KR101970492B1 - A resin composition for manufacturing a porous separator - Google Patents

Abstract

The present invention relates to a resin composition for manufacturing a porous separation membrane, which can be used for manufacturing a porous separation membrane having a uniform pore size. The resin composition comprises: a polyolefin resin; and a flow paraffin having 50 wt% or more of the content of C_30 to C_50 alkylene chain.

Description

TECHNICAL FIELD [0001] The present invention relates to a resin composition for producing a porous separator,

The present invention relates to a resin composition for producing a porous membrane, and more particularly, to a resin composition for producing a porous membrane containing liquid paraffin in which the length and content of an alkylene chain are controlled within a certain range.

Lithium secondary batteries are widely used as power sources for various electric appliances that require miniaturization and light weight such as smart phones, notebooks, and tablet PCs. As the application fields of smart grid, electric vehicles, Development of a lithium secondary battery which is large, long in life, and high in stability is required.

As a means for achieving the above object, there is provided a separator in which micropores for separating the positive electrode and the negative electrode to prevent internal short-circuiting and to facilitate the movement of lithium ions during charging and discharging are formed, Research and development of wet polyolefin microporous membrane by thermally induced phase separation have been actively carried out.

Liquid Paraffin Oil, which is used as a pore-forming agent in the production of a wet-type polyolefin separator, is a major influence factor of the heat-induced phase separation forming the pores of the separator. The porosity and the average pore size It plays a key role in determining the properties of the membrane by influencing the same microporous morphology. In particular, the microporous morphology of the separator greatly affects the operating performance and stability of a high performance, high energy lithium secondary battery.

However, studies on conventional polyolefin separators are largely concerned with process characteristics such as temperature, stretching ratio and the like in the production process leading to extrusion, stretching, extraction and drying. Particularly, in the production of a microporous polymer membrane by a wet method, there are insufficient studies to control the heat-induced phase separation phenomenon occurring during the cooling process after melt-kneading the polyolefin polymer resin and the pore-forming agent.

In the case of the conventional separator, pores of various sizes of 10 nm to 1 μm are generated in a random dispersion form. Since the migration of lithium ions is performed through the pores of the separator, the separator having a large pore size variation, Charge-discharge characteristics, long-term cycle characteristics, and rate-limiting characteristics are insufficient. Particularly, uneven pores deteriorate the ion conductivity, adversely affecting the speed of the lithium secondary battery, and cause a stability problem in that the shutdown speed of the separator, which operates when thermal runaway occurs, occurs in the lithium secondary battery.

It is an object of the present invention to provide a resin composition for producing a porous separator which can be used for producing a porous separator membrane having a uniform pore size.

An aspect of the present invention relates to a polyolefin resin; And a liquid paraffin having a C ₃₀ to C ₅₀ alkylene chain content of 50 wt% or more.

In one embodiment, the polyolefin resin comprises a first polyolefin having a viscosity average molecular weight of 1,500,000 to 3,000,000; And a second polyolefin having a viscosity average molecular weight of 500,000 to 1,000,000.

In one embodiment, the weight ratio of the first polyolefin and the second polyolefin may be 1 to 3: 7 to 9, respectively.

In one embodiment, the length distribution of the alkylene chain may be a single-ended type.

In one embodiment, the content of the C ₃₅ -C ₄₀ alkylene chain in the liquid paraffin may be at least 50% by weight.

In one embodiment, the 5% distillation point of the liquid paraffin may be 450-500 ° C.

In one embodiment, the temperature difference between the extreme point and the point of species of the liquid paraffin may be 200 ° C or less.

In one embodiment, the liquid paraffin may have a flash point of at least 250 ° C.

In one embodiment, the weight ratio of the polyolefin resin to the liquid paraffin may be 1: 1.5 to 4, respectively.

Another aspect of the present invention provides a porous separator produced using the resin composition for producing a porous membrane, wherein the ratio of pores having a pore size of 30 to 50 nm in the total pores is 80 to 100%.

According to one aspect of the present invention, a porous separation membrane having a uniform pore size can be produced.

It should be understood that the effects of the present invention are not limited to the effects described above, but include all effects that can be deduced from the description of the invention or the composition of the invention set forth in the claims.

FIG. 1 shows a result of GPC (Gel Permeation Chromatography) analysis of liquid paraffin used in one embodiment of the present invention.
2 shows a boiling point distribution obtained by GC (Gas Chromatography) measurement of liquid paraffin used in one embodiment of the present invention.
FIG. 3 is a graph showing a measurement result of a pore size distribution of a separation membrane manufactured according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" . Also, when an element is referred to as " comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Resin composition for manufacturing a porous membrane

According to one aspect of the present invention, there is provided a resin composition for producing a porous membrane, comprising: a polyolefin resin; And the content of C ₃₀ ~ C ₅₀ alkylene chain at least 50% by weight liquid paraffin; may contain.

The polyolefin resin may include one selected from the group consisting of polyethylene, polypropylene, polybutylene, polyisobutylene, and combinations of two or more thereof, but is not limited thereto.

The polyolefin resin may be from 2 to 7, preferably 3 to 5. The molecular weight distribution _{(PDI, M w / M n} ,) (PDI: Polydispersity Index, M w: Weight Average Molecular Weight, M n: Number Average Molecular Weight).

Generally, the larger the molecular weight distribution, the lower the shear stress and the lower the viscosity, so the processability is improved but the mechanical properties are lowered. The smaller the molecular weight distribution is, the lower the processability is, but the mechanical properties are improved.

The molecular weight distribution may have a different value depending on the type of the catalyst used in polymer polymerization. For example, polyethylene polymerized with a Ziegler-Natta catalyst has a molecular weight distribution generally between 6 and 10, and polyethylene polymerized with a metallocene catalyst can have a molecular weight distribution generally between 3 and 7.

If the molecular weight distribution is less than 2, the production of the polymer may be difficult. If the molecular weight distribution is more than 7, the physical properties may be uneven during the production of the separation membrane.

Wherein the polyolefin resin is a first polyolefin having a viscosity average molecular weight of 1,500,000 to 3,000,000; And a second polyolefin having a viscosity average molecular weight of 500,000 to 1,000,000.

By using a mixture of polymers having different viscosity average molecular weights, mechanical properties and processability can be complemented to produce a porous separator having excellent physical properties.

The first polyolefin may have a melt index (MI) of 0.4 to 0.6 g / 10 min, preferably 0.5 g / 10 min, measured at 190 ° C under a load of 21.6 kg.

If the melt index of the first polyolefin is less than 0.1 g / 10 min, the extrusion processability of the resin composition may be deteriorated. If the melt index is more than 0.6 g / 10 min, the physical strength of the separator may be lowered.

The second polyolefin may have a melt index of 0.05 to 0.15 g / 10 min, preferably 0.1 g / 10 min, measured at 190 ° C under a load of 21.6 kg.

If the melt index of the second polyolefin is less than 0.05 g / 10 min, the processability of the resin composition for producing a porous membrane may be deteriorated. If the melt index is more than 0.15 g / 10 min, the physical strength of the separation membrane may be deteriorated.

The weight ratio of the first polyolefin and the second polyolefin may be 1 to 3: 7 to 9, respectively.

If the weight ratio of the first polyolefin is excessively high, the workability of the resin composition for preparing a porous membrane may be deteriorated. Conversely, if the weight ratio of the second polyolefin is excessively high, the mechanical properties of the separator may be deteriorated.

The content of the C ₃₀ -C ₅₀ alkylene chain in the liquid paraffin may be 50% by weight or more, preferably 70% by weight, and more preferably 90% by weight or more.

The length distribution of the alkylene chain may be unimodal.

The narrower the length distribution of the alkylene chain, the more uniform the pore size of the prepared porous separator.

The content of the C ₃₅ -C ₄₀ alkylene chain in the liquid paraffin may be 50% by weight or more based on the total weight of liquid paraffin.

The higher the content of the C ₃₅ -C ₄₀ alkylene chain in the liquid paraffin, the higher the percentage of pores having a size of 30 to 50 nm in the prepared porous separator.

The boiling point of the multicomponent mixture such as liquid paraffin can be expressed in a certain range due to the difference in the vapor pressure of each component. The boiling point range can be represented by a distillation curve through a distillation test. In the distillation test, the temperature at which a drop of the first sample flows out is the " Initial Boiling Point ", and the temperature at the time of completion of boiling "Final Boiling Point". In addition, the temperature at the time when 5% of the mixture boiled is the " 5% distillation point ".

"Flash point" means the lowest temperature at which substances vaporized under standard atmospheric pressure can be ignited by an external flame.

The 5% distillation point of the liquid paraffin may be 450-500 ° C.

The temperature difference between the extreme point and the point of species of the liquid paraffin may be 200 ° C or less.

The use of liquid paraffin having a temperature difference of more than 200 ° C between the ultracentrifugation point and the kind point may cause uneven distribution of the pore size in the production of the separation membrane.

The flash point of the liquid paraffin may be 250 ° C or higher.

When liquid paraffin having a flash point of less than 250 ° C is used, a fire accident may occur during the separation membrane manufacturing process.

The weight ratio of the polyolefin resin and the liquid paraffin may be 1: 1.5 to 4, respectively.

If the weight ratio of liquid paraffin is less than 1.5, the porosity of the separator may be lowered or the viscosity of the resin composition may be increased to make the separator uneven or impossible to manufacture. If the weight ratio is more than 4, the mechanical strength of the separator may be lowered or the separator may not be manufactured .

Porous membrane

Another aspect of the present invention is a porous separator, which can be produced by using the resin composition for producing the porous separator.

The porous separator comprises: (a) a polyolefin resin; And liquid paraffin, to prepare a resin composition; (b) casting the resin composition to produce a base sheet; (c) stretching the base sheet to obtain a stretched film; (d) extracting and drying the liquid paraffin of the stretched film; And (e) heat-setting the stretched film.

The resin composition of the step (a) may be a resin composition for producing a porous membrane, which may be an aspect of the present invention. If necessary, the resin composition may further contain 0.1 to 1% by weight of an antioxidant and 0.5 to 1% .

The step (a) may be carried out in a twin-screw extruder having a screw length / diameter ratio (L / D) of 50 to 60 at an extrusion temperature of 200 to 250 ° C and a screw rotation speed of 60 to 120 rpm. The twin screw extruder may be a T die having a width of 300 mm or more.

The polyolefin resin may be supplied to a main feeder of a twin-screw extruder, and the liquid paraffin may be heated to 60 to 150 ° C and supplied to a side feeder.

The step (b) may be performed by passing the kneaded material discharged through the T-die through a casting roll at 40 to 60 ° C. The casting roll may include a large diameter roll and a small diameter roll.

In the step (b), a heat-induced phase separation phenomenon may occur as the kneaded product is brought into contact with the casting roll to be cooled and crystallized. The heat-induced phase separation phenomenon can determine the microporous structure such as porosity and pore size distribution of the porous separation membrane.

One side of the kneaded material discharged to the T die is brought into contact with the large diameter roll and rotated, and the other side is brought into contact with a small diameter roll having a constant interval to partially phase-separate the liquid paraffin, The pore structure can be determined. If the liquid paraffin content of the kneaded product is too low, the porosity may be lowered, and if it is excessive, the mechanical strength of the porous separation membrane may be deteriorated.

The sheet produced by the casting may have a thickness of 0.5 to 2 mm.

The stretching in the step (c) may be a biaxial stretching simultaneously in a mechanical direction (MD) and a transverse direction (TD), and may be sequential stretching in order.

For example, a biaxial stretcher of a clip type can be used for simultaneous biaxial stretching. A roll stretching method using a difference in speed of rolls in the longitudinal direction during the biaxial stretching in the sequential manner can be used, and a method in which a stretching device in the clip type is used in the transverse direction can be used.

The stretching may be 3 to 10 times at 100 to 130 ° C. If the stretching temperature is less than 100 캜, the film may be broken. If the stretching temperature is more than 130 캜, the film may be partially melted, which may make it difficult to control the microporous morphology.

The extraction and drying in the step (d) may be performed by immersing the stretched film in an extraction tank having a solvent. The extraction temperature may be 25 to 40 占 폚, and the extraction time may be 1 to 20 minutes. The solvent may be selected from the group consisting of pentane, hexane, benzene, dichloromethane, carbon tetrachloride, methyl ethyl ketone, acetone, and mixtures of two or more thereof.

Since the film shrinks as the liquid paraffin is removed in the step (d), it is necessary to minimize the lateral and longitudinal shrinkage of the film after extraction. It is possible to control and maintain the shrinkage ratio in the transverse direction and the transverse direction within the range of 6 to 13%, respectively, relative to the film before extraction, by imparting and holding a tension acting in the direction opposite to the contraction stress generated after the liquid paraffin extraction to the film. , It can be controlled in the range of 8 to 10%.

The step (e) may be performed at a temperature of 110 to 135 ° C. If the heat-setting temperature is less than 110 ° C, the heat shrinkage rate of the separator may be lowered. If the temperature is more than 135 ° C, the micropores may be partially closed to increase the air permeability.

The step (e) may be performed for 10 seconds to 10 minutes, and at the same time as the step (e), the stretching ratio may be 0.5 to 2.0 times and the stretching ratio may be 0.5 to 2.0 times.

The ratio of the pores having pore sizes of 30 to 50 nm in the total pores may be 80 to 100%, and preferably 90 to 95%.

The porous separator may have a thickness of 1 to 50 mu m, preferably 5 to 20 mu m. If the thickness is less than 1 μm, the stability of the secondary battery may be insufficient. If the thickness is more than 50 μm , the ion conductivity of the separation membrane may be insufficient or the volume of the secondary battery using the porous separation membrane may be excessively large.

The porosity of the porous separation membrane may be 50 to 550 sec / 100 ml, preferably 50 to 500 sec / 100 ml. If the air permeability is higher than 550 sec / 100 ml, the ionic conductivity of the separator may be insufficient and the performance of the secondary battery may deteriorate. If the air conductivity is less than 50 sec / 100 ml, the probability of self discharge or short circuit of the secondary battery may be high.

The porous separator may have an average pore size of 15 to 65 nm, preferably 30 to 50 nm. If the average pore size is less than 15 nm, the ionic conductivity of the separator may be insufficient. If the average pore size is more than 65 nm, the mechanical strength may be insufficient and the self-discharge or short circuit of the secondary battery may occur.

The porous separator may have a piercing strength of 150 to 750 gf, preferably 250 to 600 gf. If the puncture strength is less than 150 gf, there is a high probability that a secondary battery is short-circuited.

The porous separation membrane may have a tensile breaking strength of 1,000 to 4,000 kgf / cm ² , preferably 2,000 to 3,000 kgf / cm ² . If the tensile breaking strength is less than 1,000 kgf / cm ² , the separation membrane may be easily broken or deformed by the process of handling the separation membrane during the process of manufacturing the secondary battery by high-speed automation or by the impact or vibration of the final product.

The porous separator may have a modulus of 1,000 to 2,500 MPa, preferably 1,500 to 2,000 MPa when elongation is 0 to 1%.

The porous separator may have a heat shrinkage ratio of 20% or less in the transverse and longitudinal directions at 120 ° C / 1hr. If the heat shrinkage ratio in the horizontal and vertical directions exceeds 20%, there is a high probability that the secondary battery will be damaged due to abnormal operation or exposure to high temperature.

The ionic conductivity of the porous separation membrane may be 0.4 to 0.6 mS / cm, preferably 0.495 to 0.505 mS / cm.

The secondary battery, which is another aspect of the present invention, may include the porous separator.

Hereinafter, embodiments of the present invention will be described in more detail. However, the following experimental results only describe representative experimental results of the above embodiments, and the scope and contents of the present invention can not be construed to be limited or limited by the embodiments and the like. Each effect of the various embodiments of the present invention not expressly set forth below will be specifically described in that section.

The results of the experiment are as follows. A resin composition for preparing a porous membrane according to an embodiment of the present invention is prepared, and a porous membrane prepared using the resin composition is compared with a porous membrane made of a conventional resin composition.

Preparation of Resin Composition for Preparing Porous Membrane

Example 1

The viscosity-average molecular weight (M _v) is 1.5 million, the molecular weight distribution (PDI) 3 High density polyethylene having a polyethylene comprising a (HDPE) 25% by weight, 75% by weight of high density polyethylene (HDPE) having a viscosity average molecular weight 500,000, molecular weight distribution 3 0.5 part by weight of a phosphite ester as an antioxidant and 0.5 part by weight of sodium benzosulfonate as a polyethylene crystallizing agent were added to 100 parts by weight of the mixture, and the mixture was introduced into a twin screw extruder (inner diameter: 58 mm, L / D = 56, Twin Screw Extruder). 150 parts by weight of liquid paraffin composed of C ₂₈ to C ₄₉ alkylene chains and having a content of C ₃₅ to C ₄₀ alkylene chain of 60.2% by weight was heated to 125 ° C, fed through a side feeder of the twin screw extruder, To prepare a resin composition.

Example 2

A resin composition was prepared in the same manner as in Example 1 except that 250 parts by weight of the liquid paraffin was used.

Example 3

A resin composition was prepared in the same manner as in Example 1 except that 400 parts by weight of the liquid paraffin was used.

Example 4

Except for using 100 parts by weight of a polyethylene mixture containing 15% by weight of high density polyethylene (HDPE) having a viscosity average molecular weight of 2,500,000 and a molecular weight distribution of 4, and 85% by weight of high density polyethylene (HDPE) having a viscosity average molecular weight of 500,000 and a molecular weight distribution of 3 , A resin composition was prepared in the same manner as in Example 1.

Comparative Example 1

A resin composition was prepared in the same manner as in Example 1, except that 150 parts by weight of liquid paraffin composed of C ₂₃ to C ₄₅ alkylene chains was used.

Comparative Example 2

A resin composition was prepared in the same manner as in Example 1 except that 150 parts by weight of liquid paraffin composed of C ₂₉ to C ₅₀ alkylene chains was used.

Comparative Example 3

A resin composition was prepared in the same manner as in Example 1 except that 50 parts by weight of the liquid paraffin was used.

Comparative Example 4

A resin composition was prepared in the same manner as in Example 1, except that 500 parts by weight of the liquid paraffin was used.

Experimental Example 1

The molecular weight distributions of the liquid paraffin A used in Examples 1 to 4, the liquid paraffin B used in Comparative Example 1, and the liquid paraffin C used in Comparative Example 2 were analyzed by GPC (Gel Permeation Chromatography) Respectively.

The results of GC (Gas Chromatography) measurement of the boiling points of the liquid paraffins A, B, and C according to ASTM D-2887 are shown in FIG.

Referring to FIG. 1, it was confirmed that the liquid paraffin A was composed of only the material having an alkylene chain length of 29 to 48. Also, it was confirmed that the liquid paraffin A had a ratio of a material having an alkylene chain length of 35 to 40 in an amount of 60.2% by weight.

It was confirmed that the liquid paraffin B was composed of only the substance having the alkylene chain length of 23 to 45. It was confirmed that the proportion of the substance having an alkylene chain length of 35 to 40 in the liquid paraffin B was 27% by weight.

It was confirmed that the liquid paraffin C was composed of only the substance having an alkylene chain length of 29 to 50. It was confirmed that the ratio of the material having an alkylene chain length of 35 to 40 in the liquid paraffin C was 39 wt%.

Referring to FIG. 2, it was confirmed that the extreme point and the type point of the liquid paraffin A were 435 ° C and 570 ° C, respectively. 5% distillation point was confirmed to be 465 ° C.

It was confirmed that the extreme point and the kind point of the liquid paraffin B were 370 ° C and 575 ° C, respectively. The 5% distillation point was confirmed to be 410 ° C.

It was confirmed that the extreme point and the type point of the liquid paraffin C were 400 ° C and 615 ° C, respectively, and the 5% distillation point was 430 ° C.

It was confirmed that the slope of the boiling point curve of the liquid paraffin A was the smallest, and it was confirmed that the uniformity of the alkylene chain length of the liquid paraffin A was the highest. It is confirmed that this is a result corresponding to the result of the chain length distribution in FIG.

Preparation of porous separator

Production Example 1

The homogeneously melt-kneaded resin composition of Example 1 was discharged onto a T-die having a width of 300 mm in the biaxial extruder at 200 DEG C and a screw rotation speed of 60 rpm, and then passed through a casting roll having a temperature of 40 DEG C, 1,500 [ mu] m. The base sheet was heated at 118 DEG C in a biaxial film stretching machine and stretched 7 times at a speed of 50 mm / min in a longitudinal direction (MD), and stretched 7 times at a rate of 50 mm / min in a transverse direction (TD) And stretched to prepare a stretched film.

The stretched film was impregnated into a dichloromethane leaching tank at 25 ° C to extract and remove liquid paraffin for 10 minutes. The film in which the liquid paraffin was removed was dried at room temperature while controlling the shrinkage ratio in the transverse and longitudinal directions to 8%, respectively. Thereafter, after heating at 120 ° C in a stretching machine, stretching was 1.35 times in the transverse direction (TD) and relaxed 0.8 times. The film was cooled at room temperature to prepare a porous membrane having a thickness of 16 mu m.

Production Example 2

A porous membrane having a thickness of 16 μm was prepared in the same manner as in Preparation Example 1, except that the resin composition of Example 2 was used and liquid paraffin was extracted and removed for 12 minutes.

Production Example 3

A porous membrane having a thickness of 16 μm was prepared in the same manner as in Preparation Example 1, except that the resin composition of Example 3 was used and liquid paraffin was extracted and removed for 15 minutes.

Production Example 4

Of the resin composition of Example 4 230 ℃, screw rotation speed to the speed through the the casting roll temperature was 40 ℃ then a width of the discharge in the T-die 300mm in a twin-screw extruder under the conditions of 60rpm thickness 1,200 μ m basesheet . The base sheet was heated at 120 DEG C in a biaxial film stretching machine and then stretched 10 times at a rate of 50 mm / min in a longitudinal direction (MD), and stretched 10 times at 127 DEG C in a transverse direction (TD) at a rate of 50 mm / And stretched to prepare a stretched film.

The stretched film was impregnated into a dichloromethane leaching tank at 25 ° C to extract and remove liquid paraffin for 10 minutes. The film from which the liquid paraffin was removed was dried at room temperature while controlling the shrinkage ratio in the transverse and longitudinal directions to 9%, respectively. Thereafter, after heating at 120 ° C in a stretching machine, stretching was 1.35 times in the transverse direction (TD) and relaxed 0.8 times. The film was cooled at room temperature to prepare a porous separator having a thickness of 12 mu m.

Comparative Preparation Example 1

A porous separator having a thickness of 16 占 퐉 was prepared in the same manner as in Preparation Example 1, except that the resin composition of Comparative Example 1 was used.

Comparative Production Example 2

A porous separator having a thickness of 16 μm was prepared in the same manner as in Preparation Example 1, except that the resin composition of Comparative Example 2 was used.

Comparative Production Example 3

The porous separator was prepared in the same manner as in Preparation Example 1 except that the resin composition of Comparative Example 3 was used.

Comparative Production Example 4

The porous separator was prepared in the same manner as in Preparation Example 1 except that the resin composition of Comparative Example 4 was used. However, the separator was broken during the stretching of the base sheet.

Experimental Example 2

Test methods for the physical properties measured in the present invention are as follows. The temperature was measured at room temperature (25 ° C) unless otherwise noted.

- Thickness ( μ m): The thickness of the membrane sample was measured using a micro thickness meter.

- Gurley, sec / 100ml: Densometer of Asahi Seiko EGO2-5 model was used to measure the passage time of 100 ml of air through a separator membrane having a diameter of 29.8 mm at a measuring pressure of 0.025 MPa.

Porosity (%): The porosity of a membrane sample having a radius of 25 mm was measured using a Capillary Porometer manufactured by PMI, according to ASTM F316-03.

Pore Size (nm): The pore size of the membrane sample having a radius of 25 mm was measured using a Capillary Porometer manufactured by PMI, according to ASTM F316-03.

- Perforation strength (gf): Using a KES-G5 model of KATO TECH, a force of 0.05 cm / sec was applied to a separator sample having a size of 100 × 50 mm with a stick having a diameter of 0.5 mm, The force applied at the time of piercing was measured.

- Tensile Breaking Strength (kgf / cm ² ): The tensile fracture tester was used to measure the stress applied until the fracture of the 20 × 200 mm separation membrane specimen occurred.

Modulus (MPa): According to ASTM D882, a membrane specimen of size 20x200 mm was stretched at an elongation of 0 to 1% and the modulus measured.

Heat shrinkage percentage (%): A separator sample having a size of 200 mm × 200 mm in an oven at 120 ° C. for 1 hour was placed between A4 paper sheets, and then cooled at room temperature to measure the shrunk length of the specimen in the transverse and longitudinal directions The heat shrinkage was calculated using the formula.

(In the above equation, l ₁ is the length in the transverse or longitudinal direction of the specimen before shrinkage, and l ₂ is the length in the transverse or longitudinal direction of the specimen after shrinkage.

- Ionic conductivity (mS / cm): A separator specimen was inserted between two sheets of copper foil electrodes having a size of 52.0 × 45.5 mm and processed into a jelly roll shape. After the electrolyte was injected, the cell was sealed with an aluminum pouch. As the electrolyte solution, 0.85 g of 1.15 M LiPF 6 EC: EMC = 3: 7 (volume ratio) was used. The ion conductivity of the cell was measured five times under the conditions of a frequency of 10 ⁴ to 10 ⁶ Hz, a current of 10.0 mV and a voltage range of +/- 10 V using EPC (Electrochemical Impedance Spectroscopy), and the average value thereof was determined.

The physical properties of the membranes prepared according to the preparation examples and comparative preparation examples were measured and the results are shown in Table 1 (except for Comparative Preparation Examples 3 and 4 in which the membranes were not prepared). The pore size distributions of Production Example 1 and Comparative Production Examples 1 and 2 were measured and shown in Fig.

division Production Example 1 Production Example 2 Production Example 3 Production Example 4 Comparative Preparation Example 1 Comparative Production Example 2 Thickness ( μ m) 16.0 16.1 15.8 11.9 15.9 16.0 Air permeability (sec / 100ml) 211 174 143 209 242 223 Porosity (%) 40.6 44.2 47.0 37.8 40.5 40.1 Average pore size (nm) 40.7 40.1 40.8 42 38.2 41.2 Perforation strength (gf) 562 487 418 398 380 367 Tensile breaking strength
(kgf / cm ² ) 2,692 2,519 2,461 2,736 2,398 2,317 Modulus (MPa) 1,739 1,691 1,674 1,743 1,599 1,563 120 캜 Heat shrinkage (%) 5.8 6.5 6.3 6.9 7.9 8.8 Ion conductivity (mS / cm) 0.52 0.53 0.53 0.54 0.47 0.49

Referring to Table 1, the membranes of Preparative Examples 1 to 4 using liquid paraffin A had mechanical strengths such as puncture strength, tensile strength at break, and modulus as compared with the membranes of Comparative Preparation Examples 1 and 2 using liquid paraffin B and C . Compared with the membranes of Production Examples 1 to 4 having uniform microporous morphology, the membranes of Comparative Preparations 1 and 2 had perforations or fractures at the portions where the strength was lowered due to unevenly formed pores, The ionic conductivity of the membranes of Preparation Examples 1 to 4 was superior to that of Comparative Preparation Examples 1 and 2. This may be because the pores of the separation membrane, which is the passage through which the ions move, are uniformly formed in the separation membranes of Production Examples 1 to 4 as compared with Comparative Production Examples 1 and 2. [

In the case of the 120 ° C heat shrinkage, the separation membranes of Comparative Production Examples 1 and 2 were confirmed to have higher heat shrinkage rates than the separation membranes of Production Examples 1 to 4 due to contraction of uneven pores.

Referring to FIG. 3, it was confirmed that the separation membrane of Preparation Example 1 had a unimodal distribution with a pore size of about 40 nm. Further, it was confirmed that the pores having a size of 30 to 50 nm accounted for 90% or more of the total.

It was confirmed that the pore size distribution of Comparative Example 1 was wider than that of Preparation Example 1. It was confirmed that the pores having a size of 30 to 50 nm were less than 90% of the whole pores.

It was confirmed that the separation membrane of Comparative Production Example 2 exhibited a polymodal distribution with three peaks. It was confirmed that the pores having a size of 30 to 50 nm were less than 90% of the whole pores.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (10)

Polyolefin resins; And
And a liquid paraffin having a C ₃₀ to C ₅₀ alkylene chain content of 50 wt% or more. The method according to claim 1,
The polyolefin resin
A first polyolefin having a viscosity average molecular weight of 1,500,000 to 3,000,000; And
And a second polyolefin having a viscosity average molecular weight of 500,000 to 1,000,000. 3. The method of claim 2,
Wherein the weight ratio of the first polyolefin and the second polyolefin is 1 to 3: 7 to 9, respectively. The method according to claim 1,
Wherein the length of the alkylene chain is a single-pole type. The method according to claim 1,
Wherein the content of the C ₃₅ to C ₄₀ alkylene chain in the liquid paraffin is 50 wt% or more. The method according to claim 1,
The 5% distillation point of the liquid paraffin is 450 to 500 ° C. The method according to claim 1,
Wherein the liquid paraffin has a difference of an ultra-pure point and a kind point of 200 占 폚 or less. The method according to claim 1,
Wherein the liquid paraffin has a flash point of 250 DEG C or higher. The method according to claim 1,
Wherein the weight ratio of the polyolefin resin to the liquid paraffin is 1: 1.5 to 4, respectively. A porous separator produced using the resin composition for producing a porous membrane according to any one of claims 1 to 9, wherein the ratio of pores having pore sizes of 30 to 50 nm in the total pores is 80 to 100%.

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