JP5295064B2 - Laminated microporous film, method for producing the same, and battery separator - Google Patents

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 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, recently, in order to increase the capacity, a battery having a high voltage specification is aimed at, and a separator used for the battery is required to cope with a high voltage. For example, when storing at a high temperature under a high voltage of 4.25 V or higher, the conventional polyethylene single-layer separator tends to decrease the capacity after storage. On the other hand, since a polypropylene is superior in oxidation resistance to polyethylene under high voltage and high temperature storage, a polypropylene separator has been proposed.

  A composite microporous film (battery separator) having a laminated structure in which a polypropylene microporous film is laminated on a conventional polyethylene microporous film has also been proposed (see, for example, Patent Document 1). Furthermore, a laminated microporous film formed from polypropylene having a specific weight average molecular weight has also been proposed (see, for example, Patent Document 2).

Japanese Patent No. 3003830 Japanese Patent No. 3939778

  The reason why polypropylene is used in Patent Document 1 is to increase the film breaking temperature. However, the rupture resistance of the composite microporous film disclosed in Patent Document 1 is insufficient under severe conditions such as a battery oven test that has been carried out in recent years.

  Further, the laminated microporous film disclosed in Patent Document 2 still has room for improvement from the viewpoint of achieving both good air permeability and high film breaking temperature.

  This invention is made | formed in view of such a situation, and makes it a subject to provide the separator for batteries using the lamination | stacking microporous film which has high film-breaking temperature, its manufacturing method, and it.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have obtained a microporous film having a sea-island structure having a sea part mainly composed of a polypropylene resin and an island part mainly composed of a polyphenylene ether-based resin. Was found to have a high membrane breaking temperature. As a result, the laminated microporosity is excellent in oxidation resistance under high voltage and high temperature storage, has a high film breaking temperature, and has a puncture strength and a film breaking resistance suitable as a separator for a lithium ion secondary battery. The film was completed.

  That is, the aspect of the present invention is the first microporous layer composed of the first resin composition and the second resin composition composed of the second resin composition having a melting point lower than that of the first resin composition. A microporous layer, and a third microporous layer comprising a polypropylene resin and a thermoplastic resin composition containing 5 to 90 parts by mass of a polyphenylene ether resin with respect to 100 parts by mass of the polypropylene resin. A porous film, wherein the third microporous layer is a laminated microporous film having a sea-island structure having a sea part of a phase containing polypropylene resin and an island part of a phase containing polyphenylene ether resin. The gist.

  According to the present invention, it is possible to provide a laminated microporous film having a good balance between high puncture strength and high film breaking temperature, a method for producing the same, and a battery separator using the same.

It is the schematic 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.

  The laminated microporous film of the present embodiment is composed of a first microporous layer composed of the first resin composition and a second resin composition having a melting point lower than that of the first resin composition. A second microporous layer, a polypropylene resin, and a thermoplastic resin composition as a third resin composition containing 5 to 90 parts by mass of a polyphenylene ether resin with respect to 100 parts by mass of the polypropylene resin. 3 microporous layers. The first resin composition, the second resin composition, and the third resin composition may have different melting points (hereinafter simply referred to as “melting points”) measured by a method according to JIS K-7121. For example, the material may be the same or different.

  Here, the difference between the melting points of the first and third resin compositions and the melting point of the second resin composition is preferably 5 ° C. or more, more preferably 10 ° C. or more. If the difference in melting point is 5 ° C. or more, when the laminated microporous film is used as a battery separator, when the internal temperature of the battery rises due to abnormal current, even if the low melting point resin layer melts, the high melting point The resin layer tends to be 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.

  As described above, the laminated microporous film of the present embodiment has the first microporous layer, the second microporous layer, and the third microporous layer. The embodiment is not particularly limited. Specific examples of the embodiment include: (a) a laminated microporous film comprising one first microporous layer, one second microporous layer, and one third microporous layer; b) the first microporous layer-the second microporous layer-the third microporous layer-the first microporous layer-the second microporous layer-the third microporous layer. Examples include laminated microporous films in which porous layers are alternately arranged.

  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) co-extrusion 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 the air permeability required for the laminated microporous film obtained in the present embodiment, each resin film is extruded separately with a T-die, and then each resin film is bonded by a laminating method. The method of (b) which forms the laminated film which laminated | stacked, and extends | stretches and then makes the laminated film porous after that is preferable. On the other hand, although the air permeability is slightly inferior to the method (a), the method (c) is also preferable in that the heat shrinkage rate of the laminated microporous film can be reduced.

  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, more preferably 10 to 200 m / min.

  Furthermore, it is desirable to heat-treat (anneal) 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 body 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.

3rd comprised from the 1st resin film comprised from a 1st resin composition, and the thermoplastic resin composition containing 5-90 mass parts polyphenylene ether resin with respect to 100 mass parts polypropylene resin and polypropylene resin. The heating temperature when annealing the resin film (hereinafter referred to as “high melting point resin film”) is preferably (T _mA -50) from the viewpoint of the balance of porosity, air permeability, and thermal shrinkage. It is not lower than C ° C. and not higher than (T _mA −2) ° C., more preferably not lower than (T _mA −40) ° C. and lower than (T _mA −10) ° C. Here, T _mA is the melting point (° C.) of the first resin composition.

On the other hand, when the second resin film composed of the second resin composition having the lower melting point (hereinafter referred to as “low melting point resin film”) alone is annealed, 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 higher and (T _mB −2) ° C. or lower, more preferably (T _mB −15) ° C. or higher (T _mB −2) ° C. It is as follows.

When the laminated film is annealed after laminating the film of the first resin composition, the high melting point resin film, and the low melting point resin film, the heating temperature is a laminated microporous film having high adhesive strength. From this point of view, 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. 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 the lamination, the annealing can be performed under conditions suitable for each of the first resin composition film, 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 layer is formed by subjecting a film of the first resin composition to a predetermined stretching treatment to make it porous. The film of the first resin composition preferably has an elastic recovery rate after heat treatment of 80 to 95%, more preferably 84 to 92%.

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

  The third microporous layer is formed by subjecting the 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 after heat treatment of 80 to 95%, more preferably 84 to 92%.

Here, the “elastic recovery rate after heat treatment” of the film of the first resin composition, the low melting point resin film, and the high melting point resin film is derived as follows. The film of the first resin composition and the high melting point resin film are annealed at 130 ° C. for 1 hour in the air, and then cut into strips having a width of 10 mm and a length of 50 mm to obtain test pieces. 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 the film of a 1st resin composition and 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)

Further, 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)

When forming a laminated film in which the film of the first resin composition, the low-melting point resin film, and the high-melting point resin film are formed in advance as in (a) and (b) above, the lamination of this embodiment It is preferable that the manufacturing method of a microporous film includes the cold extending process which gives 1st extending | stretching with respect to the laminated | multilayer film, and obtains a stretched laminated film. When the first resin composition film, the low-melting point resin film, and the high-melting point resin film are separately made porous as described in (c) above, It is preferable that the manufacturing method of a porous film includes the cold extending process of giving 1st extending | stretching with respect to each film, and obtaining a stretched laminated film. The stretching temperature for cold stretching is preferably −20 ° C. or higher from the viewpoint of preventing breakage, and (T _mB −60) ° 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.

  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.

It is preferable that the manufacturing method of the lamination | stacking microporous film of this embodiment includes the heat | fever extending process which gives 2nd extending | stretching after a cold extending process and obtains an extending | stretching laminated | multilayer film. The stretching temperature in the heat stretching step is preferably (T _mB −60) ° C. or higher from the viewpoint of preventing breakage, and (T _mB −2) ° C. or lower from the viewpoint of porosity and air permeability. 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 step is the surface temperature of the film.

  The draw ratio of the heat drawing step is preferably 1.05 times or more and 5.0 times or less, more preferably 1.1 times to 5.0 times, more preferably 2.0 times to 5.0 times. is there. 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.

  It is preferable that the manufacturing method of the lamination | stacking microporous film of this embodiment includes the process of heat-setting to a laminated body 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 10 to 50% (hereinafter, this method is referred to as “relaxation”), and the dimension in the stretching direction are as follows. The method of fixing so that it may not change is mentioned.

The heat _setting temperature 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. or less. Here, the heat setting temperature is the surface temperature of the film.
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, two or more stages of uniaxial stretching and heat setting with a roll are preferable.

  After extruding each resin film separately, a laminated film is formed by laminating and laminating each resin film by a laminating method, and then the laminated film is stretched to make it porous. In the case of producing a porous film, it is preferable to pass the film of the first resin composition, the low melting point resin film, and the high melting point resin film between heated rolls and perform thermocompression bonding. In this case, each resin film is unwound from the roll roll stand, and is laminated by being nipped and pressure-bonded between heated rolls. During lamination, it is necessary to perform thermocompression bonding so that the elastic recovery rate of each resin film does not substantially decrease.

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. Moreover, if the thermocompression bonding temperature is 140 ° C. or lower, a laminated microporous film that satisfies the intended problem tends to be easily obtained without dissolving the low melting point resin film and reducing its elastic recovery rate. 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 resin film]
The 1st microporous layer which concerns on this embodiment is obtained by extending | stretching and making porous the polypropylene resin film formed from the 1st resin composition which has a polypropylene as a main component. Examples of (a) polypropylene resin (hereinafter sometimes abbreviated as “PP”) used in this embodiment include homopolymers, random copolymers, and block copolymers. 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. Further, the stereoregularity of the polypropylene resin is not particularly limited, and isotactic or syndiotactic polypropylene resin is used.

  A polypropylene resin having any crystallinity or melting point can be used alone in this embodiment. However, two types of polypropylene resins having different properties may be blended at a specific blending ratio depending on the physical properties and applications of the obtained microporous film.

  The polypropylene resin used in this embodiment usually has a melt flow rate (based on ASTM D1238, measured at 230 ° C. under a load of 2.16 kg, the same applies hereinafter), preferably 0.1 to 100 g / 10 min. Preferably, it can select from the range of 0.1-80 g / 10min.

  In addition to the above-mentioned polypropylene resin, the polypropylene resin used in the present embodiment includes JP-A Nos. 44-15422, 52-30545, 6-313078, and 2006-83294. It may be a known modified polypropylene resin as described in 1. Furthermore, the polypropylene resin used in the present embodiment may be a mixture in any proportion of the above-described polypropylene resin and the modified polypropylene resin. The first resin composition mainly composed of polypropylene has a higher melting point than the second resin composition. When the melting point of the first resin composition is, for example, 150 ° C. to 280 ° C., the balance between the film breaking temperature and the film formability becomes good, which is preferable.

[Low melting point resin film]
The second microporous layer according to this embodiment is composed of a second resin composition containing, for example, a polyolefin resin such as polyethylene resin or polypropylene resin, or a saturated polyester resin such as polyethylene terephthalate resin or polybutylene terephthalate resin. It is obtained by stretching a low melting point resin film to make it porous.

  When the second resin composition constituting the low melting point resin film has a melting point of 100 ° C. to 150 ° C. when used as a battery separator, the safety of the battery is significantly improved. In order to obtain such a second resin composition, a resin having a melting point of 100 ° C. to 150 ° C. may be included in the resin composition. Examples of such a resin include a polyethylene resin, and more specifically, so-called 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 second resin composition is preferably 0.01 to 10 g / 10 minutes, more preferably 0.1 to 3 g / 10 minutes, and further preferably 0.8 to 2 0.0 g / 10 min, most preferably 1.0 to 1.6 g / 10 min. If the MFR is 0.01 g / 10 min or more, it tends to be difficult for fish eyes to occur in the low melting point resin film. When it is 10 g / 10 min or less, drawdown hardly occurs and the film formability tends to be good.

The density of the second resin composition is preferably 945~970kg / m ^3, more preferably from 955~970kg / m ^3, more preferably from 960~967kg / m ^3, most preferably 963 to 967 kg / m ³ . If the density is 945 kg / m ³ or more, a microporous film with better air permeability tends to be obtained. If it is 970 kg / m ³ or less, the film tends to be difficult to break during stretching.

[Third resin film (high melting point resin film)]
The third microporous layer according to this embodiment is a high melting point resin formed from a thermoplastic resin composition containing a polypropylene resin and 5-90 parts by mass of a polyphenylene ether resin with respect to 100 parts by mass of the polypropylene resin. It is obtained by stretching the film to make it porous.

ここで、式（１）中、Ｒ¹、Ｒ²、Ｒ³及びＲ⁴は、それぞれ独立に、水素原子、ハロゲン原子、炭素数１〜７の低級アルキル基、フェニル基、ハロアルキル基、アミノアルキル基、炭化水素オキシ基、及び、少なくとも２個の炭素原子がハロゲン原子と酸素原子とを隔てているハロ炭化水素オキシ基、からなる群より選ばれる化学種を示す。 Hereinafter, the thermoplastic resin composition will be described in detail.
[Polyphenylene ether resin]
Examples of the (b) polyphenylene ether resin (hereinafter sometimes abbreviated as “PPE”) used in the present embodiment include those having a repeating unit represented by the following chemical formula (1).

Here, in formula (1), 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. A chemical species 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 the PPE used in the present embodiment, 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 of a radical generator or It is also possible to use a known modified PPE obtained by reacting at a temperature of 80 to 350 ° C. in the absence, in the molten state, in the solution state or in the 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.

  The thermoplastic resin composition according to the present embodiment contains 5 to 90 parts by mass of (b) polyphenylene ether resin, preferably 10 to 80 parts by mass, more preferably 20 to 100 parts by mass of (a) polypropylene resin. Contains ~ 65 parts by mass. Setting the content ratio of PPE within the above range is preferable from the viewpoint of stretchability of the obtained laminated microporous film. As PPE used in the present embodiment, in addition to the above-mentioned PPE, those obtained by adding polystyrene, high impact polystyrene, syndiotactic polystyrene and / or rubber-reinforced syndiotactic polystyrene to PPE are also preferably used. .

[Admixture]
The laminated microporous film of the present embodiment has a sea-island structure composed of a sea portion of a phase preferably containing a polypropylene resin as a main component and an island portion of a phase preferably containing a polyphenylene ether resin as a main component. It has a microporous layer. In this case, the PPE resin is dispersed in the PP resin matrix. Preferably, the particle size of the island part is 0.01 μm to 10 μm. In order to satisfy these conditions, the thermoplastic resin composition according to this embodiment particularly preferably contains a polypropylene resin, a polyphenylene ether resin, and an admixture. In the present specification, “including as a main component” and “mainly comprising” means that the specific component is preferably contained in a composition (matrix component) containing the specific component, preferably 50% by mass or more. It means that 80% by mass or more is preferably contained, and 100% by mass may be contained.

  The (c) admixture used in this embodiment acts as a dispersant for dispersing the polyphenylene ether resin in the above-described polypropylene resin matrix. Furthermore, the admixture has the effect of imparting good porosity and good air permeability to the microporous film according to the present embodiment.

  As the admixture (c) used in the present embodiment, a hydrogenated block copolymer is preferable from the viewpoint of dispersibility of the polyphenylene ether resin. The hydrogenated block copolymer includes at least one polymer block A mainly composed of a structural unit of a vinyl aromatic compound, and at least one polymer block B mainly composed of a structural unit of a conjugated diene compound. A block copolymer obtained by adding hydrogen to a block copolymer comprising

  Examples of the conjugated diene compound that provides the structural unit of the polymer block B include one or two selected from the group consisting of butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. The above is mentioned. Among these, butadiene, isoprene and combinations thereof are preferable. The polymer block B mainly composed of the structural unit of the conjugated diene compound is preferably a polymer block containing at least 70% by mass or more of the structural unit of the conjugated diene compound, and is a homopolymer block of the conjugated diene compound or a conjugated diene compound. It means a copolymer block of a 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 amount of 1,2-vinyl bonds and the amount of 3,4-vinyl bonds (hereinafter abbreviated as “vinyl bond amount”) is 40. -90% is preferable, More preferably, it is 45-85%. Here, the “vinyl bond amount” refers to the ratio of the number of vinyl bonds remaining in the polymer block B after polymerization to the number of vinyl bonds that the conjugated diene compound has before polymerization. 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 40% or more, the balance between the porosity and the permeability of the laminated microporous film of the present embodiment is further improved.

  Examples of the vinyl aromatic compound that provides the structural unit of the polymer block A include one or more selected from the group consisting of styrene, α-methylstyrene, vinyltoluene, p-tert-butylstyrene, and diphenylethylene. Is mentioned. Of these, styrene is preferred.

  The polymer block A mainly composed of a vinyl aromatic compound structural unit is preferably a polymer block containing 70% by mass or more of a vinyl aromatic compound structural unit, and a vinyl aromatic compound homopolymer block, or And a copolymer block of a vinyl aromatic compound and a monomer copolymerizable with the vinyl aromatic compound.

  The number average molecular weight of the block copolymer having the above structure is measured by gel permeation chromatography using polystyrene as a standard substance, and is preferably in the range of 5,000 to 1,000,000. 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. 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) of the polymer block B contained therein, thereby obtaining a hydrogenated block copolymer, that is, a vinyl aromatic. A hydrogenated product of the compound-conjugated diene compound block copolymer is preferable. The hydrogenation rate with respect to the aliphatic double bond is preferably 80% or more based on the total amount of the aliphatic double bond in the block copolymer before hydrogenation. 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% by mass, more preferably 1 to 15% by mass, based on the total amount of the composition. Thereby, the dispersibility of the polyphenylene ether resin and the porosity and air permeability of the laminated microporous film in the present embodiment resulting from the dispersibility are improved.

  Further, the thermoplastic resin composition according to the present embodiment includes, in addition to the above-described components, additional components such as an olefin elastomer and an antioxidant as long as the effects exerted by the present invention are not impaired. 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.), various types Colorant may be added such as mold release agents.

[Sea-island structure]
The third microporous layer according to this embodiment has a sea-island structure composed of a sea part of a phase containing a polypropylene resin and an island part of 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. 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). ).

  As described above, the particle size of the island part is preferably 0.01 μm to 10 μm, more preferably 0.1 μm to 5 μm. Setting the particle size of the islands in such a 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. Setting the ratio of the major axis diameter to the minor axis diameter in such a range is preferable 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, a laminated microporous film obtained using a high melting point resin film formed from a specific thermoplastic resin composition containing (a) a polypropylene resin and (b) a polyphenylene ether resin is a lithium ion battery. It is a laminated microporous film having excellent porosity and air permeability that can also be used for separators for use. Although this laminated microporous film is obtained using a high melting point resin film having a phase containing polypropylene resin as a sea part, the film form can be maintained even at a temperature exceeding 200 ° C. of the polypropylene resin melting point. A laminated microporous film with improved heat resistance. This improvement in heat resistance is surprising, which could never have been predicted from the prior art.

  Here, “improvement of heat resistance” refers to 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. As is clear from the above, the laminated microporous film of this embodiment can achieve a film breaking temperature of 200 ° C. or higher. The laminated microporous film having a membrane breaking temperature of 200 ° C. or higher according to this embodiment can dramatically improve the heat resistance as a battery separator. Although the details of the mechanism for realizing such a high film breaking temperature are not clear, while a porous structure is formed by using a resin composition containing PP and PPE, PP is the sea part and PPE is the island part. It can be considered that the film has a morphology as described above, so that a high melt viscosity can be maintained even after film formation, contributing to an improvement in the film breaking temperature.

[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%. By setting the porosity to 20% or more, sufficient ion permeability can be ensured when the laminated microporous film is used for battery applications. On the other hand, by setting the porosity to 70% or less, the laminated microporous film can ensure sufficient mechanical strength. 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.

In addition, the porosity 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. In addition, the porosity of the laminated microporous film is calculated by cutting 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 can contribute to 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 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 air permeability is measured using a Gurley type air permeability meter according to JIS P-8117.

  The microporous film according to this 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.

  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. In addition, the raw material used and the evaluation method of various characteristics are as follows.

First, the melt flow rate (MFR) is a value measured in accordance with JIS K 7210, polypropylene resin at 210 ° C. and 2.16 kg, polyethylene resin at 190 ° C. and 2.16 kg, and the unit is g / 10 minutes. The density of the polyethylene resin is a value measured according to JIS K 7112, and the unit is kg / m ³ . The melt viscosity is a sample (when the first microporous layer and the second microporous layer are simultaneously integrally formed as a laminated microporous film, the sample peeled off from each layer is used as a sample). Is a value obtained by producing a sheet by press molding at 200 ° C. and measuring under the same conditions as those for measuring the melt viscosity described above, and the unit is Pa · s.

The following were used as the polypropylene resin, polyethylene resin, polyphenylene ether resin, and admixture.
1. Polypropylene resin (a-1) Propylene homopolymer, MFR = 0.4, melt viscosity = 61000
2. Polyethylene (b-1) Asahi Kasei Chemicals Corporation Suntech HD S160S
Melting point (T _mB ) 133 ° C
3. Polyphenylene ether resin (c-1) PPE having a reduced viscosity of 0.54 obtained by oxidative polymerization of 2,6-xylenol

3. Admixture (d-1) Polystyrene (1) -hydrogenated polybutadiene-polystyrene (2) structure, 43% bonded styrene, number average molecular weight 95,000, 1,2 of polybutadiene before hydrogenation -Total amount of vinyl bonds and 3,4-vinyl bonds of 80%, number average molecular weight of polystyrene (1) 30,000, number average molecular weight of polystyrene (2) 10,000, polybutadiene part hydrogenation rate 99.9% Of hydrogenated styrene-butadiene block copolymer

The characteristics of various films were measured as follows.
(1) Film thickness (μm)
It was measured with a dial gauge (manufactured by Ozaki Seisakusho, trade name “PEACOCK No. 25”).
(2) 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
(3) Air permeability (sec / 100cc)
It measured with the Gurley type air permeability meter based on JIS P-8117. A value obtained by converting the film thickness to 20 μm was derived.

(4) Film tear temperature (film resistance)
FIG. 1 shows a schematic diagram of a measuring device for the film breaking temperature. FIG. 1A is an overall view thereof, and FIGS. 1B and 1C are plan views schematically showing samples in the measuring apparatus. First, as shown in FIG. 1B, a laminated microporous film 1 is laminated on a nickel foil 2A 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 2A. 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. 1C, a Teflon (registered trademark) tape was bonded to the 10 μm thick nickel foil 2B for masking. However, a 15 mm × 10 mm window (opening) portion was left in the center of the nickel foil 2B.

  Next, as shown in FIG. 1A, the nickel foil 2 </ b> A and the nickel foil 2 </ b> B processed as described above were overlapped with the laminated microporous film 1 interposed therebetween. Furthermore, two nickel foils 2A and 2B were sandwiched between the glass plates 3A and 3B from both sides. At this time, it aligned so that the window part of nickel foil 2B and the lamination | stacking microporous film 1 might face. The two glass plates 3A and 3B were sandwiched and fixed by a commercially available double clip (not shown). These were accommodated in the oven 8.

  Next, an electrical resistance measuring device (LCR meter manufactured by Ando Electric Co., Ltd., trade name “AG-4311”) 4 was connected to the nickel foils 2A and 2B. Moreover, the thermocouple 5 connected to the thermometer 6 was fixed to the glass plate 3A using Teflon (registered trademark). A data collector 7 for recording the measured electric resistance and temperature was connected to the electric resistance measuring device 4 and the thermometer 6.

Using such an apparatus, the electrical resistance between the nickel foils 2A and 2B was continuously measured while raising the temperature of the glass plate 3A from 25 ° C. to 200 ° C. at a rate of 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 2A and 2B once reached 10 ³ Ω and 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 “「 ”.

(5) Thermal contraction rate A sample of 12 cm x 12 cm square is cut out from the film, and two (total of four) marks are placed at 10 cm intervals in the MD and TD directions of the sample, and the sample is sandwiched between papers. And left in an oven at 100 ° C. or 140 ° C. for 60 minutes. After the sample was taken out from the oven and cooled, the length (cm) between the marks in the MD direction and the TD direction was measured, and the thermal shrinkage rate in the MD direction and the TD direction was calculated by the following formula.
MD direction thermal shrinkage (%) = (10−length in the MD direction after heating (cm)) / 10 × 100
Thermal contraction rate (%) in TD direction = (10−length in TD direction after heating (cm)) / 10 × 100

4). Puncture strength (N)
A handy compression tester KES-G5 manufactured by Kato Tech Co., Ltd. is attached with a needle having a diameter of 1 mm and a radius of curvature of 0.5 mm at the tip, at a temperature of 23 ± 2 ° C., and a needle moving speed of 0.2 cm / sec. A piercing test was conducted. This is converted to a thickness of 20 μm based on the measured value of the film thickness and is defined as the puncture strength.
Puncture strength (N) = Measured puncture strength × 20 / film thickness

[Production Example 1]
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). . The elastic recovery rate after heat treatment of this polypropylene film was 90%.

[Production Example 2]
A polyethylene resin (b-1) was introduced into a single-screw extruder set at 20 mm in diameter, L / D = 30, and 220 ° 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 after that, 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 (B-1). did. The elastic recovery rate after heat treatment of this low melting point resin film was 72%.

[Production Example 3]
11 parts by mass of polyphenylene ether resin (c-1) and 3 parts by mass of admixture (d-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, (c-1) component, and (d-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.

  A high melting point resin film (C-1) was molded in the same manner as in Production Example 1 except that the thermoplastic resin composition pellets obtained as described above were used instead of the polypropylene resin (a-1). . 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%. The particle size (μm) of the island portion was measured as described above, and the measured particle size range (maximum particle size to minimum particle size) was shown. As is clear from the measurement of the particle size, a sea-island structure was also observed.

[Example 1]
The low melting point resin film (B-1) is sandwiched between the polypropylene resin film (A-1) and the high melting point resin film (C-1) from both sides, and the outer layer is the polypropylene resin film (A-1) and the high melting point resin film (C -1) A three-layer laminated film having an inner layer having a structure of a low-melting point resin film (B-1) was produced as follows. First, the polypropylene resin film (A-1), the high melting point resin film (C-1), and the low melting point resin film (B-1) are unwound at an unwinding speed of 4.0 m / min. Then, thermocompression bonding was performed at a thermocompression bonding temperature of 130 ° C. and a linear pressure of 2.0 kg / cm, and then the film was guided to a 25 ° C. cooling roll at the same speed and wound to obtain a laminated film. This laminated film 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). The obtained laminated microporous film was measured for film thickness, porosity, air permeability, heat shrinkage rate, puncture strength, and film breaking temperature (film breaking resistance). The results are shown in Table 1.

[Example 2]
A laminated microporous film was obtained in the same manner as in Example 1 except that after the heat stretching step of Example 1, it was relaxed by a factor of 0.8 at a temperature of 125 ° C. and heat fixed. The obtained laminated microporous film was measured for film thickness, porosity, air permeability, heat shrinkage rate, puncture strength, and film breaking temperature (film breaking resistance). The results are shown in Table 1.

[Comparative Example 1]
A laminated microporous film was obtained in the same manner as in Example 1 except that the polypropylene resin film (A-1) was used instead of the high melting point resin film (C-1). The obtained laminated microporous film was measured for film thickness, porosity, air permeability, heat shrinkage rate, puncture strength, and film breaking temperature (film breaking resistance). The results are shown in Table 1. Although the puncture strength was good, the film breaking temperature was less than 180 ° C., which was inferior to the examples.

DESCRIPTION OF SYMBOLS 1 Laminated microporous film 2A Nickel foil 2B Nickel foil 3A Glass plate 3B Glass plate 4 Electrical resistance measuring device 5 Thermocouple 6 Thermometer 7 Data collector 8 Oven

Claims (9)

A first microporous layer composed of a first resin composition;
A second microporous layer composed of a second resin composition having a lower melting point than the first resin composition;
A third microporous layer composed of a polypropylene resin and a thermoplastic resin composition containing 5 to 90 parts by mass of a polyphenylene ether resin with respect to 100 parts by mass of the polypropylene resin;
A laminated microporous film comprising:
The laminated microporous film, wherein the third microporous layer has a sea-island structure having a sea part of a phase containing the polypropylene resin and an island part of a phase containing the polyphenylene ether resin.   The laminated microporous film according to claim 1, 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 has at least one polymer block A mainly composed of a structural unit of a vinyl aromatic compound, and the total amount of 1,2-vinyl bonds and 3,4-vinyl bonds of the conjugated diene compound is 40 to 40. The hydrogenated block copolymer obtained by adding hydrogen to a block copolymer comprising at least one polymer block B mainly composed of 90% of the structural unit of the conjugated diene compound. Laminated microporous film.   The laminated microporous film according to any one of claims 1 to 3, wherein the first resin composition is a polypropylene resin composition.   The laminated microporous film according to any one of claims 1 to 4, wherein the second resin composition is a polyethylene resin composition.   The laminated microporous film according to claim 2 or 3, 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 any one of claims 1 to 6. It is a manufacturing method of the lamination | stacking microporous film of any one of Claims 1 thru | or 6, Comprising: The manufacturing method of a lamination | stacking microporous film including the following processes (1) and (2):
(1) A first resin film composed of a first resin composition and a second resin film composed of a second resin composition having a melting point lower than the melting point of the first resin composition And a third resin film composed of a polypropylene resin and a thermoplastic resin composition containing 5-90 parts by mass of a polyphenylene ether resin with respect to 100 parts by mass of the polypropylene resin, A cold drawing step of cold drawing to 1.05 times or more and 2.0 times or less in at least one direction in a state where the temperature is maintained below 60 ° C. from the melting point of the second resin composition,
(2) The temperature obtained by subtracting 60 ° C. from the melting point of the second resin composition and the temperature obtained by subtracting 2 ° C. from the melting point of the second resin composition. A heat stretching process in which the film is stretched by 1.05 times or more and 5.0 times or less in at least one direction in a state of being kept below. The method for producing a laminated microporous film according to claim 8, further comprising the following step (3) after the step (2):
(3) The temperature of the laminate stretched in step (2) by 30 ° C. from the melting point of the second resin composition and the temperature by 2 ° C. or less from the melting point of the second resin composition The process of heat setting at a temperature of.

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