KR20200032931A - A separator and a method for manufacturing the same - Google Patents

Abstract

Provided is a separator with improved shutdown characteristics, meltdown characteristics, physical strength, and heat shrinkage rate. According to an embodiment of the present invention, the separator includes a multilayer structure in which a first layer including a matrix including a first polyolefin and a silane-modified polyolefin crosslinked in the matrix, and a second layer including a second polyolefin are alternately stacked.

Description

Separator and its manufacturing method {A SEPARATOR AND A METHOD FOR MANUFACTURING THE SAME}

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

Lithium secondary batteries are widely used as power sources for various electric products that require miniaturization and weight reduction, such as smartphones, laptops, and tablet PCs. Development of a lithium secondary battery having a large, long-life, and high stability is required.

As a means for achieving the above object, a separator formed with micropores that separates the positive electrode and the negative electrode to prevent internal short and facilitates the movement of lithium ions during the charging and discharging process, in particular, thermally induced phase separation Research and development on microporous separators using polyolefins such as polyethylene, which are advantageous for forming pores by (Thermally Induced Phase Separation), are economical and easy to meet the properties required for separators, are actively conducted.

However, a separation membrane using polyethylene having a melting point as low as 135 ° C. may cause shrinkage deformation at a high temperature above the melting point due to heat generation of the battery. When a short circuit occurs due to the deformation, a thermal runaway phenomenon of the battery may occur, and thus 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 by blending in the polyolefin has been suggested. However, since the inorganic filler contains moisture therein and thus vacuum drying is essential, the manufacturing cost is high, and if the moisture is not sufficiently removed, a ignition of the lithium secondary battery may be promoted to 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 conventional technology in which a resin having a high heat resistance is blended with a polyolefin to produce a separator or coated on the surface of the produced separator, but such a separator lacks physical strength and heat resistance, or has a complicated process and high manufacturing cost, making it difficult to commercialize. there is a problem.

The present invention is to solve the problems of the prior art described above, the object of the present invention is to provide a separator having improved shutdown characteristics, meltdown characteristics, physical strength, and heat shrinkage rate and a method of manufacturing the same.

One aspect of the present invention includes a first layer comprising a matrix comprising a first polyolefin and a silane-modified polyolefin crosslinked in the matrix; And a second layer comprising a second polyolefin; including a multilayer structure in which these layers are alternately stacked.

In one embodiment, the first and second polyolefins are in 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 of them, respectively. It may be the 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 of them.

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

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

(i) thickness 5-30 µm; (ii) porosity 30-60%; (iii) 50 ~ 500sec / 100ml air permeability; (iv) Tensile burst 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 ° C; (viii) Melt-down temperature 170-200 ° C.

In addition, another aspect of the present invention, (a) a first mixture comprising a first polyolefin, a silane-modified polyolefin, and a pore-forming agent, and a second mixture comprising a second polyolefin and a pore-forming agent, respectively, into an extruder, Forming a multi-layered base sheet; (b) manufacturing a porous film by processing the base sheet; And (c) crosslinking the silane-modified polyolefin contained in the porous membrane.

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

In one embodiment, the porous sheet may be prepared by stretching the base sheet in step (b) and extracting a pore-forming agent.

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

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

In one embodiment, the crosslinking catalyst may be premixed with the pore-forming agent and introduced through the 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, the porous membrane in step (c) may be crosslinked for 30 minutes to 48 hours at 80 to 130 ° C.

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

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

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 contraction rate and a method of 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 deduced from the configuration of the invention described in the detailed description or claims of the present invention.

Hereinafter, the present invention will be described by supplementing a part that is not revealed on the basis of the embodiment. However, the present invention may be implemented in various different forms, and thus is not limited to the embodiments described herein. In addition, in order to clearly describe the present invention in the drawings, parts irrelevant to the description are omitted, and like reference numerals are assigned to similar parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "indirectly connected" with another member in between. . Also, when a part is said to “include” a certain component, this means that other components may be further provided instead of excluding the other component unless otherwise stated.

When a range of numerical values is described herein, the values have the precision of the significant digits provided according to standard rules in chemistry for significant digits, unless their specific ranges are 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 separator according to an aspect of the present invention includes a first layer comprising a matrix comprising a first polyolefin and a silane-modified polyolefin crosslinked in the matrix; And a second layer comprising a second polyolefin; may include a multi-layer structure laminated alternately.

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

In the process of manufacturing a separation membrane containing a polyolefin and a silane-based compound in the related art, the silane-based compound is grafted after applying the silane-based compound onto the base sheet before pore forming agent extraction, or the polyolefin and the silane-based compound are pre-mixed and then grafted. And a method of preparing a crosslinked separator by preparing a base sheet was 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 in addition to the polyolefin, and the composition is discarded at every process. There is a disadvantage that the manufacturing cost rises rapidly.

Since crosslinking of the silane-modified polyolefin is performed after a series of processes including extrusion, stretching, extraction, etc., the crosslinked silane-modified polyolefin is uniformly controlled by uniformly controlling the distribution of the silane-modified polyolefin in the porous membrane from which the pore-forming agent is extracted. It is necessary to adjust the distribution to be uniform in the separation membrane. When the crosslinking reaction of the silane-modified polyolefin occurs due to bias in some areas of the separator, the required level of mechanical properties cannot be achieved, and in particular, the variation in mechanical properties according to the area of the separator is increased, significantly reducing product reliability and reproducibility. Can be.

According to an embodiment of the present invention, by adjusting the type and content of the first polyolefin constituting the matrix, the silane-modified polyolefin in the process of kneading the first polyolefin and the silane-modified polyolefin in an extruder, the matrix It can disperse uniformly.

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 of these, preferably , High density polyethylene (HDPE) with a weight average molecular weight (Mw) of 200,000 to 1,000,000 and a molecular weight distribution (M _w / M _n ) of 5 to 50, and low density polyethylene with a melt index (190 ° C, 21.6 kg) of 10 to 50 g / 10 min. (LDPE). When the first polyolefin is the mixture, it is possible to prevent phase separation or layer separation that occurs due to 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 to achieve the required level of thermal stability, and if it exceeds 70% by weight, it may be difficult to implement physical properties required for a commercial separation membrane.

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 range, dispersibility with the first polyolefin may decrease, resulting in phase separation or layer separation, and if it exceeds the above range, melt viscosity increases and unevenness during melt kneading It can cause one kneading.

The silane-modified polyolefin may be a silane-grafted 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 is more than 10 parts by weight, the mechanical properties of the separator converge to a required level, which is disadvantageous in terms of economy and productivity.

The silane may be a vinyl silane 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 of them, preferably tri It may be a methoxy vinylsilane, 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. If the second polyolefin is the homo polypropylene, thermal stability of the separator may be further improved.

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

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

(i) thickness 5-30 µm; (ii) porosity 30-60%; (iii) 50 ~ 500sec / 100ml air permeability; (iv) Tensile burst 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 ° C; (viii) Melt-down temperature 170-200 ° C. The separation membrane may have a high air permeability of 30 to 100 sec / 100 ml compared to a single-layer separation membrane of the same thickness, but the melt-down temperature may be improved by 20 to 50 ° C., thereby significantly improving thermal stability.

Method of manufacturing a separator

According to another aspect of the present invention, a method of manufacturing a separation membrane includes: (a) a first mixture comprising a first polyolefin, a silane-modified polyolefin, and a pore-forming agent, and a second mixture comprising a second polyolefin and a pore-forming agent, respectively. Putting in an extruder and forming a multilayer structure; (b) preparing a porous membrane by processing the multilayer structure; And (c) crosslinking the silane-modified polyolefin contained in the porous membrane.

The first and second polyolefins have the same effect as described above, with respect to the effect, content, and types available. 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 50 high density polyethylene 5 to 10% by weight, melt index (190 ℃, 21.6kg) may contain 10 to 50g / 10min, low density polyethylene 1 to 10% by weight, silane modified polyethylene 20 to 50% by weight, and pore-forming agent 40 to 70% by weight, and the second mixture may have a weight average molecular weight ( M _w ) may include 30 to 50% by weight of polypropylene having 100,000 to 500,000 and 50 to 70% by weight of the pore-forming agent, but is not limited thereto.

Before the step (a), the silane-modified polyolefin may be used after drying under vacuum, 80 to 100 ° C. for 5 to 10 hours. Through the drying process, curing of the silane-modified polyolefin due to moisture in the air may be prevented.

The pore forming agent is paraffin oil, paraffin wax, mineral oil, solid paraffin, soybean oil, rapeseed oil, palm oil, palm oil, di-2-ethylhexyl phthalate, dibutyl phthalate, diisononyl phthalate, diisodecyl phthalate, bis (2- Propylheptyl) phthalate, naphthene oil, and a combination of two or more of them, preferably, may be paraffin oil having a kinematic viscosity of 50 to 100 cSt at 40 ° C, more preferably at 40 ° C It may be a paraffin oil having a kinematic viscosity of 65 to 75 cSt, but is not limited thereto.

In the step (a), the first and second mixtures may be coextruded simultaneously in one or more extruders, or the first and second mixtures may be extruded and then laminated. The co-extrustion may be performed by simultaneously extruding the first and second mixtures into two or more layers by a layer multiplier, and the lamination is performed by the first and second layers. Each of the second mixture may be extruded to form a sheet, and then heat-compressed to be laminated into one multi-layer structure. Preferably, the step (a) may be to prepare a gel base sheet having a thickness of 1,000 to 2,000 μm by coextrusion.

In step (b), after passing through the base sheet between at least one casting roll having a surface temperature of 10 to 60 ° C and a nip roll to crystallize the cooling, the base sheet at 120 to 160 ° C After stretching, the pore forming agent 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 horizontal direction (MD) or the vertical 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 magnification accordingly 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 mixtures of two or more of them, Preferably, dichloromethane may be included, but is not limited thereto.

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 promoted. As such a crosslinking catalyst, carboxylic acid salts of metals such as tin, zinc, iron, lead, and cobalt, organic bases, inorganic acids and organic acids can be generally used. For example, the crosslinking catalyst is dibutyltin dilaurate, dibutyltin diacetate, stannous acetate, stannous caprylic acid, zinc naphthenate, zinc caprylate, cobalt naphthenate, ethylamine, dibutylamine , Hexylamine, pyridine, sulfuric acid, inorganic acids such as hydrochloric acid, organic acids such as toluene sulfonic acid, acetic acid, stearic acid, maleic acid, and the like, preferably, but may be dibutyltin dilaurate, but is not limited thereto.

The crosslinking catalyst was conventionally used in the production of silane-modified polyolefins, or used as a method of applying a solution or dispersion of a crosslinking catalyst to a porous membrane. However, it is difficult to uniformly disperse the crosslinking catalyst with the silane-modified polyolefin using the conventional method. As described above, before crosslinking, the silane-modified polyolefin contained in the porous membrane needs to be uniformly dispersed, and at this time, the crosslinking catalyst involved in the crosslinking reaction of the silane-modified polyolefin also needs to be uniformly dispersed.

On the other hand, by mixing the crosslinking catalyst with a pore-forming agent and introducing it through a side injector of the extruder, the crosslinking catalyst can be 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 economic efficiency and productivity.

In the step (c), it is possible to crosslink the silane-modified polyolefin contained in the porous membrane. The cross-linking may be performed for 30 minutes to 48 hours at 80 to 130 ° C., for example, may be achieved by placing the porous membrane in a constant temperature and humidity tank in which temperature and humidity are adjusted to a certain range. At this time, the step (c) may be excessively required for the crosslinking reaction since the steps (a) and (b) are discontinuous or continuous, even in a moisture environment where it is difficult to increase the temperature above a certain level. . On the other hand, in step (c), the porous membrane is passed through a water tank at or around 90 ° C., or preferably, a boiling point of 100 ° C. or higher, preferably, 120 ° C. or higher, more preferably, 150 ° C. or higher It is possible to improve productivity by remarkably shortening the time required for the crosslinking reaction by injecting and continuously passing through the supported crosslinking tank.

Specifically, since the solution contains a component having a boiling point greater than 100 ° C, a crosslinking reaction is performed by setting the temperature conditions to 100 ° C or higher, preferably 120 ° C or higher, and more preferably 120 to 130 ° C during crosslinking 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 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 a required level, and if it exceeds 10% by weight, the reaction rate converges to the required level, which is disadvantageous in terms of economic efficiency and productivity.

Hereinafter, embodiments of the present invention will be described in more detail. However, the following experimental results are only representative of the experimental results among the above examples, and the scope and contents of the present invention may be reduced or limited by examples and the like, and cannot be interpreted. Each effect of the various embodiments of the present invention, which are not explicitly set forth below, will be described in detail in the corresponding section.

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

Example 1

70 parts by weight of silane-modified polyethylene dried under vacuum, 85 ° C for 10 hours, 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 (Melt index, 190 ° C, 2.16 kg) of 15 g / 10min, and 1 part by weight of antioxidant It was put into a twin-screw extruder I (inner diameter 58 mm, L / D = 40, Twin screw extruder). Through the side injector of the twin-screw extruder I, 145 parts by weight of paraffin oil having a specific gravity (15/4 ° C) of 0.85 and a kinematic viscosity (40 ° C) of 70 cSt was supplied, and melt-kneaded at 220 ° C under a screw rotation speed of 100 rpm. 1 A polyolefin mixture was prepared.

The weight average molecular weight (M _w ) is 250,000, 100 parts by weight of homopolypropylene having a melt index of 2, and 1 part by weight of an antioxidant is uniformly mixed with a Henschel mixer, and a twin-screw extruder II (diameter 58 mm, L / D = 40, Twin Screw 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 70 cSt was supplied through the side injector of the twin-screw extruder II, and melt-kneaded under conditions of 220 ° C and screw rotation speed of 100 rpm. 2 A polyolefin mixture was prepared.

After stacking the first and second polyolefin mixtures in a structure of a first polyolefin layer / second polyolefin layer / first polyolefin layer through a multi-block (multi-layering 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.

The multilayer base sheet was stretched 7 times in the longitudinal direction (MD) in a roll stretching machine at 140 ° C, and 7 times in the transverse direction (TD) in a tenter stretching machine at 145 ° C to prepare a stretched film. The stretched film was impregnated into 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 into a crosslinking bath containing water having a temperature of 85 ° C., crosslinked for 3 hours, and then washed to prepare a multilayer separator in which a first polyolefin layer was stacked on both sides around a second polyolefin layer.

Example 2

70 parts by weight of silane-modified polyethylene dried under vacuum, 85 ° C for 10 hours, 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 ° C, 2.16 kg) of 15 g / 10min, specific gravity (15/4 ° C) of 0.85, and kinematic viscosity (40 ° C) 145 parts by weight of paraffin oil of 70 cSt, 1 part by weight of antioxidant and 5 parts by weight of dibutyltin dilaurate are uniformly mixed with a Henschel mixer and put into a twin-screw extruder I (diameter 58 mm, L / D = 40, twin screw extruder) And melt-kneaded at 220 ° C. and a screw rotation speed of 100 rpm to prepare a first polyolefin mixture.

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

The first and second polyolefin mixtures are stacked in a structure of a first polyolefin layer / second polyolefin layer / first polyolefin layer through a multi-block (multi-layering device), and then discharged through a tea die under conditions of a discharge rate of 10 kg / hr. After discharging and passing through a casting roll having a temperature of 40 ° C, a multilayer base sheet having a thickness of 1,500 mu m was prepared.

The multilayer base sheet was stretched 7 times in the longitudinal direction (MD) in a roll stretching machine at 140 ° C, and 7 times in the transverse direction (TD) in a tenter stretching machine at 145 ° C to prepare a stretched film. The stretched film was impregnated into 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 into a crosslinking bath containing water having a temperature of 85 ° C., crosslinked for 3 hours, and then washed to prepare a multilayer separator in which a first polyolefin layer was stacked on both sides around a second polyolefin layer.

Example 3

High density polyethylene with a weight average molecular weight (M _w ) of 350,000 and molecular weight distribution (M _w / M _n ) 5 with high density polyethylene with 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 with a weight average molecular weight (M _w ) of 350,000 and molecular weight distribution (M _w / M _n ) 5 with high density polyethylene with 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

A multi-layered membrane was prepared in the same manner as in Example 1, except that the stretched film was crosslinked by passing propylene glycol containing 1% by weight of dibutyltin dilaurate in a crosslinking tank heated to 120 ° C. for 3 hours in a row. Was prepared.

Example 7

Example 1 except that the stretched film was crosslinked by passing a solution in which propylene glycol and dibutyltin dilaurate were mixed in a weight ratio of 99: 1 in a crosslinking tank heated to 120 ° C. for 3 hours in a row. A multilayer separator was prepared in the same manner as.

Example 8

A multi-layered separator was prepared in the same manner as in Example 1, except that the stretched film was crosslinked by passing ethylene glycol into a crosslinking tank heated to 120 ° C. for 3 hours in a continuous manner.

Example 9

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

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 and a molecular weight distribution (M _w / M _n ) of 8, a weight average molecular weight (M _w ) of 350,000, and a molecular weight distribution (M _w / M _n) ), 9 parts by weight of high-density polyethylene (HDPE) and 1 part by weight of an antioxidant were uniformly mixed with a Henschel mixer and introduced into a twin-screw extruder I (diameter 58 mm, L / D = 40, Twin screw extruder). After adding 150 parts by weight of paraffin oil having a kinematic viscosity (40 ° C) of 50 cSt to the side injector of the twin-screw extruder, melt kneading was performed 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 were uniformly mixed with a Henschel mixer. 58mm, L / D = 40, Twin screw extruder). After the injection of 190 parts by weight of paraffin oil having a kinematic viscosity (40 ° C) of 50 cSt into the side injector of the twin-screw extruder, the mixture was 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 stacked in a structure of a first polyolefin layer / second polyolefin layer / first polyolefin layer through a multi-block (multi-layering device), and discharged through a tea die under conditions of a discharge rate of 10 kg / hr. After passing through the casting roll having a temperature of 0 ℃ to prepare a multi-layer base sheet.

The multilayer base sheet was stretched 5 times in the longitudinal direction (MD) and 5 times in the transverse direction (TD) in a tenter stretching machine at 117 ° C to prepare a stretched film. The stretched film was impregnated into a dichloromethane leaching tank at 25 ° C to extract and remove paraffin oil for 3 minutes. After the paraffin oil-removed film was dried at 25 ° C., the film was 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) with a weight average molecular weight (M _w ) of 2,000,000 and a molecular weight distribution (M _w / M _n ) of 8, 350,000 with a weight average molecular weight (M _w ), and molecular weight distribution (M _w / M _n ) 98 parts by weight of high-density polyethylene (HDPE) and 1 part by weight of antioxidant are uniformly mixed with a Henschel mixer to a twin-screw extruder I (diameter 58 mm, L / D = 40, twin screw extruder) Input. After adding 150 parts by weight of paraffin oil having a kinematic viscosity (40 ° C) of 50 cSt to the side injector of the twin-screw extruder, melt kneading was performed at 210 ° C and a screw rotation speed of 200 rpm to prepare a first polyolefin mixture.

A biaxial extruder I (internal diameter 58 mm, L / D = 40, Twin screw) by uniformly mixing 100 parts by weight of homopolypropylene with a weight average molecular weight (M _w ) of 250,000 and 1 part by weight of antioxidant with a Henschel mixer extruder). After adding 150 parts by weight of paraffin oil having a kinematic viscosity (40 ° C) of 70 cSt to the side injector of the twin-screw extruder, the mixture was melt-kneaded at 220 ° C and a screw rotation speed of 100 rpm to prepare a second polyolefin mixture.

The first and second polyolefin mixtures are stacked in a structure of a first polyolefin layer / second polyolefin layer / first polyolefin layer through a multi-block (multi-layering device), and discharged through a tea die under conditions of a discharge rate of 10 kg / hr. After passing through the casting roll having a temperature of 0 ℃ to prepare a multi-layer base sheet.

The multilayer base sheet was stretched 5 times in the longitudinal direction (MD) and 5 times in the transverse direction (TD) in a tenter stretching machine at 117 ° C to prepare a stretched film. The stretched film was impregnated into a dichloromethane leaching tank at 25 ° C to extract and remove paraffin oil for 3 minutes. After the paraffin oil-removed film was dried at 25 ° C., the film was 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 under vacuum, 85 ° C for 10 hours, 15 parts by weight of high density polyethylene (HDPE) having a weight average molecular weight (M _w ) of 350,000 and a molecular weight distribution (M _w / M _n ) of 5, 10 parts by weight of low-density polyethylene (LDPE) with a melt index of 15, specific gravity (15/4 ° C) of 0.85, 145 parts by weight of paraffin oil with a kinematic viscosity (40 ° C) of 70 cSt, and 1 part by weight of an antioxidant are uniformly mixed with a Henschel mixer To the twin-screw extruder I (inner diameter 58 mm, L / D = 40, Twin screw extruder), and melt-kneaded at 220 ° C. and a screw rotation speed of 100 rpm to prepare a polyolefin mixture.

After discharging the polyolefin mixture through a tee die at a discharge rate of 10 kg / hr, a base sheet having a thickness of 500 μm was prepared by passing a casting roll having a temperature of 40 ° C.

The base sheet was stretched 7 times in the longitudinal direction (MD) in a roll stretching machine at 140 ° C, and 7 times in the transverse direction (TD) in a tenter stretching machine at 145 ° C to prepare a stretched film. The stretched film was impregnated into 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 85 ° C. and impregnated into a crosslinking bath containing 1% by weight of dibutyltin dilaurate, crosslinked for 3 hours, and then washed to prepare a separator.

Experimental Example 1

Test methods for each of the physical properties measured in the present invention are as follows. In the absence of specific mention of temperature, measurement was performed at room temperature (25 ° C).

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

-Porosity (%): According to ASTM F316-03, the porosity of a membrane specimen having a radius of 25 mm was measured using a capillary porometer manufactured by PMI.

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

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

-Heat shrinkage rate (%): After placing a separator specimen of 200 × 200 mm in size between A4 paper in an oven at 105 ℃ or 120 ℃ for 1 hour, let it cool at room temperature to shrink the length of the specimen in the horizontal and vertical directions. The heat shrinkage was calculated using the following calculation formula.

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

-Shutdown temperature (° C): A force of 0.01 N was applied to the membrane specimen using a thermomechanical analysis (TMA), followed by heating at a rate of 5 ° C / min to measure the degree of deformation of the specimen. The temperature at which the specimen began to melt was defined as the shutdown temperature.

-Melt down temperature (° C): A force of 0.01 N was applied to the membrane specimen using a thermomechanical analysis (TMA), followed by heating at a rate of 5 ° C / min to measure the degree of deformation of the specimen. The temperature at which the specimen fractured was taken as the meltdown temperature.

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

Referring to Table 1, it can be seen that the separators of Examples 1 to 9 including silane-modified polyethylene had better mechanical properties than the separators of Comparative Examples 1 to 3. In particular, it can be seen that thermal properties such as heat shrinkage at 105 ° C and 120 ° C, shutdown temperature, and meltdown temperature are significantly improved.

Specifically, the multilayer separators of Example 1 and Comparative Examples 1 and 2 include three layers of a polyolefin porous layer, but the separator of Example 1 containing a silane-modified polyolefin has a high porosity and is equivalent to Comparative Examples 1 and 2 It can be seen that at the same time as implementing the mechanical strength of the level, the thermal contraction rate at high temperature (120 ° C) was significantly reduced. This is judged because the silane crosslinking reaction proceeded in a high temperature crosslinking tank.

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

The above description of the present invention is for illustration only, 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 distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts should be interpreted to be included in the scope of the present invention.

Claims (20)

A first layer comprising a matrix comprising a first polyolefin and a silane-modified polyolefin crosslinked in the matrix; And
A second layer comprising a second polyolefin; comprising a multi-layer structure, which are alternately stacked, a separator. According to claim 1,
The first and second polyolefins are each 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 of them. According to claim 1,
The content of the silane-modified polyolefin in the matrix is 5 to 70% by weight, separation membrane. According to claim 1,
The content of polyolefin and silane in the silane-modified polyolefin is 100: 1 to 10 parts by weight, respectively, and a separator. According to claim 1,
The silane is a vinyl silane containing an alkoxy group, the separation membrane. The method of claim 5,
The vinylsilane containing the alkoxy group is one selected from the group consisting of trimethoxyvinylsilane, triethoxyvinylsilane, triacetoxyvinylsilane, and combinations of two or more of them. According to claim 1,
The multi-layer structure comprises 3 to 100 layers, a separation membrane. According to claim 1,
The separator meets one or more of the following conditions (i) to (viii), the separator:
(i) thickness 5-30 µm;
(ii) porosity 30-60%;
(iii) 50 ~ 500sec / 100ml air permeability;
(iv) Tensile burst 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 ° C;
(viii) Melt-down temperature 170-200 ° C. (a) introducing a first mixture comprising a first polyolefin, a silane-modified polyolefin and a pore-forming agent and a second mixture comprising a second polyolefin and a pore-forming agent into an extruder and forming a multi-layered base sheet;
(b) manufacturing a porous film by processing the base sheet; And
(c) crosslinking the silane-modified polyolefin contained in the porous membrane; comprising a method for producing a separation membrane. The method of claim 9,
In the 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, thereby producing a separator. The method of claim 9,
In the step (b), a method of manufacturing a separation membrane is performed by stretching the multilayer structure and extracting a pore-forming agent to produce a porous membrane. The method of claim 11,
The stretching method of stretching the multilayer structure at 120 to 160 ° C in at least one of the longitudinal direction (MD) and the transverse direction (TD) is 3 to 10 times. The method of claim 9,
The first mixture further comprises a crosslinking catalyst, the method of producing a separation membrane. The method of claim 13,
The cross-linking catalyst is pre-mixed with the pore-forming agent and introduced through a side injector of the extruder. The method of claim 13,
The content of the crosslinking catalyst in the first mixture is 0.01 to 10% by weight, the method of producing a separation membrane. The method of claim 9,
In the step (c), the porous membrane is crosslinked for 30 minutes to 48 hours under conditions of 80 to 130 ° C, and the method for producing a separation membrane is performed. The method of claim 9,
In the step (c), a method for producing a separation membrane, in which a solution having a boiling point of 100 ° C. or higher is introduced into a crosslinking tank and continuously passed through the porous membrane. The method of claim 17,
The solution comprises a water, ethylene glycol, diethylene glycol, propylene glycol and one selected from the group consisting of a combination of two or more of them, the method of producing a separator. The method of claim 17,
The solution further comprises a crosslinking catalyst, a method for producing a separation membrane. The method of claim 19,
The content of the crosslinking catalyst in the solution is 0.1 to 1% by weight, the method of producing a separator.