US20100072655A1 - Die, system, and method for coextruding a plurality of fluid layers - Google Patents

Abstract

A die for coextruding a plurality of fluid layers generally includes a primary forming stem, one or more distribution plates, and a microlayer assembly. The microlayer assembly includes a microlayer forming stem and a plurality of microlayer distribution plates.

Description

BACKGROUND OF THE INVENTION
• The present invention relates to a coextrusion die and, more particularly, to a coextrusion die containing both a microlayer assembly and one or more distribution plates to produce coextruded films having both microlayers and thicker, conventional film layers.
• Coextrusion is a technique for producing a multilayer plastic (polymeric) film by bringing two or more molten polymers together in a die, in which the polymers are formed into a generally tubular or planar shape, juxtaposed in layered form, and then pushed out of an annular- or slot-shaped opening in the die. Once outside of the die, the still-molten multilayer film is exposed to an environment having a temperature that is maintained below the melting point of the component polymeric layers of the film, which causes the layers to melt-bond together as they cool and solidify.
• Multilayer films typically have a thickness in the range of 50-200 mils upon emergence from the die, but the films are generally stretched prior to final solidification in order to expand their surface area and reduce their final thickness to a range of about 0.5 to about 50 mils. Conventional multilayer films generally have 3-10 layers; prior to stretching and thinning, i.e., while still in the die, each such layer generally ranges from about 20-100 mils in thickness.
• Microlayer extrusion is a technique for increasing the total number of layers in a multilayer film for a given film thickness, by reducing the thickness of the component layers of the film. Thus, while conventional film layers generally range from 20-100 mils inside the die (i.e., prior to stretching and thinning), microlayers generally have an ‘in-die’ thickness ranging from about 1-20 mils. In this manner, microlayered films may have far more than 10 layers, e.g., 20, 30, 40, 50, or more layers. Such microlayered films have been found to provide certain beneficial properties relative to conventional films composed of thicker layers that are fewer in number, e.g., improved mechanical properties such as superior flex cracking and puncture resistance.
• For many applications, it is desirable to combine thicker, conventional layers with microlayers. Such thicker layers are often superior to microlayers for functions such as heat-sealing and abuse-resistance.
• Unfortunately, it has proven to be difficult to combine the flow of thin layers, such as microlayers, with relatively thick layers in such a way that the physical integrity and independent properties of the thin layers are maintained. This is primarily the result of interfacial flow instabilities, which are encountered when microlayers are merged together with thicker layers in a die. Such interfacial flow instabilities are caused by the more powerful sheer forces of the thicker layers flowing against the microlayers, which result from the higher mass flow rate of the thicker layers relative to the microlayers. The resultant loss of the integrity and independent characteristics of the microlayers diminishes or even eradicates the beneficial properties thereof.
• Accordingly, there is a need in the art for an improved die that permits microlayers to be combined with conventional, thicker layers in such a way that the integrity and independent properties of the microlayers are maintained.
SUMMARY OF THE INVENTION
• That need is met by the present invention, which, in one aspect, provides a die for coextruding a plurality of fluid layers, comprising:
• a. a primary forming stem;
• b. one or more distribution plates, each of the plates having a fluid inlet and a fluid outlet, the fluid outlet from each of the plates being in fluid communication with the primary forming stem and structured to deposit a layer of fluid onto the primary forming stem; and
• c. a microlayer assembly, comprising
• • (1) a microlayer forming stem, and
  • (2) a plurality of microlayer distribution plates, each of the microlayer plates having a fluid inlet and a fluid outlet, the fluid outlet from each of the microlayer plates being in fluid communication with the microlayer forming stem and structured to deposit a microlayer of fluid onto the microlayer forming stem, the microlayer plates being arranged to provide a predetermined order in which the microlayers are deposited onto the microlayer forming stem to form a substantially unified, microlayered fluid mass on the microlayer forming stem,
• wherein, the microlayer forming stem is in fluid communication with the primary forming stem such that the microlayered fluid mass flows from the microlayer forming stem and onto the primary forming stem.
• Another aspect of the invention is directed to a system for coextruding a plurality of fluid layers, comprising a die as described above, and one or more extruders in fluid communication with the die to supply one or more fluids to the die.
• A further aspect of the invention pertains to a method of coextruding a plurality of fluid layers, comprising:
• a. directing a fluid through a distribution plate and onto a primary forming stem, the distribution plate having a fluid inlet and a fluid outlet, the fluid outlet from the plate being in fluid communication with the primary forming stem and structured such that the fluid is deposited onto the primary forming stem as a layer;
• b. forming a substantially unified, microlayered fluid mass on a microlayer forming stem by directing at least one additional fluid through a microlayer assembly, the microlayer assembly comprising a plurality of microlayer distribution plates, each of the microlayer plates having a fluid inlet and a fluid outlet, the fluid outlet from each of the microlayer plates being in fluid communication with the microlayer forming stem and structured to deposit a microlayer of fluid onto the microlayer forming stem, the microlayer plates being arranged to provide a predetermined order in which the microlayers are deposited onto the microlayer forming stem; and
• c. directing the microlayered fluid mass from the microlayer forming stem and onto the primary forming stem to merge the microlayered fluid mass with the fluid layer from the distribution plate.
• These and other aspects and features of the invention may be better understood with reference to the following description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
• FIG. 1 is a schematic view of asystem10 in accordance with the present invention for coextruding a plurality of fluid layers, including adie12;
• FIG. 2 is a cross-sectional view of the die12 shown inFIG. 1;
• FIG. 3 is a plan view one of themicrolayer plates48 in die12;
• FIG. 4 is a cross-sectional view of themicrolayer plate48 shown inFIG. 3; and
• FIG. 5 is a magnified, cross-sectional view of die12, showing the combined flows from themicrolayer plates48 anddistribution plates32.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 schematically illustrates asystem10 in accordance with the present invention for coextruding a plurality of fluid layers.System10 generally includes a die12 and one ormore extruders14aand14bin fluid communication with the die12 to supply one or more fluids to the die.
• In a typical application, the fluid layers coextruded by die12 may comprise one or more molten thermoplastic polymers. Examples of such polymers include polyolefins, polyesters (e.g., PET), polystyrenes, polyamide homopolymers and copolymers (e.g. PA6, PA12, PA6/12, etc.), polycarbonates, etc. Within the family of polyolefins, various polyethylene homopolymers and copolymers may be used, as well as polypropylene homopolymers and copolymers (e.g., propylene/ethylene copolymer). Polyethylene homopolymers may include low density polyethylene (LDPE) and high density polyethylene (HDPE). Suitable polyethylene copolymers may include a wide variety of polymers, such as, e.g., ionomers, ethylene/vinyl acetate (EVA), ethylene/vinyl alcohol (EVOH), and ethylene/alpha-olefins, including heterogeneous (Zeigler-Natta catalyzed) and homogeneous (metallocene, single-cite catalyzed) ethylene/alpha-olefin copolymers. Ethylene/alpha-olefin copolymers are copolymers of ethylene with one or more comonomers selected from C₃to C₂₀alpha-olefins, such as 1-butene, 1-pentene, 1-hexene, 1-octene, methyl pentene and the like, including linear low density polyethylene (LLDPE), linear medium density polyethylene (LMDPE), very low density polyethylene (VLDPE), and ultra-low density polyethylene (ULDPE).
• As is conventional, the polymeric materials may be supplied to theextruders14a, bin the solid-state, e.g., in the form of pellets or flakes, viarespective hoppers16a, b.Extruders14a, bare maintained at a temperature sufficient to convert the solid-state polymer to a molten state, and internal screws within the extruders (not shown) move the molten polymer into and through die12 viarespective pipes18a, b.As will be explained in further detail below, within die12, the molten polymer is converted into thin film layers, and each of the layers are superimposed, combined together, and expelled from the die atdischarge end20, i.e., “coextruded,” to form a tubular,multilayer film22. Upon emergence from thedie12 atdischarge end20, the tubular,multilayer film22 is exposed to ambient air or a similar environment having a temperature sufficiently low to cause the molten polymer from which the film is formed to transition from a liquid state to a solid state. Additional cooling/quenching of the film may be achieved by providing a liquid quench bath (not shown), and then directing the film through such bath.
• The solidifiedtubular film22 is then collapsed by aconvergence device24, e.g., a V-shaped guide as shown, which may contain an array of rollers to facilitate the passage offilm22 therethrough. A pair ofcounter-rotating drive rollers25a, bmay be employed as shown to pull thefilm22 through theconvergence device24. The resultant collapsedtubular film22 may then be wound into aroll26 by afilm winding device28 as shown. Thefilm22 onroll26 may subsequently be unwound for use, e.g., for packaging, or for further processing, e.g., stretch-orientation, irradiation, or other conventional film-processing techniques, which are used to impart desired properties as necessary for the intended end-use applications for the film.
• Referring now toFIG. 2, die12 will be described in further detail. As noted above, die12 is adapted to coextrude a plurality of fluid layers, and generally includes a primary formingstem30, one ormore distribution plates32, and amicrolayer assembly34. In the presently illustrated die, fivedistribution plates32 are included, as individually indicated by thereference numerals32a-e.A greater or lesser number ofdistribution plates32 may be included as desired. The number of distribution plates in die12 may range, e.g., from one to twenty, or even more then twenty if desired.
• Each of thedistribution plates32 has afluid inlet36 and a fluid outlet38 (the fluid inlet is not shown inplate32b). Thefluid outlet38 from each of thedistribution plates32 is in fluid communication with the primary formingstem30, and also is structured to deposit a layer of fluid onto the primary forming stem. Thedistribution plates32 may be constructed as described in U.S. Pat. No. 5,076,776, the entire disclosure of which is hereby incorporated herein by reference thereto. As described in the '776 patent, thedistribution plates32 may have one or more spiral-shaped fluid-flow channels40 to direct fluid from thefluid inlet36 and onto the primary formingstem30 via thefluid outlet38. As the fluid proceeds along thechannel40, the channel becomes progressively shallower such that the fluid is forced to assume a progressively thinner profile. Thefluid outlet38 generally provides a relatively narrow fluid-flow passage such that the fluid flowing out of the plate has a final desired thickness corresponding to the thickness of thefluid outlet38. Other channel configurations may also be employed, e.g., a toroid-shaped channel; an asymmetrical toroid, e.g., as disclosed in U.S. Pat. No. 4,832,589; a heart-shaped channel; a helical-shaped channel, e.g., on a conical-shaped plate as disclosed in U.S. Pat. No. 6,409,953, etc. The channel(s) may have a semi-circular or semi-oval cross-section as shown, or may have a fuller shape, such as an oval or circular cross-sectional shape.
• In some embodiments,distribution plates32 may have a generally annular shape such that thefluid outlet38 forms a generally ring-like structure, which forces fluid flowing through the plate to assume a ring-like form. Such ring-like structure offluid outlet38, in combination with its proximity to the primary formingstem30, causes the fluid flowing through theplate32 to assume a cylindrical shape as the fluid is deposited onto thestem30. Each flow of fluid from each of thedistribution plates32 thus forms a distinct cylindrical layer on the primary formingstem30.
• Thefluid outlets38 of thedistribution plates32 are spaced from the primary formingstem30 to form anannular passage42. The extent of such spacing is sufficient to accommodate the volume of the concentric fluid layers flowing along the formingstem30.
• The order in which thedistribution plates32 are arranged indie12 determines the order in which the fluid layers are deposited onto the primary formingstem30. For example, if all fivedistribution plates32a-eare supplied with fluid, fluid fromplate32awill be the first to be deposited onto primary formingstem30 such that such fluid will be in direct contact with thestem30. The next layer to be deposited onto the forming stem would be fromdistribution plate32b.This layer will be deposited onto the fluid layer fromplate32a.Next, fluid fromplate32cwill be deposited on top of the fluid fromplate32b.Ifmicrolayer assembly34 were not present in the die, the next layer to be deposited would be fromdistribution plate32d,which would be layered on top of the fluid layer fromplate32c.Finally, the last and, therefore, outermost layer to be deposited would be fromplate32e.In this example (again, ignoring the microlayer assembly34), the resultanttubular film22 that would emerge from the die would have five distinct layers, which would be arranged as five concentric cylinders bonded together.
• Accordingly, it may be appreciated that the fluid layers from thedistribution plates32 are deposited onto the primary formingstem30 either directly (first layer to be deposited, e.g., fromdistribution plate32a) or indirectly (second and subsequent layers, e.g., fromplates32b-e).
• As noted above, the tubular,multilayer film22 emerges from die12 atdischarge end20. Thedischarge end20 may thus include an annular discharge opening44 to allow the passage of thetubular film22 out of the die. Such annular discharge opening is commonly referred to as a “die lip.” As illustrated, the diameter of theannular discharge opening44 may be greater than that of theannular passage42, e.g., to increase the diameter of thetubular film22 to a desired extent. This has the effect of decreasing the thickness of each of the concentric layers that make up thetubular film22, i.e., relative to the thickness of such layers during their residence time within theannular passage42. Alternatively, the diameter of theannular discharge opening44 may be smaller than that of theannular passage42.
• Microlayer assembly34 generally comprises amicrolayer forming stem46 and a plurality ofmicrolayer distribution plates48. In the presently illustrated embodiment, fifteenmicrolayer distribution plates48a-oare shown. A greater or lesser number ofmicrolayer distribution plates48 may be included as desired. The number ofmicrolayer distribution plates48 inmicrolayer assembly34 may range, e.g., from one to fifty, or even more then fifty if desired. In many embodiments of the present invention, the number ofmicrolayer distribution plates48 inmicrolayer assembly34 will be at least about 5, e.g., 10, 15, 20, 25, 30, 35, 40, 45, 50, etc., or any number of plates in between the foregoing numbers.
• Each of themicrolayer plates48 has afluid inlet50 and afluid outlet52. Thefluid outlet52 from each of themicrolayer plates48 is in fluid communication withmicrolayer forming stem46, and is structured to deposit a microlayer of fluid onto the microlayer forming stem. Similar to thedistribution plates32, themicrolayer plates48 may also be constructed as described in the above-incorporated U.S. Pat. No. 5,076,776.
• For example, as shown inFIG. 3, themicrolayer plates48 may have a spiral-shaped fluid-flow channel54, which is supplied with fluid viafluid inlet50. Alternatively, two more fluid-flow channels may be employed inplate48, which may be fed from separate fluid inlets or a single fluid inlet. Other channel configurations may also be employed, e.g., a toroid-shaped channel; an asymmetrical toroid, e.g., as disclosed in U.S. Pat. No. 4,832,589; a heart-shaped channel; a helical-shaped channel, e.g., on a conical-shaped plate as disclosed in U.S. Pat. No. 6,409,953; etc. The channel(s) may have a semi-circular or semi-oval cross-section as shown, or may have a fuller shape, such as an oval or circular cross-sectional shape.
• Regardless of the particular configuration or pattern that is selected for the flow channel(s)54, its function is to connect the fluid inlet(s)50 with thefluid outlet52 in such a manner that the flow of fluid through themicrolayer assembly34 is converted from a generally stream-like, axial flow to a generally film-like, convergent radial flow towards themicrolayer forming stem46.Microlayer plate48 as shown inFIG. 3 may accomplish this in two ways. First, thechannel54 spirals inwards towards the center of the plate, and thus directs fluid from thefluid inlet50, located near the periphery of the plate, towards thefluid outlet52, which is located near the center of the plate. Secondly, thechannel54 may be fashioned with a progressively shallower depth as the channel approaches thefluid outlet52. This has the effect of causing some of the fluid flowing through thechannel54 to overflow the channel and proceed radially-inward toward thefluid outlet52 in a relatively flat, film-like flow. Such radial-inward flow may occur inoverflow regions53, which may be located between the spaced-apart spiral sections ofchannel54. As shown inFIG. 4, theoverflow regions53 may be formed as recessed sections inplate48, i.e., recessed relative to the thicker,non-recessed region55 at the periphery of the plate. As shown inFIG. 3,overflow regions53 may begin at step-down57 and, e.g., spiral inwards towardsfluid outlet52 between the spirals ofchannel54. The non-recessed,peripheral region55 abuts against the plate or other structure above the plate, e.g., as shown inFIGS. 2 and 5, and thus prevents fluid from flowing outside the periphery of the plate. In this manner, the non-recessed,peripheral region55 forces fluid entering the plate to flow radially inward towardfluid outlet52. Step-down57 thus represents a line or zone of demarcation between the ‘no-flow’peripheral region55 and the ‘flow’regions53 and54. The fluid that remains in thechannel54 and reaches theend56 of the channel flows directly into thefluid outlet52.
• Thefluid outlet52 generally provides a relatively narrow fluid-flow passage and generally determines the thickness of the microlayer flowing out of themicrolayer plate48. The thickness of thefluid outlet52, and therefore the thickness of the microlayer flowing therethrough, may be determined, e.g., by the spacing between the plate surface atoutlet52 and the bottom of the plate or other structure (e.g., manifold76 or78) immediately above the plate surface atoutlet52.
• With continuing reference toFIGS. 2-3, each of themicrolayer distribution plates48 may have anorifice58 extending through the plate. Theorifice58 may be located substantially in the center of eachmicrolayer plate48, with thefluid outlet52 of each plate positioned adjacent tosuch orifice58. In this manner, themicrolayer forming stem46 may extend through theorifice58 of each of themicrolayer distribution plates48. With such a configuration, themicrolayer distribution plates48 may have a generally annular shape such that thefluid outlet52 forms a generally ring-like structure, which forces fluid flowing through the plate to exit the plate in a radially-convergent, ring-like flow pattern. Such ring-like structure offluid outlet52, in combination with its proximity to themicrolayer forming stem46, causes the fluid exiting themicrolayer plates48 to assume a cylindrical shape as the fluid is deposited onto themicrolayer stem46. Each flow of fluid from each of themicrolayer distribution plates48 thus deposits a distinct cylindrical microlayer on themicrolayer forming stem46.
• Themicrolayer plates48 may be arranged to provide a predetermined order in which the microlayers are deposited onto themicrolayer forming stem46. For example, if all fifteenmicrolayer distribution plates48a-oare supplied with fluid, a microlayer of fluid fromplate48awill be the first to be deposited ontomicrolayer forming stem46 such that such microlayer will be in direct contact with thestem46. The next microlayer to be deposited onto the forming stem would be frommicrolayer plate48b.This microlayer will be deposited onto the microlayer fromplate48a.Next, fluid frommicrolayer plate48cwill be deposited on top of the microlayer fromplate48b,etc. The last and, therefore, outermost microlayer to be deposited is from plate48o.In this manner, the microlayers are deposited onto themicrolayer forming stem46 in the form of a substantially unified, microlayered fluid mass60 (seeFIG. 5). In the present example, suchmicrolayered fluid mass60 would comprise up to fifteen distinct microlayers (at the downstream end of stem46), arranged as fifteen concentric cylindrical microlayers bonded and flowing together in a predetermined order (based on the ordering of themicrolayer plates48a-o) onmicrolayer forming stem46.
• It may thus be appreciated that the fluid layers from themicrolayer distribution plates48 are deposited onto themicrolayer forming stem46 either directly (the first layer to be deposited, e.g., frommicrolayer plate48a) or indirectly (the second and subsequent layers, e.g., frommicrolayer plates48b-o). Theorifices58 in each of themicrolayer plates48 are preferably large enough in diameter to space thefluid outlets52 of themicrolayer plates48 sufficiently from themicrolayer forming stem46 to form anannular passage62 for the microlayers (FIG. 2). The extent of such spacing is preferably sufficient to accommodate the volume of the concentric microlayers flowing along themicrolayer stem46.
• In accordance with the present invention, microlayer formingstem46 is in fluid communication with primary formingstem30 such that themicrolayered fluid mass60 flows from themicrolayer forming stem46 and onto the primary formingstem30. This may be seen inFIG. 5, whereinmicrolayered fluid mass60 frommicrolayer assembly34 is shown flowing frommicrolayer forming stem46 and onto primary formingstem30. Fluid communication between themicrolayer stem46 andprimary stem30 may be achieved by including in die12 anannular transfer gap64 between theannular passage62 for themicrolayer stem46 and theannular passage42 for the primary stem30 (see alsoFIG. 2).Such transfer gap64 allows themicrolayered fluid mass60 to flow out of theannular passage62 and into theannular passage42 for the primary formingstem30. In this manner, the microlayers frommicrolayer plates48 are introduced as a unified mass into the generally larger volumetric flow of the thicker fluid layers from thedistribution plates32.
• The inventors have discovered that combining the flows of the microlayers with the thicker fluid layers in this fashion minimizes the deleterious effects of interfacial flow instabilities, which generally make it difficult to combine the flow of thin layers with relatively thick layers in such a way that the physical integrity and independent properties of the thin layers are maintained. Themicrolayer forming stem46 allows the microlayers from themicrolayer plates48 to assemble into themicrolayered fluid mass60 in relative calm, i.e., without being subjected to the more powerful sheer forces of the thicker layers flowing from thedistribution plates32. As the microlayers assemble into theunified fluid mass60 onstem46, the interfacial flow instabilities created by the merger of each layer onto thefluid mass60 are minimized because all the microlayers have a similar degree of thickness, i.e., relative to the larger degree of thickness of the fluid layers fromdistribution plates32. When fully assembled, themicrolayered fluid mass60 enters the flow of the thicker layers fromdistribution plates32 onprimary stem30 with a mass flow rate that more closely approximates that of such thicker layers, thereby increasing the ability of the microlayers influid mass60 to retain their physical integrity and independent physical properties.
• As shown inFIG. 2, primary formingstem30 andmicrolayer forming stem46 may be substantially coaxially aligned with one another indie12, e.g., with themicrolayer forming stem46 being external to the primary formingstem30. This construction provides a relatively compact configuration fordie12, which can be highly advantageous in view of the stringent space constraints that exist in the operating environment of many commercial coextrusion systems.
• For example, the coaxial alignment of the primary formingstem30 with themicrolayer forming stem46 allows thedistribution plates32 and themicrolayer assembly34 to be axially positioned along the primary forming stem, as shown inFIG. 2. This reduces the width ofdie12, and also allows the fluids from both thedistribution plates32 and themicrolayer assembly34 to flow in an axial direction, e.g., in parallel paths along primary formingstem30 andmicrolayer forming stem46, then together along theprimary stem30 downstream oftransfer gap64, at which themicrolayered fluid mass60 flows from themicrolayer stem46 and onto theprimary stem30 to merge with the fluid layers from thedistribution plates32.
• Such construction also allows die12 to be set up in a variety of different configurations to produce a coextruded film having a desired combination of thick layers and microlayers. For example, one ormore distribution plates32 may be located upstream of themicrolayer assembly34. In this embodiment, fluid layers from such upstream distribution plates are deposited onto primary formingstem30 prior to the deposition of themicrolayered fluid mass60 onto theprimary stem30. With reference toFIG. 2, it may be seen thatdistribution plates32a-care located upstream ofmicrolayer assembly34 indie12. Fluid layers65 from suchupstream distribution plates32a-care thus interposed between themicrolayered fluid mass60 and the primary forming stem30 (seeFIG. 5).
• Alternatively, themicrolayer assembly34 may be located upstream of thedistribution plates32, i.e., the distribution plates may be located downstream of themicrolayer assembly34 in this alternative embodiment. Thus, the microlayers from themicrolayer assembly34, i.e., themicrolayered fluid mass60, will be deposited onto primary formingstem30 prior to the deposition thereon of the fluid layers from thedownstream distribution plates32. With reference toFIG. 2, it may be seen thatmicrolayer assembly34 is located upstream ofdistribution plates32d-eindie12. As shown inFIG. 5, themicrolayered fluid mass60 is thus interposed between the fluid layer(s)70 fromsuch distribution plates32d-eand the primary formingstem30.
• As illustrated inFIG. 2, themicrolayer assembly34 may also be positioned between one or more upstream distribution plates, e.g.,plates32a-c,and one or more downstream distribution plates, e.g.,plates32d-e.In this embodiment, fluid(s) fromupstream plates32a-care deposited first ontoprimary stem30, followed by themicrolayered fluid mass60 from themicrolayer assembly34, and then further followed by fluid(s) fromdownstream plates32d-e.In the resultant multilayered film, the microlayers frommicrolayer assembly34 are sandwiched between thicker layers from both theupstream plates32a-cand thedownstream plates32d-e.
• As a further variation, die12 may include one or more additional microlayer assemblies, which may be the same asmicrolayer assembly34 or may have a different configuration, e.g., a different number of microlayer plates. In this embodiment, any such additional microlayer assemblies may be coaxially aligned with the primary formingstem30, and may be positioned upstream and/or downstream of themicrolayer assembly34 shown inFIG. 2. Such additional microlayer assemblies may be used in place of or in addition to thedistribution plates32. Thus, additional microlayer assemblies may be positioned adjacent to themicrolayer assembly34, or may be spaced fromsuch assembly34 by one ormore distribution plates32. If two or more microlayer assemblies are included indie12, such assemblies may also be sandwiched between upstream and downstream distribution plates, e.g., between theupstream plates32a-canddownstream plates32d-eshown inFIG. 2.
• In many embodiments of the invention, most or all of themicrolayer plates48 have a thickness that is less than that of thedistribution plates32. Thus, for example, thedistribution plates32 may have a thickness T₁(seeFIG. 5) ranging from about 0.5 to about 2 inches, e.g., greater than 0.5 inch, such as 0.501 or more, 0.502 or more, 0.503 or more, etc., or less than 2, e.g., 1.999 or less, 1.998 or less, etc., such as from about 0.501 to 1.999 inches, 0.502 to 1.998 inches, etc. Themicrolayer distribution plates48 may have a thickness T₂ranging from about 0.1 to about 0.5 inch, e.g., greater than 0.1, such as 0.101 or more, 0.102 or more, etc., or less than 0.5, e.g., 0.499 or less, 0.498 or less, etc., such as from about 0.101 to 0.499 inch, 0.102 to 0.498 inch, etc. Such thickness ranges are not intended to be limiting in any way, but only to illustrate typical examples. Alldistribution plates32 will not necessarily have the same thickness, nor will all of themicrolayer plates48. For example, microlayer plate48o,the most downstream of the microlayer plates in theassembly34, may be thicker than the other microlayer plates to accommodate asloped contact surface66, which may be employed to facilitate the transfer of microlayeredfluid mass60 through theannular gap64 and onto the primary formingstem30.
• As also shown inFIG. 5, each of the microlayers flowing out of theplates48 has a thickness “M” corresponding to the thickness of thefluid outlet52 from which each microlayer emerges. The microlayers flowing from themicrolayer plates48 are schematically represented inFIG. 5 by thephantom arrows68.
• Similarly, each of the relatively thick fluid layers flowing out of theplates32 has a thickness “D” corresponding to the thickness of thefluid outlet38 from which each such layer emerges (seeFIG. 5). The relatively thick fluid layers flowing from thedistribution plates32 are schematically represented inFIG. 5 by thephantom arrows70.
• Generally, the thickness M of the microlayers will be less than the thickness D of the fluid layers from thedistribution plates32. The thinner that such microlayers are relative to the fluid layers from thedistribution plates32, the more of such microlayers that can be included in a multilayer film, for a given overall film thickness. Microlayer thickness M from eachmicrolayer plate48 will generally range from about 1-20 mils (1 mil=0.001 inch), e.g., greater than 1 mil, greater than 2 mils, greater than 3 mils, etc., less than 20 mils, less than 19 mils, less than 18 mils, etc., such as between 2 to 19 mils, 3 to 18 mils, 4 to 17 mils, etc. Thickness D from eachdistribution plate32 will generally range from about 20-100 mils, e.g., greater than 20 mils, greater than 21 mils, greater than 22 mils, etc., less than 100 mils, less than 90 mils, less than 80 mils, less than 70 mils, less than 60 mils, etc., such as between 20 to 50 mils, 21 to 49 mils, 22 to 48 mils, 23 to 47 mils, etc. The foregoing thicknesses are not intended to be limiting of the scope of the present invention in any way, and are provided solely for illustration purposes.
• The ratio of M:D may range from about 1:1 to about 1:8, e.g., greater than 1:1, greater than 1:1.1, greater than 1:1.2, greater than 1:2, greater than 1:3, etc., less than 1:8, less than 1:7.9, less than 1:7.8, less than 1:7, less than 1:6, etc., such as between 1:1.1-1:7.9; 1:1.2-1:7.8, 1:2-1:7, 1:3-1:6, 1:4-1:5, etc.
• Thickness M may be the same or different among themicrolayers68 flowing frommicrolayer plates48 to achieve a desired distribution of layer thicknesses in the microlayer section of the resultant film. Similarly, thickness D may be the same or different among thethicker layers70 flowing from thedistribution plates32 to achieve a desired distribution of layer thicknesses in the ‘thick-layer section(s)’ of the resultant film. The layer thicknesses M and D will typically change as the fluid flows downstream through the die, e.g., if the melt tube is expanded at annular discharge opening44 as shown inFIG. 2, and/or upon further downstream processing of the tubular film, e.g., by stretching, orienting, or otherwise expanding the tube to achieve a final desired film thickness and/or to impart desired properties into the film. Such downstream processing techniques are well known in the art. The flow rate of fluids through the plates will also have an effect on the final downstream thicknesses of the corresponding film layers.
• With reference back toFIGS. 1-2, it may be appreciated that a method of coextruding a plurality of fluid layers in accordance with the present invention comprises the steps of:
• a. directing one or more fluids through one ormore distribution plates32 and onto primary formingstem30 indie12;
• b. forming a substantially unified,microlayered fluid mass60 onmicrolayer forming stem46 by directing at least one additional fluid throughmicrolayer assembly34; and
• c. directing themicrolayered fluid mass60 from themicrolayer forming stem46 and onto the primary formingstem30 to merge themicrolayered fluid mass60 with the fluid layer(s) from the distribution plate(s)32.
• As described above, thedistribution plates32 andmicrolayer plates48 preferably have an annular configuration, such that primary formingstem30 and microlayer stem46 pass through the center of the plates to receive fluid that is directed into the plates. The fluid may be supplied from extruders, such asextruders14a, b. The fluid may be directed into thedie12 viavertical supply passages72, which receive fluid from feed pipes18, and direct such fluid into thedie plates32 and48. For this purpose, the plates may have one or more through-holes74, e.g., near the periphery of the plate as shown inFIG. 3, which may be aligned to provide thevertical passages72 through which fluid may be directed to one or more downstream plates.
• Although three through-holes74 are shown inFIG. 3, a greater or lesser number may be employed as necessary, e.g., depending upon the number of extruders that are employed. In general, onesupply passage72 may be used for each extruder14 that supplies fluid to die12. The extruders14 may be arrayed around the circumference of the die, e.g., like the spokes of a wheel feeding into a hub, wherein the die is located at the hub position.
• With reference toFIG. 1, die12 may include aprimary manifold76 to receive the flow of fluid from the extruders14 via feed pipes18, and then direct such fluid into a designatedvertical supply passage72, in order to deliver the fluid to the intended distribution plate(s)32 and/or microlayer plate(s)48. Themicrolayer assembly34 may optionally include amicrolayer manifold78 to receive fluid directly from one or moreadditional extruders80 via feed pipe82 (shown in phantom inFIG. 1).
• In the example illustrated inFIGS. 1-2,extruder14bdelivers a fluid, e.g., a first molten polymer, directly to thefluid inlet36 ofdistribution plate32aviapipe18bandprimary manifold76. In the presently illustrated embodiment,distribution plate32areceives all of the output fromextruder14b,i.e., such that the remaining plates and microlayer plates in the die12 are supplied, if at all, from other extruders. Alternatively, thefluid inlet36 ofdistribution plate32amay be configured to contain an outlet port to allow a portion of the supplied fluid to pass through to one or more additional plates, e.g.,distribution plates32 and/ormicrolayer plates48, positioned downstream ofdistribution plate32a.
• For example, as shown inFIGS. 3-4 with respect to the illustratedmicrolayer plate48, anoutlet port84 may be formed in the base of thefluid inlet50 of the plate.Such outlet port84 allows the flow of fluid delivered to plate48 to be split: some of the fluid flows intochannel54 while the remainder passes through the plate for delivery to one or more additionaldownstream plates48 and/or32. A similar outlet port can be included in the base of thefluid inlet36 of adistribution plate32. Delivery of fluid passing through the outlet port84 (or through a similar outlet port in a distribution plate32) may be effected via a through-hole74 in an adjacent plate (seeFIG. 5), or via other means, e.g., a lateral-flow supply plate, to direct the fluid in an axial, radial, and/or tangential direction through die12 as necessary to reach its intended destination.
• Distribution plates32b-care being supplied with fluid via extruder(s) and supply pipe(s) and/or through-holes that are not shown inFIG. 2. The fluid flow along primary formingstem30 fromdistribution plates32a-cis shown inFIG. 5, as indicated byreference numeral65.
• As shown inFIGS. 1-2,microlayer assembly34 is being supplied with fluid byextruders14aand80. Specifically,microlayer plates48a, c, e, g, i, k, m,andoare supplied byextruder14aviasupply pipe18aand vertical pipe and/orpassage72.Microlayer plates48b, d, f, h, j, l,andnare supplied with fluid byextruder80 viafeed pipe82 and avertical supply passage86. In the illustrated embodiment,vertical passage86 originates inmicrolayer manifold78 and delivers fluid only within themicrolayer assembly34. In contrast,vertical passage72 originates inmanifold76, extends throughdistribution plates32a-c(via aligned through-holes74 in such plates), then further extends throughmanifold78 viamanifold passage79 before finally arriving atmicrolayer plate48a.
• Fluid fromextruder14aandvertical passage72 entersmicrolayer plate48aatfluid inlet50. Some of the fluid passes frominlet50 and into channel54 (for eventual deposition onmicrolayer stem46 as the first microlayer to be deposited on stem46), while the remainder of the fluid may pass throughplate48aviaoutlet port84.Microlayer plate48bmay be oriented, i.e., rotated, such that a through-hole74 is positioned beneath theoutlet port84 ofmicrolayer plate48aso that the fluid flowing out of theoutlet port84 flows through themicrolayer plate48b,and not into thechannel54 thereof.Microlayer plate48cmay be positioned such that thefluid inlet50 thereof is in the same location as that ofmicrolayer plate48aso that fluid flowing out of through-hole74 ofmicrolayer plate48bflows into theinlet50 ofplate48c.Some of this fluid flows into thechannel54 ofplate48cwhile some of the fluid passes through the plate viaoutlet port84, passes through a through-hole74 in thenext plate48d,and is received byfluid inlet50 of thenext microlayer plate48e,where some of the fluid flows intochannel54 and some passes out of the plate viaoutlet port84. Fluid fromextruder14acontinues to be distributed to remainingplates48g, i, k,andmin this manner, except for microlayer plate48o,which has nooutlet port84 so that fluid does not pass through plate48o,except viachannel54 andfluid outlet52.
• In a similar manner, fluid fromextruder80 andvertical passage86 passes throughmicrolayer plate48avia a through-hole74 and then entersmicrolayer plate48batfluid inlet50 thereof. Some of this fluid flows through thechannel54 and exits the plate atoutlet52, to become the second microlayer to be deposited onto microlayer stem46 (on top of the microlayer fromplate48a), while the remainder of the fluid passes through the plate via anoutlet port84. Such fluid may pass throughmicrolayer plate48cvia a through-hole74, and be delivered to plate48dvia appropriate alignment of itsinlet50 with the through-hole74 ofplate48c,through which the fluid fromextruder80 passes. This fluid-distribution process may continue forplates48f, h, j,andl,until the fluid reachesplate48n,which has nooutlet port84 such that fluid does not pass through this plate except via itsfluid outlet52.
• In this manner, a series of microlayers comprising alternating fluids fromextruders14aand80 may be formed onmicrolayer stem46. For example, ifextruder14asupplied EVOH andextruder80 supplied PA6, the resultantmicrolayered fluid mass60 would have the structure:
• 
  EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH
• The fluids fromextruders14aand80 may be the same or different such that the resultant microlayers inmicrolayered fluid mass60 may have the same or a different composition. Only one extruder may be employed to supply fluid to theentire microlayer assembly34, in which case all of the resultant microlayers will have the same composition. Alternatively, three or more extruders may be used to supply fluid to themicrolayer assembly34, e.g., with each supplying a different fluid such that three different microlayer compositions are formed inmicrolayered fluid mass60, in any desired order, e.g., abcabc; abbcabbc; abacabac; etc.
• Similarly, the fluid(s) directed through the distribution plate(s)32 may be substantially the same as the fluid(s) directed through themicrolayer assembly34. Alternatively, the fluid(s) directed through the distribution plate(s)32 may be different from the fluid(s) directed through the microlayer assembly. The resultant tubular film may have thick layers and microlayers that have substantially the same composition. Alternatively, some of the thick layers fromdistribution plates32 may be the same as some or all of the microlayers frommicrolayer plates48, while other thick layers may be different from some or all of the microlayers.
• In the illustrated example, the extruders and supply passages fordistribution plates32d-eare not shown. One or both of such plates may be supplied fromextruder14a,14b,and/or80 by appropriate arrangement ofvertical supply passages72,86, through-holes74, and/oroutlet ports84 of theupstream distribution plates32 and/ormicrolayer plates48. Alternatively, one or bothdistribution plates32d-emay not be supplied at all, or may be supplied from a separate extruder, such as an extruder in fluid communication withprimary manifold76 and avertical supply passage72 that extends throughdistribution plates32a-candmicrolayer assembly34, e.g., via appropriate alignment of the through-holes74 ofplates32a-candmicrolayer assembly34 to create a fluid transport passage throughdie12, leading tofluid inlet50 ofdistribution plate32dand/or32e.
• If desired, one or more of thedistribution plates32 and/ormicrolayer plates48 may be supplied with fluid directly from one or more extruders, i.e., by directing fluid directly into the fluid inlet of the plate, e.g., from the side of the plate, without the fluid being first routed through one ofmanifolds76 or78 and/or without using avertical supply passage72,86. Such direct feed of one ormore plates32 and/or48 may be employed as an alternative or in addition to the use of manifolds and vertical supply passages as shown inFIG. 2.
• The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention.

Claims (19)

1. A die for coextruding a plurality of fluid layers, comprising:

a. a primary forming stem;

b. one or more distribution plates, each of said plates having a fluid inlet and a fluid outlet, the fluid outlet from each of said plates being in fluid communication with said primary forming stem and structured to deposit a layer of fluid onto said primary forming stem; and

c. a microlayer assembly, comprising

(1) a microlayer forming stem, and

(2) a plurality of microlayer distribution plates, each of said microlayer plates having a fluid inlet and a fluid outlet, the fluid outlet from each of said microlayer plates being in fluid communication with said microlayer forming stem and structured to deposit a microlayer of fluid onto said microlayer forming stem, said microlayer plates being arranged to provide a predetermined order in which the microlayers are deposited onto said microlayer forming stem to form a substantially unified, microlayered fluid mass on said microlayer forming stem,

wherein, said microlayer forming stem is in fluid communication with said primary forming stem such that said microlayered fluid mass flows from said microlayer forming stem and onto said primary forming stem.

2. The die ofclaim 1, wherein said distribution plates have a thickness ranging from about 0.5 to about 2 inches and said microlayer distribution plates have a thickness ranging from about 0.1 to about 0.5 inch.

3. The die ofclaim 1, wherein said microlayer distribution plates have one or more flow channels connecting said fluid inlet with said fluid outlet, said flow channels having a spiral-shaped configuration.

4. The die ofclaim 1, wherein

said microlayer distribution plates each have an orifice extending through said plate;

said fluid outlet of each of said microlayer distribution plates is positioned adjacent to said orifice; and

said microlayer forming stem extends through the orifice of each of said microlayer distribution plates.

5. The die ofclaim 1, wherein said primary forming stem and said microlayer forming stem are substantially coaxially aligned with one another.

6. The die ofclaim 5, wherein said microlayer forming stem is external to said primary forming stem.

7. The die ofclaim 1, wherein

said distribution plates and said microlayer assembly are axially positioned along said primary forming stem; and

the fluids from said distribution plates and said microlayer assembly flow in an axial direction along said primary forming stem.

8. The die ofclaim 7, wherein said distribution plates are located upstream of said microlayer assembly.

9. The die ofclaim 7, wherein said microlayer assembly is located upstream of said distribution plates.

10. The die ofclaim 7, wherein said microlayer assembly is positioned between one or more upstream distribution plates and one or more downstream distribution plates.

11. The die ofclaim 1, wherein said microlayer assembly comprises at least about 5 microlayer plates.

12. The die ofclaim 1, further including one or more additional microlayer assemblies.

13. A system for coextruding a plurality of fluid layers, comprising:

a. a die, comprising:

(1) a primary forming stem,

(2) one or more distribution plates, each of said plates having a fluid inlet and a fluid outlet, the fluid outlet from each of said plates being in fluid communication with said primary forming stem and structured to deposit a layer of fluid onto said primary forming stem, and

(3) a microlayer assembly, comprising

(a) a microlayer forming stem, and

(b) a plurality of microlayer distribution plates, each of said microlayer plates having a fluid inlet and a fluid outlet, the fluid outlet from each of said microlayer plates being in fluid communication with said microlayer forming stem and structured to deposit a microlayer of fluid onto said microlayer forming stem, said microlayer plates being arranged to provide a predetermined order in which the microlayers are deposited onto said microlayer forming stem to form a substantially unified, microlayered fluid mass on said microlayer forming stem, wherein, said microlayer forming stem is in fluid communication with said primary forming stem such that said microlayered fluid mass flows from said microlayer forming stem and onto said primary forming stem; and

b. one or more extruders in fluid communication with said die to supply one or more fluids to said die.

14. A method of coextruding a plurality of fluid layers, comprising:

a. directing a fluid through a distribution plate and onto a primary forming stem, said distribution plate having a fluid inlet and a fluid outlet, the fluid outlet from said plate being in fluid communication with said primary forming stem and structured such that said fluid is deposited onto said primary forming stem as a layer;

b. forming a substantially unified, microlayered fluid mass on a microlayer forming stem by directing at least one additional fluid through a microlayer assembly, said microlayer assembly comprising a plurality of microlayer distribution plates, each of said microlayer plates having a fluid inlet and a fluid outlet, the fluid outlet from each of said microlayer plates being in fluid communication with said microlayer forming stem and structured to deposit a microlayer of fluid onto said microlayer forming stem, said microlayer plates being arranged to provide a predetermined order in which the microlayers are deposited onto said microlayer forming stem; and

c. directing said microlayered fluid mass from said microlayer forming stem and onto said primary forming stem to merge said microlayered fluid mass with said fluid layer from said distribution plate.

15. The method ofclaim 14, wherein the fluid directed through said distribution plate is substantially the same as the fluid directed through said microlayer assembly.

16. The method ofclaim 14, wherein the fluid directed through said distribution plate is different from the fluid directed through said microlayer assembly.

17. The method ofclaim 14, wherein said fluid layer from said distribution plate is deposited onto said primary forming stem prior to the deposition of said microlayered fluid mass onto said primary forming stem such that said fluid layer from said distribution plate is interposed between said microlayered fluid mass and said primary forming stem.

18. The method ofclaim 14, wherein said microlayered fluid mass is deposited onto said primary forming stem prior to the deposition of said fluid layer from said distribution plate onto said primary forming stem such that said microlayered fluid mass is interposed between said fluid layer from said distribution plate and said primary forming stem.

19. The method ofclaim 14, wherein:

each of said microlayers has a thickness M,

said fluid layer from said distribution plate has a thickness D, and

the ratio of M:D ranges from about 1:1 to about 1:8.

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