DESCRIPTION

EXTRUSION DIE AND MANIFOLD SYSTEM THEREFOR

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 from polymer melts.

[0003] Various extrusion dies have been produced to extrude multiple layer films from polymer melts. 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 for extruding polymer melts 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 for extruding polymer melts 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 lip 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. However, once initial adjustments are made (i.e., once the movable lip is moved from its original adjustment), returning the lip to a known position is not so easily done, if it is even possible. Also, without a clean die and specialized equipment, it is impossible to adjust a feed gap on an industry standard flex die to a known precision gap opening.

[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

JP2008/066935

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conditions, etc. have been proposed to improve the properties of microporous polyolefin membranes.

[0011] In general, microporous polyolefm 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 microporous polyolefin membranes made from polymer solutions which contain 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 polymer solutions containing such 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] JP U3048972 proposes an extrusion die design said to eliminate flow divergence 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. [0013] 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.

[0014] WO 2004/089627 discloses a microporous polyolefϊn 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. [0015] 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".

[0016] Despite these advances in the art, there remains a need for extrusion dies and manifold systems capable of producing microporous polyolefin membranes and other high quality films or sheets from polymer solutions.

SUMMARY OF THE INVENTION

[0017] Provided is an extrusion die for producing an extrudate comprising polymer and diluent from a mixture comprising the polymer, and the diluent. The extrusion die includes a die outlet through which the mixture is extruded, a feed entrance in communication with a feed splitter for dividing the mixture into a first portion and a second portion, and a cross flow manifold comprising: 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 second cross flow manifold section for receiving the second portion of the mixture,

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.

[0018] In another aspect, a process for producing an extrudate comprising polymer and diluent is also provided. The process includes the steps of combining at least one polyolefin and a diluent (e.g., a solvent) to prepare a polyolefin solution, and extruding the polyolefin solution through an extrusion die to form an extrudate, the extrusion die comprising (i) a die outlet through which a melt stream of the polyolefin solution is extruded as a film or sheet, (ii) a feed entrance in communication with a feed splitter for dividing the polyolefin solution into a first portion and a second portion, (iii) a cross flow manifold comprising: 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 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.

[0019] It has been found that the shape memory characteristics of a polymer in a mixture of the polymer and diluent can be a factor in maintaining uniform traverse direction film and sheet thickness as the film or sheet exits an extrusion die. This shape-memory effect has now been observed in thermoplastic materials extruded from polymer solutions, such as solutions containing polyolefm and diluent. This is surprising because it was expected that the presence of the diluent would at least moderate (if not eliminate) the shape-memory effect in the extrudate. The moderation of shape-memory effects in a polymer solution was expected because the lower amount of polymer (compared to a melt) was thought to lead to fewer polymer chain entanglements, and, hence, improved rheological properties.

[0020] Consequently, the invention is based in part on the discovery that extrusion die manifold design can influence the shape memory phenomena in the extrusion of polymer solutions. As such, in an exemplary form disclosed herein, the cross flow manifold is provided with a flow path of a length sufficient to moderate or substantially eliminate the shape memory characteristics of the thermoplastic material.

[0021] 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. [0022] _. In a still further exemplary form disclosed herein, the die outlet is a slotted die outlet which includes a first die lip and a second die lip, the first die lip including a flexible lip bar having actuatable means located along a length thereof. [0023] In yet a further exemplary form disclosed herein, the actuatable means of the first die lip includes a plurality of individual lip bolts effective for varying the width of the slotted die outlet in a region adjacent a point of adjustment. [0024] These and other advantages, features and attributes of the disclosed extrusion dies and manifold systems 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

5 [0025] FIG. 1 is an exploded perspective view of an extrusion die having a cross flow manifold system for producing an extrudate of thermoplastic material, in accordance herewith.

[0026] FIG. 2 is a partially exploded perspective view of the extrusion die having a cross flow manifold system of FIG. 1 , showing a pair of die end plates for positioning I ₀ on the die, in accordance herewith.

[0027] FIG. 3 is a schematic view of an extrusion die for producing an extrudate of thermoplastic material showing the respective flow paths of the thermoplastic material, in accordance herewith.

[0028] FIG. 4 is a side view of an extrusion die for producing an extrudate of is thermoplastic material showing a flexible lip bar having actuatable means, in accordance herewith.

[0029] FIG. 5 is a perspective view of a coat hanger extrusion die showing the flow path of the thermoplastic material.

[0030] FIG. 6 is a perspective view of a cross flow extrusion die showing the flow 20 path of the thermoplastic material.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Reference is now made to FIGS. 1-6, wherein like numerals are used to designate like parts throughout.

2S [0032] Referring now to FIGS. 1-3, an extrusion die 10 for producing an extrudate comprising thermoplastic material e.g., polymer and diluent, in accordance herewith, is shown. Extrusion die 10 includes a die outlet 12, which may be a slotted die outlet, as shown, through which a mixture of polymer and diluent may be extruded as a film or

sheet (extrudate). 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

5 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. [0033] 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 ofo polymer solution F is split into a first stream Sl and a second stream S2, the first stream Sl feeding cross flow manifold section 26 and the second stream S2 feeding cross flow manifold section 28.

[0034] 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.s 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. [0035] In one form, cross flow manifold section 26 includes a first passage 26aQ 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 dies 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 polymer solution 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. [0036] 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 polymer solution 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. [0037] 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 26d and 28d, respectively, in communication with die outlet 12. [0038] 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.

[0039] When forming microporous membrane films and sheets from the polyolefin solution described hereinbelow, a surprising characteristic of these materials is their inherent propensity for shape memory similar to that which is observed in the extrusion of polymer melts. Other films and sheets formed from other polymer besides polyolefin 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.

[0040] The shape memory characteristics of a mixture of polyolefin and diluent (e.g., a polyolefin solution) can be a factor in maintaining uniform transverse direction film and sheet thickness as the film or sheet exits an extrusion die. It has been found that manifold design can influence and correct for this phenomenon. As such, in one form, cross flow manifold section 26 and cross flow manifold section 28 of cross flow manifold 20 each have a flow path of a length sufficient to substantially eliminate the shape memory characteristics of the thermoplastic material.

[0041] In operation, in one form, a portion of the combined polymer (e.g., polyolefin) and diluent traverses first cross flow manifold section 26 of the cross flow manifold 20 and second cross flow manifold section 28 of cross flow manifold 20 a distance substantially equivalent to the extrusion die's length more than once. [0042] 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. [0043] As shown with particular reference to FIG. 4, die outlet 12 of extrusion die 10, which may be a slotted die outlet, may be provided with a first die lip 46 and a second die lip 48, first die lip 46 including a flexible lip bar 60 having externally

actuatable means 62 located along a length thereof. As shown, externally actuatable means 62 includes a plurality of individual lip bolts 64, each lip bolt 64 effective for varying the width of slotted die outlet 12 in a region adjacent to a point of adjustment. [0044] 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 polyolefm membrane film or sheet process. As may be seen by reference to FIG. 5, this difficulty stems from the fact that when a coat hanger manifold (CH) die 100 is used for the extrusion of a monolayer microporous membrane film or sheet 102, 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 polyolefm solution S in the die manifold 104. Since, in coat hanger manifold die 100, the primary direction of flow in the manifold is toward the die lip 106, 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.

[0045] Referring now to FIG. 6, in the case of monolayer extrusion dies, this issue can be overcome through the use of a cross flow manifold (CF) die 200, where a mixture of polymer and diluent is made to traverse the width of the die manifold 204 before polyolefm solution S approaches the die lip 206. 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 206. Consequently, shape memory effects will occur primarily in the machine direction, resulting in a more uniform distribution of the extrudate in the transverse direction. [0046] As indicated, the extrusion dies and manifold systems disclosed herein are useful in forming microporous membrane films and sheets. These films and sheets find particular utility in the critical field of battery separators. The multi-layer films and

sheets described hereinbelow can be produced using a monolayer die and manifold system of the type described hereinabove to produce a monolayer film or sheet, with additional layers laminated thereto in a conventional manner. Co-extrusion can also be used, where a compound die (e.g., one having at least two outlets in close proximity) has at least one component die having the manifold system of the invention.

[0047] 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. [0048] 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 multilayer, 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 multilayer, 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.

[0049] 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 . In one form, the first microporous layer material can contain a first polypropylene ("PP- 1"). 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 .

[0050] 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 ^δ or less, or in the range of from about 1 x 10 ⁵ to about 1 x 10 ^δ 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 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 homoporymer or copolymer. [0051] 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. [0052] 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 polyolefms, 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. [0053] 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 polyolefϊn membrane will be mainly described in terms of two-layer and three-layer membrane.

[0054] In one form, a three-layer microporous polyolefm membrane comprises first and third microporous layers constituting the outer layers of the microporous polyolefm 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 polyolefm solution and the second (core) layer is produced from a second polyolefin solution. [0055] 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 polyolefm 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 polyolefm 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.

[0056] 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.

[0057] 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. [0058] 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. [0059] Suitable methods for combining the polymer and diluent are disclosed in WO2008/016174, US2008/0057388, and US2008/0057389, for example. [0060] 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. [0061] 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. [0062] 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.

[0063] 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 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. [0064] 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 polyolefm solution and one intermediate comprising the extruded second polyolefin solution. [0065] 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. [0066] 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 ⁰ C to about 250 ⁰ 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.

[0067] 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. [0068] 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 example. A washing solvent can be used, for example. [0069] 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.

[0070] 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.

[0071] Although it is not required, the extrudate can be treated with a hot solvent as described in WO 2000/20493. [0072] 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 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.

[0073] 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 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. [0074] 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.

[0075] 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. [0076] All 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. [0077] 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, including all features which would be treated as equivalents thereof by those skilled in the art to which this disclosure pertains. [0078] When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.