KR20190059859A - A multi-layered porous separator and a method for manufacturing the same - Google Patents

Abstract

One aspect of the present invention provides a multilayer porous separation membrane, which comprises: a first layer comprising a polypropylene resin, a polymethylpentene resin, and polypropylene wax; and a second layer comprising ultra-high molecular weight polyethylene and high density polyethylene, wherein the second layer is formed on at least one surface of the first layer. The multilayer porous separation membrane according to one aspect of the present invention has a high membrane rupture temperature, and thus has excellent heat resistance.

Description

TECHNICAL FIELD [0001] The present invention relates to a multi-layer porous separator,

The present invention relates to a multi-layer porous separator, and more particularly, to a multi-layer porous separator composed of two or more layers of different compositions.

The porous separator, in particular, the polyolefin-based porous separator is used as a microfiltration membrane, a separator for a battery, a separator for a condenser, a material for a fuel cell and the like, and is particularly used as a separator for a lithium ion battery. In addition, recently, lithium ion batteries have been used for applications in small electronic devices such as cellular phones and notebook computers, while they are also being applied to hybrid electric vehicles and the like.

Here, a lithium ion battery used for a hybrid electric vehicle requires a higher output characteristic for taking out a large amount of energy in a short time. Further, lithium ion batteries used for hybrid electric vehicles are generally large and have a high energy capacity, so that it is required to secure higher safety. The safety referred to herein is safety against short circuit of the battery due to melting of the resin used as the separator, particularly at a high temperature occurring when the battery is used. Here, it is one of the means for improving the safety of the battery that the temperature at the time of occurrence of a short circuit in the battery is set to the tap film temperature of the separator and the tap film temperature is raised.

Japanese Patent Laid-Open Publication No. 05-251069 discloses a porous separator which is a separator capable of coping with such a situation. For example, Japanese Laid-Open Patent Publication No. 05-251069 discloses a composite separator having a structure in which a polypropylene porous separator is laminated on a conventional polyethylene porous separator A porous separator (battery separator) has been proposed.

Polypropylene is used in order to increase the short-circuit temperature. That is, the separator needs to maintain the film shape even at a high temperature to maintain insulation between the electrodes. However, the polypropylene resin used as the heat-resistant layer has insufficient heat resistance to harsh conditions such as the battery oven test conducted recently.

Japanese Patent Application Laid-Open No. 03-291848 discloses that a synthetic resin porous separator made of polyethylene is coated with a specific resin porous powder polymer to improve the stability at high temperature. However, the severe conditions such as battery oven test are insufficient did.

It is an object of the present invention to provide a multi-layer porous separator which does not tear at high temperature and has good heat resistance. It is another object of the present invention to provide a multi-layer porous separator having a high wave-film temperature and a good balance of porosity and air permeability.

One aspect of the present invention is a laminate comprising a first layer comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax; And a second layer comprising ultra high molecular weight polyethylene and high density polyethylene, wherein the second layer is formed on at least one side of the first layer.

In one embodiment, the polypropylene resin may have a melt index of 0.5 to 3 g / 10 min and a density of 0.95 to 0.96 g / cm ³ .

In one embodiment, the polymethylpentene resin may have a melt index of 20 to 200 g / 10 min and a density of 0.83 to 0.84 g / cm ³ .

In one embodiment, the polypropylene wax has a dropping point is 150 ~ 170 ℃, and a viscosity of 130 ~ 40 ℃ 230mPas, may be in a density of ³ 0.87 ~ 0.89g / cm.

In one embodiment, the ultra high molecular weight polyethylene may have a weight average molecular weight (M _w ) of 700,000 to 1,000,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and an average particle size of 100 to 150 μm.

In one embodiment, the high density polyethylene may have a weight average molecular weight (M _w ) of 300,000 to 500,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and a melt index of 0.4 to 0.6 g / 10 min .

In one embodiment, the weight ratio of the polypropylene resin, the polymethylpentene resin, and the polypropylene wax may be 50 to 70: 10 to 50: 5 to 10, respectively.

In one embodiment, the weight ratio of the ultra high molecular weight polyethylene to the high density polyethylene may be 70 to 90:10 to 30, respectively.

In one embodiment, the second layer thickness may be 1.5 to 3 times the first layer thickness.

In one embodiment, the separation membrane may satisfy at least one of the following conditions (i) to (vii):

(i) a thickness of 16 to 30 占 퐉; (ii) a porosity of 30 to 60%; (iii) a puncture strength of 100 to 400 gf; (iv) tensile strength of 1,000 to 2,000 kgf / cm ² ; (v) 1 hour heat shrinkage at 150 占 폚 of 30% or less; (vi) Shutdown temperature 13-140 ° C; (vii) meltdown temperature 160 to 170 占 폚.

Another aspect of the present invention relates to a method for producing a molded article, comprising: (a) co-extruding a second composition comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax, and a second composition comprising at least two polyethylenes and a pore- Producing a multilayer sheet; (b) extracting the pore-forming agent from the multilayer sheet; And (c) stretching the multi-layer sheet to produce a multi-layer porous separator.

Another aspect of the present invention relates to a method for producing a molded article, comprising: (a) co-extruding a second composition comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax, and a second composition comprising at least two polyethylenes and a pore- Producing a multilayer sheet; (b) stretching the multilayer sheet; And (c) extracting the pore-forming agent from the multi-layer sheet to produce a multi-layered porous separation membrane.

In another aspect of the present invention, there is provided a method for producing a molded article, comprising: (a) molding a first composition comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax, and a second composition comprising two or more kinds of polyethylene and a pore- Producing a first and a second sheet; (b) stretching the first sheet and extracting a pore former of the second sheet; And (c) laminating the first and second sheets to produce a multilayer sheet.

In one embodiment, the first composition is a polypropylene resin having a melt index of 0.5 to 3 g / 10 min and a density of 0.95 to 0.96 g / cm ³ , a melt index of 20 to 200 g / 10 min, a density of 0.83 to 0.84 g / cm < ³ >, and a polypropylene wax having a dropping point of 150 to 170 DEG C, a viscosity at 40 DEG C of 130 to 230 mPas, and a density of 0.87 to 0.89 g / cm < ³ >.

In one embodiment, the second composition is an ultra high molecular weight polyethylene having a weight average molecular weight (M _w ) of 700,000 to 1,000,000, a molecular weight distribution (M _w / M _n ) of 3 to 6 and an average particle size of 100 to 150 μm And a polyethylene having a weight average molecular weight (M _w ) of 300,000 to 500,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and a melt index of 0.4 to 0.6 g / 10 min.

In one embodiment, the first composition may include 50 to 70:10 to 50: 5 to 10 weight percent of polypropylene resin, polymethylpentene resin, and polypropylene wax, respectively.

In one embodiment, the second composition may include 70 to 90:10 to 30 weight percent of ultrahigh molecular weight polyethylene and high density polyethylene, respectively.

The multi-layered porous separator according to one aspect of the present invention has a high film temperature and is excellent in heat resistance and has a good balance of porosity and air permeability.

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.

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.

Whenever a range of numerical values is set forth herein, unless otherwise specified, the value has the precision of the significant digits provided in accordance with standard rules in chemistry for the significant digits. For example, 10 comprises the range of 5.0 to 14.9, and the number 10.0 includes the range of 9.50 to 10.49.

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

Multilayer porous membrane

A multilayer porous separator according to one aspect of the present invention comprises a first layer comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax; And a second layer comprising ultra high molecular weight polyethylene and high density polyethylene, wherein the second layer may be formed on at least one side of the first layer.

The separator may be formed by laminating a first layer comprising a polypropylene resin and a polymethylpentene resin and a second layer comprising a polyethylene resin to achieve a high porosity and mechanical properties.

The pores of the first layer may be formed by the interfacial peeling between the polypropylene resin and the polymethylpentene resin.

The pores of the second layer may be formed by a heat-induced phase separation phenomenon by a wet process, and may have a smaller diameter than the pores of the first layer.

As used herein, the term " melt down " or " membrane " refers to a phenomenon in which melts are generated in a separation membrane at a specific temperature or higher and a part of the membrane is broken. If such a phenomenon occurs, a fire or an explosion may occur due to a short-circuit in which the anode and the cathode of the secondary battery are connected. Accordingly, there is a need to improve the heat resistance of the separator.

The multi-layer porous separator comprising a conventional homopolypropylene resin layer designed to improve the heat resistance of the separator was manufactured by a dry process due to the characteristics of a polypropylene resin which can not form micropores by a wet process, Or more, and the manufacturing process is complicated. In addition, there are a number of drawbacks in the stretching process, such that the mechanical properties such as the tensile strength in the transverse direction (TD) are inferior and the heat shrinkage rate at high temperature is poor.

The first layer can further improve the heat resistance such as the stability of the high-temperature dimension of the separator, and can be relatively limited in the mechanical properties and the high-temperature heat shrinkage due to the restriction of the stretching process. By mixing the polymethylpentene resin with a polypropylene resin to prepare a separator, mechanical strength and heat resistance can be achieved in a harmonious manner. In particular, heat resistance such as high temperature stability can be greatly improved.

The polypropylene resin may have a melt index of 0.5 to 3 g / 10 min and a density of 0.95 to 0.96 g / cm ³ . The polymethylpentene resin may have a melt index of 20 to 200 g / 10 min and a density of 0.83 to 0.84 g / cm ³ . The polypropylene wax has a dropping point is 150 ~ 170 ℃, and a viscosity of 40 ℃ 130 ~ 230mPas, may be in a density of ³ 0.87 ~ 0.89g / cm. The physical properties of these are not necessarily limited to the above range.

The weight ratio of the polypropylene resin, the polymethylpentene resin, and the polypropylene wax may be 50 to 70:10 to 50: 5 to 10, respectively. If the composition is out of the above range, the mechanical strength and thermal stability of the separator may be deteriorated.

The second layer imparts a shutdown characteristic to the separator to improve the stability of the secondary battery. As used herein, the term " shutdown " refers to a characteristic in which a partial melting occurs in the separator at a certain temperature or more, thereby closing the pores. The short circuit in which the anode and the cathode of the secondary battery are directly connected by thermal deformation of the separator at a high temperature is a main cause of an explosion and a fire accident but can be prevented by shutdown.

The term " ultra-high molecular weight polyethylene (UHMWPE) " as used herein refers to polyethylene having a weight average molecular weight of 700,000 to 1,000,000 and higher molecular weight than that of high density polyethylene (HDPE) it means. The weight average molecular weight can be measured by a method suitably selected by a person skilled in the art, and an error may occur depending on the measuring method, but the object of the present invention can be achieved if the above range and error ratio are 10% or less.

The ultra high molecular weight polyethylene may have a weight average molecular weight (M _w ) of 700,000 to 1,000,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and an average particle size of 100 to 150 μm. The high density polyethylene may have a weight average molecular weight (M _w ) of 300,000 to 500,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and a melt index of 0.4 to 0.6 g / 10 min. The physical properties of these are not necessarily limited to the above range.

Generally, the wider the molecular weight distribution (M _w / M _n ), the lower the shear stress and the lower the viscosity, so the processability is improved but the physical properties are lowered. The narrower the molecular weight distribution, the lower the processability but the better the physical properties. Thus, even if two or more polymeric materials are kneaded and used in the form of a composition, physical properties and processability can not be harmonized if their molecular weight distributions are similar. Therefore, by mixing different ultra-high molecular weight polyethylene and high density polyethylene having different physical properties as described above, the physical properties and processability of the separation membrane can be realized more harmoniously.

The weight ratio of the ultrahigh molecular weight polyethylene and the high density polyethylene may be 70 to 90: 10 to 30, respectively. If the composition is out of the above range, the mechanical strength of the separator may be lowered and the workability may be lowered.

The thickness of the second layer may be 1.5 to 3 times the thickness of the first layer. For example, the multi-layered porous separator may be formed in the form of a second layer / first layer / second layer, and their thickness ratio may be 40/20/40. When the thickness condition is satisfied, the aforementioned shutdown characteristics and the heat resistance of the separator can be realized in a harmonious manner.

The separation membrane may satisfy at least one of the following conditions (i) to (vii):

(i) a thickness of 16 to 30 占 퐉; (ii) a porosity of 30 to 60%; (iii) a puncture strength of 100 to 400 gf; (iv) tensile strength of 1,000 to 2,000 kgf / cm ² ; (v) 1 hour heat shrinkage at 150 占 폚 of 30% or less; (vi) Shutdown temperature 13-140 ° C; (vii) meltdown temperature 160 to 170 占 폚.

Method of manufacturing multi-layer porous separator

In the following production method, the multilayer sheet is formed by alternately laminating the first and second layers described above. The first layer is made from a first composition and the second layer is made from a second composition.

A first method of producing a multilayer porous membrane according to another aspect of the present invention comprises: (a) a first composition comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax, and at least two polyethylenes and a pore former Co-extruding the second composition to form a multilayer sheet; (b) extracting the pore-forming agent from the multilayer sheet; And (c) stretching the multilayer sheet to produce a multilayer porous separator.

In step (b), micropores may be formed by extracting the pore-forming agent contained in the second layer. The pore-forming agent may be selected from the group consisting of paraffin oil, paraffin wax, mineral oil, solid paraffin, soybean oil, rapeseed oil, palm oil, palm oil, dihexylphthalate, dibutylphthalate, diisononylphthalate, diisodecylphthalate, Propylheptyl) phthalate, naphthene oil, and combinations of at least two of the foregoing, and the multilayer sheet may be selected from the group consisting of pentane, hexane, benzene, dichloromethane, carbon tetrachloride, methyl ethyl ketone, acetone, And the pore-forming agent may be extracted by immersing the pore-forming agent in an extraction tank having one selected from the group consisting of

The step (c) may be performed at a stretching ratio of 4 to 6 times in transverse direction (TD) and machine direction (MD) at 150 to 160 ° C, respectively. Through the stretching, peeling may occur at the interface between the polypropylene resin and the polymethylpentene resin of the first composition, and micropores may be formed. This is simpler than the formation of pores of a homopolypropylene separator essentially including 1) annealing through high temperature drying, 2) low temperature stretching, and 3) high temperature stretching, and uniform pore formation and higher porosity can be achieved.

A second method of producing a multilayer porous membrane according to another aspect of the present invention comprises the steps of: (a) providing a first composition comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax, and at least two polyethylenes and a pore former Co-extruding the second composition to form a multilayer sheet; (b) stretching the multilayer sheet; And (c) extracting the pore-forming agent from the multi-layer sheet to produce a multi-layer porous separator.

The step (b) may be the same as the step (c) of the first manufacturing method described above, and the step (c) may be the same as the step (b) of the second manufacturing method. However, if the surface layer of the multi-layered porous separation membrane is a second layer, the first production method is advantageous for forming pores, and if the surface layer of the multi-layered porous separation membrane is a first layer, the second production method may be more advantageous.

A third method for producing a multilayer porous membrane according to another aspect of the present invention comprises the steps of (a) mixing a first composition comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax and at least two polyethylenes and a pore former Forming a first and a second sheet by extruding and molding the second composition, respectively; (b) stretching the first sheet and extracting a pore former of the second sheet; And (c) laminating the first and second sheets to produce a multilayer sheet.

In the third manufacturing method, the micropores of each layer are first formed and then laminated to produce a multi-layer porous separator. The lamination of step (c) may be carried out using conventional techniques related to the manufacture of multilayer films such as a thermal fusion process.

Wherein the first composition is a melt index of 0.5 ~ 3g / 10min, a density of 0.95 ~ 0.96g / cm ³ of a polypropylene resin, a melt index of 20 ~ 200g / 10min and a density of 0.83 ~ 0.84g / cm ³ of poly methyl pentene resin, and a dropping point is 150 ~ 170 ℃, the viscosity is 40 ℃ 130 ~ 230mPas, may be configured with a density of 0.87 ~ 0.89g / cm ³ of polypropylene wax.

The second composition had a weight average molecular weight (M _w) is 700,000 ~ 1,000,000 and a molecular weight distribution (M _w / M _n) is 3-6, and the ultra high molecular weight polyethylene having a weight average molecular weight and average particle diameter of 100 ~ 150㎛ (M _w ) of 300,000 to 500,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and a melt index of 0.4 to 0.6 g / 10 min.

The first composition may contain 50 to 70:10 to 50: 5 to 10 parts by weight of polypropylene resin, polymethylpentene resin and polypropylene wax, respectively.

The second composition may include ultra high molecular weight polyethylene and high density polyethylene in a weight ratio of 70 to 90:10 to 30, respectively.

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.

Example 1

(1) Production of first sheet

A polypropylene resin having a melt index of 0.5 to 3 g / 10 min and a density of 0.95 to 0.96 g / cm ³ , a melt index of 20 to 200, a density of 0.83 to 0.84 g / cm ³ and a weight ratio of polypropylene wax having a drop point of 150 to 170 캜, a density of 0.87 to 0.89 g / cm ³ and a viscosity (40 캜) of 130 to 230 mPas, 100 parts by weight of a composition having a weight ratio of 70:10 to 50: 5 to 10 was mixed with 0.2 parts by weight of an antioxidant.

100 parts by weight of the obtained mixture was fed into a twin-screw extruder, melt-kneaded under the conditions of 230 to 250 占 폚, discharged into a T-die and sufficiently cooled on a cooling roll at 40 to 60 占 폚 while molding into a sheet form.

(2) Production of second sheet

The weight average molecular weight (M _w) is 700,000 ~ 1,000,000 and a molecular weight distribution (M _w / M _n) is 3-6, the average particle diameter of 100 ~ 150㎛ of ultra high molecular weight polyethylene having 70 to 90% by weight, and the weight-average molecular weight ( M _w) is 300,000 ~ 500,000, and the molecular weight distribution (M _w / M _n) is 3-6, and the oxide on the resin 100 parts by weight consisting of 10-30% by weight of high density polyethylene having a melt index of 0.4 ~ 0.6g / 10min And 0.2 parts by weight of an inhibitor.

30 parts by weight of the obtained mixture was fed into another twin-screw extruder of the same type as the above and 70 parts by weight of paraffin oil having a kinematic viscosity (40 DEG C) of 70 cSt was supplied from a side feeder of the twin-screw extruder, And then cooled in a cooling roll at 40 to 60 DEG C while being molded into a sheet form to obtain a second sheet.

(3) Preparation of 3-layer porous separator

A first sheet / a second sheet / a first sheet or a second sheet / a first sheet / a second sheet were laminated in this order and then heat-sealed to produce a multilayer sheet.

The multilayer sheet was stretched 4 to 6 times in the transverse direction (TD) and the longitudinal direction (MD) at 150 to 160 ° C to induce the interfacial peeling of the polypropylene resin and the polymethylpentene resin to form micropores. Thereafter, the multilayer sheet was immersed in an extraction tank containing methylene chloride to extract paraffin oil to form micropores.

The multilayer sheet was heated to 120 to 130 캜, stretched 1.2 to 1.5 times in the transverse direction (TD), and relaxed to 0.8 to 0.9 times to prepare a three-layer porous separator.

Example 2

(1) Preparation of first solution

A polypropylene resin having a melt index of 0.5 to 3 g / 10 min and a density of 0.95 to 0.96 g / cm ³ , a polymethylpentene resin having a melt index of 20 to 200 and a density of 0.83 to 0.84 g / cm ³ , Wherein the weight ratio of the polypropylene wax having a drop point of 150 to 170 캜 and a density of 0.87 to 0.89 g / cm ³ and a viscosity of 40 to 230 mPas is 50 to 70:10 to 50: 5 to 10, And 0.2 parts by weight of an antioxidant were mixed.

100 parts by weight of the obtained mixture was fed into a twin-screw extruder and melted and kneaded at 230 to 250 DEG C to prepare a first solution.

(2) Preparation of the second solution

The weight average molecular weight (M _w) is 700,000 ~ 1,000,000 and a molecular weight distribution (M _w / M _n) is 3-6, the average particle diameter of 100 ~ 150㎛ of ultra high molecular weight polyethylene having 70 to 90% by weight, and the weight-average molecular weight ( M _w) is 300,000 ~ 500,000, and the molecular weight distribution (M _w / M _n) is 3-6, and the oxide on the resin 100 parts by weight consisting of 10-30% by weight of high density polyethylene having a melt index of 0.4 ~ 0.6g / 10min And 0.2 parts by weight of an inhibitor.

30 parts by weight of the obtained mixture was fed into another twin-screw extruder of the same type as the above, and 70 parts by weight of paraffin oil having a kinetic viscosity of 70 cSt (at 40 占 폚) was fed from the side feeder of the twin-screw extruder. And kneaded to prepare a second solution.

(3) Preparation of 3-layer porous separator

The first and second solutions are fed from a twin screw extruder to a three-layer T die, and co-extruded in the order of the first solution / second solution / first solution or second solution / first solution / second solution The multilayer sheet of 500 to 3,000 mu m was sufficiently cooled on a cooling roll at 40 to 60 DEG C while molding.

The multilayer sheet was immersed in an extraction vessel containing methylene chloride to extract the paraffin oil to form micropores. The multilayer sheet was stretched 4-6 times in the transverse direction (TD) and the longitudinal direction (MD) at 150 to 160 ° C, The interfacial peeling phenomenon of the propylene resin and the polymethylpentene resin was induced to form micropores. Then, the multilayer sheet was heated to 120 to 130 ° C, stretched 1.2 to 1.5 times in the transverse direction (TD), and relaxed to 0.8 to 0.9 times to prepare a three-layer porous separator.

Comparative Example 1

(1) Production of first sheet

100 parts by weight of a polypropylene resin having a weight average molecular weight (M _w ) of 500,000 was mixed with 0.2 parts by weight of an antioxidant, and the mixture was melt-kneaded at 200 ° C and discharged into a T die, Lt; 0 > C to produce a first sheet.

The first sheet was annealed at 120 DEG C for 24 hours to grow the lamella (crystal part).

After sufficiently crystallized, the first sheet was stretched by 1.2 to 1.5 times at 25 캜 in the machine direction (MD). Thereafter, the first sheet was further stretched 2 to 3 times at 120 캜, and then annealed at 130 캜.

(2) Production of second sheet

The weight average molecular weight (M _w) is 700,000 ~ 1,000,000 and a molecular weight distribution (M _w / M _n) is 3-6, the average particle diameter of 100 ~ 150㎛ of ultra high molecular weight polyethylene having 70 to 90% by weight, and the weight-average molecular weight ( M _w) is 300,000 ~ 500,000, and the molecular weight distribution (M _w / M _n) is 3-6, and the oxide on the resin 100 parts by weight consisting of 10-30% by weight of high density polyethylene having a melt index of 0.4 ~ 0.6g / 10min And 0.2 parts by weight of an inhibitor.

30 parts by weight of the obtained mixture was fed into another twin-screw extruder of the same type as the above, and 70 parts by weight of paraffin oil having a kinetic viscosity of 70 cSt (at 40 占 폚) was fed from the side feeder of the twin-screw extruder. After the kneading, the sheet was discharged into a T-die and sufficiently cooled in a cooling roll at 40 to 60 DEG C while being molded into a sheet form to prepare a second sheet.

(3) Preparation of 3-layer porous separator

The first and second sheets were laminated in the order of the first sheet / the second sheet / the first sheet or the second sheet / the first sheet / the second sheet, and then heat-sealed to produce a multilayer sheet.

Comparative Example 2

(1) Production of first sheet

100 parts by weight of a polypropylene resin having a weight average molecular weight (M _w ) of 500,000 was mixed with 0.2 parts by weight of an antioxidant, and the mixture was melt-kneaded at 200 ° C and discharged into a T die, Lt; 0 > C to produce a first sheet.

The first sheet was annealed at 120 DEG C for 24 hours to grow the lamella (crystal part).

After sufficiently crystallized, the first sheet was stretched 1.2 to 1.5 times in the machine direction (MD) at 25 캜. Thereafter, the first sheet was stretched again at a temperature of 120 ° C in the transverse direction at 1.5 to 2 times. Thereafter, the first sheet was annealed at 130 캜, stretched at 120 캜 in the longitudinal direction (MD) by 1 to 2 times, and then annealed at 130 캜.

(2) Production of second sheet

The weight average molecular weight (M _w) is 700,000 ~ 1,000,000 and a molecular weight distribution (M _w / M _n) is 3-6, the average particle diameter of 100 ~ 150㎛ of ultra high molecular weight polyethylene having 70 to 90% by weight, and the weight-average molecular weight ( M _w) is 300,000 ~ 500,000, and the molecular weight distribution (M _w / M _n) is 3-6, and the oxide on the resin 100 parts by weight consisting of 10-30% by weight of high density polyethylene having a melt index of 0.4 ~ 0.6g / 10min And 0.2 parts by weight of an inhibitor.

30 parts by weight of the obtained mixture was fed into another twin-screw extruder of the same type as the above, and 70 parts by weight of paraffin oil having a kinetic viscosity of 70 cSt (at 40 占 폚) was fed from the side feeder of the twin-screw extruder. After the kneading, the sheet was discharged into a T-die and sufficiently cooled in a cooling roll at 40 to 60 DEG C while being molded into a sheet form to prepare a second sheet.

(3) Preparation of 3-layer porous separator

The first and second sheets were laminated in the order of the first sheet / the second sheet / the first sheet or the second sheet / the first sheet / the second sheet, and then heat-sealed to produce a multilayer sheet.

Experimental Example

Test methods for the physical properties measured in the present invention are as follows. Unless otherwise noted, temperature was measured at room temperature (25 캜).

- Melt Index (g / 10 min): Measured according to ASTM D1238 under conditions of 260 캜 and 5 kg.

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

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.

- 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 strength (kgf / cm ² ): A tensile strength meter was used to measure the stress applied to the specimen with a size of 20 × 200 mm until the fracture of the specimen occurred.

- Heat Shrinkage (%): A separator sample having a size of 200 mm × 200 mm in an oven at 150 ° C. for 1 hour was put in between A4 paper, 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 formula, 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.)

- Shutdown Temperature (占 폚): A lithium ion secondary battery manufactured by using the porous separator of the present invention is heated in an oven at a rate of 2 占 폚 / min while a resistance is measured in real time and a temperature at a point exceeding 10,000? Respectively.

- Melting-down temperature (占 폚): The temperature at the time point when the resistance rapidly decreased after the shutdown temperature was set as the melting down temperature.

The properties of the membranes prepared according to the above Examples and Comparative Examples were measured and the results are shown in Table 1 below.

Referring to Table 1, it can be confirmed that the separator of the embodiment including the layer composed of the polypropylene resin and the polymethylpentene resin is superior in mechanical properties to the separator of the comparative example including the layer composed of the homopolypropylene resin. Particularly, it can be confirmed that the porosity is remarkably excellent.

This is because, compared to the comparative example in which micropores are formed by a complicated process including annealing using a polypropylene resin, the examples using the polypropylene resin and the polymethylpentene resin have easily formed micropores due to the interfacial peeling between the resins . In addition, since the annealing is unnecessary and the process is simple, productivity and economy are also excellent.

The separation membrane of Comparative Example was hard to increase the stretching ratio, and thus the dimensional stability at high temperature was significantly inferior to that of the separator of Example. It can be confirmed at 150 ℃ heat shrinkage and meltdown temperature.

Since the shutdown temperature is due to the layer composed of the polyethylene resin, the shutdown function was exhibited at similar temperatures in both of the separators of Examples and Comparative Examples.

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 (17)

A first layer comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax; And
A second layer comprising ultra high molecular weight polyethylene and high density polyethylene,
And the second layer is formed on at least one surface of the first layer. The method according to claim 1,
The polypropylene resin has a melt index of 0.5 to 3 g / 10 min and a density of 0.95 to 0.96 g / cm ³ . The method according to claim 1,
Wherein the polymethylpentene resin has a melt index of 20 to 200 g / 10 min and a density of 0.83 to 0.84 g / cm ³ . The method according to claim 1,
The polypropylene wax has a dropping point is 150 ~ 170 ℃, and a viscosity of 130 ~ 230mPas 40 ℃, a density of 0.87 ~ 0.89g / cm ³ is, the multi-layer porous membrane. The method according to claim 1,
Wherein the ultra high molecular weight polyethylene has a weight average molecular weight (M _w ) of 700,000 to 1,000,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and an average particle size of 100 to 150 μm. The method according to claim 1,
Wherein the high density polyethylene has a weight average molecular weight (M _w ) of 300,000 to 500,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and a melt index of 0.4 to 0.6 g / 10 min. The method according to claim 1,
Wherein the weight ratio of the polypropylene resin, the polymethylpentene resin, and the polypropylene wax is 50 to 70:10 to 50: 5 to 10, respectively. The method according to claim 1,
Wherein the weight ratio of the ultrahigh molecular weight polyethylene to the high density polyethylene is 70 to 90: 10 to 30, respectively. The method according to claim 1,
Wherein the second layer thickness is 1.5 to 3 times the first layer thickness. The method according to claim 1,
Wherein the separation membrane comprises at least one of the following conditions (i) to (vii):
(i) a thickness of 16 to 30 占 퐉;
(ii) a porosity of 30 to 60%;
(iii) a puncture strength of 100 to 400 gf;
(iv) tensile strength of 1,000 to 2,000 kgf / cm ² ;
(v) 1 hour heat shrinkage at 150 占 폚 of 30% or less;
(vi) Shutdown temperature 13-140 ° C;
(vii) meltdown temperature 160 to 170 占 폚. (a) co-extruding a second composition comprising a polypropylene resin, a polymethylpentene resin, and a polypropylene wax, and a second composition comprising at least two types of polyethylene and a pore-forming agent, followed by molding to form a multilayer sheet;
(b) extracting the pore-forming agent from the multilayer sheet; And
(c) stretching the multilayer sheet to produce a multilayer porous separator. (a) co-extruding a second composition comprising a polypropylene resin, a polymethylpentene resin, and a polypropylene wax, and a second composition comprising at least two types of polyethylene and a pore-forming agent, followed by molding to form a multilayer sheet;
(b) stretching the multilayer sheet; And
(c) extracting the pore-forming agent from the multi-layer sheet to produce a multi-layer porous separator. (a) a first composition comprising a polypropylene resin, a polymethylpentene resin and a polypropylene wax, and a second composition comprising at least two kinds of polyethylene and a pore-forming agent, ;
(b) stretching the first sheet and extracting a pore former of the second sheet; And
(c) laminating the first and second sheets to produce a multilayer sheet. The method according to any one of claims 11 to 13,
Wherein the first composition is a melt index of 0.5 ~ 3g / 10min, a density of 0.95 ~ 0.96g / cm ³ of a polypropylene resin, a melt index of 20 ~ 200g / 10min and a density of 0.83 ~ 0.84g / cm ³ of poly polymethylpentene resin and dropping point is 150 ~ 170 ℃, and a viscosity of 130 ~ 230mPas 40 ℃, the density is composed of 0.87 ~ 0.89g / cm ³ of polypropylene wax, a method of producing a multi-layer porous membrane. The method according to any one of claims 11 to 13,
The second composition had a weight average molecular weight (M _w) is 700,000 ~ 1,000,000 and a molecular weight distribution (M _w / M _n) is 3-6, and the ultra high molecular weight polyethylene having a weight average molecular weight and average particle diameter of 100 ~ 150㎛ (M _w ) of 300,000 to 500,000, a molecular weight distribution (M _w / M _n ) of 3 to 6, and a melt index of 0.4 to 0.6 g / 10 min. The method according to any one of claims 11 to 13,
Wherein the first composition comprises a polypropylene resin, a polymethylpentene resin, and a polypropylene wax in a weight ratio of 50 to 70:10 to 50: 5 to 10, respectively. The method according to any one of claims 11 to 13,
Wherein the second composition comprises ultra high molecular weight polyethylene and high density polyethylene in a weight ratio of 70 to 90: 10 to 30, respectively.