DESCRIPTION

IMPROVED CROSS FLOW MANIFOLD EXTRUSION DIE

FIELD OF THE INVENTION

[0001] This disclosure relates generally to an extrusion apparatus for producing a film or sheet of thermoplastic material.

BACKGROUND OF THE INVENTION

[0002] Extrusion dies are used in manufacturing processes to make a variety of goods. Some dies, for example, are used to form thin films, sheets or other elongated shapes of plastic material. Techniques have been developed for melt laminating which involves joining two or more diverse materials (e.g., thermoplastic materials) from separate molten layers under pressure within a die to emerge as a single laminated material. Such processes make use of the laminar flow principle which enables two or more molten layers under proper operating conditions to join in a common flow channel without intermixing at the contacting interfaces. These multiple layer extrusion systems have come into use as a convenient way to provide for the formation of multiple layers of similar or dissimilar materials.

[0003] Various extrusion dies have been produced to extrude multiple layer films. One general configuration of device utilized a first die section which combined the various layers of materials. The combined materials were then flattened and extruded through a second die section. An example of this type of device is illustrated by U.S. Patent No. 5,316,703, incorporated by reference herein in its entirety. This type of device was limited in effectiveness because of the requirement in thin film production that the multi-layer sheet or web have uniform thickness across the width or transverse direction (TD) of the extruded sheet.

[0004] A die assembly can be modular and is typically assembled from a plurality of parts and then set in a die station as an integral device. For example, a die assembly can comprise a first die part and a second die part, which together form the components that

allow a fluid to enter the assembly and be properly emitted therefrom. The first die part includes a first lip and the second die part includes a second lip, these lips defining a feed gap therebetween that determines the thickness of the fluid film emitted therefrom. [0005] Center feed extrusion dies are commonly used in today's plastics industry. A flow stream entering the manifold undergoes flow divergence, as a result of which there occurs a division of the stream into substreams that flow in generally opposite directions to both ends of the manifold. Pressure drop occurs as each substream flows from the centerline of the manifold to its respective manifold end. [0006] Typically, center feed extrusion dies have a tear drop-shaped, flat manifold, which may be in a form known as a coat hanger manifold, a fish tail manifold, or a T-type manifold. To overcome the pressure drop and produce a substantially equal flow volume of a stream across the stream width, this type of die may further include a flow pressure- compensating preland channel. Also known is a center feed extrusion die having a two stage, flow pressure-compensating, preland channel. This type of apparatus is exemplified in U.S. Patent No. 4,372,739 to Vetter et al. and U.S. Patent No. 5,256,052 to Cloeren.

[0007] A die assembly can have a fixed feed gap or a flexible feed gap. With a fixed feed gap, the lips are not movable relative to each other, so that the thickness of the feed gap will always be the same dimension. With a flexible feed gap, one lip is movable relative to the other lip so as to enable adjustment of the feed gap along the width of the assembly. A flexible feed gap is typically accomplished by assembling the first die part so that it contains a flexible web between its rear portion and its front portion (to which the first lip is attached), as well as means for moving the front portion in localized areas. Movement of the front portion results in the adjustment of the position of the lip relative to the other Hp and, thus, the thickness of the feed gap in the relevant localized area. [0008] In flexible feed gap operations, localized adjustments of the feed gap can usually be accomplished with conventional die assembly designs in order to accommodate a particular run. This is typically accomplished by measuring the thickness of a finished

plastic sheet or film across its width downstream from the die lips, readjusting one or more of adjustment bolts, re-measuring the thickness of a finished plastic sheet or film, and so on until the film thickness distribution is within acceptable limits.

[0009] The production of certain specialty films, such as microporous polyolefin membranes have presented additional requirements in the design of extrusion dies for their production. Microporous polyolefin membranes are useful as separators for primary batteries and secondary batteries such as lithium ion secondary batteries, lithium-polymer secondary batteries, nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, nickel-zinc secondary batteries, silver-zinc secondary batteries, etc. When the microporous polyolefin membrane is used as a battery separator, particularly as a lithium ion battery separator, the membrane's performance significantly affects the properties, productivity and safety of the battery. Accordingly, the microporous polyolefin membrane should have suitably well-balanced permeability, mechanical properties, dimensional stability, shutdown properties, meltdown properties, etc. The term "well-balanced" means that the optimization of one of these characteristics does not result in a significant degradation in another.

[0010] As is known, it is desirable for the batteries to have a relatively low shutdown temperature and a relatively high meltdown temperature for improved battery safety, particularly for batteries exposed to high temperatures under operating conditions. Consistent dimensional properties, such as film thickness, are essential to high performing films. A separator with high mechanical strength is desirable for improved battery assembly and fabrication, and for improved durability. The optimization of material compositions, casting and stretching conditions, heat treatment conditions, etc. have been proposed to improve the properties of microporous polyolefin membranes. [0011] In general, microporous polyolefin membranes consisting essentially of polyethylene (i.e., they contain polyethylene only with no significant presence of other species) have relatively low meltdown temperatures. Accordingly, proposals have been

made to provide niicroporous polyolefin membranes made from mixed resins of polyethylene and polypropylene, and multi-layer, microporous polyolefin membranes having polyethylene layers and polypropylene layers in order to increase meltdown temperature. The use of these mixed resins and the production of multilayer films having layers of differing polyolefins can make the production of films having consistent dimensional properties, such as film thickness, all the more difficult. [0012] U.S. Patent No. 2,938,201 proposes an adjustable sheet forming extrusion die having expandable adjustment bolts which may be finely adjusted by means of electric heaters which control the length of each bolt between its mounting in the die body, and the bolt juncture points in the die blades.

[0013] U.S. Patent No. 3,920,365 proposes the control of film thickness distribution by selective thermal control of isolated or localized portions of a pair of die lips by employing temperature sensors and heating elements embedded therein. By controlling localized temperature variations, the local melt viscosity, and hence local mass flow rate, of the polymeric material may be increased or decreased to maintain the film thickness distribution within acceptable limits.

[0014] U.S. Patent No. 4,124,342 proposes an automated system for control of film thickness distribution which employs an algorithm to calculate the number of turns each adjustment bolt requires to achieve a desired die gap distribution and therefore a desired film thickness distribution. As may be appreciated, one of the disadvantages of such a system is the assumption that each die bolt response is uniform.

[0015] U.S. Patent No. 4,409,160 proposes a method for controlling the thickness of an extruded, biaxially elongated film product, in which thickness deviations are controlled automatically. In the method, correlation between positions along the widthwise direction of a film sheet and positions of die manipulation bolts of an extrusion die is obtained, and initially, a profile of the film sheet prior to lateral elongation is converted into a tolerable range; thereafter, the thickness of the film sheet after lateral elongation is measured, and if

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there are thickness deviations outside the tolerable range, a thickness regulation is effected by transmitting a signal corresponding to the thickness deviations to the appropriate die manipulation bolts. [0016] U.S. Patent No. 5,045,264 proposes a method and apparatus for manufacturing a composite film of a matrix material and of a second material in the form of one or more strips of the second material, which are embedded in the matrix material at one or both surfaces of the composite film. The apparatus proposed includes a cast film die having two opposed die portions. The apparatus proposed employs a bolt that is associated with a hinged die lip for forcing the die lip toward an opposed die lip for narrowing the gap defined between die lips.

[0017] JP U3048972 proposes an extrusion die design said to eliminate flow divergence of the molten polymer within the extrusion manifold. The proposed die design is provided with two manifolds to form two slit currents. The molten polymer is fed into a first inlet at an end of a first manifold and a second inlet at the end of a second manifold on the opposite side of the first inlet. Two slit currents flow together inside the die. It is theorized that due to the absence of flow divergence of the melt inside the manifold, it may be possible to achieve uniform flow distribution within the die. This is said to result in improved thickness uniformity in the transverse direction the film or the sheet. [0018] JP7-216118A discloses a battery separator formed from a porous film comprising polyethylene and polypropylene as indispensable components and having at least two microporous layers each with different polyethylene content. The polyethylene content is 0 to 20% by weight in one microporous layer, 21 to 60% by weight in the other microporous layer, and 2 to 40% by weight in the overall film. The battery separator has relatively high shutdown-starting temperature and mechanical strength. [0019] WO 2004/089627 discloses a microporous polyolefin membrane made of polyethylene and polypropylene comprising two or more layers, the polypropylene content

being more than 50% and 95% or less by mass in at least one surface layer, and the polyethylene content being 50 to 95% by mass in the entire membrane. [0020] WO 2005/113657 discloses a microporous polyolefin membrane having conventional shutdown properties, meltdown properties, dimensional stability and high- temperature strength. The membrane is made using a polyolefin composition comprising (a) composition comprising lower molecular weight polyethylene and higher molecular weight polyethylene, and (b) polypropylene. This microporous polyolefin membrane is produced by a so-called "wet process".

[0021] Despite these advances in the art, there remains a need for extrusion dies capable of producing microporous polyolefin membranes and other high quality films or sheets.

SUMMARY OF THE INVENTION

[0022] Provided is an extrusion die for producing a film or sheet comprising thermoplastic material such as a mixture of polymer and diluent. The extrusion die includes a die outlet, which can be slotted, through which a melt stream of the mixture of polymer and diluent is extruded as a film or sheet, the die outlet comprising a first die lip and a second die lip, a feed entrance in communication with a feed splitter for dividing the mixture into a first portion and a second portion; and a first die section having a cross flow manifold comprising (i) a first cross flow manifold section for receiving the first portion of the mixture, the first cross flow manifold section comprising a first passage having a first axis positioned within a first plane of the extrusion die, a second passage in communication with the first passage and having a second axis positioned within a second plane of the extrusion die, and a third passage in communication with the second passage and having a third axis positioned within a third plane of the extrusion die, the third passage in communication with the die outlet, and a fourth passage in communication with the third passage and having a fourth axis positioned within the third plane of the extrusion

die, the fourth passage in communication with the die outlet, and (ii) a second cross flow manifold section for receiving the second portion of the thermoplastic material, the second cross flow manifold section comprising a first passage having a first axis positioned within the third plane of the extrusion die, a second passage in communication with the first passage and having a second axis positioned within a fourth plane of the extrusion die, and a third passage in communication with the second passage and having a third axis positioned within the first plane of the extrusion die, the third passage in communication with the die outlet, and a fourth passage in communication with the third passage and having a fourth axis positioned within the first plane of the extrusion die, the fourth passage in communication with the die outlet.

[0023] In another aspect, a process for producing a film or sheet of a mixture of polymer and diluent is also provided. The process includes the steps of combining at least one polymer (e.g., a polyolefin composition) and at least one diluent (e.g., a solvent); and extruding the combined polymer and diluent through an extrusion die, the extrusion die including a die outlet through which an extrudate comprising the polymer and diluent is extruded as a film or sheet, the die outlet comprising a first die lip and a second die lip, the first die lip comprising a plurality of cantilevered adjustment members extending normally from the first die lip, the plurality of cantilevered adjustment members each having an actuatable means, a feed entrance in communication with a feed splitter for dividing the combined polymer and diluent into a first portion and a second portion, and a first die section having a cross flow manifold. The cross flow manifold includes (1) a first cross flow manifold section for receiving the first portion, the first cross flow manifold section comprising a first passage having a first axis positioned within a first plane of the extrusion die, a second passage in communication with the first passage and having a second axis positioned within a second plane of the extrusion die, and a third passage in communication with the second passage and having a third axis positioned within a third plane of the extrusion die, the third passage in communication with the die outlet, and a

_g

fourth passage in communication with the third passage and having a fourth axis positioned within the third plane of the extrusion die, the fourth passage in communication with the die outlet; and (2) a second cross flow manifold section for receiving the second portion, the second cross flow manifold section comprising a first passage having a first axis positioned within the third plane of the extrusion die, a second passage in communication with the first passage and having a second axis positioned within a fourth plane of the extrusion die, and a third passage in communication with the second passage and having a third axis positioned within the first plane of the extrusion die, the third passage in communication with the die outlet, and a fourth passage in communication with the third passage and having a fourth axis positioned within the first plane of the extrusion die, the fourth passage in communication with the die outlet.

[0024] It has been found that the shape memory characteristics of a polymer, e.g., a polyolefin, can be a factor in maintaining uniform transverse direction film and sheet thickness as the film or sheet exits an extrusion die. Shape memory effects have been observed in conventional extrusion and coextrusion of sheets and films, i.e., those extrudates from polymer melts containing at most a small amount of solvent. It was, therefore, surprising to observe a shape memory effect in polymer extrudates containing a significant amount of solvent, e.g., in the range of at least 10 wt.%, or at least 25 wt.%, or at least 50 wt.%, or at least 75 wt.%, based on the weight of the extrudate. [0025] It has also been found that extrusion die manifold design can influence the shape memory phenomena. As such, in an exemplary form disclosed herein, one or more cross flow manifolds are provided with a flow path of a length sufficient to substantially eliminate the shape memory characteristics of the extrudate. [0026] In a further exemplary form disclosed herein, the first cross flow manifold section and the second cross flow manifold section of the cross flow manifold each have a flow path that substantially traverses the extrusion die's length at least two times.

[0027] In a still further exemplary form disclosed herein, the first die lip includes a plurality of cantilevered adjustment members extending normally from the first die lip, the plurality of cantilevered adjustment members each having an actuatable means. [0028] In a still yet further exemplary form disclosed herein, each actuatable means includes an individual lip bolt effective for varying the width of the die outlet in a region adjacent a point of adjustment.

[0029] These and other advantages, features and attributes of the disclosed extrusion dies and their advantageous applications and/or uses will be apparent from the detailed description that follows, particularly when read in conjunction with the figures appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is an exploded perspective view of an extrusion die having a cross flow manifold system for producing a film or sheet of thermoplastic material, in accordance herewith;

[0031] FIG. 2 is a partially exploded perspective view of the extrusion die having the cross flow manifold system of FIG. 1, showing a pair of die end plates for positioning on the die, in accordance herewith;

[0032] FIG. 3 is a schematic view of an extrusion die for producing a multilayer film or sheet of thermoplastic material showing the respective flow paths of the thermoplastic material, in accordance herewith;

[0033] FIG. 4 is a perspective view showing a first portion of a cross flow manifold for producing a skin layer of a multilayer film or sheet of thermoplastic materials, in accordance herewith; [0034] FIG. 5 is a perspective view showing a second portion of a cross flow manifold for producing a skin layer of a multilayer film or sheet of thermoplastic materials, in accordance herewith;

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[0035] FIG. 6 is a schematic view of a coextrusion die for producing a multilayer film or sheet of thermoplastic materials showing the skin layer flow paths of the thermoplastic materials, in accordance herewith;

[0036] FIG. 7 is a perspective view of an extrusion die for producing a film or sheet of thermoplastic material showing a cantilevered die lip adjustment system, in accordance herewith;

[0037] FIG. 8 is a perspective view of an extrusion die for producing a film or sheet of thermoplastic material showing a cantilevered die lip adjustment system, in accordance herewith; [0038] FIG. 9 is a perspective view of an extrusion die for producing a film or sheet of thermoplastic material showing a cantilevered die lip adjustment system having actuatable means, in accordance herewith;

[0039] FIG. 1OA is a simplified view showing a cantilevered die lip adjustment system having actuatable means, in accordance herewith; [0040] FIG. 1OB is a simplified view showing a cantilevered die lip adjustment system having actuatable means, in accordance herewith;

[0041] FIG. 11 is a perspective view of a coat hanger extrusion die showing the flow path of the thermoplastic material; and

[0042] FIG. 12 is a perspective view of a cross flow extrusion die showing the flow path of the thermoplastic material.

DETAILED DESCRIPTION OF THE INVENTION

[0043] Reference is now made to FIGS. 1-12, wherein like numerals are used to designate like parts throughout. [0044] Referring now to FIGS. 1-3, an extrusion die 10 for producing a film or sheet of thermoplastic material, in accordance herewith, is shown. Extrusion die 10 includes a die outlet 12 through which a mixture of polymer and diluent may be extruded as a film or

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sheet. In one form, extrusion die 10 is provided with a first die section 14, a second die section 16, and a third die section 18 and a cross flow manifold 20 that traverses a plurality of passageways formed within first die section 14, second die section 16, and third die section 18. As may be appreciated, the provision of extrusion die 10 having first die section 14, second die section 16 and third die section 18 facilitates the machining and easy cleaning of cross flow manifold 20.

[0045] As shown in detail by reference to FIG. 1, cross flow manifold 20 includes a feed entrance 22 and a feed splitter 24 for feeding the plurality of passageways of cross flow manifold 20 in communication with die outlet 12. In operation, a feed stream of mixed polymer and diluent F is split into a first stream Sl and a second stream S2, the first stream S 1 feeding cross flow manifold section 26 and the second stream S2 feeding cross flow manifold section 28.

[0046] First die section 14 includes a first side 30, a second side 32, a first end 34 and a second end 36, with portions of cross flow manifold 20 formed within each. Second die section 16 includes an interior side 38 and third die section 18 includes an interior side 40, with portions of cross flow manifold 20 formed within each. As may be envisioned, from FIG. 2, first end plate 42 and second end plate 44 are also provided with portions of cross flow manifold 20 formed within each. [0047] In one form, cross flow manifold section 26 includes a first passage 26a having a first axis positioned within a first plane 50 formed by first side 30 of first die section 14 and interior side 38 of second die section 16, a second passage 26b having a second axis positioned within a second plane 52 formed between first end 34 of first die section 14 and a first end plate 42 (see FIG. 2) and a third passage 26c having a third axis positioned within a third plane 54 formed between second side 32 of first die section 14 and interior side 40 of third die section 18. As may be envisioned by reference to FIG. 1, a portion of the flow of the polymer-diluent mixture will traverse directly downward from third passage 26c, while the balance of the flow will traverse through fourth passage 26d having a fourth

axis positioned within third plane 54 formed between second side 32 of first die section 14 and interior side 40 of third die section 18.

[0048] . Likewise, cross flow manifold section 28 may be provided with a first passage 28a having a first axis positioned within third plane 54 formed between second side 32 of first die section 14 and interior side 40 of third die section 18, a second passage 28b having a second axis positioned within a fourth plane 56 formed between second end 36 of first die section 14 and a second end plate 44 (see FIG. 2) and a third passage 28c having a third axis positioned within first plane 50 formed between first side 30 of first die section 14 and interior side 38 of second die section 16. As may be envisioned by reference to FIG. 1, a portion of the flow of the polymer-diluent mixture will traverse directly downward from third passage 28c, while the balance of the flow will traverse through fourth passage 28d having a fourth axis positioned within first plane 50 formed between first side 30 of first die section 14 and interior side 38 of second die section 16. [0049] In one form, the first cross flow manifold section 26 of cross flow manifold 20 and the second cross flow manifold section 28 of cross flow manifold 20 each have a pressure manifold 26e and 28e, respectively, in communication with die outlet 12. [0050] As shown, in one form, the first plane and the third plane and the second plane and the fourth plane may be aligned in substantially parallel spaced relationships, respectively. As used herein, by "substantially parallel spaced relationship" is meant that the opposing planes (i.e., first and third and second and fourth) do not intersect within the outer boundaries of extrusion die 10.

[0051] In another form, extrusion die 10 also includes a second die section 124 for producing a first skin layer. As shown in detail by reference to FIGS. 4 and 5, second die section 124 is provided with a cross flow manifold 126. As may be seen, cross flow manifold 126 may be provided with a flow path 128 that substantially traverses the length of second die section 124 at least twice. Cross flow manifold 126 also is provided with a feed entrance 130 and a pressure manifold 132 in communication with said die outlet 12.

[0052] In yet another form, when three-layer films or sheets are desired, a third die section 124 for producing a second skin layer may be provided. Third die section 124 can also be provided with a cross flow manifold 126. As with second die section 124, the cross flow manifold 126 of third die section 124 may have a flow path 128 that substantially traverses the length of third die section 124 at least twice. The cross flow manifold 126 of third die section 124 is provided with a feed entrance 130 and a pressure manifold 132 in communication with said die outlet 12.

[0053] As shown with particular reference to FIG. 6, coextrusion die 10 can be provided with a skin layer feedblock 146 for dividing a flow of polymer and diluent for producing the skin layer into a first flow Sl and a second flow S2, the first flow Sl feeding feed entrance 130 of said second die section 124 for producing a first skin layer and the second flow S2 feeding feed entrance 130 of third die section 124 for producing a second skin layer. [0054] In another form, when a bi-layer film or sheet is produced, coextrusion die 10 is provided with a skin layer feedblock (not shown) for feeding feed entrance 130 of second die section 124 for producing a first skin layer. Additional die sections (and feed entrances) can be added between the die sections for forming the outer (skin) layers of the membrane. In this way, membrane containing four or more independently selected layers can be extruded. [0055] When forming microporous membrane films and sheets from the polymers (e.g., polyolefins) described hereinbelow, a characteristic of these materials is their inherent propensity for shape memory. Other films and sheets formed from other thermoplastic materials may also exhibit these characteristics. As is known to those skilled in the art, shape-memory plastics have a thermoplastic phase and a "frozen" phase. The initial shape is "memorized" in the frozen phase, with the shape-memory effect permitting its recovery from whatever temporary shape the plastic has been formed into. As may be appreciated, a polymer chain has an ideal spatial configuration (Gaussian coil) in a melt state or in a

solution without perturbation. When the polymer is deformed by an external force, e.g., shear flow, the polymer relaxes its shape returns to the ideal Gaussian coil by allowing itself to diffuse in the polymer axis direction. The relaxation time strongly depends on the number of entanglements, therefore, the higher the molecular weight of the polymer and the higher the polymer concentration of the solution is, the longer the relaxation time required.

[0056] Coextrusion die 10 also includes a second die section 24 for producing a first skin layer. As shown in detail by reference to FIGS. 3 and 4, second die section 24 is provided with a cross flow manifold 26. As may be seen, cross flow manifold may be provided with a flow path 28 wherein a portion of a melt stream of the thermoplastic material traverses the length of second die section 24 more than once. Cross flow manifold 26 also is provided with a feed entrance 30 and a pressure manifold 32 in communication with said slotted die outlet 12. [0057] In another form, cross flow manifold section 26 and cross flow manifold section 28 of cross flow manifold 20 each have a flow path that substantially traverses the length of extrusion die 10 at least two times.

[0058] In another form, cross flow manifold 126 of second die section 124 and cross flow manifold 126 of third die section 124 each have a flow path of a length sufficient to substantially eliminate the shape memory characteristics of the polymer in the polymer- diluent mixture. In another form, where a bi-layer film or sheet is to be produced, cross flow manifold 126 of second die section 124 has a flow path of a length sufficient to substantially eliminate the shape memory characteristics of the extrudate. [0059] In yet another form, cross flow manifold 126 of second die section 124 and cross flow manifold 126 of third die section 124 each have a flow path that substantially traverses the length of second die section 124 and the length of third die section 124, respectively, at least 2.5 times. In yet another form, where a bi-layer film or sheet is to be

produced, cross flow manifold 126 of second die section 124 has a flow path that substantially traverses said second die section's length at least 2.5 times. [0060] Referring now to FIGS. 7-9, die outlet 12 of extrusion die 10 may be provided with a first die lip 46 and a second die lip 48, first die lip 46 including a plurality of cantilevered adjustment members 60 extending normally from the first die lip 46. As may be envisioned, the plurality of cantilevered adjustment members 60 is formed in a manner so as to pivot about axis 66. Each of the plurality of cantilevered adjustment members 60 has an actuatable means 62. [0061] As shown in FIG. 9, each actuatable means 62 includes an individual Hp bolt 64, effective for varying the width of die outlet 12 in a region adjacent to a point of adjustment. Each lip bolt 62 is threaded through base plate 68 and terminates in a bolt tip 72. Each of the plurality of cantilevered adjustment members 60 has an adjustment pad 74 affixed at far end 76, for contacting bolt tip 72. [0062] Advantageously, the cantilevered die lip adjustment system disclosed herein provides the ability to fine tune the width of the die gap in a localized area. This ability enables a significant reduction in transverse direction film or sheet thickness variation, providing a film or sheet of extremely high quality. For example, a conventional die lip adjustment system may typically provide Hp bolts at about 36 mm intervals along the transverse direction of the die outlet, equating to an ability to adjust the film pattern in the transverse direction at about a 180 mm interval for the case of a film or sheet that is oriented 5 times in the transverse direction. As may be appreciated, for such a conventional system, it is very difficult to finely adjust the film thickness. [0063] In the cantilevered die Hp adjustment system disclosed herein, lip bolt intervals can be reduced to about 12 mm, which corresponds to a product width of about 60 mm. As may be appreciated, while the intervals can be simply shortened in conventional designs, the bolts must be correspondingly thinner, reducing the ability to accurately adjust the die gap, since the stiffness of the Hp bolts is reduced.

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[0064] Referring now to FIGS. 1OA and 1OB, it may be visualized that the cantilevered die lip adjustment system disclosed herein makes use of the principle of leverage, in that a large torsional moment can be generated despite the narrow intervals of the lip bolts 64. Sufficient lip control force is assured by converting the torsion moment to a normal component of the force reaction. Moreover, deformation of first die lip 46, which could result from pressure from inside die 10, does not occur. Overall, the stress on the connection between the base plate 68 of the main frame and the first die lip 46 is decreased over other designs. [0065] It has been observed in the operation of the die lip adjustment system disclosed herein that excellent control of film or sheet thickness is achieved (transverse direction thickness variation equal to about ± 0.5 micron). Moreover, it has been confirmed that the die lip adjustment system disclosed herein permits film thickness adjustments at 50 mm intervals possible. [0066] Should any heat release be observed around the die lips 46 and 48, this can be easily addressed by the use of insulating material.

[0067] The extrusion dies and manifold systems disclosed herein overcome a difficulty when extruding a polyolefin solution through a die in a variety of processes, including a "wet" microporous polyolefin membrane film or sheet process. As may be seen by reference to FIG. 11, this difficulty stems from the fact that when a coat hanger manifold die 200 is used for the extrusion of a monolayer microporous polyolefin membrane film or sheet 202, shape-memory effects in the extrudate cause a thickness non-uniformity along the transverse direction of the extrudate. As may be appreciated, shape-memory effects in the extrudate tend to act in a direction perpendicular to the flow of the combined polymer and diluent, (e.g., polyolefin solution) S in the die manifold 204. Since, in coat hanger manifold die 200, the primary direction of flow in the manifold is toward the die Hp 206, the shape-memory effect tends to occur in the transverse direction of the extrudate. This

causes a redistribution of material in the extrudate toward the extrudate's center along the transverse direction.

[0068] Referring now to FIG. 12, in the case of monolayer extrusion dies, this issue can be overcome through the use of a cross flow manifold die 300, where the polyolefm solution S is made to traverse the width of the die manifold 304 before polyolefm solution S approaches the die lip 306. As may be appreciated, this results in a significant amount of polyolefin solution S in the die manifold flowing in a direction parallel to die lip 306. Consequently, shape memory effects will occur primarily in the machine direction, resulting in a more uniform distribution of the extrudate in the transverse direction. [0069] As indicated, the extrusion dies disclosed herein are useful in forming microporous polyolefin membrane films and sheets. These films and sheets find particular utility in the critical field of battery separators. The multi-layer films described hereinbelow can either be produced using a coextrusion die and manifold system employing cross flow manifold principles or be produced using a monolayer die and manifold system to produce a monolayer film or sheet, with additional layers laminated thereto in a conventional manner.

[0070] In one form, the multi-layer, microporous membrane comprises two layers. The first layer (e.g., the skin, top or upper layer of the membrane) comprises a first microporous layer material, and the second layer (e.g., the bottom or lower or core layer of the membrane) comprises a second microporous layer material. For example, the membrane can have a planar top layer when viewed from above on an axis approximately perpendicular to the transverse and longitudinal (machine) directions of the membrane, with the bottom planar layer hidden from view by the top layer. The extrusion dies described herein are also useful for producing monolayer microporous membranes, e.g., monolayer polyethylene microporous membranes and/or monolayer polyolefin membranes

of the type disclosed in PCT Publication WO2007/132942, for example, which is incorporated by reference herein in its entirety.

[0071] In another form, the multi-layer, microporous membrane comprises three or more layers, wherein the outer layers (also called the "surface" or "skin" layers) comprise the first microporous layer material and at least one core or intermediate layer comprises the second microporous layer material. In a related form, where the multi-layer, microporous polyolefin membrane comprises two layers, the first layer consists essentially of the first microporous layer material and the second layer consists essentially of the second microporous layer material. In a related form where the multi-layer, microporous polyolefin membrane comprises three or more layers, the outer layers consist essentially of the first microporous layer material and at least one intermediate layer consists essentially of (or consists of) the second microporous layer material. Such membranes are described in PCT Publication WO2008/016174, US2008/0057388, and US2008/0057389, which are incorporated by reference herein in their entirety. [0072] Starting materials having utility in the production of the afore-mentioned films and sheets will now be described. Suitable polymers, diluents, and amounts thereof are disclosed in WO2008/016174, US2008/0057388, and US2008/0057389, for example. As will be appreciated by those skilled in the art, the selection of a starting material is not critical as long as an extrusion die and manifold system employing cross flow manifold principles can be applied. In one form, the first and second microporous layer materials contain polyethylene. In one form, the first microporous layer material contains a first polyethylene ("PE-I") having an Mw value of less than about 1 x 10 ⁶ or a second polyethylene ("UHMWPE-I") having an Mw value of at least about 1 x 10 ⁶ . In one form, the first microporous layer material can contain a first polypropylene ("PP-I"). In one form, the first microporous layer material comprises one of (i) a polyethylene (PE), (ii) an ultra high molecular weight polyethylene (UHMWPE), (iii) PE-I and PP-I, or (iv) PE-I, UHMWPE-I, and PP-I.

[0073] In one form of the above (ii) and (iv), UHMWPE-I can preferably have an Mw in the range of from about 1 x 10 ⁶ to about 15 x 10 ⁶ or from about 1 x 10 ⁶ to about 5 x 10 ⁶ or from about 1 x 10 ⁶ to about 3 x 10 ⁶ ,and preferably contain greater than about 1 wt.%, or about 15 wt.% to 40 wt.%, on the basis of total amount of PE-I and UHMWPE-I in order to obtain a microporous layer having a hybrid structure as described in WO2008/016174, and can be at least one of homopolymer or copolymer. In one form of the above (iii) and (iv), PP-I can be at least one of a homopolymer or copolymer, or can preferably contain no more than about 25 wt.%, on the basis of total amount of the first layer microporous material. In one form, the Mw of polyolefin in the first microporous layer material can have about 1 x 10 or less, or in the range of from about 1 x 10 to about 1 x 10 ⁶ or from about 2 x 10 ⁵ to about 1 x 10 ⁶ in order to obtain a microporous layer having a hybrid structure defined in the later section. In one form, PE-I can preferably have an Mw ranging from about 1 x 10 ⁴ to about 5 x 10 ⁵ , or from about 2 x 10 ⁵ to about 4 x 10 ⁵ , and can be one or more of a high-density polyethylene, a medium-density polyethylene, a branched low- density polyethylene, or a linear low-density polyethylene, and can be at least one of a homopolymer or copolymer.

[0074] In one form, the second microporous layer material comprises one of: (i) a fourth polyethylene having an Mw of at least about 1 x 10 ⁶ , (UHMWPE-2), (ii) a third polyethylene having an Mw that is less than 1 x 10 ⁶ and UHMWPE-2 and the fourth polyethylene, wherein the fourth polyethylene is present in an amount of at least about 8% by mass based on the combined mass of the third and fourth polyethylene; (iii) UHMWPE- 2 and PP-2, or (iv) PE-2, UHMWPE-2, and PP-2. In one form of the above (ii), (iii) and (iv), UHMWPE-2 can contain at least about 8 wt.%, or at least about 20 wt.%, or at least about 25 wt.%, based on the total amount of UHMWPE-2, PE-2 and PP-2 in order to produce a relatively strong multi-layer, microporous polyolefin membrane. In one form of the above (iii) and (iv), PP-2 can be at least one of a homopolymer or copolymer, and can contain 25 wt.% or less, or in the range of from about 2% to about 15%, or in the range of

from about 3% to about 10%, based on the total amount of the second microporous layer material. In one form, preferable PE-2 can be the same as PE-I, but can be selected independently. In one form, preferable UHMWPE-2 can be the same as UHMWPE-I, but can be selected independently. [0075] In addition to the first, second, third, and fourth polyethylenes and the first and second polypropylenes, each of the first and second layer materials can optionally contain one or more additional polyolefins, and/or a polyethylene wax, e.g., one having an Mw in the range of about 1 x 10 ³ to about 1 x 10 ⁴ , as described in US2008/0057388. [0076] In one form, a process for producing a two-layer microporous polyolefin membrane is provided wherein an extrusion die and manifold system of the type disclosed herein is employed. In another form, the microporous polyolefin membrane has at least three layers and is produced through the use of an extrusion die and manifold system of the type disclosed herein. The production of the microporous polyolefin membrane will be mainly described in terms of two-layer and three-layer membrane. [0077] In one form, a three-layer microporous polyolefin membrane comprises first and third microporous layers constituting the outer layers of the microporous polyolefin membrane and a second (core) layer situated between (and optionally in planar contact with) the first and third layers. In another form, the first and third layers are produced from a first polyolefin solution and the second (core) layer is produced from a second polyolefin solution.

[0078] In one form, a method for producing the multi-layer, microporous polyolefin membrane is provided. The method comprises the steps of (1) combining (e.g., by melt- blending) a first polyolefin composition and at least one diluent (e.g., a membrane-forming solvent) to prepare a first mixture of polyolefin and diluent, e.g., a first polyolefin solution, (2) combining a second polyolefin composition and at least a second diluent (e.g., a second membrane-forming solvent) to prepare a second mixture of polyolefin and diluent, e.g., a second polyolefin solution, (3) extruding the first and second polyolefin solutions through

at least one die of the type disclosed herein to form a multi-layer extrudate, (4) optionally cooling the multi-layer extrudate to form a cooled extrudate, (5) removing at least a portion of the membrane-forming solvent from the extrudate or cooled extrudate to form the multilayer membrane, and (6) optimally removing from the membrane at least a portion of any volatile species. An optional stretching step (7), and an optional hot solvent treatment step (8) can be conducted between steps (4) and (5), if desired. After step (6), an optional step (9) of stretching a multi-layer, microporous membrane, an optional heat treatment step (10), an optional cross-linking step with ionizing radiation (11), and an optional hydrophilic treatment step (12), etc., can be conducted. [0079] The first polyolefin composition comprises polyolefin resins as described above that can be combined, e.g., by dry mixing or melt blending with an appropriate membrane- forming solvent to produce the first polyolefin solution. Optionally, the first polyolefin solution can contain various additives such as one or more antioxidant, fine silicate powder (pore-forming material), etc., as disclosed in WO2008/016174, US2008/0057388, and US2008/0057389, for example.

[0080] The first and second diluents can be solvents that are liquid at room temperature. Suitable diluents include those described in WO2008/016174, US2008/0057388, and US2008/0057389, for example. [0081] In one form, the resins, etc., used to produce to the first polyolefin composition are melt-blended in, e.g., a double screw extruder or mixer. For example, a conventional extruder (or mixer or mixer-extruder) such as a double-screw extruder can be used to combine the resins, etc., to form the first polyolefin composition. The diluent can be added to the polyolefin composition (or alternatively to the resins used to produce the polyolefin composition) at any convenient point in the process. For example, in one form where the first polyolefin composition and the first diluent (membrane solvent) are melt-blended, the solvent can be added to the polyolefin composition (or its components) at any of (i) before starting melt-blending, (ii) during melt blending of the first polyolefin composition, or (iii)

after melt-blending, e.g., by supplying the first membrane-forming solvent to the melt- blended or partially melt-blended polyolefin composition in a second extruder or extruder zone located downstream of the extruder zone used to melt-blend the polyolefin composition. [0082] Suitable methods for combining the polymer and diluent are disclosed in WO2008/016174, US2008/0057388, and US2008/0057389, for example. [0083] The amount of the first polyolefin composition in the first polyolefin solution is not critical. In one form, the amount of first polyolefin composition in the first polyolefin solution can range from about 1 wt.% to about 75 wt.%, based on the weight of the polyolefin solution, for example from about 20 wt.% to about 70 wt.%. The remainder of the polyolefin solution can be the solvent. For example, the polyolefin solution can be about 30 wt.% to about 80 wt.% solvent (or diluent) based on the weight of the polyolefin solution. [0084] The second polyolefin solution can be prepared by the same methods used to prepare the first polyolefin solution. For example, the second polyolefin solution can be prepared by melt-blending a second polyolefin composition with a second membrane- forming solvent.

[0085] The amount of the second polyolefin composition in the second polyolefin solution is not critical. In one form, the amount of second polyolefin composition in the second polyolefin solution can range from about 1 wt.% to about 75 wt.%, based on the weight of the second polyolefin solution, for example from about 20 wt.% to about 70 wt.%. The remainder of the polyolefin solution can be the solvent. For example, the polyolefin solution can be about 30 wt.% to about 80 wt.% solvent (or diluent) based on the weight of the polyolefin solution. [0086] Advantageously, extrusion dies of the type disclosed herein are used for forming an extrudate that can be co-extruded or laminated. In one form, extrusion dies, which can be adjacent or connected, are used to form the extrudates. The first and second

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sheet dies are connected to first and second extruders, respectively, where the first extruder contains the first polyolefin solution and the second extruder contains the second polyolefin solution. While not critical, lamination if used is generally easier to accomplish when the extruded first and second polyolefin solution are still at approximately the extrusion temperature.

[0087] In another form, first, second, and third dies are connected to first, second and third extruders, where the first and third dies contain the first polyolefin solutions, and the second die contains the second polyolefin solution. In this form, a laminated extrudate is formed constituting outer layers comprising the extruded first polyolefin solution and one intermediate comprising the extruded second polyolefin solution.

[0088] In yet another form, the first, second, and third dies are connected to first, second, and third extruders, where the second die contains the first polyolefin solution, and the first and third dies contain the second polyolefin solution. In this form, a laminated extrudate is formed constituting outer layers comprising the extruded second polyolefin solution and one intermediate comprising extruded first polyolefin solution.

[0089] The die gaps are generally not critical. For example, extrusion dies of the type disclosed herein can have a die gap of about 0.1 mm to about 5 mm. Die temperature and extruding speed are also non-critical parameters. For example, the dies can be heated to a die temperature ranging from about 140°C to about 250°C during extrusion. The extruding speed can range, for example, from about 0.2 m/minute to about 15 m/minute. The thickness of the layers of the layered extrudate can be independently selected. For example, the resultant sheet can have relatively thick skin or surface layers compared to the thickness of an intermediate layer of the layered extrudate. [0090] Optionally, the multi-layer extrudate can be cooled. Cooling rate and cooling temperature are not particularly critical. Suitable cooling methods are described in WO2008/016174, US2008/0057388, and US2008/0057389, for example.

[0091] In one form, at least a portion of the first and second membrane-forming solvents are removed (or displaced) from the multi-layer extrudate in order to form the multi-layer, microporous membrane. Suitable methods for removing the solvents (diluents) are described in WO2008/016174, US2008/0057388, and US2008/0057389, for

5 example. A washing solvent can be used, for example.

[0092] In one form, at least a portion of any remaining volatile species in the membrane (e.g., the washing solvent) are removed. Suitable methods for removing the volatile species are disclosed in WO2008/016174, US2008/0057388, and US2008/0057389, for example. io [0093] Prior to the step for removing the membrane-forming solvents, the extrudate can be stretched in order to obtain an oriented extrudate. Suitable methods for stretching the extrudate or cooled extrudate are disclosed in WO2008/016174, US2008/0057388, and US2008/0057389, for example. [0094] Although it is not required, the extrudate can be treated with a hot solvent as i s described in WO 2000/20493.

[0095] In one form, the microporous membrane can be stretched at least monoaxially after removal of at least a portion of the diluent. The stretching method selected is not critical, and conventional stretching methods can be used such as by a tenter method, etc. When the extrudate has been stretched as described above the stretching of the dry

20 microporous polyolefm membrane can be called dry-stretching, re-stretching, or dry- orientation. Suitable stretching methods are disclosed in WO2008/016174, US2008/0057388, and US2008/0057389, for example.

[0096] The stretching magnification is not critical. For example, the stretching magnification of the microporous membrane can range from about 1.1 fold to about 2.5 or 5 about 1.1 to 2.0 fold in at least one lateral (planar) direction. Biaxial stretching can be used, and the stretching magnification need not by symmetric.

[0097] In one form, the microporous membrane can be heat-treated and/or annealed. The microporous membrane can also be cross-linked if desired [e.g., by ionizing radiation rays such as a-rays, (3 -rays, 7-rays, electron beams, etc.)] or can be subjected to a hydrophilic treatment [i.e., a treatment which makes the microporous polyolefin membrane more hydrophilic (e.g., a monomer-grafting treatment, a surfactant treatment, a corona- discharging treatment, etc.)]. Suitable methods for membrane heat treatment, annealing, crosslinking, etc., are described in WO2008/016174, US2008/0057388, and US2008/0057389, for example. [0098] Alternatively, methods for producing the microporous membrane, such as those described in WO2008/016174 (for multi-layer membranes) and in WO2007/132942 (for monolayer membranes) can also be used.

[0099] While the extrusion has been described in terms of producing two and three- layer extrudates, the extrusion step is not limited thereto. For example, a plurality of dies and/or die assemblies can be used to produce multi-layer extrudates having four or more layers using the principles of the extrusion dies and methods disclosed herein. Alternative methods for producing microporous membranes as described in WO2008/016174, US2008/0057388, and US2008/0057388 are compatible with the invention. [00100] AU patents, test procedures, and other documents cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent and for all jurisdictions in which such incorporation is permitted.

[00101] While the illustrative forms disclosed herein have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside herein,

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including all features which would be treated as equivalents thereof by those skilled in the art to which this disclosure pertains.

[00102] When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.