JP2014156574A - Heat resistant modified polyolefin microporous film and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat resistant modified polyolefin microporous film excellent in gas permeability rate, compressive resistance, electrolyte impregnation properties, mechanical properties, and a low shrinkage property at high temperature, and having relatively large surface roughness and high productivity, and useful as a separator for enhancing safety of a lithium ion secondary battery; and to provide its manufacturing method.SOLUTION: A polyolefin mixture containing a super high molecular weight polyethylene of 1 to 85 mass%, polyethylene of 10 to 60 mass%, a copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms of 5 to 30 mass%, polypropylene of 0 to 30 mass%, a block polymer of polypropylene, ethylene and propylene copolymer of 0.5 to 12 mass%, a polyolefin-based elastomer resin of 0.5 to 10 mass%, and an inorganic filler of fine particles if needed are added to obtain a single layer, high productive heat resistant polyolefin microporous film having a shut down temperature around 130°C, and a feature so-called non-melt down which is not broken at a high temperature up to 160°C or higher. Due to a relatively large surface roughness, the heat resistant polyolefin microporous film is excellent in a property balance of a gas permeability rate, compressive resistance, electrolyte impregnation properties, mechanical properties, and a low shrinkage property at high temperature.

Description

The present invention relates to a heat-resistant polyolefin microporous membrane and a method for producing the same.
Specifically, the present invention relates to a polyolefin microporous membrane excellent in low shrinkage at high temperature, mechanical properties, and air permeability useful as a separator for enhancing the safety of a lithium ion secondary battery, and a production method with high productivity.

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 lithium ion secondary battery separator, the 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, technological development for further increase in 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 the shutdown characteristics, it is also required to have sufficient heat resistance from the viewpoint of not melting down (non-meltdown resistant) 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. On the other hand, the polyolefin microporous membrane has an advantage that there is almost no deterioration due to the electrolytic solution.
Recently, the separator characteristics are lithium ion permeability (it can also be seen in the air permeability in the test). 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. It is also desired to improve the separator in order to improve the electrolyte injection property.

Patent Document 1 proposes to obtain a heat-resistant polyolefin microporous membrane by a liquid-liquid phase separation method by selecting a solvent for film formation of 4-methyl-1-pentene polymer resin (TPX) alone. Yes.
Patent Document 2 proposes a heat-resistant polyolefin microporous membrane that preferably disperses heat-resistant resin in polyethylene without melting as spherical or spheroid fine particles.
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 the ultrahigh molecular weight polyethylene and the polyethylene containing the high-density polyethylene for producing the heat-resistant microporous membrane of the present invention.

JP 2005-255876 A JP 2005-343957 A JP 60-255108 A

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

The present inventor tried to improve the heat resistance of a polyethylene microporous membrane 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. However, in a melt mixture of ultrahigh molecular weight polyethylene, polyethylene, polyethylene, 4-methyl-1-pentene, and α-olefin having 3 or more carbon atoms, which have greatly different melting points and poor compatibility, The film cannot be made thin and thin.
“Islands”, which are helical crystal parts of a nano-order level of 10 nm to 50 nm, are connected to each other as a polyolefin elastomer resin of a block copolymer of polypropylene and ethylene, propylene copolymer and a copolymer of propylene and α-olefin. Then, by interposing with a network having a specific microstructure of a “network” that covers the entire amorphous part and melts and kneads in the extrusion, a uniform resin mixture melt can be obtained. The present invention finds that stretchability and thin film formation are possible, the degree of stretch of the film can be increased while reducing the amount of plasticizer used, and that the air permeability can be maintained well even when the amount of resin increases. Reached.
Conventionally, the blending ratio of the polyethylene resin mixture and the plasticizer is 10 to 40 parts by weight of the polyethylene resin mixture and 90 to 60 parts by weight of the plasticizer, with the total of both being 100 parts by weight. It was -40 mass parts. When the proportion of the polyethylene resin mixture exceeded 46 parts by mass, the moldability of the gel-like sheet molding was lowered, and the pores were small and the permeability was poor.
That is, 1-85% by weight of ultrahigh molecular weight polyethylene and 10-60% by weight of polyethylene, 5-30% by weight of copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms, polypropylene 0- Polyolefin mixture comprising 30% by mass, block polymer of polypropylene and ethylene, propylene copolymer 0.5-12% by mass, polyolefin elastomer resin 0.5-10% by mass, and if necessary fine inorganic filler The film-forming plasticizer is melt-kneaded with a twin-screw extruder, extruded from a die, and the gel-like sheet molded product obtained by cooling is stretched. The heat-resistant polyolefin microporous membrane obtained by removing, washing, stretching again at a predetermined magnification, and heat treatment has a relatively large surface roughness. From compression resistance, electrolytic solution absorbability, has excellent mechanical properties, air permeability and low shrinkage at high temperatures. Even if the ratio of the polyolefin resin mixture exceeds 46 parts by mass, the moldability of the gel-like sheet molded product does not deteriorate, and the pores can be kept large and excellent permeability can be realized. The present invention has been found by improving the productivity of the plasticizer and preventing the oily contamination of the plasticizer in the equipment.

The heat-resistant polyolefin microporous membrane of the present invention comprises a copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms, ultrahigh molecular weight polyethylene and polyethylene, and polypropylene and ethylene. “Islands” which are helical crystal parts of a nano-order level of 10 nm to 50 nm are connected to each other as a polyolefin elastomer resin of a block copolymer with a propylene copolymer and a copolymer composed of propylene and α-olefin. Interspersed with a specific net structure of the “net” that covers the entire amorphous part, the melting points differ greatly, and the resins that are not necessarily compatible with each other reduce the plasticizer in the twin screw extruder. However, the resin mixture can be melted and kneaded uniformly, and it is extruded from a die and cooled to obtain a gel-like sheet. The product can be stretched at a higher speed in both the longitudinal direction and the transverse direction to a higher degree of stretching than in the past, and is obtained by removing the plasticizer for film formation. Conventionally, it is possible to increase the ratio of the amount of resin supplied to the extruder, and it is possible to increase the production amount per m2 per hour as a microporous membrane. In addition, since the amount of plasticizer used is reduced, the line speed of the cleaning process for removing the plasticizer can be increased. Thus, the productivity per hour of the polyolefin microporous membrane, that is, the separator is improved, and oil separation from the membrane during the stretching of the plasticizer is not observed during production. There is no slip on the drawing roll, and there is almost no separation of the oily oil from the membrane.
The heat-resistant polyolefin microporous membrane during battery assembly has small changes in air permeability and film thickness when pressurized, and is excellent in compression resistance, electrolyte injection properties, mechanical properties, and air permeability. It is excellent in low shrinkage at high temperatures in both the longitudinal direction (longitudinal direction) (MD) and the transverse direction (TD).
Therefore, when the heat-resistant polyolefin microporous membrane of the present invention is used as a lithium ion secondary battery separator, the productivity of the battery is improved, and the battery has a long life due to excellent cycle characteristics. The heat-resistant polyolefin microporous membrane of the present invention obtained by uniform melting has a shutdown temperature and is 160 ° C. or higher, even though it is an economically advantageous single-layer membrane from the viewpoint of production cost and production equipment. It has a so-called melt-down resistant (non-melt down) characteristic that does not break up to 185 ° C or higher.

  Next, the heat-resistant polyolefin microporous membrane of the present invention and the production method thereof 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 is considered to be difficult to extrude and knead, and there have been few examples of use. However, ultra high molecular weight polyethylene having a viscosity average molecular weight of about 1,000,000 has a viscosity average molecular weight difference of 100. -Ultra high molecular weight polyethylene having a viscosity average molecular weight of 3.5 million or more can be used in combination by adding ultra high molecular weight polyethylene so that it remains within -2.5 million.
[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.
By mixing with a plasticizer, it is possible to use a commercially available ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 3.5 million or more and exceeding 64,000,000 to 10,000,000. 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. In addition to high density polyethylene (HDPE) having a viscosity average molecular weight of less than 500,000, medium density polyethylene (MDPE) and low density polyethylene (LDPE, L-LDPE) can be used in combination. .
In order to show the shutdown temperature remarkably, the high-density polyethylene mixing ratio is 10% by mass or more, preferably 20% by mass or more.

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 calorimeter) test. ) Is adjusted in the range of 200 to 250 ° C, preferably 220 to 240 ° C.
Furthermore, the melt flow rate (MFR) measured under the conditions of a load of 5 kg and a temperature of 260 ° C. according to ASTM D1238 is 0.05 to 250 [g / 10 minutes]. 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 5 to 30% by mass. If it is less than 5 mass%, the heat resistance improvement from a polyethylene microporous film is scarce. Moreover, even if it exceeds 30 mass%, the further heat-resistant improvement cannot be anticipated, cost becomes high and is unpreferable.

[4] Block polymer of polypropylene and ethylene-propylene copolymer Using propylene and ethylene as raw materials, first using propylene as a raw material, using a metallocene catalyst, a titanium-based catalyst, 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 continuously synthesizing an ethylene-propylene copolymer in comparable 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 in which the active site of the catalyst can polymerize both ethylene and propylene, and the active site is sufficiently stable during the polymerization time. . The block polymer of the polypropylene of the present invention and ethylene / propylene copolymer is used in the range of 0.5-12% by mass. If it is less than 0.5% by mass, there is almost no effect of addition, and if it exceeds 12% by mass, an excessive decrease in rigidity is caused as a microporous film, which is not preferable.
[5] Polyolefin-based elastomer resin The polyolefin-based elastomer resin used in the present invention is a copolymer comprising 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. It is optimal to use it in combination with a copolymer resin of 4-methyl-1-pentene and α-olefin. 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.

As the polyolefin-based elastomer resin used in the present invention, there is a random copolymer composed of a structural unit derived from propylene, a structural unit derived from ethylene, and a structural unit derived from an α-olefin having 4 to 30 carbon atoms. When the total of the unit and the structural unit derived from an α-olefin having 2 to 30 carbon atoms (excluding propylene) is 100 mol%, the configuration derived from propylene is 15 mol% or more.
Propylene / α-olefin random copolymer (“Tuffmer XM-5070” manufactured by Mitsui Chemicals, Inc.), butene-α-olefin random copolymer (“Tuffmer BL3450” manufactured by Mitsui Chemicals, Inc.) , “Tuffmer BL3110”, “Tuffmer BL2481”, “Tuffmer BL4000”, etc.), and ethylene / α-olefin random copolymers are also used. Commercially available products include Tough Selenium Series (manufactured by “Tough Selenium H3522A”) manufactured by Sumitomo Chemical Co., Ltd., VISAMAXX Series manufactured by ExxonMobil Chemical, and VERSIFY Series manufactured by The Dow Chemical Company.

Moreover, when it consists of a mixture of a completely amorphous polypropylene resin and a crystalline polypropylene resin, or when the above propylene / α-olefin random copolymer is mixed in an amount of 3% by mass or more and 30% by mass or less with respect to polypropylene or the like, propylene A structure in which the resin is dispersed in a sea-island shape in which the amorphous part is the sea and the crystal part is the island, such as an ethylene random copolymer, may be used.

On the other hand, a copolymer of ethylene and butene compatible with polyethylene such as ultrahigh molecular weight polyethylene and high density polyethylene of the present invention is a Tuffmer series manufactured by Mitsui Chemicals, Inc. (for example, “Tuffmer DF810”, “Tuffmer DF710”). ”,“ Tuffmer DF610 ”,“ Tuffmer DF605 ”), the dispersibility of the copolymer resin of 4-methyl-1-pentene and α-olefin can be further increased. Heat resistant polyolefin microporous membrane having excellent durability, heat resistance and flexibility while maintaining resin melt uniformity in a resin mixed system of 4-methyl-1-pentene and α-olefin copolymer resin It seems to become. This also makes it possible for the polyolefin resin mixture to obtain a sheet having a uniform composition with stable melting characteristics without causing any melt fracture of T-die.
In the present invention, the polyolefin-based elastomer resin can be used in the range of 0.5 to 10% by mass. If it is less than 0.5% by mass, there is almost no effect of addition, and if it exceeds 10% by mass, it causes an excessive decrease in rigidity as a microporous membrane, which is not preferable.

[6] Polypropylene resin The molecular weight of the polypropylene used in the present invention is not particularly limited. However, when a high molecular weight polypropylene having a viscosity average molecular weight of 100,000 or more and a viscosity average molecular weight of about 400,000 is used, the film has excellent heat-resistant film breaking property. A microporous membrane can be obtained. As the polypropylene resin in the present invention, homopolypropylene (propylene homopolymer), propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, etc. Examples thereof include random copolymers with α-olefins and block copolymers. These may be used alone or as a mixture. Among these, homopolypropylene is more preferable from the viewpoint of mechanical strength. In addition, the melt flow rate (MFR) of the polypropylene resin is not particularly limited. Usually, the MFR is 0.1 to 15 g as measured according to JIS K7210 at a temperature of 230 ° C. and a load of 2.16 kg. / 10 minutes is preferable, and 0.5 to 10 g / 10 minutes is more preferable. When the MFR is less than 0.1 g / 10 minutes, the melt viscosity of the resin during the molding process is high, and the productivity is lowered. On the other hand, when it exceeds 15 g / 10 min, practical problems such as insufficient mechanical strength of the obtained microporous membrane tend to occur. Polypropylene resin replaces 1% by mass to 30% by mass of the polyethylene by interposing a block polymer of the polypropylene and ethylene-propylene copolymer in order to maintain the pore size at high temperature and improve the thermal film breaking temperature. You can also When the polypropylene resin content increases, the heat resistance improves, but the mechanical strength tends to decrease, and it is preferably 20% by mass or less in view of the balance of properties.

[7] Low molecular weight polyethylene wax The low molecular weight polyethylene wax that can be used in the present invention refers to a homopolymer of ethylene, a copolymer of ethylene and an α-olefin, or a blend thereof. Preferably, an ethylene / propylene random copolymer, an ethylene / 1-butene random copolymer, an ethylene / propylene / 1-butene copolymer, and the molecular weight distribution measured by gel permeation chromatography is extremely narrow, It is prepared using a metallocene catalyst so that the component having a molecular weight in terms of polyethylene of 20,000 or more is minimized. The melting temperature is in the range of 85-110 ° C, preferably having a melting point of 89-102 ° C. One or more kinds selected from a low molecular weight ethylene / propylene random copolymer, an ethylene / 1-butene random copolymer, an ethylene / propylene / 1-butene copolymer having a melting temperature in the range of 89 to 102 ° C. An ethylene / α-olefin random copolymer is a copolymer resin 5 of ultrahigh molecular weight polyethylene 1-40% by mass and polyethylene 10-60% by mass, 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms. -30% by mass, polypropylene 0-30% by mass, block polymer 0.1-10% by mass of polypropylene and ethylene, propylene copolymer, polyolefin resin mixture consisting of 0.1-10% by mass of polyolefin elastomer resin On the other hand, it is preferable to add 0.1-5 mass%.
Preferably it is 0.1-2.5 mass%.
Heat-resistant polyolefin microporous membrane completed for the purpose of good biting into a twin-screw extruder of a copolymer resin of 4-methyl-1-pentene and α-olefin having greatly different melting points and ultrahigh molecular weight polyethylene powder Compared with the case where the sensitivity to the temperature is not added, the microporous membrane can be maintained without being melted down until the impedance is increased and the temperature of the battery is increased to 185 ° C. and the electrolyte is thermally decomposed. .

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.

[8] Inorganic filler Examples of the inorganic filler used in the present invention include nano-sized boehmite / alumina having an aspect ratio of alumina and aluminum hydroxide, silica (silicon oxide), sodium aluminosilicate, and sodium calcium aluminosilicate. Oxides such as titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, nitrides such as silicon carbide, silicon nitride, titanium nitride, boron nitride, calcium carbonate, aluminum sulfate, aluminum hydroxide, titanic acid Potassium, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, silica Examples include algae, ceramics such as silica sand, and glass fibers. 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, and preferably 1% by mass or more and 20% by mass or less from the viewpoint of wear resistance of the barrel of the extruder and screw. It is. It is preferable that the weight loss rate up to 100 ° C. by 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.

[9] Plasticizer As the plasticizer that can be used when 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 90-80% by mass of liquid paraffin and 10-20% 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 54 parts by mass of the polyolefin resin mixture and 90 to 46 parts by mass of the plasticizer, preferably 100 parts by mass of both, preferably the polyolefin resin. The mixture is 46 to 52 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 54 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.

The heat-resistant polyolefin microporous membrane of the present invention is preferably produced by a production method including the following steps. Each process will be described in detail below.
(Step 1) 1-85% by mass of ultrahigh molecular weight polyethylene and 10-60% by mass of polyethylene, 5-30% by mass of copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms, polypropylene Polyolefin resin mixture and antioxidant comprising 0-30% by mass, block polymer 0.5-12% by mass of polypropylene and ethylene, propylene copolymer, and polyolefin elastomer resin 0.5-10% by mass In response, a process of supplying inorganic filler powder to a twin screw extruder, injecting a heated mixed solution 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 molding;
(Step 3) A step of performing three-dimensional stretching in which the gel-like sheet molded product obtained in Step 2 is stretched in the biaxial direction (MD direction, TD direction) while increasing the take-up speed to prepare a thin thickness;
(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 extrusion temperature zone in the range of 200 to 300 ° C, more preferably in the range of 200 to 260 ° 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 oxidation 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 45 to 100, more preferably in the range of 50 to 70. When L / D is less than 45, melt kneading becomes insufficient. In particular, it becomes difficult to completely melt ultrahigh molecular weight polyethylene. When L / D is more than 100, the residence time in the extruder of the polyolefin mixture melt and the plasticizer is excessively increased, leading to thermal deterioration. 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 exceeds 0.55 kg / h / rpm, uniform mixing cannot be achieved. 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 of forming a gel-like sheet molding, a resin and a plasticizer are melt-kneaded with a twin-screw extruder, and the melt of the polyolefin resin mixture is directly from the twin-screw extruder or via another extruder or gear pump. It is obtained by extruding from a T-die and cooling.
Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature or less. Cooling is preferably performed to 40 ° C. or lower. By cooling at a rate of 50 ° C./min or higher to the gelling temperature or lower, 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 gel-like molded product becomes coarse, and the pseudo cell unit forming it becomes large, but when the cooling rate is high, it becomes a dense cell unit. 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 heated solution is preferably in the range of 0.2 to 50 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. If it is below 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 crystalline melting point, the polyolefin resin mixture melts 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 molding, it is biaxially stretched, or after biaxially stretching the gel-like sheet molding, the plasticizer is removed and further biaxially stretched. Alternatively, the plasticizer may be removed during each uniaxial stretching when the gel sheet is successively biaxially stretched.
Stretching the film before removing the plasticizer at least once in at least one direction (referred to as stretching before removing the plasticizer), and further stretching the film after removing the plasticizer at least once in at least one direction (plasticizer removal) (Referred to as post-stretching). 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 a gel-like sheet molded product, the stretching speed in the longitudinal direction (MD) and the transverse direction (TD) is the longitudinal direction and transverse direction when unstretched in the region where the unstretched sheet is stretched. When the length of each is defined as the ratio of the length stretched per minute, the respective 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 longitudinal direction or the transverse direction is more than 20 times / minute, the melt shrinkage resistance is deteriorated. The stretching speed in each direction is preferably 15 times / minute or less, and more preferably 10 times / minute or less.

あり、延伸倍率が２０倍以下であれば、過剰な延伸による微多孔膜の構造破壊を防ぐことが可能である。各方向の延伸下限に特に制限はないが、生産性の観点から３倍以上であるのが好ましい。機械的強度向上の観点から、ＭＤ及びＴＤに３倍以上とすることにより総面積倍率で９倍以上とするのが好ましく、ＭＤ及びＴＤに４倍以上とすることにより総面積倍率で１６倍以上とするのがより好ましい。ＭＤにおける合計延伸倍率とＴＤにおける合計延伸倍率の比（ＭＤにおける合計延伸倍率）／（ＴＤにおける合計延伸倍率）は、特に制限されないが、同時二軸延伸、逐次延伸又は段延伸のいずれの場合でも、０．５〜２であるのが好ましく、０．７〜１．３であるのがより好ましく、１であるのが最も好ましい。各方向の延伸速度は２０倍以下である限り、ＭＤとＴＤで互いに異なってもよいが、同じであるのが好ましい。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 TD 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 longitudinal direction (MD) and the transverse direction (TD) is preferably 3 to 20 times, more preferably 4 to 15 times, still more preferably 6 to 10 times. Stretch times

If the stretching ratio is 20 times or less, it is possible to prevent the microporous membrane from being broken due to excessive stretching. 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 mechanical strength, it is preferable that the total area magnification is 9 times or more by making it 3 times or more in MD and TD, and it is 16 times or more in total area magnification by making it 4 times or more in MD and TD. Is more preferable. 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, but are preferably the same.

  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 0.5 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.

  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.

[10] 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.

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 and at least uniaxial direction is 1.01-2. It is preferable to carry out at a draw ratio of 0.0, more preferably at a draw ratio of 1.02 to 1.5.
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 heat-resistant 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 shrink 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 heat-resistant 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 lithium ion secondary batteries, for example, 7-24 micrometers is preferable and 10-18 micrometers is more preferable.
The film thickness is measured according to JIS standard K7130.

The distribution of the micropore structure region and the coarse pore structure region is not particularly limited. Usually, in any cross section in the MD direction and TD direction of the microporous film, the micropore structure region and the coarse pore structure region are irregularly arranged, and the sizes of the individual regions are 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.

The heat-resistant polyolefin microporous membrane according to a preferred embodiment of the present invention has the following physical properties.
(1) 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 75%, preferably 40 to 55%. If the porosity is 35% or more, it has sufficient air permeability, and if it is 60% or less, it has sufficient mechanical strength. When used as a battery separator, the risk of short-circuiting the electrodes is small. 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.

The maximum pore size of the microporous membrane of the present invention 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 heat-resistant polyolefin microporous film is observed with a scanning electron microscope (SEM). Arbitrarily 20 holes are selected, and the diameters of these holes are calculated and averaged.
(4) As for the piercing strength, a piercing test is performed with a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mm / sec, and the piercing strength is indicated by N from the maximum piercing load g.
It is desirable that it is 2N or more. If the piercing strength is less than 2N, there is a possibility that a short circuit of the electrode may occur when the microporous membrane is incorporated in a battery as a battery separator. The puncture strength is 3N or more, more preferably 5 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 breaking strength is preferably 40 MPa or more in both the MD direction and the TD direction in order not to break the film.
(6) The tensile breaking elongation is measured by ASTM D882 using a strip-shaped test piece having a width of 10 mm. The tensile elongation at break is preferably 20% or more in both the MD direction and the TD direction because there is no fear of film breakage.
(7) The thermal shrinkage after exposure for 1 hour at a temperature of 130 ° C. marks the MD direction and the TD direction on a sample cut into 50 mm × 50 mm. Place on fine diatomaceous earth in a hot air dryer maintained at 130 ° C. for 1 hour. At the first hour, the sample is cooled to room temperature and the dimensional changes in the vertical and horizontal directions are measured, and the thermal shrinkage expressed as a percentage of the initial sample piece distance is determined. 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 thermal shrinkage rate is preferably 30% or less in both the MD direction and the TD direction. It is preferably 20%, more preferably 15% or less in both the MD direction and the TD direction.
The thermal shrinkage rate is obtained by measuring the shrinkage rate in the MD direction and the TD direction three times each when the microporous membrane is exposed at 130 ° C. for 1 hour, and calculating an average value.
When the heat shrinkage rate exceeds 30%, 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 there is a high possibility that an electrode short circuit occurs.
(8) Film thickness change rate after a film is sandwiched between a pair of stainless steel plates having a high smooth surface and heated and compressed at 90 ° C. for 5 minutes under a pressure of 2.2 MPa (22 kgf / cm ² ) using a press machine. 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 shrinkage.
(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) Evaluation of the meltdown resistance is performed by using a separator sample cut to a size of 30 mmφ in a sample holder of a small heating furnace MT-Z300 manufactured by Toyo Technica Co., Ltd., with an electrolytic solution (1M LiBF ₄ / polypropylene 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. For the impedance value, an alternating current method 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 that becomes 1000 ohms or higher in the process of increasing the impedance value is the shutdown temperature. To do. 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 meltdown resistance indicates that when it reaches 185 ° C, it does not break even after 1 minute and maintains a high impedance value as 185 ° C <and has excellent meltdown resistance Means.
(11) In battery evaluation, the separator made of the heat-resistant 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.
The amount of electricity discharged at 0.2C and 2C in the cell was measured, and the amount of electricity discharged at 2C / (amount of electricity discharged at 0.2C) × 100 was defined as the battery performance. 95% or more is regarded as good battery performance. Here, the charging condition is 0.2C4.2V CC / CV8 hours, and the discharging condition is CC discharge with 2.75V cutoff.

Thus, the heat-resistant 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. The battery is bonded to a polyethylene microporous membrane having a shutdown temperature in the range of 125 to 142 ° C. by taking advantage of the excellent meltdown resistance of the heat resistant polyolefin microporous membrane of the present invention. It can be used as a multilayer separator for a battery, or can be used in combination with the above-mentioned polyethylene 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.

13.1% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.15 million, 6.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, and 6.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 3.1 million 3.3% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.95 million, 6.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 5.7 million, and 38.0% of 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) having a mass%, a viscosity-average molecular weight of 185,000, a medium density polyethylene of 3.3% by mass, and a melting point peak of 232 ° C. / 10 min) Prime Polymer Co., Ltd. as a block polymer of 17.5% by mass and ethylene, polypropylene and ethylene, propylene copolymer R-110M 0.7% by mass, T-310E 2.0% by mass and polyolefin elastomer resin Notio [grade name SN0285] 2.5% by mass, low molecular weight ethylene / butene copolymer manufactured by Mitsui Chemicals, Inc. As an antioxidant, tetrakis [methylene-3- (3,5-) is used as an antioxidant with respect to 100.0 parts by mass of a polyolefin resin mixture consisting of 0.1% by mass of EXELEX [grade name 48070B] manufactured by Mitsui Chemicals, Inc. Ditertiarybutyl-4-hydroxyphenyl) -propionate] 2.5 parts by mass of methane and 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3 , 9-Diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] methane 0.25 A Department, were dry blended, the average melting point by calculation to prepare a polyolefin resin mixture 149 ° C.. 48 parts by mass of the resin mixture was put into a two-wheel extruder (cylinder diameter: 128 mm, screw length (L) to diameter (D) ratio L / D: 52.5, using a strong kneading type screw). From the side feeder of the shaft extruder, 52 parts by mass of liquid paraffin [68 cst (40 ° C.)] 99% by mass, polyoxyethylene stearyl ether (HLB2) 0.7% by mass, polyoxyethylene isostearyl ether (HLB2) 0.3 A plasticizer consisting of mass% is supplied while heating, and a polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 220 to 200 ° C. and a screw rotation speed of 92 rpm. 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, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinking treatment while being held at 120 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat stretching treatment step. A heat-resistant polyolefin microporous membrane is obtained. The characteristics are shown in Table 1.
As a result of the evaluation test of the meltdown resistance, the shutdown temperature showed a sudden increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 185 ° C.
The productivity per heat-resistant polyolefin microporous membrane m2 / min was 1.35 when Comparative Example 1 was 1.

13.1% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.15 million, 9.8% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, and 6.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.50 million 9.8% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 5,350,000, 3.3% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 6,580,000, and 38.0% 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) 15.0% by mass, polypropylene, ethylene, propylene copolymer having a melting point peak 232 ° C. As a block polymer, Prime Polymer Co., Ltd. R-110M 0.6 mass%, T-310E1.7 mass% and polyolefin Noteo [grade name PN3560] 2.1 mass% manufactured by Mitsui Chemicals, Inc. as an elastomer resin, Excellex [grade name 48070B] 0.1 manufactured by Mitsui Chemicals, Inc. as a low molecular weight ethylene butene copolymer 2.5 parts by mass of 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: 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] methane 0.25 parts by mass of dry blended polyolefin having a calculated average melting point of 149 ° C The resin mixture was prepared. 48 parts by mass of the resin mixture was put into a twin screw extruder (cylinder diameter: 69 mm, screw length (L) to diameter (D) ratio L / D: 52.5, using a strong kneading type screw). From the side feeder of the twin screw extruder, 52 parts by mass of liquid paraffin [68 cst (10 ° C.)] 99% by mass, polyoxyethylene stearyl ether <HLB2) 0.7% by mass, polyoxyethylene isostearyl ether (HLB2) 0. A plasticizer comprising 3% by mass is supplied while being heated, and a polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 225 to 200 ° C. and a screw rotation speed of 92 rpm. 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, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinking treatment while being held at 115 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat stretching treatment step. A heat-resistant polyolefin microporous membrane is obtained.
The characteristics are shown in Table 1.
As a result of the evaluation test of the meltdown resistance, the shutdown temperature showed a sudden increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 185 ° C.
The productivity per heat-resistant polyolefin microporous membrane m2 / min was 1.35 when Comparative Example 1 was 1.

19.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.15 million, 19.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.15 million, and 5.0% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million 4-methyl-1-pentene having a viscosity average molecular weight of 5.7 million and an ultrahigh molecular weight polyethylene of 3.0 mass%, a viscosity average molecular weight of 35.8 mass% of high density polyethylene and a melting point peak of 232 ° C. R-110M0.8 manufactured by Prime Polymer Co., Ltd. as a block polymer of 15.8% by weight of 1-decene-1 copolymer (MFR 260 ° C., 5 kg load, 9 g / 10 min), polypropylene, ethylene, and propylene copolymer Mass%, T-310E 2.4 mass% polyolefin elastomer resin notio [grade] manufactured by Mitsui Chemicals, Inc. SN0285] 2.3% by mass, Toughmer [grade name DF810] 0.3% by mass, Excelex [grade name 48070B] manufactured by Mitsui Chemicals, Inc. as a low molecular weight ethylene / butene copolymer, 0.1% by mass, Antioxidant with respect to 100.0 parts by mass of a mixture of polyolefin resin and inorganic filler consisting of 10.0% by mass of sodium calcium aluminosilicate [grade name Shilton JC-30] manufactured by Mizusawa Chemical Co., Ltd. as an inorganic filler As tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 2.0 parts by mass and 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonyl Hydroxyphenyl) -propionate] 0.20 part by weight of methane is dry blended.
46 parts by mass of the resin mixture was 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). From the side feeder of the twin screw extruder, 54 parts by mass of liquid paraffin [68 cst (40 ° C.)] 97% by mass, polyoxyethylene stearyl ether (HLB2) 2.1% by mass, polyoxyethylene isostearyl ether (HLB2) 0. A plasticizer consisting of 9% by mass is supplied while heating, and a polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 235 to 210 ° C. and a screw rotation speed of 95 rpm. 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, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinking treatment while being held at 120 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat stretching treatment step. A heat-resistant polyolefin microporous membrane is obtained.
The characteristics are shown in Table 1.
As a result of the evaluation test of the meltdown resistance, the shutdown temperature showed a sudden increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 185 ° C.
The productivity per heat-resistant polyolefin microporous membrane m2 / min was 1.30, where Comparative Example 1 was 1.

12.4 mass% of polypropylene homopolymer having a viscosity average molecular weight of 245,000, 3.3 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 2 million, and 3.3 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 39,500,000. %, Ultra high molecular weight polyethylene having a viscosity average molecular weight of 5.7 million, 6.5% by mass, ultra high molecular weight polyethylene having a viscosity average molecular weight of 6.58 million, 3.3% by mass, 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 7% by mass and melting point peak of 232 ° C. and 4 having a melting point peak of 228 ° C. 4 -2.5% by mass of poly-1-methyl-1-pentene-1-hexadecene-1-octadecene copolymer (MFR 260 ° C., 5 kg load, 25 g / 10 min) As block polymer of pyrene, ethylene and propylene copolymer, Prime Polymer Co., Ltd. R-110M 1.55% by mass, T-310E 4.65% by mass and polyolefin-based elastomer resin Notio manufactured by Mitsui Chemicals, Inc. [Grade name PN3560] 3.6% by mass, Tuffmer [Grade name DF810] 0.3% by mass, Excelex manufactured by Mitsui Chemicals, Inc. as a low molecular weight ethylene / butene copolymer [Grade name 48070B] 0.3 100.0 parts by mass of a mixture of polyolefin resin and inorganic filler consisting of 10.0% by mass of sodium calcium aluminosilicate [grade name Shilton JC-30] manufactured by Mizusawa Chemical Co., Ltd. Tetrakis [methylene-3- (3,5-ditter as an antioxidant Tert-butyl-4-hydroxyphenyl) -propionate] 2.5 parts by mass of methane and 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9 -Diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] 0.25 parts by weight of methane is dry blended to prepare a polyolefin resin mixture having a calculated average melting point of 151 ° C. 50 parts by mass of the resin mixture was 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). From 50 parts by mass of liquid paraffin [68 cst (40 ° C.)] 90% by mass, 7% by mass of polyoxyethylene stearyl ether (HLB2), 3% by mass of polyoxyethylene isostearyl ether (HLB2) from the side feeder of the twin screw extruder The resulting plasticizer is supplied while heating, and a polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 220 to 190 ° C. and a screw rotation speed of 98 rpm. 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, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinking treatment while being held at 120 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat stretching treatment step. A heat-resistant polyolefin microporous membrane is obtained.
The characteristics are shown in Table 1.
As a result of the evaluation test of the meltdown resistance, the shutdown temperature showed a sudden increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 185 ° C.
The productivity per heat-resistant polyolefin microporous membrane m2 / min was 1.30, where Comparative Example 1 was 1.

12.9% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.15 million, 9.7% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, and 6.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.50 million 6.5 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 5,350,000, 3.2 mass% of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 6,580,000, and high density polyethylene 33.6 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) 21.3% by mass, polypropylene, ethylene, propylene copolymer having mass%, melting point peak 232 ° C. As a block polymer, Prime Polymer Co., Ltd. R-110M 0.8 mass%, T-310E 2.4 mass% and polyolefin 3.0% by mass of Notio [grade name SN0285] manufactured by Mitsui Chemicals, Inc. as an elastomer resin, Excellex [grade name 48070B] 0.1 manufactured by Mitsui Chemicals, Ltd. as a low molecular weight ethylene / butene copolymer 2.5 parts by mass of 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: 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] methane 0.25 parts by mass of dry blended polyolefin having a calculated average melting point of 155 ° C The resin mixture was prepared. 48 parts by mass of the resin mixture was 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). A plasticizer consisting of 52 parts by mass of liquid paraffin [68 cst (40 ° C.)] 99.0% by mass and polyoxyethylene stearyl ether (HLB2) 1.0% by mass is supplied from the side feeder of the twin screw extruder while heating. A polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 230 to 200 ° C. and a screw rotation speed of 92 rpm. 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, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinkage treatment while being held at 125 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat stretching treatment step. A heat-resistant polyolefin microporous membrane is obtained. The characteristics are shown in Table 1.
As a result of the evaluation test of the meltdown resistance, the shutdown temperature showed a sudden increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 185 ° C.
The productivity per heat-resistant polyolefin microporous membrane m2 / min was 1.30, where Comparative Example 1 was 1.

23.0% by weight of ultra high molecular weight polyethylene with a viscosity average molecular weight of 1.15 million, 14.0% by weight of ultra high molecular weight polyethylene with a viscosity average molecular weight of 3.1 million, 15.3% by weight of ultra high molecular weight polyethylene with a viscosity average molecular weight of 5.7 million 4-methyl-1-pentene-1-hexadecene-1-octadecene copolymer (MFR 260 ° C., 5 kg load, 21 g, 40.8% by mass of high density polyethylene having a viscosity average molecular weight of 334,000 and a melting point peak of 223 ° C. / 10 min) Prime polymer Co., Ltd. R-110M 0.2 mass%, T-310E 2.4 mass% and polyolefin elastomer resin as block polymer of 5.1 mass% polypropylene and ethylene, propylene copolymer Notio [grade name PN3560] manufactured by Mitsui Chemicals, Inc. 1.3% by mass, low molecular weight Tetrakis [methylene-3] as an antioxidant with respect to 100.0 parts by mass of a polyolefin resin mixture comprising 0.1% by mass of Exelex [grade name 48070B] manufactured by Mitsui Chemicals, Inc. as a ethylene / butene copolymer. -(3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 2.5 parts by weight and 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2,4,8 , 10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) -propionate] 0.25 part by weight of methane, to prepare a polyolefin resin mixture having a calculated average melting point of 138 ° C. To do. 48 parts by weight of the resin mixture was charged 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). A plasticizer consisting of 52 parts by weight of liquid paraffin [68 cst (40 ° C.)] 93% by mass and polyoxyethylene stearyl ether (HLB2) 7% by mass is supplied from the side feeder of the twin screw extruder while heating, 220-200 A polyolefin / plasticizer mixed melt is prepared at a temperature of 160 ° C. and 160 rpm. 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 biaxially stretched using a tenter stretching machine. Next, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinking treatment while being held at 110 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat drawing treatment step. A heat-resistant polyolefin microporous membrane is obtained.
The characteristics are shown in Table 1.
As a result of the evaluation test of the meltdown resistance, the shutdown temperature showed an abrupt increase in impedance value at around 130 ° C., showed 5000 ohms or more, and the impedance value decreased at a temperature exceeding 165 ° C.
The productivity per heat-resistant polyolefin microporous membrane m2 / min was 1.38 when Comparative Example 1 was 1.
Compared to the polyethylene microporous membrane of Comparative Example 2, it was confirmed that the meltdown temperature was increased by about 15 ° C., and the productivity was improved by 38%.

Comparative Example 1

13.1% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.15 million, 9.2% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, and 6.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 3.1 million 3.3% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.95 million, 6.5% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 5.7 million, and 38.0% of 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) having a mass%, a viscosity-average molecular weight of 185,000, a medium density polyethylene of 3.3% by mass, and a melting point peak of 232 ° C. / 10 minutes) 17.5 mass% and Notio [grade name SN0285] 2.5 mass by Mitsui Chemicals, Inc. as polyolefin elastomer resin , Tetrakis as an antioxidant with respect to 100.0 parts by mass of a polyolefin resin mixture composed of 0.1% by mass of EXELEX [grade name 48070B] manufactured by Mitsui Chemicals, Inc. as a low molecular weight ethylene / butene copolymer. Methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] 2.5 parts by mass of methane and 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2, 4,8,10-tetraoxa-3,9-diphosphapi [5,5] undecanlonylhydroxyphenyl) propionate] 0.25 part by weight of methane, and a calculated average melting point of 149.5 ° C. A polyolefin resin mixture was prepared. 37 parts by mass of the resin mixture was charged 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). From a side feeder of a twin screw extruder, 63 parts by mass of liquid paraffin [68 cst (40 ° C.)] 99% by mass, polyoxyethylene stearyl ether (HLB2) 0.7% by mass, polyoxyethylene isostearyl ether (HLB2) 0. A plasticizer comprising 3% by mass is supplied while being heated, and a polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 220 to 200 ° C. and a screw rotation speed of 92 rpm. 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, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinking treatment while being held at 120 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat stretching treatment step. A heat-resistant polyolefin microporous membrane is obtained. The characteristics are shown in Table 1.
As a result of the evaluation test of the meltdown resistance, the shutdown temperature showed a sudden increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 185 ° C.
The productivity per heat-resistant polyolefin microporous membrane m2 / min is set to 1. This is compared as a standard for the productivity of the microporous membrane of the present invention.

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, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinking treatment while being held at 110 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat drawing treatment step. A heat-resistant polyolefin microporous membrane is obtained. The characteristics are shown in Table 1.
The productivity per heat-resistant polyolefin microporous membrane m2 / min was 1.0 when Comparative Example 1 was 1.
As a result of the evaluation test of the melt-down resistance, 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 melt-down temperature was 150 ° C.

Comparative Example 3

13.1% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 1.15 million, 9.8% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, and 8.8% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 39.50 million 9.8% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 5,350,000, 3.3% by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 6,580,000, and 38.0% 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) 15.0% by mass with a melting point peak of 232 ° C. and Mitsui Chemicals as polyolefin elastomer resin ( Notio [grade name PN3560] 2.1% by mass manufactured by Mitsui Chemicals, Inc. as a low molecular weight ethylene / butene copolymer Excelis [grade name 48070B] 0.1 wt% of polyolefin resin mixture 100.0 parts by mass of tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) as an antioxidant -Propionate] 2.5 parts by mass of methane and 3,9-bis (2,6-ditertiarybutyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphapi [5,5] Undecanlonylhydroxyphenyl) -propionate] 0.25 part by mass of methane was dry blended to prepare a polyolefin resin mixture having a calculated average melting point of 149 ° 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.)] 99 mass%, polyoxyethylene stearyl ether (HLB2) 0.7 mass%, polyoxyethylene isostearyl ether (HLB2) 0. A plasticizer comprising 3% by mass is supplied while being heated, and a polyolefin / plasticizer mixed melt is prepared under the conditions of a temperature of 235 to 210 ° C. and a screw rotation speed of 92 rpm. 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, it is passed through a continuous plasticizer extraction device using methylene chloride as a solvent, and further subjected to heat-shrinking treatment while being held at 120 ° C.-60 ° C. for 30 seconds in a heated second tenter as a heat stretching treatment step. A heat-resistant polyolefin microporous membrane is obtained. The characteristics are shown in Table 1.
As a result of the evaluation test of the meltdown resistance, the shutdown temperature showed a sudden increase in impedance value at around 130 ° C., showed 5000 ohms or more, and maintained a high impedance value until it exceeded 185 ° C.
The productivity per heat-resistant polyolefin microporous membrane m2 / min was 0.8 when Comparative Example 1 was 1.

According to the present invention, the high-performance lithium-ion secondary battery with high energy density, high output, and large size has high safety meltdown resistance and other good separator characteristics, and is easy to handle as a separator. Therefore, it is possible to provide a highly productive heat-resistant 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 1-85% by mass, polyethylene 10-60% by mass, copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms, 5-30% by mass, polypropylene 0-30% by mass %, A heat-resistant polyolefin microporous membrane comprising 0.5-12% by mass of a block polymer of polypropylene, ethylene, and a propylene copolymer, and 0.5-10% by mass of a polyolefin-based elastomer resin. In a twin-screw extruder, 1-85% by mass of ultrahigh molecular weight polyethylene and 10-60% by mass of polyethylene, 5-30% by mass of copolymer resin of 4-methyl-1-pentene and α-olefin having 3 or more carbon atoms Polyolefin resin mixture consisting of 0-30% by mass of polypropylene, 0.5-12% by mass of block polymer of polypropylene and ethylene, propylene copolymer, and 0.5-10% by mass of polyolefin-based elastomer resin, and for film formation 2. The heat resistance according to claim 1, wherein the film-forming solvent is removed after melt-kneading with a plasticizer, extruding from a die and cooling, and stretching a gel-like sheet molded product. A method for producing a polyolefin microporous membrane. 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. A heat-resistant 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. Heat-resistant polyolefin microporous membrane. Low molecular weight ethylene / propylene random copolymer, ethylene / 1-butene random copolymer, ethylene / propylene prepared by using a metallocene catalyst as a low molecular weight polyethylene wax and having a melting temperature in the range of 89-102 ° C. 5. One or more kinds of ethylene / α-olefin random copolymer selected from 1-butene copolymer is added to the polyolefin resin mixture in an amount of 0.1-5% by mass. The heat-resistant polyolefin microporous film according to any one of the above. A polyolefin-based elastomer resin having a melting point of 49-110 ° C., a random copolymer comprising ethylene and a structural unit derived from an α-olefin having 3 to 30 carbon atoms (excluding butene), butene and having 2 to 30 carbon atoms A random copolymer composed of a structural unit derived from α-olefin (excluding butene), and a random copolymer composed of propylene and a structural unit derived from α-olefin having 2 to 30 carbon atoms (excluding propylene). Or it is 2 or more types, The heat-resistant polyolefin microporous film in any one of Claims 1-5 characterized by the above-mentioned. 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 heat-resistant 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 heat-resistant polyolefin microporous membrane according to any one of claims 1 to 7, wherein a mixture comprising 90-80% by mass of liquid paraffin and 10-20% by mass of polyoxyalkylene alkyl ether is used as a plasticizer for film formation. . In producing the heat-resistant polyolefin microporous membrane according to claim 1. A separator for a lithium ion secondary battery, which is the heat-resistant polyolefin microporous membrane according to claim 1.