KR102206190B1 - A multi-layer separator and a method for manufacturing the same - Google Patents

Abstract

One aspect of the present invention, a first porous layer comprising a first polyolefin; And a second porous layer located on at least one surface of the first porous layer and including a crosslinked product of a polymer in which a crosslinkable compound is grafted to a second polyolefin, and a third polyolefin; and the first and second A multilayer separator having a structure in which at least a part of the second porous layer penetrates into the first porous layer in the thickness direction on the contact surface of the porous layer, and a method of manufacturing the same.

Description

A multilayer separator and its manufacturing method {A MULTI-LAYER SEPARATOR AND A METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a multilayer separator and a method for manufacturing the same, and more particularly, to a separator for a high-power, large-capacity lithium-ion battery, and a method for manufacturing the same.

Lithium secondary batteries are widely used as a power source for various electric products that require miniaturization and weight reduction, such as smart phones, notebook computers, and tablet PCs. As their application fields expand to smart grids and mid- to large-sized batteries for electric vehicles, their capacity is increased. There is a need to develop a lithium secondary battery that is large, has a long life, and has high stability.

As a means to achieve the above object, a separator having micropores that separates the anode and the cathode to prevent internal short and facilitates the movement of lithium ions during the charging and discharging process, among others, thermal-induced phase separation Research and development on microporous membranes using polyolefins such as polyethylene, which are advantageous in forming pores by (Thermally Induced Phase Separation), are economical, and are easy to meet the physical properties required for separation membranes, are active.

However, a separator using polyethylene having a melting point of about 135° C. may undergo shrinkage deformation at a high temperature above 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, and safety problems such as ignition may occur. In order to solve this problem, a method of improving heat resistance by coating an inorganic filler having 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, it may promote ignition of the lithium secondary battery, resulting in a safety problem. In addition, the inorganic filler may be detached from the inside of the battery to act as a foreign material.

There is a conventional technology in which a separator with high heat resistance is blended with polyolefin or coated on the surface of the prepared separator, but such a separator lacks physical strength and heat resistance, or is difficult to practically commercialize due to a complicated process and high manufacturing cost. there is a problem.

The present invention is to solve the problems of the prior art, and an object of the present invention is to provide a multilayer separator having improved shutdown characteristics, meltdown characteristics, physical strength, and thermal contraction rate, and a method of manufacturing the same.

One aspect of the present invention, a first porous layer comprising a first polyolefin; And a second porous layer located on at least one surface of the first porous layer and including a crosslinked product of a polymer in which a crosslinkable compound is grafted to a second polyolefin, and a third polyolefin; and the first and second It provides a multilayer separation membrane having a structure in which at least a portion of the second porous layer penetrates into the first porous layer in a thickness direction on a contact surface of the porous layer.

In one embodiment, the content of the crosslinked material in the second porous layer may be 5 to 90% by weight.

In one embodiment, the weight average molecular weight (Mw) of the first and third polyolefin is 200,000 to 1,000,000 g/mol, respectively, and the weight average molecular weight (Mw) of the second polyolefin may be 70,000 to 600,000 g/mol. have.

In one embodiment, the content of the crosslinkable compound in the polymer may be 10 to 50% by weight.

In one embodiment, the crosslinked product and the third polyolefin in the second porous layer may be a discontinuous phase and a continuous phase, respectively.

In one embodiment, the first to third polyolefins are polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof, respectively. It may be one selected from the group consisting of.

In one embodiment, the crosslinkable compound may be a vinylsilane containing an alkoxy group.

In one embodiment, the multilayer separator may satisfy one or more of the following conditions (i) to (x).

(i) 5-30 μm in thickness; (ii) 30-70 vol% porosity; (iii) Tensile strength in the longitudinal direction (MD) 1,000~3,000kgf/cm ² ; (iv) Transverse direction (TD) tensile strength 1,000~3,000kgf/cm ² ; (v) 40-150% tensile elongation in the longitudinal direction (MD); (vi) 40-150% tensile elongation in the transverse direction (TD); (vii) meltdown temperature of 210°C or higher; (viii) shutdown temperature 135-140°C; (ix) air permeability 30~300s/100ml; And (x) an interlayer peel strength of 70gf/20mm or more.

Another aspect of the present invention provides an electrochemical device including the multilayer separator, preferably a secondary battery, more preferably a lithium secondary battery or a lithium ion battery.

Another aspect of the present invention, (a) preparing a first mixture comprising a first polyolefin and a pore-forming agent; (b) reacting a second polyolefin, a crosslinkable compound, and an initiator to prepare a polymer in which the crosslinkable compound is grafted to the second polyolefin; (c) preparing a second mixture comprising 10 to 40% by weight of the polymer, 10 to 40% by weight of a third polyolefin, and 40 to 80% by weight of a pore former; (d) introducing the first and second mixtures into an extruder, respectively, to form a multilayered base sheet; (e) manufacturing a porous membrane by processing the base sheet; And (f) crosslinking the polymer contained in the porous membrane; provides a method of manufacturing a multilayer separator comprising.

In one embodiment, the second and third polyolefins are the same, and steps (b) and (c) may be performed in an in-situ manner.

In the multilayer separator and its manufacturing method according to an aspect of the present invention, a polyolefin grafted with a certain amount of a crosslinkable compound is separately prepared and synthesized, but it is mixed with a polyolefin having a certain range of physical properties in a certain ratio. By doing so, it is possible to improve mechanical properties and heat resistance in a balanced manner, and to maximize productivity and economy by solving the problem of increasing the manufacturing cost according to elution and disposal of the crosslinkable compound.

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

1 is a schematic diagram of a layered structure of a multilayer separator according to an embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be implemented in various different forms, and therefore is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and similar reference numerals are assigned to similar parts throughout the specification.

Throughout the specification, when a part is said to be "connected" to another part, this includes not only "directly connected" but also "indirectly connected" with another member interposed therebetween. . In addition, when a part "includes" a certain component, it means that other components may be further provided, rather than excluding other components unless specifically stated to the contrary.

Multilayer separator

1 is a schematic diagram of a layered structure of a multilayer separator according to an embodiment of the present invention. Referring to FIG. 1, a multilayer separator according to an aspect of the present invention includes: a first porous layer 100 including a first polyolefin; And a second porous layer 200 located on at least one surface of the first porous layer and including a crosslinked product of a polymer (hereinafter, modified polymer) grafted with a crosslinkable compound to a second polyolefin, and a third polyolefin; It may include, and at least a part of the second porous layer on the contact surface of the first and second porous layers may have a structure (P) that penetrates into the inside of the first porous layer in the thickness direction.

In the second porous layer 200, the crosslinked product may be uniformly dispersed in the third polyolefin, and the crosslinked product is at least a part of the crosslinkable compound grafted in the main chain of the second polyolefin under certain conditions. It may be formed by crosslinking with each other.

The content of the crosslinked product in the second porous layer 200 may be 5 to 90% by weight, preferably 5 to 50% by weight, more preferably 5 to 30% by weight. If the content of the crosslinked product in the second porous layer is less than 5% by weight, the required meltdown temperature cannot be achieved, and if it exceeds 90% by weight, the brittleness of the separator increases, resulting in a decrease in tensile strength and tensile elongation. I can.

The content of the crosslinkable compound in the modified polymer may be 10 to 50% by weight. If the content of the crosslinkable compound in the modified polymer is less than 10% by weight, the required meltdown temperature cannot be achieved, and if it exceeds 50% by weight, the brittleness of the multilayer separator including the second porous layer increases and tensile Not only the strength and the tensile elongation are lowered, but also processability and workability may deteriorate due to excessive oil vapor generation during manufacture of the second porous layer.

Each of the first and third polyolefins may have a weight average molecular weight (Mw) of 200,000 to 1,000,000 g/mol, and the second polyolefin may have a weight average molecular weight (Mw) of 70,000 to 600,000 g/mol. In addition, a ratio of the weight average molecular weight (Mw) of the third polyolefin to the weight average molecular weight (Mw) of the second polyolefin may be 0.1 to 5.0.

If the weight average molecular weight of the second polyolefin is less than 70,000 g/mol, it is difficult to obtain the modified polymer used to prepare the second porous layer in a pellet form due to its low molecular weight, and if it exceeds 600,000 g/mol, an excessive load on the extruder is When applied, the workability may be deteriorated.

In addition, when the weight average molecular weight of the first and third polyolefins is less than 200,000 g/mol, the melt viscosity is excessively low, so that the dispersibility of the pore former is extremely reduced. In particular, the first and third polyolefins and the pores Phase separation or layer separation may occur between the forming agents, and if it exceeds 1,000,000 g/mol, the melt viscosity increases and the processability decreases, which may cause uneven kneading during melt kneading.

In addition, the ratio of the weight average molecular weight (Mw) of the third polyolefin to the weight average molecular weight (Mw) of the second polyolefin may be 0.1 to 5.0, preferably 0.2 to 5.0. When the ratio of the weight average molecular weight (Mw) of the third polyolefin to the weight average molecular weight (Mw) of the second polyolefin is out of the above range, the compatibility and dispersibility of the crosslinked product and the third polyolefin are lowered. 2 Variation of mechanical properties according to the region of the porous layer and the multilayer separator including the same may increase, so that the reliability and reproducibility of the product may be significantly reduced.

In addition, the molecular weight distribution (Mw/Mn) of the first to third polyolefins may be 3 to 7 respectively. If the molecular weight distribution of the first to third polyolefins is less than 3, dispersibility with the pore-forming agent may be lowered, thereby reducing the uniformity of the prepared separator, and if it exceeds 7, the mechanical strength of the multilayer separator may be lowered.

The first to third polyolefins are one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more of them, respectively. May be, preferably, polyethylene, but is not limited thereto.

The content of the crosslinkable compound in the second porous layer may be 1 to 44% by weight. If the content of the crosslinkable compound in the second porous layer is less than 1% by weight, the required meltdown temperature cannot be achieved, and if it exceeds 44% by weight, the brittleness of the separator increases, resulting in a decrease in tensile strength and tensile elongation. Can be.

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

In the second porous layer, the crosslinked product and the third polyolefin may be a discontinuous phase and a continuous phase, respectively. In the second porous layer, the crosslinked product is crosslinked in a matrix composed of the third polyolefin to firmly support and fix the matrix, thereby improving heat resistance and mechanical properties of the second porous layer and a multilayer separator including the same. .

As used herein, the term "matrix" refers to a component constituting a continuous phase in a second porous layer including two or more components. That is, the third polyolefin may exist in a continuous phase in the second porous layer, and the crosslinked product may exist in a discontinuous phase therein.

In the conventional manufacturing process of a separation membrane containing a polyolefin and a crosslinkable compound, for example, a silane compound, a silane compound is applied and then grafted onto a base sheet before extraction of the pore former, or a polyolefin and a silane compound are added. A method of preparing a crosslinked separator by preparing a graft and a base sheet after premixing has been attempted, but in this case, the physical property level of the commercial separator is satisfied, but the silane-based compound is grafted with other compositions other than polyolefin, There is a disadvantage in that the manufacturing cost is rapidly increased due to the disposal of such a composition in each process.

Since the crosslinking of the modified polymer is performed after a series of processes including co-extrusion, stretching, extraction, etc., the distribution of the modified polymer is uniformly controlled in the second porous layer from which the pore former is extracted. It is necessary to adjust the crosslinked material to be uniformly distributed in the second porous layer. When the crosslinking reaction of the modified polymer occurs due to bias in some areas of the second porous layer, the required level of mechanical properties may not be realized, and in particular, the mechanical properties according to the area of the second porous layer and the multilayer separator including the same. As the deviation increases, the reliability and reproducibility of the product may be significantly reduced.

In addition, the multilayer separation membrane may have a structure (P) in which at least a portion of the second porous layer penetrates into the first porous layer in a thickness direction on a contact surface between the first and second porous layers. Such a structure may be implemented through a gel-like base sheet having a multi-layered structure obtained by preparing a composition for forming each of the first and second porous layers, and then simultaneously coextruding them.

A conventional multilayer separator, specifically, a multilayer separator including one or more layers including a crosslinked structure, has been manufactured by lamination. Since the lamination refers to extruding the composition for producing each layer, molding it into a sheet form, and bonding it to a single multilayer structure by thermocompression, the multilayer separator manufactured by the lamination has an interlayer contact surface as described above. It cannot have a structure (P) that penetrated into each other. Therefore, while achieving the required level of heat resistance due to the crosslinked structure, there is a problem that the interlayer bonding force is lowered and the laminated layer is easily peeled and separated.

In contrast, the first and second porous layers may have a structure in which the first and second porous layers are coextruded in a gel form before crosslinking so that each layer has a certain level of penetration from the contact surface in the thickness direction, and then, through crosslinking treatment, the second porous layer Can be formed. Here, the structure (P) in which at least a part of the second porous layer penetrates into the inside of the first porous layer in the thickness direction imparts a strong anchoring effect between the first and second porous layers to provide interlayer bonding force. Can be significantly improved.

As described above, in the second porous layer having a structure in which a crosslinked product of a polymer grafted with a crosslinkable compound grafted to a second polyolefin is dispersed in the third polyolefin, the content of the crosslinked product in the second porous layer, and the modified polymer By adjusting the content of the crosslinkable compound, the content of the crosslinkable compound in the second porous layer, and/or the weight average molecular weight and the ratio of the second and third polyolefins to a certain range, the following (i) to ( A separation membrane that satisfies at least one of the conditions of x) can be obtained.

(i) 5-30 μm in thickness; (ii) 30-70 vol% porosity; (iii) longitudinal direction (MD) tensile strength 1,000 to 3,000 kgf/cm ² , preferably, 2,000 to 2,800 kgf/cm ² ; (iv) transverse direction (TD) tensile strength 1,000 to 3,000 kgf/cm ² , preferably, 2,000 to 2,800 kgf/cm ² ; (v) longitudinal (MD) tensile elongation 40 to 150%, preferably 50 to 100%; (vi) transverse direction (TD) tensile elongation 40 to 150%, preferably 50 to 100%; (vii) a meltdown temperature of 210°C or higher, preferably 210 to 350°C; (viii) shutdown temperature 135-140°C; (ix) air permeability 30~300s/100ml; And (x) an interlayer peel strength of 70 gf/20 mm or more, preferably, 100 gf/20 mm or more, more preferably, 100 to 200 gf/20 mm.

Method for manufacturing a multilayer separator

Another aspect of the present invention, (a) preparing a first mixture comprising a first polyolefin and a pore-forming agent; (b) reacting a second polyolefin, a crosslinkable compound, and an initiator to prepare a polymer in which the crosslinkable compound is grafted to the second polyolefin; (c) preparing a second mixture comprising 10 to 40% by weight of the polymer, 10 to 40% by weight of a third polyolefin, and 40 to 80% by weight of a pore former; (d) introducing the first and second mixtures into an extruder, respectively, to form a multilayered base sheet; (e) manufacturing a porous membrane by processing the base sheet; And (f) crosslinking the polymer contained in the porous membrane; provides a method of manufacturing a multilayer separator comprising.

The effects of the first to third polyolefins, content, and usable types are as described above. Preferably,

In the step (a), the first mixture contains 20 to 50% by weight of high-density polyethylene and/or ultra-high molecular weight polyethylene having a weight average molecular weight (Mw) of 200,000 to 1,000,000 g/mol and 50 to 80% by weight of a pore former However, it is not limited thereto.

In the step (b), the second polyolefin having a weight average molecular weight (Mw) of 70,000 to 600,000 g/mol and a molecular weight distribution (Mw/Mn) of 3 to 7, a crosslinkable compound, and an initiator are reacted to react the second polyolefin. A polymer (hereinafter, modified polymer) in which the crosslinkable compound is grafted in the main chain of can be prepared, and the amount and ratio of the reactant can be adjusted so that the content of the crosslinkable compound in the polymer is 10-50% by weight. have.

In the step (c), the modified polymer, a third polyolefin having a weight average molecular weight (Mw) of 200,000 to 1,000,000 g/mol and a molecular weight distribution (Mw/Mn) of 3 to 7 and a second mixture comprising a pore former Can be manufactured. The second mixture may include 10 to 40% by weight of the modified polymer prepared in step (b), 10 to 40% by weight of the third polyolefin, and 40 to 80% by weight of a pore former. If the content of the modified polymer in the second mixture is less than 10% by weight, the crosslinking reaction is inhibited and the required level of mechanical properties cannot be realized, and if it exceeds 40% by weight, it is difficult to implement the physical properties required for a commercial separator.

The pore-forming agent is paraffin oil, paraffin wax, mineral oil, solid paraffin, soybean oil, rapeseed oil, palm oil, palm oil, di-2-ethylhexylphthalate, dibutylphthalate, diisononylphthalate, diisodecylphthalate, bis(2- It may be one selected from the group consisting of propylheptyl) phthalate, naphthenic oil, and a combination of two or more of them, preferably, it may be paraffin oil, and more preferably, it may be paraffin oil having a kinematic viscosity of 50 to 100 cSt at 40°C. However, it is not limited thereto.

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

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

On the other hand, by premixing the crosslinking catalyst with a pore-forming agent and introducing it through the side injector of the extruder, the crosslinking catalyst is uniformly dispersed with the crosslinked product and/or the third polyolefin to further increase the efficiency of the crosslinking reaction. have.

The content of the crosslinking catalyst in the second mixture may be 0.01 to 5% 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 5% by weight, the reaction rate converges to the required level, which is disadvantageous in terms of economy and productivity.

Meanwhile, when the second and third polyolefins are identical to each other, steps (b) and (c) may be performed in an in-situ manner. Specifically, when the second and third polyolefins are the same, a polyolefin, a crosslinkable compound, an initiator, and a pore former are reacted and extruded to obtain a modified polymer grafted with the crosslinkable compound in at least some of the main chains of the polyolefin. It is possible to prepare a second mixture containing.

In the step (d), the first and second mixtures are respectively introduced into separate extruders, for example, the first and second extruders, and co-extruded at the same time to form a multi-layered base sheet. have. The co-extrusion may be performed by simultaneously extruding the first and second mixture into two or more layers in a continuous manner by a multi-layered device (Layer Multiplier or Multi-Block), and the thickness is 800 to 2,000 μm by the co-extrusion. An in-gel base sheet can be prepared.

In the step (e), the base sheet is cooled and crystallized by passing between one or more casting rolls and/or nip rolls having a surface temperature of 10 to 60° C., and then the base at 120 to 160° C. After stretching the sheet, the pore-forming agent may be extracted from an 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 the uniaxial stretching, the stretching ratio may be 3 to 10 times in the horizontal direction (MD) or the vertical direction (TD). In the case of the biaxial stretching, the draw ratio may be 3 to 10 times in the horizontal direction (MD) and the vertical direction (TD), respectively, and the corresponding magnification may be 9 to 100 times. The extraction may be performed for 1 to 20 minutes at 25 to 40° C., and the extraction tank is one selected from the group consisting of pentane, hexane, benzene, dichloromethane, carbon tetrachloride, methyl ethyl ketone, acetone, and combinations of two or more of them, Preferably, dichloromethane may be included, but the present invention is not limited thereto.

In the step (f), the silane-modified polyolefin included in the porous membrane may be crosslinked. The crosslinking may be performed for 30 minutes to 48 hours at 80 to 130°C, and for example, may be performed by placing the porous membrane in a thermo-hygrostat in which temperature and humidity are controlled within a certain range. In this case, since the step (e) is discontinuous or continuous with the steps (a) to (e), it is performed in a moisture environment where it is difficult to raise the temperature to a certain level or more, so an excessive time may be required for the crosslinking reaction. .

On the other hand, in the step (c), the porous membrane is passed through a water bath of about 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 putting into the supported crosslinking tank and passing it continuously, 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 temperature condition during the crosslinking reaction is 100°C or more, preferably 120°C or more, more preferably 120 to 130°C to perform the crosslinking reaction. Can be promoted. As the component, one selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, and combinations of two or more of them may be used. These components are hygroscopic and may cause a crosslinking reaction with moisture contained in the components, but if necessary, a certain 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 the 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, embodiments of the present invention will be described in detail.

Manufacturing Example 1

A twin-screw extruder (internal diameter 58mm, mixed with 79 parts by weight of HDPE), 20 parts by weight of trimethoxyvinylsilane, and 1 part by weight of dicumyl peroxide with a melt index (190℃, 2.16kg) of 1g/10min. L/D=56, Twin screw extruder). A modified polymer in which trimethoxyvinylsilane was grafted onto polyethylene was prepared by discharging a 5mm diameter multi-strand die from the twin-screw extruder at 160°C and a screw rotation speed of 160rpm, and passing through a water bath and a pelletizer. .

Manufacturing Example 2

The first twin-screw extruder (internal diameter 58mm, L/) is mixed with 29.5 parts by weight of high-density polyethylene (HDPE) having a weight average molecular weight (Mw) of 700,000 and a molecular weight distribution (Mw/Mn) of 5, and 0.5 parts by weight of an anti-oxidant. D=56, Twin screw extruder), and 70 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40° C. with a side injector, and then extruded at 200° C. and a screw rotation speed of 40 rpm to prepare a first mixture. .

Example 1

Quantification by mixing 22.5 parts by weight of high-density polyethylene (HDPE) having a weight average molecular weight (Mw) of 350,000 and a molecular weight distribution (Mw/Mn) of 5, 20 parts by weight of the modified polymer obtained in Preparation Example 1, and 0.5 parts by weight of an antioxidant Insert into the second twin screw extruder (internal diameter 58mm, L/D=56, Twin screw extruder) as a feeder, and 57 parts by weight of paraffin oil with a kinematic viscosity of 70cSt at 40℃ with a side injector, then 200℃, screw rotation Extrusion was performed at a speed of 40 rpm to prepare a second mixture.

After laminating the first mixture and the second mixture obtained in Preparation Example 2 in a structure of a second mixture layer/first mixture layer/second mixture layer through a multi-block (multilayering device), a T- It was discharged at a discharge rate of 10 kg/hr through a die (T-die), and passed through a casting roll having a temperature of 40° C. to prepare a gel-like multilayer base sheet having a thickness of 800 μm.

The multilayer base sheet was stretched 6 times in the longitudinal direction (MD) in a 110°C roll stretching machine, and stretched 7 times in the transverse direction (TD) in a 125°C tenter stretching machine 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 1 minute. The film from which the paraffin oil was removed was dried for 5 minutes at 50°C. Thereafter, it was heated to 125°C in a tenter stretching machine, stretched by 1.45 times in the transverse direction (TD), and then relaxed to heat-set to 1.25 times compared to before stretching. The film was crosslinked for 20 hours in a constant temperature and humidity tank at 85° C. and 85% humidity to prepare a multilayer separator.

Example 2

22.5 parts by weight of high-density polyethylene (HDPE) having a weight average molecular weight (Mw) of 350,000 and a molecular weight distribution (Mw/Mn) of 5, 0.5 parts by weight of an antioxidant, and 1 part by weight of dicumyl peroxide were mixed and used as a quantitative feeder. Put into a screw extruder (internal diameter 58mm, L/D=56, Twin screw extruder), and add 56 parts by weight of paraffin oil and 20 parts by weight of trimethoxyvinylsilane with a kinematic viscosity of 70 cSt at 40°C with a side injector. A second mixture was prepared by extruding under conditions of °C and a screw rotation speed of 40 rpm.

After laminating the first mixture and the second mixture obtained in Preparation Example 2 in a structure of a second mixture layer/first mixture layer/second mixture layer through a multi-block (multilayering device), a T- It was discharged at a discharge rate of 10 kg/hr through a die (T-die), and passed through a casting roll having a temperature of 40° C. to prepare a gel-like multilayer base sheet having a thickness of 800 μm.

The multilayer base sheet was stretched 6 times in the longitudinal direction (MD) in a 110°C roll stretching machine, and stretched 7 times in the transverse direction (TD) in a 125°C tenter stretching machine 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 1 minute. The film from which the paraffin oil was removed was dried for 5 minutes at 50°C. Thereafter, it was heated to 125°C in a tenter stretching machine, stretched by 1.45 times in the transverse direction (TD), and then relaxed to heat-set to 1.25 times compared to before stretching. The film was crosslinked for 20 hours in a constant temperature and humidity tank at 85° C. and 85% humidity to prepare a multilayer separator.

Comparative example

29.5 parts by weight of high-density polyethylene (HDPE) with a weight average molecular weight (Mw) of 700,000 and a molecular weight distribution (Mw/Mn) of 5, and 0.5 parts by weight of an anti-oxidation agent are mixed with a twin screw extruder (internal diameter 58mm, L/D= 56, Twin screw extruder) and 70 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40° C. with a side injector. A base sheet having a thickness of 400 μm was prepared by discharging from the twin-screw extruder to a T-die having a width of 300 mm under conditions of 200°C and a screw rotation speed of 40 rpm and passing through a casting roll having a temperature of 40°C. . The base sheet was stretched 6 times in the longitudinal direction (MD) in a 110°C roll stretching machine and 7 times in the transverse direction (TD) in a 125°C tenter stretching machine 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 1 minute. The film from which the paraffin oil was removed was dried at 50° C. for 5 minutes. Thereafter, it was heated at 125°C in a tenter stretching machine, stretched by 1.45 times in the transverse direction (TD) and then relaxed to heat-set to 1.25 times compared to before stretching, thereby preparing a first porous membrane.

Quantification by mixing 22.5 parts by weight of high-density polyethylene (HDPE) having a weight average molecular weight (Mw) of 350,000 and a molecular weight distribution (Mw/Mn) of 5, 20 parts by weight of the modified polymer obtained in Preparation Example 1, and 0.5 parts by weight of an antioxidant It was put into a twin screw extruder (internal diameter 58mm, L/D=56, Twin screw extruder) as a feeder, and 57 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40° C. was added with a side injector. A base sheet having a thickness of 400 μm was prepared by discharging from the twin-screw extruder to a T-die having a width of 300 mm under conditions of 200°C and a screw rotation speed of 40 rpm and passing through a casting roll having a temperature of 40°C. The base sheet was stretched 6 times in the longitudinal direction (MD) in a 110°C roll stretching machine and 7 times in the transverse direction (TD) in a 125°C tenter stretching machine 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 1 minute. The film from which the paraffin oil was removed was dried at 50° C. for 5 minutes. Thereafter, it was heated to 125°C in a tenter stretching machine, stretched by 1.45 times in the transverse direction (TD), and then relaxed to heat-set to 1.25 times compared to before stretching. The film was crosslinked for 20 hours in a constant temperature and humidity tank at 85° C. and 85% humidity to prepare a second porous membrane.

The first and second porous membranes were stacked in the structure of a second porous membrane/first porous membrane/second porous membrane, and pressurized and heated for 10 seconds at 145°C and 0.05 MPa for 10 seconds to prepare a multilayer separator. .

Experimental example

The test method for each of the physical properties measured in the present invention is as follows. If there is no separate mention of the temperature, it was measured at room temperature (25 ℃).

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

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

-Porosity (volume%): According to ASTM F316-03, the porosity of a separator specimen having a radius of 25 mm was measured using a PMI's Capillary Porometer.

-Tensile strength (kgf/cm ² ): The applied stress was measured until fracture of the specimen occurred by applying a stress to a separator specimen having a size of 20 × 200 mm using a tensile strength meter.

-Tensile elongation (%): Using a tensile strength meter, a stress was applied to a separator specimen having a size of 20 × 200 mm to measure the maximum length extended until fracture of the specimen occurred, and the tensile elongation was calculated using the following calculation formula.

Tensile elongation (%)=(l ₁ -l ₂ )/l ₁ *100

(In the above calculation formula, l ₁ is the length in the horizontal or vertical direction of the specimen before stretching, and l2 is the length in the horizontal or vertical direction of the specimen just before fracture.)

-Punching strength (gf): Using a KES-G5 model of a punching strength measuring instrument from KATO TECH, a force is applied at a rate of 0.05cm/sec with a 0.5mm diameter stick to a 100×50mm separator specimen. The force applied at the time the specimen was pierced was measured.

-Meltdown temperature and shutdown temperature (°C): After applying a force of 0.01N to the separator specimen using a thermomechanical analysis (TMA), the specimen was heated at a rate of 5°C/min to measure the degree of deformation of the specimen. . The temperature at which the specimen breaks was taken as the meltdown temperature, and the temperature at the point of 50% of the maximum shrinkage when the specimen begins to melt was taken as the shutdown temperature.

-Heat shrinkage rate (%): A separator specimen of 200 x 200 mm in size is placed between A4 paper for 1 hour in an oven at 120° C., and then cooled at room temperature to measure the contracted length of the specimen in the horizontal and vertical directions. Heat shrinkage was calculated using the formula.

Heat shrinkage (%)=(l ₃ -l ₄ )/l ₃ *100

(In the above calculation formula, l ₃ is the length in the horizontal or vertical direction of the specimen before shrinkage, and l ₄ is the length in the horizontal or vertical direction of the specimen after shrinking.)

-Interlayer peel strength (gf/20mm): A 3M double-sided tape (No.665) was adhered to a separator specimen having a size of 20mm*200mm using a tensile strength measuring machine, and the stress applied during peeling was measured.

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

division Example 1 Example 2 Comparative example thickness 9.5 9.6 10.6 Ventilation 92 84 345 Porosity 50 52 28 MD tensile strength 2,820 2,690 1,925 MD tensile elongation 85 76 61 TD tensile strength 2,620 2,560 1,846 TD tensile elongation 76 72 64 MD heat shrinkage 7 5 4 TD heat shrinkage 11 10 6 Drilling strength 420 398 264 Meltdown temperature 235 240 212 Shutdown temperature 138 136 138 Peel strength between layers 126 142 65

The above description of the present invention is for illustrative purposes only, and those of ordinary skill in the art to which the present invention pertains will be able to 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 limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as being distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the claims to be described later, and all changes or modified forms derived from the meaning and scope of the claims and the concept of equivalents thereof should be construed as being included in the scope of the present invention.

Claims (11)

A first porous layer comprising a first polyolefin; And
Including; a second porous layer comprising a crosslinked polymer, and a third polyolefin, which is located on at least one surface of the first porous layer, a crosslinkable compound is grafted to a second polyolefin,
At least a portion of the second porous layer has a structure in which at least a portion of the second porous layer penetrates the inside of the first porous layer in the thickness direction from the contact surface of the first and second porous layers,
The weight average molecular weight (Mw) of the first and third polyolefins is 200,000 to 1,000,000 g/mol, respectively,
The weight average molecular weight (Mw) of the second polyolefin is 70,000 to 600,000 g/mol,
The ratio of the weight average molecular weight (Mw) of the third polyolefin to the weight average molecular weight (Mw) of the second polyolefin is 0.1 to 5.0. The method of claim 1,
The content of the crosslinked product in the second porous layer is 5 to 90% by weight of a multilayer separator. delete The method of claim 1,
The content of the crosslinkable compound in the polymer is 10 to 50% by weight of a multilayer separator. The method of claim 1,
In the second porous layer, the crosslinked product and the third polyolefin are a discontinuous phase and a continuous phase, respectively. The method of claim 1,
The first to third polyolefins are one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more of them, respectively. Phosphorus multilayer separator. The method of claim 1,
The crosslinkable compound is a multilayer separator of vinylsilane containing an alkoxy group. The method of claim 1,
The multilayer separator is a multilayer separator that satisfies at least one of the following conditions (i) to (x):
(i) 5-30 μm in thickness;
(ii) 30-70 vol% porosity;
(iii) Tensile strength in the longitudinal direction (MD) 1,000~3,000kgf/cm ² ;
(iv) Transverse direction (TD) tensile strength 1,000~3,000kgf/cm ² ;
(v) 40-150% tensile elongation in the longitudinal direction (MD);
(vi) 40-150% tensile elongation in the transverse direction (TD);
(vii) meltdown temperature of 210°C or higher;
(viii) shutdown temperature 135-140°C;
(ix) air permeability 30~300s/100ml; And
(x) Interlayer peel strength 70gf/20mm or more. An electrochemical device comprising the multilayer separator according to any one of claims 1, 2, and 4 to 8. (a) preparing a first mixture comprising a first polyolefin and a pore former;
(b) reacting a second polyolefin, a crosslinkable compound, and an initiator to prepare a polymer in which the crosslinkable compound is grafted to the second polyolefin;
(c) preparing a second mixture comprising 10 to 40% by weight of the polymer, 10 to 40% by weight of a third polyolefin, and 40 to 80% by weight of a pore former;
(d) coextruding the first and second mixtures to form a base sheet having a multilayer structure in which each layer penetrates from the contact surface in the thickness direction;
(e) manufacturing a porous membrane by processing the base sheet; And
(f) crosslinking the polymer contained in the porous membrane; including,
The weight average molecular weight (Mw) of the first and third polyolefins is 200,000 to 1,000,000 g/mol, respectively,
The weight average molecular weight (Mw) of the second polyolefin is 70,000 to 600,000 g/mol,
The ratio of the weight average molecular weight (Mw) of the third polyolefin to the weight average molecular weight (Mw) of the second polyolefin is 0.1 to 5.0. The method of claim 10,
The second and third polyolefins are the same,
The (b) and (c) steps are in-situ (in-situ) method of manufacturing a multi-layer separation membrane made by the method.

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