JP6000590B2 - Laminated microporous film and battery separator - Google Patents

Description

  The present invention relates to a laminated microporous film 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 the greater the difference between the temperature at which SD starts and the membrane breaking temperature, the better the safety.

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

In recent years, 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 required to reduce the resistance of ions flowing therethrough as much as possible when the separator holds the electrolytic solution. . From such a viewpoint, a separator having a low electric resistance in a state where an electrolytic solution is contained is desired.
On the other hand, from the viewpoint of safety, a separator having excellent voltage resistance is also desired. Withstand voltage refers to the insulation performance of the separator, such as to what level the separator suppresses short-circuiting and can exist as an insulator between the electrodes.
In particular, when the separator is used for a secondary battery of a hybrid electric vehicle or the like, it is necessary to satisfy these conflicting characteristics with a good balance.
However, the laminated microporous film obtained by the method of Patent Document 1 must have some characteristics such as the molding temperature of the high melting point resin and the low melting point resin, and it is difficult to mold them under the optimum conditions for each. is there. As a result, it is difficult to obtain a laminated microporous film having an excellent balance between low electric resistance and high voltage resistance, that is, excellent balance between electric resistance and voltage resistance. Also, the laminated microporous film produced by the method disclosed in Patent Document 2 is not sufficient from the viewpoint of the balance between electric resistance and voltage resistance.
This invention is made | formed in view of such a situation, and makes it a subject to provide the laminated microporous film excellent in the balance of electrical resistance and withstand voltage property, and a battery separator using the same.

  As a result of intensive studies to solve the above problems, the inventors of the present invention 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 composed of the second resin composition, and the ratio of the pore volume in the specific pore diameter range of the second microporous film is within a specific range. The present inventors have found that a film can solve the above-mentioned problems 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:
A laminated microporous film, wherein a ratio of a pore volume of 0.40 μm or more and 1 μm or less to a pore volume of a pore diameter of 0.01 μm or more and 1 μm or less of the second microporous film is 10% or less.
[2]
The laminated microporous film according to the above [1], wherein the second microporous film has an air permeability (converted to a film thickness of 20 μm) of 20 seconds / 100 cc or more and 60 seconds / 100 cc or less.
[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 island part has a particle size of 0.01 μm to 10 μm.
[5]
The battery separator containing the lamination | stacking microporous film in any one of said [1]-[4].

  ADVANTAGE OF THE INVENTION According to this invention, the lamination | stacking microporous film excellent in the balance of an electrical resistance and a withstand voltage property and the battery separator using the same can be provided.

The schematic sectional drawing of the cell for an electrical resistance measurement of a film is shown. (A) shows a schematic view of a measurement device for the tear temperature, (B) shows a plan view of a sample portion of another measurement device for the tear temperature, and (C) shows a sample portion of the tear temperature measurement device. The top view of is shown.

Hereinafter, a form for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. 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 the present embodiment is composed of a first microporous film composed of the first resin composition and a second resin composition having a melting point lower than that of the first resin composition. A laminated microporous film comprising a second microporous film, wherein the second microporous film has a fine pore size of 0.40 μm or more and 1 μm or less with respect to a pore volume of 0.01 μm or more and 1 μm or less. It is a laminated microporous film having a pore volume ratio of 10% or less.

  The laminated microporous film of the present embodiment has a structure in which the first microporous film and the second microporous film are laminated.

  In the present specification, the “resin composition” is a concept that includes only one type of resin (polymer material), and may be a mixture of two or more types of resins, and an optional additive. It 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 respective melting points (hereinafter, simply referred to as “melting points”) T _mA and T _mB measured by a method according to JIS K-7121, such that T _mA > T _mB. As long as the relationship is satisfied, 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 and the melting point T _mB is preferably 5 ° C. or more, and 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, even when the low melting point resin layer melts when the internal temperature of the battery rises due to abnormal current, The melting point 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) The first microporous film, the second microporous film, the first microporous film, and the second microporous film were alternately arranged. A laminated body is mentioned.

As a manufacturing method of the lamination | stacking microporous film of this embodiment, after shape | molding the lamination film which laminated | stacked the resin film by (a) co-extrusion method, for example using a T die or a circular die, the lamination film was extended | stretched. (B) A method of extruding resin films separately and then laminating each resin film by lamination to form a laminated film, and then stretching the laminated film to make it porous (C) A method of extruding each resin film separately, further stretching to obtain a microporous film that has been made porous, 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 separately extruded 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), the resin composition extrusion speed (linear speed in the flow direction of the molten resin passing through the die lip, unit: The value divided by m / min) is preferably in the range of 10 to 500, more preferably 100 to 400, and still more preferably 150 to 350, from the viewpoint of the air permeability of the laminated microporous film. From the viewpoint of the appearance of the film, the film is wound so that the film winding speed is preferably about 2 to 400 m / min, more preferably 10 to 200 m / min.

  Furthermore, it is preferable to heat-treat (anneal) the resin film and / or the laminated film as necessary. As the 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 these The method of performing in combination is mentioned. The conditions for these heat treatments are appropriately determined depending on the type of material constituting the film and are not particularly limited.

The heating temperature in the case where the first resin film composed of the first resin composition (hereinafter also referred to as “high melting point resin film”) is annealed alone is the porosity, the air permeability, and the heat shrinkage rate. From the viewpoint of balance, 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. The heating time is appropriately determined and is not particularly limited.

On the other hand, when the second resin film composed of the second resin composition, which is the resin composition having the lower melting point (hereinafter also referred to as “low melting point resin film”) is annealed alone, From the viewpoint of the balance of porosity, air permeability, and heat shrinkage rate, it is preferably (T _mB −30) ° C. or higher and (T _mB −2) ° C. or lower, more preferably (T _mB −15) ° C. or higher ( T _mB -2) It is not higher than ° C. The heating time is appropriately determined and is not particularly limited.

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 resin 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 laminating, that is, when annealing is performed on the laminated film, the resin films composed of the resin before annealing having a high ratio of the amorphous part are laminated. A laminated microporous film having high adhesive strength can be obtained. The resin films may be laminated by, for example, thermocompression bonding.

  The first microporous film is formed by subjecting a high melting point resin film to a predetermined stretching treatment to make it porous. When heat treatment (annealing) is performed, the high-melting point resin film preferably has an elastic recovery rate after heat treatment of 80 to 95%, more preferably 84 to 92%. In order to control the elastic recovery rate after the heat treatment within the above range, for example, the heat treatment time may be adjusted.

  The second microporous film is formed by subjecting a low melting point resin film to a predetermined stretching treatment to make it porous. When heat treatment (annealing) is performed, the low melting point resin film preferably has an elastic recovery rate after heat treatment of 50 to 80%, more preferably 60 to 75%. In order to control the elastic recovery rate after the heat treatment within the above range, for example, the heat treatment time may be adjusted.

  When the elastic recovery rate of each resin film is within the above range, a laminated microporous film having a more 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.
In the case of a high melting point resin film, the 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 was set at a predetermined position of a tensile tester (for example, product name “Tensilon” manufactured by A & D Co., Ltd., the same shall apply hereinafter), and the condition was 25 mm, 65% relative humidity, 50 mm / Stretches to 100% in the length direction at a speed of minutes (ie, to a length of 100 mm). 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)

In the case of a low melting point resin film, the 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) A cold stretching process in which at least one of a laminated film, a low-melting point resin film, and a high-melting point resin film is cold-stretched at least 1.05 times to 2.0 times in one direction.
(B) A hot stretching step in which the film after the cold stretching step is hot-stretched at least 1.05 times to 5.0 times in at least one direction.
When 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) in the production method of the laminated microporous film exemplified above, On the other hand, 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 of (c) above, the first stretching is performed on each resin film. 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, and 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. The surface temperature of the film can be measured with a contact thermometer (the same applies hereinafter).

  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 extrusion direction of the film (hereinafter referred to as “MD”) and the width direction of the film (hereinafter referred to as “TD”). Preferably, uniaxial stretching is performed only in the direction of film extrusion.

  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.

The method for producing a laminated microporous film of the present embodiment preferably includes a hot stretching step of obtaining a stretched laminated film by performing a second stretching at a temperature higher than the cold stretching temperature after the cold stretching step. . When heat 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 the heat stretching is (T _mB -60) ° C. or higher, porosity and air permeability from the viewpoint of preventing breakage. From the viewpoint of degree, (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 of the heat stretching means the surface temperature of the film in the heat stretching step.

  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 in the same direction as the cold stretching direction. The only uniaxial stretching is performed.

  When heat-stretching a high melting point resin film alone, it is preferable to stretch the film while maintaining at 90 ° C. or higher and 150 ° C. or lower from the viewpoint of air permeability of the microporous film. Further, from the same viewpoint, it is preferable to heat-stretch in at least one direction from 1.05 times to 5.0 times. Particularly preferably, the film is hot-stretched at least 1.05 times to 5.0 times in one direction while being maintained 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, from the viewpoint of the air permeability of the microporous film, it is stretched while being maintained at (T _mB -60) ° C. or higher and (T _mB −2) ° C. or lower. Is preferred. Further, from the same viewpoint, it is preferable to heat-stretch in at least one direction from 1.05 times to 5.0 times. Particularly preferably, the _film is hot-stretched at least 1.05 times to 5.0 times in at least one direction while being maintained at (T _mB −60) ° C. or more and (T _mB −2) ° C. or less.

  It is preferable that the manufacturing method of the lamination | stacking microporous film of this embodiment includes the heat setting process which heat-sets a lamination film after a heat | fever extending process. Including the 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 a method of this heat setting, a method of heat shrinking to such an extent that the length of the laminated microporous film after heat setting is reduced by 3 to 50% from the length before heat setting (hereinafter referred to as “relaxation”). And a method of fixing so that the dimension in the stretching direction does not change before and after heat setting.

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, from the viewpoint of the air permeability of the laminated microporous film, the heat setting temperature is (T _mB -30) ° C. or higher. preferably _(T mB -2) ℃ or _less, and more preferably less ℃ _(T mB -15) ℃ or higher _(T mB -2). Here, the heat setting temperature means the surface temperature of the laminated film at the time of heat setting.

  When heat-fixing a high melting point resin film alone, the heat setting temperature is preferably 100 ° C. or higher and 160 ° C. or lower, and 130 ° C. or higher and 155 ° C. or lower from the viewpoint of the heat shrinkage rate of the microporous film. Is more preferable.

On the other hand, when the low melting point resin film is heat-set alone, the heat setting temperature is (T _mB −30) ° C. or more and (T _mB −2) ° C. or less from the viewpoint of the heat shrinkage rate of the microporous film. It is more preferable that it is ( _TmB- 15) _degreeC or more and ( _TmB- 2) _degreeC or less.

  In the cold drawing step, the hot drawing step, the other drawing step and the heat setting step, one or two or more steps are used to draw or heat in a uniaxial direction and / or biaxial direction by a roll, a tenter, an autograph, or the like. A 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 or 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 When doing, from a viewpoint of the peeling strength between each resin film in a laminated | multilayer film, it is preferable to pass a high melting point resin film and a low melting point resin film between the heated rolls, and to thermocompression-bond. In this case, each resin film may be laminated by being unwound from an original roll stand, niped between heated rolls, and pressure-bonded. At the time of lamination, it is preferable to perform thermocompression bonding so that the elastic recovery rate after heat treatment of each resin film does not substantially decrease. For such thermocompression bonding, for example, the thermocompression bonding temperature may be adjusted. 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 resin films in the laminated film 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 laminated microporous film that can further suppress the melting point of the low melting point resin film and decrease its elastic recovery rate, and can solve the intended problem, It tends to be easily obtained. Although the nip pressure in thermocompression bonding is not particularly limited, for example, it is preferably 1 to ³ kg / cm ² and the unwinding speed is not particularly limited, but is preferably 0.5 to 8 m / min, for example. The peel strength of the laminated film is preferably in the range of 3 to 60 g / 15 mm, and can be controlled by adjusting the thermocompression bonding temperature as is apparent from the above. Note that the peel strength of the laminated film is such that, in a sample in which one end of the laminated film is partly peeled, one end of both peeled films is set at a predetermined position of a tensile tester and stretched in the length direction at a speed of 300 mm / min. It can measure by measuring the tension at the time of peeling.

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

The first resin composition has a higher melting point than the second resin composition, the melting point T _mA, for example, if it is 0.99 ° C. to 280 ° C., good balance of rupture temperature and the film formation properties This is preferable.

  Moreover, 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, a laminated microporous film having more excellent heat resistance is obtained. It is preferable because it 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, and a hexene are mentioned, These are used individually by 1 type or in combination of 2 or more types. 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 the polypropylene resin (based on ASTM D1238, measured under a load of 230 ° C. and 2.16 kg, the same applies hereinafter) is preferably 0.1 to 100 g / in from the viewpoint of film formability. 10 minutes, more preferably 0.1 to 80 g / 10 minutes.

  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 in 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 following PPE content includes the mass of the other polymer.

  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.

  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. The total content of these additional components is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin composition. .

[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 polyphenylene 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 scanning electron microscope, 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 order to adjust the particle size of the island portion, for example, the amount of admixture added may be adjusted. By reducing the amount of admixture added, the particle size of the islands tends to increase.

  Such a sea-island structure is also retained in the first microporous film formed by subjecting the high-melting point resin film to a porous structure including the particle diameter of the island part and stretching it.

In the present embodiment, the particle size of the island portion is measured as follows.
First, a transmission electron micrograph (magnification: 5000 times) is obtained in the same manner as the measurement method when observing the sea-island structure for the high melting point resin film or the first microporous 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. Here, the ratio of the major axis diameter to the minor axis diameter means the ratio between the major axis diameter and the minor axis diameter arithmetically averaged for the 100 particles.
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). Here, although it does not specifically limit as an admixture, For example, a hydrogenated block copolymer is mentioned from a dispersible viewpoint of polyphenylene ether resin. The hydrogenated block copolymer is, for example, at least one polymer block mainly composed of a vinyl aromatic compound such as styrene, and at least 1 mainly composed of a conjugated diene compound such as 1,3-butadiene or isoprene. It is a block copolymer obtained by hydrogenating a block copolymer composed of individual polymer blocks.

  In this embodiment, a laminated microporous film obtained 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 lithium ion batteries. 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 results in 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.

[Second microporous film]
The second microporous film in the present embodiment is preferably made porous by stretching a low melting point resin film composed of a second resin composition having a melting point lower than that of the first resin composition. It is obtained by this. The second resin composition is preferably a polyethylene resin composition (hereinafter referred to as “polyethylene resin composition Ac”) from the viewpoint of air permeability of the microporous film.
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, from the viewpoint of the air permeability of the microporous film, 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.

The density of the polyethylene resin composition Ac in 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.

  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 still more preferably 5 parts by mass or less with respect to 100 parts by mass of the polyethylene resin composition Ac.

  In the second microporous film in the present embodiment, the ratio of the pore volume having a pore diameter of 0.40 μm to 1 μm to the pore volume of 0.01 μm to 1 μm is 10% or less, preferably 5% or less. It is. In addition, the pore volume ratio in the specific pore diameter range of the second microporous film of the present embodiment can be adjusted to the above range by appropriately setting the stretching temperature, the stretching ratio, the film winding tension, and the like. .

  The inventors have found that the withstand voltage of the resulting laminated microporous film is remarkably improved by setting the above ratio to 10% or less. In addition, this numerical value is measured according to the method described in the following Example.

  The air permeability (film thickness 20 μm conversion) of the second microporous film is preferably 20 seconds / 100 cc to 60 seconds / 100 cc, more preferably 20 seconds / 100 cc to 40 seconds / 100 cc. In addition, the air permeability of the 2nd microporous film of this embodiment can be adjusted to the above-mentioned range by setting extending | stretching temperature, a draw ratio, etc. suitably. The air permeability is measured using a Gurley type air permeability meter according to JIS P-8117.

[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. For example, the porosity can be increased by increasing the density of the resin composition, increasing the thermal stretching temperature, or increasing the stretching ratio. 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 suitable from the viewpoint of securing 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.

  The film thickness of the laminated microporous film of the present embodiment is preferably 5 to 40 μm, and more preferably 10 to 30 μm. 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.

  Of the laminated microporous film of this embodiment, the average pore diameter of the second microporous film is preferably 0.10 to 0.70 μm, and more preferably 0.30 to 0.60 μm. . If the average pore diameter is in the range of 0.10 to 0.70 μm, particularly 0.30 to 0.60 μm, the residual stress in the amorphous part is reduced, or the heat shrinkage rate is excellent and the voltage resistance is excellent. There is a tendency. In order to adjust the average pore diameter, for example, the draw ratio may be adjusted. By increasing the hot draw ratio, the average pore diameter tends to increase.

  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.

  According to the present embodiment, it is possible to provide a laminated microporous film having a good balance between electric resistance and withstand voltage and having a small thermal shrinkage, a method for producing the same, and a battery separator using the same. Furthermore, surprisingly, a laminated microporous film having a small heat shrinkage rate can be obtained.

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 of various properties in the examples and comparative examples are as follows.

(1) Melting | fusing point Melting | fusing point was measured by the method based on JISK-7121. This measurement was performed at least three times, and the average value was taken as the melting point value.

(2) Melt flow rate (MFR)
According to JIS K7210, MFR (unit: g / 10 minutes) 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. This measurement was performed at least three times, and the average value was taken as the MFR value.

(3) Density The density (unit: kg / m ³ ) of the polyethylene resin composition was measured according to JIS K7112. This measurement was performed at least three times, and the average value was taken as the density value.

(4) Film thickness (μm)
The film thickness was measured with a dial gauge (manufactured by Ozaki Mfg. Co., Ltd., trade name “PEACOCK No. 25”). This measurement was performed at least 5 times, and the average value was taken as the density value.

(5) Porosity (%)
A 10 cm × 10 cm square sample was cut out from the film, and the porosity was calculated from the volume and mass of the sample using the following formula.
Porosity (%) = (Volume (cm ³ ) −Mass (g) / Density of resin composition constituting film (g / cm ³ )) / Volume (cm ³ ) × 100
This measurement was performed at least 5 times, and the average value was taken as the porosity value.

(6) Air permeability (sec / 100cc)
The air permeability was measured with a Gurley type air permeability meter based on JIS P-8117. The air permeability was converted per 20 μm thickness based on the measured value of the film thickness, the above measurement was performed at least five times, and the average value was taken as the value of the air permeability. About the low melting point resin film, after peeling a low melting point resin film from a film, the air permeability was measured by the method similar to the above.

(7) Electric resistance (Ω · cm ² )
A cell made of SUS shown in FIG. 1 was prepared. Here, reference numeral 1 in FIG. 1 denotes a cell body, reference numeral 2 denotes a polytetrafluoroethylene seal, reference numeral 3 denotes a spring, and reference numeral 4 denotes a film impregnated with an electrolytic solution.
A film sample cut into a circular shape is impregnated with an electrolytic solution, placed in the cell 1 shown in FIG. 1, and the cell 1 is accommodated in an oven set at −30 ° C. After the inner temperature was stabilized at −30 ° C., first, the electric resistance (Rs1) per film sample was measured.
Next, the cell 1 is taken out from the oven, and five more film samples impregnated with the electrolytic solution are stacked in the cell from the bottom to the top in FIG. 1, and the cell is stored in the oven at −30 ° C. Then, after sufficient time had elapsed, the temperature in the oven was stabilized at −30 ° C., and then the electrical resistance (Rs6) per six film samples was measured.
The electrical resistance of the film sample was calculated from the above Rs1 and Rs6 according to the following equation.
Electrical resistance (Ω · cm ² ) = {[Rs6 (Ω) −Rs1 (Ω)] / 5} × 2.00 (cm ² )
This measurement was performed at least 5 times, and the average value was taken as the value of electrical resistance. Note that LIPASTE-EP2BL / FSI1T (trade name) manufactured by Toyama Pharmaceutical Co., Ltd. was used as the electrolyte. The electrical resistance was measured using a Hioki 3532-80 chemical impedance meter (trade name) manufactured by Hioki Electric Co., Ltd., and the real part (resistance) of the impedance at 100 kHz was taken as the value of electrical resistance. The effective area of the electrode shown in FIG. 1 was 2.00 cm ² .

(8) Film breaking temperature (film resistance)
FIG. 2 shows a schematic diagram of a measuring device for the film breaking temperature. 2A is an overall view, and FIG. 2B and FIG. 2C are plan views schematically showing a sample in the measuring apparatus. First, as shown in FIG. 2 (B), a film 5 is laminated on a nickel foil 6A having a thickness of 10 μm, and a polytetrafluoroethylene tape (hatched line in the figure) is formed on both ends of the longitudinal direction (MD) of the film 1. A sample in which the film 5 was fixed on the nickel foil 6A was prepared. Here, the film 5 used was impregnated with a 1 mol / L lithium borofluoride solution (solvent: propylene carbonate / ethylene carbonate / γ-butyllactone = 1/1/2 (mass ratio)) as an electrolytic solution in advance. . On the other hand, as shown in FIG. 2C, a sample was prepared in which polytetrafluoroethylene tape was bonded to a 10 μm thick nickel foil 6B and masked. However, a 15 mm × 10 mm window (opening) portion was left at the center of the nickel foil 6B.

  Next, as shown in FIG. 2A, the samples shown in FIG. 2B and the sample shown in FIG. 2C, which are processed as described above, are overlapped with each other so that the nickel foils 6A and 6B sandwich the film 5. Combined. Further, two samples were sandwiched between the glass plates 7A and 7B from both sides. At this time, alignment was performed such that the window portion of the sample of (C) and the film 5 face each other. 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 a polytetrafluoroethylene tape. 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. This measurement was carried out at least 5 times, and the average value was taken as the value of the film breaking temperature. The case where the film breaking temperature was less than 180 ° C. was evaluated as “×”, and the case where the film breaking temperature was 200 ° C. or higher was evaluated as “◎”.

(9) Pore volume ratio in the specific pore diameter range of the second microporous film The pore diameter of the second microporous film was measured with a mercury porosimeter (trade name “Autopore 9520”, manufactured by Shimadzu Corporation).
The second microporous film was peeled from the laminated microporous film, cut to a width of 25 mm, and then measured from an initial pressure of 3.0 psia using a mercury porosimeter. From the obtained pore distribution data, the ratio of the pore volume of 0.40 μm to 1 μm to the pore volume of 0.01 μm to 1 μm was calculated using the following formula.
Pore volume ratio (%) of 0.40 μm to 1 μm of second microporous film = (pore volume (mL / g) of 0.40 μm to 1 μm of second microporous film) / second 2 microporous film having a pore volume of 0.01 μm or more and 1 μm or less (mL / g)) × 100

(11) Voltage resistance A 50 g load is applied to a Φ5 mm electrode whose surface has been cleaned, a 50 mm × 50 mm film sample is sandwiched, and a voltage is applied to the electrode to gradually increase the voltage. The voltage value at the time of sparking when a current of 2 mA flows was measured. This measurement was made at least 20 different points in the plane of the same film sample, and the average value was recorded. At this time, with respect to voltage resistance, 2.3 kV or more was evaluated as ◎, 1.7 kV or more as ◯, and less than 1.7 kV as x.

(12) Thermal contraction rate A sample of 12 cm × 12 cm square was cut out from the film, and the MD and TD of the sample were marked with two marks (each four in total) at 10 cm intervals, and the sample was sandwiched between paper, It left still for 60 minutes in 100 degreeC oven. After taking out the sample from the oven and cooling, the length (cm) between the marks of MD and TD was measured, and the thermal shrinkage rate of MD and TD was calculated by the following formula.
MD thermal shrinkage (%) = (10−MD length after heating (cm)) / 10 × 100
TD thermal shrinkage rate (%) = (10−length of TD after heating (cm)) / 10 × 100
This measurement was performed at least 5 times, and the average value was taken as the value of the heat shrinkage rate.

[Production Example 1]
Polypropylene resin (a-1) was introduced into a single screw extruder set under conditions of 20 mm in diameter, L / D = 30, and 260 ° C. via a feeder, and a lip having a lip thickness of 3.0 mm installed at the tip of the extruder. Extruded from the die. Immediately after that, a 25 ° C. cold air was applied to the molten resin (a-1) and a cast roll cooled to 95 ° C. was used to wind up the film at a draw ratio of 250 times and a winding speed of 10 m / min. A-1) was molded. 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 2]
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. Each said raw material port was located in the approximate center about the flow direction of resin in an extruder. Supplying the resin (a-1), resin (b-1) and admixture (c-1) components to the twin-screw extruder set at a temperature of 260 to 320 ° C. and a screw rotational speed of 300 rpm, They were melt kneaded to obtain a thermoplastic resin composition as pellets. The melting point of the obtained thermoplastic resin composition was 165 ° C. The polyphenylene ether resin (b-1) is a polyphenylene ether having a reduced viscosity of 0.54 obtained by oxidative polymerization of 2,6-xylenol, and the admixture (c-1) is (polystyrene (1) )-(Hydrogenated polybutadiene)-(polystyrene (2)), having a styrene content of 43%, a number average molecular weight of 95,000, a 1,2-vinyl bond of polybutadiene before hydrogenation and 3,4- Hydrogen of styrene-butadiene block copolymer having a total amount of 80% with vinyl bonds, a number average molecular weight of 30000 of polystyrene (1), a number average molecular weight of 10000 of polystyrene (2) and a hydrogenation rate of 99.9% of polybutadiene part. Additives were used.

  A high melting point resin film (B-1) is formed in the same manner as in Production Example 1 except that the pellets of the thermoplastic resin composition obtained as described above are used in place of the polypropylene resin (a-1). did. This high melting point resin film was observed to have a sea-island structure consisting of an island part that is a phase containing a polyphenylene ether resin and a sea part containing a polypropylene resin. As for the particle diameter of the island part which is a phase containing polyphenylene ether resin, 100 particles were in the range of 0.1 to 2.5 μm. Moreover, the elastic recovery rate after heat processing of this high melting point resin film (B-1) was 88%.

[Production Example 3]
A polyethylene resin (Ac-1) was introduced through a feeder into a single-screw extruder set at a diameter of 20 mm, L / D = 30, and 180 ° C., and a lip with a thickness of 3.0 mm was installed at the tip of the extruder. Extruded from the die. Immediately thereafter, 25 ° C. cold air was applied to the molten resin composition (Ac-1), and the cast roll cooled to 95 ° C. was used for winding at a draw ratio of 300 times and a winding speed of 10 m / min. A resin film (C-1) was molded. As the polyethylene resin (Ac-1), a polyethylene resin having a melting point of 133 ° C., an MFR of 1.3 g / 10 min, and a density of 964 kg / m ³ was used. The elastic recovery rate after heat treatment of this low melting point resin film (C-1) was 70%.

[Production Example 4]
A low melting point resin film (D-1) was formed in the same manner as in Production Example 3 except that the polyethylene resin (Ac-2) was used instead of the polyethylene resin (Ac-1). As the polyethylene resin (Ac-2), a polyethylene resin having a melting point of 133 ° C., an MFR of 0.8 g / 10 min, and a density of 959 kg / m ³ was used. The elastic recovery rate after heat treatment of this low melting point resin film (D-1) was 69%.

[Example 1]
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 Thermocompression bonding was performed at 0.0 kg / cm. The film after thermocompression bonding was led to a 25 ° C. cooling roll at the same speed as the unwinding 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 1.2 times in the machine direction at a temperature of 25 ° C. to obtain a stretched laminated film (cold stretching step). Subsequently, the stretched laminated film was uniaxially stretched 1.8 times in the longitudinal direction at a temperature of 100 ° C., and then uniaxially stretched 1.5 times in the longitudinal direction at a temperature of 125 ° C. to obtain a laminated microporous film ( Thermal stretching step). Thereafter, the laminated microporous film was relaxed by a factor of 0.8 at a temperature of 125 ° C. and heat-set, and wound with a tension of 5 N (in terms of the laminated microporous film 100 mm width). For the obtained microporous film after heat setting, the film thickness, porosity, air permeability, film breaking temperature (breaking resistance), electrical resistance, pore volume ratio and heat shrinkage in a specific range are measured. And withstand voltage was evaluated. 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). For the obtained microporous film after heat setting, the film thickness, porosity, air permeability, film breaking temperature (breaking resistance), electrical resistance, pore volume ratio and heat shrinkage in a specific range are measured. And withstand voltage was evaluated. The results are shown in Table 1.

[Example 3]
The laminated film (Af-2) of Example 2 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). Next, the stretched laminated film was uniaxially stretched 2.8 times in the longitudinal direction at a temperature of 110 ° C. to obtain a laminated microporous film (thermal stretching step). Thereafter, the laminated microporous film was relaxed by a factor of 0.8 at a temperature of 125 ° C. and heat-set, and wound with a tension of 6 N (in terms of the width of the laminated microporous film 100 mm). For the obtained microporous film after heat setting, the film thickness, porosity, air permeability, film breaking temperature (breaking resistance), electrical resistance, pore volume ratio and heat shrinkage in a specific range are measured. And withstand voltage was evaluated. The results are shown in Table 1.

[Example 4]
A laminated film (Af-3) was obtained in the same manner as in Example 2, except that the low melting point resin film (D-1) was used instead of the low melting point resin film (C-1) in Example 2. This laminated film (Af-3) was annealed for 1 hour in a hot air circulating oven heated to 130 ° C.
Next, the annealed laminated film was uniaxially stretched 1.2 times in the machine direction at a temperature of 25 ° C. to obtain a stretched laminated film (cold stretching step). Next, the stretched laminated film was uniaxially stretched 1.5 times in the longitudinal direction at a temperature of 100 ° C., and then uniaxially stretched 1.8 times in the longitudinal direction at a temperature of 125 ° C. to obtain a laminated microporous film ( Thermal stretching step). Thereafter, the laminated microporous film was relaxed by a factor of 0.8 at a temperature of 125 ° C. and heat-set, and wound with a tension of 5 N (in terms of the laminated microporous film 100 mm width). For the obtained microporous film after heat setting, the film thickness, porosity, air permeability, film breaking temperature (breaking resistance), electrical resistance, pore volume ratio and heat shrinkage in a specific range are measured. And withstand voltage was evaluated. The results are shown in Table 1.

[Example 5]
The laminated film (Af-2) of Example 2 was annealed for 1 hour in a hot air circulating oven heated to 130 ° C.
Next, the annealed laminated film was uniaxially stretched 1.25 times in the machine direction at a temperature of 25 ° C. to obtain a stretched laminated film (cold stretching step). Next, the stretched laminated film was uniaxially stretched 1.6 times in the longitudinal direction at a temperature of 100 ° C., and then uniaxially stretched 1.6 times in the longitudinal direction at a temperature of 125 ° C. to obtain a laminated microporous film ( Thermal stretching step). Thereafter, the laminated microporous film was relaxed by a factor of 0.8 at a temperature of 125 ° C. and heat-set, and wound with a tension of 5 N (in terms of the laminated microporous film 100 mm width). For the obtained microporous film after heat setting, the film thickness, porosity, air permeability, film breaking temperature (breaking resistance), electrical resistance, pore volume ratio and heat shrinkage in a specific range are measured. And withstand voltage was evaluated. The results are shown in Table 1.

[Comparative Example 1]
The laminated film (Af-2) of Example 2 was annealed for 1 hour in a hot air circulating oven heated to 130 ° C.
Next, the annealed laminated film was uniaxially stretched 1.1 times in the machine direction at a temperature of 25 ° C. to obtain a stretched laminated film. Next, the stretched laminated film was uniaxially stretched 2.6 times in the longitudinal direction at a temperature of 125 ° C. to obtain a laminated microporous film. Thereafter, the laminated microporous film was relaxed by 0.85 times at a temperature of 125 ° C. and heat-set, and wound with a tension of 9 N (converted to a laminated microporous film of 100 mm width). For the obtained microporous film after heat setting, the film thickness, porosity, air permeability, film breaking temperature (breaking resistance), electrical resistance, pore volume ratio and heat shrinkage in a specific range are measured. And withstand voltage was evaluated. The results are shown in Table 1.

[Comparative Example 2]
The laminated film (Af-2) of Example 2 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 longitudinal direction at a temperature of 25 ° C. to obtain a stretched laminated film. Subsequently, the stretched laminated film was uniaxially stretched 2.4 times in the longitudinal direction at a temperature of 125 ° C. to obtain a laminated microporous film. Thereafter, the laminated microporous film was relaxed by a factor of 0.8 at a temperature of 125 ° C. and heat-set, and wound with a tension of 10 N (converted into a laminated microporous film having a width of 100 mm). For the obtained microporous film after heat setting, the film thickness, porosity, air permeability, film breaking temperature (breaking resistance), electrical resistance, pore volume ratio and heat shrinkage in a specific range are measured. And withstand voltage was evaluated. The results are shown in Table 1.

The laminated microporous films (Examples 1 to 5) of this embodiment all exhibited low electrical resistance and high voltage resistance.
On the other hand, among the pore volumes of the second microporous film having a pore diameter of 0.01 μm or more and 1 μm or less, a laminated microporous film having a pore volume ratio of 0.40 μm or more and 1 μm or less exceeding 10% is used. The laminated microporous films of Comparative Example 1 and Comparative Example 2 showed a low withstand voltage.

  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 ... Cell, 2 ... Sealing material, 3 ... Spring, 4 ... Microporous film impregnated with electrolyte solution, 5 ... 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 (5)

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:
Ri der proportion than 10% of 1μm or less of the pore volume than 0.40μm for pore size 0.01μm or 1μm or less of the pore volume of the second microporous film,
A laminated microporous film, wherein the second microporous film has an air permeability (converted to a film thickness of 20 μm) of 20 seconds / 100 cc or more and 40 seconds / 100 cc or less . The laminated microporous film according to claim 1, wherein the second microporous film has an air permeability (converted to a film thickness of 20 μm) of 20 seconds / 100 cc or more and 25 seconds / 100 cc or less. 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 island portion has a particle size of 0.01 μm to 10 μm.   The battery separator containing the lamination | stacking microporous film of any one of Claims 1-4.