KR102064867B1 - A porous separator and a method for manufacturing the same - Google Patents

Abstract

One aspect of the present invention, the ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 700,000 ~ 1,000,000, molecular weight distribution (M _w / M _n ) of 3 to 6, the average particle diameter of 100 ~ 150㎛; And a polypropylene block 30 to 70% by weight and a polyethylene block 30 to 70% by weight, and a melt index of 0.5 to 30 polypropylene / polyethylene block copolymer.

Description

Porous separator and method for manufacturing the same {A POROUS SEPARATOR AND A METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a porous separator and a method of manufacturing the same.

Porous separators, in particular polyolefin-based porous separators, are used in microfiltration membranes, battery separators, capacitor separators, fuel cell materials and the like, and are particularly used as separators for lithium ion batteries. In recent years, lithium ion batteries have been used for small electronic devices such as mobile phones and notebook computers, and are also being applied to hybrid electric vehicles.

Here, the lithium ion battery used for hybrid electric vehicle use requires higher output characteristics for extracting a lot of energy in a short time. In addition, lithium ion batteries used for hybrid electric vehicle applications are generally large in size and have high energy capacity, and thus higher safety is required. The safety here refers to safety against battery short circuit (short) due to melting of the resin used in the separator, especially in the high temperature state generated when the battery is used. Here, one of the means for improving the safety of the battery is to set the temperature when a short occurs inside the battery as the membrane temperature of the separator, and to increase the membrane temperature.

In addition, Japanese Patent Application Laid-Open No. 05-251069 discloses a composite having a structure in which a polypropylene porous separator is laminated on a conventional polyethylene porous separator for the purpose of providing a porous separator that becomes a separator capable of coping with such a situation. Porous separators (cell separators) have been proposed.

Polypropylene is used to increase the short temperature. That is, the separator needs to maintain the film shape even at a high temperature to maintain insulation between the electrodes. However, as polypropylene resin used as a heat resistant layer, heat resistance was inadequate about the severe conditions, such as the battery oven test currently performed.

In addition, in Japanese Patent Laid-Open No. 03-291848, a specific resin porous powder polymer is coated on a polyethylene porous resin membrane made of polyethylene, thereby improving stability at high temperatures. However, heat resistance is also insufficient for harsh conditions such as the battery oven test. did.

Another problem of the polypropylene porous separator is that it is difficult to produce a porous separator using a wet process. In general, the wet process kneads and forms a pore-forming agent such as dioctylphthalate and paraffin oil with a resin, and then forms micropores using thermally induced phase separation, and ketone, xylene or methylene chloride. The porous membrane is prepared by removing it from the extraction tank in which the back is supported. However, the above-mentioned pore-forming agent merely functions as a plasticizer in polypropylene, and liquid-liquid phase separation does not occur, which makes it difficult to manufacture a porous separator using such a wet process.

The present invention is to solve the above-mentioned problems of the prior art, an object of the present invention is to provide a porous separator and a method of manufacturing the same, which does not tear well at high temperatures and has good heat resistance. It is also an object of the present invention to provide a porous membrane having a high rupture temperature and a good balance of porosity and air permeability and a method of manufacturing the same.

One aspect of the present invention, the ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 700,000 ~ 1,000,000, molecular weight distribution (M _w / M _n ) of 3 to 6, the average particle diameter of 100 ~ 150㎛; And a polypropylene block made of 30 to 70% by weight of polypropylene block and 30 to 70% by weight of polyethylene block, and having a melt index (Melt index, MI) of 0.5 to 30; and a polypropylene / polyethylene block copolymer. do.

In one embodiment, the average particle diameter of the polypropylene / polyethylene block copolymer may be 100 ~ 200㎛.

In one embodiment, the weight ratio of the ultra high molecular weight polyethylene and the polypropylene / polyethylene block copolymer may be 70 ~ 90: 10 ~ 30, respectively.

In one embodiment, the separation membrane may have a weight average molecular weight (M _w ) of 10,000 to 500,000, polypropylene having an average particle diameter of 100 ~ 200㎛; may further include.

In one embodiment, the weight ratio of the ultra high molecular weight polyethylene, the polypropylene / polyethylene block copolymer and the polypropylene may be 60 to 80: 10 to 30: 10 to 20, respectively.

In one embodiment, the separation membrane may satisfy one or more of the following conditions (i) to (vii): (i) 10 to 20㎛ thickness; (ii) porosity 35-50%; (iii) puncture strength 150-300 gf; (iv) tensile strength 1,500 ~ 2,500kgf / cm ² ; (v) 1 hour thermal shrinkage of 15% or less at 130 ° C; (vi) shutdown temperature 130-140 ° C .; (vii) Meltdown temperature 160-170 degreeC.

Another aspect of the present invention, the method comprising the steps of (a) injecting a composition comprising an ultra high molecular weight polyethylene, polypropylene / polyethylene block copolymer and a pore-forming agent into the extruder and forming and stretching in sheet form; And (b) extracting a pore-forming agent from the stretched sheet to prepare a separator.

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

In one embodiment, the polypropylene / polyethylene block copolymer is made of 30 to 70% by weight of polypropylene block and 30 to 70% by weight of polyethylene block, the melt index is 0.5 to 30, the average particle diameter is 100 ~ 200㎛ Can be.

In one embodiment, the composition may further comprise polypropylene.

In one embodiment, the polypropylene may have a weight average molecular weight (M _w ) of 10,000 to 500,000, the average particle diameter of 100 ~ 200㎛.

In one embodiment, the weight ratio of the ultra high molecular weight polyethylene and the polypropylene / polyethylene block copolymer may be 70 ~ 90: 10 ~ 30, respectively.

In one embodiment, the weight ratio of the ultra high molecular weight polyethylene, the polypropylene / polyethylene block copolymer and the polypropylene may be 60 to 80: 10 to 30: 10 to 20, respectively.

In one embodiment, the weight ratio of the pore-forming agent and the polyolefin-based resin in the composition may be 50 to 70: 30 to 50, respectively.

In one embodiment, the pore-forming agent is paraffin oil, paraffin wax, mineral oil, solid paraffin, soybean oil, rapeseed oil, palm oil, palm oil, di-2-ethylhexyl phthalate, dibutyl phthalate, diisononyl phthalate, diisodecyl Phthalate, bis (2-propylheptyl) phthalate, naphthenoyl and combinations of two or more thereof.

In one embodiment, the stretching may be performed at a stretching ratio of 16 to 100 times at 110 ~ 130 ℃.

In one embodiment, after the step (b) (c) after stretching 1.2 to 1.5 times at 120 ~ 130 ℃ stretch to 0.8 to 0.9 times; further processing; may further comprise a.

The porous membrane according to an aspect of the present invention has a high membrane temperature, excellent heat resistance, and good balance of porosity and air permeability.

It is to be understood that the effects of the present invention are not limited to the above effects, and include all effects deduced from the configuration of the invention described in the detailed description or claims of the present invention.

Hereinafter, with reference to the accompanying drawings will be described the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, it includes not only "directly connected" but also "indirectly connected" with another member in between. . In addition, when a part is said to "include" a certain component, this means that it may further include other components, without excluding the other components unless otherwise stated.

When a range of numerical values is described herein, those values have the precision of the significant digits provided according to standard rules in chemistry for significant digits unless otherwise specified. For example, 10 includes 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.

Porous membrane

The porous membrane according to an aspect of the present invention, the ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 700,000 ~ 1,000,000, molecular weight distribution (M _w / M _n ) of 3 to 6, the average particle diameter of 100 ~ 150㎛ ; And a polypropylene block 30 to 70% by weight and a polyethylene block 30 to 70% by weight, and a melt index of 0.5 to 30 polypropylene / polyethylene block copolymer.

In the present specification, "Ultra-high molecular weight polyethylene (UHMWPE)" is a weight average molecular weight of 700,000 to 1,000,000 in polyethylene, which has a higher molecular weight than that generally used high density polyethylene (HDPE) it means. The weight average molecular weight can be measured by a method appropriately selected by a person skilled in the art, and an error may occur depending on the measuring method, but the above range and error rate may be 10% or less to achieve the object of the present invention.

If the weight average molecular weight of the polyethylene is less than 700,000 it is difficult to achieve the desired mechanical properties, if the weight average molecular weight of more than 1,000,000 compatibility with the block copolymer is lowered it may be difficult to produce a separator having a uniform characteristic.

In general, the wider the molecular weight distribution (M _w / M _n ), the shear stress is reduced and the viscosity is lower, so that the workability is improved, but the physical properties are lowered, the narrower the molecular weight distribution is lowered, but the physical properties are improved. As such, even when two or more polymer materials are kneaded and used in the form of a composition, physical properties and processability may not be harmoniously implemented when the molecular weight distribution is similar. Therefore, by mixing different ultra high molecular weight polyethylene and polypropylene / polyethylene block copolymers having different physical properties as described above, physical properties and processability of the porous membrane can be more harmonized.

As used herein, “shutdown” refers to a characteristic in which some melting occurs in the separator above a specific temperature to close pores. Shutdown may improve the stability of the secondary battery at high temperatures.

As used herein, the term “meltdown” or “breaking” refers to a phenomenon in which part of the membrane is broken due to melting occurring in the separator at a specific temperature or more. When this phenomenon occurs, an accident such as a fire or explosion may occur due to a short-circuit between the cathode and the anode of the secondary battery.

Dimensional stability at high temperature is one of the important factors that determine the stability of the membrane. In order to improve the performance, there have been attempts to manufacture a separator using polypropylene, but due to the nature of polypropylene, thermal induction phase separation using a pore-forming agent is impossible, making it difficult to apply a wet process and preventing a short circuit of a secondary battery. There is no shutdown characteristic, there is a disadvantage that does not achieve the desired physical properties sufficiently and the manufacturing cost is high.

There have also been attempts to improve heat resistance by producing a separator by partially kneading polypropylene based on a polyethylene-based resin, but due to poor compatibility between polyethylene and polypropylene, polypropylene is concentrated in some regions, and as a result, plasticization of the whole membrane There is a disadvantage that the tensile strength is lowered. In addition, due to the low dispersibility, an orange peel phenomenon occurs in which unevenness occurs on the surface of the separator prepared by agglomeration of the resin, and micropore formation through a wet process is difficult, resulting in poor porosity.

On the other hand, the porous membrane of the present invention can solve the above problems by including ultra high molecular weight polyethylene and polypropylene / polyethylene block copolymer. Specifically, the polyethylene block of the block copolymer significantly improves the compatibility with the ultra high molecular weight polyethylene can produce a separator having a uniform property, it is possible to prevent a decrease in physical strength due to plasticization.

The average particle diameter of the ultra high molecular weight polyethylene is 100 ~ 150㎛, the average particle diameter of the polypropylene / polyethylene block copolymer may be 100 ~ 200㎛. By using a mixture of resins having a similar average particle size to each other, compatibility may be further improved, and mechanical properties of the separator may be improved. If the average particle diameter of the ultrahigh molecular weight polyethylene or the block copolymer is less than 100 μm, micropore formation may be reduced.

The polypropylene / polyethylene block copolymer may be composed of 30 to 70% by weight of polypropylene block and 30 to 70% by weight of polyethylene block, the melt index may be 0.5 to 30, preferably, 0.5 to 3.

By using the block copolymer, a separator having more excellent physical strength can be manufactured. In addition, unlike the polypropylene, it is easy to form micropores using the thermal induction phase transition method, it may be easy to manufacture a porous membrane. Unlike a random copolymer or a single copolymer, the block copolymer may form a homogeneous phase at a high temperature to be easily kneaded with the ultrahigh molecular weight polyethylene, and may form a fine structure at a low temperature, thereby realizing excellent physical strength. This property can be remarkable within the content and melt index of the block.

The melt index (g / 10 min) may be measured according to ASTM D1238 under test conditions of 190 ° C. and 21.6 kg.

The weight ratio of the ultrahigh molecular weight polyethylene and the polypropylene / polyethylene block copolymer may be 70 to 90: 10 to 30, respectively. When the weight ratio of the ultra high molecular weight polyethylene is less than 70, the mechanical properties of the separator may be lowered, and if it is more than 90, the heat resistance may be lowered.

The separator may include a polypropylene having a weight average molecular weight (M _w ) of 10,000 to 500,000 and an average particle diameter of 100 to 200 μm. Due to the compatibility improvement effect of the block copolymer, the above-mentioned problem may be solved even by further including polypropylene. When the polypropylene is further included, heat resistance of the separator may be further improved.

The ultra-high molecular weight polyethylene, the polypropylene / polyethylene block copolymer and the weight ratio of the polypropylene may be 60 to 80: 10 to 30: 10 to 20, respectively.

The separator may satisfy one or more of the following conditions (i) to (vii): (i) a thickness of 10-20 μm; (ii) porosity 35-50%; (iii) puncture strength 150-300 gf; (iv) tensile strength 1,500 ~ 2,500kgf / cm ² ; (v) 1 hour thermal shrinkage of 15% or less at 130 ° C; (vi) shutdown temperature 130-140 ° C .; (vii) Meltdown temperature 160-170 degreeC.

Manufacturing method of porous separator

Method for producing a porous membrane according to another aspect of the present invention, (a) a composition comprising an ultra-high molecular weight polyethylene, polypropylene / polyethylene block copolymer and a pore-forming agent into the extruder and forming in a sheet form (Casting) and Orienting; And (b) extracting a pore-forming agent from the stretched sheet to prepare a separator.

The composition may further comprise polypropylene.

The properties, content, and properties of the separator of the ultrahigh molecular weight polyethylene, polypropylene / polyethylene block copolymer and polypropylene are the same as described above.

In the step (a), the base sheet may be prepared by extruding a composition including ultra high molecular weight polyethylene, a polypropylene / polyethylene block copolymer, and a pore-forming agent at 200 to 230 ° C., discharging it through a T-die, and stretching. . In this case, the polyethylene and the block copolymer may be excellent in compatibility and easy to process.

The weight ratio of the pore-forming agent and the polyolefin-based resin in the composition may be 50 to 70: 30 to 50, respectively. The polyolefin-based resin was used to include all ultra high molecular weight polyethylene, polypropylene / polyethylene block copolymer and polypropylene. If the weight ratio of the pore-forming agent is less than 50, the processability of the separator may be poor, and if it is more than 70, the mechanical strength of the prepared separator may be lowered.

The pore-forming agent is paraffin oil, paraffin wax, mineral oil, solid paraffin, soybean oil, rapeseed oil, palm oil, palm oil, di-2-ethylhexyl phthalate, dibutyl phthalate, diisononyl phthalate, diisodecyl phthalate, bis (2- Propylheptyl) phthalate, naphthene oil and one selected from the group consisting of two or more thereof, preferably paraffin oil, but are not limited thereto.

In the step (a), the molding may be performed at 80 to 100 rpm using a casting roll having a surface temperature of 25 to 40 ° C. Thermally induced phase separation by the pore-forming agent may occur during molding to form micropores of the separator.

In the step (a), the stretching may be performed by a known method such as uniaxial stretching or biaxial stretching (sequential or simultaneous biaxial stretching). In the case of successive biaxial stretching, the draw ratio may be 4 to 10 times in the longitudinal direction (Machine direction, MD) and the transverse direction (TD), respectively, and the draw ratio may be 16 to 100 times. In addition, in the case of sequential biaxial stretching may be performed at 110 ~ 130 ℃ in the longitudinal direction, it may be performed at 120 ~ 130 ℃ in the horizontal direction.

The extraction of step (b) may be performed in an extraction tank in which a solvent capable of extracting the pore forming agent is loaded. The solvent may be one 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 shrinkage of the sheet occurs as the pore-forming agent is removed in the step (b), it is necessary to minimize the longitudinal and transverse shrinkage of the sheet after extraction. By giving and maintaining the tension (Tension) acting in the opposite direction of the shrinkage stress generated after the extraction of the pore-forming agent to the sheet can control the longitudinal and transverse shrinkage in the range of 6 to 13% than the base sheet before extraction, respectively And, preferably, it can be controlled in the range of 8 to 10%.

After the step (b) (c) 1.2 to 1.5 times stretched at 120 ~ 130 ℃ after shrinking to 0.8 ~ 0.9 times after the step; may further comprise a. Through the post-treatment process it is possible to further improve the high temperature dimensional stability of the separator.

Hereinafter, embodiments of the present invention will be described in more detail. However, the following experimental results are described only representative experimental results of the above embodiments, the scope and content of the present invention by the examples and the like can not be interpreted to be reduced or limited. The effects of each of the various embodiments of the invention, which are not explicitly set forth below, will be described in detail in that section.

Example 1

Ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 700,000 to 1,000,000, a molecular weight distribution (Mw / Mn) of 3 to 6, and an average particle diameter of 100 to 150 μm; Polypropylene having a weight average molecular weight (M _w ) of 10,000 to 500,000 and an average particle diameter of 100 to 200 μm; A polypropylene / polyethylene block copolymer composed of 30 to 70% by weight of polypropylene block and 30 to 70% by weight of polyethylene block, and having a melt index (Melt index, MI) of 0.5 to 30; Paraffin oil having a kinematic viscosity of 70 cSt (based on 40 ° C.); And an antioxidant; after kneading in a twin screw extruder, forming a base sheet having a thickness of 500 to 3,000 μm in a twin screw extruder (200 to 230 ° C.) having a T-die of 350 mm width, It cooled enough to a cooling roll. The mixing ratio (weight) of the resin and paraffin oil during the kneading was adjusted in the range of 20:80 to 40:60.

The cooled sheet was fixed in both MD / TD directions to prepare a porous sheet by extracting and removing paraffin oil contained in the sheet 100% using methylene chloride.

The porous sheet was stretched 5 to 10 times in both MD and TD in a sequential biaxial stretching machine heated to 110 to 130 ° C., and then heat-set in a hot air oven at 120 to 130 ° C. to prepare a porous separator.

Example 2

85 weight parts of ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 750,000, a molecular weight distribution (M _w / M _n ) of 4, and an average particle diameter of 100 to 150 µm; 15 parts by weight of a block copolymer composed of 30% by weight of polypropylene and 70% by weight of polyethylene having a density of 0.95 to 096, a melt index of 2 and an average particle diameter of 100 to 200 µm; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm in internal diameter, L / D = 52, Twin screw extruder). The base sheet was manufactured by discharging a T-die from the twin screw extruder under a condition of 200 ° C. and a screw rotation speed of 80 rpm, and then passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 4 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Example 3

80 weight parts of ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 850,000, a molecular weight distribution (M _w / M _n ) of 4, and an average particle diameter of 100 to 150 µm; 20 parts by weight of a block copolymer composed of 40% by weight of polypropylene and 60% by weight of polyethylene having a density of 0.95 to 096 and a melt index of 2 and an average particle diameter of 100 to 200 µm; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 210 ° C. and a screw rotational speed of 90 rpm and passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 3 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Example 4

75 weight parts of ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 950,000, a molecular weight distribution (M _w / M _n ) of 5, and an average particle diameter of 100 to 150 µm; 25 parts by weight of a block copolymer composed of 50% by weight of polypropylene and 50% by weight of polyethylene having a density of 0.95 to 096, a melt index of 2 and an average particle diameter of 100 to 200 µm; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 220 ° C. and a screw rotational speed of 100 rpm and then passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 2 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Example 5

80 parts by weight of ultra high molecular weight polyethylene having a weight average molecular weight (M _w ) of 800,000, a molecular weight distribution (M _w / M _n ) of 4, and an average particle diameter of 100 to 150 µm; 20 parts by weight of a block copolymer composed of 60% by weight of polypropylene and 40% by weight of polyethylene having a density of 0.95 to 096, a melt index of 2 and an average particle diameter of 100 to 200 µm; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 220 ° C. and a screw rotational speed of 100 rpm and then passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 3 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Example 6

80 parts by weight of ultra high molecular weight polyethylene having a weight average molecular weight (M _w ) of 800,000, a molecular weight distribution (M _w / M _n ) of 4, and an average particle diameter of 100 to 150 µm; 20 parts by weight of a block copolymer composed of 70% by weight of polypropylene and 30% by weight of polyethylene having a density of 0.95 to 096, a melt index of 2 and an average particle diameter of 100 to 200 µm; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 230 ° C. and a screw rotational speed of 100 rpm, and then passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 3 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Example 7

70 parts by weight of ultra high molecular weight polyethylene having a weight average molecular weight (M _w ) of 800,000, a molecular weight distribution (M _w / M _n ) of 4 and an average particle diameter of 100 to 150 μm; 20 parts by weight of a block copolymer composed of 50% by weight of polypropylene and 50% by weight of polyethylene having a density of 0.95 to 096, a melt index of 2 and an average particle diameter of 100 to 200 µm; 10 parts by weight of polypropylene having an average particle diameter of 100 to 200 µm; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 230 ° C. and a screw rotational speed of 100 rpm, and then passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 3 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Example 8

60 parts by weight of ultra high molecular weight polyethylene having a weight average molecular weight (M _w ) of 800,000, a molecular weight distribution (M _w / M _n ) of 4, and an average particle diameter of 100 to 150 μm; 20 parts by weight of a block copolymer composed of 60% by weight of polypropylene and 40% by weight of polyethylene having a density of 0.95 to 096, a melt index of 2 and an average particle diameter of 100 to 200 µm; 20 parts by weight of polypropylene having an average particle diameter of 100 to 200 µm; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 230 ° C. and a screw rotational speed of 100 rpm, and then passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 3 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Comparative Example 1

85 weight parts of ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 850,000, a molecular weight distribution (M _w / M _n ) of 4, and an average particle diameter of 100 to 150 µm; 15 parts by weight of polypropylene having a melting point of 160 to 165 ° C and a melt index of 7.5; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 210 ° C. and a screw rotational speed of 90 rpm and passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 3 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Comparative Example 2

80 weight parts of ultra-high molecular weight polyethylene having a weight average molecular weight (M _w ) of 850,000, a molecular weight distribution (M _w / M _n ) of 4, and an average particle diameter of 100 to 150 µm; 20 parts by weight of polypropylene having a melting point of 160 to 165 ° C and a melt index of 7.5; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 210 ° C. and a screw rotational speed of 90 rpm and passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 3 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Comparative Example 3

70 parts by weight of ultra high molecular weight polyethylene having a weight average molecular weight (M _w ) of 850,000, a molecular weight distribution (M _w / M _n ) of 4 and an average particle diameter of 100 to 150 μm; 30 parts by weight of polypropylene having a melting point of 160 to 165 ° C and a melt index of 7.5; 0.5 part by weight of antioxidant; And 150 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40 ° C. were added to a twin screw extruder (45 mm inside diameter, L / D = 52). The base sheet was manufactured by discharging a T-die from the biaxial extruder under a condition of 210 ° C. and a screw rotational speed of 90 rpm and passing a casting roll having a temperature of 30 ° C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a roll stretching machine at 120 ° C., and stretched 7 times in the transverse direction (TD) in a tenter stretching machine at 125 ° C. to prepare a stretched film. The stretched film was impregnated in a dichloromethane leaching tank at 25 ° C. to extract and remove paraffin oil for 3 minutes. The porous film from which paraffin oil was removed was dried for 3 minutes. Subsequently, after heating to 125 ° C. in a tenter drawing machine, the film was stretched to 1.35 times in the transverse direction (TD), relaxed, and heat-set to 0.85 times to prepare a porous separator having a thickness of 16 μm.

Experimental Example

Test methods for each of the physical properties measured in the present invention are as follows. Unless otherwise stated, the temperature was measured at room temperature (25 ° C.).

Melt Index (g / 10min): Measured according to ASTM D1238.

Thickness ( μm ): The thickness of the membrane specimen was measured using a micro thickness meter.

-Porosity (%): According to ASTM F316-03, the porosity of the membrane specimen with a radius of 25 mm was measured using a Capillary Porometer, PMI.

-Puncture strength (gf): Using a punching strength gauge KES-G5 model of KATO TECH Co., Ltd., a force of 0.05 cm / sec was applied to a membrane specimen of size 100 × 50 mm with a stick of 0.5 mm diameter. The force applied at the time the specimen was pierced was measured.

Tensile strength (kgf / cm ² ): A tensile strength tester was applied to the membrane specimen of size 20 × 200 mm to measure the stress applied until fracture of the specimen occurred.

-Heat shrinkage rate (%): After placing the separator specimen of size 200 × 200mm in A4 paper for 1 hour in an oven at 130 ° C., and then cooling it at room temperature to measure the contracted length of the specimen in the horizontal and vertical directions. The heat shrinkage rate was calculated using the formula.

(In the above formula, l ₁ is the transverse or longitudinal length of the specimen before contraction and l ₂ is the transverse or longitudinal length of the specimen after contraction.)

-Shutdown temperature (℃): The lithium ion secondary battery manufactured using the porous separator of the present invention is heated in an oven at a rate of 2 ℃ / min while measuring the resistance in real time to the temperature of more than 10,000Ω to the shutdown temperature It was.

Meltdown temperature (° C.): The temperature at which the resistance suddenly drops after the shutdown temperature was defined as the meltdown temperature.

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

Referring to Table 1, it can be seen that the separator of the embodiment including the ultra high molecular weight polyethylene and the polypropylene-polyethylene block copolymer has superior physical properties as compared to the separator of the comparative example including the ultra high molecular weight polyethylene and the polypropylene. In particular, it can be seen that the dimensional stability at a high temperature is significantly improved compared to the conventional polyethylene separation membrane.

This is judged to be due to the excellent compatibility between resins in the example using the polypropylene-polyethylene block copolymer compared to the comparative example using the polypropylene. In particular, in the melt kneading process it was confirmed that the working example is superior to the comparative example.

The separator of the comparative example is poor in the kneading property of polyethylene and polypropylene, so that polypropylene is localized in some regions, and the physical strength is deteriorated due to this region. As a result, the separation membrane of the comparative example has an orange peel phenomenon in which fine unevenness occurs on the surface, and thus, it is difficult to apply it to a commercial separation membrane. On the other hand, all of the separators of the Example had a good surface.

In addition, the separator of Comparative Example showed poor porosity due to poor formation of micropores, because liquid-liquid phase separation did not occur between polypropylene and paraffin oil, making it difficult to form micropores by heat-induced phase separation. In particular, paraffin oil on polypropylene localized in some regions functions as a plasticizer rather than a pore-forming agent, and as a result, porosity and tensile strength appear to decrease.

The membranes of Examples 7 and 8, which contain all of ultra high molecular weight polyethylene, polypropylene-polyethylene block copolymer, and polypropylene, have a lower physical strength than those of Examples 2 to 6, which do not include polypropylene. It can be seen that the dimensional stability of the more improved. In addition, unlike the separator of the comparative example, the porosity may also implement a range that can be used as a separator for a secondary battery. This may be because the polypropylene-polyethylene block copolymer improves the dispersibility between polyethylene and polypropylene, and thus the polyethylene is evenly distributed throughout the separator.

The foregoing description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the invention is indicated by the following claims, and it should be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalents are included in the scope of the invention.

Claims (17)

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 4, and an average particle diameter of 100 to 150 μm;
Polypropylene having a weight average molecular weight (Mw) of 10,000 to 500,000 and an average particle diameter of 100 to 200 µm; And
Polypropylene / polyethylene block copolymer consisting of 30 to 70% by weight of polypropylene block and 30 to 70% by weight of polyethylene block, having a melt index of 0.5 to 30 and an average particle diameter of 100 to 200 µm;
The ultra-high molecular weight polyethylene, the polypropylene / polyethylene block copolymer and the weight ratio of the polypropylene are each 60 ~ 80: 10 ~ 30: 10 ~ 20,
Porosity is 35-50%,
Porous separation membrane having a heat shrinkage of 10.9% or less at 130 ℃. delete delete delete delete The method of claim 1,
The separator is a porous separator that satisfies one or more of the following conditions (i) to (v):
(i) 10-20 탆 thick;
(ii) puncture strength 150-300 gf;
(iii) tensile strength 1,500 ~ 2,500kgf / cm ² ;
(iv) shutdown temperature 130-140 ° C .;
(v) Meltdown temperature 160 ~ 170 ℃. (a) injecting a composition comprising ultra high molecular weight polyethylene, polypropylene, polypropylene / polyethylene block copolymer and a pore-forming agent into an extruder, forming and stretching into sheet form; And
(b) extracting a pore-forming agent from the stretched sheet to prepare a separator;
The ultra high molecular weight polyethylene has a weight average molecular weight (Mw) of 700,000 ~ 1,000,000, a molecular weight distribution (Mw / Mn) of 3 to 6, the average particle diameter of 100 ~ 150 ㎛,
The polypropylene has a weight average molecular weight (Mw) of 10,000 to 500,000, an average particle diameter of 100 to 200 ㎛,
The polypropylene / polyethylene block copolymer is composed of 30 to 70% by weight of polypropylene block and 30 to 70% by weight of polyethylene block, the melt index is 0.5 to 30, the average particle diameter is 100 to 200 ㎛,
The ultra-high molecular weight polyethylene, the polypropylene / polyethylene block copolymer and the weight ratio of the polypropylene is 60 ~ 80: 10 ~ 30: 10 ~ 20, respectively, a method for producing a porous separator. delete delete delete delete delete delete The method of claim 7, wherein
The weight ratio of the pore-forming agent and the polyolefin-based resin in the composition is 50 to 70: 30 to 50, respectively, a method for producing a porous separator. The method of claim 7, wherein
The pore-forming agent is paraffin oil, paraffin wax, mineral oil, solid paraffin, soybean oil, rapeseed oil, palm oil, palm oil, di-2-ethylhexyl phthalate, dibutyl phthalate, diisononyl phthalate, diisodecyl phthalate, bis (2- Propylheptyl) phthalate, naphthenic oil and one selected from the group consisting of two or more thereof, a method for producing a porous separator. The method of claim 7, wherein
The stretching is performed at a stretching ratio of 16 to 100 times at 110 to 130 ° C., a method for producing a porous separator. The method of claim 7, wherein
After the step (b) (c) 1.2 to 1.5 times stretched at 120 ~ 130 ℃ after shrinkage to 0.8 ~ 0.9 times; further processing; further comprising, a method of manufacturing a porous separator.