JP6791526B2 - Heat-resistant polyolefin-based microporous membrane and its manufacturing method - Google Patents

Description

The present invention relates to a polyolefin-based resin composition, a polyolefin-based microporous membrane, and a method for producing the same.
More specifically, a heat-resistant polyolefin-based microporous membrane useful as a separator that enhances the safety of a lithium ion secondary battery, particularly a shutdown temperature of 140 ° C. or lower, and a liquid electrolytic solution of 190 ° C. or higher are thermally decomposed. A heat-resistant polyolefin microporous membrane that is an ultra-thin film that has both the characteristics of being non-melted (non-melted down) until it is deactivated, and has excellent low shrinkage at high temperatures, mechanical properties, and air permeability. And its manufacturing method.

Polyform microporous membranes are used in various applications such as battery separators, electrolytic condenser membranes, various filters, moisture permeable and waterproof clothing, reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes. When a polyolefin-based microporous membrane is used as a battery separator, particularly a separator for a lithium ion secondary battery, battery characteristics, battery productivity, and battery safety are important. For that purpose, excellent air permeability, mechanical properties, heat resistance, low shrinkage, shutdown characteristics, non-meltdown characteristics and the like are required. For example, if the mechanical strength is low, the voltage of the battery may drop due to a short circuit of the electrodes when used as a battery separator. In addition, when metallic foreign matter is mixed in the battery, or when lithium metal dendrites (dendritic protrusions) are generated due to misuse, if the piercing strength of the battery separator is low, the electrodes will short-circuit and abnormal heat generation of the battery will occur. To reach.
In recent years, lithium-ion secondary batteries have been widely used as a main power source for portable electronic devices such as notebook personal computers, mobile phones, and integrated camcorders. Due to the demand for higher performance and long-term driving of these portable electronic devices, technological development is underway to further increase the energy density, capacity, and output of lithium-ion secondary batteries. ..
From the viewpoint of increasing the battery capacity by containing as much positive and negative electrode active materials as possible in the limited internal volume of the battery, an unlimited thin film of the battery separator is required. On the other hand, in large lithium-ion secondary batteries as power sources for hybrid vehicles, electric vehicles (EVs), and aircraft, for safety reasons, the battery separator shrinks and melts, causing a short circuit due to film rupture. , It is necessary to avoid smoking and ignition. In addition to the shutdown characteristics, it is also required to have sufficient heat resistance from the viewpoint of non-meltdown characteristics. In recent years, due to the demand to increase the battery capacity, ceramics such as alumina and silica are applied to the surface of a polyethylene separator (12-9 micron thickness), which is easy to thin, to supplement heat resistance, and the thickness is 2-3 microns. Ingenuity has been made to form the surface layer of silica. However, since the ceramic particles are on the surface layer, the lithium ion conductivity after impregnation with the electrolytic solution is inferior to that without the above coating.

It also requires additional equipment for coating. The pores formed with great care are easily closed in the coating process. It is necessary to make the coating film as thin as possible so as to maintain good air permeability related to lithium ion conductivity, but this is contrary to heat resistance and increases the product cost. In addition, the ceramic coating film impairs the flexibility of the polyolefin-based microporous film, and cracks may occur in the vicinity of the winding shaft of the cylindrical battery, and powder may be generated from the coating film.
On the other hand, the polyolefin-based microporous membrane has an advantage that it is hardly deteriorated by the electrolytic solution. Recently, regarding the characteristics of a separator, the quality of lithium ion conductivity can be easily judged from the measurement result of porosity and the test result of air permeability.
In the case of forming a thin film of 12 microns or less, not only mechanical strength but also characteristics related to battery life such as cycle characteristics and characteristics related to battery productivity such as electrolyte injection property are emphasized. In particular, the electrodes of a lithium ion secondary battery repeatedly expand / contract with charging / discharging. Therefore, the load / release of the force applied to the battery separator in the thickness direction is repeated. In order to obtain a long-life battery, it is necessary to improve the adhesion at the interface between the separator and the electrode. Due to an increase in electrode size and electrode density due to an increase in battery capacity in recent years, the pressure on the separator tends to become stronger during battery assembly. In such a situation, in order to maintain the characteristics of the battery, it is required that the change in the permeability of the separator due to compression is small. If the separator is easily compressed, there is a high possibility that the capacity of the battery will decrease (cycle characteristics will deteriorate). Further, due to the increase in the electrode size due to the increase in the capacity of the battery as described above, the property of injecting the electrolytic solution into the battery is lowered, which causes a decrease in the productivity of the battery. Electrolyte injection properties must also be taken into consideration when improving the separator.

Japanese Unexamined Patent Publication No. 2011-184671 Japanese Patent No. 5766291 Japanese Unexamined Patent Publication No. 8-25007 Japanese Unexamined Patent Publication No. 10-17693 JP-A-2017-88836 JP-A-2018-76476 WO-A1-2012 / 020671 WO-A1-2017 / 170288 WO-A1-2016 / 104791 WO-A1-2016 / 104790 Special Table 2012-530619 Special Table 2012-530618

"Lithium Ion Rechargeable Battery 2nd Edition" Masayuki Yoshio and Akiya Ozawa (eds.), Atsushi Adachi (author of Chapter 8), Nikkan Kogyo Shimbun, 2000, p.107-p.120 "Unnamed Battery Development Secret Story", Isao Kuribayashi, KEE Co., Ltd., 2015, p.101-p.105

Patent Documents 1 and 2 disclose that a poly (4-methylpentene-1) resin (PMP) and a polyethylene-based resin are mixed to obtain a microporous film, but polybutadiene, polyisoprene, or butadiene- There is no mention of the hydrogenated additives in the isoprene copolymer. Patent Document 2 discloses mixing an olefin block copolymer containing ethylene as a constituent component.
Patent Documents 3 and 4 disclose that, in a film composed of three layers, a layer made of poly (4-methylpentene-1) is used as a double-sided layer and a layer made of polyethylene is used as an intermediate layer. There is no mention of a layer consisting of (4-methylpentene-1) and polyethylene.
Patent Documents 5 and 6 suggest lower limits of film thickness of 5 microns and 6 microns, preferably 7 to 25 microns. However, there is no description of a method for stably producing a microporous film without breaking the film during stretching.
Patent Document 7 aims at a three-layer structure, and the maximum amount of polymethylpentene is about 12.0% by weight (presumed to be the amount in the surface layer), in which case the appearance is about 6%. There is a description that it is inferior to the case of.
Patent Documents 8, 9 and 10 describe the composition of polyethylene and polymethylpentene, but the amount of polymethylpentene is 10% by mass or less so as not to deviate from the polyethylene-based microporous membrane. Patent Documents 11 and 12 disclose microporous membranes composed of two or more layers, and there is no reference to polypropylene elastomer or block copolymer having polyethylene blocks at both ends in any of the layers.
Non-Patent Document 1 describes a single-layer polyethylene microporous membrane, a single-layer polypropylene microporous membrane, a polyolefin-based microporous membrane composed of three layers of polyethylene / polypropylene / polyethylene, and their characteristics, all of which are described. It has been shown that above 185 ° C., the properties cannot be thermally retained. Non-Patent Document 2 shows that a heat-resistant polyolefin-based microporous membrane having a shutdown property and low shrinkage at high temperatures exists, but details of the composition and the manufacturing method are not disclosed.

An object of the present invention is to provide a polyolefin-based microporous membrane having low shrinkage at high temperature, excellent mechanical properties, air permeability, and a thin film thickness. The polyolefin-based microporous membrane has a shutdown temperature of 140 ° C. or lower, which is useful as a separator for enhancing the safety and life of a lithium ion secondary battery, and the liquid electrolyte is thermally decomposed and deactivated up to 190 ° C. or higher. It is preferable to have both characteristics of non-melting (non-meltdown) at the same time. Another object of the present invention is to provide a method for producing such a film.

The present invention comprises 25 to 50% by mass of ultrahigh molecular weight polyethylene, 1 to 15% by mass of polyethylene, and 35 to 65% by mass of a copolymer of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. Provided is a resin composition containing 0.1 to 2% by mass of a hydrogenated product of one or more polymers selected from polybutadiene, polyisoprene and a butadiene-isoprene copolymer, and 0.5 to 5% by mass of a propylene-based elastomer resin. To do. Hereinafter, the resin composition may be referred to as a “polyolefin resin composition”.
Further, in the present invention, 25 to 50% by mass of ultrahigh molecular weight polyethylene, 1 to 15% by mass of polyethylene, and 35 to 65% by mass of a copolymer of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. A resin composition containing 0.1 to 2% by mass of a hydrogenated product of one or more polymers selected from polybutadiene, polyisoprene and a butadiene-isoprene copolymer, and 0.5 to 5% by mass of a propylene-based elastomer resin. 10 parts by mass to 49 parts by mass and 90 parts by mass to 51 parts by mass of the plasticizer are supplied to a twin-screw extruder, melt-kneaded, extruded from a die, and cooled to obtain a gel-like sheet molded product. This includes biaxially stretching the molded sheet to obtain a film, and removing a part of the plasticizer from the film by dissolving it in a solvent, and further stretching the film by biaxial stretching. Provided is a method for producing a polyolefin-based microporous film.
Further, in the step 1, the present invention is a copolymer 35 of ultrahigh molecular weight polyethylene 25 to 50% by mass, polyethylene 1 to 15% by mass, 4-methyl-1-pentene, and α-olefin having 3 or more carbon atoms. Includes ~ 65% by weight, 0.1 to 2% by weight of hydrogenated one or more resins selected from polybutadiene, polyisoprene and butadiene isoprene copolymers, and 0.5 to 5% by weight of propylene elastomer resins. 10 parts by mass to 49 parts by mass of the resin composition and 90 parts by mass to 51 parts by mass of the plasticizer are supplied to a twin-screw extruder, melt-kneaded, extruded from a die, and cooled to obtain a gel sheet molded product. , The gel-like sheet molded product is biaxially stretched to obtain a film, and a part of the plasticizer is dissolved and removed from the film in a solvent, and further biaxially stretched to obtain a film A. thing,
In step 2, 25 to 50% by mass of ultrahigh molecular weight polyethylene, 1 to 15% by mass of polyethylene, and 35 to 65% by mass of a copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. , Polybutadiene, polyisoprene and butadiene-isoprene copolymers in a resin composition comprising 0.1 to 2% by weight of a hydrogenated additive of one or more resins and 0.5 to 5% by weight of a propylene-based elastomer resin. Therefore, 10 to 49 parts by mass of the resin composition and 90 to 51 parts by mass of the plasticizer in which the amount of the hydrogen additive is different from the amount of the hydrogen additive in the above step 1 are supplied to the twin-screw extruder and melt-kneaded. Then, it is extruded from a die and cooled to obtain a gel-like sheet molded product, the gel-like sheet molded product is biaxially stretched to obtain a film, and a part of a plasticizing agent is used as a solvent from the film. Dissolve and remove, and further stretch by biaxial stretching to obtain film B,
In step 3, one or more of the film A and one or more of the film B are alternately laminated, and further stretched by biaxial stretching.
Provided is a method for producing a polyolefin-based microporous membrane including.

INDUSTRIAL APPLICABILITY The present invention provides a polyolefin-based microporous membrane having low shrinkage at high temperature, excellent mechanical properties, air permeability, and a thin film thickness. The polyolefin-based microporous membrane has a shutdown temperature of 140 ° C. or lower, which is useful as a separator for enhancing the safety and life of a lithium ion secondary battery, and the liquid electrolyte is thermally decomposed and deactivated up to 190 ° C. or higher. It is preferable to have both characteristics of non-melting (non-meltdown) at the same time. The present invention also provides a method for producing such a film. Since the polyolefin-based microporous membrane having high heat resistance and high temperature and low shrinkage of the present invention has high heat resistance up to 190 ° C., it is necessary to apply ceramic particles for improving heat resistance as in a conventional polyethylene separator. do not do. Further, it is a heat-resistant polyolefin-based microporous membrane having a single-layer structure (even when two extruded and stretched membranes are laminated, they become substantially one layer in the process of further biaxial stretching). When handled as a separator in the battery assembly process, the sowing has flexibility and flexibility, so that workability is not impaired. By utilizing the existing wet separator equipment and using the resin composition of the present invention instead of polyethylene to adjust the processing temperature such as the extruder temperature and the film stretching temperature in the strong kneading screw unit, the polyolefin-based microporous Membranes can be easily mass-produced.

Further, in the present invention, the capacity of a pouch-type battery, a prism-type battery, or a cylindrical can battery is formed by applying a solution of a crosslinkable polymer to the surface of the polyolefin-based microporous film having a single-layer structure to form an ultrathin film. Surface-modified polyolefin-based microporous membranes that are surface-modified to provide longer retention life are also provided.

The microporous membrane of the present invention is suitably produced by a production method including the following steps. Hereinafter, each preferable step will be described in sequence.
(Step 1) 25 to 50% by mass of ultrahigh molecular weight polyethylene, 1 to 15% by mass of polyethylene, and 35 to 65% by mass of a copolymer of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. 10% by mass of a resin composition containing 0.1 to 2% by mass of a hydrogenated product of one or more polymers selected from polybutadiene, polyisoprene and a butadiene-isoprene copolymer and 0.5 to 5% by mass of a propylene-based elastomer resin. Parts to 49 parts by mass, and antioxidants, inorganic fillers, etc. as optional components are supplied to the twin-screw extruder. For example, 90 parts by mass to 51 parts by mass of the plasticizer is supplied from the side feeder, melt-kneaded, and then melt-kneaded. The process of extruding and cooling and rolling on a roll to obtain a gel sheet polymer;
(Step 2) A step of stretching the gel-like sheet molded product obtained in Step 1 in the biaxial direction (MD direction, TD direction) sequentially or simultaneously by the biaxial stretching method;
(Step 3) A step of extracting and removing a part of the plasticizer from the thin film on which the fibril fiber structure is formed obtained in step 2 with a solvent, and vaporizing and removing the solvent to obtain a microporous film;
(Step 4) A step of heating and pressurizing the microporous membrane obtained in Step 3. In this step, the porosity is reduced and the fibril fibers are semi-melted or melted to increase the small fibril diameter;
(Step 5) A step of additionally stretching the sheet-shaped molded product obtained in step 4 by sequentially or simultaneously biaxial stretching in the biaxial directions (MD direction, TD direction);
(Step 6) A step of extracting a plasticizer with a solvent from the thin film obtained in step 5 to substantially completely remove the solvent and vaporizing the solvent, or a step of obtaining a film in step 5 to further reduce the film thickness. The process of heating and pressurizing the thin film, extracting the plasticizer from the thin film with a solvent to remove the solvent substantially completely, and vaporizing the solvent.
(Step 7) A step of heat-treating, re-stretching, and heat-fixing the polyolefin-based microporous membrane obtained in step 6 as necessary.
The above steps 6 and 7 are optional.
Alternatively, (Step 5-2) Membranes obtained by performing Steps 1 to 5 using the film A obtained in Step 5 and a resin composition in which the amount of hydrogenated material is different from that of the resin composition in Step 1. After stacking B and further performing a step of performing additional stretching by sequentially or simultaneously biaxial stretching in the biaxial directions (MD direction, TD direction), the process can proceed to step 6.
Further, if necessary, a step of applying a crosslinkable polymer to the surface of the polyolefin-based microporous membrane obtained in step 6 or 7 and drying to form an ultrathin surface layer may be added. The crosslinkable polymer can be crosslinked, for example by UV irradiation.

If necessary, various additives such as an ultraviolet absorber, an anti-blocking agent, a nucleating agent, a pigment, a dye, and an inorganic filler are added to the polyolefin resin composition or its melt-kneaded product as long as the effects of the present invention are not impaired. Can be added. For example, fine powder silica, alumina silica and the like can be added as the pore forming agent. Further, a so-called ceramic-containing surface layer film can also be formed by applying a ceramic such as alumina or silica and an organic solvent turbid substance or a water turbid substance of a binder on the surface of the microporous film.

The method of melt-kneading is not particularly limited, but it is preferable to knead uniformly in a twin-screw extruder. This method is particularly suitable for preparing a melt of the polyolefin-based resin mixture. The melting temperature is preferably in the range of + 10 ° C. to + 60 ° C., which is the average melting point of the polyolefin-based resin mixture. In particular, the melting temperature is preferably set in the extrusion temperature zone in the range of 190 to 240 ° C., more preferably in the range of 190 to 230 ° C. The plasticizer is preferably added in portions to the twin-screw extruder during kneading.
In order to prevent oxidative deterioration of the polyolefin resin composition during melt-kneading, it is preferable to add an antioxidant. Inorganic filler can be optionally added.

The ratio (L / D) of the screw length (L) to diameter (D) of the twin-screw extruder is preferably in the range of 30 to 100, more preferably in the range of 40 to 60. If the L / D is less than 30, melt-kneading may be insufficient, and in particular, a copolymer resin of ultra-high molecular weight polyethylene, 4-methyl-1-pentene, and α-olefin having 3 or more carbon atoms. Micro perfect melt kneading becomes difficult.
If the L / D is more than 100, the residence time of the polyolefin mixture melt and the plasticizer is too long, which causes thermal deterioration of the resin. The shape of the screw is not particularly limited, but it is preferable to select a deep groove screw from the viewpoint of melting and kneading components having greatly different resin melting points. The cylinder inner diameter of the twin-screw extruder is preferably 26 to 150 mm. When the polyolefin resin composition is put into a twin-screw extruder, the ratio Q / Ns of the input amount Q (kg / h) of the polyolefin resin composition and the plasticizer to the screw rotation speed Ns (rpm) is 0.1. It is preferably about 2 kg / h / rpm, particularly 0.3 to 1.9 kg / h / rpm. Below the above lower limit, the polyolefin resin is excessively shear-broken, leading to a decrease in the strength of the membrane product and the shutdown temperature. On the other hand, if the above upper limit is exceeded, the components may not be uniformly kneaded. The screw rotation speed Ns is preferably 60 rpm or more. The upper limit of the screw rotation speed Ns is not particularly limited, but the preferred rotation speed is 150 to 300 rpm.

As a method for forming the gel-like sheet molded product, a method in which the melt produced by the twin-screw extruder is extruded directly from the twin-screw extruder or from another extruder through a die through a gear pump and cooled is preferable. ..

As the die lip, a T die lip for a sheet having a rectangular base shape is usually used, but a double cylindrical hollow die lip, an inflation die lip and the like can also be used.
In the case of T-die lips for sheets, the gap of the dies is usually in the range of 0.2 to 0.8 mm, and the temperature of the resin mixture at the time of extrusion is preferably in the range of 220 to 250 ° C. The extrusion speed is preferably in the range of 0.2 to 80 m / min.

Cooling is preferably carried out to at least the gelation temperature or lower, more preferably 40 ° C. or lower. By cooling to a temperature below the gelation temperature, a phase-separated structure in which the "island" phase composed of the polyolefin-based resin composition is separated as a micro phase can be fixed in the "sea" phase of the plasticizer. Generally, when the cooling rate is slow, the higher-order structure of the obtained gel-like molded product becomes coarse, and the "islands" which are the pseudo-cell unit microphases forming the same tend to become large. When the cooling rate is high, the "islands" are small and the structure is dense. If the cooling rate is less than 50 ° C./min, crystallization of the resin proceeds and it is difficult to obtain a gel-like molded product suitable for stretching. As the cooling method, a method of bringing the extrude into direct contact with cold air, cooling water or another cooling medium, a method of bringing the extrude into contact with a roll cooled with a refrigerant, or the like can be used. Alternatively, a method can be used in which the resin and the plasticizer are melt-kneaded with a batch kneader, then formed into a sheet film using a compression molding machine, and cooled.
As the stretching method, flat stretching, tubular stretching, roll rolling and the like can be used.
Of these, flat stretching is preferable from the viewpoint of stretching uniformity. The stretching temperature is preferably selected within the range of approximately 120 ° C. to the average melting point of the polyolefin mixture. When the stretching temperature is less than 110 ° C., an excessive stretching stress is applied, which causes film rupture and deteriorates high temperature shrinkage resistance. The stretching temperature is preferably as high as possible in order to reduce the thermal shrinkage of the microporous membrane. However, the stretching temperature is preferably equal to or lower than the average melting point of the polyolefin-based resin mixture constituting the microporous film. When the temperature is equal to or lower than the average melting point temperature of the resin mixture, it is possible to avoid film rupture due to melting of the resin. When the stretching temperature exceeds the average melting point temperature, the polyolefin-based resin composition melts and the molecular chains cannot be oriented by stretching.

Biaxial stretching is performed by heating a gel-like sheet molded product and then using a normal tenter method, a roll method, an inflation method, a rolling method, or a combination of these methods. It may be either simultaneous biaxial stretching, sequential stretching or multi-stage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching).
The phenomena that occur in the process of the manufacturing method of the present invention will be described below, but the present invention is not limited thereto. In the present invention, it is important to change the resin mixture having an island structure, which is a dispersed phase existing between the states of a continuous phase sea structure composed of a plasticizer, into a fibril fiber structure by stretching. By stretching the gel-like sheet molded product, for example, 3.5 to 6 times, the gel-like structure of the molded product is changed to a structure containing fibril fibers having an average diameter of 50 nm to 400 nm. In order to increase the breaking strength of the sheet to 20 to 70 MPa, the fibers are bundled or the fibers are adjacent to each other by partial extraction and removal of the plasticizer. Final composition In order to make the fibril with a large diameter of about 200 nm to 3000 nm, it is necessary to reduce the voids after the plasticizer is partially removed after biaxial stretching.

When biaxially stretching after forming a gel-like sheet molded product, the stretching speeds in the longitudinal direction (MD) and the transverse direction (TD) are set in the longitudinal direction and the transverse direction when the unstretched sheet is stretched. The length of each is set to 1, and it is defined as the ratio of the length to be stretched per minute, and the stretching speeds in the vertical direction and the horizontal direction are preferably 20 times / min or less. If the stretching speed in the vertical direction or the horizontal direction is more than 20 times / minute, the melt shrinkage resistance may be deteriorated. The stretching speed in each direction is more preferably 15 times / minute or less, and further preferably 10 times / minute or less.

The stretching ratio per total area (hereinafter, may be referred to as the total area stretching ratio) is preferably 500 times or less. The total area stretching ratio is the product of the stretching ratio in MD (the product of each stretching ratio in the case of multiple stretching) and the stretching ratio in TD (the product of each stretching ratio in the case of multiple stretching). ). When the total area stretching ratio is more than 500, the high temperature shrinkage resistance may be deteriorated. The total area stretching ratio is preferably 450 times or less.
The 1-stretching ratio in the longitudinal direction (MD) and the lateral direction (TD) is preferably 3 to 20 times, more preferably 4 to 15 times, and further preferably 6 to 10 times, respectively. When the draw ratio is equal to or higher than the above lower limit, sufficient draw orientation is given, so that the strength of the microporous membrane can be improved. When the draw ratio is not more than the above upper limit, it is possible to avoid structural destruction of the microporous membrane due to excessive stretching. From the viewpoint of productivity, the draw ratio is preferably 4 times or more. From the viewpoint of improving the mechanical strength, it is more preferable to set the total area stretching ratio to 16 times or more by setting MD and TD to 4 times or more, respectively. The ratio of the draw ratio in MD to the draw ratio in TD is not particularly limited, but is preferably 0.5 to 2 in any case of simultaneous biaxial stretching, sequential biaxial stretching or uniaxial stretching, and 0. It is more preferably 7 to 1.3, and most preferably 1. As long as the stretching speed in each direction of MD and TD is 20 times / minute or less, MD and TD may be different from each other, but are preferably the same.

In the present invention, a substantially one-layer microporous film can be obtained by stacking two or more films obtained by stretching a gel-like sheet molded product and further stretching the film.
That is, in step 1, a copolymer of 25 to 50% by mass of ultra-high molecular weight polyethylene, 1 to 15% by mass of polyethylene, 4-methyl-1-pentene, and α-olefin having 3 or more carbon atoms is 35 to 65% by mass. 10. A resin composition containing 0.1 to 2% by mass of a hydrogenated product of one or more resins selected from polybutadiene, polyisoprene and a butadiene isoprene copolymer, and 0.5 to 5% by mass of a propylene-based elastomer resin. A gel-like sheet molded product is obtained by supplying parts by mass to 49 parts by mass and 90 parts by mass to 51 parts by mass of a plasticizer to a twin-screw extruder, melt-kneading, extruding from a die, and cooling. The sheet molded product is biaxially stretched to obtain a film, and a part of the plasticizer is dissolved and removed from the film in a solvent, and further biaxially stretched to obtain film A.
In step 2, 25 to 50% by mass of ultrahigh molecular weight polyethylene, 1 to 15% by mass of polyethylene, and 35 to 65% by mass of a copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. , Polybutadiene, polyisoprene and butadiene-isoprene copolymers in a resin composition comprising 0.1 to 2% by weight of a hydrogenated additive of one or more resins and 0.5 to 5% by weight of a propylene-based elastomer resin. Therefore, 10 to 49 parts by mass of the resin composition and 90 to 51 parts by mass of the plasticizer in which the amount of the hydrogen additive is different from the amount of the hydrogen additive in the above step 1 are supplied to the twin-screw extruder and melt-kneaded. Then, it is extruded from a die and cooled to obtain a gel-like sheet molded product, the gel-like sheet molded product is biaxially stretched to obtain a film, and a part of a plasticizing agent is used as a solvent from the film. Dissolve and remove, and further stretch by biaxial stretching to obtain film B,
In step 3, one or more of the film A and one or more of the film B are alternately laminated, and further stretched by biaxial stretching.
A method for producing a polyolefin-based microporous membrane including the above is also an aspect of the present invention.
In step 3, it is preferable to carry out calendering after stacking two or more films having different amounts of hydrogenated substances. According to this aspect, it becomes possible to obtain an ultrathin film having a more uniform film thickness distribution and up to about 2 microns.

It is preferable to perform a treatment (heat roll treatment) in which a hot roll is brought into contact with at least one surface of the stretched microporous film before the plasticizer is removed by the solvent. The contact time between the heating roll and the microporous membrane may be 0.1 seconds to 1 minute. The rolled surface may be brought into contact with the heated plasticizer while being held. As the heating roll, a smooth roll is preferable. Further, the single leaf may be subjected to heating reduction of a flat plate (for example, for 3 to 15 minutes) by a compression molding machine, and in the present specification, this is regarded as a form of heat roll treatment. Depending on the desired physical properties, a temperature distribution may be provided in the film thickness direction for stretching. By stretching with a temperature distribution in the film thickness direction, a microporous film having excellent mechanical strength can be generally obtained.

Since the polyolefin-based resin mixture phase and the plasticizer phase are phase-separated in the stretched film, a microporous film can be obtained by removing the plasticizer with a solvent. The method for removing such a solvent and a plasticizer is known. For example, the plasticizer can be dissolved in the solvent and removed from the membrane by passing the plasticizer-containing membrane through a solvent bath or immersing it.

It is preferable to perform heat treatment (heat stretching treatment and / or heat fixing treatment and / or heat shrinkage treatment) at least once after each stretching step, before removing the plasticizer or after removing the plasticizer. The heat treatment temperature is preferably determined in consideration of changes in strength and air permeability due to heat treatment.

In order to adjust the film physical properties such as porosity in the heat fixing treatment step, it is carried out by a commonly used tenter method, roll method or rolling method, and at least once, at least once in at least one axial direction, 1.01 to 2.0 in one direction. It is preferably carried out at a stretching ratio of fold, preferably 1.02 to 1.5 times. Further, the heat fixing treatment is performed by a tenter method, a roll method or a rolling method to promote crystallization of the polyolefin resin in the polyolefin-based microporous film and reduce microvoids. The heat shrinkage treatment may be carried out by a tenter method, a roll method or a rolling method, or may be carried out by using a belt conveyor or a floating roll. The heat shrinkage treatment is carried out in at least one direction with a shrinkage rate of 50% or less, 30% or less, more preferably 15% or less.

A plurality of the above-mentioned heat stretching treatment, heat fixing treatment, and heat shrinkage treatment may be performed in combination. The treatment with a hot roll (including a heated flat plate) is performed by bringing the hot roll into contact with at least one surface of the stretched gel-like molded product before washing. Contact between a heating roll (including a heating flat plate) whose temperature has been adjusted to a crystal temperature of the polyolefin resin of + 10 ° C. or higher and lower than the average melting point of the polyolefin resin composition and the microporous membrane in a contact time of 0.5 seconds to 1 minute. It is preferable to let it. The heated oil may be brought into contact with the surface of the roll while being held. As the heating roll, a crawl-plated roll having a smooth surface is preferable. Further, the heating flat plate is preferably polished # 400 or more # 700 of a stainless steel plate. In particular, when the heat shrinkage treatment is performed after the final stretching treatment, a heat-resistant polyolefin-based microporous film having a low shrinkage rate and high breaking strength can be obtained, which is preferable.

The film thickness of the heat-resistant polyolefin-based microporous membrane according to the preferred embodiment of the present invention is 1 to 30 μm, preferably 2 to 15 μm, and more preferably 2 to 10 μm. If the film thickness is 2 μm or more, it has the mechanical strength required for battery assembly as a heat-resistant polyolefin-based microporous membrane, has sufficient permeability even at 30 μm, and has high electrolyte impregnation even at 2 microns. It becomes. The thickness of the microporous membrane can be appropriately selected depending on the intended use, but when used as a separator for a small lithium ion secondary battery, it is preferably 4 to 15 μm, more preferably 5-9 μm. The film thickness is measured according to JIS standard K7130. Even when used as a separator for a large lithium ion secondary battery of an electric vehicle (EV) drive power source, 5 to 12 μm is preferable.

The distribution of the micropore structure region and the coarse pore structure region is not particularly limited. Usually, a copolymer (PMP) of 4-methyl-1-pentene and an α-olefin having 3 or more carbon atoms and an ultra-high molecular weight polyethylene (UHMWPE) are used in both the MD direction and the TD direction of the microporous film. As a result, the fibril fiber diameter is distributed, the micropore structure region and the coarse pore structure region are irregularly intricate, and the size of each region is also irregular. .. It is presumed that this structure has both shutdown characteristics and non-meltdown characteristics, and can maintain an appropriate breaking strength. Such a structure can be observed by, for example, a transmission electron microscope (TEM) or the like, and can be measured as a maximum height difference from the surface of the pores by an atomic force microscope (AFM).

Since it has a relatively large space and a relatively large surface roughness due to the coarse pore structure as described above, it is excellent in air permeability and electrolyte absorption, and moreover, the change in air permeability when pressure is applied. Is small. Therefore, when the membrane of the present invention is used as a separator for a lithium ion secondary battery, excellent battery productivity and battery cycle characteristics can be realized.

When the heat-resistant polyolefin-based microporous membrane of the present invention is used as a lithium ion secondary battery separator, high productivity of the battery can be realized, and the excellent cycle characteristics of the membrane extend the life of the battery. The polyolefin-based microporous membrane of the present invention obtained by uniform meltdown is economically advantageous in terms of manufacturing cost and manufacturing equipment, and is a substantially single-layer membrane, yet secures high temperature and low heat shrinkage at 190 ° C. It has so-called non-meltdown characteristics that do not rupture the film. No shutdown characteristics can be seen with conventional heat-resistant separators. The polyethylene microporous membrane of the present invention maintains a shutdown temperature that contributes to battery safety, and also has non-meltdown characteristics. In addition, the fluorine-based electrolyte complex salt used in the lithium-ion secondary battery decomposes at around 190 ° C and loses its lithium-ion conductivity and becomes inactive (dead) as a battery, so that the runaway of the battery can be suppressed or prevented. .. Until the temperature is reached, the heat-resistant polyolefin-based microporous membrane of the present invention does not break or melt down, but remains at a constant shrinkage and maintains its shape as a membrane. The separator made of the film of the present invention is excellent from the viewpoint of battery safety because it can prevent a short circuit between the edge portions of the positive electrode and the negative electrode due to the characteristics of high temperature and low heat shrinkage. The film separator of the present invention is particularly useful as a separator for EV batteries of large batteries. When assembling a battery using the heat-resistant polyolefin-based microporous membrane as a lithium ion secondary battery separator, in order to wind the battery in the conventional manner, the film of the ultrathin film is formed by the wind pressure generated during the winding. It is easy to float, and it may be necessary to reduce the tension control and shaft rotation speed for winding. As the battery assembly method of the present invention, in a cylindrical can battery, a square battery, and a large battery for EV, the separator is previously attached to a positive electrode sheet and rolled down to be fixed. Similarly, the separator is attached to the negative electrode sheet and rolled down before use. The productivity of the winding coil to be inserted into the cylindrical can is improved, and the battery capacity is also improved by 10 to 20% by reducing the film thickness. By superimposing the positive electrode sheet and the negative electrode sheet in advance, workability is improved and the battery capacity is also improved by 10 to 20% as compared with the method of incorporating the conventional separator.

Next, the heat-resistant polyolefin-based microporous membrane of the present invention and the material used in the method for producing the same will be described.

[1] Ultra-high molecular weight polyethylene The ultra-high molecular weight polyethylene, which is one component of the polyolefin-based microporous membrane of the present invention, has an ultra-high molecular weight in the range of 500,000 to 10 million, which is the viscosity average molecular weight obtained from the ultimate viscosity. One type or two or more types of polyethylene. Not only the homopolymer of ethylene but also a copolymer containing a small amount of other α-olefin units may be used in combination. Examples of α-olefins other than ethylene include copolymers with α-olefins having 3 to 30 carbon atoms such as propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, and octene. Be done.
Conventionally, it has been considered difficult to extrude and knead ultra-high molecular weight polyethylene having a viscosity average molecular weight of 3.5 million or more, and there have been few cases of its use. However, by mixing an ultra-high molecular weight polyethylene having a viscosity average molecular weight of 3.5 million or more and an ultra-high molecular weight polyethylene having a viscosity average molecular weight of 1 million to 2.5 million, for example, about 1 million, together with a plasticizer, a commercially available viscosity average molecular weight of 3.5 million It has been found that it is also possible to use ultra-high molecular weight polyethylenes of more than 6.4 million and up to 10 million. Furthermore, it was found that even in ultra-high molecular weight polyethylene having a viscosity average molecular weight of 7 million to 10 million, the polyolefin-based microporous membrane of the present invention, which is particularly thin with a viscosity of 10 μm or less, can maintain good breaking strength and piercing strength.
The amount of ultra-high molecular weight polyethylene is 20 to 50% by mass, preferably 25 to 40% by mass.

[2] Polyethylene The polyethylene of the present invention is preferably high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (HDPE) having a viscosity average molecular weight in the range of 150,000 to less than 500,000, preferably 200,000 to 450,000. High-density polyethylene (LDPE) and linear-low-density polyethylene (L-LDPE), which may be used alone or in combination of two or more. Not only the homopolymer of ethylene but also a copolymer containing a small amount of other α-olefin may be used in combination. Examples of α-olefins other than ethylene include copolymers with α-olefins having 3 to 30 carbon atoms such as propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, and octene. Be done.
The amount of polyethylene is 1 to 15% by mass, preferably 2 to 10% by mass.

For the above-mentioned ultra-high molecular weight polyethylene and the viscosity average molecular weight of polyethylene, the maximum viscosity [η] is measured at a measurement temperature of 135 ° C. using decalin as a solvent, and the viscosity average molecular weight (Mv) is calculated by the following formula. To do.

[Number 1]
Mv = 53700 * [η] ^1.37

[3] Copolymer of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms It is not a poly (4-methyl-1-pentene) homopolymer but methyl 4 used in the present invention. It is a copolymer of -methyl-1-pentene and an α-olefin having 3 or more carbon atoms. The α-olefin may be, for example, an α-olefin having 3 to 30 carbon atoms, particularly propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1 -Octadecene. From the viewpoint of miscibility at the time of melting with ultra-high molecular weight polyethylene, the copolymer in powder form is preferable, and from the viewpoint of heat resistance of the polyolefin-based microporous film in addition to miscibility, the copolymer is 4- It is preferable to contain 80 mol% to 99 mol% of units derived from methyl-1-pentene. The composition ratio of 4-methyl-1-pentene to α-olefin has a melting point (Tm) of 200 to 250 ° C, preferably 220 to 240 ° C, measured based on a DSC (Differential Scanning Calorimeter) test. It is adjusted to be. Further, the copolymer has a melt flow rate (MFR) of 0.05 to 250 g / 10 minutes, preferably 1 to 100 g / 10 minutes, measured under the conditions of a load of 5 kg and a temperature of 260 ° C. according to ASTM D1238. Is preferable. If the melt flow rate is less than the above lower limit, the melt viscosity is high and the moldability is poor, and if the melt flow rate exceeds the above upper limit, the melt viscosity is low and the film forming property is poor, and the mechanical strength is also low.
The amount of the copolymer of 4-methyl-1-pentene and the α-olefin having 3 or more carbon atoms is 30 to 65% by mass, preferably 35 to 60% by mass. If it is less than the above lower limit, the degree of improving the heat resistance of the polyolefin-based microporous membrane is insufficient, and it is not preferable because it does not show high temperature and low heat shrinkage after heat exposure in a circulating hot air dryer at 190 ° C. for 1 hour. Further, even if the above upper limit is exceeded, further remarkable improvement in low heat shrinkage cannot be expected, and the cost becomes high, which is not preferable.

[4] Hydrogenated one or more polymers selected from polybutadiene, polyisoprene and butadiene-isoprene copolymers Polybutadiene, polyisoprene, butadiene-isoprene copolymers having at least one end a polyethylene block, preferably 80% or more of the diene bond. Is preferably 90% or more hydrogenated. An ethylene-ethylene / butylene-ethylene block copolymer, which is a polybutadiene hydrogenated product, is preferable. This is an elastomer saturated by hydrogenating the double bond of the butadiene portion of the block copolymer obtained by the living catalyst. For example, JSR's Dynaron CEBC (for example, Dynaron 6200P, 6100P, 6201B) can be mentioned.
The amount of the hydrogenated product is 0.1 to 2% by mass, preferably 0.1 to 1% by mass.
It is considered that the hydrogenated additive is present at the interface of other different polymer substances in the resin composition of the present invention and has a function of enhancing the compatibility between the different polymer substances. It can be said that it is a kind of interface modifier.

[5] Propylene-based elastomer resin The propylene-based elastomer resin contains a structural unit derived from propylene and a structural unit derived from an α-olefin (excluding propylene) having 2 to 30 carbon atoms. This preferably has a microstructure in which "islands", which are nano-order level spiral crystal portions of 10 nm to 50 nm, are connected to each other to form a network structure and cover the entire amorphous portion. For example, "Notio SN0285" having a syndiotactic structure having a melting point (Tm) of 155 ° C. and a melting point (Tm) measured based on a DSC (Differential Scanning Calorimeter) test manufactured by Mitsui Chemicals Co., Ltd. Examples thereof include "Notio PN3560 (currently Toughmer PN3560)", "Notio PN2060 (currently Toughmer PN2060)", and "Notio PN2070 (currently Toughmer PN2070)" at 160 ° C. The propylene-based elastomer resin is considered to act as a kind of surface modifier by combining 4-methyl-1-pentene with a copolymer resin of α-olefin and the above-mentioned [4] hydrogenated agent [4]. 4] It is possible to reduce the amount of hydrogenated material added. In addition, the flexibility generally decreases when the crystallinity of the resin is increased to increase the heat resistance, but by including the propylene-based elastomer resin in the composition, the flexibility is maintained while maintaining the heat resistance. It does not fall. It is considered that this is because the amorphous part composed of [5] hydrogenated product is incorporated in the crystal part at the nano level, and the structure is connected to the surrounding amorphous part.
The amount of the propylene-based elastomer resin is 0.5 to 5% by mass, preferably 0.6 to 4% by mass.

[6] Plasticizer The plasticizer in the present invention is preferably known as a plasticizer for polyolefins. The plasticizer may be liquid or solid at room temperature. Examples of the liquid plasticizer include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, and liquid paraffin, and mineral oil fractions having corresponding boiling points. A plasticizer that easily bleeds out in the process of obtaining a gel-like molded product is unsuitable, and in order to stably obtain a gel-like molded product, it is preferable to use a non-volatile liquid plasticizer such as liquid paraffin or mineral oil. .. The viscosity of the liquid plasticizer is preferably in the range of 30 to 500 c St at 25 ° C, more preferably in the range of 50 to 200 c St. If the viscosity of the liquid plasticizer at 25 ° C. is less than the above lower limit, the discharge of the melt of the polyolefin mixture from the die lip is non-uniform, and kneading is difficult. On the other hand, if the above upper limit is exceeded, it is difficult to dissolve or remove the plasticizer with a solvent in a subsequent step.

The solid plasticizer preferably has a melting point of 80 ° C. or lower, and as such a solid plasticizer, waxes such as paraffin wax and microcrystallin wax, higher alcohols such as ceryl alcohol and stearyl alcohol, polyoxyethylene stearyl ether, and poly Polyoxyethylene alkyl ethers such as oxyethylene isostearyl ethers, polyoxypropylene alkyl ethers such as polyoxypropylene stearyl ethers and polyoxypropyl isostearyl ethers, polyoxyethylene alkyl esters such as polyoxyethylene stearyl esters, and polyoxy Examples thereof include polyoxypropylene alkyl esters such as propylene stearyl esters. A liquid solvent and a solid solvent may be appropriately mixed before use. In particular, mixing a polyoxyethylene alkyl ether such as polyoxyethylene stearyl ether or polyoxyethylene isostearyl ether with liquid paraffin is advantageous because the mixture solidifies at room temperature. When the resin component and the plasticizer in the resin composition of the present invention are uniformly melt-kneaded at temperatures above their melting points and then cooled to below the solidification temperature of the mixed resin, a stretchable soft gel is formed. You can get things.

The amount of the plasticizer can be changed depending on the phase separation structure of the compatibility between the resin and the plasticizer and the weight ratio of the resin to the total weight of the resin and the plasticizer (polymer mass fraction). For example, the blending ratio of the polyolefin-based composition and the plasticizer is such that the total of both is 100 parts by mass, the polyolefin-based resin composition is 10 to 49 parts by mass, and the plasticizer is 90 to 51 parts by mass, preferably. The polyolefin-based resin composition is 25 to 35 parts by mass, and the plasticizer is 75 to 65 parts by mass. If the proportion of the polyolefin-based resin composition is less than the above lower limit, the swell and neck-in become large at the die outlet when extruding the melt of the polyolefin-based resin composition and the plasticizer, and the formability of the gel-like molded product and Self-support is reduced. On the other hand, when the ratio of the polyolefin-based resin composition exceeds the above upper limit, the film-forming property on the gel-like sheet molded product is lowered, and a film having small pores and inferior air permeability is formed.

[7] Solvent The solvent for removing the plasticizer is a poor solvent for the resin forming the resin composition, a good solvent for the plasticizer, and its boiling point is higher than the melting point of the film. It is preferably low. For example, hydrocarbons such as n-hexane and cyclohexane, halogenated hydrocarbons such as methylene chloride and 1,1-trichloroethane, alcohols such as ethanol and isopropanol, ethers such as diethyl ether and tetrahydrofuran, acetone and 2- Ketones such as butanone, chain fluorocarbons such as C ₆ F ₁₄ , C ₇ F ₁₆ , and hydrocarbon ethers such as C ₄ F ₉ OCH ₃ , C ₄ F ₉ OC ₂ H ₅ , C ₄ F ₉ OCF ₃ , C ₄ F ₉ OC ₂ F ₅ perfluoro ether or the like. In order to avoid shrinkage of the membrane when the plasticizer is removed by the solvent, the membrane is immersed in the solvent while being restrained in at least one direction, and after the plasticizer is removed, the solvent is dried by a heat drying method, an air drying method, etc. below the melting point of the membrane. It is preferable to remove it.

Other polyolefins may be added to the extent that the characteristics of the heat-resistant polyolefin-based microporous membrane of the present invention are not significantly impaired. The block polymer of polypropylene and ethylene-propylene copolymer uses propylene and ethylene as raw materials, and first uses propylene as a raw material, and uses a metallocene catalyst, a titanium-based catalyst, etc., while flowing it into a reactor such as a pipe for several seconds to several minutes. In, 10-40 mol% of polypropylene is synthesized, 90-60 mol% of a mixture of ethylene and propylene is introduced, and an ethylene-propylene copolymer is continuously synthesized in the same time. At this time, the ratio of ethylene and propylene can be changed, and the block chain length is changed by changing the polymerization time of each. Further, by repeating this step or changing the polymerization time when repeating this step, the material containing the multi-block body and the present block copolymer can have an arbitrary ethylene content. The block copolymer can have compatibility with polyethylene and a copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. For example, examples of Prime TPO manufactured by Prime Polymer Co., Ltd. include R110E, R110MP, T310E, and M142E. In addition, there are propylene block polymer manufactured by SunAllomer Ltd., qualia, polypropylene impact copolymer manufactured by Japan Polypropylene Corporation, Newcon, tough selenium manufactured by Sumitomo Chemical Co., Ltd., excelene and the like. It is a block polymer of polypropylene and ethylene / propylene copolymer formed by a living catalyst whose active point of the catalyst can polymerize both ethylene and propylene and whose active point is sufficiently stable during the polymerization time, and has an ethylene content ratio. Higher ones are preferable.
The molecular weight of the polypropylene resin that may be added is not particularly limited, but polypropylene having a viscosity average molecular weight of 100,000 or more and a viscosity average molecular weight of about 400,000 can be used.

[8] Optional components An optional component can be added to the polyolefin-based resin composition of the present invention or when an antioxidant is melt-kneaded with a plasticizer as long as the object of the present invention is not impaired. Optional components include, but are not limited to, antioxidants and inorganic fillers.
The antioxidant is added to prevent the resin from burning when the polyolefin resin composition and the plasticizer are melt-mixed and appearing as black spots (black specs) on the product film. Antioxidant matches are known, for example tetrakis [methylene-3- (3,5-ditershally butyl-4-hydroxyphenyl) -propionate] methane.
Examples of the inorganic filler include alumina, nano-sized boehmite alumina having an aspect ratio of aluminum hydroxide, silica (silicon oxide), sodium aluminosilicate, sodium calcium aluminosilicate titania, zirconia, magnesia, ceria, and itria. Oxide-based materials such as zinc oxide and iron oxide, nitride-based materials such as silicon carbide, silicon nitride, titanium nitride, and boron nitride, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, and kaolinite. , Halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, zeolite, calcium silicate, magnesium silicate, kaolin, ceramics such as silica sand, glass fiber and the like. One of these can be used alone, or two or more can be used in combination. Preferred are electrochemically stable silica, alumina and titanium, with silica and aluminosilicate being particularly preferred. The average particle size of the inorganic filler powder particles is preferably 1 nm or more, more preferably 10 nm or more, and the upper limit is preferably 100 nm or less. It is preferable that the average particle size is 100 nm or less from the viewpoint of suppressing the generation of macrovoids because the peeling between the polyolefin resin and the inorganic filler tends to be difficult to occur even when stretching or the like is performed. On the other hand, it is preferable that the average particle size is 1 nm or more in order to ensure the dispersibility of the inorganic filler particles at the time of melting. By adding the inorganic filler particles, the tensile strength of the microporous membrane can be increased and the heat shrinkage rate can be further reduced.

For example, take the case where n or more types of polyolefin resins having different melting points (where n represents an integer of 3 or more) are used. The average melting point T of a resin mixture consisting of ultra-high molecular weight polyethylene having a melting point of T ₁ ° C and n types of polyolefin resins having a melting point of T ₂ ° C, T ₃ ° C ... T _n ° C is defined by the following formula.

[Number 2]
T ＝ T ₁ χ ₁ + T ₂ χ ₂ + T ₃ χ _{3 ・ ・ ・}+ T _n χ _n
In the formula, χ ₁ + χ ₂ + χ ₃ ... χ _n = 1 χ ₁ ; mass fraction of ultra-high molecular weight polyethylene, χ _{2 to} χ _n ; melting point T ₂ ° C, T ₃ ° C, ... T _n It is the mass fraction of each of the polyolefin resins at ° C. Here, the melting point means the melting point obtained by differential scanning calorimetry (DSC) based on JIS K 7 1 2 1.

A polymer solution containing no ceramics, an aqueous polymer solution, preferably an aqueous solution of a crosslinkable polymer can be used for applying, for example, applying to both sides or one side of the heat-resistant polyolefin-based microporous film of the present invention. For example, an aqueous solution of a fluoropolymer having a fluoroethylene / vinyl ether alternating copolymer as a main chain, an acrylic resin / polyamide / imide resin aqueous solution, an acrylic resin / polyimide aqueous solution, a crosslinkable acrylic resin, a modified silicone resin aqueous solution, and polyvinylidene fluoride-hexa. It is any one or a mixture of two or more of an aqueous solution of fluoropropylene and a crosslinkable polymethacrylic acid resin, and an aqueous solution of polyvinylidene fluoride and a crosslinkable acrylic resin. Since no organic solvent is used as the solvent, it is environmentally friendly and preferable. An aqueous solution is applied or immersed, and then dried and crosslinked to form a surface film of 0.1-5 microns, preferably 0.1-3 microns. Alternatively, a polyimide resin, a polyamide / imide resin, or a polyamide resin dissolved in an organic solvent can also be used. Since the polyolefin-based microporous membrane of the present invention can be dried at a higher temperature than the conventional polyethylene separator, the cross-linking / curing time can be shortened. The effect of improving the battery discharge capacity is obtained by lowering the impedance after the electrolytic solution is injected into the separator made of the polyolefin-based microporous membrane of the present invention in the battery and impregnated. Further, the breaking strength of the separator is further increased, and unlike the ceramic-coated polyethylene separator which has a rigid feeling when replacing the separator when assembling the battery, the separator of the present invention has the same flexibility as the polyethylene separator which has been used in the past. It is possible to prevent work discomfort. The above is a so-called polymer coating that does not contain ceramics, unlike the ceramic coating on the separator. Further, since the heat-resistant polyolefin-based microporous film of the present invention has heat resistance as compared with the conventional polymer coating on polyethylene separators and polypropylene separators, the heat-resistant polyolefin can be cured at a higher temperature. The processing time can be shortened.

In the case of mass production, a normal coater (coating machine) can be used. For small application in the laboratory, it is better to use Bar Coater # 3. Adjust the concentration of the aqueous solution or organic solvent solution so that it is approximately 1μ dry with aluminum foil. After confirming that it is 1 μm from the micro gauge and the coating weight, the solution is coated on the PET film (for example, Torel Miller S10). While rolling the heat-resistant polyolefin-based microporous film with a stainless steel round bar, the solution is pressed against the coated PET film to transfer the solution, and then the PET film is peeled off. Confirm that there is no coating film residue on the PET film. The heat-resistant polyolefin-based microporous film coated with the coating film is appropriately dried in a temperature range of 80 ° C. to 130 ° C. In the formed surface layer film, the passage formed by the evaporation of water or the organic solvent from the micro region occupied by the water or the organic solvent becomes the pores for communication. Further, the surface layer film is required to have a property of being easily wetted with a liquid electrolytic solution. It is preferable that the surface layer film has a small degree of swelling with respect to the liquid electrolytic solution and does not dissolve. Further, it is preferable that the resin applied to the nano-order unevenness on the surface of the heat-resistant polyolefin-based microporous film bites into the surface to exert an anchor effect. The application should be done so as not to close the pores as much as possible.

The heat-resistant polyolefin-based microporous membrane of the present invention.

The heat-resistant polyolefin-based microporous membrane in a preferred embodiment of the present invention has the following physical properties.

(1) The air permeability (Garley value) is 20 to 400 seconds / 100 ml. When the air permeability is in this range, the battery capacity is large and the cycle characteristics of the battery are good when the microporous membrane is used as the battery separator. If the air permeability is less than 20 seconds / 100 ml, the shutdown will not be sufficient when the temperature inside the battery rises. The air permeability is measured using a Garley air permeability meter compliant with JIS P8117.

(2) The porosity is 10 to 40%, preferably 15% to 30%. If the porosity is 10% or more, sufficient lithium ion conductivity is exhibited, and if it is 40% or less, it has the mechanical strength required for battery assembly. If the porosity is within this range, there is little risk of short-circuiting the electrodes when used as a battery separator. Porosity is measured by the gravimetric method. The sample is cut into a 5.0 cm square and the volume (cm ³ ) and weight (g) are measured. The resin density (g / cm ³ ) used is measured according to ASTM D1505. The porosity is calculated by the following formula.

[Number 3]
Porosity (%) = {1- (mass of microporous membrane / volume of microporous membrane) / density of resin composition} x100

(3) The maximum pore size of the microporous membrane is preferably 100 to 5000 nm, more preferably 300 nm to 3000 nm, and further preferably 300 to 2000 μm. If the maximum pore size is 100 nm or more, it has the permeability of Li ions required as a separator, and if it is 5000 nm or less, it is possible to avoid a short circuit due to an electrode desorption component. The surface of the heat-resistant polyolefin-based microporous membrane is observed with a scanning electron microscope (SEM), and the fibril fiber diameter is measured. Fibril fibers include fibril fibers having a diameter of less than 200 nm to 1000 nm and fibril fibers having a diameter in the range of 1000 to 3000 nm, and the number of fibril fibers having a diameter of less than 200 nm to 1000 nm and a diameter in the range of 1000 to 3000 nm. The ratio of the number of fibril fibers to have is preferably 97: 3 to 55:45 , particularly 90: 10 to 55:45 .

(4) The piercing strength is measured as follows. A microporous membrane is sandwiched between a sample holder with an opening diameter of 11.3 mm, and a piercing test is performed with a needle tip radius of curvature of 0.5 mm, a diameter of 1.0 mm, and a piercing speed of 2 mm / sec to determine the maximum piercing load g. , The piercing strength is indicated by N. The piercing strength is preferably 0.5N or more. If the piercing strength is less than 0.5 N, a short circuit of electrodes may occur in a battery incorporating a microporous membrane as a battery separator. The puncture strength is preferably 1.0 N or more, more preferably 2.0 or more. When the separator made of the microporous membrane of the present invention is used, a short circuit does not occur due to the desorbed component from the electrode, and the separator has sufficient strength as a battery separator.

(5) The breaking strength is measured according to JIS K7127 using a strip-shaped test piece having a width of 10 mm. The breaking strength is preferably 10 MPa or more, preferably 20 MPa or more in both the MD direction and the TD direction so as not to break the film during battery assembly.

(6) The elongation at break is measured according to JIS K7127 using a strip-shaped test piece having a width of 10 mm. It is preferable that the elongation at break is 5% or more in both the MD direction and the TD direction without worrying about film rupture.

The heat shrinkage of the membrane after being exposed for 1 hour in a circulating hot air dryer at a temperature of 190 ° C. is measured as follows. The MD direction and the TD direction are marked on the sample cut out to 50 mm x 50 mm. A 451 g glass plate having a size of 210 mm x 297 mm is placed on the upper surface of the sample, and a stainless steel 304 plate is arranged below the sample, sandwiching the material, and putting the sample in a circulating hot air dryer at a temperature of 190 ° C. After 1 hour, it is taken out, cooled to room temperature, and then the dimensional changes in the vertical and horizontal directions are measured. The heat shrinkage rate is calculated as a percentage by dividing the difference between the area of the sample piece before exposure and the area of the sample after exposure by the area of the sample piece before exposure.

[Number 4]
Heat shrinkage rate (%) = (1- (190 ° C x 1 hour area after heat exposure / (area of sample before measurement)) x 100
The vertical (MD) direction is the extrusion direction during the production of the microporous membrane, and the horizontal (TD) direction is the direction orthogonal to the extrusion direction during the production of the microporous membrane.
Film after heat shrinkage, if it has been irregular, the superimposed traces paper film, tracing film around the deformed cut traces paper, by measuring the weight W _r of cut trace paper , The heat shrinkage rate is obtained from the difference from the weight (Wo) of the 50 mm × 50 mm trace paper.

[Number 5]
Heat shrinkage (%) = (1 - (weight of trace paper 190 ° C. x1 h heat after exposure, _{W r)} / (weight of trace paper 50mmx50mm, _{W o)} x100
The thermal shrinkage rate is preferably 20% or less. It is preferably 10%, more preferably 5% or less. When the heat shrinkage rate exceeds 20%, when the microporous membrane is used as a separator for a lithium ion secondary battery, the separator end shrinks during abnormal heat generation, and there is a high possibility that an electrode short circuit will occur. ..

(8) A film is sandwiched between a pair of highly smooth and flat stainless steel plates (# 700 polishing plate with a thickness of 3 mm), and a pressure of 2.2 MPa (22 kgf / cm ² ) is applied to this by a press machine. However, the rate of change in film thickness after heating and compressing at 90 ° C. for 5 minutes is preferably 20% or less, with the film thickness before compression as 100%. When the film thickness change rate is 20% or less, the battery capacity is large and the battery cycle characteristics are good when the microporous film is used as a lithium ion secondary battery separator. The film thickness is measured with a contact thickness meter (manufactured by Mitutoyo Co., Ltd.). The reached air permeability (Garley value) after heat compression under the above conditions is 500 seconds / 100 ml or less. When the reached air permeability is 500 seconds / 100 ml or less, the change in air permeability and the change in film thickness are small even when pressurized, so that the battery capacity is large when used as a lithium ion secondary battery separator. It also has excellent permeability, mechanical properties, and heat shrinkage.

(9) Surface roughness is measured by an atomic force microscope (AFM). The preferable range of the maximum height difference is 50 nm or more and 600 nm. Then, when used as a battery separator, the contact area with the electrolytic solution is large, and the electrolytic solution injectability is excellent. More preferably, it is in the range of 100 nm to 300 nm. If it is less than 50 nm, the electrolytic solution becomes significantly wet and the separator is difficult to be separated from the separator winding roll. If it exceeds 600 nm, the mechanical strength of the separator decreases, which is not preferable.

(10) The non-meltdown characteristic is evaluated as follows. A separator sample cut to a size of 30 mmφ is impregnated with an electrolytic solution (1 M Li BF ₄ / polypropylene carbonate (PC): gamma-butyrolactone (γ-BL) (1/1 volume ratio)) to make a small size manufactured by Toyo Corporation. It is sealed in the sample holder of the heating furnace MT-Z300. The holder is sandwiched between 6 mmφ electrodes and heated at a heating rate of 5 ° C./min. During this period, the temperature and impedance value of the sample are measured with an impedance analyzer 6430B manufactured by Toyo Corporation. By the AC method, an AC with an amplitude of 10 mV and a frequency of 1 kHz is applied within a range of 10 mA, the impedance value is plotted against the temperature, and the temperature at which the impedance value becomes 1000 ohm or more in the process of increasing is defined as the shutdown temperature. Further, the battery container is continuously heated at a heating rate of 5 ° C./min, the temperature of the holder and the impedance value are measured, and the temperature at which the impedance value becomes less than 300 ohm again is defined as the meltdown temperature. In the evaluation of non-meltdown characteristics, the case where the film does not break even when the temperature reaches 195 ° C and the high impedance value is maintained is displayed as "195 ° C <", which means excellent non-meltdown characteristics. To do.

(11) For measuring the impedance value of the separator, a microporous film impregnated with an electrolytic solution and having a permeability of 280 sec / 100 mL and a film thickness of 9 microns was coated with 1.0 micron of polyimide on one side and cut into 5 mm squares. , Electrolyte (1M LiBF ₄ / polyethylene carbonate (EC) / polypropylene carbonate (PC): gamma-butyrolactone (γ-BL) (2: 1: 1 volume ratio)) impregnated with 0.2 mm thick aluminum plate It is sandwiched between 7 mm squares. With an impedance value of 1 Hz as a reference 10, another polymer-coated heat-resistant polyolefin microporous film is impregnated with the electrolytic solution, sandwiched between 7 mm squares of a 0.2 mm thick aluminum plate, and shown as a relative impedance value of 1 Hz. A relatively small value indicates a more impedance value, and the battery capacity and charge / discharge cycle life are improved.

(12) The amount (%) of the residual plasticizer after the partial removal of the plasticizer is determined by the gravimetric method. The weight of the membrane before extraction and removal is measured and used as Wo. The membrane is immersed in a solvent (for example, methylene chloride, MC) for several seconds to several minutes to dissolve and remove a part of the plasticizer, and the weight of the membrane after drying is measured to obtain Wg. The percentage of the plasticizer fed to the extruder (% of the weight of the plasticizer relative to the total weight of the plasticizer and the weight of the resin composition) is defined as the% plasticizer (fo) before extraction. The residual plasticizer% (fg) is calculated by the following formula.

[Number 6]
fg / 100 = 1- (Wo / Wg) * (1-fo / 100)
The% residual plasticizer after partial removal of the plasticizer is preferably 3% to 30% or less. It is preferably 3 to 20%, more preferably 3% to 25%.

(13) There is no particular limitation on the type of battery using the separator made of the heat-resistant polyolefin-based microporous membrane, but it is particularly suitable for lithium ion secondary battery applications. A known electrode and electrolytic solution may be used for the lithium ion secondary battery using the separator made of the microporous membrane of the present invention. Further, other structures of the lithium ion secondary battery using the separator made of the microporous membrane of the present invention may be known.
For example, as positive electrode active materials, 92 parts by mass of lithium cobalt oxide (LiCoO ₂ ; 10 micron) powder, ₂ parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo), 2 parts by weight of finely powdered graphite (manufactured by Nippon Graphite Co., Ltd.), polyvinylidene fluoride A positive electrode agent paste is prepared using an N-methylpyrrolidone solution of 6% by mass polyvinylidene fluoride so that the dry weight of (Kureha Chemical Industry Co., Ltd.) is 4 parts by mass. The obtained paste is applied onto an aluminum foil having a thickness of 15 μm, dried, and pressed to prepare a positive electrode. It consists of 97 parts of graphitized carbon (manufactured by Hitachi Chemical) powder of the negative electrode active material, 1 part of CMC (carboxymethyl cellulose) (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 2 parts of solid content of carboxy-modified butadiene-based latex (manufactured by Nippon Zeon). A negative electrode agent paste is prepared using an aqueous solution. The obtained paste is applied onto a copper foil having a thickness of 12 μm, dried, and pressed to prepare a negative electrode.

(14) The positive electrode was cut out to a size of 20 mm × 50 mm and a tab was attached. Further, the negative electrode was cut out to a size of 22 mm × 52 mm and provided with a tab. The separator was cut into a size of 26 mm × 56 mm. An aluminum laminated exterior cell was produced by joining these positive electrodes / separators / negative electrodes to each other, injecting an electrolytic solution, and encapsulating the aluminum laminate film. Here, as the electrolytic solution, one in which LiPF ₆ is dissolved in ethylene carbonate / ethyl methyl carbonate (3/7 weight ratio) at 1 M is used. The amount of electricity discharged at 0.2C and 2C was measured in the cell, and (the amount of electricity discharged at 2C) / (the amount of electricity discharged at 0.2C) × 100 was defined as the battery performance. Good battery performance is 95% or more. Here, the charging condition is 0.2C 4.2V CC / CV 8 hours, and the discharging condition is a CC discharge with a 2.75V cutoff.

In the case of an aluminum-laminated exterior cell using a separator formed by applying the above polymer aqueous solution to the heat-resistant polyolefin-based microporous membrane of the present invention, the cell is pressed and sealed 3 hours after the electrolytic solution is injected. Measure the internal resistance of the battery. A potentiometer / galvanostat with a built-in impedance analyzer was used for the measurement. An AC voltage with an amplitude of 10 mV superimposed on the OCV (open circuit voltage) was applied from 300 KHz to 0.1 Hz, and the impedance was obtained from the response current. The impedance value of the PVDF coated separator at the end of 1 Hz discharge is set to 1, and is displayed as a relative value of impedance. The charge / discharge cycle under the above conditions was repeated, and the retention rate of the 50th discharge capacity was determined based on the 2nd discharge capacity.

As described above, the heat-resistant polyolefin-based microporous membrane of the present invention can be suitably used as a battery separator, a capacitor separator, a filter and the like. In particular, it is most suitable as a separator for large lithium-ion secondary batteries for EVs. Taking advantage of the excellent non-meltdown characteristics of the heat-resistant polyolefin microporous membrane of the present invention, the polyethylene microporous membrane having a shutdown temperature in the range of 125-142 ° C or the shutdown temperature is not in this range, but the discharge characteristics. It can also be used as a multi-layer separator for batteries by bonding with a polypropylene separator having excellent temperature. When assembling the battery, it can be used in combination with a conventional polyethylene separator or polypropylene separator.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.15 million 4.9% by mass, ultra-high molecular weight polyethylene with a viscosity average molecular weight of 2 million 16.9% by mass, ultrahigh molecular weight polyethylene with a viscosity average molecular weight of 3.95 million 12.7% by mass , 8.5% by mass of ultra-high molecular weight polyethylene with an average molecular weight of 5.81 million, 4.2% of ultra-high molecular weight polyethylene with an average molecular weight of 6.31 million, and 3.6% by mass of high-density polyethylene with an average molecular weight of 334,000. , 4-Methyl-1-pentene-1-decene-1 copolymer having a melting point peak of 232 ° C. (MFR 260 ° C., 5 kg load 9 g / 10 min) 46.5% by weight, and ethylene-ethylene / butylene-ethylene block co-weight [Grade name 6200P] 0.20% by weight, [Grade name 6100P] 0.20% by weight and [Grade name 6201B] 0.20% by weight, and Mitsui Chemicals as a polypropylene-based elastomer resin of the coalesced product (Dinaron CEBC manufactured by JSR). Notio [grade name SN0285] manufactured by Co., Ltd. Tetrakiss [Methylene-3- (3,5-ditershally butyl) as an antioxidant with respect to 100.0 parts by mass of a mixture of polyolefin resin consisting of 2.1% by mass. -4-Hydroxyphenyl) -propionate] 0.5 parts by weight of methane and 3,9-bis (2,6-ditersary butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9- Diphosphapi [5,5] undecanelonyl hydroxyphenyl) -propionate] 0.05 parts by weight of methane was dry-blended to prepare a polyolefin resin mixture having an average melting point of 180 ° C. of the mixed resin portion by calculation. 35 parts by mass of the resin mixture was put into a twin-screw extruder (cylinder diameter: 52 mm, screw length (L) to diameter (D) ratio L / D: 48, strong kneading type screw used). 65 parts by mass of plasticizer (liquid paraffin [68cst (40 ° C)]) is supplied from the side feeder of the shaft extruder, and the polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 220-190 ° C and a screw rotation speed of 260 rpm. Prepared. This was extruded from the T-die via a gear pump installed at the tip of the twin-screw extruder, and was taken up by a cooling roll to form a gel-like sheet molded product. Biaxial stretching was performed on the obtained gel-like sheet molded product at MD 6 times and TD 5 times using a biaxial simultaneous stretching tenter. Next, a part of the plasticizer is removed by passing it through a continuous plasticizer extractor using methylene chloride (MC) as a solvent to form a partial plasticizer removing film having a ratio of 18 parts by mass of liquid paraffin and 82 parts by mass of the resin mixture. Obtained. The film was sandwiched between two # 700 polished stainless steel plates and heated and pressurized at 135 ° C. under a pressure of 2 MPa for 10 minutes and then at 35 MPa for 15 minutes. This was stretched 4 times x 4 times by a laboratory simultaneous biaxial stretching machine. Next, the plasticizer was heated and pressurized at 135 ° C. under a pressure of 2 MPa for 10 minutes and then at 35 MPa for 15 minutes, and then the plasticizer was completely removed by MC through a continuous plasticizer extractor. Next, the film was sandwiched between two # 700 polished stainless steel plates and pressed at 140 ° C. for 2Mpa for 5 minutes and 35MPa for 3 minutes to perform a heat fixing treatment. The obtained membrane is a heat-resistant polyolefin microporous membrane, and its characteristics are shown in Table 1. In addition, as a result of a test for evaluation of non-meltdown characteristics, the impedance value showed a rapid increase around 135 ° C and reached 1000 ohms at 135 ° C (that is, the shutdown temperature was 135 ° C), and the temperature further increased. As a result, it became over 5000 ohms and maintained a high impedance value until it exceeded 195 ° C. The surface of the heat-resistant polyolefin microporous membrane was observed with a scanning electron microscope (SEM), the fibril fiber diameter was measured, and the fibril fiber diameter distribution was determined. There are fibril fibers in the range of 200 nm to less than 1000 nm and fibril fibers in the range of 1000 nm to 3000 nm, and the ratio of the number of fibril fibers having a diameter of 200 nm to less than 1000 nm to the number of fibril fibers having a diameter in the range of 1000 to 3000 nm. Was 77:23.

Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.15 million 4.9% by mass, ultra-high molecular weight polyethylene with a viscosity average molecular weight of 2 million 16.9% by mass, ultrahigh molecular weight polyethylene with a viscosity average molecular weight of 3.95 million 12.7% by mass , 8.5% by mass of ultra-high molecular weight polyethylene with an average molecular weight of 5.81 million, 4.2% of ultra-high molecular weight polyethylene with an average molecular weight of 6.31 million, and 3.6% by mass of high-density polyethylene with an average molecular weight of 334,000. , 4-Methyl-1-pentene-1-decene-1 copolymer having a melting point peak of 232 ° C. (MFR 260 ° C., 5 kg load 9 g / 10 min) 46.5% by weight, and ethylene-ethylene / butylene-ethylene block co-weight Combined (JSR Dynalon CEBC) 0.20% by weight [grade name 6200P] 0.20% by weight [grade name 6100P] 0.20% by weight and [grade 6201B] 0.20% by weight, and Mitsui Chemicals (grade name 6201B] 0.20% by weight Notio [grade name SN0285] manufactured by Co., Ltd. Tetrakiss [Methylene-3- (3,5-Ditershally Butyl-) as an antioxidant with respect to 100.0 parts by mass of a mixture of polyolefin resin consisting of 2.1% by mass. 4-Hydroxyphenyl) -propionate] 0.5% by weight of methane and 3,9-bis (2,6-ditersary butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] Undecanronyl hydroxyphenyl) -propionate] A polyolefin resin mixture having an average melting point of 180 ° C. of the mixed resin portion by calculation was prepared by dry blending with 0.05 parts by mass of methane. 35 parts by mass of the resin mixture was put into a twin-screw extruder (cylinder diameter: 52 mm, screw length (L) to diameter (D) ratio L / D: 48, strong kneading type screw used). 65 parts by mass of plasticizer (liquid paraffin [68cst (40 ° C)]) is supplied from the side feeder of the shaft extruder, and the polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 240-190 ° C and a screw rotation speed of 300 rpm. Prepared. This was extruded from the T-die via a gear pump installed at the tip of the twin-screw extruder, and was taken up by a cooling roll to form a gel-like sheet molded product. The obtained gel-like sheet molded product was subjected to biaxial stretching at MD4 times and TD4 times using a biaxial simultaneous stretching tenter. Next, a part of the plasticizer is removed by passing through a continuous plasticizer extractor using methylene chloride (MC) as a solvent, and the partial plasticizer removing film A having a ratio of 12 parts by mass of liquid paraffin and 88 parts by mass of the resin mixture is obtained. Got Similarly, a partial plasticizer removing film B having a ratio of 6 parts by mass of the plasticizer to 94 parts by mass of the resin mixture was obtained. The partial plasticizer removing film A and B are overlapped and sandwiched between two # 700 polished stainless steel plates, and heated and pressed at 135 ° C. at 2 MPa for 10 minutes and 35 MPa for 5 minutes to heat and pressurize the partial plasticizer removing film A. And B were pasted together to form a single film. This was stretched 4 times x 4 times by a laboratory simultaneous biaxial stretching machine. The plasticizer was heated and pressurized at 135 ° C. under a pressure of 2 MPa for 10 minutes and then at 35 MPa for 15 minutes, and then the plasticizer was completely removed by MC through a continuous plasticizer extractor. Next, the film was sandwiched between two # 700 polished stainless steel plates and pressed at 150 ° C. for 2Mpa for 5 minutes and 35MPa for 3 minutes to perform a heat fixing treatment. The obtained membrane is a heat-resistant polyolefin microporous membrane, and its characteristics are shown in Table 1. In addition, as a result of a test for evaluation of non-meltdown characteristics, the impedance value showed a rapid increase around 135 ° C and reached 1000 ohms at 135 ° C (that is, the shutdown temperature was 135 ° C), and the temperature further increased. The high impedance value was maintained until the temperature exceeded 5000 ohms and exceeded 195 ° C.

A polyolefin resin mixture having the same composition as in Example 2 was prepared. 35 parts by mass of the resin mixture was put into a twin-screw extruder (cylinder diameter: 52 mm, screw length (L) to diameter (D) ratio L / D: 48, strong kneading type screw used). 65 parts by mass of plasticizer (liquid paraffin [68cst (40 ° C)]) is supplied from the side feeder of the shaft extruder, and the polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 240-190 ° C and a screw rotation speed of 300 rpm. Prepared. This was extruded from the T-die via a gear pump installed at the tip of the twin-screw extruder, and was taken up by a cooling roll to form a gel-like sheet molded product. The obtained gel-like sheet molded product was subjected to biaxial stretching at MD 7 times and TD 6 times using a biaxial simultaneous stretching tenter. Next, a part of the plasticizer is removed by passing through a continuous plasticizer extractor using methylene chloride (MC) as a solvent, and the partial plasticizer removing film C having a ratio of 10 parts by mass of liquid paraffin and 90 parts by mass of the resin mixture is obtained. Got This was sandwiched between two # 700 polished stainless steel plates and heated and pressurized at 135 ° C. under a pressure of 2 MPa for 10 minutes, and then at 35 MPa for 5 minutes. This was stretched 3.5 times x 3.5 times at 135 ° C. by a laboratory simultaneous biaxial stretching machine. Next, the plasticizer was completely removed by MC after heating and pressurizing at 135 ° C. at 2 MPa for 2 minutes and 35 MPa for 15 minutes. The plasticizer was completely removed by MC. Next, the film was sandwiched between two # 700 polished stainless steel plates and pressed at 150 ° C. for 2 MPa for 5 minutes and 35 MPa for 3 minutes to perform a heat fixing treatment. The obtained membrane is a heat-resistant polyolefin microporous membrane, and its characteristics are shown in Table 1. In addition, as a result of a test for evaluation of non-meltdown characteristics, the impedance value showed a rapid increase around 135 ° C and reached 1000 ohms at 135 ° C (that is, the shutdown temperature was 135 ° C), and the temperature further increased. The high impedance value was maintained until the temperature became 5000 ohms or more and exceeded 195 ° C.

With the partial plasticizer removing film A obtained as in Example 2 on both sides and the partial plasticizer removing film C obtained as in Example 3 in the middle, three sheets were stacked, and two # 700 polished stainless steel plates. It was sandwiched between the two, heated and pressurized at 135 ° C. under a pressure of 2 MPa for 10 minutes and at 35 MPa for 10 minutes, and the integrated film was stretched 4 times × 4 times at 135 ° C. by a simultaneous biaxial stretching machine. Next, the plasticizer was completely removed by MC after heating and pressurizing at 135 ° C. at 2 MPa for 2 minutes and 35 MPa for 15 minutes. The heat fixing treatment was performed in the same manner as in Example 3. The obtained film is a heat-resistant polyolefin microporous film, and as a result of a test for evaluating its non-meltdown characteristics, it showed a rapid increase in impedance value near 136 ° C and reached 1000 ohms at 136 ° C (). That is, the shutdown temperature was 136 ° C.), and as the temperature rose, it became 5000 ohms or more and maintained a high impedance value until it exceeded 195 ° C.

Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.15 million 5.5% by mass, ultra-high molecular weight polyethylene with a viscosity average molecular weight of 2 million 13.3% by mass, ultrahigh molecular weight polyethylene with a viscosity average molecular weight of 3.95 million 15.0% by mass , Ultra-high molecular weight polyethylene with viscosity average molecular weight of 5.81 million 9.0% by mass, ultra-high molecular weight polyethylene with viscosity average molecular weight of 6.31 million 5.5%, high density polyethylene with average molecular weight of 334,000 5.0% by mass , 4-Methyl-1-pentene-1-decene-1 copolymer having a melting point peak of 232 ° C. (MFR 260 ° C., 5 kg load 9 g / 10 min) 44.0% by weight, and ethylene-ethylene / butylene-ethylene block co-weight Combined (JSR Dynalon CEBC) 0.20% by weight [grade name 6200P] 0.20% by weight [grade name 6100P] 0.20% by weight and [grade 6201B] 0.20% by weight, and Mitsui Chemicals (grade name 6201B] 0.20% by weight Notio [grade name SN0285] manufactured by Co., Ltd. Tetrakiss [Methylene-3- (3,5-Ditershally Butyl-) as an antioxidant with respect to 100.0 parts by mass of a mixture of polyolefin resin consisting of 2.1% by mass. 4-Hydroxyphenyl) -propionate] 0.5% by weight of methane and 3,9-bis (2,6-ditersary butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] Undecanronyl hydroxyphenyl) -propionate] A polyolefin resin mixture having an average melting point of 180 ° C. of the mixed resin portion by calculation was prepared by dry blending with 0.05 parts by mass of methane. 35 parts by mass of the resin mixture was put into a twin-screw extruder (cylinder diameter: 52 mm, screw length (L) to diameter (D) ratio L / D: 48, using a strong kneading type screw). 65 parts by mass of plasticizer (liquid paraffin [68cst (40 ° C)]) is supplied from the side feeder of the shaft extruder, and the polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 240-190 ° C and a screw rotation speed of 270 rpm. Prepared. This was extruded from the T-die via a gear pump installed at the tip of the twin-screw extruder, and was taken up by a cooling roll to form a gel-like sheet molded product. The obtained gel-like sheet molded product was sequentially stretched by biaxial stretching at MD5 times and TD5 times. Next, it is passed through a continuous plasticizer extractor using methylene chloride (MC) as a solvent to obtain a partial plasticizer removing film D composed of 10 parts by mass of liquid paraffin and 90 parts by mass of the resin mixture. In the same manner, however, a partial plasticizer removing film E having a ratio of 6 parts by mass of liquid paraffin and 94 parts by mass of the resin mixture is obtained. The film was laminated with three E / D / E sheets, sandwiched between two # 700 polished stainless steel plates, and heated and pressurized at 135 ° C. under a pressure of 2 MPa for 10 minutes and at 35 MPa for 5 minutes. This was stretched 4 times x 4 times by a simultaneous biaxial stretching machine. Next, the plasticizer was completely removed by MC after heating and pressurizing at 135 ° C. at 2 MPa for 2 minutes and 35 MPa for 15 minutes. Table 1 shows the characteristics of the heat-resistant polyolefin microporous film obtained by subjecting the heat-fixing treatment as described above. As a result of a test for evaluation of non-meltdown characteristics, the impedance value showed a rapid increase around 135 ° C and reached 1000 ohms at 135 ° C (that is, the shutdown temperature was 135 ° C), and as the temperature increased further. The high impedance value was maintained until the temperature became 5000 ohms or more and exceeded 195 ° C.

Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.15 million 4.9% by mass, ultra-high molecular weight polyethylene with a viscosity average molecular weight of 2 million 16.9% by mass, ultrahigh molecular weight polyethylene with a viscosity average molecular weight of 3.95 million 12.7% by mass , 8.5% by mass of ultra-high molecular weight polyethylene with an average molecular weight of 5.81 million, 4.2% of ultra-high molecular weight polyethylene with an average molecular weight of 6.31 million, and 3.6% by mass of high-density polyethylene with an average molecular weight of 334,000. , 4-Methyl-1-pentene-1-decene-1 copolymer having a melting point peak of 232 ° C. (MFR 260 ° C., 5 kg load 9 g / 10 min) 46.5% by weight, and ethylene-ethylene / butylene-ethylene block co-weight Combined (JSR Dynalon CEBC) [grade name 6200P] 0.20% by weight, [grade name 6100P] 0.20% by weight and [grade name 6201B] 0.20% by weight, and Mitsui Chemicals, Inc. as a polypropylene-based elastomer resin ) Tetio [Methylene-3- (3,5-Ditershally Butyl-4) as an antioxidant with respect to 100.0 parts by weight of a mixture of polyolefin resin consisting of 2.1% by weight of Notio [grade name SN0285] -Hydroxyphenyl) -propionate] 0.5% by weight of methane and 3,9-bis (2,6-ditersary butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [ 5,5] Undecanronyl hydroxyphenyl) -propionate] By dry blending with 0.05 parts by mass of methane, a polyolefin resin mixture having an average melting point of 180 ° C. of the mixed resin portion calculated was prepared. 30 parts by mass of the resin mixture was put into a twin-screw extruder (cylinder diameter: 52 mm, screw length (L) to diameter (D) ratio L / D: 48, strong kneading type screw used). 70 parts by mass of plasticizer (liquid paraffin [68cst (40 ° C)]) is supplied from the side feeder of the shaft extruder, and the polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 240-190 ° C and a screw rotation speed of 260 rpm. Prepared. This was extruded from the T-die via a gear pump installed at the tip of the twin-screw extruder, and was taken up by a cooling roll to form a gel-like sheet molded product. Biaxial stretching was MD 6 times and TD 5 times for the obtained gel sheet molded product using a biaxial simultaneous stretching tenter. Next, a continuous plasticizer extractor using methylene chloride (MC) as a solvent was passed through to obtain a partial plasticizer removing film F having a ratio of 15 parts by mass of liquid paraffin and 85 parts by mass of the resin mixture.
Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.15 million 11.4% by mass, ultra-high molecular weight polyethylene with a viscosity average molecular weight of 2 million 16.9% by mass, ultrahigh molecular weight polyethylene with a viscosity average molecular weight of 3.95 million 12.7% by mass , 8.5% by mass of ultra-high molecular weight polyethylene with an average molecular weight of 5.81 million, 4.2% of ultra-high molecular weight polyethylene with an average molecular weight of 6.31 million, and 3.6% by mass of high-density polyethylene with an average molecular weight of 334,000. , 4-Methyl-1-pentene-1-decene-1 copolymer having a melting point peak of 232 ° C. (MFR 260 ° C., 5 kg load 9 g / 10 min) 40.0% by weight, and ethylene-ethylene / butylene-ethylene block co-weight Combined (JSR Dynalon CEBC) [grade name 6200P] 0.18% by weight, [grade name 6100P] 0.18% by weight and [grade name 6201B] 0.18% by weight, and Mitsui Chemicals as a polypropylene-based elastomer resin ( Tetrakiss [Methylene-3- (3,5-Ditershally Butyl-) as an antioxidant with respect to 100.0 parts by weight of a mixture of polyolefin resin consisting of 2.6% by mass of Notio [grade name SN0285] manufactured by Co., Ltd. 4-Hydroxyphenyl) -propionate] 0.5% by weight of methane and 3,9-bis (2,6-ditersary butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] Undecanronyl hydroxyphenyl) -propionate] A polyolefin resin mixture having an average melting point of 176 ° C. of the mixed resin portion by calculation was prepared by dry blending with 0.05 parts by mass of methane. 30 parts by mass of the resin mixture was put into a twin-screw extruder (cylinder diameter: 52 mm, screw length (L) to diameter (D) ratio L / D: 48, strong kneading type screw used). 70 parts by mass of plasticizer (liquid paraffin [68cst (40 ° C)]) is supplied from the side feeder of the shaft extruder, and the polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 240-190 ° C and a screw rotation speed of 260 rpm. Prepared. This was extruded from the T-die via a gear pump installed at the tip of the twin-screw extruder, and was taken up by a cooling roll to form a gel-like sheet molded product. Biaxial stretching was MD 6 times and TD 5 times for the obtained gel sheet molded product using a biaxial simultaneous stretching tenter. Next, a continuous plasticizer extractor using methylene chloride (MC) as a solvent was passed through to obtain a partial plasticizer removing film G having a ratio of 20 parts by mass of liquid paraffin and 80 parts by mass of the resin mixture.
These two sheets were stacked and sandwiched between two # 700 polished stainless steel plates, and heated and pressurized at 135 ° C. under a pressure of 2 MPa for 10 minutes and at 35 MPa for 5 minutes. This was stretched 4.0 times x 4.0 times by a simultaneous biaxial stretching machine. Next, the plasticizer was completely removed by MC after heating and pressurizing at 135 ° C. at 2 MPa for 2 minutes and 35 MPa for 15 minutes. Table 1 shows the characteristics of the heat-resistant polyolefin microporous film obtained after heat-fixing treatment. As a result of a test for evaluation of non-meltdown characteristics, the impedance value showed a rapid increase around 135 ° C and reached 1000 ohms at 135 ° C (that is, the shutdown temperature was 135 ° C), and as the temperature increased further. The high impedance value was maintained until the temperature became 5000 ohms or more and exceeded 195 ° C.

To the heat-resistant polyolefin microporous film obtained in Example 2, 92 parts by weight of lithium cobalt oxide (LiCoO ₂ : 10 micron) powder as a positive electrode active material, ₂ parts by weight of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) powder, and fine powder. A positive electrode sheet made of 2 parts by weight of graphite (manufactured by Nippon Graphite Co., Ltd.), 4 parts by mass of dry weight of polyvinylidene fluoride (manufactured by Kureha Chemical Industry Co., Ltd.) and an aluminum foil having a thickness of 15 μm is bonded, rolled down, and immediately. It was supplied to the winder. Similarly, 97 parts by mass of graphitized carbon (manufactured by Hitachi Chemical) powder of the negative electrode active material, 1 part by mass of CMC (carboxymethyl cellulose) (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and solid of carboxy-modified butadiene-based latex (manufactured by Nippon Zeon). A negative electrode sheet composed of 2 parts by mass and a copper foil having a thickness of 12 μm was attached to the heat-resistant polyolefin microporous film, rolled down, and then supplied to the winding machine. Table 2 shows the productivity and electrode capacity ratio of the winding coil to be inserted into the 18 mm cylindrical can.
In order to carry out the winding by the conventional method, the film is easily lifted by the wind pressure at the time of winding, and it is necessary to reduce the tension control and the shaft rotation speed. Even in the case of stacking laminated single-wafers, workability is improved as compared with incorporating a conventional separator by laminating the microporous film on the positive electrode sheet and the negative electrode sheet in advance before the battery assembly work.

One-component Lumiflon (registered trademark) FE4300 having FEVE (fluoroethylene / vinyl ether alternating copolymer) as the main chain manufactured by Asahi Glass Co., Ltd. is 100% antifoaming agent (SN defaulter 1312) 0 .1%, surface conditioner (SNwet126) 0.30%, thickener (SN thickener 612N 20%) 4% were added, diluted with purified water, applied to aluminum foil, and the film thickness after drying was 0.9 μm. The concentration of the aqueous solution was adjusted so as to be. It was confirmed from the micro gauge and the coating amount that it was 0.9 μm, and the aqueous solution was coated on the heat-resistant polyolefin microporous membrane obtained in Example 2 with a bar coater. While raising the temperature from room temperature to 120 ° C., water was evaporated under reduced pressure to dry and crosslink. The obtained product was subjected to impedance measurement at 4 Hz with Hioki IM3590. The results are shown in Table 3.

Two-component Lumiflon (registered trademark) FE4400 (solid content 50%) having FEVE (fluoroethylene / vinyl ether alternating copolymer) manufactured by Asahi Glass Co., Ltd. as the main chain and Tosoh isocyanate AQ-130 are 100: 11. Mix with 4 (NCO / OH = 1/1), defoamer (SN copolymer 1312) 0.1%, surface conditioner (SNwet 126) 0.30%, thickening with respect to 100% of the mixed solution. 4% of the agent (SN thickener 612N 20%) was added, diluted with purified water, applied to aluminum foil, and the concentration of the aqueous solution was adjusted so that the film thickness after drying was 1.0 μm. It was confirmed from the micro gauge and the coating amount that it was 0.9 μm, and the aqueous solution was coated on the heat-resistant polyolefin microporous membrane obtained in Example 2 with a bar coater. Moisture was evaporated under reduced pressure while raising the temperature from room temperature to 120 ° C. to dry and crosslink. The obtained product was subjected to impedance measurement at 4 Hz with Hioki IM3590. The results are shown in Table 3.

The solid content of Afras (registered trademark) 150CS latex manufactured by Asahi Glass Co., Ltd., which is a fluororubber of tetrafluoroethylene and propylene alternating copolymer, and tetrafluoroethylene on the heat-resistant polyolefin microporous film obtained in Example 2. Antifoaming agent (SN defaulter) for 100% mixed latex of 70:30 with the solid content of Afras 200S latex manufactured by Asahi Glass Co., Ltd., which is a ternary fluororubber of propylene-vinylidene fluoride copolymer. 1312) 0.1%, surface conditioner (SNwet 126) 0.30%, thickener (SN thickener 612N 20%) 4% are added, diluted with purified water, applied to aluminum foil, and the thickness after drying. The concentration of the aqueous solution was adjusted so that It was confirmed from the micro gauge and the coating amount that it was 0.9 μm, and the aqueous solution was coated on the heat-resistant polyolefin microporous membrane obtained in Example 2 with a bar coater. Moisture was evaporated and dried under reduced pressure while raising the temperature from room temperature to 120 ° C. The obtained product was subjected to impedance measurement at 4 Hz with Hioki IM3590. The results are shown in Table 3.

An ultraviolet (UV) curable acrylic resin solution (HX-RSC (solid content 50%) manufactured by Kyoeisha Chemical Co., Ltd.) was applied to the aluminum foil as a crosslinkable acrylic resin, and it was confirmed that the film thickness after drying was 1.0 μm. This was applied to the heat-resistant polyolefin microporous film obtained in Example 2. After evaporation of the solvent at 80 ° C. for 30 minutes, UV irradiation was performed for cross-linking. The obtained product was subjected to impedance at 4 Hz by Hioki Electric IM3590. The measurement was performed. The results are shown in Table 3.

Acrylic resin (acrylic styrene polyol (DIC Acridic A-817: hydroxyl value 30 mg KOH / g, acid value 3 mg KOH / g) and isocyanate HMDI (isocyanurate structure, Asahi Kasei Duranate TPA-100: NCO content 23 wt%) ) And NCO / OH = 1.0, diluted with xylene, and applied to aluminum foil to adjust the film thickness after cross-linking to 1 μm. From the microgauge and the applied amount, 1.0 μm. After confirming that, the diluted product was applied to the heat-resistant polyolefin microporous film obtained in Example 2. While raising the temperature from room temperature to 120 ° C., water was evaporated under reduced pressure to dry and crosslink. The obtained product was subjected to impedance measurement at 4 Hz with Hioki Electric IM3590. The results are shown in Table 3.

Polyimide varnish (Ube Industries' Yupia AT1001 (NMP solution with a solid content of 30%) was diluted 100% with NMP and applied to aluminum foil to adjust the film thickness after drying to 0.9 μm. After confirming that the coating weight was 0.9 μm, the diluted solution was applied to the heat-resistant polyimide microporous film obtained in Example 2. The temperature was raised to 120 ° C. while evaporating NMP, and the mixture was dried. The obtained product was made into polyimide by the above-mentioned process, and the impedance was measured at 4 Hz by Hioki Electric IM3590. The results are shown in Table 3.

PMMA (A) and PVDF-HFP (weight ratio 92: 8) copolymer (B) were dissolved in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 1: 1 and applied to aluminum foil and dried. Adjust so that the film thickness is 1.0 μm. After confirming that the weight was 1.0 μm from the micro gauge and the coating weight, the solution was applied to the heat-resistant polyolefin microporous membrane obtained in Example 2. The temperature was raised to 120 ° C. while evaporating the NMP, and the mixture was dried. Impedance of this simple resin mixture was measured at 4 Hz with Hioki IM3590. The results are shown in Table 3.

PVDF-HFP was dissolved in NMP, diluted, applied to an aluminum foil, and adjusted so that the film thickness after drying was 1.0 μm. The diluted solution was applied to the heat-resistant polyolefin microporous membrane obtained in Example 2. The temperature was raised to 115 ° C. while evaporating the NMP, and the mixture was dried. The obtained uncrosslinked product was subjected to impedance measurement at 4 Hz with Hioki IM3590. The results are shown in Table 3.

MKB272 of PVDF manufactured by Elf Atofina was dissolved in NMP and applied to an aluminum foil to adjust the film thickness after drying to 1.0 μm. The solution was applied to the heat-resistant polyolefin microporous membrane obtained in Example 2. The temperature was raised to 120 ° C. while evaporating the NMP, and the mixture was dried. The obtained uncrosslinked product was subjected to impedance measurement at 4 Hz with Hioki IM3590. The results are shown in Table 3.

Crosslink catalyst CR15 (tin + aminosilane, manufactured by Momentive) is mixed with silicone (TSR116 manufactured by Momentive, straight silicone) 100 in a mass ratio of 2, diluted with xylene, applied to aluminum foil, and dried. The thickness was adjusted to 0.9 μm. The diluted solution was applied to the heat-resistant polyolefin microporous membrane obtained in Example 2. The temperature was raised to 120 ° C., dried and crosslinked. The obtained product was subjected to impedance measurement at 4 Hz with Hioki IM3590. The results are shown in Table 3.

[Comparative Example 1]
Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.15 million 4.9% by mass, ultra-high molecular weight polyethylene with a viscosity average molecular weight of 2 million 16.9% by mass, ultrahigh molecular weight polyethylene with a viscosity average molecular weight of 3.95 million 12.7% by mass , 8.5% by mass of ultra-high molecular weight polyethylene with an average molecular weight of 5.81 million, 4.2% of ultra-high molecular weight polyethylene with an average molecular weight of 6.31 million, and 3.6% by mass of high-density polyethylene with an average molecular weight of 334,000. 4-Methyl-1-pentene-1-decene-1 copolymer having a melting point peak of 232 ° C. (MFR 260 ° C., 5 kg load 9 g / 10 min) 46.5% by weight, and ethylene-ethylene / butylene-ethylene block co-weight Combined (JSR Dynalon CEBC) 0.20% by weight [grade name 6200P] 0.20% by weight [grade name 6100P] 0.20% by weight and [grade 6201B] 0.20% by weight, and Mitsui Chemicals (grade name 6201B] 0.20% by weight Notio [grade name SN0285] manufactured by Co., Ltd. Tetrakiss [Methylene-3- (3,5-Ditershally Butyl-) as an antioxidant with respect to 100.0 parts by mass of a mixture of polyolefin resin consisting of 2.1% by mass. 4-Hydroxyphenyl) -propionate] 0.5% by weight of methane and 3,9-bis (2,6-ditersary butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] Undecanronyl hydroxyphenyl) -propionate] A polyolefin resin mixture having the same composition as in Example 2 was prepared by dry blending with 0.05 parts by mass of methane and having an average melting point of 180 ° C. of the mixed resin portion calculated. .. 35 parts by mass of the resin mixture was put into a twin-screw extruder (cylinder diameter: 52 mm, slew length (L) to diameter (D) ratio L / D: 48, using a strongly kneaded type screw). 65 parts by mass of liquid paraffin [68cst (40 ° C.)] was supplied from the side feeder of the shaft extruder, and a polyolefin / plasticizer mixed melt was prepared under the conditions of a temperature of 220-190 ° C. and a screw rotation speed of 270 rpm. This was extruded from the T-die via a gear pump installed at the tip of the twin-screw extruder, and was taken up by a cooling roll to form a gel-like sheet molded product. The obtained gel-like sheet molded product was subjected to biaxial stretching by MD4 times and TD4 times by using a biaxial simultaneous stretching tenter. This was stretched 4 times x 4 times by a laboratory simultaneous biaxial stretching machine. The plasticizer was completely removed by MC. It was heat-fixed by sandwiching it between # 700 polished stainless steel plates at 150 ° C. for 5 minutes at 2 MPa and 3 minutes at 35 MPa. Table 1 shows the characteristics of the obtained heat-resistant polyolefin microporous membrane. As a result of a test for evaluation test of non-meltdown characteristics, the impedance value showed a rapid increase around 135 ° C and reached 1000 ohms at 135 ° C (that is, the shutdown temperature was 135 ° C), and as the temperature increased further. The high impedance value was maintained until the temperature became 5000 ohms or more and exceeded 195 ° C. The results are shown in Table 1.

[Comparative Example 2]
A mixture of a suspension of 10% alumina and a water-soluble polyimide binder was applied to one side of a polyethylene separator having a thickness of 8 microns to prepare a polyethylene separator having a ceramic coating film having a dry thickness of 1 μm. The results of the performance test are shown in Table 1.

[Comparative Example 3]
The impedance of a ceramic double-sided coated polyethylene separator having an alumina / water-soluble polyimide coating film obtained from the market on both sides was measured at 4 Hz by Hioki E.E. IM3590. The results are shown in Table 3.

Provided is a polyolefin-based microporous membrane having excellent low shrinkage at high temperature, mechanical properties, air permeability, and a thin film thickness. The polyolefin-based microporous membrane has a shutdown temperature of 140 ° C. or lower, which is useful as a separator for enhancing the safety and life of a lithium ion secondary battery, and the liquid electrolyte is thermally decomposed and deactivated up to 190 ° C. or higher. It is preferable to have both characteristics of non-melting (non-meltdown) at the same time. Also provided are methods of producing such films.

Claims (17)

25 to 50% by mass of ultrahigh molecular weight polyethylene, 1 to 15% by mass of polyethylene, 35 to 65% by mass of a copolymer of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms, and polybutadiene and polyisoprene. And in a microporous membrane containing a resin composition comprising 0.1 to 2% by weight of a hydrogenated product of one or more polymers selected from the butadiene-isoprene copolymer and 0.5 to 5% by weight of a propylene-based elastomer resin. The fibril fibers constituting the microporous film include fibril fibers having a diameter of 200 nm to less than 1000 nm and fibril fibers having a diameter in the range of 1000 to 3000 nm, and fibril fibers having a diameter of 200 nm to less than 1000 nm. A polyolefin-based microporous film in which the ratio of the number of fibril fibers to the number of fibril fibers having a diameter in the range of 1000 to 3000 nm is 97: 3 to 55:45 . The polyolefin-based microporous membrane according to claim 1, which has a tensile breaking strength of 20 MPa or more, a film thickness of 2 to 10 μm, and a porosity of 10 to 30%. The copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms is 80 to 99 mol% of 4-methyl-1-pentene and α-olefin 20 to 1 having 3 to 30 carbon atoms. The polyolefin-based microporous according to claim 1 or 2, which is a molar% copolymer and has a copolymer melting point (Tm) in the range of 220 to 240 ° C. measured based on a scanning calorimeter test. film. The propylene-based elastomer resin is a copolymer of propylene and α-olefin, and is composed of a propylene-derived structural unit and an α-olefin (excluding propylene) -derived structural unit having 2 to 30 carbon atoms, and has a thickness of 10 nm or more. The polyolefin according to any one of claims 1 to 3, wherein "islands", which are 50 nm nano-order spiral crystal portions, are connected to each other to form a network structure and have a microstructure covering the entire amorphous portion. System microporous film. The polyolefin-based microporous film according to any one of claims 1 to 4, wherein the hydrogenated additive of the polybutadiene is an ethylene-ethylene / butylene-ethylene block copolymer. 25 to 50% by mass of ultrahigh molecular weight polyethylene, 1 to 15% by mass of polyethylene, 35 to 65% by mass of a copolymer of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms, and polybutadiene and polyisoprene. 10 parts by mass to 49% by mass of a resin composition containing 0.1 to 2% by mass of a hydrogenated product of one or more polymers selected from the butadiene-isoprene copolymer and 0.5 to 5% by mass of a propylene-based elastomer resin. 90 parts by mass to 51 parts by mass of the part and the plasticizer are supplied to a twin-screw extruder, melt-kneaded, extruded from a die, and cooled to obtain a gel-like sheet molded product. Axial stretching is performed to obtain a film, and a part of the plasticizer is dissolved in a solvent and removed to obtain a microporous film, the microporous film is heated and pressed , and further biaxial stretching is performed. A method for producing a polyolefin-based microporous film, which comprises additionally stretching the film, and after the additional stretching, dissolving the rest of the plasticizer in a solvent and removing the residue from the film. The fibril fibers constituting the polyolefin-based microporous film include fibril fibers having a diameter of 200 nm to less than 1000 nm and fibril fibers having a diameter in the range of 1000 to 3000 nm, and the fibril fibers having a diameter of 200 nm to less than 1000 nm. The method for producing a polyolefin-based microporous film according to claim 6, wherein the ratio of the number to the number of fibril fibers having a diameter in the range of 1000 to 3000 nm is 97: 3 to 55:45 . The propylene-based elastomer resin is a copolymer of propylene and α-olefin, and "islands", which are nano-order-level spiral crystal portions of 10 nm to 50 nm, are connected to each other to form a network structure and are amorphous. The method for producing a polyolefin-based microporous film according to claim 6 or 7, which is a propylene-based elastomer resin having a microstructure that covers the entire portion. The method for producing a polyolefin-based microporous film according to any one of claims 6 to 8, wherein the hydrogenated polybutadiene is an ethylene-ethylene / butylene-ethylene block copolymer. The copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms is 80 to 99 mol% of 4-methyl-1-pentene and α-olefin 20 to 1 having 3 to 30 carbon atoms. The invention according to any one of claims 6 to 9, wherein the copolymer is a molar% copolymer and the copolymer melting point (Tm) measured based on a scanning calorimeter test is in the range of 220 to 240 ° C. Method for producing a polyolefin-based microporous film. In step 1, 25 to 50% by mass of ultrahigh-molecular-weight polyethylene, 1 to 15% by mass of polyethylene, and 35 to 65% by mass of a copolymer of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms were used. 10 parts by mass of a resin composition containing 0.1 to 2% by mass of a hydrogenated product of one or more resins selected from polybutadiene, polyisoprene and a butadiene isoprene copolymer and 0.5 to 5% by mass of a propylene-based elastomer resin. ~ 49 parts by mass and 90 parts by mass to 51 parts by mass of the plasticizer are supplied to a twin-screw extruder, melt-kneaded, extruded from a die, and cooled to obtain a gel-like sheet molded product. A film is obtained by biaxially stretching an object, and a part of the plasticizer is dissolved in a solvent and removed to obtain a microporous film, and the microporous film is heated and pressed. Further stretching by axial stretching to obtain film A,
In step 2, 25 to 50% by mass of ultrahigh molecular weight polyethylene, 1 to 15% by mass of polyethylene, and 35 to 65% by mass of a copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. , Polybutadiene, polyisoprene and butadiene-isoprene copolymers in a resin composition comprising 0.1 to 2% by mass of a hydrogenated additive of one or more resins and 0.5 to 5% by mass of a propylene-based elastomer resin. Therefore, 10 to 49 parts by mass of the resin composition and 90 to 51 parts by mass of the plasticizer in which the amount of the hydrogen additive is different from the amount of the hydrogen additive in the above step 1 are supplied to the twin-screw extruder and melt-kneaded. Then, it is extruded from a die and cooled to obtain a gel-like sheet molded product, the gel-like sheet molded product is biaxially stretched to obtain a film, and a part of a plasticizer is used as a solvent from the film. Dissolve and remove to obtain a microporous film, heat and pressurize the microporous film , and further stretch by biaxial stretching to obtain film B.
In step 3, one or more of the film A and one or more of the film B are alternately laminated, and further stretched by biaxial stretching.
After the additional stretching in step 3, the residue of the plasticizer is dissolved in a solvent and removed from the membrane.
A method for producing a polyolefin-based microporous membrane including. The propylene-based elastomer resin is a copolymer of propylene and α-olefin, and "islands", which are nano-order-level spiral crystal portions of 10 nm to 50 nm, are connected to each other to form a network structure and are amorphous. The method for producing a polyolefin-based microporous film according to claim 11, which is a propylene-based elastomer resin having a microstructure that covers the entire portion. The method for producing a polyolefin-based microporous film according to claim 11 or 12, wherein the hydrogenated additive of the polybutadiene is an ethylene-ethylene / butylene-ethylene block copolymer. The copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms is 80 to 99 mol% of 4-methyl-1-pentene and α-olefin 20 to 1 having 3 to 30 carbon atoms. The invention according to any one of claims 11 to 13, wherein the copolymer is a molar% copolymer and the copolymer melting point (Tm) measured based on a scanning calorimeter test is in the range of 220 to 240 ° C. Method for producing a polyolefin-based microporous film. The fibril fibers constituting the polyolefin-based microporous film include fibril fibers having a diameter of 200 nm to less than 1000 nm and fibril fibers having a diameter in the range of 1000 to 3000 nm, and the fibril fibers having a diameter of 200 nm to less than 1000 nm. The method for producing a polyolefin-based microporous film according to any one of claims 11 to 14 , wherein the ratio of the number to the number of fibril fibers having a diameter in the range of 1000 to 3000 nm is 97: 3 to 55:45 . A fluoropolymer having (1) a fluoroethylene / vinyl ether alternating copolymer as a main chain on one side or both sides of the polyimide-based microporous film according to any one of claims 1 to 5 , and (2) tetrafluoroethylene. -Propropylene alternating copolymer, (3) polyamide, polyvinylidene terephthalamide (PPTA), polyvinylidene isophthalamide (MPIA)), (4) crosslinkable acrylic resin, (5) polyamide-imide resin, (6) 1 selected from polyimide, (7) silicone resin, (8) polyvinylidene fluoride-hexafluoropropylene, (9) a mixture of polymethyl methacrylate resin and polyvinylidene fluoride-hexafluoropropylene, and (10) polyvinylidene fluoride. A polyolefin-based microporous film having a 0.5-3 micron thick layer composed of seeds or more. A separator for a lithium ion secondary battery having the polyolefin-based microporous membrane according to any one of claims 1 to 5 and 15.