KR20160002447A - Porous polyolefin separator and a method for preparing the same - Google Patents

Abstract

The present invention relates to a polyolefin-based separator preparing method, and a polyolefin-based separator prepared by using the method. The method includes the steps of: forming a cooled and solidified sheet by melt-kneading and extruding a composition including a polyolefin resin and a plasticizer; stretching the solidified sheet in a length direction at T1 temperature by E1 times and stretching the solidified sheet in a width direction at T2 temperature by E2 times; extracting the plasticizer from the stretched sheet; and stretching the sheet having the plasticizer extracted out in the width direction to make the final stretch ratio between 1.25-1.5 times. The temperature conditions of the stretching operation are 100°C <T1<115°C, 100°C<T2<115°C, and T2 >=T1. The stretch ratio condition is E1 x E2 = 60 to 80.

Description

TECHNICAL FIELD [0001] The present invention relates to a porous polyolefin separator and a method for preparing the porous polyolefin separator.

TECHNICAL FIELD The present invention relates to a porous polyolefin separator and a method for producing the same.

A separator for an electrochemical cell means an interlayer that keeps the ion conductivity constant while isolating the positive electrode and the negative electrode from each other in the battery to enable charging and discharging of the battery.

In recent years, electrochemical cells for increasing the portability of electronic devices have become more lightweight and miniaturized, and there is a tendency to require high-output large capacity batteries for use in electric vehicles and the like. Such a battery separator is required to have high air permeability, a thin film thickness, and a strong mechanical strength. In addition, in order to improve the productivity of a high-output battery, it is required that it is excellent in shape stability due to high temperature or high tension. Accordingly, there is a need to develop a separator suitable for use in a high-output cell because it has high air permeability and porosity, is excellent in mechanical strength, and has a small pore shape and strain rate.

Korean Patent Application Publication No. 2011-0026609 Korean Patent Application Publication No. 2008-0077191

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The present invention provides a separator having a high air permeability and porosity, a high strength and a low strain rate of the pore shape or size of the separator and excellent cell stability.

According to an embodiment of the present invention, a composition comprising a polyolefin resin and a plasticizer is melt-kneaded and extruded to form a solidified sheet, and the solidified sheet is stretched in the longitudinal direction at T ₁ Stretching E ₁ times at a temperature and stretching E ₂ times at a temperature T _{2 in a} width direction to extract a plasticizer from the stretched sheet and stretching the sheet from which the plasticizer has been extracted to a stretch ratio of 1.25 to 1.5 Wherein the stretching temperature condition is 100 占 폚 <T ₁ <115 캜, 100 캜 <T ₂ <115 캜, and T ₂ ≥T ₁ , and the stretching magnification condition is E ₁ × E ₂ = Wherein the polyolefin-based separator has a thickness of 60 to 80 mm.

According to another example of the present invention, there is provided a polyolefin resin composition containing a polyolefin resin and having a mean pore pressure (psi) / bubble point pressure (psi) of 1.8 to 2.4 in the wetting and drying curve of a membrane measured by a capillary flow porosimeter A system separation membrane is provided.

The separation membrane according to an embodiment of the present invention has higher electrolyte hygroscopicity due to the pore shape of the separation membrane.

The separation membrane according to an embodiment of the present invention also has a strong mechanical strength while having excellent air permeability and porosity by controlling the size distribution of the pores of the separation membrane.

1 is a capillary flow porometer wetting graph of a PMI company measured on a membrane according to an example of the present invention. The pressure at the starting point at which the curve is drawn in the wetting graph is referred to as a bubble point pressure (psi), and the pressure at the point where the wetting curve meets a hypothetical straight line in which the slope of the straight line is 1/2 in the drying graph It is called the mean point pressure (psi). The bubble point pressure and the average point pressure reflect the maximum pore size and average pore size of the separator, respectively.

A method of preparing a porous polyolefin membrane according to one embodiment of the present invention, polyolefin-based resin and melt kneading a composition comprising a plasticizer and extruding to form a solidified sheet cooling, and the solidified sheet in the longitudinal direction T ₁ Stretching E ₁ times at a temperature and stretching E ₂ times at a temperature T _{2 in a} width direction to extract a plasticizer from the stretched sheet and stretching the sheet from which the plasticizer has been extracted to a stretch ratio of 1.25 to 1.5 Wherein the stretching temperature condition is 100 占 폚 <T ₁ <115 캜, 100 캜 <T ₂ <115 캜, and T ₂ ≥T ₁ , and the stretching magnification condition is E ₁ × E ₂ = 60 to 80 days.

First, forming the solidified sheet includes melting and kneading and extruding a composition containing a polyolefin resin and a plasticizer to form a cold solidified sheet.

The polyolefin-based resin is a resin including a polyolefin, and includes, for example, ultrahigh molecular weight polyethylene, high molecular weight polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, highly crystalline polypropylene and polyethylene- , And the like. In another example, the polyolefin-based resin may include other resins besides the polyolefin. Examples of other resins include polyimide, polyester, polyamide, polyetherimide, polyamideimide, and polyacetal. When other resins are included, the polyolefin resin composition may be prepared by blending the polyolefin resin and other resins in an appropriate solvent. The viscosity average molecular weight (Mv) of the high-density polyethylene may be 1 × 10 ⁵ to 9 × 10 ⁵ g / mol, for example, 3 × 10 ⁵ to 6 × 10 ⁵ g / mol. The ultrahigh molecular weight polyethylene may have a viscosity average molecular weight of at least 9 × 10 ⁵ g / mol, specifically from 9 × 10 ⁵ to 5 × 10 ⁶ g / mol. For example, the high-density polyethylene may be used alone, the ultra-high-molecular-weight polyethylene may be used alone, or both the high-density polyethylene and the ultra-high molecular weight polyethylene may be used. More specifically, the ultrahigh molecular weight polyethylene may be used in an amount of 30% by weight or less based on the weight of the polyolefin resin. For example, the weight average molecular weight may be 1 10 ⁵ to 9 10 ⁵ yi g / mol in the high-density polyethylene, more than 70% by weight and a viscosity average molecular weight of 9 × 10 ⁵ and 30 wt% or less of an ultrahigh molecular weight polyethylene having a weight-average molecular weight (g / mol) of 30 or less. The polyolefin-based resin is advantageous because a high-strength separator can be produced. When two or more of the polyolefin-based resins are used, it is preferable to use at least one selected from the group consisting of a Henschel mixer, a chestnut mixer and a pneumatic mixer.

The plasticizer may be an organic compound which forms a single phase with the polyolefin-based resin at an extrusion temperature. Examples of the plasticizer usable in the present invention include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, liquid paraffin (or paraffin oil) and paraffin wax; Phthalic acid esters such as dibutyl phthalate and dioctyl phthalate; Fatty acids having 10 to 20 carbon atoms such as palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid; Fatty acid alcohols having 10 to 20 carbon atoms such as palmitic alcohol, stearic acid alcohol and oleic acid alcohol. These may be used alone or in combination of two or more. Among the above plasticizers, liquid paraffin can be preferably used. Liquid paraffin is harmless to the human body, has a high boiling point and low volatile components, and is suitable for use as a plasticizer in a wet process.

The melt-kneading of the composition comprising the polyolefin-based resin and the plasticizer may be performed by a method known to a person skilled in the art, and may be a melt-kneading of the polyolefin-based resin and the plasticizer at a temperature of 150 ° C to 250 ° C. The melt-kneaded composition may be injected into a twin-screw extruder and extruded at 150 to 250 ° C. Thereafter, the extruded polyolefin resin is cooled using a casting roll at 20 to 80 ° C or forcedly cooled by cold air blown from an air knife to crystallize the film to form a solidified sheet. The temperature of the cold air blown from the air knife may be -20 캜 to 40 캜.

Subsequently, the solidified sheet is stretched in the longitudinal direction by T ₁ Biaxial stretching is performed by stretching E ₁ times at a temperature and then stretching E ₂ times at a temperature T _{2 in a} width direction. The stretching temperature condition at the time of stretching is 100 ° C <T ₁ <115 ° C, 100 ° C <T ₂ <115 ° C, and T ₂ ≥T ₁ . MD direction stretching temperature (T ₁₎ and the TD direction orientation temperature (T ₂₎ the can both enhance the porosity if less than 115 ℃, MD direction stretching temperature (T ₁₎ to below the TD direction orientation temperature (T ₂₎ Or the like, it is possible to cause a variation in the stretching length depending on the site, and then, when stretched in the TD direction, two or more kinds of pores having different sizes can be formed in the separation membrane. Of the two or more kinds of pores having different sizes, relatively small pores are advantageous in terms of heat shrinkage, strength and pore strain, and relatively large pores are advantageous in terms of air permeability, electrolyte wettability and battery capacity. The stretching magnification condition at the time of stretching may be E ₁ x E ₂ = 60 to 80. Further, E ₁ ≥ 7.5, and E ₂ &Gt; = 8. When the stretching magnification (E ₁占 E ₂ ) is set to 60 to 80 and the MD stretching magnification ratio (E ₁ ) and the TD direction stretching magnification ratio (E ₂ ) are 7.5 times and 8 times or more, It is possible to minimize the deformation rate of the shape and size of the pores due to the external pressure of the separator due to the stretched surface magnification, thereby improving the cell stability.

The present invention can minimize the deformation rate of the shape and size of the pores due to the external pressure while securing the porosity required for the separation membrane by stretching under the conditions of the draw temperature and the draw ratio as described above. The MD stretching temperature (T ₁ ) may be lower than the TD stretching temperature (T ₂ ) by 2 ° C or more. For example, 3 DEG C or more, or 5 DEG C or more.

In one example, the MD direction stretching magnification ratio E ₁ is 7.5 times, the TD direction stretching magnification ratio E ₂ is 8 times; MD orientation draw ratio (E ₁₎ is eight times, eight times the TD orientation draw ratio (E _2); A stretching magnification ratio E _{1 in the} MD direction is 8, a stretching magnification ratio E _{2 in the} TD direction is 8.5; Or MD direction is 8.5 times the draw ratio (E _1), there TD direction draw ratio (E ₂₎ can baeil 8.5. The stretching magnifications in the width direction and the longitudinal direction may be the same or different. Specifically, the ratio of E ₁ / E ₂ may be 0.85 to 1. If the elongation ratios are in the above ranges, the effect of variation in the elongation length of each part caused by different MD and TD stretching temperatures can be further enhanced.

After the biaxial stretching, the plasticizer can be extracted. The plasticizer may be extracted by using an organic solvent. Specifically, the plasticizer may be extracted by immersing the longitudinally stretched and widthwise stretched separator in an organic solvent in a plasticizer extractor. The organic solvent used for the plasticizer extraction is not particularly limited and any solvent capable of extracting the plasticizer can be used. As the non-limiting examples of the organic solvent, methyl ethyl ketone, methylene chloride, hexane and the like which have a high extraction efficiency and are easy to dry can be used, and when liquid paraffin is used as a plasticizer, methylene chloride is preferably used as an organic solvent .

Since the organic solvent used in the step of extracting the plasticizer is highly volatile and toxic, water can be used if necessary to suppress the volatilization of the organic solvent.

The manufacturing method according to another embodiment of the present invention may include stretching the sheet from which the plasticizer is extracted so that the final stretching magnification is 1.25 to 1.5 times in the width direction. The width direction stretching is a heat fixing step for reducing the residual stress of the film to reduce the shrinkage rate of the final film. The heat shrinkage and the transmittance of the film can be controlled according to the temperature and the fixed ratio during the heat fixing. Concretely, the above-mentioned heat setting may be performed such that the stretching ratio is 1.25 times to 2 times in the width direction, and is relaxed to 70% to 100% in the stretched width direction so that the final stretching ratio is 1.25 to 1.5 times. When the pores are opened and fixed in the above arrangement, the deviation of the pores generated in the biaxial orientation can be adjusted to improve the air permeability. The heat setting may be performed at 100 to 150 ° C, for example, at 120 to 130 ° C. It is effective to remove the residual stress of the film in the above range, and the physical properties can be improved.

The present invention provides a polyolefin separator prepared by the process for producing a polyolefin separator according to the above examples.

The polyolefin-based separator may have an average point pressure (psi) / bubble point pressure (psi) of 1.8 to 2.4 in the wetting curve of the separator measured by a capillary flow porosimeter.

Capillary Flow Pore Measuring Instrument When the ratio of the average point pressure (psi) to the bubble point pressure (psi) in the wetting and drying curve is within the above range, the pore size is variously distributed and the porosity required for the separator, And can provide a separator having good air permeability and excellent electrolyte wettability and strength.

The bubble point pressure (psi) refers to the pressure at the starting point at which the wetting curve is drawn in the capillary flow porosimeter. More specifically, the membrane sample is immersed in the solution to fill the pore with the solution. When blowing air with increasing pressure, The solution filled in the inside is moved to the pressure first, and the pressure at this time is called the bubble point pressure. Referring to FIG. 1, the bubble point pressure refers to a pressure at a time point at which the flow rate starts to increase after maintaining the flow rate at 0 in the graph of the flow rate change with increasing pressure of the capillary flow pore analyzer.

The average point pressure (psi) refers to a pressure at a point where a hypothetical straight line in which the slope is 1/2 of the drying straight line and the wet curve meets a drying straight line in the capillary flow pore meter. Specifically, when air is blown while pressure is increased while the membrane sample is not wetted with a solution, a linear graph is obtained in which the flow rate increases in proportion to the pressure increase. Referring to FIG. 1, when a virtual straight line (1/2 drying graph in FIG. 1) having a slope of 1/2 in the linear graph (drying graph in FIG. 1) is drawn, this imaginary straight line and the wet curve The pressure at the point of contact is called the average point pressure.

The polyolefin-based separator according to an exemplary embodiment of the present invention may have a porosity of 40 to 50% and an air permeability of 50 to 200 sec / 100 cc. In the present application, the air permeability means the time for 100 cc of air to pass through the separator. Specifically, the air permeability may be 60 to 150 sec / 100 cc.

The polyolefin separator according to an example of the present invention has a ratio of the tensile strength (kg / cm ² ) / elongation (%) in the longitudinal direction and the transverse direction of the separator of 15 to 28 {(kg / cm ² ) /% . When the ratio of the tensile strength to the elongation is in the range, the excellent separation membrane has a mechanical strength, while the pore or separation membrane has a low strain, so that deformation due to external force or impact can be minimized. In addition, the polyolefin separator according to an example of the present invention may have a tensile strength in the longitudinal direction of the separator of 1700 kg / cm ² or more and a tensile strength in the transverse direction of 1800 kg / cm ^{2 or} more, The elongation in the width direction may be 100% or less, more specifically 98% or less. If the elongation is in the above range, the separator having improved stability against the deformation of the pore size and shape can be provided. The polyolefin-based separator according to an example of the present invention may have a water droplet contact angle of the separator of 107 ° or less, for example, 95 ° to 107 °, specifically 100 ° to 106 °. If the contact angle is within the above range, the electrolyte wettability is good and the battery performance can be improved.

The polyolefin-based separation membrane according to an embodiment of the present invention may include a coating layer on one side or both sides of the separation membrane, and the coating layer may include an organic binder, and may further include inorganic particles. The organic binder includes, for example, a polyvinylidene fluoride homopolymer having a weight average molecular weight of 1,000,000 g / mol or more, a polyvinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 800,000 g / mol or less, &Lt; / RTI &gt; Examples of the inorganic particles include Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , Ga ₂ O ₃ , TiO ₂ , and SnO ₂ . The coating layer may be formed by a dip coating method. The separation membrane having the coating layer may have a heat shrinkage of 3% or less in each of the MD and TD directions after being left in an oven at 105 ° C for 1 hour. More specifically, it may be 2% or less.

The porous polyolefin separator according to the present invention may have an average thickness of 7 μm to 20 μm and a deviation of thickness may be less than 4% of the average thickness. The porous polyolefin-based membrane according to the present invention may have an average piercing strength of 300 gf or more, specifically 400 gf or more.

In addition, the porous polyolefin separator or coating separator according to the present invention is manufactured by cutting the prepared separator into a size of 50 × 50 mm, shrinking it for 1 hour after putting it in an oven at 120 ° C., measuring the size of the shrinked separator, The shrinkage in the longitudinal direction may be 5% or less and the shrinkage in the width direction may be 3% or less, more specifically, the shrinkage in the longitudinal direction may be 4% or less and the shrinkage in the width direction may be 2% or less.

The present invention also provides a battery cell comprising the porous polyolefin separator, the anode, the cathode and the electrolyte disclosed in the present invention. The kind of the electrochemical cell is not particularly limited and may be a kind of electricity known in the technical field of the present invention. The electrochemical cell of the present invention is preferably a lithium secondary battery such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The method for producing the electrochemical cell of the present invention is not particularly limited and a method commonly used in the technical field of the present invention can be used. A non-limiting example of the method for producing the electrochemical cell is as follows: After the separator or coating separator of the present invention is positioned between the positive electrode and the negative electrode of the battery, the battery can be manufactured by filling the electrolyte with the electrolyte. have. The electrode constituting the electrochemical cell of the present invention can be produced by binding an electrode active material to an electrode current collector by a method commonly used in the technical field of the present invention. Of the electrode active materials used in the present invention, the positive electrode active material is not particularly limited and a positive electrode active material conventionally used in the technical field of the present invention may be used. Specifically, the positive electrode includes a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions, and the positive electrode active material may be a composite metal oxide of lithium and at least one selected from cobalt, manganese, and nickel . In addition to these metals, the employment rate of the metals may be varied. In addition to these metals, Mg, Al, Co, Ni, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Fe, Sr, V, and a rare earth element. The anode may be, for example, a composite metal oxide of lithium and a metal selected from the group consisting of Co, Ni, Mn, Al, Si, Ti and Fe, and specifically lithium cobalt oxide (LiCoO ₂ ), lithium nickel manganese cobalt oxide (NCM) such as Li [Ni (x) Co (y) Mn (z)] O ₂ ), lithium manganese oxide LMO. for example can be used, such as LiMn ₂ O4, LiMnO _2), lithium iron phosphate (lithium Iron phosphate, LFP. for example, LiFePO _4), lithium nickel oxide (LNO, for example, LiNiO _2). The negative electrode includes a negative electrode active material capable of inserting and desorbing lithium ions. Examples of the negative electrode active material include a carbonaceous anode active material (thermally decomposed carbon, coke, graphite) of crystalline or amorphous carbon or carbon composite material, An organic polymer compound, a carbon fiber, a tin oxide compound, a lithium metal, or an alloy of lithium and another element may be used. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1,500 ° C or less, and mesophase pitch-based carbon fiber (MPCF). The crystalline carbon is a graphite-based material, specifically natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The cathode may comprise, for example, crystalline or amorphous carbon.

The positive electrode or the negative electrode may be prepared by dispersing a binder, a conductive material and, if necessary, a thickener in a solvent in addition to an electrode active material, preparing an electrode slurry composition, and applying the slurry composition to an electrode current collector. The binder, the conductive material and the thickener may be those conventionally used in the technical field of the present invention. Examples of the binder include polyvinylidene-fluoride (PVdF), styrene-butadiene rubber (SBR), and the like. Examples of the binder include carbon black, carbonate methylcellulose (Carbonate methyl cellulose, CMC) can be used.

The electrode current collector used in the present invention is not particularly limited, and electrode current collectors commonly used in the technical field of the present invention can be used. Non-limiting examples of the positive electrode current collector material among the electrode current collectors include aluminum, nickel, or foil produced by a combination of these materials. As a non-limiting example of the cathode current collector material of the electrode current collector, copper, gold, nickel, a copper alloy, or a foil produced by a combination of these materials can be used.

The anode current collector and the anode current collector may be in the form of a foil or a mesh.

-Butyrolactone) 등을 들 수 있다. 이들은 단독으로 사용되거나 2 종 이상을 혼합하여 사용될 수 있다.
The electrolytic solution used in the present invention is not particularly limited, and electrolytic solutions for electrochemical cells commonly used in the technical field of the present invention can be used. The electrolytic solution may be a salt having a structure such as A ⁺ B ^- dissolved or dissociated in an organic solvent. Non-limiting examples of the A ⁺ include alkali metal cations such as Li ⁺ , Na ^+, or K ⁺ , or cations made of combinations thereof. Non-limiting examples of B ^- include PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N ₃ SO ₂ ) ₂ ^- or C (CF ₂ SO ₂ ) ₃ ^- , or an anion composed of a combination of these. Nonlimiting examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dimethylformamide (DMF), Dipropyl carbonate (DPC), Dimethyl sulfoxide (DMSO), Acetonitrile, Dimethoxyethane, Diethoxyethane, Tetrahydrofuran Tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC) or gamma-butyrolactone

-Butyrolactone). These may be used alone or in combination of two or more.

Hereinafter, the present invention will be described in more detail by describing Examples, Comparative Examples and Experimental Examples. However, the following examples, comparative examples and experimental examples are merely examples of the present invention and should not be construed as limiting the scope of the present invention.

Example

Example  1: Porosity Polyolefin series  Preparation of Membrane

High-density polyethylene (HDPE, manufactured by Mitsui Chemical Co., Ltd.) having a viscosity average molecular weight of 600,000 g / mol was fed to a twin-screw extruder, and then a liquid paraffin (Far East oil) 70, and the mixture was extruded.

After the extrusion, the gel phase obtained through the T-die was formed into a sheet-form separator using a cooling roll. The separator was subjected to machine direction (MD) stretching at 110 ° C and transverse direction (TD) stretching at 113 ° C (stretching magnification: 8.0 (MD) x 8.0 (TD)).

The stretched polyolefin-based separator was immersed in methylene chloride (Samsung Fine Chemicals) to extract liquid paraffin, and then dried on a drier roll.

Next, the dried film was heat-set in a secondary direction in the transverse direction (transverse stretching ratio: 1.0 → → 1.4, stretching temperature: 128 ° C) to prepare a porous polyolefin separator having a thickness of 12.5 μm.

Example  2: Porosity Polyolefin series  Preparation of Membrane

Except that the machine direction (MD) stretching at 103 占 폚 and the transverse direction (TD) stretching at 105 占 폚 (stretching magnification: 8.5 (MD) 占 8.5 (TD)) in Example 1 were repeated A separation membrane having a thickness of 12.3 탆 was prepared in the same manner as in Example 1.

Comparative Example  1: Porosity Polyolefin series  Preparation of Membrane

Except that the machine direction (MD) stretching at 120 ° C. and the transverse direction (TD) stretching at 123 ° C. (stretching magnification: 8 (MD) × 8 (TD) A separation membrane having a thickness of 12.2 탆 was prepared in the same manner as in Example 1.

Comparative Example  2: Porosity Polyolefin series  Preparation of Membrane

The same procedure as in Example 2 was carried out except that the stretching magnification in the machine direction (MD) and the transverse direction (TD) in the Example 2 were changed to 7 (MD) x 7 (TD) To prepare a 12.3 μm thick separator.

Production conditions of the separators according to Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Stretching Drawing method rotor rotor rotor rotor Drawing magnification (MD x TD) 8.0 x 8.0 8.5 x 8.5 8 x 8 7 × 7 MD stretching temperature 110 ° C 103 ° C 120 DEG C 103 ° C TD stretching temperature 113 ℃ 105 ℃ 123 ℃ 105 ℃ Second TD stretching temperature 128 ° C 128 ° C 128 ° C 128 ° C 2nd TD final draw ratio 1.4 1.4 1.4 1.4

Experimental Example

The porosity, air permeability, tensile strength, elongation, shrinkage, bubble point, average point pressure, and water drop contact angle of the separation membranes prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured by the measurement method described below The results are shown in Table 2.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Average point pressure (psi) 258.856 272.12 201.34 282.24 Bubble Point Pressure (psi) 121.675 113.31 121.54 113.35 Average point pressure / bubble point pressure 2.13 2.40 1.66 2.49 Porosity (%) 44.5 43 53.1 38.5 Air permeability (sec / 100cc) 122 115 95 223 Tensile strength (kg / cm ² )
(MD, TD) 2120, 2214  2250, 2305 1653,1622 1742,1783 Elongation (%)
(MD, TD) 89, 92 86, 88 95, 110 93, 98 Tensile Strength / Elongation
(MD, TD) 23.8, 24.1 26.2, 26.2 17.4, 14.7 18.7, 18.2 Water Drop Contact Angle (°) 102 103 111 111 Shrinkage rate
(MD, TD) 2.0 2.0 8,3 2.0

1. In the capillary flow pore measurement graph bubble  Point pressure and average point pressure measurement

Each of the separation membranes prepared in the above Examples and Comparative Examples was sampled in a circle having a diameter of 26 mm. The membrane itself is mounted on a PMI capillary flow pore gauge and sufficiently soaked with a Galwick ^™ solution (surface tension 15.9 dyne / cm). The device is set up in the Wet up Calc. mode and measure the flow rate of N _{2 per} pressure to draw a wet curve. The pressure at which the first bubble is sensed in the wetting curve is reported as the bubble point pressure (psi). Each of the separation membranes prepared in the above Examples and Comparative Examples was sampled in a circle having a diameter of 26 mm, and the separation membrane itself was mounted on the apparatus. mode, and the flow rate of N _{2 per} pressure is measured and is shown as a drying curve graph. A straight line extending from the origin to a point having linearity in the measured drying curve graph is drawn and a virtual straight line which is half the slope of the straight line is drawn and the pressure at the point where the imaginary straight line meets the wetting curve is defined as an average point pressure psi).

2. Porosity

A sample of 10 cm x 10 cm of each of the membranes prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was cut out to determine its volume (cm 3) and mass (g), and the volume and mass of the sample The porosity was calculated from the density (g / cm 3) using the following equation.

Porosity (%) = (volume-mass / density of sample) / volume × 100

Density of sample = Density of polyethylene

3. Ventilation

Each of the separation membranes prepared in the above Examples and Comparative Examples was cut into 10 samples at a different size so that a circle having a diameter of 1 inch could be entered. Then, 10 samples were cut and measured with an air permeability measuring device The time for passing 100 cc of air through each of the samples was measured. The time was measured five times in each case and the average value was calculated.

4. The tensile strength

Each of the separation membranes prepared in the above Examples and Comparative Examples was cut into 10 pieces at 10 different points in MD (10 mm) × 50 (TD) in length (TD) The strength was measured by pulling it up and down. The tensile strength of each of the samples was measured three times, and the average value was calculated.

5. Elongation

For each of the separation membranes prepared in the Examples and Comparative Examples, the length of the original length and the length at the breaking point were compared ((length of fracture point - 20) / 20 mm) As a percentage.

6. Contraction ratio

Each of the separation membranes prepared in the above Examples and Comparative Examples was cut into 10 pieces at different MD 50 mm × TD 50 mm. Each of the samples was allowed to stand in an oven at 105 ° C for 1 hour, and the degree of shrinkage in the MD and TD directions of each sample was measured to calculate an average heat shrinkage rate.

7. Drops of water Contact angle (Evaluation of electrolyte wettability)

Each of the separation membranes prepared in the above Examples and Comparative Examples was cut into 20 mm width (MD) 20 mm width (MD) to prepare five samples. The sample was placed on a contact angle meter (DSA-100, manufactured by Matech Co., Ltd.), and water was dropped with a dropper, and the contact angle was measured. The contact angles of the five samples were averaged.

Claims (16)

A composition comprising a polyolefin resin and a plasticizer is melt-kneaded and extruded to form a cold solidified sheet,
The solidified sheet is stretched E ₁ times at a temperature of T ₁ in the longitudinal direction and stretched E ₂ times at a temperature of T _{2 in a} width direction,
The plasticizer is extracted from the stretched sheet,
And stretching the sheet from which the plasticizer is extracted so that the final stretch ratio is 1.25 to 1.5 times in the width direction,
Wherein the stretching temperature condition is 100 ° C <T ₁ <115 ° C, 100 ° C <T ₂ <115 ° C, and T ₂ ≥T ₁ ,
Wherein the elongation at the time of stretching is E ₁ x E ₂ = 60 to 80. The polyolefin- The process for producing a polyolefin-based separator according to claim 1, wherein the ratio of E ₁ / E ₂ is 0.85 to 1 under the magnification condition. The polyolefin resin according to claim 1, wherein the polyolefin resin is a high density polyethylene having a viscosity average molecular weight of 1 10 ⁵ to 9 10 ⁵ g / mol and an ultra high molecular weight polyethylene having a viscosity average molecular weight of 9 10 ⁵ g / mol or higher Selected alone or a mixture thereof. 4. The method according to any one of claims 1 to 3, wherein E _1? 7.5 and E ₂ ? 8. The method according to any one of claims 1 to 3, wherein the stretching is performed so that the final stretch ratio in the transverse direction is 1.25 to 1.5, preferably in the range of 1.25 to 2 times in the transverse direction, 0.0 &gt; 70% &lt; / RTI &gt; to 100%. The production method according to any one of claims 1 to 3, further comprising coating one or both sides of the polyolefin-based separation membrane with a coating composition containing an organic polymer and inorganic particles. A polyolefin resin,
Wherein the ratio of the average point pressure (psi) to the bubble point pressure (psi) in the wetting and drying curve of the membrane measured by a capillary flow porometer is 1.8 to 2.4. The polyolefin-based separator according to claim 7, wherein the ratio of the tensile strength (kg / cm ² ) / elongation (%) in the longitudinal direction and the transverse direction of the separator is 15 to 28, respectively. The polyolefin separator according to claim 7, wherein the separator has a porosity of 40 to 50%. The polyolefin-based separator according to claim 7, wherein the separation membrane has an air permeability of 50 to 200 sec / 100 cc. The polyolefin-based separator according to claim 7, wherein the separating film has a water droplet contact angle of 107 ° or less. Of claim 7 to claim 11 according to any one of the preceding claims, wherein the average molecular weight of said polyolefin resin viscosity of 1 × 10 ⁵ to 9 × 10 ⁵ g / mol of high density polyethylene and a viscosity average molecular weight of 9 × 10 ⁵ g / molecular weight polyethylene having a molecular weight of more than 1 mol, or a mixture thereof. Of claim 7 to claim 11 according to any one of the preceding claims, wherein the polyolefin-based separator to a longitudinal T ₁ At a temperature in E direction _one time stretching and width as the E ₂ times longer in the T ₂ temperature, the temperature during stretching is _{100 ℃ <T 1 <115 ℃} , 100 ℃ <T 2 <115 ℃, and T ₂ ≥ T ₁ , the stretching magnification condition is E ₁ x E ₂ = 60 to 80, E ₁ ≥ 7.5, and E ₂ &Gt; = 8. The method of claim 13 wherein the ratio is 0.85 to 1, the polyolefin-based separator of E ₁ / E ₂ at the magnification conditions. An electrochemical cell comprising the polyolefin-based separator according to any one of claims 7 to 11. The electrochemical cell according to claim 15, wherein the electrochemical cell is a lithium secondary battery.

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