzle outlet (outlet 448) that is open in this position.

[0060] Finally, the fourth position is the fully closed position, in which the end 433 of the valve stem 432 advances within the gate area 430 to... Figure 4 The axial position is marked "Stop 0". When the valve stem 432 is in this position, it blocks each of the inner outlet 444, the intermediate outlet 446, and the outer outlet 448, thereby preventing molding material from flowing out of any of these outlets. This valve stem position can be referred to as position 0, with the number 0 reflecting the number of open nozzle outlets (i.e., none).

[0061] The gap between valve stem 432 and each of these outlets can be, for example, on the order of micrometers. The gap can vary between embodiments based on, for example, the viscosity of the molten molding material in the respective channels 424, 426 and 428, the pressure of the melt in the nozzle 400 immediately upstream of valve stem 432, and other factors.

[0062] Figure 4A More detailed schematic description Figure 1 A portion of an injection molding machine 100. The depicted portion of the machine 100 includes an inner layer material injection unit 106, a surface layer material injection unit 104, a portion of a hot runner 388, a portion of a single co-injection nozzle 400, and a portion of an associated mold cavity 800 for forming the preform 200. Figure 4A The diagram generally illustrates the manner in which surface layer material 455 and inner layer material 466 are supplied to the co-injection nozzle 400.

[0063] Figure 4A The injection unit 106 includes a reciprocating helical screw 110 housed within an extruder barrel 112. The barrel 112 can be selectively heated, for example, by a belt heater (not explicitly depicted). The barrel also has an inlet (not explicitly depicted) for receiving, for example, an inner layer material 466 in granular form. The screw 110 can rotate within the heated barrel 112 to mix and plasticize the inner layer material. An outlet nozzle valve 113 ( Figure 4A (Open in the middle) can be controlled by controller 108 ( Figure 1 Selectively open or close to selectively establish fluid communication between the inner layer material injection unit 106 and the passage 391 within the hot runner 388 for delivering the inner layer material 466 to the nozzle 400.

[0064] Figure 4AThe injection unit 106 also includes an injection actuator 114 or is otherwise associated with an injection actuator 114. The injection actuator 114 (or simply "actuator 114") is configured to cause the screw 110 to reciprocate longitudinally within the barrel 112 to perform the injection and recovery operation phases of the inner layer material injection unit 106. The depicted actuator 114 is controlled by a controller 108.

[0065] The surface layer material injection unit 104 has a similar structure to the inner layer material injection unit 106. The outlet nozzle valve 115 (in...) Figure 4A (Open in the middle) can be controlled by controller 108 ( Figure 1 The control is configured to selectively establish fluid communication between the surface layer material injection unit 104 and the passage 393 within the hot runner 388 for delivering the surface layer material 455 to the nozzle 400.

[0066] Figure 4A The flow path of the molding material from injection units 104 and 106 to nozzle 400 via hot runner 388 is illustrated schematically. As shown, surface layer material injection unit 104 supplies surface layer material 455 to hot runner passage 393. Passage 393 in turn supplies the inner channel 424 and outer channel 428 of nozzle 400. Similarly, as shown, inner layer material injection unit 106 supplies inner layer material 466 to hot runner passage 391, which in turn supplies the intermediate channel 426 of nozzle 400. Figure 4A The arrows at the downstream ends of passages 391 and 393 schematically depict the main flow direction of the corresponding conveyed material. It should be understood that other nozzles (not depicted) of the injection molding machine 100 supply melt in a similar manner.

[0067] Figure 5 The operation 500 of a molding machine 100 for co-injection of conventional multilayer articles is depicted in the form of a flowchart. This will be combined with... Figure 6-10 Description of operation 500, Figure 6-10 The various stages of preform 200 formation during a single injection molding cycle are schematically depicted in longitudinal cross-section. Figure 4 A portion of the nozzle 400 and at least a portion of the associated mold cavity 800.

[0068] Reference Figure 6 At the start of the injection molding cycle, the valve stem 432 of the nozzle 400 is in position 0, i.e., the fully closed position. In this position, the valve stem 432 blocks (i.e., closes) the inner outlet 444, the intermediate outlet 446, and the outer outlet 448, thereby preventing the flow of any surface layer material 455 or any inner layer material 466. The mold cavity 800 associated with the nozzle 400 (only...) Figure 6(shown in the middle) It is initially empty, where any preforms from the previous molding cycle have been discharged, and the nozzle 400 defines the negative space of the shape of the preform 200.

[0069] exist Figure 6 In the illustrated embodiment, it can be seen that the distal end of the intermediate channel 426, directly upstream of the intermediate outlet 446, initially contains a small amount of surface layer material 455. This is unrelated to the fact that the intermediate channel 426 is intended to convey the inner layer material 466 from the injection unit 106 toward the mold cavity 800. The manner in which the distal end of the channel 426 is filled with surface layer material 455 at the end of the previous molding cycle and the principle behind doing so are described below.

[0070] Reference Figure 5 In the first operation 502, the valve stem 432 moves from position 0 (fully closed position) to position 3 (fully open position), and surface layer material 455 is injected via injection unit 104 to initiate the operation of valve 115 in the open position (see...). Figure 4A The surface layer material 455 flows through the passage 393 of the hot runner 388 into the inner channel 424 and outer channel 428 of the nozzle 400. It is noteworthy that during operation 502, the injection unit 106 is not yet activated, i.e., the inner layer material has not yet flowed into the intermediate channel 426. The initial flow of the molding material is limited to the surface layer material 455. This results in the neck region 206 of the preform 200 at the distal end of the mold cavity being primarily composed of the surface layer material 455.

[0071] Figure 7 Depicting in Figure 5 During operation 502, the states of nozzle 400 and mold cavity 800 are as follows. As shown, surface layer material 455 from both internal channel 424 and external channel 428 flows into mold cavity 800 via gate area 430. It should be understood that the flow of surface layer material 455 from internal channel 424 through intermediate outlet 446 may have a tendency to entrain or “drag” some material from outlet 446. Given the extent to which this does occur, the dragged material will also be surface layer material 455, as a small amount of surface layer material 455 occupies the far end of channel 426. This is intended to limit the neck portion 206 of preform 200 from contamination by inner layer material 466.

[0072] As the melt front 459 (leading edge) of the flowing surface layer material 455 advances within the mold cavity 800, the central portion of the fastest flow exhibits a "fountain flow," meaning it tends to spread laterally toward the mold cavity wall on both the core and cavity sides of the mold (see [link]). Figure 7(Dashed arrow FF). Upon contact with the cavity surface 802 or core surface 804 of the mold cavity 800, the flowing surface layer material 455 cools rapidly and adheres thereto. This is because the cavity and core surfaces 802 and 804 of the mold cavity 800 are colder than the surface layer material 455. As a result, a hardened “skin” layer 805 of the surface layer material 455 rapidly forms on the core and cavity sides of the mold (see dashed arrow FF). Figure 7 ).

[0073] In subsequent operation 506 ( Figure 5 In this process, controller 108 moves valve stem 432 to position 2, such as... Figure 8 As shown. Furthermore, the controller 108 triggers the injection unit 106 to inject the inner layer material 466 from the middle outlet 446 of the nozzle 400 into the mold cavity 800, that is, to initiate the injection of the inner layer section 224. Figure 3 ).

[0074] like Figure 8 As shown, the inner layer material 466 entering the mold cavity 800 is sandwiched between the surface layer material 455 and flows together with it. The surface layer material 455 continues to be injected from the external channel 428 into the mold cavity 800. Simultaneously, the molten surface layer material 455 closest to the hardened surface layer 805 itself cools and hardens from the outside (see...). Figure 8 This further thickens the hardened surface layer 805 of the surface layer material 455.

[0075] The inventors believe that the rate of hardening of the surface layer material 455 on both the core and cavity sides of the mold cavity 800 from the outside in during this stage is at least partially responsible for limiting the amount of inner layer material 466 that can be injected into the conventional multilayer preform 200. Rapid hardening is believed to restrict or narrow the open space within the mold cavity 800 through which the additional inner layer material 466 can flow. In one exemplary implementation, the inventors found that the proportion of inner layer material 466 in a fully formed multilayer preform made in this manner does not exceed 40% by volume.

[0076] In subsequent operation 508 ( Figure 5 In this process, the inner layer material injection unit 106 is appropriately controlled to terminate the injection of the inner layer material 466. Thus, the formation of the inner layer portion 224 is completed. The surface layer material 455 continues to be injected from the outer outlet 448 (see...). Figure 9 ).

[0077] With the intermediate outlet 446 open and the surface layer material injection unit 104 in the "holding phase," where the surface layer material 455 is still under positive pressure and flowing (albeit slowly) from the outer outlet 448, the controller 108 slightly pulls the inner layer material injection unit 106 back (operation 510). Figure 5The pullback has the effect of reducing the pressure on the inner layer material 466 within the extruder barrel 112 and intermediate channel 426. The reduced pressure, in turn, allows a small amount of pressurized surface layer material 455 to flow into the far end of the intermediate channel 426, such as... Figure 10 The longitudinal cross-section is shown. It should be understood that the flow direction is upstream, i.e., in the direction of the injection stage (as described above). Figure 5 During operation 506), the flow direction of the intermediate layer material 466 through channel 426 is reversed. Therefore, filling the distal end of channel 426 with surface layer material 455 in operation 510 can be referred to as "backfilling". Backfilling is performed for the reasons mentioned above.

[0078] Finally, in operation 512 ( Figure 5 In this process, controller 108 returns valve stem 432 to its initial fully closed position, i.e., position 0. This closure has the effect of capturing a small amount of surface layer material at the distal end of intermediate channel 426, preparing it for the next molding cycle. As a result, at the end of operation 512, the state of nozzle 400 will be related to its position. Figure 6 Their initial states are the same.

[0079] It should be understood that alternative embodiments of the injection molding machine 100 may implement operation 500 slightly differently. For example, in operation 506, lever 432 may remain in position 3 instead of moving to position 2, and surface layer material 455 may be injected from both the inner and outer outlets 444, 448 of nozzle 400 instead of only from outer outlet 448. In operation 510, lever 432 may be in position 3 instead of position 2, thereby supplying surface material 455 for backfilling from both outer outlet 448 and inner outlet 444. Aspects of operation 500 may also differ slightly based on the design of the molding machine's co-injection nozzle. Figure 5 The aspects shown. For example, in some embodiments, the co-injection nozzle has a gap ring between the valve stem and each of the intermediate outlet and the outer outlet. Such embodiments can still achieve backfilling at the distal end of their intermediate channel, even if their valve stem cannot mechanically block the intermediate or outer outlet or mechanically capture the surface layer material 455 at the distal end of the intermediate channel, as described in operation 512.

[0080] Figure 11A This is a longitudinal cross-section of a sample multilayer container preform 600 manufactured using a machine similar to machine 100, which uses PET for both the surface layer material 455 and the inner layer material 466. Different colorants are added to materials 455 and 466 respectively to facilitate visual inspection of the distribution of these materials in the resulting preform.

[0081] In many ways, precast component 600 is similar to Figure 2 and Figure 3Preform 200. For example, preform 600 has an elongated tubular body 602 located at the open end 226 of the preform, a dome-shaped closed base 604, and a neck 606. The body portion 602 has a transition region 609. Preform 600 includes an inner layer 632 of inner layer material 466 sandwiched between an inner layer 634 and an outer layer 636 of surface layer material 455. The inner layer material 466 is completely encapsulated by surface layer material 455. The thicknesses of layers 632, 634, and 636 vary throughout preform 600, with the inner layer 632 being the thickest in the body portion 602 of preform 600.

[0082] Figure 11A An enlarged view 631 of the preform wall in the main body portion 602 of the preform 600 is shown. Reference numerals W1, W2, and W3 denote the thicknesses of the outer layer 636, inner layer 632, and inner layer 634, respectively, measured along a plane P perpendicular to the preform wall. In this sample preform 600, the relationship between these thicknesses is W1 > W2 > W3. The thickness W2 of the inner layer 632 in the main body portion 602 is less than approximately 40% of the total thickness of the preform wall and less than 50% of the sum of the thicknesses W1 and W3 of the inner layer 634 and the outer layer 636.

[0083] With the internal section 224 of prefabricated component 200 Figure 3 Unlike other preforms, the inner layer 632 of the preform 600 extends into and through the entire dome-shaped base region 604. Taking into account the thickness of the gate junction 605, the thickness of the inner layer 632 gradually decreases to less than 10% of the total thickness of the base 604 in the base region 604, or even less.

[0084] It is worth noting that the volume proportion of the inner layer material 466 within the preform 600 is approximately 20%. It should be understood that this proportion may depend in part on the injection volume of the inner layer material 466 (i.e., the amount of inner layer material 466 injected during the molding of a single preform), and an increased injection volume may result in an inner layer material 466 proportion of up to approximately 40%.

[0085] Figure 11B It is a longitudinal cross-section of the base portion of another preform 600' manufactured using a machine similar to machine 100, again using PET for both the surface layer material 455 and the inner layer material 466. Preform 600' is similar in many ways to... Figure 11AThe preform 600. For example, the preform 600' has an inner layer 632' of inner layer material 466 sandwiched between an inner layer 634' and an outer layer 636' of surface layer material 455. However, in the base region 604' of the preform 600', tongues 635 of surface layer material 455 extend from the gate junction 605' toward the body 602' into the tail end of the intermediate layer 632', thereby effectively splitting layer 632' into two conical fingers 637, 639. The tongues 635 may be the result of a holding or filling phase of the injection molding operation, wherein the surface layer material 455 injected at the end of the injection molding cycle is pushed down into the mold cavity and penetrates the intermediate layer 632'.

[0086] The volume ratio of the inner layer material 466 in the preform 600' is approximately the same as the volume ratio of the preform 600, that is, about 20%.

[0087] The inventor has considered methods for modifying Figure 5 Various methods have been employed to increase the proportion of inner layer material in multi-layer precast components, but many of these methods have been found to be disadvantageous in various respects.

[0088] One approach considered is to increase the temperature of the cavity walls 802, 804 relative to the temperature of the injected surface layer material 455. The basic principle of this method is to slow down the rate of hardening of the surface layer material 455 from the outside in, to provide more time and space for injecting the inner layer material 466 into the cavity 800 during the injection molding cycle. However, it is considered that the corresponding increase in in-mold cooling time would unacceptably reduce the molding machine's throughput.

[0089] Another approach to consider is to reduce in Figure 7 and Figure 8 The amount of surface layer material 455 injected during the stage shown is intended to leave "more space" for an increased proportion of inner layer material 466 in the molded article. However, this method is considered to unacceptably increase the risk of defective preforms. In particular, when the amount of injected surface layer material 455 is reduced, there is a greater risk that the material may harden prematurely, allowing the inner layer material 466 to "catch up" with the melt front 459. In this case, the inner layer material 466 at the melt front can spread laterally from the melt front and come into direct contact with the core side or cavity side of the mold cavity. This will deposit the inner layer material 466 on the outer surface of the molded article, causing defects in the article in at least some applications, for example, due to the reasons described above.

[0090] To avoid these problems, the inventors have developed a novel method that significantly increases the proportion of inner layer material within a multi-layer preform. This new method is unconventional because it is used in a completely different way than nozzles are designed for use, for example, with nozzle 400 in... Figure 5The operation 500 uses different methods of using known co-injection nozzles, for example Figure 4 The nozzle 400. Specifically, the new method reverses the function of the intermediate channel and the internal and external channels (and their corresponding outlets) of the co-injection nozzle 400 as follows. The intermediate channel 426 of the nozzle delivers the surface layer material (instead of the inner layer material) into the mold cavity, and the internal and external channels 424, 428 of the nozzle deliver the inner layer material (instead of the surface layer material) into the mold cavity.

[0091] This new method is counterintuitive because the placement of the intermediate channel outlet 446 between the internal and external channel outlets 444, 448 of the nozzle is specifically designed to facilitate the encapsulation of the inner layer material flowing from the internal channel outlet 446 by the surface layer material flowing from the internal channel outlet 446 on either side. Essentially, the new method uses these outlets in a manner opposite to their intended design. Therefore, the new method can be viewed not only as counterintuitive but also as a paradigm shift from conventional co-injection molding techniques.

[0092] To achieve this result, the new injection molding machine uses features similar to conventional injection molding machines (e.g., Figure 1 The new injection molding machine (100) features a different melt distribution network and a hot runner system. Furthermore, the controller of the new injection molding machine implements a different control sequence than that conventionally used for molding multi-layer preforms, for example, as described above regarding... Figure 5 Other components of the new injection molding machine (such as the injection unit and nozzle) may be similar to or equivalent to those of a conventional injection molding machine, but the control systems differ. The reuse of these other components can advantageously minimize the cost of retrofitting an existing injection molding machine installation to implement the new method.

[0093] Figure 12 This is a perspective view of an injection molding machine 100' used for injection molding multilayer articles having a high proportion of inner layer material. As described above, some components of the molding machine 100' are similar to or equivalent to their counterparts in the above-described molding machine 100. These components include a housing 102, certain encapsulated sub-components (e.g., clamping units), a fixed pressure plate, a movable pressure plate, and a mold including a mold cavity 800 mounted therebetween. Figure 12 The mold cavity 800, surface layer material injection unit 104, inner layer material injection unit 106, and common injection nozzle 400 are not explicitly depicted. Each of these components of the injection molding machine 100' is referred to using the same reference numerals as those used above for the machine 100, to reflect the fact that the component may be the same as its counterpart in the machine 100, but may be controlled differently.

[0094] Figure 12 Other parts of the injection molding machine 100' are different Figure 1The injection molding machine 100 and its corresponding components. These components include the controller 108' and the hot runner 388' (the latter is not included in the...). Figure 12 The diagram in the middle is shown but Figure 13 (See diagram below). Controller 108' differs from controller 108 in at least the operational steps triggered during the injection molding cycle. These operational steps can be controlled by program code stored on tangible medium 190, which is read and executed by controller 108' to control machine operation. Hot runner 388' differs from hot runner 388 in its provision of a "pipeline" between injection units 104, 106 and nozzle 400, as will be described below. Controller 108' and hot runner 388' are referred to herein by a variation of reference numerals used to identify their counterparts in molding machine 100, namely the same reference numerals but with an appended apostrophe ("prime number") (') symbol.

[0095] Figure 13 More detailed schematic description Figure 12 Part of the injection molding machine 100'. Figure 13 Adopting the above Figure 4A The same convention. Figure 13 The depicted portion of machine 100' includes an inner layer material injection unit 106, a surface layer material injection unit 104, a portion of a single co-injection nozzle 400, and a portion of an associated mold cavity 800 for forming multi-layer preforms. These components are structurally compatible with... Figure 4A The corresponding parts are the same.

[0096] Figure 13 A portion of the hot runner 388', including passages 391' and 393', is also depicted. It should be understood that the functions of passages 391' and 393' are substantially related to... Figure 4A The passages 391 and 393 of the hot runner 388 function in opposite directions. Specifically, passage 391' is configured to deliver inner layer material 466 to the inner channel 424 and outer channel 428 of the nozzle 400, while passage 393' is configured to deliver surface layer material 455 to the intermediate channel 426 of the nozzle 400. This contrasts with the hot runner 388, in which passage 391 is configured to deliver inner layer material 466 to the intermediate channel 426, and passage 393 is configured to deliver surface layer material 455 to the inner and outer channels 424, 428, as previously described.

[0097] Figure 14 The process 1400, which involves molding a multi-layered article with a high proportion of inner layer material using machine 100, is described in flowchart form. The following will combine... Figure 15-17 Description of operation 1400, Figure 15-17A portion of the nozzle 400 and associated mold cavity 800 of machine 100' are schematically depicted in longitudinal cross-section at various stages of preform formation during a single injection molding cycle.

[0098] exist Figure 14 In operation 1402, a common injection nozzle 400 is provided having an inner outlet 444, an outer outlet 448, and an intermediate outlet 446 between the inner and outer outlets. It should be understood that nozzle 400 is related to the above-described... Figure 4 The nozzles shown are the same. Figure 13 The state of nozzle 400 is shown at the start of the injection molding cycle.

[0099] like Figure 13 As shown, the valve stem 432 of nozzle 400 is in position 0, i.e., the fully closed position. In this position, valve stem 432 blocks the inner outlet 444, the intermediate outlet 446, and the outer outlet 448, thereby preventing the flow of any surface layer material 455 or any inner layer material 466. The mold cavity 800 associated with nozzle 400 (only in...) Figure 13 (shown in the middle section) It is initially empty, where any preforms from previous molding cycles have been discharged, and the nozzle 400 defines the negative space of the preform shape.

[0100] exist Figure 13 In the illustrated embodiment, the distal end of the internal channel 424, directly upstream of the internal outlet 444, contains a small amount of surface layer material 455. Similarly, the distal end of the external channel 428, directly upstream of the external outlet 448, contains a small amount of surface layer material 455. This is unrelated to the fact that the internal and external channels 424, 428 are used to transport the inner layer material 466 from the injection unit 106 into the mold cavity 800. The manner in which the distal ends of these channels 424, 428 are backfilled with surface layer material 455 at the end of the previous molding cycle and the principle for doing so are described below.

[0101] In operation 1404 ( Figure 14 In this embodiment, the controller 108' initiates the injection of surface layer material 455 into the mold cavity 800 by moving the valve stem 432 of the nozzle 400 from position 0 (fully closed position) to position 3 (fully open position) and triggering the injection of surface layer material 455 by the injection unit 104. The resulting flow of surface layer material 455 is conveyed through the passage 393' of the hot runner 388' to the intermediate channel 426 of the nozzle 400 and from the intermediate outlet 446 into the mold cavity 800 (see [link to relevant documentation]). Figure 13 It is worth noting that the other injection unit 106 has not yet been activated in operation 1404, meaning that no inner layer material 466 flows out from the inner outlet 444 and the outer outlet 448. Therefore, the initial flow of molding material within the mold cavity 800 is limited to the surface layer material 455.

[0102] Figure 15 Depicting in Figure 14 The state of nozzle 400 and mold cavity 800 during operation 1404. It can be understood that the flow 756 of surface layer material 455 exiting from the intermediate outlet 446 flows through the outer outlet 448 of nozzle 400. In terms of this flow of surface layer material 455 carrying or "dragging" some material from outlet 448 along with it, the dragged material will also be surface layer material 455. This is because the distal end of channel 428 is pre-filled with a small amount of surface layer material 455. Therefore, the material flowing into mold cavity 800 via gate region 430 to form melt front 759 will consist of surface layer material 455 with little or no inner layer material 466. Therefore, the outermost layer of the preform formed by melt front 759 (due to the previously described fountain flow effect) will also contain very little or no inner layer material 466. Therefore, backfilling the distal end of the external channel 428 with surface layer material 455 tends to reduce the likelihood of exposed inner layer material on the surface of the multilayer molded article, which can be considered a defect in at least some applications.

[0103] In subsequent operation 1406 ( Figure 14 In the process, the inner layer material 466 is injected into the mold cavity 800 from the inner outlet 444 and the outer outlet 448 of the co-injection nozzle 400. This is completed as the flow 756 of the surface layer material 455 continues to be injected into the mold cavity 800 from the intermediate outlet 446. The two combined flows or layers 754, 758 of the inner layer material 466 sandwich the flow of the surface layer material and flow behind the melt front 759. The sandwiched flow 756 continues to supply the surface layer material 455 to the melt front 759, at least until the melt front 759 approaches the far end of the mold cavity 800, for example, reaching the mold cavity area that defines the neck of the preform (or more generally, the mold cavity area that defines the neck of the molded article). Figure 16 The state of nozzle 400 and mold cavity 800 is shown when operation 1406 is in progress.

[0104] Two conditions are generated within the mold cavity 800 by means of the timing of operation 1406 (relative to operation 1404) and the injection rates of injection units 104 and 106 (in operations 1404 and 1406).

[0105] The first condition is that as the melt front 759 flows to the far end of the mold cavity 800, the flow 756 of the surface layer material 455 from the intermediate outlet 446 continues to supply the surface layer material 455 to the melt front 759. This ensures that the preform taking shape within the mold cavity 800 will be completely encapsulated by a thin shell of surface layer material 455, which has been “formed” from the melt front 759.

[0106] The second condition is that the two injection streams 754 and 758 of the inner layer material 466 flow closely behind the melt front 759. This condition is intended to maximize the proportion of the inner layer material 466 within the preform for the following reasons.

[0107] As the melt front 759 advances through the mold cavity 800, a thin outer surface layer 705 is formed from surface layer material 455, which has been formed from the melt front 759 and has been rapidly cooled and hardened. (Refer to...) Figure 16 The hardened surface layer on the cavity side and the core side of the mold cavity 800 is indicated by reference numerals 705A and 705B (collectively referred to as surface layer 705), respectively.

[0108] Because the inner layer materials 466 flow 754, 758 closely behind the melt front 759, they pass near the newly hardened surface layers 705B, 705A and cool rapidly. Therefore, the next material to be hardened adjacent to the outer layer 705 is the inner layer material 466. This tends to keep the outer surface layer 705 of the surface layer material 455 relatively thin, at least compared to the outer layer of the surface layer material 455 in conventional injection-molded multilayer articles.

[0109] Simultaneously, the interlayer flow 756 of the surface layer material 455 remains thermally isolated from the ongoing outside-to-inside cooling process, and this interlayer flow 756 tends to flow centrally relative to the width direction of the mold cavity 800. Therefore, the interlayer flow 756 remains relatively hot and thus flows relatively quickly. Even if the amount of injected surface layer material 455 is less than the amount of injected inner layer material 466, this facilitates a continuous supply of surface layer material 455 to the melt front 759. The relative widths of flows 754, 756, and 758 can be controlled by setting the relative volumetric flow rates of the inner material 466 and the surface material 455. For example, if the inner material flow rate is higher than the surface material flow rate, the widths of flows 754 and 758 can be wider than that of flow 756.

[0110] refer to Figure 14 In subsequent operation 1408, the injection of the inner layer material 466 is terminated. In this embodiment, this is accomplished by appropriately controlling the inner layer material injection unit 106 to stop the injection. The timing of this operation may depend in part on the expected speed and volume of the melt front 759. In some embodiments, the injection of the inner layer material 466 may be terminated when the cavity is nearly filled, i.e., when the melt front 759 may have reached the neck or threaded area of ​​the preform cavity.

[0111] Figure 17The state of the nozzle 400 and mold cavity 800 produced by operation 1408 is shown. As shown, the container preform 700 is now almost completely formed within the mold cavity 800. After the inner layer material injection unit 106 stops, some minor "tailing" (thinning or tapering) of the trailing edge of the material 466 from the outer outlet 448 may occur. The flow 756 of the surface layer material 455 continues to be injected from the intermediate outlet 446, although it may be injected at a slower rate as the mold cavity 800 fills and the newly formed preform cools. This can be considered the hold or filling phase of the operation, where the base region 704 (described below) is filled with the surface layer material 455 at the end of the injection molding cycle.

[0112] It should be understood that, due to the holding or packaging operation performed by the surface layer material injection unit 104 at the end of the injection molding cycle, the intermediate layer of the surface layer material 455 may be thicker in the dome-shaped base region 704 than in the body portion 702 (described below). The holding or packaging operation may push the inner layer material 466 from the gate region 430 of the nozzle 400 toward the body of the preform 700.

[0113] It can also be understood that the intermediate layer 707 of the surface layer material 455 is thicker in the neck region 706 than in the body portion 702, because the volume of the surface layer material 455 in the melt front 759 is before the inner laminar flow 754 and 758 (see example). Figure 16 The volume of surface layer material 455 at the melt front 759 may be required to ensure that the inner layer flows 754 and 758 do not exceed the melt front. The precise volume of surface layer material 455 that may be required at the melt front 759 can depend on various factors, such as the injection rates of the surface and inner layer materials 455 and 466, the timing of the injection of the inner layer material 466, the temperatures of the materials 455 and 466, and variations in the leading edge shape of the inner layer material 466. The latter term refers to the potential non-uniformity (“wavyness”) of the melt front of the inner layer material flows 754 and 758 distributed radially along the circumference of the preform. More specifically, if the melt front of the inner layer material flows 754 and 758 is wavy, the amplitude of the waves can also play a role in determining the volume of surface material 455 that should be in the melt front 759.

[0114] In operation 1410 ( Figure 14In the process of preparing for the next molding cycle, the inner outlet 444 and outer outlet 448 of the co-injection nozzle 400 are backfilled with surface layer material 455. Operation 1410 can be implemented as follows. With the surface layer material injection unit 104 in the "holding phase," where the surface layer material 455 is still under positive pressure and flowing (albeit slowly) from the intermediate outlet 446, the controller 108' pulls the inner layer material injection unit 106 slightly backward. The pullback has the effect of reducing the pressure of the inner layer material 466 in each of the inner channel 424 and the outer channel 428. The reduced pressure, in turn, allows a small amount of pressurized surface layer material 455 from the intermediate outlet 446 to flow upstream into the distal ends of the inner channel 424 and the outer channel 428. For clarity, the backfilling of the distal end of the inner channel 424 advantageously prevents the inner layer material 466 from being trapped near the inner outlet 444.

[0115] After operation 1410, controller 108' returns valve stem 432 to its initial fully closed position, i.e., position 0. This closure has the effect of trapping a small amount of surface layer material in the distal ends of the inner channel 424 and the outer channel 428, preparing for the next molding cycle. As a result, nozzle 400 will return to Figure 13 The initial state.

[0116] It should be understood that alternative embodiments of the injection molding machine 100 may achieve operation 1400 with slightly different designs based on the co-injection nozzle of the molding machine. For example, in some embodiments, the co-injection nozzle has a gap ring between the valve stem and each of the intermediate outlet and the outer outlet. Such embodiments can achieve backfilling at the distal end of their outer channels even if their valve stem cannot mechanically capture the surface layer material 455 at the distal end of the outer channel as in operation 1410.

[0117] Figure 18 It is based on Figure 14 Operation 1400 uses a longitudinal cross-section of a sample multilayer preform 700 manufactured using a machine identical or similar to machine 100'. In the sample preform 700, the surface layer material 455 and the inner layer material 466 are both PET, possibly with different colorants added to each material (e.g., titanium dioxide (white) and black colorants added to materials 455 and 466, respectively). Similar to preform 600, preform 700 has a tubular body 702, a dome-shaped base 704 at the closed end of the tubular body, and a neck nozzle 706 at the open end 726 of the tubular body, which defines a top sealing surface 713. The neck nozzle 706 of this example preform includes various external features, including threads for receiving and retaining a closure (e.g., a threaded cap), lock beads, and support lugs. Figure 18(Not explicitly marked in the text). The neck of the bottle in the alternative embodiment may vary and may include only a subset of these features or may not include these features at all. The body has a transition region 709, which may not necessarily be present in the alternative embodiment.

[0118] like Figure 18 Best visible in the magnified region 731, the precast wall in the main body 702 consists of five adjacent layers: an outer surface layer 705A, an outer inner layer 758, a middle layer 756, an inner inner layer 754, and an inner surface layer 705B, arranged in this order. Layers 705A, 756, and 705B are made of surface layer material 455, and layers 758 and 754 are made of inner layer material 466. Figure 18 In the middle, the three intermediate layers 758, 756, and 754 are identified using the same reference numerals as the corresponding material flows that form them (see...). Figure 16 In other words, the tubular body 702 includes an intermediate layer 756 of surface layer material 455 sandwiched between two layers 754, 758 of inner layer material 466, and an encapsulation shell 705 of surface layer material 455.

[0119] In the enlarged region 731, reference numerals T1, T2, T3, T4, and T5 respectively denote the thicknesses of layers 705A, 758, 756, 754, and 705B measured along a plane P perpendicular to the preform wall. In this sample preform 700, the sum of the thicknesses of the inner material layers 758 and 754 is at least 50% of the total thickness of the preform wall. It should be understood that this is greater than using... Figure 5 The inner layer 632 in the body portion 602 of the preform 600 (FIG. 11) made by conventional methods is much thicker. The reason layer 756 may appear thinner compared to other layers is likely due to the distribution of the injection rate of the surface layer material 455. Specifically, the injection rate can be reduced during the injection cycle to prolong the filling time of the surface layer material 455. This can facilitate the encapsulation of the inner layer material 466 by the surface layer material 455 before the injection of the surface layer material 455 is terminated. In the illustrated embodiment, layer 756 of the surface layer material 455 is thinned to a degree that it is not easily visible directly above the enlarged region 731 within the preform wall. This thinning may be due to the low injection rate of the surface layer material 455 during the relevant time of the injection molding cycle, resulting in the molding material entering the molding cavity being primarily the inner layer material 466.

[0120] Preform 700 also differs structurally from known injection-molded multilayer preforms, such as preform 600 or 600'.

[0121] First, the sum of the thicknesses of the two layers 758 and 754 of the inner layer material 466 in the base region 704 of the preform 700 is approximately the same as that of the conventional preform 600. Figure 11A The thickness of the inner layer material 466 in the base region 604 is twice that of a single inner layer 632. More specifically, in this embodiment, the total thickness of layers 758, 754 is approximately 20% of the total thickness of the base 704. The thickness of the inner layer material 466 in the base region 704 can be increased, for example, by slowing down the material injection rates of the inner and surface layers to increase the frozen layer thickness of the inner layer material 466 in the base region 704. The thickness of the inner layer material 466 in the base region 704 may also be affected by the amount of inner layer injection and the duration of the surface layer material retention phase.

[0122] A thicker inner layer of material within the base of a multilayer preform can offer benefits not available in conventional multilayer preforms. For example, if the inner layer material 466 is a blocking material, such as for blocking light, the increased thickness of the inner layer material 466 in the base region can correspond to greater opacity. Greater opacity may be required for some applications, such as to conceal package contents from view or to protect contents from the potentially harmful effects of overexposure.

[0123] Secondly, an intermediate layer 756 of the surface layer material 455 from the main body 702 extends through the neck nozzle 706 to form its top sealing surface 713. This feature is lacking in conventional injection-molded preforms (such as preform 600 in Figure 11).

[0124] exist Figure 18 In the middle, the outer layer 758 of the inner layer material 466 extends further into the neck bottle mouth region 706 than the inner layer 754 of the inner layer material 466. This difference may be due to the backfill operation (1410) in the previous molding cycle. Figure 14 During this process, the surface layer material 455 is further drawn upward into the inner channel 424 instead of the outer channel 428. In this case, the inner layer material 466 in the outer flow 758 will have a "head start" compared to the inner layer material 466 in the inner flow 754. Conversely, Figure 17 The opposite scenario is depicted, which can occur alternatively. In some embodiments, the extent of these layers within the neck region 706 may be substantially the same.

[0125] It is worth noting that the volume proportion of the inner layer material 466 in the preform 700 is about 54%, which is significantly higher than the proportion of the inner layer material 466 in conventionally manufactured multilayer preforms 600 or 600'.

[0126] Therefore, although the material comprising preform 700 can harden in injection molding machine 100' as quickly as the material forming preform 600 or 600' in injection molding machine 100, the preform 700 formed by machine 100' will contain more inner layer material 466 than the preform formed by machine 100. Thus, the preform 700 with a high proportion of inner layer material can be manufactured with little or no loss of machine production compared to preform 600 or 600'.

[0127] Figure 19 It is based on Figure 14 Operation 1400 shows a longitudinal sectional view of another sample multilayer container preform 900 manufactured using a machine similar to or the same as machine 100'. Similar to preform 700, sample preform 900 is made of PET and optionally has different colorants added to the surface layer material 455 and the inner layer material 466, respectively. Container preform 900 has a tubular body 902, a dome-shaped base 904 at the closed end of the tubular body, and a neck 906 at the open end 926 of the tubular body, which defines a top sealing surface 913. The body portion 902 has a transition region 909, which is not necessarily present in alternative embodiments.

[0128] like Figure 19 Best visible in magnified region 931, the precast wall in the main body 902 consists of five adjacent layers: outer surface layer 905A, outer inner layer 958, intermediate layer 956, inner inner layer 954, and inner surface layer 905B arranged in this order. Layers 905A, 956, and 905B are made of surface layer material 455, and layers 958 and 954 are made of inner layer material 466. Reference numerals U1, U2, U3, U4, and U5 denote the thicknesses of layers 905A, 958, 956, 954, and 905B, respectively, measured along a plane P perpendicular to the precast wall. Inner surface layer 905A and outer surface layer 905B can be collectively referred to as surface layer 905.

[0129] It should be understood that Figure 18 One difference between preform 900 and preform 700 lies in the thickness of layers 956 and 954 in the main body 902 compared to the thickness of layers 756 and 754 in the main body 702. Specifically, the thickness U3 of the surface layer material layer 956 of preform 900 is several times greater than the thickness T3 of the inner layer material layer 756 of preform 700. This is likely at least partly due to the smaller injection size of the surface layer material used to mold preform 900 compared to the injection size of the surface layer material in preform 700. Conversely, the thickness U4 of the inner layer material layer 954 of preform 900 is less than half the thickness T4 of the inner layer material layer 756 of preform 700. These differences can be achieved by appropriately controlling the injection rate of the inner layer material.

[0130] The sum of the thicknesses of layers 905A, 956, and 905B is expected to remain approximately constant for a given injection amount of surface layer material 455. If the injection amount of surface layer material (i.e., the amount of surface layer material 455 injected during molding of the preform) increases, then the thickness of layer 956 can increase. Similarly, the sum of the thicknesses of layers 958 and 954 can be a function of the injection amount of inner layer material 466, and should be approximately constant for a given injection amount of inner layer material. The ratio of layer thicknesses 954 to 958 can be limited by closing the channel with valve stem 432 to restrict the flow of layer 954 from channel 424 ( Figure 17 The thickness will change due to the flow of the material. The total thickness of layers 958 and 954 will remain the same, but layer 954 will be thinner and layer 958 will be thicker, with the thickness remaining essentially the same.

[0131] The thicknesses U1, U2, and U5 of the other layers 905A, 958, and 905B of preform 900 are not significantly different from the corresponding thicknesses T1, T2, and T5 of layers 705A, 758, and 705B of preform 700.

[0132] The ratio of inner layer material 466 to surface layer material 455 in preform 700 is higher than that in preform 900. The optimal ratio can be specific to a particular application.

[0133] Various alternative implementations can be envisioned.

[0134] Both molding machines 100 and 100' described above are used to mold multilayer articles as preforms. In alternative embodiments, the molding machines can be used to mold other types of multilayer articles, such as other types of containers or closures, such as caps. In the case of closures, the area referred to as the neck or opening can refer to the skirt or neck of the cap, while the area referred to above as the top sealing surface can refer to the annular edge surface of the cap.

[0135] It should be understood that preforms 700 and 900 are merely examples of preforms that can be manufactured using Operation 1400. Other types of preforms may differ in shape or appearance. For example, some preforms may lack transition areas.

[0136] In some embodiments, if injection units 104 and 106 are interchanged, a conventional hot runner, such as hot runner 399, can be used. The resulting injection molding machine will be similar to... Figure 1 The injection molding machine 100 will be modified so that the surface layer material injection unit 104 and the inner layer material injection unit 106 are interchanged, and the controller 108 will be replaced or reprogrammed to achieve a similar effect. Figure 14 The operation shown is illustrated.

[0137] The exemplary embodiments discussed above are for injection-molded multilayer preforms. It should be understood that the methods described herein, for example... Figure 14Operation 1400 can be used for injection molding of other types of multi-layer articles, such as coffee boxes / capsules, closures, or barrels.

[0138] In some embodiments, injection of the surface layer material 455 from the intermediate exit 446 may be terminated before operation 1408 occurs. In such embodiments, the injection molding sequence may end with injection of the inner layer material 466 instead of the surface layer material 455. This may result in the inner layer material 466 being exposed on the outer surface of the base region of the preform. In some applications, such exposure of the inner layer material 466 may be acceptable, for example, for aesthetic reasons.

[0139] In some embodiments, such as for aesthetic reasons, exposure of the inner layer material 466 at the inner or outer surface of the base region of the preform may be considered acceptable. This may depend on factors such as the application of the molded article and the type of inner layer material used. In such embodiments, the inner layer material 466 may be omitted. Figure 14 The backfilling operation is 1410.

[0140] Other modifications may be made within the scope of the following claims.

Claims

1. An injection molding machine (100') for molding a multi-layer article (700, 900), comprising: a co-injection nozzle (400) having inner, outer, and middle channels (424, 428, 426) terminated by inner, outer, and middle outlets (444, 448, 446), respectively, the middle outlet being between the inner and outer outlets; a skin material injection unit (104); an inner layer material injection unit (106); and a hot-runner (388') defining: a first passageway (393') for communicating a skin material (455) from the skin material injection unit to the middle channel of the co-injection nozzle; and a second passageway (391') for communicating an inner layer material (466) from the inner layer material injection unit to the inner and outer channels of the co-injection nozzle; a mold cavity (800) associated with the co-injection nozzle; and a controller (108') operable to: cause the skin material injection unit to initiate injection of a flow (756) of the skin material from the middle outlet of the co-injection nozzle into the mold cavity; then as the injection of the skin material flow from the middle outlet proceeds, cause the inner layer material injection unit to inject two respective flows (754, 758) of the inner layer material from the inner and outer outlets of the co-injection nozzle into the mold cavity, the two inner layer material flows sandwiching the flow of skin material and flowing behind a melt front of the skin material, such that the sandwiched flow of skin material continues to supply the skin material to the melt front at least until the melt front approaches a distal end of the mold cavity.

2. The injection molding machine of claim 1, wherein the controller is operable to cause the inner layer material injection unit to inject an amount of inner layer material that is at least 50% by volume of the multi-layer article.

3. The injection molding machine of claim 2, wherein the controller is operable to cause the inner layer material injection unit to inject an amount of inner layer material that is at least 54% by volume of the multi-layer article.

4. The injection molding machine of claim 1, wherein the controller is operable to cause the inner layer material injection unit to inject an amount of inner layer material that is less than 50% by volume of the multi-layer article.

5. The injection molding machine of claim 4, wherein the controller is operable to cause the inner layer material injection unit to inject an amount of inner layer material that is 3% by volume of the multi-layer article.

6. The injection molding machine of claim 1, wherein the controller is further operable at the end of a molding cycle to: cause the skin material injection unit to exert a holding pressure on the skin material; and cause a retraction stroke to occur at the inner layer material injection unit to reduce a pressure of the inner layer material in the inner and outer channels of the co-injection nozzle, the reduction in pressure being sufficient to allow pressurized skin material to flow in an upstream direction into each of a distal end of the inner channel and a distal end of the outer channel. ​ 7. A method (1400) of molding a multi-layered article (700, 900) comprising: providing a co-injection nozzle (400) having an inner outlet (444), an outer outlet (448), and an intermediate outlet (446) between the inner and outer outlets; injecting a flow (756) of a surface layer material (455) into a mold cavity (800) from the intermediate outlet of the co-injection nozzle; then with the injection of the surface layer material flow from the intermediate outlet, injecting into the mold cavity from the inner and outer outlets of the co-injection nozzle two respective flows (754, 758) of an inner layer material (466), the two flows of the inner layer material sandwiching the flow of surface layer material and flowing behind a melt front of the surface layer material, such that the sandwiched flow of surface layer material continues to supply the surface layer material to the melt front at least until the melt front approaches a distal end of the mold cavity.

8. The method of molding a multi-layered article of claim 7, wherein the injecting injects an amount of inner layer material that is at least 50% by volume of the multi-layered article.

9. The method of molding a multi-layered article of claim 8, wherein the injecting injects an amount of inner layer material that is at least 54% by volume of the multi-layered article.

10. The method of molding a multi-layered article of claim 7, wherein the injecting injects an amount of inner layer material that is less than 50% by volume of the multi-layered article.

11. The method of molding a multi-layered article of claim 10, wherein the injecting injects an amount of inner layer material that is at least 3% by volume of the multi-layered article.

12. A tangible medium (190) storing computer readable program code that, when executed by a controller (108') of an injection molding machine (1000') having a surface layer material injection unit (104), an inner layer material injection unit (106), and a co-injection nozzle (400) having an inner outlet (444), an outer outlet (448), and an intermediate outlet (446) between the inner and outer outlets, causes the controller to: cause the surface layer material injection unit to begin injecting a flow (455) of surface layer material into a mold cavity (800) from the intermediate outlet of the co-injection nozzle; then with the injection of the surface layer material flow from the intermediate outlet, cause the inner layer material injection unit to begin injecting into the mold cavity from the inner and outer outlets of the co-injection nozzle, two respective flows (466) of inner layer material sandwiching the surface layer material flow and flowing behind a melt front of the surface layer material, such that the sandwiched flow of surface layer material continues to supply the surface layer material to the melt front at least until the melt front approaches a distal end of the mold cavity.

13. The tangible medium of claim 12, wherein the computer readable program code, when executed by the controller, further causes the controller to: cause a holding pressure to be applied to the surface layer material supplied to the intermediate outlet of the co-injection nozzle; and cause the holding pressure to be applied to the surface layer material supplied to the intermediate outlet of the co-injection nozzle; and The pressure of the inner layer material supplied to the inner and outer outlets of the co-injection nozzle is sufficiently reduced to allow the flow of pressurized surface layer material in an upstream direction into each of the inner and outer outlets.

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