JP2011255654A - Laminated microporous film, method for producing the same and separator for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated microporous film having low electric resistance, a method for producing the same and a separator for a battery using the laminated microporous film.SOLUTION: The laminated microporous film comprises a first microporous film consisting of a first resin composition and a second microporous film consisting of a second resin composition having a melting point lower than that of the first resin composition. The second resin composition contains a polyethylene resin and a ratio (η/η) of elongational viscosity ηto shear viscosity ηis 15 to 100.

Description

  The present invention relates to a laminated microporous film, a method for producing the same, and a battery separator.

  Microporous films, especially polyolefin-based microporous films, are used in microfiltration membranes, battery separators, capacitor separators, fuel cell materials, etc., and are particularly preferably used as lithium ion battery separators. Yes. In recent years, lithium-ion batteries have been used for small electronic devices such as mobile phones and notebook personal computers, while being applied to hybrid electric vehicles and the like.

  Here, a lithium ion battery for a hybrid electric vehicle is required to have higher output characteristics for taking out a lot of energy in a short time. Moreover, since lithium ion batteries for hybrid electric vehicles are generally large and require high energy capacity, higher safety is required.

The battery separator included in the lithium ion battery is required to have a shutdown (SD) function in order to ensure safety. The SD function is a function that, when the temperature inside the battery rises excessively, stops the battery reaction by abruptly increasing the electric resistance of the battery separator and prevents further temperature rise. As a mechanism for expressing the SD function, for example, in the case of a battery separator made of a microporous film, when the internal temperature of the battery rises to a predetermined temperature, the porous structure is lost to make it non-porous and block ion permeation. Can be mentioned. However, even if the pores are made non-porous in this way and the ion permeation is blocked, if the temperature further rises and the entire film melts and breaks, the electrical insulation cannot be maintained. The temperature at which the film cannot maintain its shape and cannot block ion permeation is called the membrane breaking temperature. It can be said that the higher the film breaking temperature, the better the battery separator. Moreover, it can be said that it is excellent in safety, so that the difference between the temperature at which SD starts and the membrane breaking temperature is large.
Furthermore, in order to improve the discharge performance at a large current and the discharge performance at a low temperature of a lithium ion battery, it is necessary to reduce the resistance of flowing ions in a state where the separator retains the electrolyte solution. A separator having a low electrical resistance in the contained state is desired.

For the purpose of providing a microporous film serving as a separator that can cope with such circumstances, for example, Patent Document 1 discloses a laminated film having a high melting point resin layer and a low melting point resin layer by a coextrusion molding method. A method for producing a laminated microporous film by molding and stretching is proposed.
Patent Document 2 discloses a method of producing a laminated microporous film having good air permeability by separately forming a polypropylene film and a polyethylene film, then laminating, annealing, and stretching. .

Japanese Patent No. 2883726 Japanese Patent No. 3003830

However, the battery separator obtained by the method of Patent Document 1 needs to match the molding temperatures of the high melting point resin and the low melting point resin to some extent, and it is difficult to mold them under optimum conditions. It is difficult to obtain a laminated microporous film having a low thickness.
Also, the laminated microporous film produced by the method disclosed in Patent Document 2 is not sufficient from the viewpoint of electrical resistance.
This invention is made | formed in view of such a situation, and makes it a subject to provide the separator for batteries using the laminated microporous film with low electrical resistance, its manufacturing method, and it.

  As a result of intensive studies to solve the above problems, the present inventors have a first microporous film composed of the first resin composition and a melting point lower than that of the first resin composition. And a second microporous film comprising a second polyethylene resin composition containing a polyethylene resin and having a ratio between a specific elongational viscosity and a shear viscosity. The present inventors have found that the above problems can be solved, and have completed the present invention.

That is, the present invention is as follows.
[1]
A first microporous film composed of a first resin composition;
A second microporous film composed of a second resin composition having a lower melting point than the first resin composition;
A laminated microporous film comprising:
The second resin composition contains a polyethylene resin, a ratio of the extensional viscosity eta _e to shear viscosity η _s η _{e /} η _s is 15 to 100, the laminated microporous film.
[2]
The laminated microporous film according to the above [1], wherein the polyethylene resin contained in the second resin composition has 3.0 or less terminal vinyl groups per 10,000 carbon atoms.
[3]
The first resin composition is a thermoplastic resin composition containing a polypropylene resin and 1 to 90 parts by mass of a polyphenylene ether resin with respect to 100 parts by mass of the polypropylene resin.
The first microporous film composed of the first resin composition has a sea-island structure composed of a sea part that is a phase containing the polypropylene resin and an island part that is a phase containing the polyphenylene ether resin. The laminated microporous film according to the above [1] or [2].
[4]
The laminated microporous film according to the above [3], wherein the thermoplastic resin composition further contains 1 to 20 parts by mass of an admixture with respect to 100 parts by mass of the polypropylene resin.
[5]
The admixture is mainly composed of at least one polymer block A mainly composed of a structural unit derived from a vinyl aromatic compound, and a structural unit derived from a conjugated diene compound. The hydrogenated block copolymer according to the above [4], which is a hydrogenated block copolymer obtained by adding hydrogen to a block copolymer comprising at least one polymer block B having a total 4-vinyl bond content of 40 to 90%. Laminated microporous film.
[6]
The laminated microporous film according to any one of [3] to [5] above, wherein the island part has a particle size of 0.01 μm to 10 μm.
[7]
The battery separator containing the lamination | stacking microporous film in any one of said [1]-[6].
[8]
A method for producing a laminated microporous film according to any one of the above [1] to [6], comprising the following steps (A) and (B):
(A) Cold-stretching step of cold-stretching the film at least in one direction by 1.05 to 2.0 times (B) After the cold-stretching step, the film is at least in one direction by 1.05 to 5.0 times A heat stretching process for heat stretching.

  ADVANTAGE OF THE INVENTION According to this invention, the laminated microporous film with low electrical resistance, its manufacturing method, and the battery separator using the same can be provided.

The schematic of the cell for an electrical resistance measurement of a film | membrane is shown. (A) The schematic of the measuring apparatus of a film breaking temperature is shown. (B) The top view which shows the sample part of the measuring apparatus of a film breaking temperature. (C) The top view which shows the sample part of the measuring apparatus of a film breaking temperature.

Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist.
Unless otherwise specified in this specification, “including as a main component” and “mainly including” are preferable as a ratio in which a specific component is contained in a composition (matrix component) including the specific component. Means 50% by mass or more, more preferably 80% by mass or more, and may contain 100% by mass.

The laminated microporous film of this embodiment is
A first microporous film composed of a first resin composition;
A second microporous film composed of a second resin composition having a lower melting point than the first resin composition;
A laminated microporous film comprising:
The second resin composition is a laminated microporous film containing a polyethylene resin and having a ratio η _e / η _s of an extensional viscosity η _e to a shear viscosity η _s adjusted to 15 to 100.

The laminated microporous film of the present embodiment includes a first microporous film composed of the first resin composition and an extension with respect to the shear viscosity η _s having a lower melting point than the first resin composition. A second microporous film composed of a polyethylene resin composition (hereinafter also referred to as “polyethylene resin composition Ac”) having a viscosity η _e ratio η _e / η _s of 15 to 100 was laminated. It has a structure.

  In the present specification, the “resin composition” is a concept that includes only one kind of resin (polymer material), and may be a mixture of two or more kinds of resins, and further contains an optional additive. You may contain. The “polyethylene resin” refers to a polymer whose main component is ethylene. Here, the “main component” means that ethylene accounts for 50% by mass or more with respect to the total amount of the monomer of the polyethylene resin, preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably. It means 95% or more, still more preferably 98% or more, particularly preferably 100% by mass, ie occupying the total amount.

The first resin composition and the second resin composition have a melting point (hereinafter simply referred to as “melting point”) T _mA and T _mB measured by a method according to JIS K-7121, and T _mA > T _mB is satisfied. If it does, the material may be the same or different. Here, T _mA represents the melting point of the first resin composition, and T _mB represents the melting point of the second resin composition.

The difference between the melting point T _mA of the first resin composition and the melting point T _{mB of} the second resin composition is preferably 5 ° C. or more, more preferably 10 ° C. or more. When the difference in melting point is 5 ° C. or more, when the laminated microporous film is used as a battery separator, the high melting point is obtained even when the low melting point resin layer melts when the internal temperature of the battery rises due to abnormal current. The resin layer is easily held without melting. As a result, the film shape or sheet shape of the battery separator is maintained, and the safety tends to be improved.

  The laminated microporous film of the present embodiment is a laminate of a first microporous film and a second microporous film, but the lamination mode is not particularly limited. Specific examples of the embodiment include (a) a laminate composed of one first microporous film and one second microporous film, and (b) one first microporous film and its A laminate comprising a second microporous film laminated on both sides, (c) a laminate comprising one second microporous film and a first microporous film laminated on both sides thereof, (D) Laminate in which the respective resin films are alternately arranged, such as first microporous film-second microporous film-first microporous film-second microporous film. Is mentioned.

As a manufacturing method of the lamination | stacking microporous film of this embodiment, after shape | molding the lamination | stacking film which laminated | stacked each resin film by (a) coextrusion method, for example using a T die or a circular die, the lamination | stacking film is extended | stretched (B) After each resin film is extruded separately, each resin film is laminated and laminated to form a laminated film, and then the laminated film is stretched to make it porous And (c) a method of extruding each resin film separately and further stretching to obtain a microporous film that has been made porous, respectively, and then laminating those microporous films. Among these, from the viewpoint of physical properties and applications required for the obtained laminated microporous film, each resin film is extruded separately with a T-die, and then laminated by laminating each resin film by a laminating method. Then, the method (b) in which the laminated film is stretched to make it porous is preferable. On the other hand, although the air permeability is slightly inferior to the method (a), the method (c) is also preferable from the viewpoint that the heat shrinkage rate of the laminated microporous film can be reduced.
In the present specification, “resin film” refers to a resin composition formed into a film shape, and a microporous film can be obtained by stretching the resin composition to make it porous.

  In any of the production methods, the draw ratio after extrusion, that is, the film winding speed (unit: m / min) is determined by the resin composition extrusion speed (linear speed in the flow direction of the molten resin passing through the die lip). Yes, the unit is m / min) is preferably in the range of 10 to 500, more preferably 100 to 400, and even more preferably 150 to 350. The film is wound so that the film winding speed is preferably about 2 to 400 m / min, and more preferably 10 to 200 m / min.

  Furthermore, it is preferable to perform a heat treatment (annealing) on the film obtained by molding as necessary. As an annealing method, for example, a method in which a film is brought into contact with a heating roll, a method in which the film is exposed to a heated gas phase, a method in which the film is wound on a core and exposed to a heated gas phase or a heated liquid phase, and a combination thereof And the like. The conditions for these heat treatments are appropriately determined depending on the type of material constituting the film.

The heating temperature when annealing the first resin film composed of the first resin composition (hereinafter also referred to as “high melting point resin film”) is a balance of porosity, air permeability, and heat shrinkage. From the viewpoint, it is preferably (T _mA- 50) ° C. or higher and (T _mA −2) ° C. or lower, more preferably (T _mA −40) ° C. or higher and (T _mA −10) ° C. or lower.

On the other hand, when the second resin film composed of the polyethylene resin composition Ac having a lower melting point (hereinafter also referred to as “low melting point resin film”) is annealed alone, the heating temperature is the porosity, the air permeability. From the viewpoint of the balance between the degree of heat shrinkage and the thermal shrinkage rate, it is preferably (T _mB −30) ° C. or more and (T _mB −2) ° C. or less, more preferably (T _mB −15) ° C. or more and (T _mB −2) ° C. It is as follows.

When the laminated film is annealed after laminating the high melting point resin film and the low melting point resin film, the heating temperature is preferably (T _mB- 30) from the viewpoint of obtaining a laminated microporous film having high adhesive strength. It is more than ( _TmB- 2) _degreeC , More preferably, it is ( _TmB- 15) _degreeC or more and ( _TmB- 2) _degreeC or less. The heating time is preferably 10 seconds to 100 hours, more preferably 1 minute to 10 hours.

  Annealing may be performed before each film is laminated or after lamination. When annealing is performed before lamination, annealing can be performed under conditions suitable for each of the high melting point resin film and the low melting point resin film. Thereby, a laminated microporous film having a better balance of porosity, air permeability, and heat shrinkage rate can be obtained. On the other hand, when annealing is performed after lamination, the resin films are laminated by thermocompression bonding in a state where the ratio of the amorphous part of the resin before annealing is high, so that a laminated microporous film with high adhesive strength is obtained. .

  The first microporous film is formed by subjecting a high melting point resin film to a predetermined stretching treatment to make it porous. The high melting point resin film preferably has an elastic recovery rate of 80 to 95% after heat treatment, and more preferably 84 to 92%.

  The second microporous film is formed by subjecting a low melting point resin film to a predetermined stretching treatment to make it porous. The low melting point resin film has an elastic recovery rate after heat treatment of preferably 50 to 80%, more preferably 60 to 75%. When the elastic recovery rate of each resin film is within the above range, a laminated microporous film having a sufficient degree of porosity tends to be obtained.

Here, the “elastic recovery rate after heat treatment” of the high melting point resin film and the low melting point resin film is derived as follows, respectively.
The high melting point resin film is annealed in air at 130 ° C. for 1 hour, and then cut into a strip shape having a width of 10 mm and a length of 50 mm to obtain a test piece. The test piece is set in a predetermined position of a tensile tester and is 100% in the length direction at a speed of 50 mm / min under the conditions of 25 ° C. and 65% relative humidity (that is, until the length becomes 100 mm). Elongate. Thereafter, the test piece is immediately relaxed at the same speed (50 mm / min), and the length of the test piece when the load becomes zero is measured. And based on following formula (1), the "elastic recovery rate after heat processing" of a high melting point resin film is derived | led-out.
Elastic recovery rate after heat treatment (%) = ((length of test piece when 100% stretched) − (length of test piece when relaxed to zero load)) / (test piece before stretching) Length) x 100 (1)
The low melting point resin film is annealed in air at 130 ° C. for 1 hour, and then cut into a strip shape having a width of 15 mm and a length of 2 inches (5.08 cm) to obtain a test piece. The specimen is set in place on a tensile tester and is up to 50% in length (ie, 3 inches long) at a speed of 2 inches / minute under conditions of 25 ° C. and 65% relative humidity. Elongate). The specimen is then held in its stretched state for 1 minute, and then the specimen is relaxed at the same speed (2 inches / minute) and the length of the specimen when the load becomes zero is measured. And based on following formula (2), the "elastic recovery rate after heat processing" of a low melting-point resin film is derived | led-out.
Elastic recovery rate after heat treatment (%) = ((length of test piece at 50% extension) − (length of test piece when relaxed and load becomes zero)) / ((at 50% extension) Test piece length) − (length of test piece before stretching)) × 100 (2)

Although it does not specifically limit as a manufacturing method of the lamination | stacking microporous film of this embodiment, It is preferable that the process of the following (A) and (B) is included.
(A) Cold-stretching step of cold-stretching the film at least in one direction by 1.05 to 2.0 times (B) After the cold-stretching step, the film is at least in one direction by 1.05 to 5.0 times In the case of forming a laminated film in which a high melting point resin film and a low melting point resin film are laminated in advance as in the methods (a) and (b) above, with respect to the laminated film It is preferable to include a cold stretching step in which the first stretching is performed to obtain a stretched laminated film. When the low melting point resin film and the high melting point resin film are separately made porous after lamination as in the method (c) above, each film is stretched by first stretching. It is preferable to include a cold stretching step for obtaining a laminated film.
When cold stretching is performed on a laminated film in which a high melting point resin film and a low melting point resin film are laminated, the stretching temperature of cold stretching is −20 ° C. or more from the viewpoint of preventing breakage, from the viewpoint of porosity and air permeability. ( _TmB- 60) ° C. or lower is preferable. More preferably, the temperature is 0 ° C. or higher and 50 ° C. or lower. Here, the drawing temperature of cold drawing means the surface temperature of the film in the cold drawing process. Here, the surface temperature of the film can be measured by a contact thermometer.

  The draw ratio in the cold drawing step is preferably 1.05 to 2.0 times, more preferably 1.1 times or more and less than 2.0 times. The cold stretching is performed in at least one direction, but may be performed in both the film extrusion direction (hereinafter referred to as “MD direction”) and the film width direction (hereinafter referred to as “TD direction”). Preferably, uniaxial stretching is performed only in the film extrusion direction.

  When the high melting point resin film is cold-drawn alone, the stretching temperature is preferably −20 ° C. or higher from the viewpoint of preventing breakage, and 90 ° C. or lower from the viewpoint of porosity and air permeability. More preferably, the temperature is 0 ° C. or higher and 50 ° C. or lower.

On the other hand, the temperature when the low melting point resin film is cold-drawn alone is preferably (T _mB −30) ° C. or higher (T _mB −2) ° C. from the viewpoint of the balance of porosity, air permeability and heat shrinkage. It is below, More preferably, it is ( _TmB- 15) _degreeC or more and ( _TmB- 2) degrees C or less.

It is preferable that the manufacturing method of the lamination | stacking microporous film of this embodiment includes the heat | fever extending process which gives a 2nd extending | stretching after a cold stretching process and obtains a stretched laminated film. When heat stretching is performed on a laminated film obtained by laminating a high melting point resin film and a low melting point resin film, the stretching temperature in the heat stretching step is (T _mB −60) ° C. or higher, porosity, permeability, from the viewpoint of preventing breakage. From the viewpoint of temper, (T _mB -2) ° C. or lower is preferable. More preferably, it is (T _mB −30) ° C. or higher and (T _mB −2) ° C. or lower. Here, the stretching temperature in the heat stretching process means the surface temperature of the film.

  The draw ratio in the heat drawing step is preferably 1.05 to 5.0 times, more preferably 1.1 to 5.0 times, and still more preferably 2.0 to 5.0 times. . The hot stretching may be performed in at least one direction and may be performed in both the MD and TD directions, but is preferably performed in the same direction as the cold stretching direction, and more preferably only in the same direction as the cold stretching direction. It is to perform uniaxial stretching.

  When the high melting point resin film is hot stretched alone, it is preferably hot stretched at least 1.05 times to 5.0 times in at least one direction while being kept at 90 ° C. or higher and 150 ° C. or lower.

On the other hand, when the low melting point resin film is hot stretched alone, it is maintained at (T _mB -60) ° C. or higher and (T _mB −2) ° C. or lower, at least 1.05 times to 5.0 times in one direction. It is preferable to heat-draw to the following.

  It is preferable that the manufacturing method of the lamination | stacking microporous film of this embodiment includes the process of heat-setting to a lamination | stacking film after a heat | fever extending process. Providing a heat setting step not only can suppress shrinkage in the stretching direction of the laminated microporous film due to residual stress acting during stretching, but also from the viewpoint of improving the delamination strength of the resulting laminated microporous film. Is preferred. As the heat setting method, a method of heat shrinking to the extent that the length of the laminated microporous film after heat setting is reduced by 3 to 50% (hereinafter, this method is referred to as “relaxation”), the dimension in the stretching direction is as follows. The method of fixing so that it may not change is mentioned.

When heat setting is performed on a laminated film in which a high melting point resin film and a low melting point resin film are laminated, the heat setting temperature is preferably (T _mB −30) ° C. or more and (T _mB −2) ° C. or less. More preferably, the temperature is (T _mB −15) ° C. or higher and (T _mB −2) ° C. or lower. Here, the heat setting temperature means the surface temperature of the film.

  The temperature when heat-fixing the high melting point resin film alone is preferably 100 ° C. or higher and 160 ° C. or lower, and more preferably 130 ° C. or higher and 155 ° C. or lower.

On the other hand, the temperature when the low melting point resin film is heat-set alone is preferably (T _mB −30) ° C. or higher and (T _mB −2) ° C. or lower, and (T _mB −15) ° C. or higher (T _mB ). -2) It is more preferable that it is below ℃.

  In the cold drawing step, the hot drawing step, other drawing steps and the heat setting step, the drawing is carried out in one or two or more stages in a uniaxial direction and / or biaxial direction by a roll, a tenter, an autograph or the like. A heat fixing method may be employed. Among these, from the viewpoint of physical properties and applications required for the laminated microporous film obtained in the present embodiment, it is preferable to perform two or more stages of uniaxial stretching and heat setting with a roll.

  After each resin film is extruded separately, a laminated film is formed by laminating and laminating each resin film by a laminating method, and then the laminated film is stretched and made porous to produce a laminated microporous film In this case, it is preferable to pass the high melting point resin film and the low melting point resin film between heated rolls and perform thermocompression bonding. In this case, each resin film is unwound from an original roll stand, and is laminated by being nipped and pressure-bonded between heated rolls. At the time of lamination, thermocompression bonding is performed so that the elastic recovery rate of each resin film does not substantially decrease. The same applies to the case where each resin film is extruded separately and further stretched to obtain a microporous film which has been made porous, and then the microporous film is bonded.

The temperature of the heated roll, in other words, the thermocompression bonding temperature is preferably 120 ° C. or higher and 140 ° C. or lower, more preferably 127 ° C. or higher and 132 ° C. or lower. When the thermocompression bonding temperature is 120 ° C. or higher, the peel strength between the laminated films increases, and peeling tends to hardly occur in each subsequent stretching step. In addition, when the thermocompression bonding temperature is 140 ° C. or lower, a low melting point resin film dissolves and its elastic recovery rate does not decrease, and a laminated microporous film that can solve the intended problem tends to be obtained. It is in. The nip pressure is suitably 1 to 3 kg / cm ² and the unwinding speed is suitably 0.5 to 8 m / min. Moreover, the range of 3-60g / 15mm is suitable for the peeling strength of a laminated film.

[First microporous film]
The first microporous film in this embodiment is made of polyethylene (PE), polypropylene (PP), polybutene-1, poly-4-methylpentene, polyolefin such as ethylene-propylene copolymer, ethylene-tetrafluoroethylene. It is preferably formed from a first resin composition mainly composed of a polymer containing an olefin hydrocarbon such as a copolymer as a monomer component.

The first resin composition has a higher melting point than the second resin composition, and the melting point T _mA is, for example, 150 ° C. to 280 ° C., and the balance between the film breaking temperature and the film formability is good. This is preferable.

  Further, when the first resin composition is a thermoplastic resin composition containing 100 parts by mass of polypropylene resin and 1 to 90 parts by mass of polyphenylene ether resin, the laminated microporous material is more excellent in heat resistance. This is preferable because a film tends to be obtained.

Hereinafter, the thermoplastic resin composition will be described in detail.
[Polypropylene resin]
The polypropylene resin (hereinafter sometimes abbreviated as “PP”) in the present embodiment is a polymer containing polypropylene as a monomer component, and may be a homopolymer or a copolymer. When it is a copolymer, it may be a random copolymer or a block copolymer. Moreover, when it is a copolymer, there is no limitation in a copolymerization component, For example, ethylene, butene, hexene, etc. are mentioned. When the polypropylene resin is a copolymer, the copolymerization ratio of propylene is preferably 50% by mass or more, 70% by mass or more, or 90% by mass or more.

A polypropylene resin is used individually by 1 type or in mixture of 2 or more types. The polymerization catalyst used for obtaining the polypropylene resin is not particularly limited, and examples thereof include a Ziegler-Natta catalyst and a metallocene catalyst.
Moreover, there is no restriction | limiting in particular also about the stereoregularity of a polypropylene resin, An isotactic or syndiotactic polypropylene resin is used.

  The polypropylene resin may have any crystallinity or melting point. In addition, two or more kinds of polypropylene resins having different crystallinity and melting point may be blended at a specific blending ratio depending on the physical properties and applications of the obtained microporous film.

  The melt flow rate (MFR) of polypropylene resin (according to ASTM D1238, measured under a load of 230 ° C. and 2.16 kg, the same applies hereinafter) is preferably 0.1 to 100 g / 10 minutes, more preferably 0.00. 1 to 80 g / 10 min.

  The polypropylene resin is a known modified polypropylene resin as described in JP-A-44-15422, JP-A-52-30545, JP-A-6-313078, and JP-A-2006-83294. There may be. Furthermore, the polypropylene resin may be a mixture in any proportion of the above-described polypropylene resin and the modified polypropylene resin.

[Polyphenylene ether resin]
Examples of the polyphenylene ether resin (hereinafter also referred to as “PPE”) in the present embodiment include those having a repeating unit represented by the following general formula (3).

Here, in formula (3), R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, a halogen atom, a lower alkyl group having 1 to 7 carbon atoms, a phenyl group, a haloalkyl group, or an aminoalkyl. And a group selected from the group consisting of a group, a hydrocarbonoxy group, and a halohydrocarbonoxy group in which at least two carbon atoms separate a halogen atom and an oxygen atom.

  Specific examples of PPE include poly (2,6-dimethyl-1,4-phenylene ether), poly (2-methyl-6-ethyl-1,4-phenylene ether), and poly (2-methyl-6). -Phenyl-1,4-phenylene ether) and poly (2,6-dichloro-1,4-phenylene ether). Further, as PPE, for example, polyphenylene ether copolymer such as a copolymer of 2,6-dimethylphenol and other phenols (for example, 2,3,6-trimethylphenol and 2-methyl-6-butylphenol). Examples include coalescence. Among these, poly (2,6-dimethyl-1,4-phenylene ether) and a copolymer of 2,6-dimethylphenol and 2,3,6-trimethylphenol are preferable, and poly (2 , 6-dimethyl-1,4-phenylene ether) is more preferable.

Moreover, it does not specifically limit regarding the manufacturing method of PPE, If it is PPE obtained by a well-known manufacturing method, it can be used for this embodiment.
As PPE, the above-mentioned PPE and a styrenic monomer and / or an α, β-unsaturated carboxylic acid or a derivative thereof (for example, an ester compound, an acid anhydride compound) in the presence or absence of a radical generator, It is also possible to use a known modified PPE obtained by reacting at a temperature of 80 to 350 ° C. in a molten state, a solution state or a slurry state. Furthermore, the mixture of the above-mentioned PPE and this modified PPE in arbitrary ratios may be sufficient. The reduced viscosity of PPE used in the present embodiment is preferably 0.15 to 2.5, and more preferably 0.30 to 2.00. Here, the reduced viscosity of PPE is a value measured using an Ubbelohde viscosity tube under the condition of a chloroform solution having a concentration of 0.5 g / dl at 30 ° C.

  As the PPE in this embodiment, in addition to the above-mentioned PPE, a so-called polymer alloy in which other polymers such as polystyrene, high impact polystyrene, syndiotactic polystyrene and / or rubber reinforced syndiotactic polystyrene are added to PPE. Are also preferably used. In this case, the amount of PPE below includes the mass of other polymers.

  The thermoplastic resin composition in this embodiment is preferably a polyphenylene ether resin, preferably 1 to 90 parts by weight, more preferably 5 to 90 parts by weight, and still more preferably 10 to 100 parts by weight of polypropylene resin and polypropylene resin. It contains 80 parts by mass, particularly preferably 20 to 65 parts by mass. Setting the content ratio of PPE within the above range is preferable from the viewpoint of stretchability of the laminated microporous film.

[Admixture]
The first microporous film in the present embodiment preferably has a sea-island structure composed of a sea part which is a phase containing a polypropylene resin and an island part which is a phase containing a polyphenylene ether resin. Here, the sea-island structure means that the polyphenylene ether resin is dispersed in the polypropylene resin matrix.

  The particle size of the island part is preferably 0.01 μm to 10 μm. In order to control the size (particle size) of the island part, the thermoplastic resin composition particularly preferably contains an admixture in addition to the polypropylene resin and the polyphenylene ether resin.

  The admixture acts as a dispersant for dispersing the polyphenylene ether resin in the above-described polypropylene resin matrix. Furthermore, the admixture has an effect of imparting good porosity and air permeability to the laminated microporous film.

  The admixture in the present embodiment is preferably a hydrogenated block copolymer from the viewpoint of dispersibility of the polyphenylene ether resin. As the hydrogenated block copolymer, for example, at least one polymer block A mainly composed of a structural unit derived from a vinyl aromatic compound and at least one composed mainly of a structural unit derived from a conjugated diene compound. And a block copolymer obtained by adding hydrogen to the block copolymer.

  Examples of the vinyl aromatic compound include one or more selected from the group consisting of styrene, α-methylstyrene, vinyltoluene, p-tert-butylstyrene, and diphenylethylene. Of these, styrene is preferred.

  The polymer block A mainly composed of a structural unit derived from a vinyl aromatic compound is preferably a polymer block containing 70% by mass or more of a structural unit derived from a vinyl aromatic compound. Examples thereof include a polymer block or a copolymer block of a vinyl aromatic compound and a monomer copolymerizable with the vinyl aromatic compound.

  Examples of the conjugated diene compound include one or more selected from the group consisting of butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Among these, butadiene, isoprene and combinations thereof are preferable. The polymer block B mainly composed of a structural unit derived from a conjugated diene compound is preferably a polymer block containing at least 70% by mass of a structural unit derived from a conjugated diene compound, and a homopolymer of a conjugated diene compound Examples thereof include a block or a copolymer block of a conjugated diene compound and a monomer copolymerizable with the conjugated diene compound.

  Regarding the microstructure (bonded form of the conjugated diene compound) in the polymer block B, the sum of the 1,2-vinyl bond amount and the 3,4-vinyl bond amount (hereinafter simply referred to as “vinyl bond amount”) is used. It is preferable that it is 40 to 90%, More preferably, it is 45 to 85%.

  Here, the “vinyl bond amount” is the number of 1,2- and 3,4-vinyl bonds remaining in the polymer block B after polymerization with respect to the total number of vinyl bonds that the conjugated diene compound had before polymerization. The percentage of the total number. The bond form and “vinyl bond amount” of these conjugated diene compounds are derived from infrared spectroscopy. However, the “vinyl bond amount” derived using the NMR spectrum may be converted into a value derived from the infrared spectrum. The conversion can be carried out by deriving the “vinyl bond amount” from the infrared spectrum and the NMR spectrum for a polymer having the same vinyl bond amount, and creating a calibration curve between these measurement methods. it can. When the vinyl bond amount is in the above range, the dispersibility of the polyphenylene ether resin tends to be improved.

The number average molecular weight of the block copolymer having the above structure is preferably in the range of 5,000 to 1,000,000 when measured by gel permeation chromatography using polystyrene as a standard substance. When the number average molecular weight of the block copolymer is within the above range, the dispersibility of the polyphenylene ether resin tends to be improved. The molecular weight distribution, which is the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) measured by gel permeation chromatography using polystyrene as a standard substance, is preferably 10 or less. When the molecular weight distribution of the block copolymer is 10 or less, the dispersibility of the polyphenylene ether resin tends to be improved.
Furthermore, the molecular structure of this block copolymer may be any of linear, branched, radial, or any combination thereof.

  The block copolymer having such a structure is obtained by adding hydrogen to an aliphatic double bond (vinyl bond) contained in the block copolymer, thereby providing a hydrogenated block copolymer, that is, a vinyl aromatic compound-conjugated diene compound. It becomes a hydrogenated product of a block copolymer and is used as an admixture.

  The hydrogenation rate of the block copolymer (the proportion of the aliphatic double bonds of the block copolymer that are hydrogenated (%)) is the aliphatic double of the block copolymer before hydrogenation. It is preferably 80% or more, more preferably 90% or more, based on the total amount of bonds. When the hydrogenation rate of the block copolymer is in the above range, the dispersibility of the polyphenylene ether resin tends to be improved. This hydrogenation rate is derived from the infrared spectrum as in the case of the vinyl bond described above, but the value of the hydrogenation rate derived from the NMR spectrum is converted to a value derived from the infrared spectrum. May be.

  The proportion of the admixture in the thermoplastic resin composition is preferably 1 to 20 parts by mass, more preferably 1 to 15 parts by mass with respect to 100 parts by mass of the polypropylene resin. When the proportion of the admixture is in the above range, the dispersibility of the polyphenylene ether resin is improved, and the porosity and air permeability of the laminated microporous film resulting from the dispersibility are improved.

  In addition to the above components, the thermoplastic resin composition according to the present embodiment includes, as necessary, additional components such as an olefin elastomer and an antioxidant within a range that does not impair the effects exhibited by the present invention. Agent, metal deactivator, heat stabilizer, flame retardant (organic phosphate ester compound, ammonium polyphosphate compound, aromatic halogen flame retardant, silicone flame retardant, etc.), fluorine polymer, plasticizer (low (Molecular weight polyethylene, epoxidized soybean oil, polyethylene glycol, fatty acid esters, etc.), flame retardant aids such as antimony trioxide, weathering (light) improvers, polyolefin nucleating agents, slip agents, inorganic or organic fillers and Reinforcing materials (polyacrylonitrile fiber, carbon black, titanium oxide, calcium carbonate, conductive metal fiber, conductive carbon black, etc.), Seed colorants, mold release agents and the like may be added.

[Sea-island structure]
The high melting point resin film according to the present embodiment preferably has a sea-island structure composed of a sea part which is a phase containing a polypropylene resin and an island part which is a phase containing a polyphenylene ether resin. In the present embodiment, the “sea-island structure” is a structure in which a skeleton of a phase including a polypropylene resin as a sea part is formed between island components composed of phase particles including a polyphenylene ether resin. In other words, it refers to a structure in which a polyolefin ether resin is dispersed in a plurality of islands in a matrix (matrix) made of polypropylene resin.
The sea-island structure (dispersed state) as described above can be easily measured and observed using a transmission electron microscope or the like. For example, after a high melting point resin film to be measured is loaded on a sample stage, the high melting point resin film is coated with an osmium coating with a thickness of about 3 nm and an acceleration voltage is set to 1 kV (HITACHI S-4700). ).

The particle size of the island is preferably 0.01 μm to 10 μm, more preferably 0.1 μm to 5 μm. Setting the particle size of the islands in the above range can contribute to more uniformly dispersing the apertures of the finally obtained laminated microporous film in the film thickness direction and the film surface direction. A laminated microporous film in which the apertures are uniformly dispersed is suitable as a battery separator.
In the present embodiment, the particle size of the island portion is measured as follows.
First, a transmission electron micrograph (magnification: 5,000 times) is obtained in the same manner as the measurement method when observing the sea-island structure for the high melting point resin film to be measured. Next, 100 particles of a phase (island part) containing a polyphenylene ether resin dispersed in a phase containing a polypropylene resin as a matrix (sea part) are arbitrarily selected from the photograph. Then, the maximum length of each selected particle is measured as the major axis diameter, and the minimum length is measured as the minor axis diameter. The particle diameter is defined as the major axis diameter. As for this particle size, the arithmetic average value for 100 particles is preferably in the above range, and more preferably in the above range for all 100 particles.

The ratio of the major axis diameter to the minor axis diameter (major axis diameter / minor axis diameter) is preferably 1 to 5, and more preferably 1 to 3. It is preferable to adjust the ratio of the major axis diameter to the minor axis diameter in the above range from the viewpoint of the openability of the laminated microporous film.
In addition, by appropriately selecting the polypropylene resin, polyphenylene ether resin, and admixture to be used, particles of the phase containing the polyphenylene ether resin having the above-mentioned particle diameter, ratio of major axis diameter to minor axis diameter (island part) ) Can be dispersed in a phase containing a polypropylene resin which is a matrix (sea part).

  In this embodiment, the laminated microporous film obtained by using a high melting point resin film formed from a specific thermoplastic resin composition containing a polypropylene resin and a polyphenylene ether resin has excellent porosity and air permeability. And can be suitably used as a separator for a lithium ion battery. This laminated microporous film includes a high melting point resin film formed from a thermoplastic resin composition having a polypropylene resin as a base material (matrix), but at a temperature exceeding the melting point of the polypropylene resin of 200 ° C. It is a laminated microporous film with improved heat resistance capable of maintaining its form as a film.

  When the laminated microporous film is applied to a battery separator, the improvement in heat resistance brings about an increase in the film breaking temperature as shown in a battery oven test or the like that has been carried out in recent years. The laminated microporous film of the present embodiment can realize a film breaking temperature of 200 ° C. or higher, and the laminated microporous film having such a film breaking temperature has greatly improved the heat resistance as a battery separator. Can be improved.

[Low melting point resin film]
The second microporous film in the present embodiment has a melting point lower than that of the first resin composition, contains a polyethylene resin, and has a ratio η _e / extension viscosity η _e to shear viscosity η _s . It is obtained by stretching and making a low melting point resin film composed of the second resin composition (polyethylene resin composition Ac) having η _s of 15 to 100. Polyethylene resin composition in the present embodiment Ac is the ratio of the extensional viscosity eta _e for the shear viscosity η _s η _e / η _s is 15 to 100, preferably 20 to 80, more preferably 30 to 50 is there. If η _e / η _s is 15 or more, the air permeability of the laminated microporous film is good, and if it is 100 or less, it is difficult to break during film formation. In this specification, the units of the shear viscosity η _s and the extension viscosity η _e are both “Pa · s”.

The elongation viscosity η _e of the polyethylene resin composition Ac is a value measured under the conditions of a temperature of 180 ° C. and an elongation strain rate of 10 s ⁻¹ , and the Cogswell theory [Polymer Engineering] is used by using an inflow pressure loss method with a twin capillary rheometer. Science, 12, 64 (1972)]. Further, the shear viscosity η _s is a value measured under the conditions of a temperature of 180 ° C. and a shear strain rate of 100 s ⁻¹ , and the Cogswell's theory using the inflow pressure loss method with a twin capillary rheometer as in the case of the extension viscosity η _e Can be measured according to.

The present inventors have found that the electrical resistance value of the obtained laminated microporous film is remarkably improved by using the polyethylene resin composition Ac having the ratio η _e / η _s within the above range. This factor is not completely elucidated, and the present inventors consider the following as one of them. That is, by increasing the elongation viscosity to some extent with respect to the shear viscosity, the melted polyethylene resin in the polyethylene resin composition Ac is easily oriented in the extrusion direction during film forming, and as a result, the crystal orientation of the polyethylene resin. Is thought to improve. When the crystal orientation of the polyethylene resin is improved, it is considered that cleavage between crystals occurs uniformly in each stretching step described later, and the electric resistance value of the resulting laminated microporous film is improved.

  When the melting point of the polyethylene resin composition Ac constituting the low melting point resin film is 100 ° C. to 150 ° C., the safety of the battery tends to improve when the laminated microporous film is used as a battery separator. This is preferable. In order to obtain the polyethylene resin composition Ac having the above melting point, a polyethylene resin having a melting point of 100 ° C. to 150 ° C. may be contained in the resin composition. Examples of the polyethylene resin having a melting point of 100 ° C. to 150 ° C. include high density polyethylene, medium density polyethylene, and low density polyethylene. Among these, a high density polyethylene resin is preferably used.

  The melt flow rate (MFR) of the polyethylene resin composition Ac in the present embodiment is preferably 0.01 to 20 g / 10 minutes, more preferably 0.1 to 10 g / 10 minutes, and still more preferably 0. .5 to 5.0 g / 10 min. When the MFR is 0.01 g / 10 min or more, it tends to be difficult for fish eyes to occur in the raw film obtained by molding the polyethylene resin composition Ac (hereinafter also referred to as “raw film Af”). In addition, if it is 20 g / 10 min or less, draw-down hardly occurs and the film formability tends to be good. The MFR of the polyethylene resin composition Ac is measured according to the method described in the following examples.

  In general, fisheye is a small sphere formed in a film-like or sheet-like product, as defined in Polymer Editorial Board, Polymer Dictionary, Taiseisha, 2000, 6th edition, 337 pages, etc. The name was given because there are many things that are transparent, like fish eyes. Fisheye is distinguished from its production factors, with unmelted lumps resulting from insufficient kneading of molding materials, lumps due to part of the raw material gelling, lumps due to partial deterioration of the material being molded, and foreign matter as the core. Various things, such as a thing, are mentioned. However, in this specification, the fish eye originates from the material used as the raw material of the microporous film, and excludes those having foreign matter as the core. In addition, the foreign material includes, for example, cellulose, dust, metal pieces, resin carbide, plastics of different types, lint, and pieces of paper.

  The portion of the fish eye in the raw film Af often does not become porous even when stretched. Therefore, if a large amount of fish eye exists, the air permeability of the microporous film decreases. Further, when the film is heat-stretched, the film may break from the fish eye, which is not preferable from the viewpoint of productivity of the microporous film. Therefore, in the raw film Af obtained from the polyethylene resin composition Ac, the number of fish eyes of 0.1 mm or more is preferably 100 or less per 10 g of the raw film Af, more preferably 50 or less. preferable. As a method of reducing the number of fish eyes of the raw film Af, a method of increasing the MFR of the polyethylene resin composition Ac to, for example, 0.01 g / 10 min or more, the molecular weight distribution of the polyethylene resin composition Ac, for example, 2 to The method of adjusting to the range of 30 is mentioned. In addition, the number of fish eyes of the raw fabric film Af is measured according to the method described in the following examples.

The density of the polyethylene resin composition Ac according to the present embodiment is preferably 945~970kg / ^{m 3,} more preferably from 955~965kg / ^{m 3,} more preferably from 960~965kg / ^{m 3.} When the density of the polyethylene resin composition Ac is 945 kg / m ³ or more, a microporous film with better air permeability tends to be obtained, and when it is 970 kg / m ³ or less, the film breaks when stretched It tends to be difficult. The density of the polyethylene resin composition Ac is measured according to the method described in the following examples.

  The molecular weight distribution of the polyethylene resin composition Ac in the present embodiment is a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (hereinafter referred to as “Mw / Mn”), and is 2.0 to 30.0. It is preferable that it is preferably 6.0 to 10.0, and more preferably 7.0 to 9.0. When Mw / Mn is 2.0 or more, heat generation when the polyethylene resin composition Ac is formed into the raw film Af is suppressed, and fish eyes due to resin deterioration tend to be hardly generated, and 30.0 or less. When it is, it exists in the tendency for the fish eye derived from a high molecular weight component to decrease. Mw and Mn are obtained from gel permeation chromatography (hereinafter referred to as “GPC”) using polystyrene as a standard sample, and are measured in detail according to the methods described in the Examples below.

  In the polyethylene resin composition Ac in the present embodiment, the number of terminal vinyl groups per 10,000 carbon atoms of the polyethylene resin is preferably 5.0 or less, more preferably 3.0 or less, and 1.0 More preferably, the number is less than or equal to. When the number of terminal vinyl groups per 10,000 carbon atoms is 5.0 or less, the thermal stability at the time of molding the polyethylene resin composition Ac becomes good, and fish eyes due to resin deterioration tend not to occur. The number of terminal vinyl groups per 10,000 carbon atoms of the polyethylene resin is measured according to the method described in the following examples.

  The polyethylene resin composition Ac is a polyethylene resin having a long branched chain produced by polymerizing ethylene and, if necessary, other monomers using a chromium-based catalyst (hereinafter also referred to as “polyethylene resin Bp”). In addition, an ultrahigh molecular weight polyethylene resin (hereinafter, also referred to as “polyethylene resin Cp”) produced by other-stage polymerization of ethylene and, if necessary, other monomers using a titanium-based catalyst. It is also preferable to contain, and it is more preferable to contain both of these polyethylene resins.

For example, in the polyethylene resin composition Ac, a η _e / η _s produced using a chromium-based catalyst is greater than 100, and a η _e / η _s produced using a titanium-based catalyst is more than 15. A small polyethylene resin can be used, and the polyethylene resin composition as a whole can have a ratio η _e / η _s adjusted to a range of 15 to 100. Alternatively, the polyethylene resin composition Ac is obtained by melt-kneading a polyethylene resin having a ratio η _e / η _s smaller than 15 together with a crosslinking agent such as an organic peroxide, and appropriately crosslinking the resin to obtain a ratio η _e / η _s of 15 to You may contain the polyethylene resin adjusted to the range of 100.

  Next, a resin composition containing polyethylene resin Bp (hereinafter, also referred to as “polyethylene resin composition Bc”) will be described.

  Examples of the chromium-based catalyst used for producing the polyethylene resin Bp include a solid catalyst in which a chromium compound is supported on an inorganic oxide carrier, or a catalyst obtained by mixing or reacting the solid catalyst and an organometallic compound. The catalyst may be a known catalyst. Specifically, JP-B Nos. 44-2996, 47-1365, 44-3827, 44-2337, 47-19985, 45-40902, 49 No. 38986, No. 56-18132, No. 59-5602, No. 59-50242, No. 59-5604, Japanese Patent Publication No. 1-1277, No. 1-112778, No. 1 -12781, JP-A-11-302465, JP-A-9-25312, JP-A-9-25313, JP-A-9-25314, JP 7-503739, US Pat. No. 5,104,841 No. 5,137,997 and the like are exemplified as the chromium-based catalyst.

  As polyethylene resin composition Bc in this embodiment, what contains polyethylene resin Bp manufactured by the method described in Unexamined-Japanese-Patent No. 2001-294613 etc. is preferable. That is, the polyethylene resin composition Bc is a mixture of a chromium oxide catalyst supported on a refractory compound and activated by heat treatment in a non-reducing atmosphere, and an organoaluminum compound having both an alkoxy group and a hydrosiloxy group. Polyethylene resin produced by polymerization of ethylene and, if necessary, other monomers in the presence of a polymerization catalyst obtained by mixing or reacting a solid catalyst component obtained by reaction with an organoaluminum compound having an alkoxy group It is preferable to contain Bp.

In order to obtain the polyethylene resin Bp of the present embodiment, a particularly preferred polymerization catalyst is a chromium oxide catalyst supported on a refractory compound and activated by heat treatment in a non-reducing atmosphere, and represented by the following general formula (4). A solid catalyst component obtained by mixing or reacting an organoaluminum compound having both an alkoxy group and a hydrosiloxy group, and an organoaluminum compound having an alkoxy group represented by the following general formula (5) Alternatively, it is a polymerization catalyst obtained by reaction.
_{^{AlR 1 p H q (OR 2}} ) x (OSiHR 3 R 4) y (4)
Here, in the formula (4), p, q, x, and y are p ≧ 1, 0 ≦ q ≦ 1, x ≧ 0.25, y ≧ 0.15, 0.5 ≦ x + y ≦ 1.5 and p + q + x + y = 3 is satisfied, and R ¹ , R ² , R ³ and R ⁴ represent a hydrocarbon group having 1 to 20 carbon atoms which may be the same or different from each other.
AlR ⁵ _3-n (OR ⁶ ) _n (5)
Here, in formula (5), n satisfies 0 <n ≦ 1, and R ⁵ and R ⁶ represent a hydrocarbon group having 1 to 20 carbon atoms which may be the same or different from each other.

  The polyethylene resin Bp in the present embodiment is produced by a known polymerization method such as suspension polymerization, solution polymerization, or gas phase polymerization.

  The polyethylene resin composition Bc only needs to contain the polyethylene resin Bp obtained as described above, and may further contain various catalysts such as unreacted ethylene and a polymerization catalyst used for polymerization, and additives. Good.

  The MFR of the polyethylene resin composition Bc is preferably 0.5 to 10 g / 10 minutes, more preferably 0.5 to 3 g / 10 minutes, and further preferably 0.8 to 2.0 g / 10 minutes. Yes, particularly preferably 1.0 to 1.6 g / 10 min. When the MFR of the polyethylene resin composition Bc is 0.5 g / 10 min or more, it tends to be difficult for fish eyes to occur in the raw film Af, and when it is 10 g / 10 min or less, drawdown hardly occurs. The film formability tends to be good.

Moreover, the density of the polyethylene resin composition Bc is preferably 945 to 970 kg / m ³ . When the density of the polyethylene resin composition Bc is 945 kg / m ³ or more, the rigidity of the laminated microporous film of the present embodiment tends to increase. The density of the polyethylene resin composition Bc is more preferably 955 to 970 kg / m ³ , still more preferably 960 to 967 kg / m ³ , and particularly preferably 963 to 967 kg / m ³ . When the density is 945 kg / m ³ or more, a laminated microporous film with better air permeability tends to be obtained, and when it is 970 kg / m ³ or less, the film tends to be difficult to break when stretched. is there.

  Next, a resin composition containing the polyethylene resin Cp (hereinafter also referred to as “polyethylene resin composition Cc”) will be described.

  Examples of the titanium-based catalyst used for producing the polyethylene resin Cp include a titanium compound on a carrier such as a porous polymer material, an inorganic solid oxide of an element belonging to Group 2, 3, 4, 13 or 14 of the periodic table. And a known catalyst may be used. In the above porous polymer material, examples of the matrix material include polyethylene, polypropylene, polystyrene, ethylene-propylene copolymer, ethylene-vinyl ester copolymer, styrene-divinylbenzene copolymer, ethylene-vinyl ester copolymer. Examples thereof include polyolefins such as coalesced parts or completely saponified products and modified products thereof, thermoplastic resins such as polyamide, polycarbonate, and polyester, and thermosetting resins such as phenol resin, epoxy resin, urea resin, and melamine resin. Examples of the inorganic solid oxide include silica, alumina, magnesia, magnesium chloride, zirconia, titania, boron oxide, calcium oxide, zinc oxide, barium oxide, vanadium pentoxide, chromium oxide, thorium oxide, and the like. A mixture or a composite oxide thereof may be mentioned.

  Specifically, Japanese Patent Publication Nos. 52-36788, 52-36790, 52-36791, 52-35792, 52-50070, 52-36794, 52 No. -36795, No. 52-36796, No. 52-36915, No. 52-36917, No. 53-6019, JP-A-50-21876, No. 50-31835, The catalyst described in 50-72044 gazette, 50-78619 gazette, 53-40696 gazette, and a pamphlet of WO99 / 28353 is illustrated as said titanium-type catalyst.

Examples of the titanium-based catalyst include: (a) a solid catalyst component obtained by reacting an organic magnesium compound represented by the following general formula (6) and (b) a titanium compound having at least one halogen atom; A polymerization catalyst obtained by mixing or reacting with a metal compound, or the group consisting of (a) an organomagnesium compound, (b) a titanium compound, and (c) Al, B, Si, Ge, Sn, Te, and Sb A polymerization catalyst obtained by mixing or reacting a solid catalyst component obtained by reacting a halide compound of an element selected with an organic metal compound is preferred.
^{_{M α Mg β R 1 p R}} 2 q X r Y s (6)
Here, in the formula (3), α is 0 or a number greater than 0, p, q, r, and s are 0 or a number greater than 0, and the relationship of p + q + r + s = mα + 2β is satisfied. M represents a metal element belonging to Group 1, Group 2 or Group 3 of the periodic table, and m represents the valence of M. R ¹ and R ² each represent a hydrocarbon group having 1 to 20 carbon atoms which may be the same or different, and X and Y are monovalent groups which may be the same or different, each having a halogen atom, ^{-OR 3, -OSiR 4 R 5 R} 6, -NR 7 R 8, or an -SR ^{9. R 3, R 4, R 5} , R 6, R 7, R 8 represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, ^{R 9} represents a hydrocarbon group having 1 to 20 carbon atoms.

  The organometallic compound is preferably a compound having a metal element belonging to Group 1, Group 2 or Group 3 of the periodic table, and particularly preferably an organoaluminum compound or an organomagnesium compound complex containing an organoaluminum compound.

  The reaction between the solid catalyst component and the organometallic compound can be carried out by adding both components in the polymerization system and under the polymerization conditions with the progress of the polymerization, or may be performed in advance prior to the polymerization. Moreover, it is preferable that the reaction ratio of both components is the range of 1-3000 mmol of organometallic compounds with respect to 1g of solid catalyst components.

  The polyethylene resin Cp in the present embodiment is produced by a known polymerization method such as suspension polymerization, solution polymerization, or gas phase polymerization.

The polyethylene resin Cp is preferably a polymer composed of a low molecular weight polymer component and a high molecular weight polymer component, which are two-stage polymerized using a titanium-based catalyst. Here, the MFR of the low molecular weight polymer component is preferably 1 to 200 g / 10 minutes, more preferably 5 to 100 g / 10 minutes, and still more preferably 10 to 50 g / 10 minutes. The density of the low molecular weight polymer component is preferably 945 to 975 kg / m ³ , more preferably 955 to 975 kg / m ³ . The low molecular weight polymer component is obtained by homopolymerization of ethylene or copolymerization of ethylene and an α-olefin having 3 to 20 carbon atoms. When producing a low molecular weight polymer component by suspension polymerization, the low molecular weight polymer component is preferably produced in a solution containing 2.0 mol% or less of an α-olefin.

  In addition, since the high molecular weight polymer component obtained by the two-stage polymerization is mixed with the low molecular weight polymer component in the polyethylene resin Cp, its MFR and density cannot be measured, but the polyethylene resin Cp containing it or It is preferable that the polyethylene resin composition Cc has a physical property range described later. The high molecular weight polymer component is obtained by adding ethylene and, if necessary, an α-olefin having 3 to 20 carbon atoms and polymerizing them in the presence of the low molecular weight polymer component obtained as described above. It is done. The content ratio of the high molecular weight polymer component to the total amount of the polymer composed of the low molecular weight polymer component and the high molecular weight polymer component is preferably 30 to 70% by mass.

  The MFR of the polyethylene resin composition Cc is preferably 0.1 to 5.0 g / 10 minutes, more preferably 0.2 to 2.0 g / 10 minutes, still more preferably 0.4 to 1.6 g / 10. Min, particularly preferably 0.6 to 1.4 g / 10 min. When the MFR of the polyethylene resin composition Cc is 0.1 g / 10 min or more, fish eyes tend to be hardly generated in the raw film Af, and when it is 5.0 g / 10 min or less, drawdown occurs. It becomes difficult and the film formability tends to be good.

The density of the polyethylene resin composition Cc is preferably 935 to 970 kg / m ³ , more preferably 940 to 965 kg / m ³ , and still more preferably 950 to 963 kg / m ³ . When the density of the polyethylene resin composition Cc is 935 kg / m ³ or more, a laminated microporous film having better air permeability tends to be obtained, and when it is 970 kg / m ³ or less, the film is stretched when stretched. It tends to be difficult to break.

  The polyethylene resin Cp is obtained by homopolymerizing ethylene to produce a low molecular weight polymer component and then copolymerizing the low molecular weight polymer component, ethylene and an α-olefin having 3 to 20 carbon atoms. Is preferred.

  Here, examples of the α-olefin having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene and 1-dodecene. , 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicocene are selected from one or more compounds.

  The polyethylene resin composition Cc only needs to contain the polyethylene resin Cp obtained as described above, and may further contain various catalysts such as unreacted ethylene and a polymerization catalyst used for polymerization, and additives. Good.

When the polyethylene resin composition Ac contains the polyethylene resin composition Bc and the polyethylene resin composition Cc, the mass ratio (B / C) of the polyethylene resin composition Bc to the polyethylene resin composition Cc is B / C. C = 5/95 to 95/5 is preferable, and 30/70 to 70/30 is more preferable. When the mass ratio (B / C) is 5/95 or more, it becomes easy to obtain a polyethylene resin composition Ac with a ratio η _e / η _s of 15 to 100, and the resulting laminated microporous film has good air permeability. It tends to be. On the other hand, when the mass ratio is 95/5 or less, it becomes easy to obtain a polyethylene resin composition Ac having a terminal vinyl group number of 5.0 or less, and a raw film having good thermal stability and less fish eyes due to resin deterioration. Af tends to be obtained.

  There is no particular limitation on the mixing method when the polyethylene resin composition Ac is produced by mixing the polyethylene resin composition Bc and the polyethylene resin composition Cc, and a normal method of mixing in a powder state, a slurry state, a pellet state, or the like. Is used. When kneading them, they may be kneaded at a temperature of 150 to 300 ° C. using a uniaxial or biaxial extruder, a kneader or the like.

  In addition, the polyethylene resin composition Ac in the present embodiment includes, in addition to the above-described components, other additional components as necessary within a range not impairing the features and effects of the present invention, such as olefin elastomers and antioxidants. , Metal deactivators, heat stabilizers, flame retardants (organic phosphate compounds, ammonium polyphosphate compounds, aromatic halogen flame retardants, silicone flame retardants, etc.), fluoropolymers, plasticizers (low molecular weight Polyethylene, epoxidized soybean oil, polyethylene glycol, fatty acid esters, etc.), flame retardant aids such as antimony trioxide, weather resistance (light) improvers, polyolefin nucleating agents, slip agents, inorganic or organic fillers, Reinforcing materials (polyacrylonitrile fiber, carbon black, titanium oxide, calcium carbonate, conductive metal fiber, conductive carbon black ), Various coloring agents, may contain a releasing agent. The total content of these additional components is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less with respect to 100 parts by mass of the polyethylene resin composition Ac. is there.

[Physical properties of laminated microporous film]
The porosity of the laminated microporous film of the present embodiment is preferably 20% to 70%, more preferably 35% to 65%, and still more preferably 45% to 60%. When the porosity is 20% or more, sufficient ion permeability can be secured when the laminated microporous film is used as a battery separator. On the other hand, when the porosity is 70% or less, the laminated microporous film can ensure sufficient mechanical strength.

The porosity of the laminated microporous film of the present embodiment can be adjusted to the above range by appropriately setting the composition of the resin composition constituting each layer, the stretching temperature, the stretching ratio, and the like. The porosity of the laminated microporous film is calculated by cutting out a 10 cm × 10 cm square sample from the film and using the following formula from the volume and mass of the sample.
Porosity (%) = (volume (cm ³ ) −mass (g) / density of resin composition (g / cm ³ )) / volume (cm ³ ) × 100

  The air permeability of the laminated microporous film of the present embodiment is preferably 10 seconds / 100 cc to 5000 seconds / 100 cc, more preferably 50 seconds / 100 cc to 1000 seconds / 100 cc, and even more preferably 100 seconds / 100 cc to 500 seconds. / 100cc. Setting the air permeability to 5000 seconds / 100 cc or less is preferable from the viewpoint of ensuring sufficient ion permeability of the laminated microporous film. On the other hand, setting the air permeability to 10 seconds / 100 cc or more is preferable from the viewpoint of obtaining a more uniform laminated microporous film having no defects. In addition, the air permeability of the laminated microporous film of this embodiment can be adjusted to the above-mentioned range by appropriately setting the composition of the resin composition constituting each layer, the stretching temperature, the stretching ratio, and the like. The air permeability is measured using a Gurley type air permeability meter according to JIS P-8117.

  5-40 micrometers is preferable and, as for the film thickness of the lamination | stacking microporous film of this embodiment, 10-30 micrometers is more preferable. When the film thickness is 5 μm or more, the mechanical strength tends to be excellent, and when it is 40 μm or less, the battery tends to be effective for downsizing.

  The laminated microporous film in the present embodiment is suitably used as a battery separator, more specifically as a lithium secondary battery separator. In addition, it is used as various separation membranes.

  In addition, each physical property in this specification can be measured according to the method described in the following Examples, unless otherwise specified.

Next, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist.
The evaluation methods for various characteristics in Examples and Comparative Examples are as follows.

(1) Melting point It measured by the method based on JIS K-7121.

(2) Melt flow rate (MFR)
The MFR was measured under the conditions of 210 ° C. and 2.16 kg for the polypropylene resin and 190 ° C. and 2.16 kg for the polyethylene resin in accordance with JIS K7210. The unit of MFR is g / 10 minutes.

(3) Density The density of the polyethylene resin composition was measured according to JIS K7112. The unit of density is kg / m ³ .

(4) Molecular weight distribution (Mw / Mn)
The molecular weight distribution of the polyethylene resin composition was calculated as the ratio Mw / Mn between the weight average molecular weight (Mw) and the number average molecular weight (Mn) obtained from gel permeation chromatography (GPC). The GPC measurement was performed using a GPS device (trade name “HLC-8121GPC / HT”) manufactured by Tosoh Corporation. As the column, trade name “TSKgel GMHHR-H (20)” (2) manufactured by Tosoh Corporation was used, mobile phase o-dichlorobenzene (o-DCB), column temperature 155 ° C., flow rate 1.0 mL / min, sample The concentration was 0.5 mg / mL (o-DCB), the injection amount was 500 μL, the sample dissolution temperature was 160 ° C., and the sample dissolution time was 3 hours. The molecular weight was calibrated with polystyrene, and Mw and Mn were obtained from the polystyrene-equivalent molecular weight to derive the molecular weight distribution.

(5) Elongation viscosity (η _e ), shear viscosity (η _s )
The elongational viscosity η _e and the shear viscosity η _s of the polyethylene resin composition were measured using the inflow pressure loss method according to Cogswell's theory [Polymer Engineering Science, 12, 64 (1972)]. As a measuring device, a twin capillary rheometer manufactured by Rosand was used, and the orifice was measured at 180 ° C. using a long die and a short die shown below. A value at an elongation strain rate of 10 s ⁻¹ was used as the elongation viscosity η _e , and a value at a shear strain rate of 100 s ⁻¹ was used as the shear viscosity η _s .
Long die: length 16mm, diameter 1mm, inflow angle 180 °
Short die: Length 0.25mm, diameter 1mm, inflow angle 180 °

(6) Number of terminal vinyl groups The number of terminal vinyl groups per 10,000 carbon atoms of the polyethylene resin in the polyethylene resin composition was determined using a Fourier transform infrared spectrophotometer manufactured by JASCO Corporation. Specifically, using a sheet-like polyethylene resin composition that has been made non-porous by heating and pressing, the absorbance near the absorption wavelength of 909 cm ⁻¹ of the IR spectrum measured by the spectrophotometer was determined. This absorption wavelength is a wavelength resulting from the terminal vinyl group in the polyethylene resin. From the obtained absorbance, the number of terminal vinyl groups per 10,000 carbon atoms was determined by the following formula.
(Number of terminal vinyl groups per 10,000 carbon atoms) = 11.4 × absorbance / ((true sample density) × (sample thickness))
Here, the unit of the true density of the sample is g / cm ³ and the unit of the thickness of the sample is mm.

(7) Film thickness (μm)
It was measured with a dial gauge (manufactured by Ozaki Seisakusho, trade name “PEACOCK No. 25”).

(8) Porosity (%)
A 10 cm × 10 cm square sample was cut out from the film, and calculated from the volume and mass of the sample using the following formula.
Porosity (%) = (volume (cm ³ ) −mass (g) / density of resin composition (g / cm ³ )) / volume (cm ³ ) × 100

(9) Air permeability (sec / 100cc)
It measured with the Gurley type air permeability meter based on JIS P-8117. In addition, the value which converted the film thickness into 20 micrometers was made into air permeability.

(10) Electric resistance (Ω · cm ² )
A laminated microporous film cut out in a circular shape is impregnated with an electrolytic solution and placed in a cell as shown in FIG. 1, and this cell is accommodated in an oven at −30 ° C. After the inner temperature was stabilized, first, the electrical resistance (Rs1) per laminated microporous film was measured.
Next, the cell was taken out of the oven, and five more microporous films of the same layer impregnated with the electrolytic solution were added to the cell, and the cell was accommodated in an oven at -30 ° C. After the temperature in the oven was stabilized, the electric resistance (Rs6) per six laminated microporous films was measured.
The electrical resistance of the laminated microporous film was calculated from the above Rs1 and Rs6 by the following formula.

Electrical resistance (Ω · cm ² ) = {[Rs6 (Ω) −Rs1 (Ω)] / 5} × 2.00 (cm ² )
The electrolyte used was LIPASTE-EP2BL / FSI1T (trade name) manufactured by Toyama Pharmaceutical Co., Ltd., and the electrical resistance was measured using a Hioki 3532-80 chemical impedance meter manufactured by Hioki Electric Co., Ltd. The real part (resistance) was defined as the electric resistance value. The effective area of the electrode shown in FIG. 1 was 2.00 cm ² .

(11) Film breaking temperature (film resistance)
FIG. 2 shows a schematic diagram of a measuring device for the film breaking temperature. FIG. 2A is an overall view thereof, and FIGS. 2B and 2C are plan views schematically showing a sample in the measuring apparatus. First, as shown in FIG. 2B, a laminated microporous film 1 is laminated on a nickel foil 6A having a thickness of 10 μm, and the longitudinal direction (MD direction) of the laminated microporous film 1 (direction X in the drawing). ) A Teflon (registered trademark) tape (shown by diagonal lines in the figure; the same applies hereinafter) was applied from above the end, and the laminated microporous film 1 was fixed on the nickel foil 6A. Here, the laminated microporous film 1 is impregnated in advance with a 1 mol / L lithium borofluoride solution (solvent: propylene carbonate / ethylene carbonate / γ-butyllactone = 1/1/2 (mass ratio)) as an electrolytic solution. Used. On the other hand, as shown in FIG. 2C, a Teflon (registered trademark) tape was bonded to the 10 μm thick nickel foil 6B for masking. However, a 15 mm × 10 mm window (opening) portion was left at the center of the nickel foil 6B.

  Next, as shown in FIG. 2 (A), the nickel foil 6A and the nickel foil 6B processed as described above were overlapped with the laminated microporous film 1 interposed therebetween. Further, two nickel foils 6A and 6B were sandwiched between the glass plates 7A and 7B from both sides. At this time, it aligned so that the window part of nickel foil 6B and the lamination | stacking microporous film 1 might face. The two glass plates 7A and 7B were fixed by being sandwiched between commercially available double clips (not shown). These were accommodated in the oven 12.

  Next, an electrical resistance measuring device (LCR meter manufactured by Ando Electric Co., Ltd., trade name “AG-4311”) 8 was connected to the nickel foils 6A and 6B. Moreover, the thermocouple 9 connected to the thermometer 10 was fixed to the glass plate 7A using Teflon (registered trademark). A data collector 11 for recording the measured electrical resistance and temperature was connected to the electrical resistance measuring device 8 and the thermometer 10.

Using such an apparatus, the electrical resistance between the nickel foils 6A and 6B was continuously measured while increasing the temperature of the glass plate 7A from 25 ° C. to 200 ° C. at 2 ° C./min. The electrical resistance was measured with an alternating current of 1 kHz. The temperature at which the electrical resistance value between the nickel foils 6A and 6B once reached 10 ³ Ω and then the electrical resistance value again falls below 10 ³ Ω was defined as the film breaking (short) temperature. The case where the film breaking temperature was less than 180 ° C. was evaluated as “X”, the case where the film breaking temperature was 180 ° C. to less than 200 ° C. was evaluated as “◯”, and the case where the film breaking temperature was 200 ° C. or more was evaluated as “「 ”.

[Production Example 1]
(1) Synthesis of chromium oxide catalyst (I) 4 mol of chromium trioxide was dissolved in 80 liters of distilled water to obtain a solution, and 20 kg of silica (manufactured by WR Grace and Company, Grade 952) was immersed in this solution. And stirred for 1 hour at room temperature to obtain a slurry. Thereafter, the slurry is heated to distill off water, followed by drying under reduced pressure at 120 ° C. for 10 hours, and then baking by flowing dry air at 600 ° C. for 5 hours to obtain 1.0% of chromium. A chromium oxide catalyst (I) containing mass% was obtained.

(2) Synthesis of organoaluminum compound (II) 100 moles of triethylaluminum, 50 moles of methyl hydropolysiloxane (viscosity at 30 ° C .: 30 centistokes) (Si standard), and 150 liters of n-hexane were placed in a nitrogen atmosphere. Weighed in a pressure vessel and allowed to react at 50 ° C. for 24 hours with stirring, and expressed by the composition formula Al (C ₂ H ₅ ) _2.5 (OSi · H · CH ₃ · C ₂ H ₅ ) _0.5. A hexane solution of an organoaluminum compound was prepared. Next, 100 moles (Al standard) of this hexane solution was transferred to a 600 liter reactor under a nitrogen atmosphere, and a mixed solution of 50 liters of ethanol and 50 liters of n-hexane was stirred while stirring the hexane solution in the reactor. Added at -10 ° C. After adding the mixed solution, the temperature in the reactor was raised to 50 ° C. and reacted at this temperature for 1 hour, and the composition formula Al (C ₂ H ₅ ) _2.0 (OC ₂ H ₅ ) _0.5 (OSi. H · CH ₃ · C ₂ H ₅ ) A hexane solution of an organoaluminum compound (II) having both an alkoxy group and a hydrosiloxy group represented by _0.5 was prepared.

(3) Polymerization of polyethylene resin composition (Bc-1) In a single-stage polymerization process, the polyethylene resin composition (Bc-1) was polymerized in a polymerization vessel having a volume of 230 L. The polymerization temperature was set to 78 ° C., and the polymerization pressure was set to 0.98 MPa. Specifically, first, 50 g of the chromium oxide catalyst (I) was placed in the polymerization vessel, and then 5 mmol of the organoaluminum compound (II) (Al basis) was added and reacted at room temperature for 1 hour. A solid catalyst was obtained. Separately, an organoaluminum compound (III) having an alkoxy group was obtained by reacting ethanol and trihexylaluminum at a molar ratio of 0.98: 1 at a rate of 2 g / hour. The organoaluminum compound (III) was supplied to the polymerization vessel containing the solid catalyst so that its concentration (based on the hexane solution of the organoaluminum compound (II) in the reactor) was 0.08 mmol / liter. At the same time, purified n-hexane is fed to the polymerizer at a rate of 60 L / hr, and ethylene as a monomer is fed at a rate of 12 kg / hr and hydrogen is used as a molecular weight regulator so that the gas phase concentration becomes 20 mol%. At the same time, the polymerization was carried out by feeding the polymerization vessel. The polymer in the obtained polymerization vessel was dried to obtain a powdery polyethylene resin composition (Bc-1). The obtained polyethylene resin composition (Bc-1) had an MFR of 1.8 g / 10 min and a density of 966 kg / m ³ .

[Production Example 2]
(1) Synthesis of Titanium Catalyst (IV) 3 liters of trichlorosilane as an n-heptane solution having a concentration of 2 mol / liter was charged into a 15 liter reactor sufficiently purged with nitrogen, and kept at 65 ° C. with stirring. Then, 7 liters of an n-heptane solution of an organic magnesium component represented by the composition formula AlMg ₆ (C ₂ H ₅ ) ₃ (nC ₄ H ₉ ) _6.4 (On-C ₄ H ₉ ) _5.6 (5 mol in terms of magnesium) was added over 1 hour, and the reaction was further stirred at 65 ° C. for 1 hour. After completion of the reaction, the supernatant was removed from the reaction product and washed 4 times with 7 liters of n-hexane to obtain a slurry containing solids. As a result of separating and drying the slurry containing this solid, 7.45 mmol of Mg was contained per gram of the solid.

  Among these, a slurry containing 500 g of solid was mixed with 0.93 liter of n-hexane solution of 1 mol / liter of n-butyl alcohol, and reacted at 50 ° C. for 1 hour with stirring. After completion of the reaction, the supernatant was removed from the reaction product and washed once with 7 liters of n-hexane. The slurry thus obtained was kept at 50 ° C., and 1.3 liters of n-hexane solution of 1 mol / liter of diethylaluminum chloride was added with stirring, and further reacted for 1 hour. After completion of the reaction, the supernatant was removed from the reaction product and washed twice with 7 liters of n-hexane. The obtained slurry was kept at 50 ° C., 0.2 liter of n-hexane solution of 1 mol / liter of diethylaluminum chloride and 0.2 liter of n-hexane solution of 1 mol / liter of titanium tetrachloride were added, The reaction was further continued for 2 hours. After completion of the reaction, the supernatant was removed from the reaction product, the solid catalyst was isolated, and the solid catalyst was washed with hexane until no free halogen was detected. The titanium catalyst (IV), which was a solid catalyst thus obtained, had 2.3% by mass of titanium.

(2) Polymerization of polyethylene resin composition (Cc-1) First, in the first stage polymerization, a stainless polymerizer 1 having a reaction volume of 300 liters was used for polymerization under the conditions of a polymerization temperature of 83 ° C and a polymerization pressure of 1 MPa. A molecular weight polymer component was obtained. As the catalyst, the titanium catalyst (IV) was supplied to the polymerizer 1 at a rate of 1.4 mmol / hour in terms of Ti atoms and triisobutylaluminum at a rate of 20 mmol / hour in terms of Al atoms. Further, n-hexane was introduced into the reactor 1 at a rate of 40 liters / hour. Polymerization was performed by using hydrogen as a molecular weight regulator and supplying ethylene and hydrogen as monomers so that the gas phase concentration of hydrogen was 38 mol%. The obtained polymer slurry solution containing the low molecular weight polymer component in the polymerization vessel 1 is led to a flash drum having a pressure of 0.1 MPa and a temperature of 75 ° C., and unreacted ethylene and hydrogen are separated, and then a polymerization with a reaction volume of 250 liters is performed. The pressure was introduced into the vessel 2 by a slurry pump. In the polymerization vessel 2, triisobutylaluminum was introduced at a rate of 7.5 mmol / hour and n-hexane was introduced at a rate of 40 liter / hour under the conditions of a temperature of 83 ° C. and a pressure of 0.5 MPa. Into this, ethylene as a monomer and hydrogen and butene-1 as molecular weight regulators were introduced so that the gas phase concentration of hydrogen was 6.8 mol% and the gas phase concentration of butene was 1.0 mol%. did. Thus, the mass ratio of the high molecular weight polymer component generated in the polymerization device 2 to the low molecular weight polymer component generated in the polymerization device 1 (high molecular weight polymer component) / (low molecular weight polymer component) is high so as to be 50/50. The molecular weight polymer component was polymerized and further dried to produce a powdery polyethylene resin composition (Cc-1) having an MFR of 1.3 g / 10 min and a density of 962 kg / m ³ . In addition, MFR of the low molecular weight polymer component produced | generated with the polymerization device 1 was 30 g / 10min, and the density was 967 kg / m < ³ >.

[Production Example 3]
Polypropylene resin (a-1) was introduced into a single screw extruder set at 20 mm in diameter, L / D = 30, and 260 ° C. via a feeder, and from a T die having a lip thickness of 3.0 mm installed at the tip of the extruder. Extruded. Immediately thereafter, 25 ° C. cold air was applied to the molten resin, and the film was wound up with a cast roll cooled to 95 ° C. under a draw ratio of 250 times and a winding speed of 10 m / min to form a polypropylene resin film (A-1). . As the polypropylene resin (a-1), a polypropylene resin having a melting point of 165 ° C. and an MFR of 0.4 g / 10 min was used. The elastic recovery rate after heat treatment of this polypropylene resin film (A-1) was 90%.

[Production Example 4]
11 parts by mass of polyphenylene ether resin (b-1) and 3 parts by mass of admixture (c-1) were prepared for 100 parts by mass of polypropylene resin (a-1) and polypropylene resin (a-1). Moreover, the twin-screw extruder which has a 1st raw material supply port and a 2nd raw material supply port was prepared. The nuclear material port was located at the approximate center of the extruder. (A-1) component, (b-1) component, (c-1) component are supplied to the above twin screw extruder set at a temperature of 260 to 320 ° C. and a screw rotation speed of 300 rpm, and are melt-kneaded to produce a thermoplastic resin. The composition was obtained as a pellet. The melting point of the obtained thermoplastic resin composition was 165 ° C. The polyphenylene ether resin (b-1) is PPE having a reduced viscosity of 0.54 obtained by oxidative polymerization of 2,6-xylenol, and the admixture (c-1) is polystyrene (1) -hydrogen. It has the structure of added polybutadiene-polystyrene (2), the amount of bonded styrene is 43%, the number average molecular weight is 95,000, the total of 1,2-vinyl bond and 3,4-vinyl bond of polybutadiene before hydrogenation Hydrogenated styrene-butadiene block copolymer having an amount of 80%, polystyrene (1) number average molecular weight of 30,000, polystyrene (2) number average molecular weight of 10,000 and polybutadiene portion hydrogenation rate of 99.9% Was used.

  A high melting point resin film (B-1) is formed in the same manner as in Production Example 3 except that the pellets of the thermoplastic resin composition obtained as described above are used in place of the polypropylene resin (a-1). did. The particle diameter of the island part which is a phase containing PPE in this high melting point resin film was 0.1 to 2.5 μm. Moreover, the elastic recovery rate after heat processing of this high melting point resin film was 88%. As is clear from the fact that this particle size could be measured, a sea-island structure was also observed in the high melting point resin film.

[Example 1]
A commercially available polyethylene resin composition (Ac-1) was introduced into a single-screw extruder set at 20 mm in diameter, L / D = 30, 180 ° C. via a feeder, and a lip thickness of 3.0 mm installed at the tip of the extruder. Extruded from the T-die. Immediately thereafter, 25 ° C. cold air was applied to the molten resin, and the film was wound with a cast roll cooled to 95 ° C. under a draw ratio of 300 times and a winding speed of 10 m / min, to form a low melting point resin film (C-1). did. As the polyethylene resin composition (Ac-1), a polyethylene resin composition having a melting point of 133 ° C., an MFR of 1.3 g / 10 min, a density of 964 kg / m ³ and η _e / η _s of 37 is used. It was. This low melting point resin film (C-1) had 28 fish eyes, and the elastic recovery after heat treatment was 70%.

  The both sides of the low melting point resin film (C-1) are sandwiched between polypropylene resin films (A-1), the outer layer has a structure of a polypropylene resin film (A-1), and the inner layer has a structure of a low melting point resin film (C-1) 3 A layer laminated film was produced as follows. First, the polypropylene resin film (A-1) and the low-melting point resin film (C-1) are each unwound at an unwinding speed of 4.0 m / min and led to a heating roll, where the thermocompression bonding temperature is 130 ° C. and the linear pressure is 2 The film was thermocompression-bonded at 0.0 kg / cm, then led to a 25 ° C. cooling roll at the same speed and wound up to obtain a laminated film (Af-1). The laminated film (Af-1) was annealed for 1 hour in a hot air circulating oven heated to 130 ° C.

  Next, the annealed laminated film was uniaxially stretched 1.3 times in the machine direction at a temperature of 25 ° C. to obtain a stretched laminated film (cold stretching process). Subsequently, the stretched laminated film was uniaxially stretched 3.0 times in the longitudinal direction at a temperature of 125 ° C. to obtain a laminated microporous film (thermal stretching step). Thereafter, it was relaxed 0.8 times at a temperature of 125 ° C. and heat-fixed to obtain a laminated microporous film. The resulting laminated microporous film was measured for film thickness, porosity, air permeability, film breaking temperature (film resistance), and electrical resistance. The results are shown in Table 1.

[Example 2]
A laminated film (Af-2) was obtained in the same manner as in Example 1 except that the high melting point resin film (B-1) was used instead of the polypropylene resin film (A-1) in Example 1. Next, a laminated microporous film was obtained in the same manner as in Example 1 except that the laminated film (Af-2) was used instead of the laminated film (Af-1). The resulting laminated microporous film was measured for film thickness, porosity, air permeability, film breaking temperature (film resistance), and electrical resistance. The results are shown in Table 1.

[Example 3]
The polyethylene resin composition (Bc-1) and the polyethylene resin composition (Cc-1) powder are mixed at a mixing ratio of (Bc-1) / (Cc-1) = 50/50 based on their mass. Next, calcium stearate was added to this mixture to a concentration of 60 ppm, and the mixture was stirred and mixed with a mixer. The resulting mixture was kneaded using a twin-screw extruder having a cylinder diameter of 44 mm (trade name “TEX44HCT-49PW-7V” manufactured by Nippon Steel Works) under the conditions of a cylinder temperature of 180 ° C. and an extrusion rate of 45 kg / hour. Extrusion gave a polyethylene resin composition (Ac-2). About the obtained polyethylene resin composition (Ac-2), melting | fusing point, MFR, a density, (eta) _e / (eta) _s , Mw / Mn was measured. The results are shown in Table 1.
Next, a low melting point resin film (C-2) was molded in the same manner as in Example 1 except that the polyethylene resin composition (Ac-2) was used instead of the polyethylene resin (Ac-1) in Example 1. did. The number of fish eyes of this low melting point resin film (C-2) and the elastic recovery after heat treatment were measured. The results are shown in Table 1.
Next, a laminated film (Af-3) was obtained in the same manner as in Example 2 except that the low melting point resin film (C-1) was used instead of the low melting point resin film (C-1). Next, a laminated microporous film was obtained in the same manner as in Example 2 except that the laminated film (Af-3) was used instead of the laminated film (Af-2). The resulting laminated microporous film was measured for film thickness, porosity, air permeability, film breaking temperature (film resistance), and electrical resistance. The results are shown in Table 1.

[Example 4]
The mixing ratio of the polyethylene resin composition (Bc-1) and the polyethylene resin composition (Cc-1) in Example 3 was changed from (Bc-1) / (Cc-1) = 50/50 to 80/20. Except for this, a polyethylene resin composition (Ac-3) was obtained in the same manner as in Example 3. About the obtained polyethylene resin composition (Ac-3), melting | fusing point, MFR, a density, (eta) _e / (eta) _s , Mw / Mn was measured. The results are shown in Table 1.
Next, a low melting point resin film (C-3) was obtained in the same manner as in Example 1 except that the polyethylene resin composition (Ac-3) was used instead of the polyethylene resin (Ac-1) in Example 1. It was. The number of fish eyes of this low melting point resin film (C-3) and the elastic recovery rate after heat treatment were measured. The results are shown in Table 1.
A laminated film (Af-4) was obtained in the same manner as in Example 2 except that the low melting point resin film (C-1) of Example 2 was used instead of the low melting point resin film (C-1). Next, a laminated microporous film was obtained in the same manner as in Example 2 except that the laminated film (Af-4) was used instead of the laminated film (Af-2).
The resulting laminated microporous film was measured for film thickness, porosity, air permeability, film breaking temperature (film resistance), and electrical resistance. The results are shown in Table 1.

[Example 5]
The mixing ratio of the polyethylene resin composition (Bc-1) and the polyethylene resin composition (Cc-1) in Example 3 was changed from (Bc-1) / (Cc-1) = 50/50 to 10/90. Except for this, a polyethylene resin composition (Ac-4) was obtained in the same manner as in Example 3. About the obtained polyethylene resin composition (Ac-4), melting | fusing point, MFR, a density, (eta) _e / (eta) _s , Mw / Mn was measured. The results are shown in Table 1.
Next, a low-melting point resin film (C-4) was obtained in the same manner as in Example 1 except that the polyethylene resin composition (Ac-4) was used instead of the polyethylene resin (Ac-1) in Example 1. It was. The number of fish eyes of this low melting point resin film (C-4) and the elastic recovery rate after heat treatment were measured. The results are shown in Table 1.
A laminated film (Af-5) was obtained in the same manner as in Example 2 except that the low melting point resin film (C-1) of Example 2 was used instead of the low melting point resin film (C-1). Next, a laminated microporous film was obtained in the same manner as in Example 2 except that the laminated film (Af-5) was used instead of the laminated film (Af-2).
The resulting laminated microporous film was measured for film thickness, porosity, air permeability, film breaking temperature (film resistance), and electrical resistance. The results are shown in Table 1.

[Comparative Example 1]
The low melting point resin film (C-5) was obtained in the same manner as in Example 1 except that the commercially available polyethylene resin composition (Ac-5) was used instead of the polyethylene resin composition (Ac-1) of Example 1. Got. As the polyethylene resin composition (Ac-5), a polyethylene resin composition having a melting point of 132 ° C., an MFR of 1.0 g / 10 min, a density of 961 kg / m ³ , and η _e / η _s of 13 is used. It was. The number of fish eyes of this low melting point resin film (C-5) and the elastic recovery after heat treatment were measured. The results are shown in Table 1.
A laminated film (Af-6) was obtained in the same manner as in Example 1 except that the low melting point resin film (C-1) of Example 1 was used instead of the low melting point resin film (C-1). Next, a laminated microporous film was obtained in the same manner as in Example 1 except that the laminated film (Af-6) was used instead of the laminated film (Af-1).
The resulting laminated microporous film was measured for film thickness, porosity, air permeability, film breaking temperature (film resistance), and electrical resistance. The results are shown in Table 1.

[Comparative Example 2]
Example except that the mixing ratio of the polyethylene resin composition (Bc-1) and the polyethylene resin composition (Cc-1) was changed from (Bc-1) / (Cc-1) = 50/50 to 0/100 In the same manner as in Example 1, an attempt was made to produce a low melting point resin film. However, the molten resin was easily broken and the raw film could not be formed. In addition, (eta) _e / (eta) _s of the polyethylene resin composition (Cc-1) was 150.

All the laminated microporous films (Examples 1 to 5) of the present embodiment exhibited extremely low electrical resistance.
On the other hand, Comparative Example 1 using a polyethylene resin composition having a ratio η _e / η _s smaller than 15 exhibited high electrical resistance. Further, in Comparative Example 2 in which the ratio η _e / η _s exceeded 100, it was difficult to form a raw film, and a laminated microporous film could not be obtained.

  The laminated microporous film of the present embodiment has industrial applicability as a battery separator, particularly a lithium ion secondary battery separator.

DESCRIPTION OF SYMBOLS 1 SUS cell 2 Teflon (registered trademark) 3 Spring 4 Microporous film impregnated with electrolyte 5 Laminated microporous film 6A Nickel foil 6B Nickel foil 7A Glass plate 7B Glass plate 8 Electrical resistance measuring device 9 Thermocouple 10 Thermometer 11 Data collector 12 Oven

Claims (8)

A first microporous film composed of a first resin composition;
A second microporous film composed of a second resin composition having a lower melting point than the first resin composition;
A laminated microporous film comprising:
The second resin composition contains a polyethylene resin, a ratio of the extensional viscosity eta _e to shear viscosity η _s η _{e /} η _s is 15 to 100, the laminated microporous film.   The laminated microporous film according to claim 1, wherein the polyethylene resin contained in the second resin composition has 3.0 or less terminal vinyl groups per 10,000 carbon atoms. The first resin composition is a thermoplastic resin composition containing a polypropylene resin and 1 to 90 parts by mass of a polyphenylene ether resin with respect to 100 parts by mass of the polypropylene resin.
The first microporous film composed of the first resin composition has a sea-island structure composed of a sea part that is a phase containing the polypropylene resin and an island part that is a phase containing the polyphenylene ether resin. The laminated microporous film according to claim 1 or 2.   The laminated microporous film according to claim 3, wherein the thermoplastic resin composition further contains 1 to 20 parts by mass of an admixture with respect to 100 parts by mass of the polypropylene resin.   The admixture is mainly composed of at least one polymer block A mainly composed of a structural unit derived from a vinyl aromatic compound, and a structural unit derived from a conjugated diene compound. The laminate according to claim 4, which is a hydrogenated block copolymer obtained by adding hydrogen to a block copolymer comprising at least one polymer block B having a total 4-vinyl bond content of 40 to 90%. Microporous film.   The laminated microporous film according to any one of claims 3 to 5, wherein the island portion has a particle size of 0.01 µm to 10 µm.   A battery separator comprising the laminated microporous film according to claim 1. It is a manufacturing method of the lamination | stacking microporous film of any one of Claims 1-6, Comprising: The manufacturing method of the lamination | stacking microporous film containing each process of the following (A) and (B):
(A) Cold-stretching step of cold-stretching the film at least in one direction by 1.05 to 2.0 times (B) After the cold-stretching step, the film is at least in one direction by 1.05 to 5.0 times A heat stretching process for heat stretching.