JP2017523570A - Porous polyolefin separation membrane and method for producing the same - Google Patents

Abstract

In the present invention, a composition containing a polyolefin resin and a plasticizer is melt-kneaded and extruded to form a sheet. The solidified sheet is stretched E1 times at the T1 temperature in the longitudinal direction and E2 times at the T2 temperature in the width direction. Stretching, extracting a plasticizer from the stretched sheet, and stretching the sheet from which the plasticizer has been extracted in a width direction so that a final stretching ratio is 1.25 to 1.5 times, Polyolefin separation in which the temperature conditions at the time of stretching are 100 ° C. <T1 <115 ° C., 100 ° C. <T2 <115 ° C., and T2 ≧ T1, and the magnification condition at the time of stretching is E1 × E2 = 60-80 The present invention relates to a membrane production method and a polyolefin-based separation membrane produced by the method. [Selection] Figure 1

Description

  The present invention relates to a porous polyolefin separation membrane and a method for producing the same.

  The separator for an electrochemical cell refers to an intermediate membrane that allows the battery to be charged and discharged while maintaining ionic conductivity while isolating the positive electrode and the negative electrode from each other in the battery.

  Recently, in addition to the trend of reducing the weight and miniaturization of electrochemical cells for enhancing the portability of electronic devices, there is a tendency to require high-power, large-capacity batteries for use in electric vehicles and the like. In the case of such a battery separation membrane, high air permeability, thin film thickness, and strong mechanical strength are required. Moreover, in order to improve the productivity of high-power batteries, it is required to have excellent shape stability due to high heat and high tension. Therefore, it is necessary to develop a separation membrane that is excellent in mechanical strength while having high air permeability and porosity, and that has a small deformation rate of pore shape and size and is suitable for use in high-power batteries. .

  The present invention provides a separation membrane that is excellent in air permeability and porosity but has strong strength, and has a low deformation rate of the shape or size of the pores of the separation membrane and is excellent in battery stability.

According to one example of the present invention, a composition comprising a polyolefin resin and a plasticizer melt-kneading extrusion to form a sheet, E ₁ time stretching and transverse direction of the solidified sheet in the longitudinal direction by T ₁ temperature E ₂ times stretched at T ₂ temperature, a plasticizer is extracted from the stretched sheet, and the final stretch ratio is 1.25 times to 1.5 times in the width direction of the sheet from which the plasticizer is extracted. Stretching, the temperature conditions at the time of stretching are 100 ° C. <T ₁ <115 ° C., 100 ° C. <T ₂ <115 ° C., and T ₂ ≧ T ₁ , and the magnification condition at the time of stretching is E ₁ × a _E 2 = 60-80, a manufacturing method of a polyolefin-based separator is provided.

  According to another example of the present invention, the average point pressure (psi) / bubble point pressure (psi) is 1.8 on the wetting and drying curves of a separation membrane containing a polyolefin resin and measured with a capillary flow pore meter. A polyolefin-based separation membrane of ~ 2.4 is provided.

  The separation membrane according to an example of the present invention has higher electrolyte hygroscopicity depending on the pore shape of the separation membrane.

  The separation membrane according to an example of the present invention also has a strong mechanical strength while controlling the pore size distribution of the separation membrane while being excellent in air permeability and porosity.

FIG. 1 is a wet graph of a PMI capillary flow pore meter measured on a separation membrane according to an example of the present invention. The pressure at the starting point at which a curve is drawn in the wet graph is referred to as a bubble point pressure (psi), and the pressure at the point where the wet curve intersects an imaginary straight line whose slope of the straight line is halved in the dry graph. Is referred to as the mean point pressure (psi). The bubble point pressure and the average point pressure reflect the maximum pore size and the average pore size of the separation membrane, respectively.

Method for producing a porous polyolefin-based separator according to an example of the present invention, a composition comprising a polyolefin resin and a plasticizer melt-kneading extrusion to form a sheet, T ₁ temperature the solidified sheet in the longitudinal direction E ₁ times stretching and E ₂ times stretching at T ₂ temperature in the width direction, a plasticizer is extracted from the stretched sheet, and the final stretch ratio is 1.25 in the width direction of the sheet from which the plasticizer has been extracted. Stretching to be 1.5 to 1.5 times, and the temperature conditions during the stretching are 100 ° C. <T ₁ <115 ° C., 100 ° C. <T ₂ <115 ° C., and T ₂ ≧ T ₁ The magnification condition at the time of the stretching may be E ₁ × E ₂ = 60-80.

  First, forming the solidified sheet specifically includes melt-kneading and extruding a composition containing a polyolefin resin and a plasticizer to form a cooled and solidified sheet.

The polyolefin resin is a resin containing polyolefin, for example, ultrahigh molecular weight polyethylene, high molecular weight polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, high crystalline polypropylene, and polyethylene-propylene copolymer. You may include 1 type, or 2 or more types selected from the group which consists of coalescence. In another example, the polyolefin-based resin may include other resins in addition to the polyolefin. Examples of other resins include polyimide, polyester, polyamide, polyetherimide, polyamideimide, polyacetal and the like. When other resins are included, a polyolefin resin composition can be produced by blending a polyolefin resin and another resin 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 viscosity average molecular weight of the ultrahigh molecular weight polyethylene is preferably 9 × 10 ⁵ g / mol or more, specifically 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 the high density polyethylene and the ultra high molecular weight polyethylene may all be used. More specifically, the ultra high molecular weight polyethylene is used at 30 wt% or less based on the weight of the polyolefin-based resin, for example, a high viscosity average molecular weight of 1 × 10 ^{5 to} 9 × 10 ⁵ g / mol. A polyolefin-based resin containing 70% by weight or more of density polyethylene and 30% by weight or less of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 9 × 10 ⁵ g / mol or more may be used. The polyolefin resin is advantageous because it can produce a high-strength separation membrane. Moreover, when 2 or more types of the said polyolefin-type resin are included, you may mix using 1 or more types selected from the group which consists of a Henschel mixer, a Banbury mixer, and a planetary mixer.

  The plasticizer may be an organic compound that forms a single phase with the polyolefin resin at an extrusion temperature. Examples of plasticizers that can be used in the present invention include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, liquid paraffin (or paraffin oil), paraffin wax; phthalates such as dibutyl phthalate and dioctyl phthalate; C10-20 fatty acids such as acid, stearic acid, oleic acid, linoleic acid, and linolenic acid; C10-20 fatty acid alcohols such as palmitic acid alcohol, stearic alcohol, and oleic alcohol. . These may be used alone or in combination of two or more. Among the plasticizers, liquid paraffin can be preferably used. Liquid paraffin is harmless to the human body, has a high boiling point and a small amount of volatile components, and is suitable for use as a plasticizer in a wet process.

  In the present application, a method known to those skilled in the art can be used to melt and knead a composition containing a polyolefin resin and a plasticizer, and the polyolefin resin and the plasticizer are melted at a temperature of 150 ° C. to 250 ° C. It may be kneaded. The melt-kneaded composition can be poured into a twin screw extruder and extruded at 150 to 250 ° C. Thereafter, the extruded polyolefin resin is cooled using a casting roll of 20 to 80 ° C. or forcedly cooled by cold air jetted from an air knife to crystallize the film. A solidified sheet is formed. The temperature of the cold air ejected from the air knife may be -20 ° C to 40 ° C.

Then, after E ₁ times stretched by T ₁ temperature the solidified sheet in the longitudinal direction, it performs biaxial stretching of stretching _twice E at T ₂ temperature in the width direction. The stretching temperature conditions at the time of stretching are 100 ° C. <T ₁ <115 ° C., 100 ° C. <T ₂ <115 ° C., and T ₂ ≧ T ₁ . If the MD direction stretching temperature (T ₁ ) and the TD direction stretching temperature (T ₂ ) are all lower than 115 ° C., the porosity can be increased, and the MD direction stretching temperature (T ₁ ) is changed to the TD direction stretching temperature (T _2). ) If stretched lower or the same, it is possible to cause variation in the stretch length of each part, and if stretched in the TD direction thereafter, two or more kinds of pores having different sizes can be formed in the separation membrane. Can do. Among two or more types of pores having different sizes, pores having a relatively small size are advantageous in terms of heat shrinkage rate, strength, and pore deformation rate, and pores having a relatively large size are air permeability, electrolysis This is advantageous in terms of liquid wettability and battery capacity. The draw ratio condition at the time of the drawing is preferably E ₁ × E ₂ = 60-80. Furthermore, it is good that E ₁ ≧ 7.5 and E ₂ ≧ 8. In the draw ratio, if the MD direction draw ratio (E ₁ ) and the TD direction draw ratio (E ₂ ) are 7.5 times and 8 times or more, respectively, and the draw surface ratio (E ₁ × E ₂ ) is 60 to 80, The stability of the battery can be improved by minimizing the deformation rate of the shape and size of the pores due to the external pressure of the separation membrane due to the high stretched surface magnification.

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

In one example, the MD direction stretch ratio (E ₁ ) is 7.5 times, and the TD direction stretch ratio (E ₂ ) is 8 times; the MD direction stretch ratio (E ₁ ) is 8 times, and the TD direction stretch ratio (E ₂ ) is 8 times; MD direction stretch ratio (E ₁ ) is 8 times and TD direction stretch ratio (E ₂ ) is 8.5 times; or MD direction stretch ratio (E ₁ ) is 8.5 times and TD The directional stretch ratio (E ₂ ) is preferably 8.5 times. The draw ratios in the width direction and the longitudinal direction may be the same or different. _{Specifically,} the ratio of E 1 / _{E 2} may When it is 0.85. If it is the range of the said extending | stretching ratio, the dispersion | variation effect of the extending | stretching length for every site | part produced by varying the extending | stretching temperature of MD and TD direction can further be strengthened.

  After the biaxial stretching, the plasticizer can be extracted. The extraction of the plasticizer is performed using an organic solvent. Specifically, the plasticizer is extracted by immersing the separation membrane stretched in the longitudinal direction and the width direction in the organic solvent in the plasticizer extraction apparatus. You can proceed with. The organic solvent used for the extraction of the plasticizer is not particularly limited, and any solvent that can extract the plasticizer can be used. As a non-limiting example of the organic solvent, methyl ethyl ketone, methylene chloride, hexane, etc. that have high extraction efficiency and can be easily dried can be used. When liquid paraffin is used as the plasticizer, methylene as the organic solvent. Preference is given to using chloride.

  Since most organic solvents used in the step of extracting the plasticizer are highly volatile and toxic, if necessary, water may be used 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 ratio is 1.25 to 1.5 times in the width direction. The stretching in the width direction is a heat setting step for removing the residual stress of the film and reducing the shrinkage rate of the final film, and the heat shrinkage rate and permeability of the film according to the temperature and fixing ratio at the time of the heat setting. Etc. may be adjusted. Specifically, the heat setting is performed by stretching the stretching direction in the width direction to a stretching ratio of 1.25 to 2 times, and relaxing to 70% to 100% with respect to the stretched width direction length, so that the final stretching ratio is It is good to make it 1.25 times-1.5 times. Heat setting in the arrangement has the effect of improving the air permeability by adjusting the variation in pores generated during the biaxial stretching. The heat setting is performed at 100 to 150 ° C, for example, 120 to 130 ° C. Within the above range, it is effective for removing the residual stress of the film, and the physical properties can be improved.

  The present invention provides a polyolefin separation membrane manufactured by the method of manufacturing a polyolefin separation membrane according to the above example.

  The polyolefin-based separation membrane may have an average point pressure (psi) / bubble point pressure (psi) of 1.8 to 2.4 in a wetting curve of the separation membrane measured with a capillary flow pore meter.

  If the ratio of the average point pressure (psi) / bubble point pressure (psi) is within the above range in the wet and dry curves of the capillary flow pore meter, the pores required for the separation membrane are distributed in various sizes. For example, it is possible to provide a separation membrane having good air permeability while achieving a porosity of 40% or more, and having excellent wettability and strength of the electrolytic solution.

  The bubble point pressure (psi) means the pressure at the starting point where a wetting curve is drawn by a capillary flow pore meter. Specifically, the separation membrane sample is immersed in the solution to fill the pores with the solution, and the pressure is increased. When air is blown in, the solution filled in the large hole is first pushed by the pressure and moves, and the pressure at this time is called bubble point pressure. Referring to FIG. 1, the bubble point pressure refers to a pressure at which a flow rate changes according to an increase in pressure in a capillary flow pore measuring device, and then starts to increase after the flow rate maintains zero.

  The average point pressure (psi) is a pressure at a point where an imaginary straight line having a slope of ½ on the drying straight line intersects the wetting curve with a capillary flow pore measuring device. Specifically, when air is blown while increasing the pressure in a state where the separation membrane sample is not immersed in the solution, a linear graph in which the flow rate increases in proportion to the increase in pressure is obtained. Referring to FIG. 1, when drawing a virtual straight line [1/2 drying graph in FIG. 1] having an inclination of 1/2 in the straight line graph [dry graph in FIG. 1], this virtual straight line is drawn. The pressure at the point where the wetting curve intersects with the wetting curve is called the average point pressure.

  The polyolefin-based separation membrane according to an example 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 separation membrane. Specifically, the air permeability is preferably 60 to 150 sec / 100 cc.

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

The polyolefin-based separation membrane according to an example of the present invention may include a coating layer on one or both sides of the separation membrane, and the coating layer may include an organic binder or may further include inorganic particles. Examples of the organic binder include 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, or Mixtures of these may also be included. 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 is formed by a dip coating method. The separation membrane having the coating layer may have a thermal shrinkage of 3% or less in 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 separation membrane according to the present invention has an average thickness of 7 μm to 20 μm, and the variation in thickness is preferably less than 4% of the average thickness. The porous polyolefin separation membrane according to the present invention may have an average puncture strength of 300 gf or more, and specifically 400 gf or more.

  In addition, the porous polyolefin-based separation membrane or the coating separation membrane according to the present invention was prepared by cutting the produced separation membrane into a size of 50 × 50 mm and placing it in an oven at 120 ° C., and then shrinking for 1 hour, When measuring the size of the contracted separation membrane and measuring the shrinkage rate reflecting the reduced size, the longitudinal direction shrinkage rate may be 5% or less and the width direction shrinkage rate may be 3% or less. More specifically, it is preferable that the longitudinal direction shrinkage rate is 4% or less and the width direction shrinkage rate is 2% or less.

  The present invention also provides a battery chemical battery comprising the porous polyolefin-based separation membrane disclosed in the present invention, a positive electrode, a negative electrode, and an electrolyte. The type of the electrochemical cell is not particularly limited, and may be a type of electricity known in the technical field of the present invention. The electrochemical battery 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 usually used in the technical field of the present invention may be used. A non-limiting example of a method for manufacturing the electrochemical cell is as follows: the separation membrane or the coating separation membrane of the present invention is positioned between the positive electrode and the negative electrode of the battery and then electrolyzed thereto. The battery can be manufactured in a manner that fills the liquid. The electrode constituting the electrochemical cell of the present invention can be manufactured in a form in which an electrode active material is bound to an electrode current collector by a method usually used in the technical field of the present invention. Among the electrode active materials used in the present invention, the positive electrode active material is not particularly limited, and a positive electrode active material usually used in the technical field of the present invention can be used. Specifically, the positive electrode includes a positive electrode active material capable of reversibly inserting and desorbing lithium ions, and as such a positive electrode active material, at least one selected from cobalt, manganese, nickel, and It may be a composite metal oxide with lithium. The solid solution ratio between metals varies, and besides these metals, Mg, Al, Co, Ni, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn And an element selected from the group consisting of Cr, Fe, Sr, V, and rare earth elements. The positive electrode 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, specifically, lithium cobalt oxide. (Lithium cobalt oxide, LCO. For example, LiCoO ₂ ), lithium nickel cobalt manganese oxide (NCM. For example, Li [Ni (x) Co (y) Mn (z)] O ₂ ), lithium manganese Oxide (Lithium manganese oxide, LMO. For example, LiMn ₂ O ₄ , LiMnO ₂ ), Lithium iron phosphate (LFP. For example, LiFePO ₄ ), Lithium nickel Oxides (LNO, such as LiNiO ₂ ) and the like can be used. The negative electrode includes a negative electrode active material into which lithium ions can be inserted and desorbed. Examples of the negative electrode active material include crystalline or amorphous carbon, or a carbon composite carbon negative electrode active material (thermal Carbon, coke, graphite), burned organic polymer compounds, carbon fibers, tin oxide compounds, lithium metal, or alloys of lithium with other elements can be used. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1,500 ° C. or less, mesophase pitch-based carbon fiber (MPCF), and the like. is there. Examples of crystalline carbon include graphite-based materials, and specific examples include natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The negative electrode may include, for example, crystalline or amorphous carbon.

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

  The electrode current collector used in the present invention is not particularly limited, and an electrode current collector normally used in the technical field of the present invention may be used. Non-limiting examples of the positive electrode current collector material among the electrode current collectors include foils manufactured from aluminum, nickel, or a combination thereof. Among the electrode current collectors, non-limiting examples of negative electrode current collector materials include copper, gold, nickel, copper alloys, or foils manufactured by combinations thereof.

  Moreover, foil and a mesh form are mentioned as a form of the said positive electrode collector and a negative electrode collector.

The electrolytic solution used in the present invention is not particularly limited, and an electrolytic solution for electrochemical cells that is usually used in the technical field of the present invention may be used. The electrolytic solution may be one in which a salt having a structure such as A ⁺ B ⁻ is dissolved or dissociated in an organic solvent. Non-limiting examples of A ⁺ include cations composed of alkali metal cations such as Li ⁺ , Na ⁺ , or K ⁺ , or combinations thereof. Non-limiting examples of the B ⁻ include PF ₆ ⁻ , BF ₄ ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , CH ₃ CO ₂ ⁻ , CF ₃ SO ₃ ⁻ , N Examples include an anion such as (CF ₃ SO ₂ ) ₂ ^— , C (CF ₂ SO ₂ ) ₃ ^— , or a combination thereof. Non-limiting examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dimethylformamide. (Dimethylformamide, DMF), Dipropyl carbonate (Dipropyl carbonate, DPC), Dimethyl sulfoxide (Dimethyl sulfoxide, DMSO), Acetonitrile, Dimethoxyethane, diethoxyx, Rahidorofuran (Tetrahydrofuran), N- methyl-2-pyrrolidone (N-methyl-2-pyrrolidone, NMP), ethylmethyl carbonate (Ethyl methyl carbonate, EMC), or gamma - like 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 the contents of the present invention are not construed as being limited thereto.

Example 1 Production of Porous Polyolefin Separation Membrane After supplying high-density polyethylene (High-density polyethylene, HDPE; Mitsui Chemicals Co., Ltd.) having a viscosity average molecular weight of 600,000 g / mol to a twin screw extruder, liquid paraffin was used. (Far East Oily) was injected into the twin-screw extruder in an amount such that the weight ratio of the polyethylene to the polyethylene 30 to the liquid paraffin 70 was extruded.

  After the extrusion, a sheet-like separation membrane was produced from the gel phase obtained through the T-die using a cooling roll. The longitudinal direction (Machine Direction, MD) stretching at 110 ° C. and the width direction (Transverse Direction, TD) stretching at 113 ° C. (stretching ratio: 8.0 (MD) × 8.0 (TD)) with respect to the separation membrane. Went.

  The stretched polyolefin-based separation membrane was immersed in methylene chloride (Samsung Fine Chemical) to extract liquid paraffin, and then moved to a drying roll and dried.

  After that, the dried film was heat-set by secondary stretching in the width direction (width direction stretching ratio: 1.0 → 1.6 → 1.4, stretching temperature 128 ° C.) to obtain a thickness of 12.5 μm. A porous polyolefin separation membrane was produced.

Example 2 Production of Porous Polyolefin Separation Membrane In Example 1, the longitudinal direction (Machine Direction, MD) stretching at 103 ° C. and the transverse direction (Transverse Direction, TD) stretching at 105 ° C. (stretching ratio: 8.5). A separation membrane having a thickness of 12.3 μm was manufactured in the same manner as in Example 1 except that (MD) × 8.5 (TD).

Comparative Example 1 Production of Porous Polyolefin Separation Membrane In Example 1, the longitudinal direction (Machine Direction, MD) stretching at 120 ° C. and the width direction (Transverse Direction, TD) stretching at 123 ° C. (stretching ratio: 8 (MD ) × 8 (TD)) A separation membrane having a thickness of 12.2 μm was manufactured in the same manner as in Example 1.

Comparative Example 2: Production of Porous Polyolefin Separation Membrane In Example 2, the longitudinal direction (Machine Direction, MD) stretching and the width direction (Transverse Direction, TD) stretching ratio was 7 (MD) × 7 (TD). Except for this, a separation membrane having a thickness of 12.3 μm was manufactured in the same manner as in Example 2.

  The production conditions of the separation membranes according to Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

Experimental Example For the separation membranes produced in Examples 1 and 2 and Comparative Examples 1 and 2, the porosity, the air permeability, the tensile strength, the elongation rate, the shrinkage rate, the bubble were measured by the measurement methods disclosed below. The point and average point pressure, and the water droplet contact angle were measured and the results are shown in Table 2.

1. Measurement of Bubble Point Pressure and Average Point Pressure in Capillary Flow Pore Measurement Graph Each of the separation membranes produced in the above Examples and Comparative Examples was sampled with a circle having a diameter of 26 mm. After attaching the separation membrane itself to a capillary flow pore measuring instrument of PMI, fully immerse it in Galwick ^™ solution (surface tension 15.9 dyne / cm). The device is connected to Wet up Calc. After setting to mode, the flow of N ₂ flow rate by pressure is measured and a wetting curve is drawn. The pressure at which the first bubble is sensed in the wetting curve is recorded as the bubble point pressure (psi). In addition, each of the separation membranes manufactured in the examples and comparative examples was sampled with a circle having a diameter of 26 mm, and after attaching the separation membrane itself to the device, the device was connected to Dry up Calc. Set to mode, the flow rate of N ₂ by pressure was measured, and this was shown in the drying curve graph. In the measured drying curve graph, a straight line is extended from the origin to a point having linearity, a virtual straight line that is half the slope of the straight line is drawn, and the pressure at the intersection of the virtual straight line and the wet curve is averaged. Record as point pressure (psi).

2. Porosity A 10 cm × 10 cm sample of each separation membrane produced in Examples 1 and 2 and Comparative Examples 1 and 2 was cut to determine its volume (cm ³ ) and mass (g). From the mass and the density of the separation membrane (g / cm ³ ), the porosity was calculated using the following formula.

Porosity (%) = (Volume−Mass / Sample density) / Volume × 100

Sample density = density of polyethylene

3. Air Permeability After preparing 10 samples, each of the separation membranes manufactured in the above Examples and Comparative Examples was cut at 10 points different from each other in the size of a 1 inch diameter circle, the air permeability Using a measuring device (Asahi Seiko Co., Ltd.), the time required for 100 cc of air to pass through each sample was measured. After measuring the said time 5 times each, the average value was calculated.

4). Tensile strength After preparing 10 samples each of the separation membranes manufactured in the above examples and comparative examples cut at 10 points different from each other in the width (MD) 10 mm × length (TD) 50 mm, the UTM was 20 mm. After biting the part, the strength was measured by pulling up and down. After measuring the tensile strength of each sample three times, the average value was calculated.

5. Elongation rate For each of the separation membranes produced in the above examples and comparative examples, 4. When measuring the tensile strength, the original length and the length at the breaking point are compared ((length of breaking point−20) / 20 mm), and the value of X100 is displayed as a percentage.

6). Shrinkage rate Ten samples were prepared by cutting each of the separation membranes manufactured in the examples and comparative examples at 10 points different from each other in the width (MD) 50 mm × length (TD) 50 mm. Each sample was allowed to stand in an oven at 105 ° C. for 1 hour, and then the degree of shrinkage in the MD direction and TD direction of each sample was measured to calculate an average heat shrinkage rate.

7). Water drop contact angle (wetability evaluation of electrolyte)
Each of the separation membranes manufactured in the examples and comparative examples was cut into a width (MD) 20 mm × a length (TD) 20 mm to prepare five samples. The sample was placed on a contact angle measuring device (DSA-100, Marktec Trade Co., Ltd.), and after dropping one drop of water with a dropper, the contact angle was measured. The contact angles of 5 samples were calculated by averaging.

Claims (16)

A composition containing a polyolefin resin and a plasticizer is melt-kneaded and extruded to form a sheet,
Wherein the solidified sheet was stretched _twice E at T ₂ temperature E _1-time stretching and transverse directions by T ₁ temperature in the longitudinal direction,
Extracting a plasticizer from the stretched sheet,
Stretching the sheet from which the plasticizer has been extracted in the width direction so that the final stretching ratio is 1.25 to 1.5 times,
The temperature conditions during the stretching are 100 ° C. <T ₁ <115 ° C., 100 ° C. <T ₂ <115 ° C., and T ₂ ≧ T ₁ .
The stretching at a magnification condition is _{E 1} × _E 2 = _60~80, producing a polyolefin-based separator. It is the ratio of _E 1 / _{E 2} is 0.85 at the magnification conditions, producing a polyolefin-based separator according to claim 1. The polyolefin resin is selected from the group consisting of high density polyethylene having a viscosity average molecular weight of 1 × 10 ^{5 to} 9 × 10 ⁵ g / mol and ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 9 × 10 ⁵ g / mol or more. The manufacturing method of Claim 1 containing these carried out individually or in mixture of these. The manufacturing method according to claim 1, wherein E ₁ ≧ 7.5 and E ₂ ≧ 8.   Stretching in the width direction so that the final stretching ratio is 1.25 to 1.5 times, stretching in the width direction is 1.25 to 2 times, and the length in the width direction is The manufacturing method according to any one of claims 1 to 3, comprising relaxing to 70% to 100%.   The production according to any one of claims 1 to 3, further comprising coating one or both surfaces of the produced polyolefin-based separation membrane with a coating composition containing an organic polymer and inorganic particles. Method. Contains polyolefin resin,
Polyolefin-based separations having a mean point pressure (psi) / bubble point pressure (psi) ratio of 1.8-2.4 on the wetting and drying curves of the separation membrane measured with a capillary flow porometer film. The polyolefin-type separation membrane of Claim 7 whose ratio of the tensile strength (kg / cm < ² >) / elongation rate (%) of the longitudinal direction and the width direction of the said separation membrane is 15-28, respectively.   The polyolefin-based separation membrane according to claim 7, wherein the porosity of the separation membrane is 40 to 50%.   The polyolefin-type separation membrane of Claim 7 whose air permeability of the said separation membrane is 50-200sec / 100cc.   The polyolefin-type separation membrane of Claim 7 whose water droplet contact angle of the said separation membrane is 107 degrees or less. The polyolefin resin is selected from the group consisting of high-density polyethylene having a viscosity average molecular weight of 1 × 10 ^{5 to} 9 × 10 ⁵ g / mol and ultrahigh molecular weight polyethylene having a viscosity average molecular weight exceeding 9 × 10 ⁵ g / mol. The polyolefin-type separation membrane of any one of Claims 7 thru | or 11 containing these made alone or a mixture thereof. The polyolefin-based separator is longitudinally one that is _{E 2-fold} stretched at _{T 2} temperature _{E 1-time} stretching and transverse directions by _{T 1} temperature, the temperature conditions during the stretching 100 ℃ _<T 1 _<115 ℃ 100 ° C. <T ₂ <115 ° C. and T ₂ ≧ T ₁ , and the magnification conditions during the stretching are E ₁ × E ₂ = 60 to 80, E ₁ ≧ 7.5, and E ₂ ≧ 8 The polyolefin-type separation membrane of any one of Claims 7 thru | or 11. Wherein the ratio of _E 1 / _{E 2} at a magnification condition are 0.85, polyolefin separation membrane according to claim 13.   The electrochemical cell containing the polyolefin-type separation membrane of any one of Claims 7 thru | or 11.   The electrochemical cell according to claim 15, wherein the electrochemical cell is a lithium secondary battery.

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