JP2017088836A - Low heat shrinkable polyolefin microporous film and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low heat shrinkable polyolefin microporous film excellent in low shrinkage property as a separator for increasing safety of a lithium ion secondary battery, relatively large in useful gas permeability, compressive resistance, electrolyte impregnation property, mechanical property and low shrinkage property at high temperature, relatively large in surface hardness and having high productivity and a manufacturing method therefor.SOLUTION: Provided a low heat shrinkable polyolefin microporous film obtained by adding polyolefin mixture consisting of ultra-high molecular weight polyethylene of 3 to 35 mass% and polyethylene of 1 to 20 mass%, a copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms of 17 to 70 mass%, an olefin block copolymer containing ethylene as a constitutional component of 0.01 to 3 mass%, a polyolefin elastomer resin of 0.1 to 5 mass% and a fine particle inorganic filler if needed, and having a shutdown temperature around 130°C, characteristic of so-called non-melt down without breaking the film at high temperature by 190°C.SELECTED DRAWING: None

Description

The present invention relates to a low heat shrinkable polyolefin microporous membrane and a method for producing the same.
Specifically, the present invention relates to a low heat-shrinkable polyolefin microporous membrane excellent in low shrinkage, mechanical properties, and air permeability when exposed to high temperatures, which is useful as a separator for enhancing the safety of a lithium ion secondary battery, and a method for producing the same.

Polyolefin microporous membranes are used in various applications such as battery separators, electrolytic capacitor membranes, various filters, moisture permeable and waterproof clothing, reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes. When the polyolefin microporous membrane is used as a battery separator, particularly as a separator for a lithium ion secondary battery, its performance is deeply related to battery characteristics, battery productivity, and battery safety. Therefore, excellent air permeability, mechanical properties, heat-resistant and low shrinkage properties, shutdown properties, non-meltdown properties, etc. are required. For example, when the mechanical strength is low, when used as a battery separator, the voltage of the battery may decrease due to a short circuit of the electrode.
If metal foreign matter is mixed in the battery, if the puncture strength of the battery separator is low, the electrode is short-circuited, leading to abnormal heat generation of the battery.
In recent years, lithium ion secondary batteries have become widespread as main power sources for portable electronic devices such as notebook personal computers, mobile phones, and single-camcorders. Due to the demand for higher performance and longer driving time of these portable electronic devices, technology development for higher energy density, higher capacity, and higher output is being promoted in lithium ion secondary batteries. .
On the other hand, in the power supply for hybrid vehicles and electric vehicles, from the viewpoint of safety of large lithium ion secondary batteries, it is necessary to avoid contraction and melting of the separator, causing a short circuit due to film breakage, resulting in smoke and ignition. I must. In addition to shutdown characteristics, it is also required to have sufficient heat resistance from the viewpoint of non-meltdown (non-meltdown) characteristics.

The current lithium-ion secondary battery separator uses a polyethylene microporous membrane mainly composed of polyethylene, which has shutdown characteristics as a function to ensure the safety of the battery. It is difficult to devise not to go down, judging from the melting point of polyethylene. In recent years, in order to improve heat resistance, it has been proposed to apply a heat-resistant resin further containing ceramic particles on a polyethylene microporous film or a polypropylene microporous film and then dry it.
However, it requires additional equipment for application, and it is easy to close the formed pores in the application process, and it is necessary to apply as thin as possible in order to keep the air permeability related to lithium ion conductivity well. This is contrary to the improvement of heat resistance, which increases the product cost.
On the other hand, the polyolefin microporous membrane has an advantage that there is almost no deterioration due to the electrolytic solution. Recently, regarding the characteristics of the separator, the quality of the lithium ion conductivity can be easily judged from the measurement result of the porosity and the test result of the air permeability.
In addition to mechanical strength, characteristics related to battery life such as cycle characteristics and characteristics related to battery productivity such as electrolyte injection properties are also emphasized. In particular, the electrode of the lithium ion secondary battery repeats expansion / contraction associated with charge / discharge. Therefore, loading / releasing of the force applied to the separator in the thickness direction is repeated. Due to the increase in electrode size and electrode density accompanying the increase in capacity of batteries in recent years, the pressure on the separator tends to become stronger during battery assembly.
In order to maintain the characteristics of the battery in such a situation, it is required that the change in permeability of the separator due to compression is small. If the separator is easily compressed, there is a high risk of battery capacity reduction (deterioration of cycle characteristics). Moreover, due to the increase in the electrode size accompanying the increase in capacity of the battery as described above, the electrolyte injection property to the battery is reduced, which causes a decrease in battery productivity. The electrolyte injection property must also be taken into account when improving the separator.

JP 2005-255876 A JP 2009-160933 A Japanese Patent Publication No. 5-62130 JP 2011-184671 A JP2013-57045A JP 2014-156574 A

"Lithium ion secondary battery second edition", Nikkan Kogyo Shimbun 1996, p. 107-p. 120

In Patent Document 1, poly (4-methylpentene-1) resin (TPX) alone is selected as a film-forming solvent, phthalic acid esters, trimellitic acid esters, etc. and heat resistant by a liquid-liquid phase separation method. It has been proposed to obtain a conductive microporous membrane.
Patent Document 2 proposes a polyolefin microporous membrane in which polymethylpentene (PMP) as a heat resistant resin is preferably dispersed in polyethylene as an organic heat resistant filler without melting as spherical or spheroid fine particles. There is.
Patent Document 3 proposes a method for producing a porous film of 4-methyl-1-pentene polymer resin (TPX) alone. Neither mention nor suggestion about the combination of polyethylene containing molecular weight polyethylene and high density polyethylene for producing the heat-resistant microporous membrane of the present invention.
Patent Document 4 discloses a heat-resistant polyolefin microporous membrane containing 10 to 60% by weight of ultrahigh molecular weight polyethylene and 70 to 30% by weight of 4-methyl-1-pentene polymer resin (TPX). However, it has only been shown that the thermal shrinkage after exposure to heat in a hot air dryer at 160 ° C. for 1 hour is low.
Patent Document 5 discloses a heat-resistant polyolefin fine particle containing 50 to 85% by weight of polyethylene containing ultrahigh molecular weight polyethylene and high density polyethylene and 12.5 to 30% by weight of 4-methyl-1-pentene polymer resin (TPX). A porous membrane is disclosed. However, it is only shown that the heat shrinkage rate after exposure to heat in a hot air dryer at 130 ° C. for 1 hour is low.
Patent Document 6 discloses a heat-resistant polyolefin microporous membrane containing 5-30% by mass of 4-methyl-1-pentene polymer resin (TPX) and may contain up to 30% by mass of polypropylene. However, it is only shown that the heat shrinkage rate after exposure to heat in a hot air dryer at 130 ° C. for 1 hour is low.
Non-Patent Document 1 shows the characteristics of a single-layer polyethylene microporous membrane, a single-layer polypropylene microporous membrane, and a three-layer polyethylene micropolypropylene membrane made of polyethylene / polypropylene / polyethylene. The above shows that the characteristics cannot be maintained thermally.

A heat-resistant polyolefin microporous membrane with excellent low shrinkage, mechanical properties, and permeability at high temperatures useful as a separator that can improve productivity and increase the safety of lithium ion secondary batteries, and a method for producing the same Is to provide.

The present inventors tried to improve the heat resistance of a microporous polyethylene film by paying attention to a copolymer resin of 4-methyl-1-pentene and an α-olefin having 3 or more carbon atoms as a heat-resistant polyolefin. Polyolefin elastomer resin having a specific microstructure of “net” in which “islands” which are helical crystal parts of nano-order level of 10 nm to 50 nm are connected to each other to form a network structure and cover the entire amorphous part as an elastomer resin And melted and kneaded in the extrusion by interposing a block polymer of ethylene and propylene copolymer containing ethylene and ethylene, and ethylene-ethylene-butylene-ethylene block copolymer. You can get things.
Polyolefin microporous membrane showing low heat shrinkage even after exposure for 1 hour in a circulating hot air dryer at 190 ° C., found that it is highly stretchable, thin film can be formed, and air permeability can be maintained well, and its production method The present invention has been reached.

Since the polyolefin microporous film having low heat shrinkability at high temperatures of the present invention has low heat shrinkability up to 190 ° C., no further heat-resistant coating of ceramic particles is required.
Moreover, it is a polyolefin microporous membrane having a single layer structure, and since flexibility and flexibility are maintained as a separator in the battery assembly process, workability is not impaired.
It can be easily manufactured by utilizing existing wet separator equipment, changing to the resin composition of the present invention, and adjusting processing temperatures such as extruder temperature and membrane stretching temperature.

The low heat-shrinkable polyolefin microporous membrane of the present invention is suitably produced by a production method including the following steps. Each process will be described in detail below.
(Step 1) Ultrahigh molecular weight polyethylene 5-45% by mass and polyethylene 10-30% by mass, copolymer resin 17-70% by mass of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms, ethylene A polyolefin resin mixture comprising 0.01 to 3% by mass of an olefin block copolymer containing 0.1 to 5% by mass and 0.1 to 5% by mass of a polyolefin-based elastomer resin and an antioxidant, and 2 inorganic filler powders as required. Supplying to a screw extruder, injecting a heated mixture of plasticizer, and melt-kneading;
(Step 2) A step of extruding the melt-kneaded material prepared in Step 1 from a T-die, cooling and rolling with a roll, and forming into a gel-like sheet molded product;
(Step 3) The gel-like sheet molding obtained in Step 2 is stretched in the biaxial direction (longitudinal direction, MD direction, lateral direction, TD direction) simultaneously in the biaxial direction, or sequentially stretched in the MD direction and TD direction. A step of performing three-dimensional stretching to increase the take-up speed while making the thickness thinner;
(Step 4) Step of extracting and removing the plasticizer from the thin film obtained in Step 3 with a solvent, and drying;
(Step 5) A step of heat-treating, re-stretching and heat-setting the microporous membrane obtained in Step 4 as necessary;

If necessary, various additives such as an ultraviolet absorber, an antiblocking agent, a nucleating agent, a pigment, a dye, and an inorganic filler are added to the melt-kneaded product of the polyolefin resin mixture as long as the effects of the present invention are not impaired. be able to. For example, finely divided silicic acid can be added as a pore forming agent.

Although the method of melt kneading is not particularly limited, it is usually carried out by uniformly kneading in a twin screw extruder. This method is suitable for preparing a melt of the polyolefin mixture. The melting temperature is preferably within the range of the average melting point of the polyolefin resin + 70 ° C. to + 120 ° C.
Specifically, the melting temperature is preferably set in the range of 200 to 300 ° C in the extrusion temperature zone, and more preferably in the range of 210 to 280 ° C. The plasticizer may be added before the start of kneading or may be added in the middle of the twin screw extruder during kneading.
In melt-kneading, it is preferable to add an antioxidant in order to prevent oxidative deterioration of the polyolefin resin mixture.

Further, the ratio (L / D) of the screw length (L) to the diameter (D) of the twin screw extruder is preferably in the range of 30 to 100, and more preferably in the range of 40 to 60. If L / D is less than 30, melt kneading may be insufficient. In particular, it becomes difficult to completely melt ultrahigh molecular weight polyethylene.
When L / D is more than 100, the residence time of the polyolefin mixture melt and the plasticizer is excessively increased, leading to thermal degradation. The shape of the screw is not particularly limited, but it is preferable to select a 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 mixture is put into the twin screw extruder, the ratio Q / Ns of the input amount Q (kg / h) of the polyolefin resin mixture and the plasticizer to the screw rotation speed Ns (rpm) is 0.1 to 0.55 kg / h / rpm is preferred. When Q / Ns is less than 0.1 kg / h / rpm, the polyolefin resin resin is excessively sheared, leading to a decrease in strength and shutdown temperature. On the other hand, when Q / Ns is more than 0.55 kg / h / rpm, it may not be uniformly kneaded. The ratio Q / Ns is more preferably 0.2 to 0.5 kg / h / rpm. 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 150 to 300 rpm is a preferable range.

As a method for forming a gel-like sheet molding, a resin and a plasticizer are melt-kneaded with a twin-screw extruder, and a melt of the polyolefin resin mixture is directly from the twin-screw extruder or from another extruder via a gear pump. It is obtained by extruding from a T-die and cooling.
Cooling is preferably performed to at least the gelation temperature or lower. Cooling is preferably performed to 40 ° C. or lower. By cooling to below the gelation temperature, the phase separation structure in which the polyolefin resin mixture phase is microphase-separated by the plasticizer can be fixed.
In general, when the cooling rate is low, the higher-order structure of the obtained gel-like molded product becomes coarse, and the pseudo cell units forming the gel structure tend to be large. When the cooling rate is high, the cells become dense cell units. When the cooling rate is less than 50 ° C./min, the degree of crystallinity increases, and it is difficult to obtain a gel-like product suitable for stretching.
As a cooling method, a method of directly contacting cold air, cooling water, or other cooling medium, a method of contacting a roll cooled by a refrigerant, or the like can be used. In addition, after melt-kneading the resin and the plasticizer with a batch-type kneader, a method of cooling into a sheet / film using a compression molding machine can be used.

As the die lip, a sheet die lip having a rectangular base shape is usually used, but a double cylindrical hollow die lip, an inflation die lip, or the like can also be used. In the case of a sheet die lip, the die lip gap is usually in the range of 0.2 to 8 mm, and is heated to a temperature of 190 to 250 ° C. during extrusion. The extrusion rate of the melt is preferably in the range of 0.2 to 80 m / min.

As the stretching method, flat stretching, tubular stretching, roll rolling and the like can be used. Of these, flat stretching is preferred from the viewpoint of stretching uniformity. The stretching temperature is preferably selected within the range of about 120 ° C. to the average melting point of the polyolefin mixture. When the stretching temperature is less than 110 ° C., film breakage due to excessive stretching stress is caused and the melt shrinkage resistance is deteriorated. The upper limit of the stretching temperature is preferably not more than the average melting point of the polyolefin resin mixture constituting the microporous membrane. When the temperature is equal to or lower than the average melting point temperature of the resin mixture, it becomes possible to prevent film breakage due to melting of the resin. When the stretching temperature exceeds the average melting point temperature, the polyolefin resin mixture is melted and molecular chains cannot be oriented by stretching. The stretching temperature is desirably as high as possible in order to reduce the thermal shrinkage of the microporous membrane.

Biaxial stretching is performed by heating a gel-like sheet molded article and then using a normal tenter method, roll method, inflation method, rolling method, or a combination of these methods. Any of simultaneous biaxial stretching, sequential stretching or multistage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching) may be used.
Although the order of biaxial stretching and plasticizer removal can be arbitrarily set, it is preferable to remove the plasticizer after biaxially stretching the gel-like sheet molding. However, it is not intended to limit in this order. For example, after removing the plasticizer from the gel-like sheet molded product, biaxial stretching is performed. The gel-like sheet molded product is biaxially stretched, and then the plasticizer is removed and further biaxially stretched. The plasticizer may be removed during each uniaxial stretching when the gel sheet is sequentially biaxially stretched. Stretching at least once in the film before removing the plasticizer in at least one direction (referred to as stretching before removing the plasticizer), and further stretching the film at least once in at least one direction (stretching after removing the plasticizer) Can be implemented).
The stretching at least once means that one-stage stretching, multi-stage stretching, or multi-stage stretching is performed. The stretching in at least one direction means longitudinal uniaxial stretching, transverse biaxial stretching, simultaneous biaxial stretching, and sequential biaxial stretching.

When biaxial stretching is performed after forming the gel-like sheet molding, the stretching speed in the machine direction (MD) and the transverse direction (TD) is the same as that in the longitudinal direction and the transverse direction when unstretched in the region where the unstretched sheet is stretched. If each length is defined as 1 and the ratio of the length stretched per minute, the stretching speeds in the longitudinal direction and the transverse direction of biaxial stretching are both 20 times / min or less.
When the stretching speed in the machine direction or the transverse direction exceeds 20 times / minute, the melt shrinkage resistance deteriorates.
The stretching speed in each direction is preferably 15 times / minute or less, and more preferably 10 times / minute or less.

The stretch ratio is 50 times or less in terms of the total area ratio. The total area magnification is the product of the total draw ratio in MD and the total draw ratio in TD. If the draw ratio is more than 50 times in terms of total area, the melt shrinkage resistance may be deteriorated. The stretching ratio is preferably 40 times or less in terms of the total area ratio. The magnification in the uniaxial direction in the machine direction (MD) and the transverse direction (TD) is preferably 3 to 20 times, more preferably 4 to 15 times, and further preferably 6 to 10 times. If the stretching ratio is 3 times or more, sufficient stretching orientation is provided, so that the strength of the microporous film can be improved. If the stretching ratio is 20 times or less, the structure of the microporous film is destroyed due to excessive stretching. Is to prevent. Although there is no restriction | limiting in particular in the extending | stretching minimum of each direction, It is preferable that it is 3 times or more from a viewpoint of productivity. From the viewpoint of improving the mechanical strength, the total area magnification is preferably 9 times or more by stretching 3 times or more to MD and TD, and the total area magnification is preferably 16 times or more by increasing 4 times or more to MD and TD. The ratio of the total stretch ratio in MD and the total stretch ratio in TD (total stretch ratio in MD) / (total stretch ratio in TD) is not particularly limited, but in any case of simultaneous biaxial stretching, sequential stretching or step stretching. 0.5 to 2 is preferable, 0.7 to 1.3 is more preferable, and 1 is most preferable. As long as the stretching speed in each direction is 20 times or less, MD and TD may be different from each other.

Depending on the desired physical properties, the film may be stretched by providing a temperature distribution in the film thickness direction. By providing a temperature distribution in the film thickness direction and stretching, a microporous film generally excellent in mechanical strength can be obtained.
You may perform the process (hot roll process) which makes a hot roll contact at least one surface of the stretched gel-like molding before washing | cleaning. The stretched gel-like molded product is brought into contact with the heating roll.
The contact time between the heating roll and the stretched gel-like molded product may be 0.1 second to 1 minute.
You may make it contact in the state which hold | maintained heating oil on the roll surface. The heating roll may be either a smooth roll or an uneven roll that may have a suction function.

Since the polyolefin mixture resin phase is phase-separated from the plasticizer for film formation, a porous film can be obtained by removing the plasticizer for film formation using a cleaning solvent. As a method for removing the cleaning solvent and the plasticizer for film formation using the cleaning solvent, known methods can be used.

Heat treatment (heat drawing treatment and / or heat setting treatment and / or heat shrinking treatment) may be performed at least once after the drawing step or after removal of the plasticizer. The heat treatment temperature is determined in consideration of a change in strength, a change in air permeability and the like due to the heat treatment.

In order to adjust the physical properties such as porosity in the hot stretching process, the tenter method, roll method or rolling method that is usually used is used, and the draw ratio in one direction is at least once in at least one uniaxial direction. It is preferable to carry out at a draw ratio of 2.0 times, and more preferably at a draw ratio of 1.02 to 1.5 times. The heat setting treatment is performed by a tenter method, a roll method, or a rolling method to stabilize the crystallization of the polyolefin resin in the low heat shrinkable polyolefin microporous film.
The heat shrinking treatment may be performed by a tenter method, a roll method or a rolling method, or may be performed using a belt conveyor or a floating roll. The heat shrink treatment is preferably performed in a range of 50% or less in at least one direction, 30% or less, and more preferably 20% or less.

You may perform combining the above-mentioned heat | fever extending process, heat setting process, and heat shrink process many.
In the hot roll treatment, a treatment (hot roll treatment) in which a hot roll is brought into contact with at least one surface of the stretched gel-like molded product before washing may be performed. The stretched gel-like molded product is brought into contact with a heating roll whose temperature is adjusted to a crystal temperature of the polyolefin resin mixture + 10 ° C. or higher and lower than the average melting point of the polyolefin resin mixture. The contact time between the heating roll and the stretched gel-like molded product is preferably 0.5 seconds to 1 minute.
You may make it contact in the state which hold | maintained heating oil on the roll surface. The heating roll may be either a smooth roll or an uneven roll that may have a suction function.
In particular, it is preferable to perform a heat shrinking treatment after the heat stretching treatment because a microporous film having a low shrinkage rate and a high strength can be obtained.

The film thickness of the low heat-shrinkable polyolefin microporous membrane according to a preferred embodiment of the present invention is 5 to 100 μm, preferably 6 to 40 μm, more preferably 10 to 25 μm.
If the film thickness is 5 μm or more, the film has sufficient strength as a microporous film, and if it is 100 μm or less, the film has sufficient permeability and has a high electrolyte solution impregnation property.
In addition, although the thickness of a microporous film can be suitably selected according to a use, when using as a separator for small lithium ion secondary batteries, 7-25 micrometers is preferable and 10-18 micrometers is more preferable. The film thickness is measured according to JIS standard K7130. When used as a separator for a large lithium ion secondary battery of an electric vehicle driving power source, 20 to 40 μm is preferable.

The distribution of the micropore structure region and the coarse pore structure region is not particularly limited. Usually, as a result of the fibril fiber structure being expressed in both cross sections in the MD direction and TD direction of the microporous membrane, the micropore structure region and the coarse pore structure region are irregularly interlaced. The size is also irregular. Such a structure can be observed, for example, with a transmission electron microscope (TEM) or the like, and can be measured as a maximum height difference with 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 has excellent air permeability and electrolyte absorption, and changes in air permeability when pressurized are small. Therefore, when used as a separator for a lithium ion secondary battery, excellent battery productivity and battery cycle characteristics can be realized.

When the low heat-shrinkable polyolefin microporous membrane of the present invention is used as a lithium ion secondary battery separator, it becomes possible to maintain high productivity of the battery and prolong the life of the battery by excellent cycle characteristics. The low heat-shrinkable polyolefin microporous membrane of the present invention obtained by uniform melting ensures a low heat-shrinkage while being economically advantageous from the viewpoint of manufacturing cost and manufacturing equipment, and breaks down to 190 ° C or higher. A polyethylene microporous film that has a so-called melt-down (non-melt-down) characteristic that does not form a film and that is not found in other heat-resistant separators also maintains a shutdown temperature that has contributed to battery safety. Further, the fluorine-based electrolyte complex salt used in the lithium ion secondary battery is thermally decomposed at around 190 ° C. and loses lithium ion conductivity and becomes inactive as a battery, so that runaway of the battery can be suppressed or prevented. Since the separator can prevent a short circuit between the edge portions of the positive electrode and the negative electrode due to the low heat shrinkage characteristic, it is also excellent from the viewpoint of battery safety.

Next, the low heat-shrinkable polyolefin microporous membrane of the present invention and materials used in the production method will be described.

[1] Ultra high molecular weight polyethylene The ultra high molecular weight polyethylene constituting the polyolefin microporous membrane of the present invention has a viscosity average molecular weight determined from the intrinsic viscosity in the range of 500,000 to 10 million, and the ultra high molecular weight polyethylene is used alone or Two or more types are used in combination. Not only an ethylene homopolymer, but also a copolymer containing a small amount of other α-olefin may be used in combination. Other 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. It is done.
Conventionally, ultra-high molecular weight polyethylene of 3.5 million or more was considered to be difficult to extrude and knead, and was rarely used. However, ultra high molecular weight polyethylene with a viscosity average molecular weight of about 1 million was mixed with a plasticizer. By adding ultra-high molecular weight polyethylene so that the difference in viscosity average molecular weight is within 1 to 2.5 million, it is also possible to use ultra high molecular weight polyethylene with a viscosity average molecular weight of over 3.5 million and exceeding 6 million to 10 million. Can be. Furthermore, it has been found that even with ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 7 million to 10 million, even if it is a thin film of 15 μm or less, the tensile strength and the piercing strength can be maintained satisfactorily.

[2] High density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE, L-LDPE) having a polyethylene viscosity average molecular weight in the range of 150,000 to less than 500,000, preferably 200,000 to 400,000 Etc. Polyethylene is used alone or in combination of two or more. Not only an ethylene homopolymer, but also a copolymer containing a small amount of other α-olefin may be used in combination. Other 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. It is done. The amount of polyethylene added is 1% by mass or more and 20% by mass or less.

For the viscosity average molecular weight, decalin is used as a solvent, the intrinsic viscosity [η] is measured at a measurement temperature of 135 ° C., and the viscosity average molecular weight (Mv) is calculated by the following formula.

[3] Copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms The present invention uses methyl 4 instead of poly (4-methyl-1-pentene) homopolymer. -Copolymer resin polymer resin of methyl-1-pentene and α-olefin having 3 or more carbon atoms. 4-methyl-1-pentene and at least one α-olefin such as propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1- It is a copolymer with an α-olefin having 3 to 30 carbon atoms such as octadecene. From the viewpoint of miscibility with the ultrahigh molecular weight polyethylene of the present invention, a powder is preferable, and from the viewpoint of miscibility and heat resistance retained after mixing, 4-methyl-1-pentene is preferably contained in an amount of 80 mol% or more. It is a copolymer mainly composed of methyl-1-pentene, and the composition ratio of 4-methyl-1-pentene and α-olefin is a melting point (Tm) measured based on a DSC (Differential Scanning Calorimetry) test. ) Is adjusted in the range of 200 to 250 ° C, preferably 220 to 240 ° C.
Further, the melt flow rate (MFR) measured under conditions of a load of 5 kg and a temperature of 260 ° C. according to ASTM D1238 is 0.05 to 250 [g / 10 min].
It is preferably in the range of 1 to 100 g / 10 minutes. When the melt flow rate is less than 0.05 g / 10 min, the melt viscosity is high and the moldability is poor, and when the melt flow rate exceeds 250 g / 10 min, the melt viscosity is low and the film formability is poor, and the mechanical strength is also low. In the present invention, a copolymer resin of 4-methyl-1-pentene and an α-olefin having 3 or more carbon atoms is used in the range of 17 to 70% by mass. If it is less than 17% by mass, the degree of improvement in heat resistance from the polyethylene microporous membrane is poor, and after heat exposure in a circulating hot air dryer at 190 ° C. for 1 hour, low heat shrinkability is not exhibited, which is not preferable. Moreover, even if it exceeds 70 mass%, the further low heat shrinkability cannot be anticipated, cost becomes high and is unpreferable.

[4] Olefin block copolymer ethylene-ethylene-butylene-ethylene block copolymer containing ethylene as a constituent component is saturated by hydrogenating the double bond of the butadiene portion of the block copolymer obtained with the living catalyst This is a modified elastomer. There is JSR Dynalon CEBC (Dynalon 6200P as an example).
The block polymer of polypropylene and ethylene-propylene copolymer is made from propylene and ethylene as raw materials. First, propylene is used as a raw material, using a metallocene catalyst, titanium system, etc., and flowing in a reactor such as a pipe for several seconds to several 10-40 mol% of polypropylene is synthesized in a minute, followed by 90-60 mol% of a mixture of ethylene and propylene, and an ethylene-propylene copolymer is synthesized continuously in a similar 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. Further, by repeating this step or changing the polymerization time at the time of repeating, the material containing the multi-block body and the present block copolymer can have any ethylene content. The block copolymer can have compatibility with a copolymer resin of 4-methyl-1-pentene and an α-olefin having 3 or more carbon atoms and polyethylene. For example, R110E, R110MP, T310E, M142E etc. are mentioned as Prime TPO by Prime Polymer Co., Ltd.
Further, there are propylene block polymer, qualia manufactured by Sun Allomer Co., Ltd., polypropylene impact copolymer manufactured by Nippon Polypro Co., Ltd., Newcon, tufselen, exelen manufactured by Sumitomo Chemical Co., Ltd., and the like. Particularly preferred is a block polymer of polypropylene, ethylene and a propylene copolymer, which is made of a living catalyst whose active site of the catalyst can polymerize both ethylene and propylene and whose polymerization active site is sufficiently stable. A thing with a high ratio is preferable. The olefin block copolymer containing ethylene as a constituent component of the present invention is an ethylene-ethylene / butylene-ethylene block copolymer alone or a mixture of polypropylene and ethylene-propylene copolymer in an amount of 0.01-3 mass. Used in the range of%.
If it is less than 0.01% by mass, there is almost no effect of addition, and if it exceeds 3% by mass, rigidity of the microporous membrane is reduced, which is not preferable.

[5] Polyolefin-based elastomer resin The polyolefin-based elastomer resin used in the present invention is a copolymer composed of a structural unit derived from propylene and a structural unit derived from an α-olefin having 2 to 30 carbon atoms (excluding propylene). Yes, containing 10 mol% or more of a propylene-derived structural unit (here, the total of the propylene-derived structural unit and the C2-C30 α-olefin-derived structural unit is 100 mol%), and a copolymer component As the α-olefin of 2 to 30 carbon atoms (excluding propylene), ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, Examples include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene and the like.

The most preferable polyolefin-based elastomer resin is composed of a propylene-derived structural unit and a structural unit derived from an α-olefin having 2 to 30 carbon atoms (excluding propylene), and has a nano-order helical crystal portion of 10 nm to 50 nm. Certain “islands” are connected to each other to form a network structure and have a microstructure that covers the entire amorphous part.
For example, “Notio SN0285”, “Notio PN3560”, “Notio PN2060”, “Notio PN2070”, etc., manufactured by Mitsui Chemicals, Inc.) are available. Use in combination with a copolymer resin of 4-methyl-1-pentene and α-olefin and the ethylene-ethylene-butylene-ethylene block copolymer can minimize the amount of addition. Is optimal. In addition, the flexibility generally decreases when the crystallinity is increased to increase the heat resistance, but when the propylene-based elastomer resin is mixed, the amorphous part is incorporated at the nano level inside the crystal part, Even if the heat resistance is increased, the flexibility does not decrease because it is connected to the surrounding amorphous part.

In the present invention, a polyolefin-based elastomer resin can be used in the range of 0.01-5 mass%.
If it is less than 0.01% by mass, there is almost no effect of addition, and if it exceeds 5% by mass, the heat shrinkage rate is reduced as a microporous film, which is not preferable.

For example, when n or more types of polyolefin resins having different melting points are used (here, n represents an integer of 3 or more), the melting point T ₁ ° C. of the high molecular weight polyethylene and the melting point T ₂ ° C. of the polyolefin resin used, T ₃ ° C. .. The average melting point T of the resin mixture composed of _Tn.degree. C. is defined as the following formula.

式中、χ_１＋χ_２＋χ_３・・・χ_ｎ＝１ χ_１；超高分子ポリエチレンの質量分率、χ_２〜χ_ｎ；融点Ｔ_２℃、Ｔ_３℃、・・・Ｔ_ｎ℃の他に使用されるポリオレフィン樹脂のそれぞれの質量分率である。ここで融点とはＪＩＳＫ７１２１に基づいて示差走査熱量測定（ＤＳＣ）により求められる値を言う。

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 ° C. It is the mass fraction of each polyolefin resin used elsewhere. Here, the melting point refers to a value obtained by differential scanning calorimetry (DSC) based on JISK7121.

[6] Inorganic filler
Examples of the inorganic filler used in the present invention include alumina, nano-sized boehmite / alumina having an aspect ratio of aluminum hydroxide, silica (silicon oxide), sodium aluminosilicate, sodium calcium aluminosilicate titania, zirconia, Oxides such as magnesia, ceria, yttria, zinc oxide, iron oxide, nitrides such as silicon carbide, silicon nitride, titanium nitride, boron nitride, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, Kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, etc. Mix, such as 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, and silica and aluminosilicate are 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.
When the average particle size is 100 nm or less, peeling between the polyolefin resin and the inorganic filler tends not to occur even when stretching or the like is performed, which is preferable from the viewpoint of suppressing the generation of macrovoids. On the other hand, setting the average particle size to 1 nm or more is preferable for ensuring the dispersibility of the inorganic filler particles during melting.

The proportion of the inorganic filler particles in the total amount of the polyolefin resin and the inorganic filler particles is 1% by mass or more and 40% by mass or less, preferably 1% by mass or more and 30% from the viewpoint of wear resistance of the barrel and screw of the extruder. It is below mass%. It is preferable that the weight loss rate up to 100 ° C. by the thermogravimetric analysis of the inorganic filler particles is 5% or less.
By adding inorganic filler particles, the tensile strength of the microporous membrane can be increased and the thermal shrinkage rate can be lowered.

[7] Plasticizer As the plasticizer that can be used in producing the microporous membrane of the present invention, either a liquid plasticizer or a solid plasticizer can be used. 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 boiling points corresponding to these. In order to obtain a gel-like molded article having a stable solvent content, 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 cSt at 25 ° C., and more preferably in the range of 50 to 200 cSt. When the viscosity of the liquid plasticizer at 25 ° C. is less than 30 cSt, 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 it exceeds 500 cSt, it is difficult to remove the plasticizer.

The solid plasticizer preferably has a melting point of 80 ° C. or lower. As such a solid plasticizer, waxes such as paraffin wax and microcrystalline wax, higher alcohols such as seryl alcohol and stearyl alcohol, polyoxyethylene stearyl ether, poly Polyoxyethylene alkyl ethers such as oxyethylene isostearyl ether, polyoxypropylene stearyl ether, polyoxypropylene alkyl ether such as polyoxypropylisostearyl ether, polyoxyethylene alkyl esters such as polyoxyethylene stearyl ester, polyoxy And polyoxypropylene alkyl esters such as propylene stearyl ester.
You may use it, mixing a liquid solvent and a solid solvent suitably.
In particular, it is useful because the mixture is solidified at room temperature by mixing polyoxyethylene alkyl ether such as polyoxyethylene steryl ether and polyoxyethylene isostearyl ether with liquid paraffin. It is used in the range of 95-75% by mass of liquid paraffin and 5-25% by mass of polyoxyalkylene alkyl ether, preferably 99-80% by mass of liquid paraffin and 1-20% by mass of polyoxyalkylene alkyl ether.
Forming a soft gel-like sheet that can be stretched when the resin and plasticizer are uniformly melt-kneaded at a temperature equal to or higher than their melting points, and then the kneaded product is cooled to below the solidification temperature of the mixed resin at an arbitrary cooling rate. You can get things.

The amount of the plasticizer that can be used can be changed depending on the compatibility of the resin and the plasticizer in the phase separation structure 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 resin mixture and the plasticizer is 10 to 55 parts by mass of the polyolefin resin mixture and 90 to 45 parts by mass of the plasticizer, preferably 100 parts by mass of both, preferably the polyolefin resin. The mixture is 30 to 50 parts by mass and the plasticizer is 70 to 50 parts by mass. When the ratio of the polyolefin resin mixture is less than 10 parts by mass, when extruding the polyolefin mixture melt, swell and neck-in are increased at the die outlet, and the moldability and self-supporting property of the gel-like molded product are lowered. On the other hand, when the proportion of the polyolefin mixture exceeds 50 parts by mass, the film formability of the gel-like sheet molding is lowered, and the pores are small and the gas permeability is poor.

[8] The solvent for removing the solvent plasticizer is preferably a poor solvent for the resin used, a good solvent for the plasticizer, and a boiling point lower than the melting point of the film. . 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 and C ₇ F _16, hydrofluoroethers such as C ₄ F ₉ OCH ₃ and C ₄ F ₉ OC ₂ H ₅ , C ₄ F ₉ OCF ₃ and C ₄ F ₉ OC ₂ F ₅ perfluoroether or the like can be used. In order to prevent shrinkage of the film during removal of the plasticizer / solvent, the film is immersed in a solvent while constraining the film in at least one direction, and after removal of the plasticizer, the solvent is dried and removed by a heat drying method, an air drying method or the like below the melting point of the film. This method can be suitably used.

The low heat shrinkable polyolefin microporous membrane according to a preferred embodiment of the present invention has the following physical properties.

(1) The air permeability (Gurley value) is 20 to 350 seconds / 100 ml. When the air permeability is within this range, the battery capacity is large when the microporous membrane is used as a battery separator, and the cycle characteristics of the battery are also good. When the air permeability is less than 20 seconds / 100 ml / 20 μm, shutdown is not sufficiently performed when the temperature inside the battery rises. The air permeability is measured using a Gurley type air permeability meter according to JIS P8117.

(2) The porosity is 35 to 60%, preferably 40 to 50%.
If the porosity is 35% or more, it has sufficient air permeability, and if it is 50% or less, it has sufficient mechanical strength, and when used as a battery separator, the electrode is less likely to be short-circuited. The porosity is measured by a gravimetric method. A sample is cut into a square of 5.0 cm square, and the volume (cm 3) and weight (g) are measured. The resin density (g / cm3) used is measured according to ASTM D1505.
Calculate by the following formula.

(3) The maximum pore size of the microporous membrane is preferably 0.1 to 5 μm, more preferably 0.3 to 3 μm, and still more preferably 0.3 to 1.5 μm. If the maximum pore diameter is 0.1 μm or more, the required permeability as a separator is obtained, and if it is 5 μm or less, it is possible to prevent a short circuit due to an electrode desorption component.
The surface of the low heat shrinkable polyolefin microporous membrane is observed with a scanning electron microscope (SEM). Arbitrarily 20 holes are selected, and the diameters of these holes are calculated and averaged.

(4) For the puncture strength, a puncture test is performed at a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm / sec, and the puncture strength is indicated by N from the maximum puncture load g.
It is desirable that it is 2N or more. If the piercing strength is less than 2N, there is a possibility that an electrode short circuit may occur when the microporous membrane is incorporated in a battery as a battery separator. The puncture strength is 3N or more, more preferably 5N or more.
A short circuit due to a desorbed component from the electrode does not occur, and the separator has sufficient strength.

(5) The tensile strength at break is measured by ASTM D882 using a strip-shaped test piece having a width of 10 mm.
The tensile strength at break is preferably 10 MPa or more in both the MD direction and the TD direction in order to prevent film breakage.

(6) The tensile elongation at break is measured by ASTM D882 using a strip-shaped test piece having a width of 10 mm.
It is preferable that the tensile elongation at break is 5% or more in both the MD direction and the TD direction without fear of film breakage.

(7) The thermal shrinkage after exposure for 1 hour in a circulating hot air dryer at a temperature of 190 ° C. marks the MD and TD directions of a sample cut out to 50 mm × 50 mm. The upper surface is put between a glass plate having a size of 210 mm × 297 mm of 451 g and a lower plate between stainless steel 304 plates for 1 hour. At the first hour, the sample was cooled to room temperature and the dimensional changes in the vertical and horizontal directions were measured. The heat shrinkage ratio was the difference between the area of the first sample piece and the area of the first sample piece after exposure. Divide by to get the percentage. The longitudinal (MD) direction is the extrusion direction during the production of the microporous membrane, and the transverse (TD) direction is the direction orthogonal to the extrusion direction during the production of the microporous membrane. The heat shrinkage rate is preferably 20% or less.
Preferably it is 10%, More preferably, it is 5% or less. When the thermal shrinkage rate exceeds 20%, when the microporous membrane is used as a separator for a lithium ion secondary battery, the end of the separator shrinks during abnormal heat generation, and the possibility of short-circuiting of the electrodes increases. .

(8) A film thickness change rate after sandwiching a film between a pair of stainless steel plates having a high smooth surface and heating and compressing the film at 90 ° C. for 5 minutes under a pressure of 2.2 MPa (22 kgf / cm ² ). Is preferably 20% or less, assuming that the film thickness before compression is 100%.
When the film thickness change rate is 20% or less, when the microporous membrane is used as a lithium ion secondary battery separator, the battery capacity is large and the cycle characteristics of the battery are also good. The film thickness is measured with a contact thickness meter (manufactured by Mitutoyo Corporation). The ultimate air permeability (Gurley value) after heat compression under the above conditions is 600 seconds / 100 ml / 20 μm or less. When the ultimate air permeability is 500 seconds / 100 ml / 20 μm or less, the air permeability change and the film thickness change are small even when pressurized, and the battery capacity is large when used as a lithium ion secondary battery separator, Excellent permeability, mechanical properties and heat shrinkability.

(9) The surface roughness is measured with an atomic force microscope (AFM). A preferable range of the maximum height difference is 250 nm or more and 600 nm. More preferably, it is the range of 300 nm to 600 nm. When the thickness is less than 250 nm, the wetness of the electrolytic solution is also deteriorated, and the separator is hardly detached from the separator winding roll. If it exceeds 600 nm, the mechanical strength of the separator is lowered, which is not preferable. When used as a battery separator, the contact area with the electrolyte is large, and the electrolyte injection property is excellent.

(10) Melt-down (non-mel-down) properties were evaluated by using an electrolytic solution (1M LiBF ₄ / polypropylene) as a separator sample cut into a 30 mmφ size sample holder of a small heating furnace MT-Z300 manufactured by Toyo Technica Co., Ltd. Carbonate (PC): gamma-butyrolactone (γ-BL) (1/1 volume ratio)) is impregnated and sealed.
It is sandwiched between 6 mmφ electrodes and heated at a rate of 5 ° C./min. The temperature and impedance value of the sample are measured with an impedance analyzer 6430B manufactured by Toyo Technica. The impedance value is an alternating current method with an amplitude of 10 mV and a frequency of 1 kHz applied within a range of 10 mA. The impedance value is plotted against the temperature, and the temperature that becomes 1000 ohms or higher in the process of increasing the impedance value is the shutdown temperature. And Further, the battery container is continuously heated at a temperature rising rate of 5 ° C./minute, the temperature of the battery container and the impedance value are measured, and the temperature when the impedance value becomes less than 300 ohms again is defined as the meltdown temperature. The evaluation of the non-melt down property indicates that when it reaches 190 ° C., it does not break even after 1 minute and retains a high impedance value as 190 ° C. <and has excellent non-melt down properties. Means.

(11) In battery evaluation, the separator made of the low heat-shrinkable polyolefin microporous membrane is not particularly limited in the type of battery using the separator, but is particularly suitable for lithium ion secondary battery applications. For the lithium ion secondary battery using the separator made of the microporous membrane of the present invention, a known electrode and electrolyte may be used.
The structure of the lithium ion secondary battery using the separator made of the microporous membrane of the present invention may also be a known one.
For example, as a positive electrode active material, 92 parts by weight of lithium cobalt oxide (LiCoO ₂ ; 10 micron) powder, ₂ parts by weight of acetylene black (manufactured by Denki Kagaku Kogyo), 2 parts by weight of fine graphite (manufactured by Nippon Graphite), polyvinylidene fluoride A positive electrode agent paste is prepared using 6% by mass of an N-methylpyrrolidone solution of 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 produce a positive electrode.
It consists of a graphitized carbon (manufactured by Hitachi Chemical) powder 97 as a negative electrode active material, 1 part of CMC (carboxymethylcellulose) (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 2 parts of a solid content of a carboxy-modified butadiene latex (manufactured by Nippon Zeon). A negative electrode 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 produce a negative electrode.

The positive electrode was cut into a size of 20 mm × 50 mm and attached with a tab. The negative electrode was cut into a size of 22 mm × 52 mm and attached with a tab. The separator was cut into a size of 26 mm × 56 mm. These positive electrode / separator / negative electrode were joined, an electrolytic solution was injected, and sealed in an aluminum laminate film to produce an aluminum laminate exterior cell.
Here, a 1M solution of LiPF ₆ dissolved in ethylene carbonate / ethyl methyl carbonate (3/7 weight ratio) is used as the electrolytic solution.
In this cell, the amount of discharge electricity at 0.2C and 2C was measured, and the battery performance was defined as (discharge amount of electricity at 2C) / (discharge amount of electricity at 0.2C) × 100. 95% or more is regarded as good battery performance. Here, the charging condition is 0.2 C 4.2 V CC / CV 8 hours, and the discharging condition is CC discharge with a 2.75 V cutoff.

Thus, the low heat shrinkable polyolefin 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 optimal as a separator for lithium ion secondary batteries. Taking advantage of the excellent non-meltdown characteristics of the low heat-resistant polyolefin microporous membrane of the present invention, a shutdown temperature is bonded to a polyethylene-based microporous membrane having any temperature in the range of 125 to 142 ° C, It can also be used as a multilayer separator for batteries. It is also possible to use together with the above-mentioned polyethylene-based microporous membrane at the time of battery assembly.

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.

11.9% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.09 million, 23.9% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, 6.0% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.50 million , 6.0 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 5,810,000, 6.0 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 631,000, and high density polyethylene 7.2 having a viscosity average molecular weight of 334,000. 4-methyl-1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load 9 g / 10 min) having a melting point peak of 232 ° C. and 30.5% by mass of 4-methyl-1-pentene-1-decene-1 copolymer having a melting point peak of 232 ° C. -1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load, 25 g / 10 min), 7.6% by mass, polyolefin elastomer resin Notio [grade name SN0285] 0.54 mass% manufactured by Mitsui Chemicals, Inc., Dynalon CEBC [grade name Dynalon 6200P] 0.24 mass% made of JSR as an ethylene-ethylene butylene-ethylene block copolymer, polypropylene R-110M 0.12 mass% manufactured by Prime Polymer Co., Ltd. as a block polymer of ethylene, propylene copolymer, and EXELEX [grade name 48070B manufactured by Mitsui Chemicals, Inc. as a low molecular weight ethylene butene copolymer ] Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane as an antioxidant with respect to 100.0 parts by mass of a polyolefin resin mixture comprising 0.06% by mass. 5 parts by mass and 3,9-bis (2,6-dita Dry blending 0.25 parts by weight of (salibutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] methane, A polyolefin resin mixture having a calculated resin average melting point of 171 ° C. was prepared. 40 parts by mass of the resin mixture is put into a twin screw extruder (cylinder diameter: 128 mm, screw length (L) to diameter (D) ratio L / D: 52.5, using a strong kneading type screw). 60 parts by mass of liquid paraffin 68 cst (40 ° C.) is supplied as a plasticizer from the side feeder of the twin screw extruder while heating, and a polyolefin / plasticizer mixed melt is prepared at a temperature of 240 ° C. and a screw rotation speed of 92 rpm. To do.
This is extruded from a T-die through a gear pump installed at the tip of a twin-screw extruder, and is taken out with a cooling roll to form a gel-like sheet molding.
The resulting gel-like sheet molding is stretched in the MD and TD directions by a simultaneous biaxial stretching machine. Subsequently, it passes through a continuous plasticizer extraction apparatus using methylene chloride as a solvent. Further, a heat-shrinkable low-shrinkage polyolefin microporous membrane is obtained by applying a heat-shrinkage treatment for 30 seconds while lowering from 125 ° C to 60 ° C in a heated second tenter as a heat stretching treatment step. The characteristics are shown in Table 1.
As a result of the evaluation test of the non-melt down characteristics, the shutdown temperature showed a rapid increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 190 ° C.

10.1% by mass of ultra high molecular weight polyethylene with a viscosity average molecular weight of 1.09 million, 20.2% by mass of ultra high molecular weight polyethylene with a viscosity average molecular weight of 2 million, 5.1% by mass of ultra high molecular weight polyethylene with a viscosity average molecular weight of 39.50 million 5.1 mass% of ultra high molecular weight polyethylene having a viscosity average molecular weight of 5,811,000, 5.1 mass% of ultra high molecular weight polyethylene having a viscosity average molecular weight of 631,10,000, and high density polyethylene 6.1 having a viscosity average molecular weight of 334,000. 4-methyl-1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load, 9 g / 10 min) having 3 mass% and melting point peak 232 ° C. -1-pentene-1-decene-1 copolymer (MFR260 ° C., 5 kg load, 25 g / 10 min), 9.7% by mass, polyolefin elastomer resin Notio [grade name SN0285] 0.46 mass% manufactured by Mitsui Chemicals, Inc., Dynalon CEBC [grade name Dynalon 6200P] 0.20 mass% manufactured by JSR as an ethylene-ethylene butylene-ethylene block copolymer, REX-110M 0.10 mass% made by Prime Polymer Co., Ltd. as a block polymer of polypropylene, ethylene, and propylene copolymer, Excelex [Grade made by Mitsui Chemicals, Inc. as a low molecular weight ethylene / butene copolymer Name 48070B] Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane as an antioxidant with respect to 100.0 parts by mass of a polyolefin resin mixture comprising 0.05% by mass 0.5 parts by mass and 3,9-bis (2,6-dita -Shiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] 0.25 parts by mass of methane is dry blended and calculated A polyolefin resin mixture having an average melting point of 180 ° C. was prepared.
40 parts by mass of the resin mixture is put into a twin screw extruder (cylinder diameter: 128 mm, screw length (L) to diameter (D) ratio L / D: 52.5, using a strong kneading type screw). 60 parts by mass of liquid paraffin [68 cst (40 ° C.)] as a plasticizer is supplied from the side feeder of the twin screw extruder while heating, and the polyolefin / plasticizer mixed melt is supplied at a temperature of 240 ° C. and a screw rotation speed of 92 rpm. To prepare.
This is extruded from a T-die through a gear pump installed at the tip of a twin-screw extruder, and is taken out with a cooling roll to form a gel-like sheet molding. The resulting gel-like sheet molding is stretched in the MD and TD directions by a simultaneous biaxial stretching machine.
Subsequently, it passes through a continuous plasticizer extraction apparatus using methylene chloride as a solvent. Further, a heat-shrinkable low-shrinkage polyolefin microporous membrane is obtained by applying a heat-shrinkage treatment for 30 seconds while lowering from 125 ° C to 60 ° C in a heated second tenter as a heat stretching treatment step. The characteristics are shown in Table 1.
As a result of the evaluation test of the non-melt down characteristics, the shutdown temperature showed a rapid increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 190 ° C. The characteristics are shown in Table 1.

5.2% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.09 million, 13.4% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, 2.6% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.50 million , 3.0 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 581,000, 3.0 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 631,000, and 3.9 high density polyethylene having a viscosity average molecular weight of 334,000. 4-methyl-1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load, 9 g / 10 min) having 5 mass% and melting point peak of 232 ° C. and 4-methyl having a melting point peak of 228 ° C. 1-pentene-1-decene-1 copolymer (MFR260 ° C., 5 kg load, 25 g / 10 min), 13.6% by mass, polyolefin elastomer resin Notio [grade name SN0285] manufactured by Mitsui Chemicals Co., Ltd. 0.65% by mass, Dynalon CEBC [grade name Dynalon 6200P] manufactured by JSR as an ethylene-ethylene butylene-ethylene block copolymer 0.13% by mass, REX-110M 0.06 mass% manufactured by Prime Polymer Co., Ltd. as a block polymer of polypropylene, ethylene, and propylene copolymer, and EXELEX [Grade Name] manufactured by Mitsui Chemicals, Inc. as a low molecular weight ethylene / butene copolymer 48070B] Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 2 as an antioxidant with respect to 100.0 parts by mass of a polyolefin resin mixture comprising 0.06% by mass .5 parts by mass and 3,9-bis (2,6-di -Shiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] 0.25 parts by mass of methane is dry blended and calculated A polyolefin resin mixture having an average resin melting point of 200 ° C. was prepared.
40 parts by mass of the resin mixture is put into a twin screw extruder (cylinder diameter: 128 mm, screw length (L) to diameter (D) ratio L / D: 52.5, using a strong kneading type screw). 60 parts by mass of liquid paraffin [68 cst (40 ° C.)] as a plasticizer is supplied while heating from the side feeder of the twin screw extruder, and the polyolefin / plasticizer mixed melt is supplied at a temperature of 245 ° C. and a screw rotation speed of 92 rpm. To prepare. This is extruded from a T-die through a gear pump installed at the tip of a twin-screw extruder, and is taken out with a cooling roll to form a gel-like sheet molding. The resulting gel-like sheet molding is stretched in the MD and TD directions by a simultaneous biaxial stretching machine. Subsequently, it passes through a continuous plasticizer extraction apparatus using methylene chloride as a solvent. Further, a low-shrinkage polyolefin microporous film heat-treated at 125 ° C. with a hot press is obtained.
The characteristics are shown in Table 1. As a result of the evaluation test of the non-melt down characteristics, the shutdown temperature showed a rapid increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 190 ° C.

15.9% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.09 million, 31.8% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, and 8.0% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.95 million , High-molecular-weight polyethylene having a viscosity-average molecular weight of 5,810,000, 8.0% by mass, ultra-high-molecular-weight polyethylene having a viscosity-average molecular weight of 63,110,000, and high-density polyethylene having a viscosity-average molecular weight of 334,000 4-methyl-1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load 9 g / 10 min) having 1 mass% and melting point peak 232 ° C. 14.0 mass% and 4-methyl having melting point peak 228 ° C. -1-pentene-1-decene-1 copolymer (MFR260 ° C., 5 kg load, 25 g / 10 min), 3.5% by mass, polyolefin elastomer resin Notio [grade name SN0285] manufactured by Mitsui Chemicals Co., Ltd. 0.72% by mass, Dynalon CEBC [grade name Dynalon 6200P] 0.30% by mass as an ethylene-ethylene butylene-ethylene block copolymer, polypropylene R-110M 0.10 mass% manufactured by Prime Polymer Co., Ltd. as a block polymer of ethylene and propylene copolymer, and EXELEX [Grade name 48070B manufactured by Mitsui Chemicals, Inc. as a low molecular weight ethylene / butene copolymer. ] Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane as an antioxidant with respect to 100.0 parts by mass of a polyolefin resin mixture comprising 0.08% by mass. 5 parts by mass and 3,9-bis (2,6-dita Dry blending 0.25 parts by weight of (salibutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] methane, A polyolefin resin mixture having a calculated resin average melting point of 152 ° C. was prepared.
40 parts by mass of the resin mixture is put into a twin screw extruder (cylinder diameter: 128 mm, screw length (L) to diameter (D) ratio L / D: 52.5, using a strong kneading type screw). 60 parts by mass of liquid paraffin [68 cst (40 ° C.)] as a plasticizer is supplied while being heated from the side feeder of the twin screw extruder, and a polyolefin / plasticizer mixed melt at a temperature of 235 ° C. and a screw rotation speed of 92 rpm. To prepare. This is extruded from a T-die through a gear pump installed at the tip of a twin-screw extruder, and is taken out with a cooling roll to form a gel-like sheet molding. The resulting gel-like sheet molding is stretched in the MD and TD directions by a simultaneous biaxial stretching machine. Subsequently, it passes through a continuous plasticizer extraction apparatus using methylene chloride as a solvent. Further, a heat-shrinkage treatment is performed while lowering the temperature from 125 ° C. to 60 ° C. in a heated second tenter as a heat stretching treatment step, thereby obtaining a heat-shrinkable low-shrinkage polyolefin microporous membrane.
The characteristics are shown in Table 1. As a result of the evaluation test of the non-melt down characteristics, the shutdown temperature showed a rapid increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 190 ° C.

10.1% by mass of ultra high molecular weight polyethylene with a viscosity average molecular weight of 1.09 million, 10.0% by mass of ultra high molecular weight polyethylene with a viscosity average molecular weight of 2 million, 5.5% by mass of ultra high molecular weight polyethylene with a viscosity average molecular weight of 39.50 million , 5.5 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 5,810,000, 5.5 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 631,000, and 6.7 high density polyethylene having a viscosity average molecular weight of 334,000. 4-methyl-1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load 9 g / m) having a mass%, a viscosity average molecular weight of 185,000, medium density polyethylene 3.3% by mass, and a melting point peak 232 ° C. 10 minutes) 4-methyl-1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load, 25 g) having 34.0% by mass and a melting point peak of 228 ° C. 10 minutes) 8.0% by mass, Notio [grade name SN0285] manufactured by Mitsui Chemicals, Inc. as a polyolefin-based elastomer resin, 0.84% by mass, Dynalon manufactured by JSR as an ethylene-ethylene-butylene-ethylene block copolymer CEBC [grade name Dynalon 6200P] 0.32% by mass, as a block polymer of polypropylene, ethylene, and propylene copolymer R-110M 0.16% by mass, Prime Polymer Co., Ltd., low molecular weight ethylene / butene copolymer Exelex [grade name 48070B] manufactured by Mitsui Chemicals Co., Ltd. 0.08 mass%, sodium calcium aluminosilicate [grade name Shilton JC-30] 10.0 mass% manufactured by Mizusawa Chemical Co., Ltd. as an inorganic filler Polyolefin resin mixture 1 Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 2.5 parts by mass and 3,9bis (2,6) as an antioxidant with respect to 0.0 parts by mass -Ditertiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] 0.25 parts by weight of methane, dry blended A polyolefin resin mixture having an average melting point of the resin portion of 179 ° C. calculated was prepared.
40 parts by mass of the resin mixture is charged into a twin screw extruder (cylinder diameter: 128 mm, screw length (L) diameter (D) ratio L / D: 52.5, using a strong kneading type screw). 60 parts by mass of liquid paraffin [68 cst (40 ° C.)] is supplied as a plasticizer from the side feeder of the shaft extruder while heating, and the polyolefin / plasticizer mixed melt is heated at a temperature of 240 ° C. and a screw rotation speed of 92 rpm. Prepare. This is extruded from a T-die through a gear pump installed at the tip of a twin-screw extruder, and is taken out with a cooling roll to form a gel-like sheet molding. The resulting gel-like sheet molding is stretched in the MD and TD directions by a simultaneous biaxial stretching machine. Subsequently, it passes through a continuous plasticizer extraction apparatus using methylene chloride as a solvent. Furthermore, it is kept for 30 seconds while being reduced from 125 ° C. to 60 ° C. in a second heated tenter as a heat stretching treatment step, and heat shrink treatment is performed. Further, the film is heat-set at 125 ° C. with a hot press to obtain a low-shrinkage polyolefin microporous film.
The characteristics are shown in Table 1. As a result of the evaluation test of the non-melt down characteristics, the shutdown temperature showed a rapid increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 190 ° C.

Comparative Example 1

12.6% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.09 million, 23.9% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, 6.0% by weight of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.50 million , 6.0 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 5,810,000, 6.0 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 631,000, and high density polyethylene 7.2 having a viscosity average molecular weight of 334,000. 4-methyl-1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load 9 g / 10 min) having a melting point peak of 232 ° C. and 30.5% by mass of 4-methyl-1-pentene-1-decene-1 copolymer having a melting point peak of 232 ° C. -1-pentene-1-decene-1 copolymer (MFR 260 ° C., 5 kg load, 25 g / 10 min), 7.6% by mass, polyolefin elastomer resin Notio [grade name SN0285] 0.001 mass% manufactured by Mitsui Chemicals, Inc., Dynalon CEBC [grade name Dynalon 6200P] 0.01 mass% manufactured by JSR as an ethylene-ethylene butylene-ethylene block copolymer, REX-110M 0.12 mass% made by Prime Polymer Co., Ltd. as a block polymer of polypropylene, ethylene, and propylene copolymer, and EXELEX [Grade Name] made by Mitsui Chemicals Co., Ltd. as a low molecular weight ethylene / butene copolymer 48070B] Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 5 as an antioxidant with respect to 100.0 parts by mass of a polyolefin resin mixture comprising 0.07% by mass Part by weight and 3,9-bis (2,6-dita Dry blending 0.25 parts by weight of (salibutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] methane, A polyolefin resin mixture having a calculated resin average melting point of 171 ° C. was prepared.
40 parts by mass of the resin mixture is put into a twin screw extruder (cylinder diameter: 128 mm, screw length (L) to diameter (D) ratio L / D: 52.5, using a strong kneading type screw). 60 parts by mass of liquid paraffin [68 cst (40 ° C.)] as a plasticizer is supplied from the side feeder of the twin screw extruder while heating, and the polyolefin / plasticizer mixed melt is supplied at a temperature of 240 ° C. and a screw rotation speed of 92 rpm. To prepare. This is extruded from a T-die through a gear pump installed at the tip of a twin-screw extruder, and is taken out with a cooling roll to form a gel-like sheet molding. The resulting gel-like sheet molded product was stretched in the MD and TD directions with a simultaneous biaxial stretching machine, but film formation was impossible.

Comparative Example 2

Tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 2.5 parts by mass as an antioxidant with respect to 100 parts by mass of high-density polyethylene having a viscosity average molecular weight of 490,000 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] methane 0.25 part by mass was dry blended to prepare a polyethylene resin mixture having a melting point of 135 ° C.
40 parts by mass of the resin mixture is put into a twin screw extruder (cylinder diameter: 128 mm, screw length (L) to diameter (D) ratio L / D: 52.5, using a strong kneading type screw). 60 parts by mass of liquid paraffin [68 cst (40 ° C.)] is supplied as a plasticizer while heating from the side feeder of the twin screw extruder, and mixed with polyethylene resin and plasticizer under the conditions of temperature 205-190 ° C. and screw rotation speed 92 rpm. Prepare the melt. This is extruded from a T-die through a gear pump installed at the tip of a twin-screw extruder, and is taken out with a cooling roll to form a gel-like sheet molding.
Biaxial stretching is performed on the resulting gel-like sheet molding using a tenter stretching machine. Next, the solution was passed through a continuous plasticizer extraction apparatus using methylene chloride as a solvent, and further subjected to heat shrinkage treatment while being held at 110 ° C. to 60 ° C. for 30 seconds in a heated second tenter as a heat stretching treatment step. A polyolefin microporous membrane is obtained. The characteristics are shown in Table 1.
As a result of the evaluation test of the non-meltdown characteristics, the shutdown temperature showed a sudden increase in impedance value around 138 ° C., but the impedance value suddenly dropped around 150 ° C., making measurement impossible. The meltdown temperature was 150 ° C.

Comparative Example 3

As a result of the evaluation test of the non-melt-down property of the polypropylene microporous membrane ceramic coated article manufactured by the dry stretching method obtained from the Chinese market, the shutdown temperature does not reach around 130-160 ° C, and does not show a rapid increase in impedance value. It was greatly deformed and shrunk by heat exposure at 190 ° C for 1 hour in a circulating hot air dryer.

According to the present invention, the high-performance lithium ion secondary battery with high energy density, high output, and large size has high safety non-meltdown characteristics and other good separator characteristics, and is easy to handle as a separator. Therefore, it is possible to provide a low heat-shrinkable polyolefin microporous membrane that is an excellent separator for a lithium ion secondary battery and a method for producing the same.

Claims (9)

Ultrahigh molecular weight polyethylene 3-35% by mass, polyethylene 1-20% by mass, copolymer resin 17-70% by mass of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms, ethylene as a constituent A low heat-shrinkable polyolefin microporous membrane comprising 0.01 to 3% by mass of an olefin block copolymer and 0.1 to 5% by mass of a polyolefin-based elastomer resin. In a twin-screw extruder, 3-35 mass% of ultra high molecular weight polyethylene and 1-20 mass% of polyethylene, 17-70 mass% of copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. A polyolefin resin mixture composed of 0.01 to 3% by mass of an olefin block copolymer containing ethylene as a constituent component and 0.1 to 5% by mass of a polyolefin-based elastomer resin and a plasticizer for film formation are melt-kneaded, and a die The method for producing a low heat-shrinkable polyolefin microporous film according to claim 1, wherein the film-forming solvent is removed after the gel-like sheet molded product obtained by further extruding and cooling is stretched. The copolymer resin of 4-methyl-1-pentene and an α-olefin having 3 or more carbon atoms contains 4-methyl-1-pentene containing 80 mol% or more of 4-methyl-1-pentene and 3 to 30 carbon atoms. The melting point (Tm) measured on the basis of a DSC (Differential Scanning Calorimeter) test is in the range of 220 to 240 ° C. 2. The low heat shrinkable polyolefin microporous membrane according to 2. Polyolefin elastomer resin is a copolymer of propylene and α-olefin having a specific structure, and consists of a structural unit derived from propylene and a structural unit derived from α-olefin having 2 to 30 carbon atoms (excluding propylene). The “islands”, which are nano-order helical crystal parts of 10 nm to 50 nm, are connected to each other to form a network structure and have a microstructure that covers the entire amorphous part. Low heat shrinkable polyolefin microporous membrane. The low heat shrinkable olefin microporous membrane according to claim 1, wherein the olefin block copolymer containing ethylene as a constituent component is an ethylene-ethylene / butylene-ethylene block copolymer. The low heat-shrinkable polyolefin microporous membrane according to claim 1, wherein the olefin block copolymer containing ethylene as a constituent component is a block polymer of polypropylene, ethylene, and a propylene copolymer. The proportion of the inorganic filler particles in the total amount of the polyolefin resin and the inorganic filler particles is 1% by mass or more and 40% by mass or less, and the weight loss rate of the inorganic particles up to 100 ° C. by thermogravimetric analysis is 5% or less. The low heat-shrinkable polyolefin microporous membrane according to any one of claims 1 to 6, wherein the average particle size is from 1 nm to 100 nm. The low heat-shrinkable polyolefin microporous material according to claim 1, wherein a mixture of 99-80% by mass of liquid paraffin and 1-20% by mass of polyoxyalkylene alkyl ether is used as a plasticizer for film formation. film. A separator for a lithium ion secondary battery, which is the low heat-shrinkable polyolefin microporous membrane according to claim 1.