KR102022595B1 - Crosslinked polyolefin separator and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a method for manufacturing a crosslinked polyolefin separation membrane and a separation membrane, the method comprising the following steps of: (S1) manufacturing a silane grafted polyolefin composition by injecting polyolefin, a diluent, an initiator, a vinyl group-including alkoxy silane compound, a vinyl group-including phosphorus compound, and a crosslinking catalyst into an extruder, mixing the same, and extruding the mixture; (S2) molding and stretching the extruded silane grafted polyolefin composition into a sheet form; (S3) manufacturing a porous membrane by extracting the diluent from the stretched sheet; (S4) thermally fixing the porous membrane; and (S5) crosslinking the porous membrane in the presence of moisture. According to the present invention, it is possible to provide a crosslinked polyolefin separation membrane with improved heat resistance by having a large gap between a shutdown temperature and a melt down temperature, and also with secured flame retardancy.

Description

Cross-linked Polyolefin Separator and Manufacturing Method Thereof {CROSSLINKED POLYOLEFIN SEPARATOR AND MANUFACTURING METHOD THEREOF}

The present invention relates to a crosslinked polyolefin separator and a method for producing the same.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the most attracting field in this respect, and the development of a secondary battery capable of charging and discharging has been the focus of attention, and in recent years in the development of such a battery in order to improve the capacity density and specific energy The research and development of the design of the battery is progressing.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and greater energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.

The lithium secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Among them, the separator has a high ion conductivity to increase the permeability of lithium ions based on insulation and high porosity for electrically insulating the positive electrode and the negative electrode. Is required.

In addition, in order to ensure the safety of the lithium secondary battery, such a separator must have a wide interval between a shutdown temperature and a melt down temperature. To widen the gap between the shutdown temperature and the meltdown temperature, the shutdown temperature must be decreased in the direction of decreasing the meltdown temperature.

On the other hand, there is a method of increasing the melt down temperature using a crosslinked polyolefin porous membrane. However, the effect of lowering the shutdown temperature was inadequate with this conventional crosslinking method.

Accordingly, an object of the present invention is to provide a method for producing a crosslinked polyolefin membrane having a high meltdown temperature and a low shutdown temperature, and a method for preparing a crosslinked polyolefin membrane having safety and a separator prepared thereby.

One aspect of the present invention provides a method for producing a crosslinked polyolefin separator according to the following embodiments.

The first embodiment,

(S1) A polyolefin, a diluent, an initiator, a vinyl group-containing alkoxy silane compound, a vinyl group-containing phosphorus compound, and a crosslinking catalyst are added to an extruder, mixed, and extruded to form a silane compound and a phosphorus compound in the main chain of the polyolefin. Preparing a grafted polyolefin composition;

 (S2) molding and stretching the grafted polyolefin composition into a sheet form;

(S3) extracting a diluent from the stretched sheet to prepare a porous membrane;

(S4) heat setting the porous membrane; And

(S5) crosslinking the porous membrane in the presence of water; relates to a method for producing a crosslinked polyolefin separation membrane comprising a.

The second embodiment, in the first embodiment,

The vinyl group-containing phosphorus compound is diphenylvinylphosphine oxide, diphenylvinylphosphine, diphenylvinylphosphine, dimethyl vinyl phosphonate, diethyl vinyl phosphonate, diethyl vinyl phosphonate, Diphenylvinylphosphate, Dimethylvinylphosphate, Diethylvinylphosphate, Ethenyl dihydrogen phosphate, Isopropenyl dihydrogen phosphate, Vinyl phosphate (Vinylphosphonic acid), or a method for producing a crosslinked polyolefin separator comprising at least two or more thereof.

The third embodiment, in the first or second embodiment,

The total content of the vinyl group-containing alkoxy silane compound and the vinyl group-containing phosphorus compound is 0.1 to 3 parts by weight based on 100 parts by weight of the total of the polyolefin and the diluent, and relates to a method for producing a crosslinked polyolefin separator.

The fourth embodiment is any one of the first to third embodiments,

The weight ratio of the vinyl group-containing alkoxy silane compound: vinyl group-containing phosphorus compound is 90:10 to 30:70, and relates to a method for producing a crosslinked polyolefin separator.

The fifth embodiment is any one of the first to fourth embodiments,

The vinyl group-containing alkoxy silane compound relates to a method for producing a crosslinked polyolefin separator comprising a compound represented by the following formula (1):

[Formula 1]

In Formula 1, R _1, R _2, and R ₃ is each independently an alkoxy group having 1 to 10 carbon atoms or an alkyl group having 1 to 10 carbon atoms, wherein R _1, R _2, and At least one of R ₃ is an alkoxy group;

R is a vinyl group, an acryloxy group, a methacryloxy group, or an alkyl group having 1 to 20 carbon atoms, wherein at least one hydrogen of the alkyl group is substituted with a vinyl group, an acryloxy group, or a methacryloxy group.

The sixth embodiment, in the fifth embodiment,

The vinyl group-containing alkoxy silane compound may be vinyl trimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, (3-methacryloxypropyl) trimethoxysilane, (3-methacryloxypropyl) triethoxy It relates to a method for producing a crosslinked polyolefin separation membrane comprising silane, vinylmethyldimethoxysilane, vinyl-tris (2-methoxyethoxy) silane, vinylmethyldiethoxysilane, or a mixture of at least two of them.

The seventh embodiment is any one of the first to sixth embodiment,

The shutdown temperature of the separator is 133 ℃ or less, the meltdown temperature of the separator relates to a method for producing a crosslinked polyolefin separator.

The eighth embodiment is any one of the first to seventh embodiments,

It relates to a method for producing a cross-linked polyolefin separation membrane, the difference between the shutdown temperature and the meltdown temperature of the separator is 30 ℃ or more.

Another aspect of the present invention provides a crosslinked polyolefin separator according to the following embodiments.

In a ninth embodiment,

A silane compound and a phosphorus compound are grafted in the main chain of a polyolefin, and it is related with the crosslinked polyolefin separator which contains a silane derived crosslinked structure.

The tenth embodiment, in the ninth embodiment,

The silane-derived crosslinked structure relates to a crosslinked polyolefin separator comprising a -Si-O-Si- bond group.

The eleventh embodiment may further comprise the ninth or tenth embodiment,

The shutdown temperature of the separator is 133 ℃ or less, the meltdown temperature of the separator relates to a cross-linked polyolefin membrane.

The twelfth embodiment is any one of the ninth to eleventh embodiments,

It relates to a crosslinked polyolefin separation membrane having a difference in shutdown temperature and meltdown temperature of 30 ° C. or more.

The thirteenth embodiment is any of the ninth through twelfth embodiments,

It relates to a crosslinked polyolefin separator having a limited oxygen index (LOI) of 20 to 30 of the separator.

The fourteenth embodiment is any one of the ninth to thirteenth embodiments,

The separator relates to a crosslinked polyolefin separator, which is for a lithium secondary battery.

In the method for preparing a crosslinked polyolefin membrane according to an embodiment of the present invention, by adding a vinyl group-containing alkoxy silane compound and a vinyl group-containing phosphorus compound as a crosslinking agent, the gap between the melt down temperature and the shutdown temperature can be widened to ensure heat resistance. At the same time, it is possible to provide a separation membrane having high flame resistance.

Hereinafter, the present invention will be described in detail. The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The present invention relates to a method for producing a crosslinked polyolefin separator and a separator prepared thereby.

Electrochemical devices such as lithium secondary batteries including a separator having a large difference in shutdown temperature and meltdown temperature have excellent safety.

Accordingly, a separator having a low shutdown temperature and a high melt down temperature is required.

The present inventors have prepared a crosslinked polyolefin porous membrane using a crosslinking reaction to prepare a separator having a high melt down temperature but are still insufficient to lower the shutdown temperature.

In view of this, the present inventors have a high melt down temperature and a low shutdown temperature to improve the heat resistance and at the same time to provide a method for producing a crosslinked polyolefin membrane having improved flame retardancy and a crosslinked polyolefin membrane produced thereby.

Method for producing a crosslinked polyolefin separation membrane according to an aspect of the present invention,

(S1) A polyolefin, a diluent, an initiator, a vinyl group-containing alkoxy silane compound, a vinyl group-containing phosphorus compound, and a crosslinking catalyst are added to an extruder, mixed, and extruded to form a silane compound and a phosphorus compound in the main chain of the polyolefin. Preparing a grafted polyolefin composition;

(S2) molding and stretching the grafted polyolefin composition into a sheet form;

(S3) extracting a diluent from the stretched sheet to prepare a porous membrane;

(S4) heat setting the porous membrane; And

(S5) crosslinking the porous membrane in the presence of water; includes.

A feature of the present invention is to provide a separation membrane and a method for manufacturing the same, which include a vinyl group-containing alkoxy silane compound and a vinyl group-containing phosphorus compound at the same time, thereby improving heat resistance and flame retardancy according to a decrease in shutdown temperature and an increase in melt down temperature.

Hereinafter, a method of manufacturing the separator according to the present invention will be described in detail.

First, a polyolefin, a diluent, an initiator, a vinyl group-containing alkoxy silane compound, a vinyl group-containing phosphorous compound, a crosslinking catalyst, and a crosslinking catalyst are charged and mixed, followed by reaction extrusion to form a silane compound and a phosphorus compound in the main chain of the polyolefin. To prepare a grafted polyolefin composition (S1).

When the polyolefin, the initiator, the vinyl group-containing alkoxy silane compound, and the crosslinking catalyst are added to the extruder at once, the melt down temperature can be increased, but the effect of reducing the shutdown temperature is still insufficient.

However, to increase the safety of the separator, the gap between the shutdown temperature and the meltdown temperature must be high. In addition, in order to prevent possible explosions in advance, a separator having improved flame retardancy is required.

The present inventors solved this problem by simultaneously using a vinyl group containing alkoxy silane compound and a vinyl group containing phosphorus type compound as a crosslinking agent. Specifically, unlike the case where only the vinyl group-containing alkoxy silane compound is added, in the case of the present invention, by including the vinyl group-containing phosphorus compound at the same time it is possible to lower the shutdown temperature of the separation membrane, it is possible to improve the flame retardancy.

In one specific embodiment of the present invention, the polyolefin is polyethylene; Polypropylene; Polybutylene; Polypentene; Polyhexene; Polyoctene; Copolymers of two or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; Or mixtures thereof.

In particular, the polyethylene includes low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and the like, and among these, high density polyethylene having high crystallinity and high melting point of resin is most preferred.

In one specific embodiment of the present invention, the weight average molecular weight of the polyolefin may be 200,000 to 1,000,000 or 220,000 to 700,000 or 250,000 to 500,000. In the present invention, by using a high molecular weight polyolefin having a weight average molecular weight of 200,000 to 1,000,000 as a starting material for the production of the separator, it is possible to obtain a separator having excellent strength and heat resistance while ensuring uniformity and film forming processability of the separator.

In one specific embodiment of the present invention, the diluent may be used liquid or solid paraffin oil, wax, soybean oil (soybean oil) and the like commonly used in the manufacture of wet separators.

In one specific embodiment of the present invention, the diluent may be a diluent capable of liquid-liquid phase separation with the polyolefin, for example, dibutyl phthalate, dihexyl phthalate, Phthalic acid esters such as dioctyl phthalate; Aromatic ethers such as diphenyl ether and benzyl ether; Fatty acids having 10 to 20 carbon atoms such as palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid; Fatty acid alcohols having 10 to 20 carbon atoms, such as palmitic alcohol, stearic acid alcohol, and oleate alcohol; Palmitic acid mono-, di-, or triesters, stearic acid mono-, di-, or triesters. Saturated and unsaturated fatty acids having 4 to 26 carbon atoms of fatty acid groups such as mono-oleic acid, mono-, di- or triester, linoleic acid mono-, di- or triester, or one in which double bonds of unsaturated fatty acids are substituted by epoxy Alternatively, two or more fatty acids may include 1 to 8 hydroxy groups, and fatty acid esters ester-bonded with alcohols having 1 to 10 carbon atoms.

The diluent may be used alone or in a mixture containing at least two kinds of the above components.

In one specific embodiment of the present invention, the total content of the diluent may be 100 to 350 parts by weight, or 125 to 300 parts by weight, or 150 to 250 parts by weight based on 100 parts by weight of the polyolefin. When the total content of the diluent satisfies the above numerical range, as the polyolefin content increases, the porosity decreases, the pore size decreases, the interconnection between pores decreases, and the permeability decreases greatly, and the viscosity of the polyolefin composition rises to increase the extrusion load. As a result, the problem that processing may be difficult may be reduced, and as the polyolefin content is low, the kneading property of the polyolefin and the diluent decreases, so that the polyolefin is not thermodynamically kneaded with the diluent, but is extruded in the form of a gel, resulting in breakage and thickness unevenness. Etc. problems can be reduced.

In one specific embodiment of the present invention, the vinyl group-containing alkoxy silane compound is a crosslinking agent that causes a silane crosslinking reaction, and is grafted into a polyolefin by a vinyl group, and undergoes a crosslinking reaction by an alkoxy group to crosslink the polyolefin. . Accordingly, the melt down temperature of the separator may be increased.

In one specific embodiment of the present invention, it may include a compound represented by the following formula (1):

[Formula 1]

In Formula 1, R _1, R _2, and R ₃ is each independently an alkoxy group having 1 to 10 carbon atoms or an alkyl group having 1 to 10 carbon atoms, wherein R _1, R _2, and At least one of R ₃ is an alkoxy group;

R is a vinyl group, an acryloxy group, a methacryloxy group, or an alkyl group having 1 to 20 carbon atoms, wherein at least one hydrogen of the alkyl group is substituted with a vinyl group, an acryloxy group, or a methacryloxy group.

Meanwhile, R may further include an amino group, an epoxy group, or an isocyanate group.

In one specific embodiment of the present invention, the vinyl group-containing alkoxy silane compound is vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, (3-methacryloxypropyl) trimethoxysilane, ( 3-methacryloxypropyl) triethoxysilane, vinylmethyldimethoxysilane, vinyl-tris (2-methoxyethoxy) silane, vinylmethyldiethoxysilane, or mixtures of at least two or more thereof.

In the preparation of the crosslinked polyolefin separator according to an aspect of the present invention, the extruder comprises a vinyl group-containing phosphorus compound.

The vinyl group-containing phosphorus compound may include a phosphorus compound to increase flame retardancy.

The vinyl group-containing phosphorus compound is grafted to the main chain of the polyolefin by a vinyl group. The grafted vinyl group-containing phosphorus compound may lower the crystallinity of the polyolefin and consequently lower the melting temperature of the polyolefin, thereby lowering the shutdown temperature of the separator.

That is, in the present invention, as the vinyl group-containing alkoxy silane compound is added, the meltdown temperature of the separator may be increased, and as the vinyl group-containing phosphorus compound is further added, the shutdown temperature may be lowered and flame retardancy may be increased.

On the other hand, in this invention, a phosphorus compound contains a vinyl group and can lower the crystallinity degree of a polyolefin. In addition, the shutdown temperature can be lowered by using a phosphorus compound and a silane compound containing a vinyl group simultaneously. On the other hand, when the phosphorus compound does not contain a vinyl group, the effect of lowering the shutdown temperature is inadequate.

In one specific embodiment of the present invention, the vinyl group-containing phosphorus compound is silver diphenylvinyl phosphine oxide (Diphenylvinylphosphine oxide), diphenylvinyl phosphine (Diphenylvinylphosphine), dimethyl vinyl phosphonate (Dimethyl vinyl phosphonate, diethyl Dimethyl vinyl phosphonate, Diphenylvinylphosphate, Dimethylvinylphosphate, Diethylvinylphosphate, Ethenyl dihydrogen phosphate, Isopropenyl dihydro Genophosphate (Isopropenyl dihydrogen phosphate), vinylphosphonic acid (Vinylphosphonic acid), or a mixture of at least two or more thereof.

In one specific embodiment of the present invention, the total content of the vinyl group-containing alkoxy silane compound and the vinyl group-containing phosphorus compound is 0.1 to 3.0 parts by weight, or 0.2 to 2.0 parts by weight based on 100 parts by weight of the total of the polyolefin and the diluent. Parts, or 0.3 to 1.5 parts by weight. When the total content of the vinyl group-containing alkoxy silane compound and the vinyl group-containing phosphorus-based compound satisfies the numerical range, the content of the vinyl group-containing alkoxy silane compound is small so that the graft ratio is lowered, thereby lowering the crosslinking or the vinyl group-containing alkoxy silane compound. A large amount of unreacted silane may remain to prevent problems such as poor appearance of the extruded sheet. In addition, a flame retardant effect according to the vinyl group-containing phosphorus-based compound can be obtained, and due to proper grafting with the polyolefin, the crystallinity of the polyolefin can be lowered to lower the shutdown temperature.

In a specific embodiment of the present invention, the weight ratio of the vinyl group-containing alkoxy silane compound: vinyl group-containing phosphorus compound is 90:10 to 30:70, or 80:20 to 40:60, or 70:30 to 50: It can be 50. When the weight ratio of the silane compound and the phosphorus compound satisfies the numerical range, the crystallinity of the polyolefin may be lowered by the grafting effect of the vinyl group-containing alkoxy silane compound and the vinyl group in the vinyl group-containing phosphorus compound, and at the same time, the phosphorus compound is present. Therefore, the flame retardant effect can be obtained at the same time.

In one specific embodiment of the present invention, the initiator may be used without limitation so long as it is an initiator capable of generating radicals. Non-limiting examples of the initiator include 2,5-dimethyl-2,5-di- (tert-butylperoxy) hexane (2,5-dimethyl-2,5-di (tert-butylperoxy) hexane , (DHBP)), benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-ter-butyl peroxide, dicumyl peroxide, cumyl peroxide, hydroperoxide, potassium persulfate and the like.

In one specific embodiment of the present invention, the content of the initiator is 0.1 to 20 parts by weight, or 0.5 to 10 parts by weight, or 100 parts by weight of the total of the vinyl group-containing alkoxy silane compound and the vinyl group-containing phosphorus compound It may be 1 to 5 parts by weight. When the content of the initiator satisfies the numerical range, the silane graft rate may be lowered as the content of the initiator is low, or the content of the initiator may be prevented from crosslinking between the polyolefins in the extruder.

In one specific embodiment of the present invention, the crosslinking catalyst is added to promote the silane crosslinking reaction.

In one specific embodiment of the present invention, the crosslinking catalyst may be a carboxylate, organic base, inorganic acid and organic acid of a metal such as tin, zinc, iron, lead, cobalt. Non-limiting examples of the crosslinking catalyst include carboxylate salts of the metal, such as dibutyl tin dilaurate, dibutyl tin diacetate, stannous acetate, first tin caprylate, zinc naphthenate, zinc caprylate, Cobalt naphthenic acid, and the like, and the organic base includes ethylamine, dibutyl amine, hexyl amine, pyridine, and the like, and the inorganic acid includes sulfuric acid and hydrochloric acid, and the organic acid includes toluene sulfonic acid, acetic acid, stearic acid, Maleic acid and the like. In addition, the crosslinking catalyst may be used alone or a mixture of two or more thereof.

In one specific embodiment of the present invention, the content of the crosslinking catalyst is 0.1 to 20 parts by weight, or 0.5 to 10 parts by weight, based on 100 parts by weight of the total content of the vinyl group-containing alkoxy silane compound and the vinyl group-containing phosphorus compound, Or 1 to 5 parts by weight. When the content of the crosslinking catalyst satisfies the numerical range, a desired level of silane crosslinking reaction may occur and does not cause unwanted side reactions in the lithium secondary battery. In addition, cost problems such as waste of the crosslinking catalyst do not occur.

In one specific embodiment of the present invention, the silane grafted polyolefin composition may further include general additives for improving specific functions, such as surfactants, oxidative stabilizers, UV stabilizers, antistatic agents, nucleating agents, etc., as necessary. May be included.

In one specific embodiment of the present invention, the reaction extrusion step may use a single screw extruder or a twin screw compressor.

Next, the extruded silane-grafted polyolefin composition is molded and stretched into a sheet form (S2).

For example, the reaction extruded silane-grafted polyolefin composition is extruded using an extruder equipped with a tee-die or the like, and then cooled extrudates using a general casting or calendering method using water cooling and air cooling. Can be formed.

In one specific embodiment of the present invention, it is possible to provide a separator having improved mechanical strength and puncture strength by going through the stretching step as described above.

In one specific embodiment of the present invention, the stretching may be carried out in a roll manner or a tender manner sequential or simultaneous stretching. The draw ratio may be 3 times or more, or 4 times to 10 times, respectively, in the longitudinal and transverse directions, and the total draw ratio may be 14 to 100 times. When the draw ratio satisfies the numerical range, the orientation in one direction is not sufficient, and at the same time, the property balance between the longitudinal direction and the transverse direction is broken, thereby preventing the problem of lowering the tensile strength and the puncture strength, and the total draw ratio is within the numerical range. By satisfying the problem, it is possible to prevent the problem that unstretched or pore formation does not occur.

In one specific embodiment of the present invention, the stretching temperature may vary depending on the melting point of the polyolefin used, the concentration and type of diluent used.

In one specific embodiment of the present invention, for example, when the polyolefin used is polyethylene, the diluent is liquid paraffin, and the kinematic viscosity of the liquid paraffin is 50 to 150 cSt at 40 ° C., the stretching temperature is longitudinally stretched (MD). ) May be 70 to 160 ° C, or 90 to 140 ° C, or 100 to 130 ° C, or 90 to 180 ° C, or 110 to 160 ° C or 120 to 150 ° C for transverse stretching (TD), When simultaneously stretching in both directions, it may be 90 to 180 ° C, or 110 to 160 ° C, or 110 to 150 ° C.

When the stretching temperature satisfies the numerical range, as the stretching temperature has a low temperature range, there is no softness to prevent breakage or unstretching, and it occurs as the stretching temperature is high. Partial over-stretching or physical property difference can be prevented.

Thereafter, a diluent is extracted from the molded and stretched sheet to prepare a porous membrane (S3).

In one specific embodiment of the present invention, an organic solvent may be used in the porous membrane to extract a diluent and dry the porous membrane.

In one specific embodiment of the present invention, the organic solvent is not particularly limited as long as it can extract the diluent, but methyl ethyl ketone, methylene chloride, hexane and the like having high extraction efficiency and fast drying are suitable.

In a specific embodiment of the present invention, the extraction method may be any or a combination of all common solvent extraction methods, such as an immersion method, a solvent spray (solvent spray) method, an ultrasonic (ultrasonic) method. The content of residual diluent after the extraction treatment should preferably be 1% by weight or less. When the content of the residual diluent exceeds 1% by weight, the physical properties decrease and the permeability of the porous membrane decreases. The amount of residual diluent may be affected by the extraction temperature and extraction time. In order to increase the solubility of the diluent and the organic solvent, the extraction temperature is high, but the temperature is preferably 40 ° C. or lower in consideration of the safety problem due to boiling of the organic solvent. . If the extraction temperature is less than the freezing point of the diluent, the extraction efficiency is greatly reduced and must be higher than the freezing point of the diluent.

In addition, the extraction time depends on the thickness of the porous membrane to be produced, but in the case of a 5 to 15 μm thick porous membrane, 2 to 4 minutes is suitable.

Thereafter, the porous membrane is heat-set (S4).

The heat setting is to fix the porous membrane and apply heat to forcibly grasp the porous membrane to shrink to remove residual stress.

In one specific embodiment of the present invention, when the polyolefin is polyethylene, the heat setting temperature may be 100 to 140 ℃, or 105 to 135 ℃, or 110 to 130 ℃. In the case where the polyolefin is polyethylene, when the heat setting temperature satisfies the numerical range, rearrangement of the polyolefin molecules may occur to remove residual stress of the porous membrane, and may reduce the problem of clogging of the pores of the porous membrane due to partial melting. have.

In one specific embodiment of the present invention, the time of the heat setting temperature may be 10 to 120 seconds, or 20 to 90 seconds, or 30 to 60 seconds. When heat-setting at this time, rearrangement of the polyolefin molecules may occur to remove residual stress of the porous membrane, and may reduce the problem of clogging the pores of the porous membrane due to partial melting.

Next, the heat-set porous membrane includes the step of crosslinking in the presence of water (S5).

In one specific embodiment of the present invention, the crosslinking may be carried out at 60 to 100 ℃, or 65 to 95 ℃, or 70 to 90 ℃.

In one specific embodiment of the present invention, the crosslinking may be performed at a humidity of 60 to 95% for 6 to 50 hours.

In one specific embodiment of the present invention, the shutdown temperature of the separator is 133 ℃ or less, the meltdown temperature of the separator may be 175 ℃ or more.

In one specific embodiment of the present invention, the shutdown temperature and the meltdown temperature difference of the separator may be 45 ℃ or more.

According to another aspect of the present invention, a silane and a phosphorus-based compound is grafted to the main chain of the polyolefin, and a crosslinked polyolefin separation membrane including a silane-derived crosslinked structure is provided.

In one specific embodiment of the present invention, the silane-derived crosslinked structure may comprise a -Si-O-Si- bonding group.

In one specific embodiment of the present invention, the shutdown temperature of the separator is 133 ℃ or less, the meltdown temperature of the separator may be 175 ℃ or more.

In one specific embodiment of the present invention, the shutdown temperature and the meltdown temperature difference of the separator may be 30 ℃, or 40 ℃ or more.

In one specific embodiment of the present invention, the limited oxygen index (LOI) of the separator may be 20 to 30. Separation membrane according to an aspect of the present invention has a higher limit oxygen index (17.4) than when using a polyolefin substrate alone, it is possible to ensure a higher safety at the battery cell level.

In the present invention, the term 'Limiting Oxygen Index (LOI)' is an abbreviation known in the art and is an index for evaluating the combustibility and the flame retardancy of a polymer material. The amount of oxygen is shown. This can typically be determined using the ASTM D 2863 test method.

In one specific embodiment of the present invention, the separator may be for a lithium secondary battery.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example  One

First, 7.0kg / hr of high-density polyethylene (Korean emulsion, VH035) having a weight average molecular weight of 350,000 as polyolefin in the extruder, 13.0kg / hr as liquid paraffin oil (Far Copper Emulsification, LP 350F, 68cSt) as diluent, 2,5 as initiator -Dimethyl-2,5-di- (tert-butylperoxy) hexane (2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, (DHBP)) 4 g / hr, containing vinyl group 100 g / hr of vinyltrimethoxysilane as the alkoxy silane compound, 100 g / hr of diphenylvinylphosphine oxide as the vinyl group-containing phosphorus compound, and 4 g / hr of dibutyl tin dilaurate were added and mixed as a crosslinking catalyst. At this time, the weight ratio of the vinyl group-containing alkoxy silane compound: vinyl group-containing phosphorus compound was 1: 1.

Then, the reaction was extruded at a temperature of 200 ℃ to prepare a silane-grafted polyethylene composition.

The prepared silane grafted polyethylene composition was molded into a sheet form through a tee die and a cold casting roll, and then biaxially stretched using a tenter type stretching machine of TD stretching after MD stretching. MD draw ratio and TD draw ratio were both 7.0 times. As for extending | stretching temperature, MD was 110 degreeC and TD was 125 degreeC.

The stretched sheet was extracted with a methylene chloride diluent and heat set at 126 ℃ to prepare a porous membrane. The porous membrane was crosslinked at 85 ° C. and 85% relative humidity for 24 hours to prepare a crosslinked polyethylene separator.

Example  2

A crosslinked polyolefin separator was manufactured in the same manner as in Example 1, except that diphenyl vinyl phosphate was used instead of diphenyl vinyl phosphine oxide as the vinyl group-containing phosphorus compound introduced into the extruder.

Example  3

A crosslinked polyolefin separator was prepared in the same manner as in Example 1 except that vinyl phosphonic acid was used instead of diphenyl (vinyl) phosphine oxide as the vinyl group-containing phosphorus compound introduced into the extruder.

Example  4

A crosslinked polyolefin separator was prepared in the same manner as in Example 1 except that dimethyl vinyl phosphonate was used instead of diphenyl (vinyl) phosphine oxide as the vinyl group-containing phosphorus compound introduced into the extruder.

Example  5

A crosslinked polyolefin separator was prepared in the same manner as in Example 1 except that dimethyl vinyl phosphate was used instead of diphenyl (vinyl) phosphine oxide as the vinyl group-containing phosphorus compound introduced into the extruder.

Example  6

Ethylyl dihydrogen phosphate instead of diphenylvinylphosphine oxide

Except for using the cross-linked polyolefin membrane was prepared in the same manner as in Example 1.

Comparative example  One

A crosslinked polyolefin separator was manufactured in the same manner as in Example 1, except that 200 g / hr of vinyltrimethoxysilane was added to the vinyl group-containing alkoxy silane compound without introducing the vinyl group-containing phosphorus compound into the extruder.

Comparative example  2

A crosslinked polyolefin separator was prepared in the same manner as in Example 1 except that only polyolefin and a diluent were added to the extruder hopper.

Specifically, 7.0 kg / hr of high-density polyethylene (DAE, VH035) having a weight average molecular weight of 350,000 as polyolefin was added to the extruder hopper, and only 13.0 kg / hr of liquid paraffin oil (Far East Emulsification, LP 350F, 68cSt) was added and mixed as a diluent. .

Comparative example  3

A crosslinked polyolefin separator was manufactured in the same manner as in Example 1, except that trimethyl phosphate, which is a phosphorus-based compound containing no vinyl group, was used instead of the vinyl-containing phosphorus-based compound introduced into the extruder.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Remarks Phosphorus compound type difference Phosphorus compound type difference Phosphorus compound type difference Phosphorus compound type difference Phosphorus compound type difference Phosphorus compound type difference Inject only silane compound No silane phosphorus compound added Trimethyl phosphate is used instead of the vinyl group-containing phosphorus compound Phosphorus compound type Diphenyl (vinyl) phosphine oxide Diphenyl vinyl phosphate Vinyl phosphonic acid Dimethylvinylphosphonate Dimethyl Vinyl Phosphate Ethenyl dihydrogen phosphate - - Trimethyl phosphate Shutdown temperature (℃) 132 131 132 132 131 132 136 139 138 Melt Down Temperature (℃) 179 178 179 181 181 182 180 151 179 Shutdown temperature and meltdown temperature difference (℃) 47 47 47 49 50 50 44 12 41 Marginal oxygen index 24.5 23.2 25.1 24.2 23.7 24.7 18.2 17.4 19.2

Experimental Example

The evaluation results of the separators prepared according to Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1 above.

Examples 1-6 are the case where both a vinyl group containing alkoxy silane compound and a vinyl group containing phosphorus compound were thrown in. On the other hand, in Comparative Example 1, only the vinyl group-containing alkoxy silane compound was added. In Comparative Example 2, neither the vinyl group-containing alkoxy silane compound nor the vinyl group-containing phosphorus-based compound was added.

As can be seen from Table 1, when both the alkoxy silane compound and the vinyl group-containing phosphorus compound were added (Examples 1 to 6), the shutdown temperature and the meltdown temperature difference were greater than 45 ° C., which increased the safety of the separator. You can check it. In addition, in the case of Examples 1 to 6, the shutdown temperature was significantly lower than that of Comparative Examples 1 and 2.

On the other hand, Comparative Example 3 is a case where a phosphorus compound containing no vinyl group is used. In the case of the comparative example 3, the shutdown temperature reduction effect was inferior compared with the case where a vinyl group containing phosphorus compound was used at 138 degreeC.

In Table 1, specific measurement methods for each evaluation are as follows.

(One) shut down  How to measure temperature

The shutdown temperature was exposed to increasing temperature conditions (increasing at a rate of 5 ° C./min starting at 30 ° C.) while measuring the air permeability of the porous membrane. The shutdown temperature of the porous membrane is defined as the temperature at which the air permeability (Gurley value) of the microporous membrane exceeds the first 100,000 seconds / 100 cc. In this case, the air permeability of the porous membrane may be measured using an air permeability meter (Asahi Seiko, EGO-IT) according to JIS P8117.

(2) Melt  How to measure down temperature

Melt down temperature was measured using TMA (Thermomechanical Analysis). Specifically, a load of 0.01 N was applied to the separator and the degree of deformation was observed while increasing the temperature at a rate of 5 ° C./min. Melt down temperature of the separator '. As the melt down temperature is higher, the melt dimensional stability (Melt Integrity) is maintained at high temperature and the dimensional stability can be said.

(3) How to measure the marginal oxygen index

Limit oxygen index was calculated using the ASTM D 2863 test method.

Claims (14)

(S1) A polyolefin, a diluent, an initiator, a vinyl group-containing alkoxy silane compound, a vinyl group-containing phosphorus compound, and a crosslinking catalyst are added to an extruder, mixed, and extruded to form a silane compound and a phosphorus compound in the main chain of the polyolefin. Preparing a grafted polyolefin composition;
(S2) molding and stretching the grafted polyolefin composition into a sheet form;
(S3) extracting a diluent from the stretched sheet to prepare a porous membrane;
(S4) heat setting the porous membrane; And
(S5) crosslinking the porous membrane in the presence of water;
The vinyl group-containing phosphorus compound is diphenylvinylphosphine oxide, diphenylvinylphosphine, diphenylvinylphosphine, dimethyl vinyl phosphonate, diethyl vinyl phosphonate, diethyl vinyl phosphonate, Diphenylvinylphosphate, Dimethylvinylphosphate, Diethylvinylphosphate, Ethenyl dihydrogen phosphate, Isopropenyl dihydrogen phosphate, Vinyl phosphate (Vinylphosphonic acid), or a mixture of at least two or more thereof,
The shutdown temperature of the separator is 133 ℃ or less, the meltdown temperature of the separator is 175 ℃ or more method for producing a crosslinked polyolefin separator.
delete The method of claim 1,
The total content of the vinyl group-containing alkoxy silane compound and the vinyl group-containing phosphorus-based compound is 0.1 to 3 parts by weight based on a total of 100 parts by weight of the polyolefin and diluent, the method for producing a crosslinked polyolefin separator.
The method of claim 1,
The weight ratio of the said vinyl group containing alkoxy silane compound: vinyl group containing phosphorus compound is 90: 10-10: 70, The manufacturing method of the crosslinked polyolefin membrane.
The method of claim 1,
The vinyl group-containing alkoxy silane compound comprises a compound represented by the following formula (1), a method for producing a crosslinked polyolefin separator:
[Formula 1]

In Formula 1, R _1, R _2, and R ₃ are each independently an alkoxy group having 1 to 10 carbon atoms or an alkyl group having 1 to 10 carbon atoms, wherein R _1, R _2, and At least one of R ₃ is an alkoxy group;
R is a vinyl group, an acryloxy group, a methacryloxy group, or an alkyl group having 1 to 20 carbon atoms, wherein at least one hydrogen of the alkyl group is substituted with a vinyl group, an acryloxy group, or a methacryloxy group.
The method of claim 5,
The vinyl group-containing alkoxy silane compound is vinyl trimethoxysilane, vinyl triethoxysilane, vinyl triacetoxysilane, (3-methacryloxypropyl) trimethoxysilane, (3-methacryloxypropyl) triethoxy A method for producing a crosslinked polyolefin separation membrane comprising silane, vinylmethyldimethoxysilane, vinyl-tris (2-methoxyethoxy) silane, vinylmethyldiethoxysilane, or a mixture of at least two of them.
delete The method of claim 1,
Method for producing a cross-linked polyolefin separation membrane, the difference between the shutdown temperature and the meltdown temperature of the separator is 30 ℃ or more.
A silane compound and a phosphorus compound are grafted to the main chain of the polyolefin, and include a silane-derived crosslinked structure,
A crosslinked polyolefin separation membrane, characterized in that the shutdown temperature of the separator is 133 ° C. or less, and the meltdown temperature of the separator is 175 ° C. or more.
The method of claim 9
Cross-linked polyolefin separator, wherein the silane-derived crosslinked structure comprises a -Si-O-Si- bonding group.
delete The method of claim 9,
Cross-linked polyolefin separation membrane, the difference between the shutdown temperature and the meltdown temperature of 30 ℃ or more.
The method of claim 9,
Cross-linked polyolefin separator of the separator has a limited oxygen index (LOI, Limited Oxygen Index) of 20 to 30.
The method of claim 9,
The separator is a cross-linked polyolefin separator for lithium secondary batteries.