JP5639578B2 - Microporous membrane manufacturing method and microporous membrane manufacturing apparatus - Google Patents

Description

  The present disclosure relates generally to methods and apparatus for producing microporous membranes, such as those useful as battery separators.

  Microporous membranes, in particular microporous polymer membranes, are used in primary batteries and, for example, lithium ion secondary batteries, lithium-polymer secondary batteries, nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, nickel-zinc secondary batteries. It is useful as a separator for secondary batteries such as secondary batteries and silver-zinc secondary batteries. When a microporous membrane is used as a battery separator, particularly as a lithium ion battery separator, the properties of the membrane, such as flatness and thickness uniformity, significantly affect the properties, productivity and safety of the battery. . Usually, the aim is to provide a microporous membrane with well-balanced properties, where the term “well-balanced” means that one membrane property can be optimized by optimizing another membrane property. It means that it does not mean that it will decline.

The microporous polymer membrane can be manufactured according to a wet method, in which at least one polymer (for example, one or more polyolefins) and at least one diluent (or solvent) are mixed to form a polymer solution. Is then extruded to form an extrudate. The extrudate is then stretched in at least one planar direction. After stretching, at least a portion of the diluent is removed from the stretched extrudate to form a film. Additional steps such as membrane drying, further stretching, heat treatment, etc. may be used downstream of the diluent removal step. As an example of a reference disclosing the conventional wet method,
US Pat.No. 5,051,183, US Pat. No. 6,096,213 , International Publication No. 2008/016174, International publication No. 2005/113657 is mentioned.

  US Pat. No. 5,830,554 [Patent Document 5] discloses cooling the extrudate prior to stretching. In this reference it is desirable to control the cooling rate to control the pore diameter of the membrane, but cooling at a rate of less than 50 ° C. per minute will impair thickness uniformity, ie extrudate. Is disclosed to be rough.

In US Pat. No. 4,734,196, a process for producing relatively uniform microporous films from ultra high molecular weight alpha-olefin polymers having a weight average molecular weight greater than 5 × 10 ⁵ Is disclosed. In order to form a gel from a solution of an alpha-olefin polymer having a weight average molecular weight greater than 5 × 10 ⁵ , so that the gel contains 10-90 wt% alpha-olefin polymer. At least 10% by weight of the solvent contained in the gel is removed and the gel is oriented at a temperature below 10 ° C. above the melting point of the alpha-olefin polymer and the remaining solvent from the oriented product. Is removed to obtain a microporous membrane. By pressing the oriented product at a temperature below the melting temperature of the alpha-olefin polymer, a film is made from the oriented product to obtain a relatively uniform product.

  In US Patent Publication No. 2007/0012617 [Patent Document 7], a method for producing a microporous thermoplastic resin film is proposed, and this method involves melt blending a thermoplastic resin and a film-forming solvent. A step of extruding the solution obtained through the die, a step of cooling the extrudate to form a gel-like molding, a step of removing the film-forming solvent from the gel-like molding with a washing solvent, and then the step Removing the washing solvent. The molten polymer is fed to a first inlet at the end of the first manifold and a second inlet at the end of the second manifold opposite the first inlet. Two thin streams flow together inside the die. It has been theorized that due to the absence of melt flow branching inside the manifold, it may be possible to achieve a uniform flow distribution within the die. This is said to provide improved thickness uniformity across the film or sheet.

  Although improvements have been made in the production of relatively uniform microporous membranes, further improvements are desired.

In one embodiment, the present invention relates to an apparatus for producing a microporous membrane for releasing heat from a molten extrudate comprising a polymer and a diluent, wherein the assembly comprises:
a) first and second rolls positioned to receive opposite surfaces of the extrudate, said first roll contacting the extrudate along an arcuate path with a first contact angle ≦ 100 °; And the second and second rolls contact the extrudate along an arcuate path at a second contact angle ≦ 100 °,
b) a third roll downstream of the first and second rolls, wherein the first, second, and third rolls receive the extrudate from at least one of the first and second rolls. And a third roll, wherein the third roll contacts the extrudate along an arcuate path at a third contact angle to form a cooled extrudate. In certain embodiments, the third roll contacts the extrudate along an arcuate path of 180 ° or greater. In other embodiments, the third roll contacts the extrudate along an arcuate path with a third contact angle of 90 ° to 180 °, preferably 100 ° to 150 °, more preferably 110 ° to 130 °. To do.

  Since these rolls act to dissipate heat from the extrudate, they are sometimes referred to as “cooling rolls”, especially when these rolls contain cooling means.

In another aspect, the present invention relates to a method for producing a microporous membrane comprising:
a) mixing polyolefin and diluent;
b) extruding the mixed polyolefin and diluent through an extrusion die to form an extrudate;
c) i) first and second rolls positioned to receive opposite surfaces of the extrudate, the first roll contacting the extrudate along an arcuate path with a first contact angle ≦ 100 ° And the second roll is in contact with the extrudate along an arcuate path with a second contact angle ≦ 100 °, ii) a third roll downstream of the first and second rolls The first, second, and third rolls are aligned so that the third roll can receive extrudates from at least one of the first and second rolls, and the third roll The roll passes through a plurality of rolls, including a third roll, which contacts the extrudate along a circular path with a third contact angle of ≧ 180 ° to form the extrudate and cools the extrudate through heat. Forming an extrudate; and d) a solvent or diluent. Forming a film by removing at least a portion of the cooling extrudate.

  These and other advantages, features and characteristics of the disclosed methods and systems and their advantageous applications and / or uses will be read from the detailed description that follows, particularly in conjunction with the drawings attached hereto. It will be clear.

  In the description that follows, the present disclosure will be further described with reference to the drawings. The drawings illustrate various embodiments without limiting the embodiments and are as follows:

1 is a schematic view of one form of a system for producing stretched films or sheets of thermoplastic material as attached herein. FIG.

1 is a side view of a chill roll assembly for releasing heat from an extrudate formed by extruding a polyolefin solution through an extrusion die, as attached herein. FIG.

  It has been observed that producing microporous polyolefin membranes by a “wet process” can cause problems in the cooling operation, particularly in connection with the design of the chill roll apparatus. If an excessive amount of extrudate cooling occurs on one surface of the extrudate before cooling of the opposite surface is achieved, a reduction in extrudate thickness uniformity may occur.

  This problem is one for contacting and receiving the opposite surface of the extrudate from the extrusion die along an arcuate path at a contact angle of 100 ° or less, for example in the range of 55 ° to 75 °. At least one pair of upstream cooling rolls and at least one downstream roll positioned to receive extrudate from the upstream roll, greater than 100 ° or greater than 180 °, eg, 190 ° -220 ° It has been found that this can be overcome at least in part by using a downstream roll in contact with the extrudate along an arcuate path at a contact angle of By increasing the thickness uniformity of the extrudate, process passability and yield are improved. This is, for example, because there are fewer relatively thin areas of the film, otherwise there will be a risk of breaking during downstream stretching operations. In addition, the better uniformity of the extrudate thickness improves the thickness uniformity of the finished film, thereby reducing the machine direction to remove abnormally thick or thin areas of the film. The need to slit the membrane along is reduced.

  In the following, various aspects will be described with reference to specific forms chosen for purposes of explanation. It is to be understood that the spirit and scope of the methods and assemblies disclosed herein are not limited to the selected form. Further, it should be noted that the figures presented herein are not drawn to any particular proportion or size, and that many variations on the described forms are possible. . In the following, reference is made to the figures, and like numerals shall be used consistently to designate like parts throughout.

  Where amounts, concentrations, or other values or parameters are given as a list of upper and lower limits, this is a certain upper limit and whether or not multiple ranges are disclosed separately It should be understood that all ranges formed from any pair of lower limits are specifically disclosed.

  In the following, referring to FIGS. 1 and 2, it is assumed that like numerals are used to designate like parts throughout.

  FIG. 1 shows a system 10 for producing a microporous membrane of thermoplastic material. The system 10 includes an extruder 12, which has a feed hopper 15 for receiving one or more polymer materials or processing additives, etc., fed by a line. The extruder 12 also receives a diluent, such as paraffin oil, via the solvent supply line 16. The polymer and diluent mixture is prepared in the extruder 12 by mixing the polymer and diluent while heating and mixing.

  The heated mixture is then extruded from the die 20 of the extruder 12 into a sheet 18. The extruded sheet 18 is cooled to a temperature below the gelling temperature so that the extruded sheet 18 gels by the assembly 100 for releasing heat from the extrudate.

  In one form schematically shown in FIG. 1, assembly 100 for releasing heat from an extrudate includes at least one pair of upstream rolls 102 positioned to receive extrudate 18. If desired, each of the at least one pair of upstream rolls 102 may have a diameter of less than about 200 mm, such as in the range of 50 mm to 150 mm. As shown, at least one pair of upstream rolls 102 includes a first roll 104 and a second roll 106. The assembly 100 also includes at least one downstream roll 114. As will be appreciated, the at least one pair of upstream rolls 102 and the at least one downstream (or “third”) roll 114 are such that the at least one downstream roll 114 is from the at least one pair of upstream rolls 102. Aligned to receive extrudate 18. In one form, the at least one downstream roll 114 has a diameter greater than or equal to about 250 mm, such as in the range of 275 mm to 400 mm. In another form, each of the at least one pair of upstream rolls 102 has a diameter of about 150 mm or less or about 100 mm or less.

  If desired, the assembly 100 may also include a second pair 108 of upstream rolls, as schematically shown in FIG. As shown, the second pair of upstream rolls 108 includes a first roll 110 and a second roll 112. The second pair of upstream rolls 108 may be disposed at a position downstream of the at least one pair of upstream rolls 102 and upstream of the downstream roll 114. In one form, each of the second pair of upstream rolls 108 has a diameter of less than about 200 mm, for example in the range of 50 mm to 150 mm. In another form, each of the second pair of upstream rolls 108 has a diameter of about 100 mm or less. Although not required, two rolls of the first pair of upstream rolls may have equal diameters. Similarly, two rolls of the second pair of upstream rolls may have equal diameters, which are optimally the same as the diameter selected for the first pair of upstream rolls. . In one form, the rolls constituting the first and second pairs of upstream rolls all have the same diameter and contact the extrudate along multiple arcuate paths with equal contact angles.

  If desired, the cooled extrudate 18 'may be directed to a first orientation device 24, which may be a roll type stretcher as shown. The cooled extrudate 18 'is oriented in the machine direction (MD) while being heated, using a roll-type stretching machine 24, or optionally using a tenter-type stretching machine (not shown). This cooled extrudate 18 'may then be passed through a second orientation device 26, if desired, to obtain an oriented film or sheet 18 "to be oriented at least in the transverse direction (TD). The second orientation device 26 may be a tenter type stretching machine or may be used for further stretching in the MD.

  The cooled extrudate (or oriented film or sheet 18 ″ as desired) is then passed through a solvent extraction device 28. In the solvent extraction device 28, an easily volatile solvent such as methylene chloride is supplied via the line 30. The volatile solvent contacts the extrudate and removes at least a portion of the diluent from the extrudate. A volatile solvent containing the diluent to be extracted (usually a non-volatile solvent) is recovered from the solvent effluent line 32. The oriented film or sheet 18 ″ is then passed through a drying device 34. In the drying device 34, at least a portion of any remaining volatile species (eg, volatile solvent 36) evaporates from the oriented film or sheet 18 ''.

  The oriented film or sheet 18 ″ is then passed through a dry orientation device 38 as desired. In this apparatus, the dried film is stretched at a magnification of about 1.1 to about 2.5 times in at least one direction to form a stretched film. Next, the oriented film or sheet 18 ″ is passed through the heat treatment apparatus 44. In this apparatus, in order to adjust the porosity in the film or sheet 18 ″ and to remove residual stress in the film or sheet 18 ″, the oriented film or sheet 18 ″ is heat-treated, An oriented film or sheet 18 ″ is rolled up to form a product roll 48.

  Referring now to FIG. 2, another form of assembly 200 is shown for releasing heat from an extrudate 18 formed by extruding a polyolefin solution through an extrusion die 20. The assembly 200 includes at least one support frame 220 and at least one pair of upstream rolls 202 positioned to receive the extrudate 18. Each of the at least one pair of upstream rolls 202 typically has a diameter of about 150 mm or less. As shown, the at least one pair of upstream rolls 202 includes a first roll 204 and a second roll 206 mounted on the at least one support frame 220 and also in contact with the extrudate 18 and extruded. Arranged in a position to receive the object 18. In another form, each of the at least one pair of upstream rolls 102 has a diameter of about 125 mm or less or a diameter of about 100 mm or less.

  If desired, the assembly 200 may also include a second pair 208 of upstream rolls, as schematically shown in FIG. As shown, the second pair 208 of upstream rolls includes a first roll 210 and a second roll 212. The second pair of upstream rolls 208 may be disposed downstream of the at least one pair of upstream rolls 202 and upstream of the downstream roll 214. In one form, each of the second pair of upstream rolls 208 has a diameter of less than about 250 mm.

  The assembly 200 also includes at least one downstream roll 214 mounted on the at least one support frame 220. The at least one pair of upstream rolls 202 and the at least one downstream roll 214 are arranged such that the at least one downstream roll 214 can receive the extrudate 18 from the at least one pair of upstream rolls 202. In one form, the at least one downstream roll 214 has a diameter of about 250 mm or greater. As shown, the assembly 200 is mounted on the at least one support frame 220 and is positioned to contact the extrudate 18 and receive the extrudate 18 from the at least one downstream roll 214. The second downstream roll 222 may also be included. Additional downstream rolls 224 and 226 may be provided as desired. In one form, the second downstream roll 214 has a diameter of about 300 mm or greater. Other cooling rolls are selected as desired, but can be included as shown in the figure.

  Still referring to FIG. 2, the chill roll assembly 200 further includes one or more drive motors 230 mounted on the support frame 220, including at least a pair of upstream rolls 202, and a second if provided. And a pair of upstream rolls 208. One or more drive motors 232 are provided to rotate the at least one downstream roll 214 and, if provided, the second downstream roll 222, for example, by using a gear box 234 or the like. May be. Where provided, one or more drive motors 236 are provided to rotate the additional downstream rolls 224 and 226 by using, for example, a chain drive 238 or gearbox (not shown). May be. The drive moves the extrudate 18 through the assembly 200 in contact with the at least one pair of upstream rolls 202 and the at least one downstream roll 214. As shown, the drive engine may include a plurality of motors 216 that drive a plurality of gears 218 via chain and sprocket devices, as will be readily appreciated by those skilled in the art. In one form, only the at least one downstream roll 214 is driven to rotate. In another form, additional rolls may be driven. These rolls can be driven, for example, by a single drive using a suitable chain, or a second, third, fourth, etc. drive can be used. If two or more rolls have separate drive units, the drive units are usually synchronized to reduce the risk of the extrudate breaking.

  To assist in controlling the temperature of the extrudate 18 (eg, by cooling the extrudate), the assembly 200 includes the at least one pair of upstream rolls 202 and the at least one for cooling the extrudate 18. A cooling engine associated with the downstream roll 214 can further be included. The cooling engine may include a plurality of pumps (not shown) for circulating coolant through one or more cooling circuits (not shown), which cooling circuit includes the at least one pair of upstream rolls 202. And in fluid communication with the at least one downstream roll 214, each of which has an internal flow path for circulating a coolant and allows heat to escape from the extrudate 18. In one form, the upstream and downstream rolls have interlocking cooling engines. In another form, the at least one pair of upstream rolls 202 or the at least one downstream roll 214 can include a cooling engine. Although not necessary, the second downstream roll 222 can include a cooling engine, and the second downstream roll 222 can be driven and rotated by a drive engine.

  As will be appreciated, in operation, the extrudate 18 is in an arcuate path around the at least one pair of upstream rolls 202 and the at least one downstream roll 214, and the at least one pair of upstream rolls 202; The linear path between the at least one downstream roll 214 is moved. In one form, the upstream roll pair has an equal diameter in the range of 50 mm to 150 mm or 75 mm to 125 mm, and the downstream roll has a diameter in the range of 275 mm to 400 mm. In this form, the opposite surface of the extrudate has a plurality of equal arcuate paths with contact angles ranging from 55 ° to 75 ° (from the point where the extrudate first contacts the roll to the point where the extrudate exits the roll). The at least one surface of the extrudate is in the range of 120 ° to 250 °, for example in the range of 190 ° to 220 °. It contacts the downstream roll along an arcuate path at a contact angle. In another form, the opposite surface of the extrudate contacts these upstream rolls along a plurality of equal arcuate paths with a contact angle in the range of 60 ° to 70 °, and at least one surface of the extrudate is It contacts the downstream roll along an arcuate path with a contact angle in the range of 195 ° to 205 °.

  These paths can be seen in FIG. 2, where the extrudate 18 is shown as a solid line. As is conventional, the at least one pair of upstream rolls 202 can be positioned in close proximity to each other, thereby defining a nip therebetween. Typically, nip rolls can be used to reduce friction and prevent slippage or movement of the sheet covering the roll surface. In this configuration, a gap is defined between the first upstream roll 204 and the second upstream roll 206, the gap being equal to or less than the sheet thickness. The at least one downstream roll 214 may be provided with a relatively rough surface in order to generate a relatively large frictional force capable of conveying the sheet through the device 200. Accordingly, it is desired to use one or more nip rolls. In one form, the gap between the first upstream roll 204 and the second upstream roll 206 is greater than 1.05 times, or 2 to 200 times, or 4 to 100 times the sheet thickness.

  As shown above and as shown in FIG. 2, a plurality of rolls arranged in series are used. Compared to more conventional one-stage operation, this multi-stage operation has the advantage that both sides of the extrudate can be uniformly cooled while holding the extrudate in intimate contact with the entire surface of the roll. This results in improved thickness uniformity of the extrudate and the finished film, despite the fact that lower tensions can be used, thereby minimizing the distortion and warpage of the extrudate.

During operation, a substantial amount, if not all, of the cooling solidification process is performed using the upstream cooling roll. Typically, from the temperature of the extrudate “T _d ” at the downstream end of the extrusion die (usually at or near the die mouth), the extrudate has its gelling temperature (ie, the extrudate sheet is a gel It is desirable to cool the extrudate until it reaches below " _Tg ". In one embodiment, the average temperature T at the surface of the extrudate on the upstream roll is either T _g, or less than (cold).

The roll assembly has three rolls, for example, a pair of upstream rolls and a downstream roll. The extrudate derived from the die mouth has a surface temperature T ₁ in the range of 200 ° C to 235 ° C. The extrudate derived from the upstream roll has a surface temperature T ₂ that is lower than T ₁ , where T ₂ is in the range of 25 ° C. to 120 ° C., eg, 65 ° C. to 115 ° C. The extrudate derived from the downstream roll has a surface temperature T ₃ that is lower than T ₂ , where T ₃ is in the range of 20 ° C. to 100 ° C. This temperature drop (T ₁ −T ₃ ) can be represented by a parameter ΔT _1-3 . In one form, T ₂ is equal to KΔT _1-3 , where K is a multiplicative constant in the range of 40% to 95%, or 45% to 85%, or 50% to 75%. is there. Usually, the average surface temperature of the extrudate derived from the pair of upstream rolls is _Tc or lower (cold). Here, _Tc is the crystallization temperature of polyethylene.

  While not being bound by any theory or model, using at least one pair of upstream chill rolls to dissipate a significant amount (50% or more) of heat from the extrudate results in a reasonably uniform surface. ,it is conceivable that. In addition, using a downstream roll to dissipate a relatively smaller amount of heat from the extrudate (typically less than 50% of the heat released) reduces the amount of air entrapment and solvent leaching and provides adequate friction. Occurs to move the extrudate, which results in better extrudate thickness uniformity, and thus better membrane thickness uniformity.

  The films and sheets disclosed herein are particularly useful in the critical field of battery separators, such as in lithium ion primary batteries and lithium ion secondary batteries. Such a battery is useful as a power source for, for example, electric vehicles and hybrid electric vehicles. The films and sheets disclosed herein provide a good balance of important properties, including improved surface smoothness and thickness uniformity.

  Although the focus of the chill roll assembly described above has been focused on the production of single layer films and sheets, it provides multilayer, coextruded films and sheets or laminated films and sheets as will be readily appreciated by those skilled in the art. That is within the scope of this disclosure.

The following describes representative starting materials that are useful in the production of the films and sheets described above. As those skilled in the art will appreciate, the choice of starting material is not critical. In one form, the starting material contains polyethylene. In another form, the starting material is a first polyethylene having a Mw value less than about 1 × 10 ⁶ (“PE-1”) or a second polyethylene having a Mw value of at least about 1 × 10 ⁶ (“PE-2”). )). In one form, the starting material can contain a first polypropylene ("PP-1"). In one form, the starting materials are (i) PE-1 (PE), (ii) PE-2, (iii) PE-1 and PP-1, (iv) PE-1, PE-2 and PP-1. Or (v) one or more of PE-1 and PE-2.

In one form, PE-2 has a Mw in the range of about 1 × 10 ⁶ to about 15 × 10 ⁶ or about 1 × 10 ⁶ to about 5 × 10 ⁶ or about 1 × 10 ⁶ to about 3 × 10 ^6. May be. When PE-2 is mixed with PE-1, the amount of PE-2 is the total amount of PE-1 and PE-2 in order to obtain a film or sheet having a hybrid structure as defined below. It may range from about 0% to about 40%, or from about 1% to about 30%, or from about 1% to 20% by weight. PE-2 may be at least one of a homopolymer or a copolymer. In one form of (iii) and (iv) above, PP-1 can be at least one of a homopolymer or a copolymer, or about 50 weight based on the total amount of microporous film or sheet material. % Or less. In one form, the Mw of the polyolefin in the microporous film or sheet material may be about 1.5 × 10 ⁶ or less to obtain a microporous film or sheet having a hybrid structure as defined below, or , About 1.0 × 10 ⁵ to about 2.0 × 10 ^6, or about 2.0 × 10 ⁵ to about 1.5 × 10 ⁶ . In one form, PE-1 may have a Mw in the range of about 1 × 10 ⁴ to about 9 × 10 ⁵ , or about 2 × 10 ⁵ to about 8 × 10 ⁵ , and high density polyethylene, It may be one or more of medium density polyethylene, branched low density polyethylene, or linear low density polyethylene, and may be at least one of a homopolymer or a copolymer. PE-2 may be an ultra high molecular weight polyethylene having a Mw in the range of 1 × 10 ^{6 to} 2.5 × 10 ⁶ , or 1.5 × 10 ⁶ to 2 × 10 ⁶ .

In one form, PP-1 may be one or more of, for example, (i) a propylene homopolymer or (ii) a copolymer of propylene and a fifth olefin. The copolymer may be a random polymer or a block copolymer. The fifth olefin is an α-olefin such as, for example, ethylene, butene-1, pentene-1, hexene-1,4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, and styrene; and For example, one or more of diolefins such as butadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene, and the like. The amount of the fifth olefin in the copolymer may be within a range that does not adversely affect the properties of the microporous film, such as heat resistance, compression resistance, and heat shrinkage. For example, the amount of the fifth olefin may be less than 10 mol% based on 100 mol% of the total copolymer. Optionally, the polypropylene has one or more of the following properties: (i) the polypropylene is about 1 × 10 ⁴ to about 4 × 10 ⁶ , or about 3 × 10 ⁵ to about 3 × 10 ⁶ , or Having a Mw in the range of about 6 × 10 ⁵ to about 1.5 × 10 ⁶ , and (ii) polypropylene is about 1.01 to about 100, or about 1.1 to about 50, or about 3 to about 30 (Iii) the stereoregularity of the polypropylene may be isotactic; (iv) the polypropylene is at least about 90 joules / gram or from about 100 J / g to 120 J / (v) the polypropylene may have a melting peak (second melting) of at least about 160 ° C. and (vi) the polypropylene has a temperature of about 230 ° C. and 25 seconds. distortion speed of ^-1 When measured at (strain rate), it may have at least about 15 Trouton ratio; and / or, in (vii) polypropylene, strain rate of 230 ° C. temperature and 25 sec ^-1, at least about 50 It may have an elongational viscosity of 1,000 Pa seconds. Optionally, the polypropylene has a Mw / Mn in the range of about 1.01 to about 100, or about 1.1 to about 50.

  In one form, the microporous film or sheet has a hybrid structure. The hybrid structure is a relatively dense domain having a main peak in the range of 0.01 μm to 0.08 μm and a range of 0.08 μm to 1.5 μm in the pore size distribution curve. It is characterized by a pore size distribution showing a relatively coarse domain showing at least one sub-peak. The ratio of the pore volume of the dense domain (calculated from the main peak) to the pore volume of the coarse domain (calculated from the sub-peak) is not important, for example in the range of about 0.5 to about 49. It's okay.

The microporous film or sheet material may optionally contain one or more additional polyolefins identified as the seventh polyolefin, for example polybutene-1, polypentene-1, poly-4-methylpentene-1 , Polyhexene-1, polyoctene-1, polyvinyl acetate, polymethyl methacrylate, polystyrene, and ethylene / α-olefin copolymers (excluding ethylene-propylene copolymers), about 1 × 10 ^It may have a Mw in the range of ⁴ to about 4 × 10 ⁶ . In addition to or in addition to the seventh polyolefin, the microporous film or sheet material further comprises a polyethylene wax, such as one having a Mw in the range of about 1 × 10 ³ to about 1 × 10 ^4. But you can.

In one aspect, a method for producing a single layer microporous membrane is provided. The method includes mixing a polyolefin composition and a solvent or diluent to form a polyolefin solution, the polyolefin composition comprising polypropylene and at least a first polyethylene having a crystal dispersion temperature (T _cd ). The polyolefin solution is extruded through an extrusion die to form an extrudate. These steps can be performed using conventional starting materials under conventional conditions, for example, as described in US Pat. No. 5,051,183 and US Pat. No. 6,096,213. . This US Pat. No. 5,051,183 and US Pat. No. 6,096,213 are hereby incorporated by reference in their entirety. The film may be, for example, a single layer film. After extrusion, i) at least one pair of upstream rolls positioned to receive the extrudate, each of the at least one pair of upstream rolls along an arcuate path with a contact angle of 100 ° or less At least one pair of upstream rolls in contact with the extrudate; and ii) at least one downstream roll, wherein the at least one pair of upstream rolls and the at least one downstream roll are such that the at least one downstream roll is the at least one At least one, arranged to receive the extrudate from a pair of upstream rolls, and wherein the at least one downstream roll contacts the extrudate along an arcuate path at a contact angle of 180 ° or more Cool the extrudate by letting heat out of the extrudate through multiple rolls, including a downstream roll, forming a cooled extrudate Orienting the cooled extrudate at least about 2 to about 400 times in one direction at a temperature of about T _{cd to} T _m + 10 ° C. and removing at least a portion of the diluent from the cooled extrudate Form.

  In one form, the microporous polyolefin membrane is a bilayer membrane. In another form, the microporous polyolefin membrane has at least three layers. Such membranes and methods of manufacture are described, for example, in PCT patent application WO 2008/016174, which is incorporated by reference in its entirety. Those skilled in the art will appreciate that the same techniques can be applied to the production of membranes or membranes having four or more layers, but for the production of microporous polyolefin membranes, mainly two-layer membranes and three-layer membranes. It demonstrates from a viewpoint of a film | membrane.

  In one form, the three-layer microporous polyolefin membrane is between the first and third microporous layers that constitute the outer layer of the microporous polyolefin membrane, and between the first and third layers (and desired). A second layer in planar contact with the first layer and the third layer. In another form, the first and third layers are made from a first polyolefin solution and the second (or inner) layer is made from a second polyolefin solution. In another form, the first and third layers are made from a second polyolefin solution and the second layer is made from a first polyolefin solution.

  A first method for producing a multilayer film comprises (1) mixing a first polyolefin composition and a diluent (eg, by melt blending) to prepare a first mixture, (2) second Mixing the two polyolefin composition and the second diluent to prepare a second mixture; (3) extruding the first and second mixtures through at least one die to form an extrudate; ) I) at least one pair of upstream rolls positioned to receive the extrudate, each of the at least one pair of upstream rolls to the extrudate along an arcuate path with a contact angle of 100 ° or less At least one pair of upstream rolls in contact, and ii) at least one downstream roll, wherein the at least one pair of upstream rolls and the at least one downstream roll are the at least one Two downstream rolls are arranged to receive the extrudate from the at least one pair of upstream rolls, and the at least one downstream roll enters the extrudate along an arcuate path with a contact angle of 180 ° or more. Passing a plurality of cooling rolls including at least one downstream roll in contact to dissipate heat from the extrudate to form a cooled extrudate, such as a multilayer gel sheet, (5) Diluent (one or Removing at least a portion of the plurality) from the cooled extrudate and optionally removing any remaining volatile species to form a multilayer microporous membrane. If desired, a stretching step (6) selected as desired, a thermal solvent treatment step (7) selected as desired, and the like may be performed between steps (4) and (5). it can. If desired, after step (5), optionally selected, a multi-layer microporous membrane stretching step (8), optionally selected heat treatment step (9), optionally selected ionizing radiation The cross-linking step (10) can be performed, and the hydrophilic treatment step (11) selected if desired. The order of steps selected as desired is not critical.

  In the first step of the method, the polyolefin, usually in the form of a polyolefin resin (eg, a composition of at least one polyolefin species optionally containing other non-polyolefin species or non-polymer species), for example, Mix by dry mixing or melt blending with a suitable diluent (eg solvent, eg liquid paraffin) to make a first mixture. If desired, the first mixture (which may be described as a solution, slurry, etc.) may contain various additives such as one or more antioxidants, silicate fine powder (pore forming material), etc. However, they should be used in a concentration range that does not significantly reduce the desired properties of the multilayer microporous membrane. In one form, the first polyolefin composition contains PE-1 and optionally PE-2 and / or PP-1. For example, based on the weight of the first polyolefin composition, the amount of PE-1 in the first polyolefin composition may range from 1 wt% to 100 wt%, and the PE- The amount of 2 may range from 0 wt% to 99 wt%, and the amount of PP-1 in the first polyolefin composition may range from 0 wt% to 80 wt%. In the second polyolefin composition, for example, based on the weight of the second polyolefin composition, the amount of PE-1 may range from 1 wt% to 100 wt%, and the amount of PE-2 is 0 wt%. % To 99% by weight, and the amount of PP-1 may be in the range of 0% to 80% by weight.

  The first and second diluents may be solvents for the polyolefin, for example, solvents that are liquid at room temperature. Conventional solvents such as those described in International Publication No. 2008/016174 can be used. In another form, the resin or the like used to prepare the first polyolefin composition is dry mixed or melt blended, for example, in a twin screw extruder or mixer, prior to mixing them with a solvent or diluent. . Conventional conditions such as mixing, melt blending, and dry mixing, such as those described in International Publication No. 2008/016174, can be used.

  The amount of the first polyolefin composition in the first polyolefin solution is not critical. In another form, the amount of the first polyolefin composition in the first mixture ranges from about 1 wt% to about 75 wt%, such as from about 20 wt% to about 70 wt%, based on the weight of the polyolefin solution. It may be. The amount of the first polyethylene in the first mixture is not critical and may be, for example, 1-50% by weight or 20-40% by weight per 100% by weight of the first mixture.

  The second mixture can be prepared by the same method used to prepare the first mixture. The second diluent can be selected from the same diluent as the first diluent. Also, the second diluent can be selected independently of the first diluent (and usually selected independently), but the second diluent is the same as the first diluent. Alternatively, the first diluent may be used at the same relative concentration as used in the first mixture.

  The second polyolefin composition is usually selected independently of the first polyolefin composition. The second polyolefin composition may include, for example, a second polyethylene resin and / or a second polypropylene resin.

  In another form, the first mixture is directed from the first extruder to the first die and the second mixture is directed from the second extruder to the second die. A layered extrudate of a sheet mold (ie, a body that is significantly larger in the planar direction than in the thickness direction) can be extruded from the first and second dies. Optionally, the first and second mixtures may be brought into contact with the flat surface of the first extrudate layer formed from the first mixture with the flat surface of the second extrudate layer formed from the second mixture. Coextrusion from first and second dies. The flat surface of the extrudate can be defined by a first vector in the machine direction of the extrudate and a second vector in the cross direction of the extrudate.

  In another form, the first die and the second die share a common partition, for example, between a region in the die assembly containing the first mixture and a second region in the die assembly containing the second mixture. As in some cases, a die assembly is used, including first and second dies.

  In another form, multiple dies are used and each die is connected to an extruder for directing either the first or second mixture to the die. For example, in one form, a first extruder containing a first mixture is connected to a first die and a third die, and a second extruder containing a second mixture is connected to a second die. As in the previous embodiment, the resulting layered extrudate is coextruded from the first, second, and third dies (eg, simultaneously) to form a surface layer (eg, top layer and bottom layer). A first layer and a third layer made from the first mixture; and constituting an intermediate or intermediate layer of the extrudate that is between both surface layers and in planar contact with both surface layers; A three-layer extrudate can be formed that includes a second layer made from the second mixture.

  In yet another form, the same die assembly is used, but the mixture is reversed. That is, the second extruder containing the second mixture is connected to the first die and the third die, and the first extruder containing the first mixture is connected to the second die.

  In any of the foregoing embodiments, die extrusion can be performed using conventional die extrusion equipment, such as that described in WO 2008/016174.

  Extrusion has been described with respect to the form of making two-layer and three-layer extrudates, but the extrusion process is not limited thereto. For example, by using multiple dies and / or die assemblies, a multi-layer extrudate having four or more layers can be made using an extrusion process of the form described above. In such a layered extrudate, each surface layer or intermediate layer can be made using a first mixture and / or a second mixture.

  For example, by cooling, the multilayer extrudate can be made into a cooled extrudate, such as a multilayer gel-like sheet. The cooling rate and cooling temperature are not particularly important. In one form, the temperature of the multilayer gel sheet (cooling temperature) is approximately equal to (or lower than) the gel temperature of the multilayer gel sheet at a cooling rate of at least about 10 ° C./min. Until it can be cooled. In another form, the extrudate is cooled to a temperature of about 100 ° C. or less to form a multilayer gel-like sheet.

  Cooling can be achieved using the apparatus described in any of the above embodiments, for example, a first pair (and optionally a second pair) of upstream cooling rolls having equal diameter, where Each roll of the pair contacts the extrudate along an arcuate path with a contact angle of 100 ° or less, and the downstream cooling roll contacts the extrudate along an arcuate path with a contact angle of 180 ° or more. To do. In one form, 50% or more of the extrudate cooling is achieved before the extrudate contacts the downstream roll.

  In order to form a microporous membrane, after cooling, at least a portion of the first and second diluents are removed (or replaced) from the multilayer gel sheet. A displacement (or “wash”) solvent can be used to remove (wash or replace) the first and second diluents. Conventional cleaning solvents and cleaning techniques such as those described in WO 2008/016174 can be used.

  The amount of diluent removed is not particularly important, but usually a higher quality (more porous) membrane when removing at least the majority of the first and second diluent from the gel-like sheet Occurs. In another form, the film-forming solvent is removed from the gel-like sheet (eg, by washing) and the amount of diluent remaining in the microporous membrane sheet is less than 1% by weight based on the weight of the gel-like sheet. Remove until

  In another form, the membrane obtained by removing at least a portion of the diluent is dried to remove the wash solvent. Any method capable of removing the cleaning solvent can be used, including conventional methods such as heat drying, air drying (moving air), etc., as described in WO2008 / 016174.

  Although not essential, drying can be performed until the amount of residual cleaning solvent is about 5% by weight or less on a dry basis, that is, based on the weight of the microporous membrane. In another form, drying is performed until the amount of residual washing solvent is about 3% by weight or less based on the amount of drying. Inadequate drying may be seen, usually because it causes an undesirable decrease in the porosity of the microporous membrane. If this is observed, the drying temperature should be increased and / or the drying time should be increased. The microporous membrane is formed as a result of removal of the washing solvent, such as by drying or other methods.

  In order to obtain a stretched multilayer gel sheet, the multilayer gel sheet may be stretched as desired before the step of removing the diluent. It is believed that the presence of the first and second diluents in the multilayer gel sheet results in a relatively uniform draw ratio. Heating the multi-layer gel sheet is also considered to help stretch uniformity, particularly at the start of stretching or at a relatively early stage of stretching (eg, before 50% of stretching is complete). It has been.

  The selection of the stretching method, the degree of stretching ratio, and the treatment conditions (temperature, etc.) during stretching are not particularly important, and conventional stretching methods such as those described in International Publication No. 2008/016174, Can be used. Since the polymer in the gel-like sheet is oriented by stretching, the stretching is sometimes referred to as “orientation”.

  Without being bound by any theory or model, we believe that such stretching results in cleavage between polyethylene lamellae, thereby making the polyethylene phase finer and forming a larger number of fibrils. It is done. These fibrils form a three-dimensional network structure (a network structure irregularly connected in three dimensions). Thus, when stretching is used, it becomes easier to produce a relatively high mechanical strength multilayer microporous polyolefin membrane having a relatively large pore size. Such a multilayer microporous membrane is considered to be particularly suitable for use as a battery separator.

  Although not required, the multilayer gel-like sheet may be treated with a hot solvent, as described in WO2008 / 016174 and WO2000 / 20493.

  In another form, if desired, the dried multilayer microporous membrane of step (6) can be stretched at least uniaxially. Biaxial stretching may be used, and the amount of stretching along each axis need not be the same. The selected stretching method is not important, and a conventional stretching method such as a tenter method may be used. Although not important, the membrane may be heated during stretching. Selection is not critical, but stretching may be uniaxial or biaxial. When biaxial stretching is used, stretching may be performed simultaneously in both axial directions, or a multilayer microporous polyolefin membrane is sequentially stretched, for example, first in the machine direction, then in the transverse direction, etc. May be. In another form, simultaneous biaxial stretching is used. When the multilayer gel-like sheet is stretched as described in step (6), the stretching of the dry multilayer microporous polyolefin film in step (9) is dry stretching, re-stretching, or dry stretching. Can be called. Conventional stretching techniques and conditions, such as those described in International Publication No. 2008/016174, can be used.

  In another form, the dried multilayer microporous membrane can be heat treated after step (5). As described in WO 2008/016174, conventional heat treatments such as heat setting and annealing can be used.

  In another form, the multilayer microporous polyolefin membrane can be subjected to a hydrophilic treatment (ie, a treatment that makes the multilayer microporous polyolefin membrane more hydrophilic). The hydrophilic treatment may be, for example, monomer graft treatment, surfactant treatment, corona discharge treatment or the like. In another form, a monomer grafting process is used after the cross-linking process.

When the surfactant treatment is used, any one of a nonionic surfactant, a cationic surfactant, an anionic surfactant and an amphoteric surfactant is used, for example, alone or in combination. be able to. In another form, a nonionic surfactant is used. The choice of surfactant is not critical. For example, a multilayer microporous polyolefin membrane can be immersed in a solution of a surfactant and water or a lower alcohol such as methanol, ethanol, isopropyl alcohol, or coated with the solution, for example, by a doctor blade method. it can.
Microporous membrane structure, properties, and composition
Construction

  The final film thickness is usually in the range of 3 μm or more. For example, the membrane may have a thickness in the range of about 3 μm to about 300 μm, such as about 5 μm to about 50 μm. The thickness of the microporous membrane can be calculated, for example, by measuring the thickness of the microporous membrane over a width of 10 cm with a longitudinal distance of 1 cm using a contact-type thickness meter, and then obtaining an average value. For example, a thickness meter such as Lightmatic commercially available from Mitutoyo Corporation is suitable. A non-contact type thickness measuring method such as an optical thickness measuring method is also suitable.

  The microporous membrane exhibits a standard deviation of thickness values of 1 micron or less, for example from about 0.25 microns to about 0.75 microns, whereby the microporous membrane is an excellent battery separator, particularly lithium ion An excellent battery separator for batteries.

  It has been found that films produced by methods in the prior art show significant thickness variations along the TD of the film. Some of this variation in thickness is due to deformation along the end of the membrane caused by, for example, a tenter clip that grips the membrane during processing. This variation in thickness is also due to the variation in the thickness of the cooled extrudate. Edges are cut from the end of the extrudate and / or membrane to produce a membrane with a standard deviation of acceptable thickness values, typically less than 1 micron, for example in the range of 0.25 to 0.75 microns. Is done.

  Edge removal can be done continuously, for example, by rotating a cutting blade placed parallel to the MD of the membrane at a desired distance in the center direction (along TD) from the edge of the membrane. it can. This edge is then excluded from processing. In conventional microporous membranes, the ratio of membrane weight per unit length to edge weight per unit length is 75% or greater.

  The method of the present invention is advantageous because the method results in improved thickness uniformity of the cooled extrudate, and this improvement results in a film with improved thickness uniformity along the TD. is there. Thus, less slitting is required to produce a film with a desired amount of thickness variation or less, thereby fewer edges and improved microporous membrane yield. . In the microporous membrane of the present invention, the ratio of the weight of the membrane per unit length to the weight of the edge per unit length is in the range of 75% to 99%. In one embodiment, the slitting of the film to remove edges reduces the film width by a factor of about 90% to about 99% of the film width exiting the heat setting process. This slitting process is referred to as the “first” slitting process when further slitting is used downstream, for example, to produce a microporous membrane having a desired final width for battery manufacturing. May be.

  The average thickness of the membrane can be measured at a plurality of selected points along the TD (ie, across the membrane). Although not necessary, the standard deviation of the measured values using a plurality of measurement points, which are arranged at almost equal intervals along the TD and are based on the center line (parallel to the machine direction) of the film. And determine the average thickness of the membrane. Since the thickness value is measured at a plurality of points with respect to the center line of the film, this measurement can be performed before or after slitting.

  In one embodiment, the selected thickness measurement points are along the TD and are located between the start and end points, where the start and end points are, if desired, the membrane Assume equidistant from the center line along TD. The distance between the start and end points is after the heat setting process, but before slitting, i.e. the width of the membrane before the first slitting and any slitting downstream of the first slitting, e.g. , About 75%, or alternatively about 80%, or alternatively 90%, or alternatively about 95%. The standard deviation and average thickness of the thickness measurement can be determined only by the start and end points, but usually these points and points along the TD are used to determine these values; , At least 5 points, or at least 10 points, or at least 20 points, or at least 40 points. For example, the number of points may be in the range of 10-30 points and, if desired, these points are arranged at equal intervals along the TD at convenient intervals. For example, the distance between adjacent measurement points may range from about 25 mm to about 100 mm.

と定義され、式中、Ｔは、各測定点における厚さ測定値を表し、Ｎは、測定点の数である。厚さの均一性は、厚さ測定値と平均厚さ値との間の差（Δ）、すなわち、Δ＝Ｔ−μ、で表すこともできる。
特性 The term “μ” refers to the arithmetic average of thickness measurements (measured in microns) determined at measurement points along the TD. The standard deviation “σ” of the thickness measurement is the square root of the variance, ie,

Where T represents the thickness measurement at each measurement point and N is the number of measurement points. Thickness uniformity can also be expressed as the difference (Δ) between the thickness measurement and the average thickness value, ie, Δ = T−μ.
Characteristic

In a preferred embodiment, the microporous membrane of the present invention has at least one of the following properties.
(A) Standardized air permeability of 35 seconds / 100 cm ³ / μm or less.

The air permeability is measured according to JIS P8117, and the result is normalized to a value at a thickness of 1.0 μm using the formula A = (X) / T ₁ . Where X is the measured air permeability of the film having the actual thickness T ₁ and A is the standardized air permeability at a thickness of 1.0 μm. In one embodiment, normalized air permeability is not more than 30 seconds / 100 cm ³ / [mu] m, for example, in the range of 10 seconds / 100cm ³ / μm~25 seconds / 100cm ³ / μm.
(B) Porosity of about 20 to about 80%

The porosity of the membrane is obtained by comparing the actual weight of the membrane with the weight of an equivalent 100% polyethylene non-porous membrane (equivalent in the sense of having the same length, width and thickness) Measure by conventional method. The porosity is then determined using the formula: porosity% = 100 × (w2−w1) / w2. Where “w1” is the actual weight of the microporous membrane and “w2” is the weight of an equivalent 100% polyethylene nonporous membrane having the same size and thickness.
(C) Standardized puncture strength of 15 gF / μm or more

The puncture strength is obtained when a microporous membrane having a thickness of T ₁ is pierced at a speed of 2 mm / sec using a 1 mm diameter needle having a spherical tip surface (curvature radius R: 0.5 mm) (grams). It is defined as the maximum load measured (in units of force or “gF”). This pin puncture strength is normalized to a value at a film thickness of 1.0 μm using the formula L ₂ = (L ₁ ) / T ₁ . Where L ₁ is the measurement pin puncture strength, L ₂ is the standardized puncture strength, and T ₁ is the average thickness of the membrane.

In one embodiment, the standardized puncture strength ranges from 20 gF to 35 gF, or 25 gF to 30 gF.
(D) 900Kg / cm ² or more tensile strength of tensile strength and 800 Kg / cm ² or more TD of MD

Tensile strength is measured in MD and TD according to ASTM D-882A. In one embodiment, the membrane has a MD tensile strength in the range of 1000 Kg / cm ^{2 to} 2,000 Kg / cm ² and a TD tensile strength in the range of 900 Kg / cm ^{2 to} 1300 Kg / cm ² .
(E) Tensile elongation of MD and TD of 50% or more

Tensile elongation is measured according to ASTM D-882A. In one embodiment, the MD and TD tensile elongations of the membrane each range from 50% to 350%. In another embodiment, the tensile strength of the membrane MD is, for example, in the range of 150% to 300%, and the tensile elongation of TD is, for example, in the range of 150% to 400%.
(F) Shutdown temperature below 140 ° C

The shutdown temperature of the microporous membrane is measured with a thermomechanical analyzer (TMA / SS6000 commercially available from Seiko Instruments Inc.) as follows: A rectangular sample of 3 mm × 50 mm is measured with a long axis of the sample being fine. Cut out from the microporous membrane so that it is aligned with the transverse direction of the porous membrane and the short axis is aligned with the machine direction. This sample is set in a thermomechanical analyzer with a chuck distance of 10 mm. That is, the distance from the upper chuck to the lower chuck is 10 mm. The lower chuck is fixed, and a load of 19.6 mN is applied to the sample with the upper chuck. These chuck and sample are sealed in a heatable tube. Starting at 30 ° C, increasing the temperature inside the tube at a rate of 5 ° C / min and measuring the change in sample length under a load of 19.6 mN at 0.5 second intervals. Record. The temperature is increased to 200 ° C. “Shutdown temperature” is defined as the temperature of the inflection point observed near the melting point of the polymer with the lowest melting point among the polymers used to make the membrane. In one embodiment, the shutdown temperature is 140 ° C. or lower, for example in the range of 128 ° C. to 133 ° C.
(G) Melt down temperature of 142 ° C or higher

  The meltdown temperature is measured by the following procedure: A rectangular sample of 3 mm × 50 mm is so aligned that the long axis of the sample is aligned with the transverse direction of the microporous membrane when producing the microporous membrane in this method. And it cuts out from a microporous film so that a short axis may be in line with a machine direction. This sample is set in a thermomechanical analyzer (TMA / SS6000 commercially available from Seiko Instruments Inc.) with a distance between chucks of 10 mm. That is, the distance from the upper chuck to the lower chuck is 10 mm. The lower chuck is fixed, and a load of 19.6 mN is applied to the sample with the upper chuck. These chuck and sample are sealed in a heatable tube. Starting at 30 ° C, increasing the temperature inside the tube at a rate of 5 ° C / min and measuring the change in sample length under a load of 19.6 mN at 0.5 second intervals. Record. The temperature is increased to 200 ° C. The meltdown temperature of a sample is defined as the temperature at which the sample breaks, and is typically in the range of about 142 ° C to about 200 ° C.

In one embodiment, the meltdown temperature ranges from 143 ° C to 190 ° C.
Composition of microporous membrane

  The microporous membrane usually contains the same polymer used to make the polymer composition, usually in the same relative amounts. A washing solvent and / or processing solvent (diluent) may also be present, usually in an amount of less than 1% by weight, based on the weight of the microporous membrane. A small amount of polymer molecular weight reduction can occur during processing, which is acceptable. In one embodiment in which the polymer is a polyolefin and the membrane is produced by a wet process, if the molecular weight reduction during processing occurs, the value of Mw / Mn of the polyolefin in the membrane is such that the polyolefin composition This results in a difference of about 5% or less, or about 1% or less, or about 0.1% compared to the Mw / Mn of the polymer used to make the.

In one embodiment, the microporous membrane includes first and second polyethylene, for example, from about 25 wt% to about 35 wt% first polyethylene and from about 65 wt% to about 75 wt%, based on the weight of the membrane. % Second polyethylene. In one embodiment, the membrane contains about 30% by weight first polyethylene and about 70% by weight second polyethylene.
Battery separator

In one embodiment, the microporous membrane in any of the above embodiments is useful for separating electrodes in a conversion device, such as a lithium ion battery, and energy storage.
battery

The microporous membrane of the present invention is useful as a battery separator in, for example, lithium ion primary batteries and lithium ion secondary batteries. Such a battery is described in PCT publication WO 2008/016174.
[Example]
Extrudate

  The extrudates used in Examples 1, 2, and 3 and Comparative Examples 1, 2, 3, and 4 are made as follows. The thickness of the extrudate (measured at the mouth of the extrusion die) is presented in Table 1.

20 mass having a weight average molecular weight (Mw) of 2.0 × 10 ⁶ , a molecular weight distribution of 5.0 (Mw / Mn), a melting point (T _m ) of 135 ° C., and a crystal dispersion temperature (T _cd ) of 100 ° C. 99.8 parts by weight of a polyolefin composition containing ⁵ % ultra high molecular weight polyethylene (UHMWPE), 5.6 × 10 ⁵ Mw and 4.6 Mw / Mn, T _{m of} 135 ° C., and T _m of 100 ° C. 80% by weight high density polyethylene (HDPE) with _cd , and 0.2 parts by weight of tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) as an antioxidant -Propionate] Dry blend with methane. The polyolefin composition has a Mw / Mn of 8.6, a T _{m of} 135 ° C., and a T _cd of 100 ° C.

  30 parts by weight of the resulting mixture was loaded into a high strength twin screw extruder having an inner diameter of 58 mm and an L / D of 52.5 and 70 parts by weight of liquid paraffin [50 cSt (40 ° C.)]. Is fed to the twin screw extruder through a side feeder. Melt blending is performed at 210 ° C. and 200 rpm to prepare a first polyolefin solution.

  Mw and Mw / Mn of each UHMWPE and HDPE are measured by gel permeation chromatography (GPC) method under the following conditions.

The Mw and Mn of these polyethylenes are determined using a high temperature size exclusion chromatograph equipped with a differential refractive index detector (DRI), ie “SEC” (GPC PL 220 from Polymer Laboratories). Three PLgel Mixed-B columns (commercially available from Polymer Laboratories) are used. The nominal flow rate is 0.5 cm ³ / min. The nominal injection volume was 300 μL. The transfer line, column, and the DRI detector were placed in an oven maintained at 145 ° C. The measurement is performed according to the procedure disclosed in “Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001)”.

  The GPC solvent used is a filtered Aldrich reagent grade 1,2,4-trichlorobenzene (TCB) containing approximately 1000 ppm butylated hydroxytoluene (BHT). Prior to introduction into the SEC, the TCB was degassed using an online degasser. A polymer solution was prepared by placing the dried polymer in a glass container, adding the desired amount of the TCB solvent, and then heating the mixture at 160 ° C. with continuous stirring for about 2 hours. The concentration of the UHMWPE solution was 0.25 to 0.75 mg / ml. The sample solution is filtered off-line using a SP260 Model Prep Station (commercially available from Polymer Laboratories) with a 2 μm filter prior to injection into GPC.

  The separation efficiency of the column set is calibrated by a calibration curve prepared using 17 individual polystyrene standards with Mp ranging from about 580 to about 10,000,000, which are used to create a calibration curve. These polystyrene standards are obtained from Polymer Laboratories (Amherst, Mass.). A calibration curve (logMp vs. retention capacity) is created by recording the retention capacity at the peak of the DRI signal for each PS standard and fitting this data set to a second order polynomial. Samples are analyzed using IGOR Pro, commercially available from Wave Metrics.

The polyolefin solution is fed at 210 ° C. from the twin screw extruder to a T-die for forming a single layer sheet having a width of 250 mm to form an extrudate having a first surface and a second surface. . The extrudate is cooled using a chill roll assembly as described in the following examples and comparative examples.
Example 1

  The extrudate made with a thickness of 1.2 mm is led to a first chill roll (CR-1) having a diameter of 100 mm and a surface temperature of 15 ° C. as shown in Table 1. The first surface of the extrudate contacts the chill roll at a contact angle of 65 °, so that the extrudate is cooled. This cooled extrudate is led from the first cooling roll to a second cooling roll (CR-2) having a diameter of 100 mm and a surface temperature of 15 ° C. The second chill roll contacts the second surface of the extrudate (opposite the first surface) at a contact angle of 70 °. The first and second cooling rolls constitute an upstream pair of cooling rolls. The extrudate is led from the first upstream pair of chill rolls to the second upstream pair of chill rolls. This second pair includes a third (CR-3) and fourth (CR-4) chill roll. This third chill roll has a diameter of 100 mm and a surface temperature of 15 ° C. and contacts the first surface of the extrudate with a contact angle of 70 °. From here, the extrudate is led to a fourth chill roll having a diameter of 100 mm and a surface temperature of 15 ° C. The second surface of the extrudate contacts the fourth chill roll at a contact angle of 70 °.

  The extrudate is led from a second pair of chill rolls to a downstream chill roll (CR-5) having a diameter of 300 mm, a surface temperature of 15 ° C., and a contact angle of 200 °. The extrudate derived from the downstream chill roll (“cooled extrudate”) has a temperature of 35 ° C., an average thickness of 1040 μm, and a thickness deviation from an average value in the range of 5 μm to 11 μm.

The extrudate is then stretched biaxially at a temperature of 115 ° to a magnification of 5 × 5 (MD × TD). Liquid paraffin is removed from the stretched extrudate to form a film, which is then heat set at 124.7 ° C. for 30 seconds. The properties of this final microporous membrane are shown in Table 1.
Example 2

Example 2 is that the extrudate thickness produced by the die is 0.6 mm, the thickness of the cooled extrudate before biaxial stretching is 520 μm, the cooled extrudate has a temperature of 30 ° C., The thickness deviation is in the range of 5 μm to 10 μm, and the heat set temperature is 124.5 ° C., which is the same as in Example 1. The properties of this final film are shown in Table 1.
Example 3

In Example 3, the thickness of the extrudate produced by the die is 2.3 mm, the cooled extrudate has a temperature of 40 ° C., the thickness of the cooled extrudate is 2070 μm, and the thickness deviation is It is the same as Example 1 except that it is the range of 5 micrometers-13 micrometers, biaxial stretching temperature is 116.5 degreeC, and heat set temperature is 123.5 degreeC. The properties of this final film are shown in Table 1.
Comparative Example 1

In Comparative Example 1, the diameter of the first cooling roll having a contact angle of 210 ° is 300 mm, the diameters of the second and third cooling rolls having a contact angle of 170 ° are each 300 mm, and the contact of 150 ° The diameter of the fourth chill roll having a corner is 300 mm, the diameter of the downstream chill roll having a contact angle of 80 ° is 100 mm, the cooled extrudate has a temperature of 35 ° C., and the thickness of the cooled extrudate is It is the same as Example 1 except that it is 960 micrometers and thickness deviation is the range of 15 micrometers-35 micrometers. The properties of this final film are shown in Table 1.
Comparative Example 2

In Comparative Example 2, the thickness of the extrudate produced by the die is 0.6 mm, the cooled extrudate has a temperature of 30 ° C., the thickness of the cooled extrudate is 480 μm, and the thickness deviation is 15 μm. It is the same as that of the comparative example 1 except that it is -30 micrometers and biaxial stretching temperature is 114.4. The properties of this final film are shown in Table 1.
Comparative Example 3

In Comparative Example 3, the thickness of the extrudate produced by the die is 0.9 mm, the cooled extrudate has a temperature of 35 ° C., the contact angle of the first cooling roll is 165 °, and the second cooling The contact angle of the roll is 150 °, the diameter of the third cooling roll having a contact angle of 225 ° is 450 mm, the diameter of the fourth cooling roll having a contact angle of 200 ° is 450 mm, and the contact of 170 ° The downstream cooling roll having a corner has a diameter of 200 mm, the thickness of the cooled extrudate is 810 μm, the thickness deviation is in the range of 15 μm to 30 μm, the biaxial stretching temperature is 114.8 ° C., and The same as Comparative Example 1 except that heat setting is performed at 125.3 ° C. for 10 seconds.
Comparative Example 4

In Comparative Example 4, the thickness of the extrudate produced by the die is 1.4 mm, the first cooling roll has a contact angle of 40 °, the fourth cooling roll has a contact angle of 170 °, There is no downstream cooling roll, the thickness of the cooled extrudate is 1220 μm, the thickness deviation is in the range of 20 μm to 35 μm, the biaxial stretching temperature is 116.4 ° C., and the heat set temperature is 125. The same as Comparative Example 2 except that the temperature was 5 ° C. The properties of this completed film are shown in Table 1.

  The results in Table 1 show that when at least one pair of upstream chill rolls contact the extrudate with a contact angle of 100 ° or less and at least one downstream chill roll contacts the extrudate with a contact angle of 180 ° or more. Shows that the thickness uniformity of the cooled extrudate is significantly improved. Furthermore, this improvement in thickness uniformity is surprisingly brought about by subsequent processing of the film (biaxial orientation, heat set). Even if these additional processing steps reduce the film thickness by an order of magnitude or more, the improvement in thickness uniformity is retained.

  All patents, test procedures, and other documents cited herein, including priority documents, are fully incorporated by reference to the extent that such disclosure does not conflict, and such incorporation is permitted. Fully incorporated into the full scope of legal jurisdiction

  Although the illustrative forms disclosed herein have been described in detail, various other modifications will be apparent to those skilled in the art, and others will be apparent to those skilled in the art without departing from the spirit and scope of the disclosure. It will be understood that various modifications of can be easily made. Therefore, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions described herein, but rather the claims will not To be interpreted as encompassing all patentable and novel features found in the specification, including all features that would be treated as equivalent by one of ordinary skill in the art to which this disclosure pertains. Is intended.

  When numerical lower limit values and numerical upper limit values are described in this specification, a range from an arbitrary lower limit value to an arbitrary upper limit value is intended.

Claims (13)

A method for producing a microporous membrane, comprising:
a) mixing polyolefin and diluent b) extruding the mixed polyolefin and diluent through an extrusion die to form an extrudate;
c) i) In the step of transporting the extrudate by a plurality of rolls, the first and second rolls are used to be disposed at positions that receive the opposite surfaces of the extrudate, and the first roll has a first angle of 100 ° or less. Contacting the extrudate along an arcuate path at one contact angle, and the second roll contacts the extrudate along an arcuate path at a second contact angle of 100 ° or less, ii) A third roll disposed downstream of the first and second rolls is aligned to receive the extrudate from at least one of the first and second rolls, and the third roll is 180 ° the contact with the extrudate to form a cooled extrudate, to discharge heat to form a cooled extrudate from the extrudate by using a plurality of rolls along an arcuate path in the third contact angle of above,
d) A method for producing a microporous membrane wherein the membrane is formed by removing at least a portion of the diluent from the cooled extrudate.   Each of the first and second rolls has a diameter in the range of 50 mm to 150 mm, the third roll has a diameter in the range of 275 mm to 400 mm, and the first and second contact angles are 55 ° to 75 mm. The method for producing a microporous membrane according to claim 1, wherein the third contact angle is in the range of 190 ° to 220 °.   The first and second rolls are arranged at a position where the first roll receives the extrudate from the die, and the second roll is arranged at a position where the extrudate is received from the first roll. The first pair of rolls, the second pair of rolls disposed at positions downstream of the first pair of rolls and upstream of the third roll, and the second pair of rolls and the second pair of rolls. The method for producing a microporous membrane according to claim 1 or 2, wherein each of the pairs has a diameter of 200 mm or less.   The method for producing a microporous membrane according to claim 3, wherein the first and second pairs of rolls have an equal diameter of 100 mm or less, and the third roll has a diameter of 300 mm or more. An assembly for releasing heat from a molten extrudate comprising a polymer and a diluent,
a) first and second rolls arranged to receive opposite surfaces of the extrudate, wherein the first roll contacts the extrudate along an arcuate path with a first contact angle of 100 ° or less. And the second roll contacts the extrudate along an arcuate path with a second contact angle of 100 ° or less,
b) a third roll downstream of the first and second rolls, wherein the first, second and third rolls are extruded from at least one of the first and second rolls. An apparatus for producing a microporous membrane that is aligned to receive an article and that contacts the extrudate along an arcuate path in which the third roll has a third contact angle of 180 ° or greater.   The first, second and third rolls are mounted on at least one support frame so that the extrudate travels in the arcuate path around the first, second and third rolls. The apparatus for producing a microporous membrane according to claim 5, wherein the microporous membrane is arranged such that the extrudate moves along a linear path toward the third roll.   The apparatus for producing a microporous membrane according to claim 5 or 6, further comprising a drive engine mounted on the support frame for moving the extrudate between the rolls and rotating the third roll.   The apparatus for producing a microporous membrane according to any one of claims 5 to 7, wherein at least one of the first and second rolls is provided with a cooling engine for releasing heat from the extrudate.   The apparatus for producing a microporous membrane according to any one of claims 5 to 8, wherein at least one of the first and second rolls is rotated by any one of a second drive engine synchronized with the first drive engine. (I) Each of the first and second rolls has a diameter of 200 mm or less, and the third roll has a diameter of 250 mm or more,
(Ii) the first and second contact angles are equal and in the range of 55 ° to 75 °;
(Iii) The third contact angle is in a range of 190 ° to 220 °.
The apparatus for producing a microporous membrane according to any one of claims 5 to 9.   The apparatus for producing a microporous membrane according to any one of claims 5 to 10, wherein each of the first and second rolls has an average surface temperature of 40 ° C or lower.   The first and second rolls have a first pair of rolls, the first roll is disposed at a position to receive the extrudate from the die, and the second roll is from the first roll to the extrudate. And a second pair of rolls disposed at positions downstream of the first roll and upstream of the third roll, each of the second pair of rolls comprising: 6. Contact the extrudate along an arcuate path with a contact angle equal to or greater than i) less than 100 [deg.] and (ii) the first pair of contact angles of the roll. The microporous membrane production apparatus according to any one of 11. The microporous membrane manufacturing apparatus according to claim 12, wherein each roll of the second pair of rolls has a diameter of 100 mm or less, and the third roll has a diameter of 300 mm or more.

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