Method for preparing crosslinked polyolefin microporous membrane

Abstract

The present invention relates to a method for preparing a crosslinked polyolefin separation membrane and, more specifically, to a method for preparing a crosslinked polyolefin separation membrane, comprising the steps of: introducing a raw material into an extruder so as to extrude same, the raw material comprising a polyolefin, an oil and a polypropylene-supported crosslinking agent; and stretching a product of the extrusion step. Therefore, the separation membrane has an average molecular weight higher than that of the used polyolefin, and thus increases rigidity, increases meltdown temperature and minimizes gel generation.

Description

Method for manufacturing a cross-linked polyolefin microporous membrane

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0172367 filed November 27, 2024, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.

[0003] Technology field

[0004] The present invention relates to a method for manufacturing a cross-linked polyolefin microporous membrane.

[0005]

[0006] Lithium-ion batteries, which have high power, high capacity, lightweight, and miniaturization characteristics, are composed of four elements: a positive electrode, a negative electrode, an electrolyte, and a separator. Among these, the separator plays a role in increasing the stability of the battery by electrically separating the positive and negative electrodes.

[0007] The required characteristics of separators vary depending on their application and purpose. For general small devices, polyolefin-based microporous membranes with a thickness of approximately 15 µm to 25 µm and pores of 50 nm to 1 µm are generally used. Characteristics required include insulation to prevent short circuits between electrodes, a thin thickness for high capacity, high tensile strength and tensile strength to prevent deformation during battery assembly and rupture caused by metal impurities, low shrinkage at high temperatures, and excellent electrochemical stability. Additionally, characteristics such as an air permeability of approximately 400 sec / 100 cc and a porosity of approximately 40% are required for smooth ion conduction of the electrolyte and excellent impregnation.

[0008] In contrast, for applications requiring high power characteristics such as HEVs and PHEVs, the air permeability value is lowered to improve power characteristics, and the melt-down temperature is higher than approximately 180°C to prevent short circuits between electrodes even when exposed to high temperatures due to abnormal battery behavior.

[0009] Methods for manufacturing microporous separation membranes are classified into dry and wet methods depending on whether a solvent is used. The dry method involves producing a separation membrane by melt-extruding a crystalline polyolefin-based polymer material, molding it into a plate-like sheet, heat-treating it, and then forming pores through stretching at low and high temperatures. Since no solvent is used, the process is simplified and productivity is excellent; however, it is disadvantageous for producing products with wide width dimensions, and there are drawbacks such as the membrane thickness being prone to non-uniformity and directional dependence of mechanical strength due to uniaxial stretching. The wet method involves mixing a low-molecular-weight organic material (pore-forming agent), such as liquid paraffin or solid wax, with a polyolefin-based polymer material, heating and melting it in an extruder, and producing a sheet by passing it through a T-die and a casting roll. The sheet is then stretched at a temperature near the crystal melting point, washed with a non-volatile solvent to remove residual solvent, and the pore structure is fixed through drying and heat treatment.

[0010] Among the components of lithium-ion batteries, the separator is a critical technology, and its physical properties and quality characteristics are key factors determining battery performance. In particular, since physical properties such as tensile strength and puncture strength are contradictory to pore characteristics such as air permeability and porosity, it is essential to adjust these properties according to the battery's application. Although various attempts have been made to address this issue, there is currently no commercially available solution that is sufficiently satisfactory.

[0011] As a method to increase the tensile strength and spindle strength of polyethylene membranes, it is intended to use high molecular weight polyethylene with a molecular weight of 1 million g / mol or more when manufacturing membranes. However, high molecular weight polyethylene has a very high melt viscosity, which causes a greater processing load during the extrusion process, resulting in a decrease in extrusion speed and membrane production speed.

[0012] Since polyethylene separators melt down at around 160 degrees, if the internal temperature of the secondary battery rises above that level, they melt and shrink, causing a short circuit between the positive and negative electrodes and potentially leading to thermal runaway. Therefore, to ensure the stability of secondary batteries, technological development is proceeding in the direction of increasing the meltdown temperature, and cross-linking the polyethylene separator is one such method.

[0013] The reactive extrusion crosslinking method commonly used for crosslinking polyolefins involves introducing the resin and a crosslinking initiator into an extruder and allowing crosslinking to occur under high-temperature extruder conditions. However, this method has the disadvantage of poor overall uniformity because the crosslinking reaction occurs locally before the crosslinking agent is uniformly spread within the extruder due to the rapid reaction speed. While this method is applicable to applications such as thick pipes, it has the disadvantage that when applied to thin films like separators, a large amount of crosslinked gel is generated, significantly degrading the appearance and performance of the separator.

[0014] Conventional water-crosslinked membranes are manufactured by adding silane during the extrusion stage to produce a silane-grafted membrane, followed by a crosslinking process for more than 24 hours in a high-temperature and high-humidity environment. Since the current manufacturing linear velocity of membranes is very fast, ranging from 5 m / min to 100 m / min, water-crosslinked membranes using silane are not suitable.

[0015] The reactive extrusion crosslinking method commonly used for crosslinking polyolefins involves introducing the resin and a crosslinking agent into an extruder and allowing crosslinking to occur under high-temperature extruder conditions. However, this method has the disadvantage of reduced overall uniformity because the crosslinking reaction occurs locally before the crosslinking agent is uniformly spread within the extruder due to the rapid reaction speed. While this method is applicable to applications such as thick pipes, it has the disadvantage that when applied to thin films like separators, a large amount of crosslinked gel is generated, degrading the appearance and properties of the separator.

[0016]

[0017] Prior art literature

[0018] Republic of Korea Registered Patent No. 10-1857156

[0019]

[0020] The present invention, aimed at solving the problems described above, provides a method for manufacturing a cross-linked polyolefin membrane by adding a polypropylene-supported crosslinking agent and proceeding with crosslinking during the extrusion of a polyolefin, followed by stretching, extraction, and heat setting processes.

[0021] The problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description below.

[0022] To solve the problems of strength and meltdown temperature of the separation membrane as described above, the present invention provides a method for manufacturing a cross-linked polyolefin separation membrane comprising: a step of extruding a raw material by feeding it into an extruder and extruding it, wherein the raw material comprises a polyolefin, an oil, and a polypropylene-supported crosslinking agent; and a step of stretching the product of the extruding step.

[0023] The molecular weight of the above-mentioned cross-linked polyolefin separator may be increased by more than 300,000 compared to the polyolefin used.

[0024] The above polypropylene-supported crosslinking agent may be a hydrocarbon containing a functional group that generates active oxygen upon decomposition.

[0025] In the above polypropylene-supported crosslinking agent, the ratio A:B of the weight of the polypropylene support (A) and the weight of the active oxygen (B) included in the crosslinking agent component may be 99.9:0.1 to 90:10.

[0026] The above cross-linked polyolefin separator may have a meltdown temperature of 150°C or higher.

[0027] The roughness with respect to the basis weight of the above separator is 80 gf / (g / m 2 It may be more than )

[0028] The thickness of the above separation membrane may be 3 μm to 20 μm.

[0029] The above oil may be a paraffinic oil.

[0030] The weight ratio of polyolefin and oil of the raw materials supplied during the above extrusion may be 10:90 to 40:60.

[0031] The step of stretching the product of the extrusion step may include: a first stretching step of stretching the product of the extrusion step at 100°C to 125°C in the machine direction (MD) at a ratio of 2 to 6 times; and a second stretching step of stretching the extruded product stretched in the first stretching step at 116°C to 135°C in the width direction (TD) at a ratio of 7 to 12.5 times.

[0032] After the above stretching step, an extraction step to remove oil through extraction may be further included.

[0033] After the extraction step above, a step of heat-fixing at 110°C to 135°C at a magnification of 1 to 1.8 times in the width direction (TD) may be further included.

[0034] The weight of active oxygen / weight of polyolefin of the above polypropylene-supported crosslinking agent may be 2.5 to 100 ppm.

[0035] The separator manufactured according to the present invention is crosslinked during the extrusion step, thereby increasing the molecular weight and improving strength, and the melt-down temperature can be increased. Additionally, by using a polypropylene-supported crosslinking agent, a uniform degree of crosslinking is exhibited within the extruder, which can minimize the amount of gel appearing on the surface of the separator.

[0036] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by a person skilled in the art from the description below.

[0037] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described in detail below. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the present invention, and the present invention is defined only by the scope of the claims.

[0038] Prior to the explanation, the meanings of the terms used in this specification are briefly explained. However, since the explanation of terms is intended to aid in understanding this specification, it should be noted that they are not used to limit the technical scope of the invention unless explicitly stated to be a limiting factor.

[0039] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used in this specification, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned. Throughout the specification, "and / or" includes each of the components mentioned and all combinations of one or more. Although terms such as "primary," "secondary," etc., are used to describe various components, these components are not limited by these terms. These terms are used merely to distinguish one component from another.

[0040] Unless otherwise defined, all terms used herein (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0041]

[0042] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0043] The present invention provides a method for manufacturing a cross-linked polyolefin membrane, comprising: a step of extruding a raw material by feeding it into an extruder and extruding it, wherein the raw material comprises a polyolefin, an oil, and a polypropylene-supported crosslinking agent; and a step of stretching the product of the extruding step.

[0044] The above polyolefin may be an ethylene homopolymer, an ethylene-alphaolefin copolymer, or a mixture of the two polymers, and the viscosity-average molecular weight of the polyolefin used may be 250,000 g / mol to 3,000,000 g / mol.

[0045] Conditions such as the temperature at which the extrusion is performed can be controlled to conditions favorable for extrusion processing, such that the polyolefin resin melts and has excellent mixability with oil. The temperature at which the extrusion is performed may be, for example, 150°C to 250°C, preferably 180°C to 250°C, more preferably 190°C or higher and less than 220°C, and most preferably 190°C to 215°C.

[0046] In one embodiment, the raw material may further include a neutralizing agent. The neutralizing agent may be one or more selected from the group consisting of calcium stearic acid, zinc stearic acid, magnesium aluminum hydroxycarbonate, zinc oxide, and magnesium hydroxystearic acid. As a specific example, the neutralizing agent may be calcium stearic acid.

[0047] In one embodiment, the raw material may further include an antioxidant. The antioxidant is 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 1,6-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamido]hexane, 1,6-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamido]propane, tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane, pentaerythritol-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenol)propionate), The antioxidant may be one or more selected from the group consisting of 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazinan-2,4,6-trione, bis(octadecyl)hydroxyamine, tris(2,4-di-tert-butylphenyl)-phosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphite, and bis(2,4-di-tert-butylphenyl)pentaerythritol-di-phosphite. As a specific example, the antioxidant may be a mixture of pentaerythritol-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenol)propionate) and tris(2,4-di-tert-butylphenyl)-phosphite.

[0048] The above polypropylene-supported crosslinking agent refers to a polypropylene support in which a crosslinking agent component is impregnated. The polypropylene support used for support may be in the form of a powder produced after the polymerization of propylene and a comonomer, or it may be polypropylene pelletized through an extruder. The above polypropylene-supported crosslinking agent can be manufactured by dissolving a crosslinking agent component in a non-polar solvent, impregnating it into polypropylene powder or pellets, and drying. In the above polypropylene-supported crosslinking agent, the amount of the polypropylene crosslinking agent component loaded on the polypropylene is calculated as the ratio A:B of the weight of the polypropylene support (A) and the weight of the active oxygen contained in the crosslinking agent component (B), which may be 99.9:0.1 to 90:10.

[0049] The above-mentioned crosslinking agent component may be an organic peroxide as a compound capable of thermally decomposing to generate free radicals. Specifically, the initiator may be at least one selected from the group consisting of diacyl peroxide, peroxyester, peroxyketal, dialkyl peroxide, hydroperoxide, peroxydicarbonate, azo ester, and peroxyphthalide.

[0050] For example, the crosslinking agent component may be benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexine, di-t-butyl peroxide, 1,3-bis(t-butylperoxy-isopropyl)benzene, di-t-butylperoxyazelate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumyl peroxide, t-butylperoxy-3,5,5-trimethylhexoate, p-chlorobenzoyl peroxide, t-butyloxybenzoate, methyl ethyl ketone peroxide, tris(t-butylperoxy)triazine, t-butylperoxyacetate, t-butylperoxyisopropylcarbonate, etc., but is not particularly limited to these.

[0051] The microporous membrane produced by the method for producing a cross-linked polyolefin separation membrane according to the present invention can have small, uniform pores formed inside.

[0052] In one embodiment, the molecular weight of the cross-linked polyolefin separator may be increased by 300,000 or more compared to the polyolefin used, and preferably by 400,000 or more. When this range is satisfied, there is an effect of increasing the rigidity of the separator.

[0053] In one embodiment, the polypropylene-supported crosslinking agent may be a hydrocarbon containing a functional group that generates active oxygen upon decomposition.

[0054] In one embodiment, in the polypropylene-supported crosslinking agent, the ratio A:B of the weight of the polypropylene support (A) and the weight of the active oxygen (B) included in the crosslinking agent component may be 99.9:0.1 to 90:10.

[0055] In one embodiment, the cross-linked polyolefin separator may have a meltdown temperature of 150°C or higher, preferably 150°C to 240°C, more preferably 160°C to 230°C, and most preferably 160°C to 220°C.

[0056] In one embodiment, the protrusion strength with respect to the basis weight of the separator is 80 gf / (g / m²) 2 ) or more, preferably 80 gf / (g / m²) 2 ) to 150 gf / (g / m 2 ), more preferably 82 gf / (g / m²) 2 ) to 140 gf / (g / m 2 The polyolefin microporous membrane having a roughness strength for a basis weight within the aforementioned range can prevent the polyolefin microporous membrane from breaking due to external forces during the secondary battery assembly process or internal foreign matter after assembly.

[0057] In one embodiment, the thickness of the separator may be 3 μm to 20 μm, preferably 5 μm to 17 μm, more preferably 8 μm to 10 μm, and most preferably 8 μm to 15 μm. The thickness may be measured according to ASTM D374. The polyolefin microporous membrane has a constant thin thickness within the aforementioned range and can improve the stability of a secondary battery including it as a separator.

[0058] In one embodiment, the oil may be a paraffinic oil. The paraffinic oil may be any paraffinic hydrocarbon oil commonly used in the industry without limitation.

[0059] In one embodiment, the weight ratio of the polyolefin and oil of the raw materials supplied during the extrusion may be 10:90 to 40:60, preferably 15:85 to 35:65, and more preferably 18:82 to 30:70. When the polyolefin and the oil are supplied to an extruder and mixed within the aforementioned ranges, the mixing properties and extrusion processability are improved, and pores can be appropriately formed in the polyolefin microporous membrane being manufactured.

[0060] In one embodiment, the step of stretching the product of the extrusion step can be performed through a biaxial stretching process. In the biaxial stretching process, a stable biaxial stretching process can be performed on the extruded material in the machine direction (MD) and width direction (TD) through a tenter frame process. Through this, the extruded material can be stretched with a high elongation rate to achieve sufficient crystal orientation and form a polyolefin microporous membrane of uniform thickness, thereby obtaining the desired effect of improving physical properties.

[0061] In one embodiment, the step of stretching the product of the extrusion step may include: a first stretching step of stretching the product of the extrusion step at 100°C to 125°C in the machine direction (MD) at a ratio of 2 to 6; and a second stretching step of stretching the extruded product stretched in the first stretching step at 116°C to 135°C in the width direction (TD) at a ratio of 7 to 12.5. During the stretching step, the polyolefin resin and the oil undergo phase separation, thereby forming pores in the polyolefin microporous membrane that is finally manufactured.

[0062] In one embodiment, after the stretching step, an extraction step for removing oil through extraction may be further included, said extraction step may include: a step of dissolving oil present in the polyolefin microporous membrane in an organic solvent; and a step of drying and removing the organic solvent in which the oil is dissolved. The organic solvent may be any conventional organic solvent used in the art to dissolve oil without limitation, and for example, the organic solvent may be methylene chloride.

[0063] In one embodiment, after the extraction step, a heat-setting step may be further included at 110°C to 135°C at a magnification of 1 to 1.8 times in the width direction (TD), preferably at a magnification of 1 to 1.5 times. Residual stress can be removed by further undergoing the heat-setting step in the aforementioned range.

[0064] In one embodiment, the weight of active oxygen of the polypropylene-supported crosslinking agent / weight of the polyolefin may be 2.5 to 100 ppm.

[0065] In one embodiment, the number of gel contents of the cross-linked polyolefin separator prepared above may be 50 or fewer, preferably 25 or fewer, in a square range of 0.25 m * 0.25 m.

[0066]

[0067] [Examples and Comparative Examples]

[0068] Examples 1 to 5 and Comparative Examples 1 to 3: Preparation of Cross-linked Polyolefin Separators

[0069] First, a polypropylene-supported crosslinking agent was prepared. Polypropylene (Hanwha Total Energy Co., Ltd., HJ400, Melt index (2.16 kg): 8 g / 10 min, homopolymer) was used as the support, and 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane (Arkema Co., Luperox-101, molecular weight 290.44 g / mol, containing 4 active oxygen molecules) was used as the crosslinking agent.

[0070] 474g of the above crosslinking agent component was dissolved in 10L of normal hexane, mixed with 10kg of HJ400, and dried at room temperature to prepare a polypropylene-supported crosslinking agent supported with 1 wt% active oxygen and 4.53 wt% crosslinking agent component. [Amount of crosslinking agent component loaded = 1 wt% * 290.44 / (4 * 16) = 4.53 wt%]

[0071] A mixed powder was prepared using polypropylene-supported crosslinking agent and polyethylene (Hanwha Total Energy, V0603, molecular weight 600,000 g / mol) according to the ratios shown in Table 1. Subsequently, 600 ppm of Ca-stearate, a neutralizing agent, was added to the prepared mixed powder, and a mixture was prepared using a Henschel mixer. While feeding the prepared mixture from a hopper through a metering feeder, paraffin oil (Kukdong Oil & Chemical, LP-350F) was injected into the front of the extruder with a polyethylene / oil weight ratio of 20 / 80.

[0072] After the sheet exiting the extruder passed through a casting roll, a microporous membrane was manufactured by stretching the sheet 5 times in the MD (Machine direction) direction and 10 times in the TD (transverse direction) direction at 120°C to ensure a uniform thickness. The oil from the manufactured microporous membrane was removed by passing it through an extraction tank containing methylene chloride (MC), and the microporous membrane was heat-set in the TD direction at 125°C by 1.5 times to complete the final polyolefin separator.

[0073] The types of polyolefins and the mixing ratios of polyolefins were used as shown in Table 1 below, and the manufacturing conditions of the microporous membranes were all the same.

[0074]

[0075] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Crosslinking agent: Polypropylene - Supported crosslinking agent (HJ400-Luperox 101) - Luperox 101 Crosslinking agent ratio (active oxygen weight / polyethylene weight, ppm): 5 10 20 10 0 10 15 0 - 10 Extrusion temperature (°C): 20 20 20 20 20 20 20 20 20 0

[0076]

[0077] Evaluation: Measurement of physical properties of cross-linked polyolefin separators

[0078]

[0079] thickness

[0080] A VL-50 instrument from Mitutoyo, Japan was used, and the thickness was measured according to ASTM D374.

[0081]

[0082] Pin Puncture

[0083] Using the KES-G5 instrument from Kato Tech, Japan, the strength was measured at a speed of 10 mm / sec using a tip with a tip diameter of 1 mm in accordance with ASTM D-4833.

[0084]

[0085] Basic weight

[0086] A 50 mm x 50 mm sample was taken from the polyolefin microporous membrane, weighed, and the basis weight was calculated.

[0087]

[0088] melt-down temperature

[0089] The meltdown temperature was measured using thermomechanical analysis (TMA) after collecting membrane samples in the machine direction and the transverse direction. Specifically, a 10 mm long sample was placed in a TMA instrument (TA Instrument, Q400) and observed while applying a tension of 19.6 mN and varying the temperature conditions (starting at 30°C and changing by 5°C / min). The temperature at which the sample breaks due to rapid elongation as the temperature rises was measured, and the MD and TD were measured separately; the higher temperature was defined as the meltdown temperature of the corresponding sample.

[0090]

[0091] Viscosity average molecular weight

[0092] The viscosity-average molecular weight (Mw) was calculated from the intrinsic viscosity [η] according to ASTM D 4020. For polymers, viscosity in dilute solutions can provide useful information. The value obtained by dividing the polymer's viscosity by the solution's viscosity and concentration is called specific viscosity, and the extrapolated value of specific viscosity as the polymer's concentration approaches zero is defined as intrinsic viscosity (IV). Since the IV value of linear polymers is mainly influenced by the polymer's size, it has a high correlation with molecular weight. For ultra-high molecular weight polyethylene, the Margolies equation shown below is widely used.

[0093] Mw = 5.37 X 10 4 Х [η] 1.49

[0094] (Mw represents the viscosity-average molecular weight (g / mol), and η represents the intrinsic viscosity (dl / g).)

[0095]

[0096] Gel contents

[0097] The gel content was determined by cutting the prepared cross-linked polyolefin separator into a 0.25 m * 0.25 m square, observing the surface using a Dino-lite digital camera, and measuring the number of cross-linked gels appearing with a size of 20 μm or larger.

[0098]

[0099] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Thickness (㎛) 9.5 9.8 9.9 9.2 8.9 Sheet not stretched 9.1 9.2 Strain strength (gf) 500 5555 204 104 304 304 10 Basis weight (g / m² 2 )5.15.24.954.84.95.2 Stone Strength / Basis Weight (gf / (g / m 2Meltdown temperature (°C) 16 2 1 7 0 1 7 1 8 0 1 7 0 1 4 6 1 7 0 Molecular weight of cross-linked membrane (g / mol) 900,000 1 300,000 1 500,000 1 300,000 1 100,000 580,000 1 150,000 Gel content (number) -3 8 1 5 2 5->100

[0100]

[0101] In Examples 1 to 4, it was confirmed that as the ratio of the polypropylene-supported crosslinking agent increased, the crosslinking rate increased and the meltdown temperature increased. It was observed that the gel content increased rapidly when the polypropylene-supported crosslinking agent was added at 20 ppm or more, and that the strength per unit weight (spin strength / basis weight) reached a maximum value at 10 ppm. As shown in Comparative Example 1, when the ratio of the polypropylene-supported crosslinking agent was increased to 150 ppm, the elasticity increased to the point where the sheet stretching process could not proceed, making it impossible to manufacture a separator. In Example 5, when the extrusion temperature was raised to 220 degrees at 10 ppm, the gel content increased due to a non-uniform crosslinking reaction, and when compared to Example 2, it was confirmed that no increase in spin strength was observed. Through Comparative Example 3, it was confirmed that when a general crosslinking agent is used instead of a polypropylene-supported crosslinking agent, a problem of excessive gel formation occurs.

[0102] It can be confirmed that by using the cross-linked polyolefin separator manufacturing method of the present invention, the molecular weight can be improved relative to the polyolefin raw material used through the cross-linking reaction, and the meltdown temperature can also be improved by increasing the ratio of polypropylene-supported cross-linking agent input. In addition, it can be seen that the gel content can be suppressed to a minimum, unlike general cross-linking methods.

[0103] Although embodiments of the present invention have been described above, those skilled in the art will understand that the present invention may be implemented in other specific forms without altering its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A step of extruding by feeding raw materials into an extruder, wherein the raw materials comprise a polyolefin, an oil, and a polypropylene-supported crosslinking agent; and A method for manufacturing a cross-linked polyolefin separator comprising a step of stretching the product of the extrusion step.

2. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator in which the viscosity-average molecular weight of the cross-linked polyolefin separator increases by more than 300,000 compared to the polyolefin used.

3. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator, characterized in that the above-mentioned polypropylene-supported crosslinking agent is a hydrocarbon containing a functional group that generates active oxygen upon decomposition.

4. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator, characterized in that, in the above-mentioned polypropylene-supported crosslinking agent, the ratio A:B of the weight of the polypropylene support (A) to the weight of the active oxygen (B) included in the crosslinking agent component is 99.9:0.1 to 90:

10.

5. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator characterized in that the cross-linked polyolefin separator has a meltdown temperature of 150°C or higher.

6. In Paragraph 1, The roughness with respect to the basis weight of the above separator is 80 gf / (g / m 2 Method for manufacturing a cross-linked polyolefin separator membrane ) or more 7. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator having a thickness of 3 μm to 20 μm.

8. In Paragraph 1, The above oil is a paraffin-based oil. Method for manufacturing a cross-linked polyolefin separator.

9. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator, wherein the weight ratio of the polyolefin and oil of the raw materials supplied during the above extrusion is 10:90 to 40:

60.

10. In Paragraph 1, The step of stretching the product of the above extrusion step is, A first stretching step of stretching the product of the extrusion step above at 100°C to 125°C in the machine direction (MD) at a ratio of 2 to 6 times; and A method for manufacturing a cross-linked polyolefin separator, comprising a second stretching step of stretching the extruded material stretched in the first stretching step at 116 ℃ to 135 ℃ in the width direction (TD) at a ratio of 7 to 12.

5.

11. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator, further comprising an extraction step for removing oil through extraction after the above-mentioned stretching step.

12. In Paragraph 11, A method for manufacturing a cross-linked polyolefin separator, comprising further a step of heat-setting at 110°C to 135°C with a magnification of 1 to 1.8 in the width direction (TD) after the extraction step.

13. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator characterized in that the weight of active oxygen of the polypropylene-supported crosslinking agent / weight of the polyolefin is 2.5 to 100 ppm.

14. In Paragraph 1, A method for manufacturing a cross-linked polyolefin separator, characterized in that the temperature of the extrusion step is 190 ℃ or higher and less than 220 ℃.