KR100946581B1 - Process For Preparation Of Film For Battery Separator Having Improved Heat Resistant Property - Google Patents

Abstract

The present invention, when producing a film for heat-resistant separator by the extrusion of the polymer substrate and the pore-forming agent and the heat resistance enhancer, the stretching of the sheet, etc., during the extrusion process, the stream of the mixture fluid is continuously divided and re-mixed by the non-back-mixing method. By mixing, the temperature gradient in the fluid is reduced, the degree of dispersion of the pore-forming agent is made uniform, and the heat resistance enhancer is evenly distributed in the small dispersed particle size, so that the uniformity of the morphology and porosity of the polymer substrate in the finally produced film It provides a method for producing a film for a separator to improve the properties and further improved heat resistance, a separator of excellent physical properties thus prepared, and a secondary battery using the same.

Description

Process For Preparation Of Film For Battery Separator Having Improved Heat Resistant Property}

 1 is an axial front view with a Sulzer SMV-type static mixing element mounted inside the barrel in one exemplary static mixer that may be used in the present invention;

FIG. 2 is a top perspective view of the Sulzer SMV-type static mixing element of FIG. 1; FIG.

3 is an enlarged top perspective view of the Sulzer SMV-type static mixing element of FIG. 1;

4 is a top view of the Sulzer SMV-type static mixing element of FIG. 1;

5 is a perspective view of the top cut away with a number of Sulzer SMV-type static mixing elements of FIG. 1 mounted in a barrel;

6 is a partial cross-sectional perspective view of three Kenics KM-type static mixing elements axially arranged in a barrel in one exemplary static mixer that may be used in the present invention, illustrating the movement and rotation of fluid flowing along the barrel; To show;

7 is a perspective view of the Kenics KM-type static mixing elements of FIG. 6;

Description of the main symbols in the drawings

10: Sulzer SMV-type static mixing element

12, 14, 16, 18, 20: corrugated plate

22, 22A, 24, 24A, 26, 28, 30: plate groove

32: fluid profile

34, 100: barrel

35, 36, 38, 40, 42, 44: fluid stream

50: static mixer

54, 56: mixing element fixing means

70: mixing structure

72, 74, 76: Kenics KM-type Static Mixing Elements

80, 82, 84, 86: mixing element intersection

90, 92: direction of fluid rotation

94: fluid flow path

The present invention relates to a method for producing a battery separator film having excellent heat resistance, and more particularly, a battery separator film having excellent heat resistance by extrusion of a mixture containing a polymer substrate, a pore-forming agent and a heat resistance enhancer, stretching of a sheet, and the like. In the process of producing a mixture, the stream of mixture fluid is continuously divided and remixed by the non-rear-mixing method in the extrusion process, thereby reducing the temperature gradient of the fluid, making the pore-forming agent uniform, and dispersing particles of the heat resistance enhancer. Its size is reduced and its dispersibility is increased, ultimately increasing the thickness of the prepared porous film, the morphology of the polymer substrate and the pore morphology, and the heat resistance enhancer is uniformly distributed in the smaller particle size. Method for producing an improved heat resistant film for battery separator, battery separator thus prepared, and using the same It provides a secondary battery.

As technology development and demand for mobile devices increase, the demand for batteries as energy sources is rapidly increasing, and accordingly, many studies on batteries that can meet various demands have been conducted. Among them, the demand for secondary batteries capable of charging and discharging is increasing, and in recent years, the ratio of high power and high capacity lithium secondary batteries to weight has increased significantly.

The secondary battery includes a positive electrode having a positive electrode active material coated on a current collector, a negative electrode having a negative electrode active material coated on a current collector, and interposed between two electrodes to allow lithium ions to move while electrically insulating these positive and negative electrodes. It includes an electrode assembly composed of a porous separator.

The separator is generally manufactured in a thickness of 5 to 300 μm, and pores of about 0.01 to 10 μm through which lithium ions can move are formed. As such a separator, for example, a film made of an olefin polymer such as polyethylene or polypropylene having excellent chemical resistance, a glass fiber or the like, or a nonwoven fabric is used. Among them, porous polyethylene films are frequently used as separators for secondary batteries. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

As the field of use of secondary batteries expands, the demand for batteries that can operate in more severe conditions increases. In addition, the lithium secondary battery, such as the application of external force, exposure to high temperatures, such as the risk of ignition and explosion in an abnormal operating state, the safety issue is addressed as one of the important issues in the secondary battery development process. Therefore, there is a need for a separator having excellent heat resistance.

The heat resistance enhancers used to improve the heat resistance of the separator include reactive monomers such as polypropylene, polyvinylidene fluoride, maleic anhydride, mineral particles having a layered crystal structure such as mica, smectite, or kaolin, and silica or alumina of 100 nm or less. And the addition of these materials is reported to improve meltdown temperature and short circuit resistance.

Specifically, Japanese Patent Nos. 3,281,086, 3,581,772, 3,236,359, 3,252,016, 3,281,086, and Japanese Patent Laid-Open Nos. 2001-72792, 2002-194132, 2001-105235, and 2002 -321323, 2003-183432, 2003-192822, 2004-18838, and the like disclose polyolefin microporous separators comprising a mixture of polyethylene and polypropylene having a weight average molecular weight of at least 5 × 10 ⁵ . The addition of propylene has increased moldability, strength and heat resistance.

In addition, Japanese Patent Laid-Open No. 2001-226515 used polyvinylidene fluoride mixed with high density polyethylene, and Japanese Patent Laid-Open Nos. 2002-343326 and 2003-321569 used maleic anhydride as a reactive monomer. In Patent Publication No. 2002-226639, polyamide was used.

In addition, Japanese Patent Laid-Open Publication Nos. 2003-183440, 2003-238718, 2004-10701, and the like are disclosed for separators having improved heat resistance by the addition of layered mineral particles. Patent Nos. 2003-238720 and 2003-292665 and the like.

Looking at the schematic process of a lithium ion battery separator manufactured using these additives, first, a polymer base material, a pore former, and a heat resistance enhancer are mixed in a twin screw extruder, followed by a gear pump. The sheet is extruded through a T-die using a pump or a single screw extruder. Then, the extruded sheet is stretched, the pore-former is extracted using a solvent, and then heat-set to finally prepare a porous separator.

The inventors of the present invention have conducted in-depth studies on the heat-resistant separation membrane manufacturing process as described above. As a result, it has been confirmed that the prior art has some problems.

When fluid flows inside an extruder (or gear pump) consisting of an internal screw (or gear) and a barrel, the mixing in the direction perpendicular to the flow direction of the fluid tends to be restricted. Therefore, in the manufacturing process according to the prior art, the temperature gradient (Temperature Gradient) is increased between the fluid located in the center and the fluid located in the barrel periphery when viewed from the flow cross section, the temperature uniformity (Temperature Uniformity) is lowered, thereby extruded Morphology of the polymer substrate becomes uneven in the width and thickness directions of the sheet. In particular, the network morphology due to the polymer fiber phase is uneven in the MD (Mechanical Direction) and TD (Transverse Direction) directions. The extruded sheet has, for example, a width of 600 mm and a thickness of 0.5 mm and is thinned to a thickness of about 20 μm by stretching to a width of, for example, 280 cm. Thus, non-uniform morphology of the polymer substrate in the sheet state results in large non-uniformity of the film internal tissue in the stretched state.

In addition, since the pore-former mixed with the polymer substrate is stretched and then extracted by a solvent or the like to form micropores, the pore distribution is uniform in the finally prepared separator only when it is uniformly dispersed in the substrate. However, in the manufacturing process according to the prior art, the uniformity of mixing of the polymer substrate and the pore-forming agent is not excellent due to the flow characteristics of the fluid as described above, so that the uniformity of dispersion of the pore-forming agent in the sheet state is reduced, thereby There is a problem that the uniformity of dispersion of pores in the separator formed through stretching and solvent extraction is lowered.

In addition, the heat resistance enhancer may contribute to heat resistance improvement without lowering the basic physical properties of the separator when uniformly distributed in a small size in the polymer substrate. Generally, as heat resistance enhancers, polymers having excellent heat resistance than polyethylene or inorganic particles having high heat resistance are mainly used. Such heat resistance enhancers are present in the form of particles and are not mixed with the polymer substrate at the molecular level, and tend to aggregate with each other in the polymer substrate. Thus, the heat resistance enhancer may be present in agglomerated form in the polymer substrate and its distributive mixing is low, thereby lowering the uniformity of the tissue of the extruded sheet and the stretched film and providing a desired degree of heat resistance. Not only does it exert, but also is a major cause of increasing the surface roughness of the film and lowering the mechanical properties.

As such, when a film having poor internal uniformity, low pore size and uniformity of dispersion, a large particle size of the heat resistance enhancer in the polymer substrate, and a low dispersibility film are used as the separator in the battery, the battery performance is uniform. It causes a problem of failing safety.

Therefore, there is a high demand for development of a new technology capable of manufacturing a film for a high quality membrane without significantly changing the conventional membrane manufacturing process.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

Specifically, it is an object of the present invention to distribute the morphology of the internal tissues after stretching and extraction because the temperature gradient in the fluid during extrusion is excellent, the uniformity of dispersion of the pore-forming agent and the heat resistance enhancer are uniformly distributed in the size of the dispersed particles. It is to provide a method for producing a membrane film having a homogeneous distribution of pores and heat resistance enhancers.

Still another object of the present invention is to provide a battery separator having excellent physical properties prepared by such a method.

Another object of the present invention is to provide a secondary battery including the separator.

Method for producing a film for separation membrane according to the present invention for achieving this object,

(a) mixing the pore former and the heat resistance enhancer with the liquid polymer substrate;

(b) extruding the stream of mixture fluid into a sheet shape while continuously dividing and remixing by non-rear-mixing;

(c) stretching the extruded sheet to produce a film shape; And

(d) removing and heat-setting the pore former from the film;

It is configured to include.

One of the characteristics of the production process according to the present invention is that by continuously dividing and remixing the stream of the liquid mixture (fluid) by the non-rear blending process in the process of extruding the polymer substrate, the pore former and the heat resistance enhancer into a sheet form. To reduce the temperature gradient of the fluid, to make the pore-forming agent more uniform in size and dispersion in the polymer substrate, and to distribute the heat-resistance enhancer evenly in a small form. , Uniformity of the dispersion of pores and heat resistance enhancers.

The term "liquid polymer substrate" in the present invention means that the polymer forming the base material of the separator is in a liquid phase to enable extrusion. Such liquid phase can be achieved, for example, by melting the polymer as the substrate or dissolving it in a solvent. The polymer is not particularly limited as long as it is a material used as a substrate of a battery separator, and preferably, polyolefin such as polyethylene or polypropylene, and among them, polyethylene, particularly, one containing high molecular weight polyethylene (HMWPE). desirable.

The pore-forming agent is a substance that is dispersed in a liquid polymer substrate, exhibits heterogeneity in a polymer substrate of a separator prepared through extrusion, stretching, and the like, and is subsequently removed from the polymer substrate. Therefore, the site where the pore-forming agent is located in the polymer substrate of the film is left as pores. The pore-forming agent is preferably a liquid material in the extrusion process, but a material that maintains a solid phase may be used. The pore-forming agent is not particularly limited as long as the material satisfies the above conditions. Preferably, the pore-forming agent is liquid paraffin, DOP (Di-2-ethylhexyl phthalate), DBP (Di-butyl-phthalate) or DINP (Di-isononyl). Plasticizers such as phthalate, di-isodecyl phthalate (DIDP) and butyl benzyl phthalate (BBP) may be used, and among these, liquid paraffin is particularly preferable.

The heat resistance enhancer is a material added to improve heat resistance of the polymer substrate, and polymers and inorganic particles having better heat resistance than the polymer substrate may be preferably used. Preferred examples of the heat resistant polymer include polypropylene, nylon, polyethylene terephthalate, and the like. Among them, polypropylene having excellent chemical resistance is more preferable, and among the polypropylenes, particularly high isotactic PP is particularly preferable for improving heat resistance. However, polypropylene is not mixed to the molecular level with polyethylene, which can be preferably used as a polymer substrate, so that polypropylene is present as a particle phase in the polyethylene matrix when they are melt mixed. Therefore, the size of the polypropylene dispersive particles in the polyethylene matrix will vary greatly depending on the mixing conditions. In addition, the inorganic particles, which may be preferably used as heat resistance enhancers, also have low affinity with polyethylene, and thus tend to exist in the polyethylene matrix in a plurality of particles aggregated with each other. When the heat resistance enhancer is evenly distributed in the polymer substrate with a small particle size, the heat resistance may be improved without substantially reducing the basic physical properties of the prepared separator film.

The mixing in step (a) may preferably be carried out by a Twin Screw Extruder. For example, polyethylene, which is a polymeric substrate, is heated to melt above its melting point and passed through a twin screw extruder with liquid paraffin as a pore-forming agent and polypropylene or inorganic particles as a heat resistance enhancer to mix the fluid streams of these components. In some cases, in addition to these components, other materials known in the art may be further added.

The fluid stream is extruded onto the sheet while continuously dividing and remixing in a step (b) by the non-rear-mixing method, by which the fluid has a small temperature gradient, Pore formers are uniformly dispersed in the polymeric substrate. In addition, the heat resistance enhancer may be divided into smaller size dispersed particles and uniformly distributed in the polymer substrate.

The non back-mixing manner provides substantially better radial homogeneity than substantially axial diffusion, preferably a static mixing element capable of continuous splitting and remixing of the fluid stream. May be provided by Such a static mixing element may be located in the barrel to form a static mixer. Basically, the static mixer itself does not have a driving force for the flow of the fluid, but because the mixing energy is transferred to the liquid mixtures by a special internal structure, that is, a static mixing element, the driving force for the extrusion is a separate device. Should be provided by Thus, in one preferred example, step (b) may be performed by a static mixer provided with an extrusion drive force by a gear pump or a Single Screw Extruder. Such a drive may be located in front and / or rear of the static mixer.

In the static mixer, the static mixing elements may be formed integrally by projecting inwardly from the circumferential surface inside the barrel, but preferably inserted into and fixed in the barrel.

A representative example of a static mixer is a Sulzer ^TM SMV-type static mixer, in which the corrugated sheet shaped mixing elements are flat-stacked to provide a substantially longitudinal fluid stream, substantially spirally. Kenics ^TM KM-type static mixers, in which one or more helical mixing elements are arranged axially as the mixing element to provide a fluid stream of the other. Other distributed / distributed static mixers, KAM static mixers, wipers Type static mixers, Komax static mixers, Kenics HEV-type mixers Sulzer ^™ SMX-type static mixers, Multiflux static mixers, Ross ISG-type static mixers, and the like can also be used, but are not limited to these.

The liquid mixture uniformly mixed by the static mixer is extruded into a sheet through a die and solidified.

In step (c), the extruded sheet is stretched, preferably biaxially stretched, to produce a film having a very thin thickness and a large width. Thus, even with a small temperature gradient difference in the extruded sheet, the morphology unevenness in the stretched film becomes very large, and the somewhat low dispersion uniformity of the pore-forming agent in the extruded sheet shows greater non-uniformity in the stretched film and also heat resistance. Enhancers are large sized dispersed particles which are distributed in the stretched film with very high heterogeneity. In view of this, the uniform non-rear-mixing in step (b) has a great influence on the physical properties of the finally produced porous film.

Finally, in step (d), the pore-former present in the polymer substrate on the film is removed, followed by heat-setting to prepare a separator film that can be used in a battery. Removal of the pore-forming agent is preferably removed using an extraction solvent, the type of the extraction solvent may vary depending on the type of the pore-forming agent. For example, when liquid paraffin is used as the pore-forming agent, methylene chloride (MC) can be preferably used as the extraction solvent.

Other processes may be added or some processes may be modified in the manufacturing method of the present invention without departing from the effect of the present invention, all of which should be construed as being included in the scope of the present invention.

The present invention also provides a separator for a battery produced by the above method.

The separator according to the present invention exhibits homogeneity due to the characteristics of the manufacturing process as described above. This homogeneity is exhibited in the morphology of the polymer, the size of the pores, the degree of dispersion of the pores as the separator substrate.

The present invention also provides a secondary battery, particularly preferably a lithium secondary battery, comprising the separator.

A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and a lithium salt-containing nonaqueous electrolyte.

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive agent, and a binder (positive electrode mixture) on a positive electrode current collector, followed by drying, and optionally adding a filler to the mixture. .

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive agent is typically added in an amount of 1 to 50% by weight based on the total weight of the positive electrode mixture including the positive electrode active material. Such a conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding the active material and the conductive agent to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like.

The filler is optionally used as a component for inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The negative electrode is manufactured by applying and drying a negative electrode active material on a negative electrode current collector, and if necessary, some or all of the positive electrode mixture components as described above may be included.

The negative electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode active material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The lithium salt-containing non-aqueous electrolyte consists of a nonaqueous electrolyte and lithium. As the nonaqueous electrolyte, a nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Low lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, aceto Nitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to be dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

Hereinafter, specific examples of the static mixer that can be used in the manufacturing method of the present invention with reference to the drawings, but the scope of the present invention is not limited thereto.

1 to 5 schematically show the mixing elements in a Sulzer SMV-type static mixer that can be used in the present invention.

Referring to these figures, there is shown a static mixing element 10 consisting of a plurality (here five) of stacked corrugated plates 12, 14, 16, 18, 20, where each The corrugated plate grooves 22, 22A, 24, 24A, 26, 28, 30 are substantially perpendicular to the grooves of each immediately corrugated plate (i.e., the plate immediately above and the plate just below). Here, the term "stacked" means "flat-stacked" state. That is, referring to the top enlarged perspective view of FIG. 3, the grooves (eg, 24, 24A) of the corrugated plate (eg, 14) are defined by the grooves of the immediately adjacent corrugated plate (eg, 12, 16, respectively). For example, they are generally directed towards (ie, generally facing) 22A, 26). In this mixing element 10, a plurality of accumulated corrugated plates divide and mix the fluid stream in use transversely across the plate. As disclosed in FIG. 1, the mixing element is substantially cylindrical in the outer profile 32 and the cylindrical axis is substantially relative to the plane of the corrugated plates 12-20 so that the mixing element can be stably located in the barrel 34. Parallel to

As disclosed in FIG. 2, the mixing elements 10, when located inside the barrel, for example, continuously divide and remix fluid streams 35-44 to facilitate mass and heat transfer. Thus, even with low flow rates and Reynolds numbers, a uniform flow profile with vortex fluid flow can be achieved.

As can be seen in FIG. 5, in the static mixer 50 a number of mixing elements 10 (in this case 6 denoted by 10A-F) are arranged substantially axially in a long barrel, where the corrugated plates 12 18) are arranged such that the fluid flows longitudinally along the mixer 50. Adjacent mixing elements 10 abut one another, but are not bonded or fused together. The mixing elements 10A-F can be stably fixed in the mixer 50 by the mixing element fixing means 54, 56. The fastening means 54, 56 disclosed are configured to comprise an open end cap (S-shaped as shown) which can be fixed or fixed across both ends of the mixer 50; They are configured to allow fluid to flow through them and may hold and / or compress the mixing elements 10A-F together in the mixer 50. Each of the mixing elements in the mixer 50, for example 10C, is positioned at either side thereof in a rotated orientation (about 90 degrees here) about the longitudinal axis of the mixer 50 relative to the mixing elements such as 10B, 10D. Statically arranged so that

In the arrangement disclosed in FIG. 5, the first element 10A divides and mixes the stream from side to side, and the second element 10B divides and mixes the stream up and down, and the third element 10C. Splits and mixes the stream from side to side. This arrangement ensures rapid mixing and splitting of the stream in both directions transverse to the axial direction and is suitable for vortices in immiscible liquid streams.

6 and 7 schematically show the mixing elements in a Kenics KM-type static mixer that can be used in the present invention.

6 and 7, the mixing structure 70 consists of three Kenics KM static mixing elements 72, 74, and 76, which are either fused together or separately but in contact with each other. . The mixing elements 72, 74, 76 are plates that are twisted spirally about the transverse axis. The mixing elements are arranged in series in the axial direction and are inserted axially therein in a substantially static relationship to the barrel 100 in use. The series of mixing elements 72, 74, 76, as disclosed, have alternating spirally twisted right and left orientations, ie alternately rotating directions 90, 92.

Each of the mixing elements 72, 74, 76 are spirally twisted plates of about 180 degrees, as disclosed in FIGS. 6 and 7. The leading edge of each element 72, 74 is located about 90 degrees to the trailing edge 82, 86 of the next element 74, 76. As the fluid passes through each element, the fluid is divided into two because each successive element is deflected about 90 degrees. The spiral twist angle, offset angle, width, height and number of mixing elements may vary depending on the properties of the feed.

As disclosed in FIGS. 6 and 7, the spiral twist of the mixing elements 72, 74, 76 provides a spiral fluid flow path 94 between the inner circumferential wall of the barrel 100 and the plates 72-76. ), Where the flow path is divided into two at each element intersection (80 to 82, 84 to 86), and the next spiral path is in the opposite angular direction (comparison 92). 6 shows the movement and rotation 92 of the fluid flowing through the barrel. The figures show that the mixing elements 72-76 improve the degree of fluid mixing by imparting some rotational moment and angular momentum to the fluid. The total number of mixing elements 72-74 in barrel 100 may vary with the mixing performance per mixing element, which depends on the size and flow rate of the mixing element used.

As described above, according to the present invention, when preparing a membrane film by extrusion of a mixture consisting of a polymer substrate and a pore-forming agent and a heat resistance enhancer, stretching of a sheet, etc., the stream of the mixture fluid is non-rear- By continuously dividing and remixing by mixing method, the temperature gradient of the fluid is reduced, the dispersion of pore former is made uniform, and the heat resistance enhancer is uniformly distributed in small dispersed particle size, so that in the finally produced film It is possible to increase the uniformity of the morphology and pores of the polymer substrate and to provide further improved heat resistance.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (16)

(a) mixing a pore-forming agent and a heat resistance enhancer with the liquid polymer substrate; (b) extruding the stream of mixture fluid into a sheet shape while continuously dividing and remixing by non-rear-mixing; (c) stretching the extruded sheet to produce a film shape; And (d) removing and heat-setting the pore former from the film; Method for producing a film for a battery separator is configured to include. The method of claim 1, wherein the polymer is polyethylene. The method of claim 2, wherein the polymer comprises Ultra High Molecular Weight Polyethylene (HMWPE). The method of claim 1 wherein the pore former is liquid paraffin. The method of claim 1, wherein the heat resistance enhancer is polypropylene or inorganic particles. 6. A process according to claim 5 wherein the polypropylene comprises high isotactic polypropylene. The method of claim 1 wherein the mixing in step (a) is performed by a Twin Screw Extruder. The method according to claim 1, wherein the non-rear-mixing in step (b) is performed by a static mixing element. 9. A method according to claim 8, wherein said non-rear-mixing is carried out by a static mixer comprising a static mixing element. 10. The static mixer of claim 9, wherein the static mixer is a Sulzer SMV-type static mixer, a Kenics KM-type static mixer, a KAM static mixer, a Komax static mixer, a Kenics HEV-type mixer, a Sulzer SMX-type static mixer, a Multiflux static mixer, or Ross ISG-type static mixer, characterized in that the manufacturing method. The method according to claim 1, wherein the step (b) is performed by a static mixer provided with an extrusion driving force by a gear pump or a single screw extruder. The method of claim 1, wherein the pore-forming agent is removed using a solvent in step (d). 13. The process according to claim 12, wherein the extractant is methylene chloride. delete delete delete

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