KR102377260B1 - A separator and a method for manufacturing the same - Google Patents

Abstract

An embodiment of the present invention includes a matrix including a first polyolefin and a first layer including a silane-modified polyolefin crosslinked in the matrix; and a second layer including a second polyolefin; it provides a separator including a multilayer structure in which the alternately stacked multilayer structure is used.

Description

Separator and its manufacturing method

The present invention relates to a separator, and more particularly, to a separator for a non-aqueous electrolyte lithium secondary battery and a method for manufacturing the same.

Lithium secondary batteries are widely used as a power source for various electrical products that require miniaturization and weight reduction, such as smartphones, laptops, and tablet PCs. The development of large, long-life, and high-stability lithium secondary batteries is required.

As a means for achieving the above object, a separator with micropores that separates the positive electrode and the negative electrode to prevent an internal short and facilitates the movement of lithium ions during charging and discharging, in particular, heat-induced phase separation (Thermally Induced Phase Separation) R&D on microporous membranes using polyolefins such as polyethylene, which is advantageous for pore formation, economical, and easy to meet the physical properties required for membranes, is active.

However, a separator using polyethylene having a low melting point of about 135° C. may undergo shrinkage deformation at a high temperature higher than the melting point due to heat generation of the battery. When a short circuit occurs due to such deformation, a thermal runaway phenomenon of the battery may occur, resulting in safety problems such as ignition. In order to solve this problem, a method of improving heat resistance by coating an inorganic filler with high heat resistance on a polyolefin separator or blending in the polyolefin has been proposed. However, since the inorganic filler contains moisture inside and vacuum drying is essential, the manufacturing cost is high, and if the moisture is not sufficiently removed, ignition of the lithium secondary battery may be accelerated, which may cause safety problems. In addition, the inorganic filler may be detached from the inside of the battery and act as a foreign material.

There is a prior art in which a separator is manufactured by blending a resin with high heat resistance with polyolefin or coated on the surface of the prepared separator, but these separators lack physical strength and heat resistance, or have a complicated process and high manufacturing cost, which makes practical commercialization difficult. there is a problem.

SUMMARY OF THE INVENTION The present invention is to solve the problems of the prior art, and an object of the present invention is to provide a separator having improved shutdown characteristics, meltdown characteristics, physical strength, and thermal shrinkage, and a method for manufacturing the same.

One aspect of the present invention provides a first layer comprising a matrix including a first polyolefin and a silane-modified polyolefin crosslinked in the matrix; and a second layer including a second polyolefin; it provides a separator including a multilayer structure in which the alternately stacked multilayer structure is used.

In one embodiment, the first and second polyolefins are each from the group consisting of high-density polyethylene, low-density polyethylene, polypropylene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof. It may be a selected one.

In one embodiment, the content of the silane-modified polyolefin in the matrix may be 5 to 70% by weight.

In one embodiment, the polyolefin and the silane content in the silane-modified polyolefin may be 100:1 to 10 parts by weight, respectively.

In one embodiment, the silane may be a vinyl silane containing an alkoxy group.

In one embodiment, the vinylsilane containing the alkoxy group may be one selected from the group consisting of trimethoxyvinylsilane, triethoxyvinylsilane, triacetoxyvinylsilane, and combinations of two or more thereof.

In one embodiment, the multi-layer structure may include 3 to 100 layers.

In one embodiment, the separation membrane may satisfy one or more of the following conditions (i) to (viii).

(i) thickness of 5-30 μm; (ii) 30-60% porosity; (iii) air permeability 50~500sec/100ml; (iv) tensile rupture strength 1,000~3,000kgf/cm2; (v) 105° C. (1 hr) heat shrinkage of 5% or less; (vi) 120°C (1 hr) heat shrinkage of 20% or less; (vii) shutdown temperature 135~140℃; (viii) Meltdown temperature 170~200℃.

In another aspect of the present invention, (a) a first mixture including a first polyolefin, a silane-modified polyolefin, and a pore former and a second mixture including a second polyolefin and a pore former are respectively introduced into an extruder, forming a multi-layered base sheet; (b) manufacturing a porous membrane by processing the base sheet; and (c) crosslinking the silane-modified polyolefin included in the porous membrane;

In one embodiment, the first and second mixtures may be simultaneously extruded in one or more extruders in step (a), or the first and second mixtures may be respectively extruded and then laminated.

In one embodiment, the porous membrane may be manufactured by stretching the base sheet in step (b) and extracting a pore former.

In an embodiment, the stretching may be performed by stretching the base sheet 3 to 10 times in at least one of a longitudinal direction (MD) and a transverse direction (TD) at 120 to 160°C.

In one embodiment, the first mixture may further include a crosslinking catalyst.

In one embodiment, the cross-linking catalyst may be pre-mixed with the pore-forming agent and introduced through a side injector of the extruder.

In one embodiment, the content of the crosslinking catalyst in the first mixture may be 0.01 to 10% by weight.

In one embodiment, in step (c), the porous film may be crosslinked at 80 to 130° C. for 30 minutes to 48 hours.

In one embodiment, in the step (c), the porous membrane may be introduced into a crosslinking tank in which a solution having a boiling point of 100° C. or higher is supported and continuously passed therethrough.

In one embodiment, the solution may include one selected from the group consisting of water, ethylene glycol, diethylene glycol, propylene glycol, and a combination of two or more thereof.

In one embodiment, the solution may further include a crosslinking catalyst.

In one embodiment, the content of the crosslinking catalyst in the solution may be 0.1 to 1% by weight.

According to one aspect of the present invention, it is possible to provide a separator having improved shutdown characteristics, meltdown characteristics, physical strength, and thermal shrinkage, and a method for manufacturing the same.

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

Hereinafter, based on the examples, the present invention will be described by supplementing the parts not revealed. However, the present invention may be embodied in several different forms, and thus is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is "connected" with another part, this includes not only the case where it is "directly connected" but also the case where it is "indirectly connected" with another member interposed therebetween. . In addition, when a part "includes" a certain component, this means that other components may be further provided without excluding other components unless otherwise stated.

When a range of numerical values is recited herein, the values have the precision of the significant figures provided in accordance with the standard rules in chemistry for significant figures, unless the specific range is otherwise stated. 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.

separator

A separation membrane according to an aspect of the present invention includes a matrix including a first polyolefin and a first layer including a cross-linked silane-modified polyolefin in the matrix; and a second layer including a second polyolefin; it may include a multilayer structure in which these are alternately stacked.

In the separator, the silane-modified polyolefin is crosslinked in the matrix to firmly support and fix the matrix, thereby improving the mechanical properties of the separator. As used herein, the term “matrix” refers to a component constituting a continuous phase in a separation membrane including two or more components. That is, in the first layer, the first polyolefin may exist as a continuous phase, and the silane-modified polyolefin crosslinked therein may exist as a discontinuous phase.

In the conventional manufacturing process of a separation membrane containing polyolefin and silane compound, the silane compound is applied on the base sheet before extraction of the pore former and then grafted, or the polyolefin and the silane compound are premixed and then grafted And a method of preparing a cross-linked separator by preparing a base sheet was attempted, but in this case, the physical property level of a commercial separator is satisfied, but the silane-based compound is grafted with other compositions in addition to polyolefin, and this composition is discarded in every process This has the disadvantage of rapidly increasing the manufacturing cost.

Since the crosslinking of the silane-modified polyolefin is performed after a series of processes including extrusion, stretching, extraction, etc., the cross-linked silane-modified polyolefin is obtained by uniformly controlling the distribution of the silane-modified polyolefin in the porous membrane from which the pore former is extracted. It is necessary to control so that it is uniformly distributed in the separation membrane. When the crosslinking reaction of the silane-modified polyolefin is biased in some areas of the separation membrane, the required level of mechanical properties cannot be realized. can be

According to an embodiment of the present invention, by controlling the type and content of the first polyolefin constituting the matrix, the first polyolefin and the silane-modified polyolefin are kneaded in the extruder, and the silane-modified polyolefin is mixed with the matrix. It can be uniformly dispersed in

The first polyolefin may be one selected from the group consisting of high density polyethylene, low density polyethylene, homo polypropylene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof, preferably , High-density polyethylene (HDPE) with a weight average molecular weight (Mw) of 200,000 to 1,000,000 and molecular weight distribution (M _w /M _n ) of 5-50, and low-density polyethylene with a melt index (190℃, 21.6kg) of 10-50g/10min (LDPE). When the first polyolefin is the mixture, it is possible to prevent phase separation or layer separation caused by a decrease in dispersibility of the silane-modified polyolefin.

The content of the silane-modified polyolefin in the matrix may be 5 to 70% by weight, preferably, 20 to 50% by weight. If the content of the silane-modified polyolefin is less than 5% by weight, the silane crosslinking reaction is inhibited, so that the required level of thermal stability cannot be implemented.

The silane-modified polyolefin may have a weight average molecular weight (M _w ) of 100,000 to 500,000, and a molecular weight distribution (M _w /M _n ) of 3 to 10. If the weight average molecular weight and molecular weight distribution of the silane-modified polyolefin are less than the above ranges, the dispersibility with the first polyolefin may be lowered and phase separation or layer separation may occur. It may cause a mix-up.

The silane-modified polyolefin may be one in which silane is grafted onto polyolefin, and the content of polyolefin and silane in the silane-modified polyolefin may be 100:1 to 10 parts by weight, respectively. If the content of the silane is less than 1 part by weight, the silane crosslinking reaction may be inhibited, and if it exceeds 10 parts by weight, the mechanical properties of the separator converge to a required level, which is disadvantageous in terms of economic efficiency and productivity.

The silane may be a vinylsilane containing an alkoxy group. For example, the vinylsilane containing the alkoxy group may be one selected from the group consisting of trimethoxyvinylsilane, triethoxyvinylsilane, triacetoxyvinylsilane, and combinations of two or more thereof, preferably, It may be methoxyvinylsilane, but is not limited thereto.

The second polyolefin may be one selected from the group consisting of high-density polyethylene, low-density polyethylene, polypropylene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof, preferably, It may be a homo polypropylene having a weight average molecular weight (Mw) of 100,000 to 500,000. When the second polyolefin is the homo polypropylene, the thermal stability of the separator may be further improved.

The multi-layer structure may include 3 to 100 layers, and preferably, may be a three-layer structure in which the second layer is laminated between two first layers. The multi-layer structure may be more suitable for a non-aqueous electrolyte lithium secondary battery because there is no moisture absorption by laminating a hydrophobic layer, unlike a conventional coated separator that improves thermal stability by applying an inorganic filler.

The separation membrane may satisfy one or more of the following conditions (i) to (viii).

(i) thickness of 5-30 μm; (ii) 30-60% porosity; (iii) air permeability 50~500sec/100ml; (iv) tensile rupture strength 1,000~3,000kgf/cm2; (v) 105° C. (1 hr) heat shrinkage of 5% or less; (vi) 120°C (1 hr) heat shrinkage of 20% or less; (vii) shutdown temperature 135~140℃; (viii) Meltdown temperature 170~200℃. The separator may have a higher air permeability of 30 to 100 sec/100ml compared to a single-layer separator of the same thickness, but the meltdown temperature may be improved by 20 to 50° C., so that thermal stability may be remarkably improved.

Separation Membrane Manufacturing Method

According to another aspect of the method for manufacturing a separation membrane of the present invention, (a) a first mixture including a first polyolefin, a silane-modified polyolefin, and a pore-forming agent, and a second mixture including a second polyolefin and a pore-forming agent, respectively putting it into an extruder and forming a multi-layer structure; (b) manufacturing a porous membrane by processing the multilayer structure; and (c) crosslinking the silane-modified polyolefin included in the porous membrane.

The functional effects, content and usable types of the first and second polyolefins are the same as described above. Preferably, the first mixture has a weight average molecular weight (M _w ) of 200,000 to 1,000,000, and a molecular weight distribution (M _w /M _n ) of 5 to 10% by weight of high density polyethylene, a melt index (190 ℃, 21.6 kg) may include 1 to 10% by weight of low density polyethylene of 10 to 50g/10min, 20 to 50% by weight of silane-modified polyethylene, and 40 to 70% by weight of a pore former, and the second mixture has a weight average molecular weight ( M _w ) may include 30-50 wt% of polypropylene of 100,000-500,000 and 50-70 wt% of a pore former, but is not limited thereto.

Before step (a), the silane-modified polyolefin may be dried under vacuum and 80 to 100° C. for 5 to 10 hours before use. Through the drying process, it is possible to prevent curing of the silane-modified polyolefin by moisture in the air.

The pore former 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- It may be one selected from the group consisting of propylheptyl) phthalate, naphthenoyl, and combinations of two or more thereof, preferably paraffin oil having a kinematic viscosity of 50 to 100 cSt at 40° C., more preferably, at 40° C. It may be paraffin oil having a kinematic viscosity of 65 to 75 cSt, but is not limited thereto.

In step (a), the first and second mixtures may be co-extruded simultaneously in one or more extruders, or the first and second mixtures may be respectively extruded and then laminated. The co-extrusion may be performed by simultaneously extruding the first and second mixtures into two or more layers in a continuous manner by a Layer Multiplier, and the lamination may include the first and second mixtures. Each of the second mixtures may be extruded and molded into a sheet, followed by thermocompression bonding to form a single multi-layer structure. Preferably, the step (a) may be to prepare a gel-like base sheet having a thickness of 1,000 ~ 2,000㎛ by co-extrusion.

In step (b), the base sheet is cooled and crystallized by passing it between one or more casting rolls and nip rolls having a surface temperature of 10 to 60° C., and then the base sheet at 120 to 160° C. After stretching, the pore former may be extracted from the extraction tank. The stretching may be performed by a known method such as uniaxial stretching or biaxial stretching (sequential or simultaneous). In the case of uniaxial stretching, the stretching ratio may be 3 to 10 times in the transverse direction (MD) or longitudinal direction (TD). In the case of biaxial stretching, the stretching magnification may be 3 to 10 times in the transverse direction (MD) and the longitudinal direction (TD), respectively, and the resulting magnification may be 9 to 100 times. The extraction may be performed at 25-40 ° C. for 1 to 20 minutes, and the extraction tank is one selected from the group consisting of pentane, hexane, benzene, dichloromethane, carbon tetrachloride, methyl ethyl ketone, acetone, and a mixture of two or more thereof, Preferably, it may include, but is not limited to, dichloromethane.

The first mixture may further include a crosslinking catalyst. When the first mixture further includes a crosslinking catalyst, the crosslinking reaction in step (c) may be accelerated. As the crosslinking catalyst, in general, carboxylate salts of metals such as tin, zinc, iron, lead, and cobalt, organic bases, inorganic acids, and organic acids can be used. For example, the crosslinking catalyst is dibutyltindilaurate, dibutyltindiacetate, stannous acetate, stannous caprylic acid, zinc naphthenate, zinc caprylate, cobalt naphthenate, ethylamine, dibutylamine , inorganic acids such as hexylamine, pyridine, sulfuric acid, hydrochloric acid, etc., organic acids such as toluene sulfonic acid, acetic acid, stearic acid, maleic acid, etc., preferably, dibutyltin dilaurate, but is not limited thereto.

The cross-linking catalyst was conventionally added during the production of silane-modified polyolefin, or a solution or dispersion of the cross-linking catalyst was applied to the porous membrane. However, in this conventional method, it is difficult to uniformly disperse the crosslinking catalyst together with the silane-modified polyolefin. As described above, the silane-modified polyolefin contained in the porous membrane needs to be uniformly dispersed before crosslinking, and in this case, the crosslinking catalyst involved in the crosslinking reaction of the silane-modified polyolefin needs to be uniformly dispersed as well.

In contrast, by premixing the crosslinking catalyst with the pore former and injecting it through a side injector of the extruder, the crosslinking catalyst is uniformly dispersed together with the silane-modified polyolefin to further increase the efficiency of the crosslinking reaction.

The content of the crosslinking catalyst in the first mixture may be 0.01 to 10% by weight. If the content of the crosslinking catalyst is less than 0.01% by weight, the crosslinking reaction cannot be promoted to a required level, and if it exceeds 10% by weight, the reaction rate converges to the required level, which is disadvantageous in terms of economy and productivity.

In step (c), the silane-modified polyolefin included in the porous membrane may be cross-linked. The crosslinking may be performed for 30 minutes to 48 hours at 80 to 130° C., for example, by placing the porous membrane in a thermo-hygrostat in which temperature and humidity are controlled within a certain range. At this time, since step (c) is discontinuous or continuous with steps (a) and (b), it is performed in a moisture environment in which it is difficult to raise the temperature above a certain level, so excessive time may be required for the crosslinking reaction. . On the other hand, in step (c), the porous membrane is passed through a water tank around 90 ° C., or preferably, a solution having a boiling point of 100 ° C. or higher, preferably 120 ° C. or higher, more preferably 150 ° C. or higher. By introducing into the supported crosslinking tank and continuously passing it through, the time required for the crosslinking reaction can be significantly shortened and productivity can be improved.

Specifically, since the solution contains a component having a boiling point of more than 100 ° C., the crosslinking reaction is carried out by composing the temperature condition at 100 ° C. or higher, preferably 120 ° C. or higher, more preferably 120 to 130 ° C. during the cross-linking reaction. can promote As the component, one selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, and combinations of two or more thereof may be used. These components are hygroscopic and may cause a crosslinking reaction with moisture contained in the components, but if necessary, a predetermined amount of water may be additionally mixed and used.

In addition, the solution may further include a crosslinking catalyst. The content of the crosslinking catalyst in the solution may be 0.01 to 10% by weight, preferably 0.1 to 1% by weight. If the content of the crosslinking catalyst is less than 0.01% by weight, the crosslinking reaction cannot be promoted to a required level, and if it exceeds 10% by weight, the reaction rate converges to the required level, which is disadvantageous in terms of economy and productivity.

Hereinafter, an embodiment of the present invention will be described in more detail. However, the following experimental results describe only representative experimental results among the above examples, and the scope and contents of the present invention may not be construed as being reduced or limited by the examples. Each effect of the various embodiments of the present invention not explicitly presented below will be specifically described in the corresponding section.

As silane-modified polyethylene, SH-100X of TSC and XHE740N of MCPP were used individually or in combination.

Example 1

70 parts by weight of silane-modified polyethylene dried for 10 hours under vacuum and 85° C., the weight average molecular weight (M _w ) is 350,000, the molecular weight distribution (M _w /M _n ) is 5, and the average particle size is 100 to 200 μm. 15 parts by weight of powder of high density polyethylene (HDPE), 10 parts by weight of low density polyethylene (LDPE) having a melt index (Melt index, 190℃, 2.16kg) of 15 g/10min, and 1 part by weight of antioxidant It was put into twin screw extruder I (inner diameter 58mm, L/D=40, twin screw extruder). 145 parts by weight of paraffin oil having a specific gravity (15/4 ℃) of 0.85 and a kinematic viscosity (40 ℃) of 70 cSt is supplied through the side injector of the twin-screw extruder I, and melt-kneaded at 220 ℃ and a screw rotation speed of 100 rpm. 1 A polyolefin mixture was prepared.

100 parts by weight of homopolypropylene having a weight average molecular weight (M _w ) of 250,000 and a melt index of 2 and 1 part by weight of an antioxidant were uniformly mixed with a Henschel mixer in a twin screw extruder II (inner diameter 58mm, L/D=40, twin screw into the extruder). 150 parts by weight of paraffin oil having a specific gravity (15/4°C) of 0.85 and a kinematic viscosity (40°C) of 70cSt is supplied through the side injector of the twin screw extruder II, and melt-kneaded at 220°C and a screw rotation speed of 100rpm. 2 A polyolefin mixture was prepared.

After laminating the first and second polyolefin mixtures in a structure of a first polyolefin layer/second polyolefin layer/first polyolefin layer through a multi-block (multilayering device), a discharge rate of 10 kg through a T-die Discharged under the condition of /hr, and passed through a casting roll having a temperature of 40° C. to prepare a multilayer base sheet having a thickness of 1,500 μm.

A stretched film was prepared by stretching the multilayer base sheet 7 times in the longitudinal direction (MD) in a roll stretching machine at 140°C, and stretching 7 times in the transverse direction (TD) in a tenter stretching machine at 145°C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 1 minute. The film from which the paraffin oil was removed was dried at 35°C. Thereafter, the film was impregnated in a crosslinking bath containing water having a temperature of 85° C., crosslinked for 3 hours, and washed to prepare a multilayer separator in which the first polyolefin layer was laminated on both sides with the second polyolefin layer as the center.

Example 2

70 parts by weight of silane-modified polyethylene dried for 10 hours under vacuum and 85° C., the weight average molecular weight (M _w ) is 350,000, the molecular weight distribution (M _w /M _n ) is 5, and the average particle size is 100 to 200 μm. 15 parts by weight of high-density polyethylene (HDPE) as powder, 10 parts by weight of low-density polyethylene (LDPE) having a melt index (190℃, 2.16kg) of 15g/10min, specific gravity (15/4℃) of 0.85, and kinematic viscosity (40℃) 145 parts by weight of paraffin oil of 70 cSt, 1 part by weight of antioxidant, and 5 parts by weight of dibutyltin dilaurate were uniformly mixed with a Henschel mixer and put into twin screw extruder I (inner diameter 58mm, L/D=40, twin screw extruder) and melt-kneading under the conditions of 220° C. and 100 rpm screw rotation speed to prepare a first polyolefin mixture.

150 parts by weight of paraffin oil having a weight average molecular weight (M _w ) of 250,000, a melt index of 2, 100 parts by weight of a homopolypropylene, a specific gravity (15/4°C) of 0.85, and a kinematic viscosity (40°C) of 70 cSt, and antioxidant 1 The weight part was uniformly mixed with a Henschel mixer, put into twin screw extruder II (inner diameter 58 mm, L/D = 40, twin screw extruder), and melt-kneaded at 220 ° C. and screw rotation speed of 100 rpm to prepare a second polyolefin mixture. .

The first and second polyolefin mixtures were laminated in a structure of a first polyolefin layer/second polyolefin layer/first polyolefin layer through a multi-block (multilayering device), and then through a T-die at a discharge rate of 10 kg/hr. It was discharged and passed through a casting roll having a temperature of 40° C. to prepare a multilayer base sheet having a thickness of 1,500 μm.

A stretched film was prepared by stretching the multilayer base sheet 7 times in the longitudinal direction (MD) in a roll stretching machine at 140°C, and stretching 7 times in the transverse direction (TD) in a tenter stretching machine at 145°C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 1 minute. The film from which the paraffin oil was removed was dried at 35°C. Thereafter, the film was impregnated in a crosslinking bath containing water having a temperature of 85° C., crosslinked for 3 hours, and washed to prepare a multilayer separator in which the first polyolefin layer was laminated on both sides with the second polyolefin layer as the center.

Example 3

High-density polyethylene having a weight average molecular weight (M _w ) of 350,000 and molecular weight distribution (M _w /M _n ) of 5 is converted to high-density polyethylene having a weight average molecular weight (M _w ) of 750,000 and molecular weight distribution (M _w /M _n ) of 4. A multilayer separator was prepared in the same manner as in Example 1, except that it was replaced.

Example 4

High-density polyethylene having a weight average molecular weight (M _w ) of 350,000 and molecular weight distribution (M _w /M _n ) of 5 is converted to high-density polyethylene having a weight average molecular weight (M _w ) of 750,000 and molecular weight distribution (M _w /M _n ) of 4. A multilayer separator was prepared in the same manner as in Example 2, except that it was replaced.

Example 5

A multilayer separator was prepared in the same manner as in Example 1, except that the water supported in the crosslinking tank contained 1% by weight of dibutyltin dilaurate.

Example 6

Multilayer separator in the same manner as in Example 1, except that the stretched film was crosslinked by introducing propylene glycol containing 1% by weight of dibutyltin dilaurate into a crosslinking tank heated to 120° C. and passing it continuously for 3 hours. was prepared.

Example 7

Example 1 above, except that the stretched film was crosslinked by introducing a solution in which propylene glycol and dibutyltin dilaurate were mixed in a weight ratio of 99:1, respectively, into a crosslinking tank heated to 120° C., and passing it continuously for 3 hours. A multi-layer separator was prepared in the same manner as described above.

Example 8

A multilayer separator was prepared in the same manner as in Example 1, except that the stretched film was put into a crosslinking tank in which ethylene glycol was heated to 120° C. and passed continuously for 3 hours for crosslinking.

Example 9

Example 1 above, except that the stretched film was crosslinked by introducing a solution in which ethylene glycol and dibutyltin dilaurate were mixed in a weight ratio of 99:1, respectively, into a crosslinking tank heated to 120° C., and passing it continuously for 3 hours. A multi-layer separator was prepared in the same manner as described above.

Comparative Example 1

2 parts by weight of ultra-high molecular weight polyethylene (UHMWPE) having a weight average molecular weight (M _w ) of 2,000,000, molecular weight distribution (M _w /M _n ) of 8, weight average molecular weight (M _w ) of 350,000, molecular weight distribution (M _w /M _n ) ) of 9, 98 parts by weight of high-density polyethylene (HDPE) and 1 part by weight of an antioxidant were uniformly mixed with a Henschel mixer and put into twin screw extruder I (inner diameter 58mm, L/D=40, twin screw extruder). 150 parts by weight of paraffin oil having a kinematic viscosity (40° C.) of 50 cSt was added to the side injector of the twin-screw extruder, and then melt-kneaded at 210° C. and a screw rotation speed of 200 rpm to prepare a first polyolefin mixture.

9.9 parts by weight of ultra-high molecular weight polyethylene (UHMWPE) having a weight average molecular weight (M _w ) of 2,000,000 and a molecular weight distribution (M _w /M _n ) of 8 and 0.1 parts by weight of an antioxidant are uniformly mixed with a Henschel mixer, and the twin screw extruder I (inner diameter 58mm, L/D=40, twin screw extruder). 190 parts by weight of paraffin oil having a kinematic viscosity (40° C.) of 50 cSt was added to the side injector of the twin-screw extruder, and then melt-kneaded at 210° C. and a screw rotation speed of 200 rpm to prepare a second polyolefin mixture.

The first and second polyolefin mixtures are laminated in a structure of a first polyolefin layer/second polyolefin layer/first polyolefin layer through a multi-block (multilayering device), and discharged through a T-die at a discharge rate of 10 kg/hr. After making it, a multilayer base sheet was prepared by passing through a casting roll having a temperature of 0°C.

A stretched film was prepared by stretching the multilayer base sheet 5 times in the longitudinal direction (MD) and 5 times in the transverse direction (TD) in a tenter stretching machine at 117°C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 3 minutes. The film from which the paraffin oil was removed was dried at 25° C., stretched 1.4 times in the transverse direction (TD) at 127° C., and heat-set for 10 minutes to prepare a multilayer separator.

Comparative Example 2

2 parts by weight of Ultra High Molecular Weight Polyethylene (UHMWPE) having a weight average molecular weight (M _w ) of 2,000,000 and a molecular weight distribution (M _w /M _n ) of 8, a weight average molecular weight (M _w ) of 350,000, molecular weight distribution (M _w /M _n ) 98 parts by weight of high-density polyethylene (HDPE) of 9 and 1 part by weight of antioxidant were uniformly mixed with a Henschel mixer, was put in. 150 parts by weight of paraffin oil having a kinematic viscosity (40° C.) of 50 cSt was added to the side injector of the twin screw extruder, and then melt-kneaded at 210° C. and a screw rotation speed of 200 rpm to prepare a first polyolefin mixture.

100 parts by weight of homopolypropylene having a weight average molecular weight (M _w ) of 250,000, a melt index of 2, and 1 part by weight of an antioxidant were uniformly mixed with a Henschel mixer in a twin-screw extruder I (inner diameter 58mm, L/D=40, twin screw into the extruder). After adding 150 parts by weight of paraffin oil having a kinematic viscosity (40° C.) of 70 cSt to the side ejector of the twin-screw extruder, melt-kneading was performed at 220° C. and a screw rotation speed of 100 rpm to prepare a second polyolefin mixture.

The first and second polyolefin mixtures are laminated in a structure of a first polyolefin layer/second polyolefin layer/first polyolefin layer through a multi-block (multilayering device), and discharged through a T-die at a discharge rate of 10 kg/hr. After making it, a multilayer base sheet was prepared by passing through a casting roll having a temperature of 0°C.

A stretched film was prepared by stretching the multilayer base sheet 5 times in the longitudinal direction (MD) and 5 times in the transverse direction (TD) in a tenter stretching machine at 117°C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 3 minutes. The film from which the paraffin oil was removed was dried at 25° C., stretched 1.4 times in the transverse direction (TD) at 127° C., and heat-set for 10 minutes to prepare a multilayer separator.

Comparative Example 3

70 parts by weight of silane-modified polyethylene dried for 10 hours under vacuum and 85° C., weight average molecular weight (M _w ) of 350,000, molecular weight distribution (M _w /M _n ) of 5 parts by weight of high-density polyethylene (HDPE) 15 parts by weight, 10 parts by weight of low-density polyethylene (LDPE) having a melt index of 15, 145 parts by weight of paraffin oil having a specific gravity (15/4℃) of 0.85 and a kinematic viscosity (40℃) of 70cSt, and 1 part by weight of an antioxidant are uniformly mixed with a Henschel mixer Thus, it was put into twin screw extruder I (inner diameter 58mm, L/D=40, twin screw extruder), and melt-kneaded at 220° C. and screw rotation speed of 100 rpm to prepare a polyolefin mixture.

The polyolefin mixture was discharged through a T-die at a discharge rate of 10 kg/hr, and then passed through a casting roll having a temperature of 40° C. to prepare a base sheet having a thickness of 500 μm.

A stretched film was prepared by stretching the base sheet 7 times in the longitudinal direction (MD) in a roll stretching machine at 140°C, and stretching 7 times in the transverse direction (TD) in a tenter stretching machine at 145°C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 1 minute. The film from which the paraffin oil was removed was dried at 35°C. Thereafter, the film was immersed in a crosslinking bath having a temperature of 85° C. and containing 1% by weight of dibutyltindilaurate, crosslinked for 3 hours, and washed to prepare a separation membrane.

Experimental Example 1

The test method for each of the physical properties measured in the present invention is as follows. Unless otherwise stated, measurements were made at room temperature (25° C.).

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

- Porosity (%): Based on ASTM F316-03, the porosity of a separator having a radius of 25 mm was measured using a capillary porometer manufactured by PMI.

-Permeability (Gurley, sec/100ml): Using the Densometer EGO2-5 model of Asahi Seiko Co., Ltd., the time taken for 100ml of air to pass through the membrane specimen having a diameter of 29.8mm at a measurement pressure of 0.025MPa was measured.

-Tensile rupture strength (kgf/cm ² ): Using a tensile strength measuring instrument, stress was applied to a 20 × 200 mm separator specimen, and the applied stress was measured until the specimen fractured.

-Heat shrinkage rate (%): After placing a 200 × 200 mm separator sample in an oven at 105 ° C or 120 ° C for 1 hour, put it between A4 papers, and then cool it to room temperature to measure the shrinkage length of the specimen in the horizontal and vertical directions. was measured and heat shrinkage was calculated using the following 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 (°C): Using a thermomechanical analysis (TMA), a force of 0.01 N was applied to the separator specimen, and then the temperature was increased at a rate of 5° C./min to measure the degree of deformation of the specimen. The temperature at which the specimen starts to melt was set as the shutdown temperature.

- Meltdown temperature (℃): Using a thermomechanical analysis (TMA), a force of 0.01N was applied to the separator specimen, and then the temperature was raised at a rate of 5°C/min to measure the degree of deformation of the specimen. The temperature at which the specimen was fractured was taken as the meltdown temperature.

The physical properties of the separation membranes prepared according to 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 separators of Examples 1 to 9 including the silane-modified polyethylene have superior mechanical properties compared to the separators of Comparative Examples 1 to 3. In particular, it can be seen that thermal properties such as thermal contraction rate, shutdown temperature, and meltdown temperature at 105°C and 120°C are significantly improved.

Specifically, the multilayer separator of Example 1 and Comparative Examples 1 and 2 includes three polyolefin porous layers, but the separator of Example 1 including silane-modified polyolefin has a high porosity and is equivalent to Comparative Examples 1 and 2 It can be seen that the high-temperature (120°C) thermal contraction rate was significantly reduced while realizing a level of mechanical strength. This is considered to be because the silane crosslinking reaction proceeded in the high temperature crosslinking tank.

Additionally, as compared to the separation membrane of Example 1 in which silane is cross-linked in a high-temperature cross-linking tank without a separate cross-linking catalyst, Example 2 in which a cross-linking catalyst is dispersed during kneading of silane-modified polyolefin or silane is cross-linked in a cross-linking tank containing a cross-linking catalyst The mechanical strength and thermal stability of Examples 3 to 8 are more excellent. This means that the silane crosslinking reaction did not proceed sufficiently within a relatively short time of 3 hours simply by immersion in a high-temperature crosslinking bath, but the conversion rate of the crosslinking reaction was improved in the presence of a crosslinking catalyst.

The description of the present invention described above is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into 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 illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a dispersed form, and likewise components described as distributed may also be implemented in a combined form.

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

Claims (19)

a first layer comprising a continuous phase matrix including a first polyolefin and a discontinuous phase silane-modified polyolefin crosslinked in the matrix to support the matrix; and
A second layer comprising a second polyolefin; It includes a multilayer structure in which the alternately stacked,
The content of the silane-modified polyolefin in the matrix is 5 to 70% by weight,
The first polyolefin is a mixture of high-density polyethylene (HDPE) having a weight average molecular weight (Mw) of 200,000 to 1,000,000 and low-density polyethylene (LDPE) having a melt index (190° C., 21.6 kg) of 10 to 50 g/10 min, the separator. According to claim 1,
The second polyolefin is one selected from the group consisting of high-density polyethylene, low-density polyethylene, polypropylene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof. According to claim 1,
The polyolefin and the silane content in the silane-modified polyolefin are each 100: 1 to 10 parts by weight, the separation membrane. According to claim 1,
The silane is a vinyl silane containing an alkoxy group, the separation membrane. 5. The method of claim 4,
The alkoxy group-containing vinylsilane is one selected from the group consisting of trimethoxyvinylsilane, triethoxyvinylsilane, triacetoxyvinylsilane, and a combination of two or more thereof. According to claim 1,
Separation membrane, wherein the multi-layer structure comprises 3 to 100 layers. The method of claim 1,
Wherein the separation membrane satisfies one or more of the following conditions (i) to (viii), a separation membrane:
(i) thickness of 5-30 μm;
(ii) 30-60% porosity;
(iii) air permeability 50~500sec/100ml;
(iv) Tensile rupture strength 1,000~3,000kgf/cm ² ;
(v) 105° C. (1 hr) heat shrinkage of 5% or less;
(vi) 120°C (1 hr) heat shrinkage of 20% or less;
(vii) shutdown temperature 135~140℃;
(viii) Meltdown temperature 170~200℃. (a) adding a first mixture including a first polyolefin, a silane-modified polyolefin, and a pore former and a second mixture including a second polyolefin and a pore former into an extruder, respectively, to form a multi-layered base sheet;
(b) manufacturing a porous membrane by processing the base sheet; and
(c) crosslinking the silane-modified polyolefin included in the porous membrane to prepare a multilayer separator including first and second layers respectively formed from the first and second mixture;
The first mixture comprises 20 to 50% by weight of the silane-modified polyolefin,
The first polyolefin is a mixture of high-density polyethylene (HDPE) having a weight average molecular weight (Mw) of 200,000 to 1,000,000 and low-density polyethylene (LDPE) having a melt index (190°C, 21.6 kg) of 10-50 g/10min,
In the first layer, the first polyolefin and the crosslinked silane-modified polyolefin constitute a continuous phase and a discontinuous phase, respectively,
The silane-modified polyolefin is crosslinked in the first polyolefin to support the first polyolefin. 9. The method of claim 8,
In step (a), the first and second mixtures are simultaneously extruded in one or more extruders, or the first and second mixtures are respectively extruded and then laminated. 9. The method of claim 8,
In step (b), the multilayer structure is stretched and a pore former is extracted to prepare a porous membrane, a method of manufacturing a separation membrane. 11. The method of claim 10,
The stretching is a method of manufacturing a separator, wherein the multilayer structure is stretched 3 to 10 times in at least one of a longitudinal direction (MD) and a transverse direction (TD) at 120 to 160 °C. 9. The method of claim 8,
The first mixture further comprises a cross-linking catalyst, a method for producing a separation membrane. 13. The method of claim 12,
A method for producing a separation membrane, wherein the crosslinking catalyst is pre-mixed with the pore former and injected through a side injector of the extruder. 13. The method of claim 12,
The content of the crosslinking catalyst in the first mixture is 0.01 to 10% by weight, a method of manufacturing a separation membrane. 9. The method of claim 8,
In step (c), the porous membrane is cross-linked at 80-130° C. for 30 minutes to 48 hours, a method for producing a separation membrane. 9. The method of claim 8,
A method for producing a separation membrane, in which the porous membrane in step (c) is introduced into a crosslinking tank in which a solution having a boiling point of 100° C. or higher is supported and continuously passed therethrough. 17. The method of claim 16,
Wherein the solution comprises one selected from the group consisting of water, ethylene glycol, diethylene glycol, propylene glycol, and a combination of two or more thereof, a method of manufacturing a separation membrane. 17. The method of claim 16,
The solution further comprises a crosslinking catalyst, the method of manufacturing a separation membrane. 19. The method of claim 18,
The content of the crosslinking catalyst in the solution is 0.1 to 1% by weight, a method of manufacturing a separation membrane.