JP2010095629A - Polyolefin resin porous membrane and battery separator using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefin resin battery separator that easily achieves a uniform dispersion in a production process, has a shutdown function in spite of a simple resin composition, a small pore diameter and high porosity with high productivity. <P>SOLUTION: The polyolefin resin porous membrane is prepared by melting and kneading a polyolefin resin composition (G) comprising a polyolefin resin (C) made of a crystalline polypropylene (A) and a copolymer (B) that is dispersed in the crystalline polypropylene (A) and composed of at least one selected from α-olefins except ethylene and propylene, and propylene, a high-density polyethylene (D) having a melt mass flow rate MFR<SB>(D)</SB>of ≥1 g/10 min and <30 g/10 min, a crystalline polypropylene (E) having a melt mass flow rate MFR<SB>(E)</SB>of ≥0.1 g/10 min and <10 g/10 min and a block copolymer (CEBC) (F) having a triblock of a crystalline polyolefin-ethylene-butylene copolymer-a crystalline polyolefin to give a film-like melt, forming the film-like melt into a film-like formed product at a draft ratio in the range of 1-10 and stretching the film-like formed product at least in one direction to form a porous membrane. The battery separator uses the same. The polyolefin resin porous membrane has pores communicating with the region of the copolymer (B). The battery separator uses the above membrane. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyolefin resin porous membrane and a battery separator using the same.

  Plastic porous membranes with continuous pores are used in a variety of applications. Separation membranes used for medical and industrial filtration and separation, separators for battery separators, electrolytic capacitor separators, and paper diapers It is widely used for sanitary materials such as bag sheets, building materials such as house wraps and roof base materials. In particular, since the polyolefin resin porous membrane has resistance to an organic solvent or an alkaline or acidic solution, it is widely used for these applications.

Among polyolefin resin porous membranes, porous membranes mainly composed of polyethylene resin or polypropylene resin are suitable for organic solvent-based battery separators from the viewpoint of chemical resistance, and the following production methods are generally known. ing.
(a) A method of obtaining a porous film by heating a crystalline polypropylene sheet formed at a high draft ratio as necessary and stretching it in at least one direction to fibrillate between crystal lamellae (hereinafter referred to as “single component stretching”). Law ").
(b) A method of extracting the organic liquid material, the inorganic filler and the like from a sheet formed by mixing an organic liquid material, an inorganic filler and the like with a polyolefin resin, and performing stretching before and after the extraction as necessary (hereinafter referred to as the following) "Mixed extraction method").
(c) A method in which a sheet formed by mixing polyethylene and polypropylene is stretched in at least one direction to form voids (pores) at the interface between different polymers (hereinafter referred to as “multi-component stretching method”).

  In the multi-component stretching method, it is difficult to finely disperse a different polymer in a matrix polymer, and since the stretchability is also inferior, it is difficult to obtain a battery separator with a small pore diameter or a battery separator with a large porosity. Battery separators using a mixed extraction method or a single component stretching method are the mainstream.

On the other hand, in the case of an organic solvent battery, in order to prevent the temperature inside the battery from rising abnormally due to misuse of the battery, etc. and causing an accident such as ignition, the separator does not break when the temperature reaches a certain level. There is a demand for a function (hereinafter referred to as “shutdown function”) that shuts down the current by closing the hole. A sufficient shutdown function can be obtained by this shutdown function to only the single component stretching method or a solvent extraction method technology, film tear temperature (hereinafter "film break temperature" referred to) T _b and the temperature to occlude the pores ( It is desired to reduce the hole closing temperature in order to increase the difference in T _s (hereinafter referred to as “hole closing temperature”) ΔT = T _b −T _s and stop the abnormal reaction at an earlier stage to suppress the temperature rise. Yes.

  In response to this requirement, using the characteristics of the melting point difference between polypropylene and polyethylene, the polypropylene microporous membrane and the polyethylene microporous membrane are multi-layered, and the difference between the pore clogging temperature and the membrane breaking temperature is increased. Has been disclosed (see, for example, Patent Document 1). However, in this case, not only is the manufacturing process complicated, but it is difficult to reduce the thickness of the separator, which is insufficient as a battery separator that is required to be reduced in size and weight.

  In addition, a technique for improving the hole closing temperature and the film breaking temperature of a battery separator by mixing polypropylene and polyethylene at a specific ratio to form a film and then stretching the film is disclosed (for example, see Patent Document 2). ). Battery separators need to have small pore diameters in order to prevent the detached positive electrode material from passing through the separator, but the pores obtained by this technique are the interface between polypropylene and polyethylene. Since it is formed by peeling, it has been difficult to use for a battery separator having a large pore diameter and requiring fine pores.

  On the other hand, component A composed of ethylene-propylene block copolymer, component B composed of propylene homopolymer or random copolymer, and component C composed of low molecular weight polypropylene, and optionally composed of component D composed of calcium carbonate and beta spherulite nucleating agent A porous membrane comprising a polymer composition to which component E has been added and a method for producing the same are disclosed (for example, see Patent Document 3).

In these technologies, sufficient porosity and air permeability cannot be obtained by using only the ethylene-propylene block copolymer, so that improvement is attempted by a multi-component system. However, the diameter of the formed pores is large, and the positive electrode material not only short circuit between the positive and negative electrodes is concerned with a transmission, since the difference [Delta] T = T _b -T _s of film breakage temperature T _b and pore closing temperature T _s is small, there is a problem in the shutdown function. In addition, since the pore diameter is large, it is difficult to reduce the thickness of the membrane and increase the porosity, and it is difficult to improve the electric capacity of the battery. Using this porous membrane as a battery separator difficult.

  In order to solve these problems related to battery separators using conventional polyolefin resin porous membranes, a random copolymer (RC) in which a specific ethylene / propylene block copolymer is stretched in at least one direction and finely dispersed in the copolymer. A battery separator (see, for example, Patent Document 4) composed of a porous film in which pores are formed in the partial region has been proposed. This polyolefin resin separator is excellent in productivity, has a shutdown function despite a simple resin composition, and has advantages such as a small pore diameter and a high porosity.

However, this polyolefin resin separator has good characteristics with improvement in the heat resistance of the porous characteristics, the film breaking characteristics at a temperature rising rate of 10 ° C./min or less and the pore closing characteristics as a battery separator. in the 20 ° C. / min or more heating rate, the difference [Delta] T ₌ T b -T _s of film breakage temperature _{T b} and pore closing temperature _{T s} is small, has a problem in shutdown function, film tear properties, The hole closing temperature characteristic is not always satisfactory.
JP-A-6-98395 JP-A-4-206257 JP-A-4-309546 JP 2003-129435 A

  The present invention has been made to solve the above-described problems related to battery separators using conventional polyolefin resin porous membranes, and has a shutdown function despite a simple resin composition, and has a small pore diameter and a high porosity. An object is to provide a polyolefin resin porous membrane and a battery separator using the same with excellent productivity.

As a result of intensive studies, the present inventors have found that a combination of propylene with crystalline polypropylene (A) and at least one selected from the group of α-olefins other than ethylene and propylene dispersed in the crystalline polypropylene (A). Specific polyolefin resin (C) comprising polymer (B) and melt mass flow rate MFR _(D) (measured in accordance with JIS K 7210, temperature 190 ° C., nominal load 2.16 kg) 1 g / High-density polyethylene (D) within a range of 10 min or more and less than 30 g / 10 min and melt mass flow rate MFR _(E) (measured in accordance with JIS K 7210, temperature 230 ° C., nominal load 2.16 kg) A crystalline polypropylene (E) in a range of 0.1 g / 10 min or more and less than 10 g / 10 min; A polyolefin resin composition (G) containing a block copolymer (CEBC) (F) having a triblock of an ethylene / ethylene / butylene copolymer / crystalline polyolefin is melt-kneaded to form a film-like melt, A porous film formed by stretching a film-shaped melt into a film-shaped molding within a draft ratio of 1 to 10 and then stretching the film-shaped molding in at least one direction, and a battery separator using the porous film The present inventors have found that this problem can be solved by a polyolefin resin porous membrane having pores communicating with the copolymer (B) region and a battery separator using the polyolefin resin porous membrane. The present invention has been completed based on this finding. In the present invention, the continuous pores are pores that are continuously formed in the copolymer (B) region, resulting in a path that connects both surfaces of the polyolefin resin porous membrane and the battery separator using the same. Say.

The present invention is constituted by the following.
1. Copolymer (B) 30 of 30 to 70% by weight of crystalline polypropylene (A), propylene and at least one selected from the group of α-olefins other than ethylene and propylene dispersed in crystalline polypropylene (A) Polyolefin resin (C) consisting of ˜70 wt%, 35 g to 89 wt%, melt mass flow rate MFR _(D) (measured in accordance with JIS K 7210, temperature 190 ° C., nominal load 2.16 kg) 1 g / 10 min or more and less than 30 g / 10 min, high density polyethylene (D) 5 to 25 wt%, melt mass flow rate MFR _(E) (according to JIS K 7210, temperature 230 ° C., nominal load 2.16 kg Crystalline polypropylene whose measured value is 0.1 g / 10 min or more and less than 10 g / 10 min (E) A polyolefin resin composition containing 5 to 25% by weight and a block copolymer (CEBC) (F) having a triblock of crystalline polyolefin / ethylene-butylene copolymer / crystalline polyolefin (F) of 1 to 15% by weight The product (G) is melt-kneaded to form a film-like melt, and the film-like melt is formed into a film-like molding within a draft ratio of 1 to 10, and then the film-like molding is stretched in at least one direction. A polyolefin resin porous membrane having continuous pores formed by cleaving caused by cleaving.

2. The melt mass flow rate of crystalline polypropylene (A) is MFR _PP (measured in accordance with JIS K 7210, temperature 230 ° C., nominal load 2.16 kg), and selected from the group of α-olefins other than ethylene and propylene. When the melt mass flow rate of at least one copolymer of propylene and propylene (B) is MFR _RC (measured in accordance with JIS K 7210, temperature 230 ° C., nominal load 2.16 kg), 2. The polyolefin resin porous membrane according to 1 above, wherein the rate ratio MFR _PP / MFR _RC is in the range of more than 10 and 1,000 or less.

3. 3. The polyolefin resin porous membrane according to 1 or 2 above, wherein a draft ratio when the film-shaped melt is formed into a film-shaped molded product is in the range of 1 to 5.

4). 4. The polyolefin according to any one of 1 to 3 above, wherein the propylene content of the copolymer (B) of at least one selected from the group of α-olefins other than ethylene and propylene is 30 to 80% by weight. Resin porous membrane.

5. Polyolefin resin (C) produces crystalline polypropylene (A) in the first stage, and in the second stage, at least one selected from the group of α-olefins other than ethylene and propylene and the copolymer weight of propylene The polyolefin resin porous membrane according to any one of 1 to 4 obtained by a multistage polymerization method including a step of producing a combined body (B).

6). The pore resistance distribution (Gurley) of the porous membrane is within the range of 10 to 20,000 s / 100 ml, the average pore diameter measured according to ASTM F316 is within the range of 0.05 to 0.2 μm, and the pore size distribution. 6. The polyolefin resin porous membrane according to any one of 1 to 5 above, wherein the index (maximum pore diameter / average pore diameter) is in the range of 1.3 to 2.0.

7). 7. The polyolefin resin porous membrane according to any one of 1 to 6 above, wherein the film forming method for forming the polyolefin resin composition (G) into a film-shaped product is a calendar molding method.

8). The battery separator using the polyolefin resin porous membrane of any one of said 1-7.

The polyolefin resin porous membrane of the present invention is a copolymer of propylene and at least one selected from the group of α-olefins other than ethylene and propylene in crystalline polypropylene (A) under a specific processing method. ) Is a specific polypropylene resin (C) finely dispersed in a specific high density polyethylene (D), crystalline polypropylene (E), crystalline polyolefin / ethylene-butylene copolymer / crystalline polyolefin triblock By using the copolymer (CEBC) (F) in combination, the stretchability at the low temperature in the production of the porous membrane is improved, the lamellar crystal in the copolymer (B) region is developed, and the copolymer (B) It is a porous film in which pores are formed by cleavage between lamellae.
Moreover, the battery separator using the polyolefin resin porous membrane of the present invention is an economical battery separator obtained without using a complicated manufacturing process as in the prior art, and has a low pore blocking temperature and a high membrane breaking temperature. It is a battery separator with high safety. Furthermore, since the pores are fine and excellent in stretchability and high porosity, it is an excellent battery separator suitable not only for safety but also for the purpose of high battery capacity and thinning.

Hereinafter, embodiments of the present invention will be described.
(1) Polyolefin resin composition (G)
For the polyolefin resin porous membrane of the present invention and the battery separator using the same, the copolymer (B) of crystalline polypropylene (A) and at least one selected from the group of α-olefins other than ethylene and propylene (B) (Hereinafter, simply referred to as “copolymer (B)”), a polyolefin resin (C) in which the copolymer (B) is finely dispersed as domains in a matrix of crystalline polypropylene (A), Polyolefin resin composition comprising high-density polyethylene (D), crystalline polypropylene (E), and block copolymer (CEBC) (F) having a crystalline polyolefin / ethylene-butylene copolymer / crystalline polyolefin triblock (G) is used.

(I) Crystalline polypropylene (A)
The crystalline polypropylene (A) is a crystalline polymer mainly composed of propylene polymerized units, preferably polypropylene having 90% by weight or more of propylene polymerized units. Specifically, it may be a homopolymer of propylene, or a copolymer of 90% by weight or more of propylene polymer units and 10% by weight or less of ethylene and / or α-olefin. As the α-olefin used when the crystalline polypropylene (A) is a copolymer, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl- Examples thereof include 1-pentene and 3-methyl-1-pentene. Among these, it is preferable from the viewpoint of production cost to use a propylene homopolymer or a propylene-ethylene copolymer having a propylene polymer unit content of 90% by weight or more.

The melt mass flow rate MFR _PP of crystalline polypropylene (A) is preferably 0.1 to 50 g / 10 min when crystalline polypropylene (E) is not used in the resin composition (G) because of the stability of film formation. More preferably, those within the range of 30 to 40 g / 10 min are used.

(ii) Copolymer (B)
The copolymer (B) is a random copolymer of propylene and at least one selected from the group of α-olefins other than ethylene and propylene. The content of the propylene polymerized unit is preferably in the range of 30 to 80% by weight, more preferably 35 to 75% by weight, still more preferably 40 to 70% by weight, based on the weight of the entire copolymer (B). Most preferably, it is 60 to 70% by weight. When the content of the propylene polymerized unit is within the above range, pores are easily formed in the copolymer (B) region existing in the matrix of the crystalline polypropylene (A), and the content of the propylene polymerized unit is the same as that of the crystalline polypropylene (A). Since interfacial peeling of the polymer (B) is difficult to occur, there is no decrease in low-temperature stretchability, and the pore diameter tends to be fine.

  Examples of the α-olefin other than propylene used in the copolymer (B) include 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and 4-methyl-1-pentene. , 3-methyl-1-pentene and the like. Among these, a propylene-ethylene copolymer using ethylene as an α-olefin is preferably used from the viewpoint of production cost.

The melt mass flow rate MFR _RC of the copolymer (B) is not particularly limited, but a range of 0.05 to 20 g / 10 min is preferable because of excellent molding processability.

(iii) Polyolefin resin (C)
The polyolefin resin (C) is composed of crystalline polypropylene (A) and a copolymer (B). The melt mass flow rate ratio MFR _PP / MFR _RC (hereinafter referred to as “MFR ratio”) between the melt mass flow rate MFR _PP of the crystalline polypropylene (A) and the melt mass flow rate MFR _RC of the copolymer (B) is not particularly limited. However, from the viewpoint of moldability, it is preferably in the range of more than 10 and 1,000 or less, and more preferably 500 to 800.

  In the polyolefin resin (C), the content of the crystalline polypropylene (A) is preferably 30 to 70% by weight, more preferably 40 to 60% by weight, and the content of the copolymer (B) is preferably 70 to 30% by weight, 60 to 40% by weight is more preferable. If the content of the crystalline polypropylene (A) and the copolymer (B) is within the above range, continuous pores are obtained and the dispersibility of the copolymer (B) is good.

  The production method of the polyolefin resin (C) is not particularly limited, and any production method may be used as long as the above conditions are satisfied. For example, the polyolefin resin (C) may be produced by mixing the crystalline polypropylene (A) and the copolymer (B) obtained by separately polymerizing by melt kneading or the like. Specifically, a copolymer (B) polymerized using a Ziegler-Natta catalyst such as a titanium-supported catalyst or a commercially available ethylene-propylene rubber corresponding to the copolymer (B) and crystalline polypropylene (A) are melted. The method of mixing can be illustrated.

  Alternatively, the polyolefin resin (C) may be produced by continuously polymerizing the crystalline polypropylene (A) and the copolymer (B) by multistage polymerization. For example, by using a plurality of polymerization vessels, a crystalline polypropylene (A) is produced in the first stage, and then a copolymer (B) is produced in the presence of the crystalline polypropylene (A) in the second stage. A method for continuously producing the resin (C) can be exemplified. This continuous polymerization method is lower in production cost than the melt mixing method described above, and a polyolefin resin (C) in which the copolymer (B) is uniformly dispersed in the crystalline polypropylene (A) can be stably obtained. Therefore, it is preferable.

  In the present invention, a particularly preferred polyolefin resin (C) is produced by the above continuous polymerization method and adjusted so that the MFR ratio is more than 10 and 1,000 or less, more preferably in the range of 500 to 800. is there. By setting the MFR ratio within this range, the copolymer (B) is uniformly and finely dispersed in the crystalline polypropylene (A). Therefore, when the polyolefin resin (C) is stretched, Uniform and fine pores are formed between the lamellar crystals in the copolymer (B) region dispersed in the polypropylene (A), and as a result, a polyolefin resin battery separator having a small pore size and a high porosity is obtained.

  Further, taking the case where the copolymer (B) is an ethylene-propylene copolymer as an example, the polyolefin resin battery separator of the present invention has pores formed in the low melting point copolymer (B). It is recognized that the crystalline polypropylene (A), which is a matrix polymer, does not break up to around 180 ° C. due to its high melting point, and has an excellent shutdown function, while closing with increasing temperature.

  In the present invention, the copolymer (B) region means a region occupied by the copolymer (B) itself. Therefore, the pore generated between the lamella crystals in the copolymer (B) region is a pore due to cleavage generated between the lamella crystals in the copolymer (B) region.

Specifically, the polyolefin resin (C) having the MFR ratio as described above can be produced by a method described in International Publication No. 97/19135, JP-A-8-27238, and the like.
In addition, the polyolefin resin (C) can be produced by the above-described method, and one having a desired specification may be selected from commercially available products.

The MFR ratio is usually determined by measuring MFR _PP of the crystalline polypropylene (A) and MFR _RC of the copolymer (B). However, when the polypropylene resin is continuously produced by multistage polymerization (when the crystalline polypropylene (A) is first polymerized and then the copolymer (B) is polymerized), the MFR _{RC of the} copolymer (B) is used. Can not be measured directly, MFR _PP of crystalline polypropylene (A) that can be directly measured, melt flow rate MFR _{WHOLE of} the resulting polyolefin resin (C) (according to JIS K 7210, temperature 230 ° C., nominal load 2.16 kg) MFR _RC can be calculated by the following formula from the content W _RC (% by weight) of the copolymer (B) in the polyolefin resin (C) and the MFR ratio.
log (MFR _RC ) = {log (MFR _WHOLE ) − (1−W _RC / 100) log (MFR _PP )} / (W _RC / 100)

(iv) High density polyethylene (D)
The high-density polyethylene (D) is a polymer mainly composed of ethylene polymerized units, preferably polyethylene having 90% by weight or more of ethylene polymerized units. Specifically, it may be a homopolymer of ethylene or a copolymer of 90% by weight or more of ethylene polymer units and 10% by weight or less of α-olefin. The α-olefin used when the high-density polyethylene (E) is a copolymer is propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4- Examples thereof include methyl-1-pentene and 3-methyl-1-pentene. Of these, it is preferable from the viewpoint of production cost to use an ethylene homopolymer or a propylene-ethylene copolymer having an ethylene polymer unit content of 90% by weight or more.

By using a specific high-density polyethylene (D) in combination, a lamellar crystal in the copolymer (B) region is developed, and cleavage between the lamellae of the copolymer (B) becomes active, and the porosity, air permeability, The porous membrane characteristics such as the pore diameter are improved. Melt mass flow rate _MFR of the high-density polyethylene _(D) (D) is 1 g / 10min or more and less than 30 g / 10min. Moreover, the addition amount is 5 to 25% by weight. If the melt mass flow rate MFR _(D) and the addition amount are within this range, there is no adhesion to the roll during film formation, and the lamellar crystals in the copolymer (B) region are sufficient and the porosity is improved. There is no problem in stretchability.

(V) Crystalline polypropylene (E)
The crystalline polypropylene (E) is a crystalline polymer mainly composed of propylene polymerized units, preferably polypropylene having 90% by weight or more of propylene polymerized units. Specifically, it may be a homopolymer of propylene, or may be a random or block copolymer of 90% by weight or more of propylene polymer units and 10% by weight or less of ethylene and / or α-olefin. . As the α-olefin used when the crystalline polypropylene (E) is a copolymer, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl- Examples thereof include 1-pentene and 3-methyl-1-pentene. Among these, it is preferable from the viewpoint of production cost to use a propylene homopolymer or a propylene-ethylene copolymer having a propylene polymer unit content of 90% by weight or more.

The melt mass flow rate MFR _(E) of the crystalline polypropylene (E) is 0.1 g / 10 min or more and less than 10 g / 10 min, preferably 0.1 to 8.0 g / 10 min, more preferably 4 to 7 g / 10 min. is there. Further, the addition amount is 5 to 25% by weight, preferably 10 to 20% by weight. Within this range, there is no problem in stretchability when forming a polyolefin resin battery separator, and the pore diameter is A small porous film is formed.

(VI) Block copolymer (CEBC) (F)
The block copolymer (CEBC) (F) is composed of a crystalline polyolefin block that is composed of a crystalline polyolefin block that is a hard portion and an ethylene-butylene copolymer block that is an amorphous portion (rubber portion) that is a soft portion. A block copolymer having a triblock of a butylene copolymer / crystalline polyolefin.
Specific examples of commercially available products include Dynalon 6200P (trade name, JSR Corporation) in which the polyolefin of the crystalline polyolefin block is polyethylene.
A block copolymer (F) can be used individually by 1 type or in mixture of 2 or more types. In addition, the content of the block copolymer (F) in the polyolefin resin composition (G) is 1 to 15% by weight, preferably 2 to 10% by weight. There is no problem in stretchability at the time of forming, and a polyolefin resin porous film having a small pore size and a uniform pore size distribution is formed.

  In the polyolefin resin porous membrane of the present invention, many fine cleavages are observed between the lamella crystals in the copolymer (B) region finely dispersed in the crystalline polypropylene (A). The copolymer (B) has compatibility with the crystalline polypropylene (E) because it contains a certain amount of propylene component, and the high-density polyethylene (D) and the block copolymer (CEBC) (F) are Since it is compatible with the copolymer (B), lamellar crystals develop in the copolymer (B) region. Since the interlamellar crystal region in the copolymer (B) region having compatibility with the crystalline polypropylene (A) is lower in strength than the crystalline polypropylene (A), the copolymer (B) region is caused by stretching stress. It is inferred that cleavage occurred between the lamellar crystals. This mechanism is fundamentally different from the conventional multicomponent stretching method in which inorganic fillers and different polymers are mixed and stretched. As a result, the battery separator using the resulting polyolefin resin porous membrane is safe because of its small pore size. In addition, the electric capacity can be increased because of the high porosity and the high porosity.

  The porosity of the olefin resin porous membrane of the present invention is not particularly limited, but is preferably 10 to 90%, more preferably 30 to 80%, and still more preferably 50 to 80%. If the porosity is in the above range, a function as a battery separator can be obtained, and there is no fear that the strength is lowered. In particular, when the porosity is 50 to 80%, the capacity and size of the battery can be reduced.

  The gas resistance (Gurley) of the olefin resin porous membrane of the present invention is not particularly limited, but is preferably 10 to 20,000 s / 100 ml, more preferably 30 to 1,000 s / 100 ml, and 30 to 200 s / More preferably 100 ml. If the air permeability resistance (Gurley) is within the above range, the function as a battery separator can be obtained, and there is no fear that the strength is lowered. In particular, when the air resistance (Gurley) is 30 to 200 s / 100 ml, it is possible to increase the capacity and size of the battery.

In order to prevent the battery separator from rising abnormally due to misuse of the battery and causing an accident such as ignition, the battery separator does not break the membrane when the temperature reaches a certain level. Is required to shut down the current and shut down the current (hereinafter referred to as “shutdown function”). Further, to increase the difference [Delta] T = T _b -T _s temperature T _b and the temperature to occlude the pores (hereinafter referred to as "Shutdown temperature") T _s to film breakage, and the temperature to stop the abnormal reaction in the earlier stage In order to suppress the rise, it is desired to reduce the shutdown temperature.
In the present invention, a battery separator, by using a porous film obtained by processing the polyolefin resin composition (G) in specific manufacturing conditions, the difference in film breakage temperature T _b and the shutdown temperature T _s 30 ° C. or higher It can be. The high-density polyethylene (D) and the crystalline polypropylene (E) in the polyolefin resin composition (G) exhibit shutdown function characteristics in proportion to their total content, while the block copolymer (CEBC) ( F) synergistically exhibits shutdown function characteristics.
5 to 25% by weight of high-density polyethylene (D) having a melt mass flow rate MFR _(D) of 1 g / 10 min or more and less than 30 g / 10 min, and a melt mass flow rate MFR _(E) of 0.1 g / 10 min or more. When a porous membrane using 5 to 25% by weight of crystalline polypropylene (E) within a range of less than 10 g / 10 min and 1 to 15% by weight of a block copolymer (CEBC) (F) is used. Thus, a battery separator having a difference ΔT = T _b −T _s of 30 ° C. or higher between the temperature T _{b at} which the film is torn and the hole closing temperature T _s is obtained. Within these ranges, there is no problem in drawing properties during membrane fabrication, the difference in film breakage temperature T _b and the shutdown temperature T _s can provide high battery separators 30 ° C. or higher safety.

(2) Polyolefin resin composition (G)
The polyolefin resin composition (G), which is a molding material for the polyolefin resin porous membrane of the present invention, includes an antioxidant, a neutralizing agent, an α crystal nucleating agent, a β crystal nucleating agent, a hindered amine type, which are usually used for polyolefins. A surfactant such as a weathering agent, an ultraviolet absorber, an antifogging agent and an antistatic agent, an inorganic filler, a lubricant, an antiblocking agent, an antibacterial agent, an antifungal agent and a pigment can be blended as necessary.

  Antioxidants include tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane, 2,6-di-t-butyl-4-methylphenol, Phenolic compounds such as n-octadecyl-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate and tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate Antioxidant, or tris (2,4-di-t-butylphenyl) phosphite, tris (nonylphenyl) phosphite, distearyl pentaerythritol diphosphite, tetrakis (2,4-di-t-butylphenyl) Examples thereof include phosphorus-based antioxidants such as -4,4'-biphenylene-diphosphonite.

  Examples of neutralizing agents include higher fatty acid salts such as calcium stearate. Examples of inorganic fillers and anti-blocking agents include calcium carbonate, silica, hydrotalcite, zeolite, aluminum silicate, magnesium silicate, and the like. Can be exemplified by higher fatty acid amides such as stearic acid amide, and the antistatic agent can be exemplified by fatty acid esters such as glycerol monostearate.

  Alpha crystal nucleating agents include talc, aluminum hydroxy-bis (4-t-butylbenzoate), 1,3,2,4-dibenzylidene sorbitol, 1,3,2,4-bis (p-methylbenzylidene) Sorbitol, 1,3,2,4-bis (p-ethylbenzylidene) sorbitol, 1,3,2,4-bis (2 ′, 4′-dimethylbenzylidene) sorbitol, 1,3,2,4-bis ( 3 ', 4'-dimethylbenzylidene) sorbitol, 1,3-p-chlorobenzylidene-2,4-p-methylbenzylidenesorbitol, 1,3,2,4-bis (p-chlorobenzylidene) sorbitol, sodium-bis (4-t-Butylphenyl) phosphate, sodium-2,2′-methylene-bis (4,6-di-t-butylphenyl) phosphate Calcium-2,2′-methylene-bis (4,6-di-t-butylphenyl) phosphate, aluminum dihydroxy-2,2′-methylene-bis (4,6-di-t-butylphenyl) Known α-crystal nucleating agents such as phosphate can be used. These may be used alone or in combination of two or more.

  The compounding amount of these additives can be appropriately selected depending on the purpose of use of the polyolefin resin porous membrane, and is usually about 0.001 to 5% by weight with respect to the total amount of the resin composition (G). preferable.

  In addition, the polyolefin resin composition (G) of the present invention includes two or more of a propylene homopolymer and a monomer other than propylene mainly composed of propylene within a range not impairing the effects of the present invention. You may use together 1 or more types of other olefin resins, such as a random copolymer, a polyethylene resin, a polybutene resin, and a polymethylpentene resin.

  Further, an ethylene-diene elastic copolymer, an ethylene-propylene elastic copolymer polymerized with a single site catalyst or a known multi-site catalyst in order to reduce the plugging temperature of the pores of the battery separator or improve the flexibility, An elastic copolymer such as a styrene-butadiene elastic copolymer may be added.

  The method of blending the above-mentioned additives into the resin composition (G) is not particularly limited. For example, the blending is performed by a usual blending apparatus such as a mixer with a high-speed stirrer such as a Henschel mixer (trade name), a ribbon blender, and a tumbler mixer. And a method of pelletizing using a normal single-screw extruder or a twin-screw extruder.

(3) Formation of polyolefin resin porous film The polyolefin resin porous film of the present invention is obtained by melting and kneading the resin composition (G) to form a film-shaped melt, and the film-shaped melt is a film within a draft ratio of 1 to 10. After forming into a shaped product, the film-like product can be formed by stretching in at least one direction at a temperature of 100 ° C. or lower. The process consists of a film forming process and a stretching process.

(i) Film-forming process In the film-forming process for obtaining a film-shaped molded product from the resin composition, known methods such as an inflation film molding method, a T-die film molding method, and a calendar molding method are used. A calendar molding method in which the ratio can be easily controlled is preferably used.

  In the case of an inflation film molding method and a T-die film molding method, the resin composition can be formed at an extrusion molding temperature of 180 ° C. or higher, but the purpose is to reduce the pressure inside the die and reduce the draft ratio described later. , By improving the rigidity of the crystalline polymer (A), which is a matrix polymer, it is easy to form uniform and fine pores between the lamellar crystals in the copolymer (B) region dispersed in the crystalline polypropylene (A). Therefore, an extrusion temperature of 220 to 300 ° C. is preferably used.

The melt-kneaded resin composition is extruded from the die lip. At this time, the linear velocity V _{CL in} the flow direction (MD) of the resin composition passing through the die lip and the flow direction (MD) line of the film-shaped molded product The draft ratio (V _CL / V _f ) defined by the ratio of the speed V _f is an important factor for achieving the present invention. Generally, the draft ratio is about 10 to 50 when a thermoplastic resin film is formed. In the present invention, the draft ratio when forming the resin composition is 1 to 10, and the resulting film-like molded product is excellent in stretchability, and fine continuous pores are easily formed by stretching. Become.

  In the case of the calendar molding method, the pre-kneading of the composition before charging into the calendar is performed using a Banbury mixer, a method using a pre-kneading roll, a method using a single screw, a twin screw, a planetary, etc. Although a known method is used, the rigidity of the crystalline polypropylene (A), which is the matrix polymer, is improved and uniform between the lamella crystals in the copolymer (B) region dispersed in the crystalline polypropylene (A). In order to facilitate the formation of fine pores, a temperature of 220 to 300 ° C. is preferably used, and in order to put the pre-kneaded material into a stable calendar while maintaining the temperature, an extruder is preferable. used.

In the calendering method, a known calender apparatus such as 2 to 6 rolls and L-type, reverse L-type, Z-type, and roll diameters can be used. For thin film formation, four or more rolls are preferably used from the viewpoint of thickness accuracy, and the temperature of the calendar roll is preferably 160 to 220 ° C.
The film from which the final roll has been peeled is taken up by a take-off roll. The ratio (V1 / V0) between the rotation surface speed (V0) of the calendar final roll and the rotation surface speed (V1) of the take-off roll is defined as the draft ratio. In this case as well, in this case, in the present invention, the draft ratio when forming the resin composition is 1 to 10, more preferably the draft ratio is 1 to 5, and the film-like molding obtained thereby The product is excellent in stretchability, and fine continuous pores are easily formed by stretching.

Further, the rigidity of the crystalline polypropylene (A) which is a matrix polymer is improved, and uniform and fine pores are generated between the lamella crystals in the copolymer (B) region dispersed in the crystalline polypropylene (A). In order to facilitate the cooling of the film-like molded product extruded from the die lip, it is desirable to gradually cool, in the case of inflation molding, an air-cooling type cooling method is desirable, and in the case of the T-die film molding method, take-off rolls 100 to 100 It is desirable to cool within the range of 150 degreeC and the temperature of a cooling roll 70-120 degreeC.
Moreover, in the case of the calendering method, it is desirable to cool within the range of the take-off roll 100-150 degreeC and the temperature of a cooling roll 70-120 degreeC. If it is in the said temperature range, desired porosity will be easy to be obtained, and molten resin will contact | adhere to a roll and productivity will not be reduced.

  The thickness of the film-like molded product obtained in the film forming process is not particularly limited, but is determined by the stretching and heat treatment conditions in the next stretching process and the required characteristics of the use of the porous film, and is preferably 20 μm to 2 mm. Is about 50 μm to 500 μm, and the film forming speed is preferably in the range of 1 to 100 m / min. The film-shaped moldings having these thicknesses are composed of a combination of an inflation molding apparatus, an air knife having the cooling roll and an air outlet, the cooling roll and a pair of metal rolls, the cooling roll and a stainless belt, and the like. It can be obtained by various film forming apparatuses such as a T-die film forming apparatus and a calendar forming apparatus.

  Furthermore, the polyolefin resin porous membrane of the present invention is formed into a film-shaped product by co-extrusion of the resin composition (G) and a resin composition containing a known inorganic filler, organic filler, etc. in the film-forming step. It does not matter. In this case, the polymer constituting the resin composition containing a filler or the like is preferably a polyolefin resin such as a polypropylene resin or a polyethylene resin from the viewpoint of compatibility.

  In addition, you may heat-process in order to further improve a crystallinity degree before using for the obtained film-form molding to the next extending process. The heat treatment is performed, for example, by heating at a temperature of about 80 to 150 ° C. for about 1 to 30 minutes with a heated air circulation oven or a heating roll.

(ii) Stretching process The film-shaped molded product formed in the film-forming process is then stretched in at least one of the machine direction (MD) direction or the transverse (TD) direction, and into the crystalline polypropylene (A). Fine pores communicating between the lamellar crystals in the finely dispersed copolymer (B) region are formed. In this respect, the production method of the present invention is fundamentally different from the conventional single-component stretching method, multi-component stretching method, mixed extraction method and the like. Thus, the production method of the present invention is a single component stretching method in which pores are expressed by fibrillation between lamellar crystals of a crystalline polyolefin (A), such as complicated extraction and drying steps such as a mixed extraction method. In addition to eliminating the need for a crystallization step by heat treatment after film formation as seen in Fig. 1, the stretchability is poor and the average pore size is large in the case of the multicomponent stretching method that creates voids at the interface between the matrix polymer and the filler. Problems such as easy and low porosity are greatly improved, and a battery separator having an arbitrary average pore diameter and porosity can be provided with excellent productivity.

  In addition to the uniaxial stretching method of stretching in one direction, the stretching method includes a sequential biaxial stretching method of stretching in the other direction after stretching in one direction, a simultaneous biaxial stretching method of stretching simultaneously in the longitudinal and transverse directions, and A method of performing multi-stage stretching in a uniaxial direction or a method of further stretching after sequential biaxial stretching or simultaneous biaxial stretching may be used, and any method may be used. Incidentally, since the film-shaped molded product is drafted in the film-forming process, even a film-shaped molded product formed at a low draft ratio is a finely dispersed copolymer (in the crystalline polypropylene (A)). B) is oriented along the resin flow direction, that is, the longitudinal (MD) direction, and the first stage of stretching is preferably performed by a uniaxial stretching method in the transverse direction or a simultaneous biaxial stretching method in the longitudinal and transverse directions. A sequential biaxial stretching method in which stretching in the longitudinal direction in the first stage and stretching in the lateral direction in the second stage may be performed.

The first stage stretching temperature is preferably lower than the melting point T _mα of the copolymer (B), and a temperature range of 10 to 100 ° C. is suitably used. In the present invention, the resin composition (G) is further used. Has been found to be excellent in low-temperature stretchability in these temperature regions. The stretching ratio is not particularly limited and is determined from the second stage stretching conditions performed as necessary and the required characteristics of the use of the porous membrane, but is usually in the range of 1.5 to 7 times.
If the draw ratio is in the above range, a porous film having excellent characteristics can be obtained, and there is no risk of a decrease in productivity due to frequent stretching. In the case of simultaneous biaxial stretching, the area ratio (= longitudinal stretching ratio × lateral stretching ratio) is preferably 2 to 50 times, and more preferably 4 to 40 times. If the area magnification is within this range, a polyolefin resin porous membrane having excellent characteristics can be obtained, and there is no fear of a decrease in productivity due to frequent stretching.

The polyolefin resin porous membrane of the present invention is subjected to second-stage stretching as necessary. The second-stage stretching temperature is preferably 10 ° C. or more lower than the melting point T _mc of the high-density polyethylene (D). Further, when the _stretching temperature is higher than the melting point T _mα of the copolymer (B), the porosity does not increase so much and the thickness of the resulting porous film tends to decrease. Furthermore, when the _stretching temperature is lower than T _mα , the porosity increases, but the thickness tends not to decrease much.

The draw ratio in the second stage is determined by the required characteristics of the application of the polyolefin resin porous membrane, but is usually in the range of 1.5 to 7 times.
If the draw ratio is within the above range, the drawing effect is sufficient, and there is no fear of a decrease in productivity due to the drawing being cut.

  It is preferable that the membrane-shaped molded product that has been formed into pores by the above stretching step and then becomes porous is then heat-treated. This heat treatment is mainly intended for heat fixation for maintaining the formed pores, and is usually carried out on heating rolls, between heating rolls or through a hot air circulating furnace.

In this heat treatment (heat setting), the film-like molded product that has become porous while maintaining the stretched state is heated to a temperature 5 to 60 ° C. lower than the melting point T _mc of the high-density polyethylene (D). It is carried out by setting it to 50%. If the heating temperature is within the above range, the formed pores will not be clogged, and since the heat fixation is sufficient, the pores are difficult to close later, and when using a polyolefin resin porous membrane as a battery separator However, heat shrinkage is less likely to occur due to temperature changes.

  The thickness of the polyolefin resin porous membrane of the present invention is not particularly limited, but is preferably about 5 to 100 μm, more preferably 10 to 50 μm from the viewpoint of productivity.

  The polyolefin resin porous membrane of the present invention can be subjected to hydrophilic treatment such as surfactant treatment, corona discharge treatment, low temperature plasma treatment, sulfonation treatment, ultraviolet treatment, radiation graft treatment, etc., if necessary. A coating film can be formed.

  The polyolefin resin porous membrane of the present invention may be used by laminating nonwoven fabrics, woven fabrics, porous membranes of other materials, etc. for the purpose of imparting known properties such as reinforcement of the porous membrane itself and improvement of battery capacity. Absent.

  The secondary battery using the polyolefin resin porous membrane of the present invention configured as described above as a battery separator exhibits the same battery performance as before, and can provide a safe battery excellent in shutdown characteristics and meltdown characteristics. . Here, the ionic species is not particularly limited, but lithium ion is particularly preferable in terms of versatility. The secondary battery according to the present invention can be produced according to a conventional method except that the polyolefin resin porous membrane of the present invention is used as a battery separator.

  In a lithium secondary battery, a positive electrode and a negative electrode are laminated via a battery separator, and the battery separator contains an electrolytic solution (electrolyte). The structure of the electrode is not particularly limited, and may be a known structure. For example, an electrode structure (coin type) in which disc-shaped positive electrodes and negative electrodes are opposed to each other, an electrode structure in which flat plate-like positive electrodes and negative electrodes are alternately stacked (stacked type), and belt-shaped positive electrodes and negative electrodes are stacked. It is possible to obtain a wound electrode structure (winding type) or the like.

The positive electrode usually has (a) a current collector and (b) a layer containing a positive electrode active material formed on the surface thereof and capable of occluding and releasing lithium ions. Examples of the positive electrode active material include transition metal oxides, composite oxides of lithium and transition metals (lithium composite oxides), and inorganic compounds such as transition metal sulfides. Transition metals include V, Mn, and Fe. , Co, Ni and the like. Preferable examples of the lithium composite oxide include lithium nickelate, lithium cobaltate, lithium manganate, and a layered lithium composite oxide based on an α-NaFeO ₂ type structure. The negative electrode has (a) a current collector and (b) a layer formed on the surface thereof and containing a negative electrode active material. Examples of the negative electrode active material include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black.

The electrolytic solution can be obtained by dissolving a lithium salt in an organic solvent. Lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , Examples include LiN (C ₂ F ₅ SO ₂ ) ₂ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , lower aliphatic carboxylic acid lithium salt, LiAlCl _{4 and the} like. These may be used alone or as a mixture of two or more. Examples of the organic solvent include high boiling point and high dielectric constant organic solvents such as ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and γ-butyrolactone, and tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane, dimethyl carbonate, diethyl carbonate, and the like. Examples include organic solvents having a low boiling point and a low viscosity. These may be used alone or as a mixture of two or more. In particular, a high dielectric constant organic solvent has a high viscosity, and a low viscosity organic solvent has a low dielectric constant. Therefore, it is preferable to use a mixture of the two.

  When assembling the battery, the battery separator is impregnated with the electrolyte. Thereby, ion permeability can be imparted to the battery separator. Usually, the impregnation treatment is performed by immersing the battery separator in an electrolytic solution at room temperature. When assembling a cylindrical battery, for example, a positive electrode sheet, a battery separator, and a negative electrode sheet are laminated in this order, and the obtained laminate is wound up from one end to obtain a wound electrode element. The obtained electrode element is inserted into a battery can, impregnated with the above electrolyte, and a battery lid that also serves as a positive electrode terminal provided with a safety valve is caulked through a gasket to produce a battery.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these.
The polyolefin resin (C) used in the examples and comparative examples was obtained by polymerizing crystalline polypropylene (A) in the first stage by a continuous polymerization method, and copolymer (B) (propylene-ethylene copolymer in the second stage. ).
As the high density polyethylene (D), M6901 (trade name, manufactured by Keiyo Polyethylene Co., Ltd.) having an MFR _(D) of 13 g / 10 min was used.
As the crystalline polypropylene (E), a propylene homopolymer having an MFR _(E) of 5.3 g / 10 min was used.
Furthermore, as a block copolymer (CEBC) (F) having a crystalline polyolefin / ethylene-butylene copolymer / crystalline polyolefin triblock, Dynalon 6200P (trade name, manufactured by JSR Corporation, Melt Mass Flow Rate MFR ( According to JIS K 7210, measured under the conditions of a temperature of 230 ° C. and a nominal load of 2.16 kg) 2.5 g / 10 min) was used.

In addition, the measuring method and evaluation method used by the Example and the comparative example are as follows.
(1) Porosity: The bulk specific gravity is obtained from a stretched porous membrane sample 100 × 100 mm, and from the non-porous sample 100 × 100 mm before stretching, an automatic hydrometer DENSIMTER, D manufactured by Toyo Seiki Seisakusho Co., Ltd. The true specific gravity was determined at -S, and the porosity was determined from the following formula.
Porosity (%) = (1-bulk specific gravity / true specific gravity) × 100

(2) Average pore diameter and maximum pore diameter: In accordance with ASTM F316, the pore diameter of the polyolefin resin porous membrane was measured using a Perm-Porometer manufactured by PMI using a reagent of Galwick (trade name), and the average flow rate fine The pore diameter was defined as the average pore diameter, and the bubble point pore diameter was defined as the maximum pore diameter.

(3) Hole blocking temperature and membrane breakage temperature [Method for producing evaluation cell]
As shown in FIG. 1, the cell piece A which prepared the glass substrate (A, B), arrange | positioned the substantially square-shaped 10-micrometer aluminum foil C to one glass base A, and affixed the imide tape D on the surface of aluminum foil. A cell piece B in which a substantially square 10 μm aluminum foil C is arranged on a glass substrate B is prepared. And as shown in FIG. 2, the porous film obtained by the Example and the comparative example was pinched | interposed as each battery separator E below between the cell piece A and the cell piece B, and these are fixed with a clip, and evaluation cell F Was made.

The reason why the imide tape D is affixed is to prevent a short circuit due to burrs, and a hole G having a diameter of 19 mm is formed in the approximate center of the imide tape D. further,
As an electrolytic solution of this evaluation cell F, LiBF ₄ as a solute was propylene carbonate / ethylene carbonate / γ-butyrolactone (solvent volume ratio 1 / l) so as to have a concentration of 1.0 mol / liter.
What was dissolved in 1/2) was used.

[Evaluation equipment]
The pore clogging temperature and the membrane breaking temperature are evaluated using an electric furnace TS-25K • R type manufactured by Isuzu Seisakusho and an electrochemical measurement impedance measuring device 1280C type manufactured by Toyo Technica.

[Measurement method of SD temperature and MD temperature]
The evaluation cell was set in an electric furnace, and the room temperature (at a temperature rising rate of 5 ° C./min and 25 ° C./min)
23 ° C.) to 200 ° C. The impedance change at this time is measured with an impedance measuring apparatus under the condition of AC 20 kHz. In this measurement, the heating rate is 5 ° C./m.
The temperature at the time when the impedance at the time of in measurement reaches 1,000Ω is defined as the hole closing temperature (SD), and the temperature at the time when the impedance falls below 1,000Ω is defined as the film breaking temperature (MD). In addition, the hole closing temperature at the time of measuring the heating rate of 25 ° C./min is the high speed hole closing temperature (HRSD).
The film breaking temperature is defined as a high-speed film breaking temperature (HRMD).

(4) Melt mass flow rate (MFR): Measured in accordance with JIS K 7210 under conditions of a temperature of 230 ° C. and a nominal load of 2.16 kg. However, only MFR _(D) was measured in accordance with JIS K 7210 under conditions of a temperature of 190 ° C. and a nominal load of 2.16 kg.

(5) Air permeability resistance (Gurley): According to JIS P 8117, the time required for 100 ml of air to pass through was measured with a B-type Gurley densometer (manufactured by Tester Sangyo Co., Ltd.).

Example 1
1) Creation of Resin Composition for Forming Porous Film Tetrakis [methylene-3- (3 ′, 5′-di-t-) as a phenolic antioxidant was added to the resin composition (G) shown in Example 1 of Table 1. Butyl-4′-hydroxyphenyl) propionate] 0.1% by weight of methane, 0.1% by weight of tris (2,4-di-t-butylphenyl) phosphite as a phosphorus antioxidant, and as a neutralizing agent 0.1% by weight of calcium stearate and 0.4% of special fatty acid ester (trade name EW-100, manufactured by Riken Vitamin Co., Ltd.) as a lubricant are mixed and mixed with a Henschel mixer (trade name). (Polymer 50 mm) was melt kneaded and pelletized to obtain a porous film forming resin composition.

2) [Film forming process / Creation of unstretched film-shaped product]
Using a planetary roller extruder, the pellet-shaped resin composition (G) was melted at an extrusion temperature of 240 ° C. and a discharge rate of 15 kg / h, extruded into a rod shape from a head, and arranged in an inverted L shape. After being fed and rolled to a calender apparatus comprising the rolls of No. 1, the film was taken up by a take-off roll and solidified by cooling on an annealing roll to prepare a film-like molded product having a width of 600 mm and a thickness of 100 μm. The calender roll temperature, take-off roll temperature, and annealing roll temperature were 180 ° C., 140 ° C., and 90 ° C., respectively, and the draft ratio of the surface speed ratio of the final calendar roll and take-off roll was 2. Table 1 shows the evaluation results of the film formability and stretchability of the obtained film-like molded product.

3) [Stretching process / Creation of porous film]
The film-like molded product was stretched in the MD direction in the sequential stretching apparatus manufactured by Mitsubishi Heavy Industries, Ltd. under the conditions of a stretching temperature of 23 ° C. and a stretching ratio of 3 times, and further, the stretching temperature of 120 ° C. in the TD direction. The polyolefin resin porous membrane was obtained by stretching under the condition of a stretching ratio of 3 times. Table 1 shows the characteristics of the obtained battery separator. Regarding the battery separator made of polyolefin resin obtained in Example 1, the membrane breaking temperature MD, the hole closing temperature SD, the high-speed membrane breaking temperature HRMD, and the hole closing temperature HRSD were measured. As a result, MD 190 ° C., SD 140 ° C., HRMD 185 ° C., HRSD 145, respectively. ° C. ΔT was 50 ° C. and ΔHRT was 40 ° C., which had an excellent shutdown function as a battery separator.

(Example 2)
A polyolefin resin porous membrane was obtained according to Example 1 except that the resin composition (G) shown in Example 2 of Table 1 was used. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. As for the polyolefin resin porous membrane obtained in Example 2, the membrane breaking temperature MD, the pore closing temperature SD, the high-speed membrane breaking temperature HRMD, and the pore closing temperature HRSD were measured. As a result, MD185 ° C, SD135 ° C, HRMD180 ° C, HRSD140 ° C, respectively. Met. ΔT was 50 ° C. and ΔHRT was 40 ° C., which had an excellent shutdown function as a battery separator.

(Example 3)
A polyolefin resin porous membrane was obtained in the same manner as in Example 1 except that the resin composition (G) shown in Example 3 of Table 1 was used. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. About the polyolefin resin porous membrane obtained in Example 3, as a result of measuring the membrane breaking temperature MD, the pore closing temperature SD, the high-speed membrane breaking temperature HRMD, and the pore closing temperature HRSD, MD 190 ° C., SD 140 ° C., HRMD 185 ° C., HRSD 145 ° C., respectively. Met. ΔT was 50 ° C. and ΔHRT was 40 ° C., which had an excellent shutdown function as a battery separator.

Example 4
A polyolefin resin porous membrane was obtained according to Example 1 except that the resin composition (G) shown in Example 4 of Table 1 was used. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. About the polyolefin resin porous membrane obtained in Example 4, as a result of measuring the membrane breaking temperature MD, the pore closing temperature SD, the high-speed membrane breaking temperature HRMD, and the pore closing temperature HRSD, MD 190 ° C., SD 145 ° C., HRMD 185 ° C., HRSD 150 ° C., respectively. Met. ΔT was 45 ° C. and ΔHRT was 35 ° C., and it had an excellent shutdown function as a battery separator.

(Example 5)
A polyolefin resin porous membrane was obtained according to Example 1 except that the resin composition (G) shown in Example 5 of Table 1 was used. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. With respect to the polyolefin resin porous membrane obtained in Example 5, the membrane breaking temperature MD, the pore closing temperature SD, the high-speed membrane breaking temperature HRMD, and the pore closing temperature HRSD were measured. As a result, MD185 ° C. and SD138, respectively.
° C, HRMD 180 ° C, HRSD 142 ° C. ΔT was 47 ° C. and ΔHRT was 38 ° C., which had an excellent shutdown function as a battery separator.

(Example 6)
A polyolefin resin porous membrane was obtained according to Example 1 except that the resin composition (G) shown in Example 6 of Table 1 was used. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. As for the polyolefin resin porous membrane obtained in Example 6, the membrane breaking temperature MD, the pore closing temperature SD, the high-speed membrane breaking temperature HRMD, and the pore closing temperature HRSD were measured.
° C, HRMD 185 ° C, and HRSD 152 ° C. ΔT was 43 ° C. and ΔHRT was 33 ° C., which had an excellent shutdown function as a battery separator.

(Comparative Example 1)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (G) shown in Comparative Example 1 of Table 1. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. The polyolefin resin porous membrane obtained in Comparative Example 1 was measured for a membrane breaking temperature MD, a pore closing temperature SD, a high-speed membrane breaking temperature HRMD, and a pore closing temperature HRSD. As a result, MD 180 ° C., SD 160 ° C., HRMD 175 ° C., HRSD 165 ° C., respectively. Met. Although ΔT was 20 ° C. and ΔHRT was 10 ° C., the battery separator had a slight shutdown function at a rate of temperature increase of 5 ° C./min. The difference in temperature became small, and there was a problem with the shutdown function.

(Comparative Example 2)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (G) shown in Comparative Example 2 of Table 1. Table 1 shows the stretchability of the porous membrane. In Comparative Example 2, when stretched in the longitudinal direction, stretching breakage occurred at a stretch ratio of less than 1.5 times, resulting in poor stretchability. With a slight stretch of about 1.3 times the stretch ratio, the characteristics as a battery separator were It was not obtained.

(Comparative Example 3)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (G) shown in Comparative Example 3 of Table 1. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. The polyolefin resin porous membrane obtained in Comparative Example 3 was measured for a membrane breaking temperature MD, a pore closing temperature SD, a high-speed membrane breaking temperature HRMD, and a pore closing temperature HRSD. As a result, MD 170 ° C., SD 160 ° C., HRMD 165 ° C., HRSD 165 ° C., respectively. Met. Although ΔT was 10 ° C. and ΔHRT was 0 ° C., the battery separator had a slight shutdown function at a temperature increase rate of 5 ° C./min. There was no temperature difference and no shutdown function was observed.

(Comparative Example 4)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (G) shown in Comparative Example 4 of Table 1. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. The polyolefin resin porous membrane obtained in Comparative Example 4 was measured for membrane breaking temperature MD, pore closing temperature SD, high-speed membrane breaking temperature HRMD, and pore closing temperature HRSD. As a result, MD175 ° C., SD155 ° C., HRMD 170 ° C., HRSD 160 ° C., respectively. Met. Although ΔT was 20 ° C. and ΔHRT was 10 ° C., the battery separator had a slight shutdown function at a rate of temperature increase of 5 ° C./min. The difference in temperature became small, and there was a problem with the shutdown function.

(Comparative Example 5)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (G) shown in Comparative Example 5 of Table 1. Table 1 shows the stretchability of the porous membrane and the characteristics of the porous membrane. The polyolefin resin porous membrane obtained in Comparative Example 5 was measured for a membrane breaking temperature MD, a pore closing temperature SD, a high-speed membrane breaking temperature HRMD, and a pore closing temperature HRSD. As a result, MD 180 ° C., SD 160 ° C., HRMD 175 ° C., HRSD 165 ° C., respectively. Met. Although ΔT was 20 ° C. and ΔHRT was 10 ° C., the battery separator had a slight shutdown function at a rate of temperature increase of 5 ° C./min. The difference in temperature became small, and there was a problem with the shutdown function.

(Comparative Example 6)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (G) shown in Comparative Example 6 of Table 1. Table 1 shows the stretchability of the porous membrane. In Comparative Example 6, when stretched in the longitudinal direction, stretching breakage occurred at a stretch ratio of less than 1.5 times, resulting in poor stretchability. With a slight stretch of about 1.3 times the stretch ratio, the characteristics as a battery separator were It was not obtained.

(Comparative Example 7)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (G) shown in Comparative Example 7 of Table 1. Table 1 shows the stretchability of the porous membrane. In Comparative Example 7, when stretched in the longitudinal direction, stretching breakage occurred at a stretch ratio of less than 1.5 times, resulting in poor stretchability. It was not obtained.

(Comparative Example 8)
Instead of using the polyolefin resin porous membrane obtained in Example 1, a commercially available battery separator (trade name Celgard 2400, manufactured by Celgard, thickness 27 μm, porosity 38%, air resistance 600 s / 100 ml) is used. The measurement test of SD temperature, MD temperature, HRMD temperature, and HRSD temperature was conducted in the same manner as in Example 1. As a result of measurement, they were MD 170 ° C., SD 160 ° C., HRMD 165 ° C., and HRSD 165 ° C., respectively. Although ΔT was 10 ° C. and ΔHRT was 0 ° C., the battery separator had a slight shutdown function at a temperature increase rate of 5 ° C./min. There was no temperature difference and no shutdown function was observed.

(Comparative Example 9)
Instead of using the polyolefin resin porous membrane obtained in Example 1, a commercially available battery separator (trade name Hypore H6022, manufactured by Asahi Kasei Chemicals Corporation, thickness 27 μm, porosity 49%, air resistance 90 s / 100 ml) The SD temperature, MD temperature, HRMD temperature, and HRSD temperature were measured and tested in the same manner as in Example 1 except that they were used. As a result of measurement, they were MD155 ° C, SD135 ° C, HRMD135 ° C, and HRSD135 ° C, respectively. Although ΔT was 20 ° C. and ΔHRT was 0 ° C., the battery separator had a slight shutdown function at a rate of temperature increase of 5 ° C./min. There was no temperature difference and no shutdown function was observed.

The battery separator using the polyolefin resin porous membrane of the present invention is a battery separator that can increase the battery capacity because of its high porosity, and has an excellent shutdown function. It is suitably used for organic solvent battery separators such as secondary batteries and lithium secondary batteries.
In addition to the battery separator, the polyolefin resin porous membrane of the present invention is also suitably used for sanitary materials such as separation membranes, building materials such as breathable waterproof materials, and breathable sheets for disposable diapers.

It is a decomposition | disassembly top view of the evaluation cell for evaluating the hole obstruction | occlusion temperature and membrane tearing temperature of a polyolefin battery separator. It is sectional drawing of the evaluation cell for evaluating the hole obstruction | occlusion temperature and membrane tearing temperature of a polyolefin battery separator.

Explanation of symbols

A glass substrate B glass substrate C aluminum foil D imide tape E battery separator F evaluation cell

Claims (8)

Copolymer (B) 30 of 30 to 70% by weight of crystalline polypropylene (A), propylene and at least one selected from the group of α-olefins other than ethylene and propylene dispersed in crystalline polypropylene (A) Polyolefin resin (C) consisting of ˜70 wt%, 35 g to 89 wt%, melt mass flow rate MFR _(D) (measured in accordance with JIS K 7210, temperature 190 ° C., nominal load 2.16 kg) 1 g / 10 min or more and less than 30 g / 10 min, high density polyethylene (D) 5 to 25 wt%, melt mass flow rate MFR _(E) (according to JIS K 7210, temperature 230 ° C., nominal load 2.16 kg Crystalline polypropylene whose measured value is 0.1 g / 10 min or more and less than 10 g / 10 min (E) A polyolefin resin composition containing 5 to 25% by weight and a block copolymer (CEBC) (F) having a triblock of crystalline polyolefin / ethylene-butylene copolymer / crystalline polyolefin (F) of 1 to 15% by weight The product (G) is melt-kneaded to form a film-like melt, and the film-like melt is formed into a film-like molding within a draft ratio of 1 to 10, and then the film-like molding is stretched in at least one direction. A polyolefin resin porous membrane having continuous pores formed by cleaving caused by cleaving. The melt mass flow rate of crystalline polypropylene (A) is MFR _PP (measured in accordance with JIS K 7210, temperature 230 ° C., nominal load 2.16 kg), and selected from the group of α-olefins other than ethylene and propylene. When the melt mass flow rate of at least one copolymer of propylene and propylene (B) is MFR _RC (measured in accordance with JIS K 7210, temperature 230 ° C., nominal load 2.16 kg), The polyolefin resin porous membrane according to claim 1, wherein the rate ratio MFR _PP / MFR _RC is in a range of more than 10 and 1,000 or less.   The polyolefin resin porous membrane according to claim 1 or 2, wherein a draft ratio when the film-shaped melt is formed into a film-shaped molding is in the range of 1 to 5.   The polyolefin according to any one of claims 1 to 3, wherein the propylene content of the copolymer (B) of propylene with at least one selected from the group of α-olefins other than ethylene and propylene is 30 to 80% by weight. Resin porous membrane.   Polyolefin resin (C) produces crystalline polypropylene (A) in the first stage, and in the second stage, at least one selected from the group of α-olefins other than ethylene and propylene and the copolymer weight of propylene The polyolefin resin porous membrane according to any one of claims 1 to 4, which is obtained by a multistage polymerization method including a step of producing a coalescence (B). The pore resistance distribution (Gurley) of the porous membrane is within the range of 10 to 20,000 s / 100 ml, the average pore diameter measured according to ASTM F316 is within the range of 0.05 to 0.2 μm, and the pore size distribution. The polyolefin resin porous membrane according to any one of claims 1 to 5, wherein an index (maximum pore diameter / average pore diameter) is within a range of 1.3 to 2.0.   The polyolefin resin porous membrane according to any one of claims 1 to 6, wherein a film forming method for forming the polyolefin resin composition (G) into a film-shaped product is a calender molding method.   The battery separator using the polyolefin resin porous membrane of any one of Claims 1-7.

Images