JP6627616B2 - Laminated porous film, battery separator, and battery - Google Patents

Description

  The present invention relates to a laminated porous film, in particular, when used as a separator for a lithium ion secondary battery, has excellent air permeability that contributes to battery performance and excellent electric resistance due to control of the porous structure. And a laminated porous film effective for improving the functionality of the battery. The present invention also relates to a battery separator and a battery using the laminated porous film.

Secondary batteries are widely used as power supplies for portable devices such as OA, FA, household appliances, and communication devices. In particular, portable equipment using a lithium-ion secondary battery has been increasing because it has good volumetric efficiency and leads to downsizing and weight saving of the equipment when installed in the equipment.
On the other hand, large secondary batteries have been researched and developed in many fields related to energy / environmental issues, including load leveling, UPS, electric vehicles, and have excellent capacity, high output, high voltage, and long-term storage stability. From this point of view, applications of lithium ion secondary batteries, which are a kind of non-aqueous electrolyte secondary batteries, are expanding.

  The operating voltage of the lithium ion secondary battery is usually designed with an upper limit of 4.1 V to 4.2 V. At such a high voltage, the aqueous solution undergoes electrolysis and cannot be used as an electrolyte. Therefore, a so-called non-aqueous electrolytic solution using an organic solvent is used as an electrolytic solution that can withstand a high voltage.

  As the solvent for the non-aqueous electrolyte, a high dielectric constant organic solvent capable of allowing more lithium ions to exist is used, and as the high dielectric constant organic solvent, organic carbonates such as polypropylene carbonate and ethylene carbonate are mainly used. It is used. In addition, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in a solvent and used as a supporting electrolyte serving as a lithium ion source in the solvent.

  In a lithium ion secondary battery, a battery separator is interposed between a positive electrode and a negative electrode in order to prevent an internal short circuit. Naturally, the battery separator is required to have insulation from its role. Further, it is necessary to have a microporous structure in order to provide a gas permeability as a passage for lithium ions and a function of diffusing and holding the electrolyte. To satisfy these requirements, a porous film is used as a battery separator.

  Lithium ion secondary battery separators are desired to have high safety and low electrical resistance. High safety in battery separators means that when a lithium ion secondary battery becomes abnormal and goes into a thermal runaway state, it maintains insulation and prevents short-circuiting between electrodes without causing film breakage or shrinkage. This function prevents accidents such as ignition due to abnormal heat generation of the battery. Such a separator with improved safety, filled with inorganic particles in a resin composition and then made porous, or a solution containing inorganic particles coated on a porous membrane, and a high melting point heat-resistant resin And the like are known. In addition, in order to improve the discharge performance of a battery at a large current and the discharge performance at a low temperature as a low electric resistance, it is necessary to reduce the resistance of the ions flowing while the separator holds the electrolytic solution as small as possible. There is a demand for a separator having a low electric resistance value in a state where the liquid is contained. In the use of battery separators, in recent years, there has been an increasing demand for porous films having improved ionic permeability and low electric resistance for the purpose of improving the performance and production efficiency of batteries.

  Conventionally, as a film having a microporous structure used as a battery separator, Japanese Patent Application Laid-Open No. 10-50287 (Patent Document 1) discloses an inorganic material comprising a polyolefin resin and an inorganic powder and / or an inorganic fiber and having excellent heat resistance. Substance-containing porous films have been proposed.

  Further, in order to increase the permeability of a porous film, a method of incorporating a β crystal, which is one of the crystal forms, into a polypropylene resin and stretching the polypropylene film to obtain a porous film is disclosed in JP-A-6-100720. It is proposed in a gazette (Patent Document 2).

  Further, as a laminated porous film, a film in which a porous layer made of a polyolefin resin is formed on both sides of a particle layer made of an inorganic particle and a thermoplastic resin is disclosed in JP-A-2012-22911 (Patent Document 3). Japanese Patent Application Laid-Open No. 2009-185093 (Patent Literature 4) proposes a method of obtaining a separator by co-extruding two layers containing and not containing a layer.

  JP-A-2012-131990 (Patent Document 5) and JP-A-2012-92213 (Patent Document 6) have been proposed as porous films obtained by adding inorganic particles and an elastomer to a polyolefin-based resin. In these porous films, the mechanical strength of the film can be improved by adding an elastomer.

JP-A-10-50287 JP-A-6-100720 JP 2012-22911 A JP 2009-185093 A JP 2012-131990 A JP 2012-92213 A

  However, since the separator of Patent Document 1 contains inorganic particles in all layers in the porous film, the pore structure formed from the inorganic particles at the time of stretching tends to be coarse, and the mechanical strength is uneasy.

  In addition, the porous film of Patent Document 2 cannot be said to have sufficient heat resistance to be used as a battery separator, and there is room for improvement in securing battery safety.

  Further, the laminated separator of Patent Document 3 and the microporous polyolefin membrane of Patent Document 4 are said to have excellent heat resistance by having a porous layer containing inorganic particles, but have relatively low air permeability resistance with respect to the thickness of the entire porous film. Because of the high electric resistance, it is presumed that the electric resistance when a battery is assembled using these is high, and there is room for improvement.

  Further, with the addition of the elastomer, Patent Document 5 states that the elongation retention rate should be improved, and Patent Document 6 that the tear strength should be improved. However, these documents consider the effect of the addition of the elastomer on pore formation. However, there is room for improvement in the electrical resistance, which is greatly affected by the porous structure and the communication between the holes.

  In addition, according to Patent Documents 1 and 4, when producing a porous film, a plasticizer is mixed with a polyolefin-based resin and inorganic particles, and this mixture is formed into a sheet by primary processing, and the sheet is stretched and rolled. After performing secondary processing to provide holes, it is necessary to perform a step of extracting and removing the blended plasticizer with an organic solvent, and a large amount of an organic solvent is used in this extraction step. In addition, production efficiency may decrease.

  The present invention has been made in view of the above problems, and is not only excellent in air permeability, but also excellent in stability at the time of film formation, excellent in productivity, improved in ion permeability, and low in electric resistance value. An object of the present invention is to provide a film, a method for producing the film, and a battery separator and a battery using the laminated porous film.

  The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that a porous layer (I layer) mainly composed of a polypropylene resin (A), a polypropylene resin (A), inorganic particles (B ) And a laminated porous film having at least two layers of a heat-resistant layer (II layer) composed of a resin composition containing a specific vinyl aromatic elastomer (C), and found that the above-mentioned problems were solved. The invention has been completed.

That is, the present invention is as follows.
[1] A resin composition containing a porous layer (I layer) mainly composed of a polypropylene resin (A), a polypropylene resin (A), inorganic particles (B), and a vinyl aromatic elastomer (C) ( The vinyl aromatic elastomer (C) has a melt flow rate (MFR) of 1 g / 10 minutes or less at a temperature of 230 ° C. and a load of 2.16 kg having at least two layers with a heat-resistant layer (II layer) composed of II). A laminated porous film, characterized in that:
[2] The laminated porous film according to [1], wherein the vinyl aromatic elastomer (C) is contained in an amount of 1 to 30 parts by mass in 100 parts by mass of the resin composition (II).
[3] The laminated porous film according to [1] or [2], wherein the porous layer (I layer) has β-crystal activity.
[4] The laminated porous film according to any one of [1] to [3], wherein the porous layer (I layer) contains a β crystal nucleating agent.
[5] The laminated porous film according to any one of [1] to [4], which is a stretched film.
[6] The laminate according to any one of [1] to [5], wherein the air permeability measured at 25 ° C. in accordance with JIS P8117 (2009) is 100 seconds / 100 ml or less. Porous film.
[7] Impregnated with a propylene carbonate: ethyl methyl carbonate = 1: 1 (v / v) solution containing 1 M lithium perchlorate, and the electrical resistance in the thickness direction measured at 25 ° C. is 0.7Ω or less. The laminated porous film according to any one of [1] to [6].
[8] A battery separator using the laminated porous film according to any one of [1] to [7].
[9] A battery using the battery separator according to [8].
[10] The method for producing a laminated porous film according to any one of [1] to [7], wherein the polypropylene-based resin composition constituting the I layer and the polypropylene-based resin constituting the II layer (A), a step of coextruding a resin composition (II) containing the inorganic particles (B) and the vinyl aromatic elastomer (C) to produce a nonporous film, and the nonporous film. At least in a uniaxial direction to make the film porous, and the method does not include the step of removing the additive with a solvent.

  The laminated porous film of the present invention has a specific porous layer (I layer) and a heat-resistant layer (II layer), and the II layer has inorganic particles (B) and a vinyl aromatic elastomer (C) having a specific MFR. By containing the compound, the pores have high continuity, excellent air permeability, low electric resistance associated with excellent ion permeability, and excellent heat resistance. Therefore, the efficiency and safety of a battery using the laminated porous film of the present invention as a battery separator can be improved.

  Further, the laminated porous film of the present invention does not require strict control of the production conditions, melt-kneads the raw materials, and stretches at least uniaxially a nonporous film-like material produced using the obtained resin composition. It is possible to produce a porous material by simply performing the process, and it is not necessary to perform a step of removing the additive with a solvent, so that the productivity is excellent and the adverse effect on the environment can be reduced.

1 is a schematic internal development perspective view of a battery containing a laminated porous film of the present invention. It is a figure explaining the fixing method of the lamination porous film in wide-angle X-ray diffraction measurement.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the description of constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the gist thereof. However, the present invention is not limited to the following contents, and can be appropriately modified and implemented.

[Laminated porous film]
1. Porous layer (I layer)
In the laminated porous film of the present invention, the porous layer (I layer) is a layer mainly composed of the polypropylene resin (A), and is a polypropylene resin composition mainly composed of the polypropylene resin (A). (Hereinafter sometimes referred to as “resin composition (I)”), and preferably formed of a resin composition (I) containing a polypropylene resin (A) and a β crystal nucleating agent (D). It is a layer that has a β-crystal activity and is formed into a homogeneous porous film after stretching.
Here, the main component preferably contains 50% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more, as a component in the porous layer (I layer) or the resin composition (I). That means.

1-1. Polypropylene resin (A)
Examples of the polypropylene resin (A) in the present invention include homopolypropylene (propylene homopolymer) or propylene, ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and 1-nonene. Alternatively, a random copolymer or a block copolymer with an α-olefin such as 1-decene may be used. Among them, homopolypropylene is more preferably used from the viewpoint of mechanical strength.

In addition, the polypropylene resin (A) preferably has an isotactic pentad fraction exhibiting stereoregularity of 80 to 99%, more preferably 83 to 98%, and still more preferably 85 to 97%. is there. If the isotactic pentad fraction is 80% or more, there is little possibility that the mechanical strength will decrease. On the other hand, the upper limit of the isotactic pentad fraction is specified by the upper limit that can be obtained industrially at the present time. is not.
The isotactic pentad fraction is a three-dimensional structure in which all five methyl groups, which are side chains with respect to the main chain formed by any five consecutive propylene units, are located in the same direction with respect to the main chain. Or it means the ratio. Assignment of signals in the methyl group region is described in A. Zambelli et al. (Macromol. 8, 687 (1975)).

Moreover, it is preferable that Mw / Mn which is a parameter which shows molecular weight distribution of the polypropylene resin (A) is 1.5 to 10.0. Mw / Mn of the polypropylene resin (A) is more preferably from 2.0 to 8.0, and still more preferably from 2.0 to 6.0. The smaller the Mw / Mn, the narrower the molecular weight distribution. However, when the Mw / Mn is 1.5 or more, sufficient extrudability is obtained, and industrial mass production is possible. On the other hand, when Mw / Mn is 10.0 or less, sufficient mechanical strength can be secured.
Mw / Mn of the polypropylene resin (A) is measured by GPC (gel permeation chromatography).

Further, the melt flow rate (MFR) of the polypropylene resin (A) is not particularly limited, but is usually preferably 0.5 to 15 g / 10 min, and is preferably 1.0 to 10 g / 10 min. More preferably, there is. When the MFR of the polypropylene resin (A) is 0.5 g / 10 min or more, the polypropylene resin has a sufficient melt viscosity at the time of molding and can secure high productivity. On the other hand, when the MFR of the polypropylene-based resin (A) is 15 g / 10 minutes or less, sufficient strength can be obtained.
The MFR of the polypropylene resin (A) is measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210-1 (2014).

  The method for producing the polypropylene resin (A) is not particularly limited, and may be a known polymerization method using a known polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. And a polymerization method using a single-site catalyst.

  Examples of the polypropylene-based resin (A) include “Novatec PP”, “WINTEC” (all manufactured by Nippon Polypropylene), “Natio”, “Tuffmer XR” (all manufactured by Mitsui Chemicals), and “Zeras”. , "Thermorun" (above, manufactured by Mitsubishi Chemical Corporation), "Sumitomo Noblen", "Tafselen" (above, manufactured by Sumitomo Chemical), "Prime Polypro", "Prime TPO" (Prime Polymer), "Adflex", Commercially available products such as "Adsyl", "HMS-PP (PF814)" (manufactured by Sun Allomer), "Versify", and "Inspire" (manufactured by Dow Chemical) can be used.

  As the polypropylene-based resin (A), only one kind may be used, or two or more kinds having different compositions and physical properties may be used in combination.

  In the laminated porous film of the present invention, the porous layer (I layer) preferably has β-crystal activity. The β-crystal activity can be regarded as an index indicating that the polypropylene-based resin has produced β crystals in the film before stretching. If the polypropylene-based resin in the film before stretching generates β crystals, even if no additives such as fillers are used, many fine and uniform pores are formed by stretching afterwards. Further, a laminated porous film having high mechanical strength, excellent air permeability, and capable of improving battery characteristics as a battery separator can be obtained.

  In the laminated porous film of the present invention, when the crystal melting peak temperature derived from the β crystal of the polypropylene resin is detected by the following differential scanning calorimeter (1), and / or X in the following (2) When a diffraction peak derived from β-crystal is detected by the measurement using a line diffraction apparatus, it is determined to have “β-crystal activity”.

  The β crystal activity of the polypropylene resin can be measured for the laminated porous film of the present invention in the state of all the laminated porous films.

(1) In the case of using a differential scanning calorimeter The laminated porous film is heated with a differential scanning calorimeter from 25 ° C to 240 ° C at a heating rate of 10 ° C / min, held for 1 minute, and then from 240 ° C to 25 ° C. When the temperature is lowered at a cooling rate of 10 ° C./min and held for 1 minute, and then re-heated at a heating rate of 10 ° C./min from 25 ° C. to 240 ° C., the crystal derived from β-crystal of the polypropylene resin at the time of re-heating When the melting peak temperature (Tmβ) is detected, it is determined that the compound has β-crystal activity.

The β crystal activity is calculated from the following equation using the detected crystal melting heat (ΔHmα) and β crystal derived crystal melting heat (ΔHmβ) of the polypropylene resin.
β crystal activity (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100
For example, when the polypropylene-based resin is a homopolypropylene, the heat of crystal fusion (ΔHmβ) derived from β crystal mainly detected in the range of 145 ° C. to less than 160 ° C. and mainly detected in the range of 160 ° C. to 170 ° C. It can be calculated from the heat of crystal fusion (ΔHmα) derived from the α-crystal. For example, when the polypropylene-based resin is a random polypropylene in which ethylene is copolymerized with 1 to 4 mol%, the β-crystal-derived heat of crystal fusion (ΔHmβ) mainly detected in a range of 120 ° C. or more and less than 140 ° C. Can be calculated from the heat of crystal fusion (ΔHmα) derived from the α crystal mainly detected in the range of 140 ° C. or more and 165 ° C. or less.

The β-crystal activity of the porous layer (I layer) is preferably higher, specifically, it is preferably at least 20%, more preferably at least 40%, even more preferably at least 60%. If the porous layer (I layer) has a β-crystal activity of 20% or more, it is shown that a large amount of β-crystals of the polypropylene-based resin can be generated even in the film-like material before stretching. In addition, many uniform pores are formed, and as a result, a laminated porous film having high mechanical strength and excellent air permeability can be obtained.
The upper limit of the β crystal activity is not particularly limited, but the higher the β crystal activity, the more effective the above-mentioned effects can be obtained, and therefore, the closer to 100%, the more preferable.

(2) In the case of using an X-ray diffractometer When judging the presence or absence of β-crystal activity from a diffraction profile obtained by wide-angle X-ray diffraction measurement of a laminated porous film subjected to a specific heat treatment, specifically, a polypropylene resin is used. A heat treatment at 170 to 190 ° C., which is a temperature exceeding the crystal melting peak temperature, is performed, and a wide angle X-ray measurement is performed on the laminated porous film that has been slowly cooled to produce and grow β crystals. When a diffraction peak derived from the (300) plane is detected in the range of 2θ = 16.0 ° to 16.5 °, it is determined that there is β crystal activity.
For details on the β crystal structure and wide-angle X-ray diffraction of a polypropylene-based resin, see Macromol. Chem. 187, 643-652 (1986), Prog. Polym. Sci. Vol. 16, 361-404 (1991), Macromol. Symp. 89, 499-511 (1995), Macromol. Chem. 75, 134 (1964), and references cited therein. The detailed evaluation method of β-crystal activity using wide-angle X-ray diffraction will be described in Examples below.

  As a method for obtaining the above-mentioned β-crystal activity, a method in which a substance that promotes the formation of α-crystals of the polypropylene resin (A) is not added to the resin composition (I), or a method in which the resin composition (I) is disclosed in Japanese Patent No. 3739481. And a method of adding a β crystal nucleating agent to the resin composition (I). Among them, it is particularly preferable to add a β crystal nucleating agent (D) to the resin composition (I) to obtain β crystal activity. By adding the β crystal nucleating agent (D), the generation of β crystal of the polypropylene resin (A) can be promoted more uniformly and efficiently, and a porous layer (I layer) having β crystal activity is provided. Thus, a laminated porous film for a battery can be obtained.

1-2. β crystal nucleating agent (D)
As described above, in the present invention, in order to obtain a fine porous structure, the porous layer (I layer) preferably has β crystal activity, and among them, it is preferable to use the β crystal nucleating agent (D). Examples of the β crystal nucleating agent (D) used in the present invention include the following, but are not particularly limited as long as it increases the generation and growth of β crystal of the polypropylene resin (A). Also, two or more kinds may be used as a mixture.

  Examples of the β crystal nucleating agent (D) include an amide compound; a tetraoxaspiro compound; a quinacridone; an iron oxide having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, and phthalate. Alkali or alkaline earth metal salts of carboxylic acids such as magnesium silicate; aromatic sulfonic acid compounds such as sodium benzenesulfonate and sodium naphthalenesulfonate; di- or triesters of di- or tribasic carboxylic acids A phthalocyanine pigment represented by phthalocyanine blue, etc .; a two-component compound comprising component A which is an organic dibasic acid and component B which is an oxide, hydroxide or salt of a metal of Group 2 of the periodic table; Consists of compound and magnesium compound Such as the formation thereof.

  Specific examples of the commercially available β crystal nucleating agent (D) include a β crystal nucleating agent “NJESTA NU-100” manufactured by Shin Nippon Rika Co., Ltd., and specific examples of the polypropylene resin to which the β crystal nucleating agent is added. And polypropylene "Bepol B-022SP" manufactured by Aristech, polypropylene "Beta (β) -PP BE60-7032" manufactured by Borealis, polypropylene "BNX BETAPP-LN" manufactured by Mayzo, and the like.

  The ratio of the β crystal nucleating agent (D) to be added to the polypropylene resin (A) needs to be appropriately adjusted depending on the type of the β crystal nucleating agent (D) or the composition of the polypropylene resin (A), The β crystal nucleating agent (D) is preferably 0.0001 to 5.0 parts by mass, more preferably 0.001 to 3.0 parts by mass, and more preferably 0. 01 to 3.0 parts by mass with respect to 100 parts by mass of the polypropylene resin (A). More preferably, it is 0.01 to 1.0 part by mass. If the amount of the β crystal nucleating agent (D) is at least 0.0001 part by mass with respect to 100 parts by mass of the polypropylene resin (A), the β crystals of the polypropylene resin (A) can be sufficiently generated and grown during the production. As a result, a sufficient β crystal activity can be secured, and a sufficient β crystal activity can be secured even when a laminated porous film is formed, and desired air permeability can be obtained. On the other hand, if the amount of the β crystal nucleating agent (D) is 5.0 parts by mass or less with respect to 100 parts by mass of the polypropylene resin (A), it is economically advantageous, and the β crystal nuclei on the film surface It is preferable because there is no bleeding of the agent (D).

1-3. Other components In the resin composition (I) forming the porous layer (I layer), additives such as a heat stabilizer, an antioxidant, an ultraviolet absorber, a light stabilizer, and a colorant are added to such an extent that the properties are not impaired. Various additives such as an agent, an antistatic agent, a hydrolysis inhibitor, a lubricant, and a flame retardant may be appropriately compounded. Further, other resins may be contained to such an extent that their properties are not impaired. In particular, the addition of an elastomer can improve the air permeability.

2. Heat resistant layer (II layer)
In the laminated porous film of the present invention, the heat-resistant layer (II layer) is a resin composition containing a polypropylene resin (A), inorganic particles (B), and a specific vinyl aromatic elastomer (C) (hereinafter referred to as “resin composition”). (II) "). The heat-resistant layer (II layer) and the resin composition (II) contain the polypropylene-based resin (A), the inorganic particles (B), and the vinyl aromatic elastomer (C) as main components in a total amount of 50% by mass or more, particularly 70% by mass. As mentioned above, it is particularly preferable to contain 90 to 100 mass%.

2-1. Polypropylene resin (A)
In the present invention, it is important that the heat-resistant layer (II layer) contains the polypropylene resin (A). By containing the polypropylene resin (A), not only the II layer has good air permeability, heat resistance, mechanical strength, and productivity, but also the interlayer when the II layer is in direct contact with the porous layer (I layer). Excellent adhesion.

  As the polypropylene resin (A) constituting the heat resistant layer (II layer), one or more of those exemplified as the polypropylene resin (A) constituting the porous layer (I layer) can be used. The polypropylene resin (A) constituting the porous layer (I layer) and the polypropylene resin (A) constituting the heat resistant layer (II layer) may be the same or different, but are the same. This is preferable in terms of material procurement, coextrusion moldability described below, and the like.

2-2. Inorganic particles (B)
In the present invention, it is important that the heat-resistant layer (II layer) contains the inorganic particles (B). When the heat-resistant layer (II layer) contains the inorganic particles (B), a heat-resistant layer (II layer) having good air permeability and dimensional stability can be formed.

  Specific examples of the inorganic particles (B) that can be used in the present invention include metal carbonates such as calcium carbonate, magnesium carbonate, and barium carbonate; metal sulfates such as calcium sulfate, barium sulfate, and magnesium sulfate; Metal oxides such as calcium oxide, magnesium oxide, zinc oxide, aluminum oxide, silica, and titanium oxide; metal chlorides such as sodium chloride, magnesium chloride, silver chloride, and calcium chloride; clay minerals such as talc, clay, mica, and montmorillonite Is mentioned. Among them, when used as a battery separator, a metal oxide is preferred, and aluminum oxide is particularly preferred, from the viewpoint of being chemically inert when incorporated into a battery.

The lower limit of the average particle size of the inorganic particles (B) is preferably 0.01 μm or more, more preferably 0.1 μm or more, and further preferably 0.2 μm or more. On the other hand, the upper limit is preferably 3.0 μm or less, more preferably 1.5 μm or less. It is preferable that the average particle size of the inorganic particles (B) is 0.01 μm or more because the laminated porous film of the present invention can exhibit sufficient heat resistance. Further, it is preferable that the average particle size of the inorganic particles (B) is 3.0 μm or less from the viewpoint of improving the dispersibility of the inorganic particles (B).
In the present embodiment, the “average particle size of the inorganic particles (B)” is measured using, for example, a laser diffraction / scattering type particle size distribution analyzer.

The specific surface area of the inorganic particles (B) is preferably 1 m ² / g or more and less than 30 m ² / g. When the specific surface area of the inorganic particles (B) is 1 m ² / g or more, when the laminated porous film of the present invention is incorporated as a separator in a lithium ion secondary battery, the permeation of the electrolytic solution becomes faster, and the productivity is good. Is preferred. Further, it is preferable that the specific surface area of the inorganic particles (B) is less than 30 m ² / g because adsorption of the electrolyte component can be suppressed.

2-3. Vinyl aromatic elastomer (C)
In the present invention, it is important that the heat-resistant layer (II layer) contains the vinyl aromatic elastomer (C). When the heat-resistant layer (II layer) contains the vinyl aromatic elastomer (C), a highly uniform porous structure can be obtained efficiently, the shape and diameter of the pores can be easily controlled, and air permeability can be improved. And a laminated porous film having excellent ion permeability can be obtained.

  The vinyl aromatic elastomer (C) in the present invention is one kind of a thermoplastic elastomer having a styrene component as a base material, and is formed of a continuum of a soft component (for example, a butadiene component) and a hard component (for example, a styrene component). It is a polymer. The type of the copolymer is not particularly limited, and includes a random copolymer, a block copolymer, and a graft copolymer. In general, various block copolymers such as a linear block structure and a radially branched block structure are known. In the present invention, any structure may be used.

It is important that the vinyl aromatic elastomer (C) used in the present invention has a melt flow rate (MFR) of 1 g / 10 minutes or less at a temperature of 230 ° C. and a load of 2.16 kg. The shape of the vinyl aromatic elastomer (C) dispersed in the resin composition (II) changes depending on the difference in viscosity from the polypropylene resin (A), but the vinyl aromatic elastomer (C) having an MFR equal to or less than the upper limit is used. If so, the shape tends to be spherical. The domain dispersed in a sphere is different from the domain having a large aspect ratio, because the uniformity of the porous structure obtained by the subsequent stretching step is easily increased and the physical property stability is excellent. Further, in the vinyl aromatic elastomer (C) having an MFR equal to or less than the above upper limit, stress tends to concentrate on a matrix interface having a high elastic modulus and a domain interface having a low elastic modulus in a stretching step, so that an opening origin is easily generated. It has the feature that it is easily porous.
From such a viewpoint, the MFR of the vinyl aromatic elastomer (C) is more preferably 0.7 g / 10 minutes or less, and further preferably 0.5 g / 10 minutes or less. By using the vinyl aromatic elastomer (C) having an MFR of 0.5 g / 10 minutes or less, it is possible to further promote the porosity in the film at the time of stretching.

  Further, the vinyl aromatic elastomer (C) in the present invention preferably has a styrene content of 10 to 40% by mass, more preferably 10 to 35% by mass. When the styrene content of the vinyl aromatic elastomer (C) is 10% by mass or more, domains can be effectively formed in the heat-resistant layer (II layer). On the other hand, when the styrene content of the vinyl aromatic elastomer (C) is 40% by mass or less, formation of an excessively large domain can be suppressed. In the present invention, by blending the vinyl aromatic elastomer (C), continuity between the holes can be obtained, and a low electric resistance value can be obtained.

  The specific type of the vinyl aromatic elastomer (C) is not particularly limited, but includes a styrene-butadiene block copolymer (SBR), a hydrogenated styrene-butadiene block copolymer (SEB), and a styrene-butadiene-styrene block. Copolymer (SBS), styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene-ethylene-butadiene-styrene block copolymer (SEBS), styrene-isoprene block copolymer (SIR), styrene- Ethylene-propylene block copolymer (SEP), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block Click copolymer (SEEPS), and the like.

  In order to efficiently disperse the vinyl aromatic elastomer (C) in the resin composition (II), among the vinyl aromatic elastomers (C), ethylene having high compatibility with the polypropylene resin (A) is used. And a styrene-ethylene-propylene block copolymer (SEP), a styrene-ethylene-propylene-styrene block copolymer (SEPS), and a styrene-ethylene-butylene-styrene block copolymer. Polymer (SEBS) is more preferred.

  As the vinyl aromatic elastomer (C), only one kind may be used, or two or more kinds having different compositions and physical properties may be mixed and used.

2-4. Mixing ratio The vinyl aromatic elastomer (C) is preferably contained in an amount of 1 to 30 parts by mass, more preferably 10 to 20 parts by mass, per 100 parts by mass of the resin composition (II). When the content of the vinyl aromatic elastomer (C) is 1 part by mass or more, porosity is easily generated by stretching, and the air permeability can be improved. On the other hand, when the content of the vinyl aromatic elastomer (C) is 30 parts by mass or less, it is preferable because the porous structure can be prevented from becoming coarse due to stretching and the mechanical strength can be improved. Further, the heat-resistant layer (II layer) can be sufficiently filled with inorganic particles (B) useful for improving heat resistance.

  The mixing ratio of the polypropylene resin (A), the inorganic particles (B) and the vinyl aromatic elastomer (C) in the heat-resistant layer (II layer) and the resin composition (II) is such that the polypropylene resin (A) and the inorganic particles As a mixing ratio of (B) and the vinyl aromatic elastomer (C), (A) / (B) / (C) = 20 to 60% by mass / 20 to 60% by mass / 1 to 30% by mass (where ( A) + (B) + (C) = 100% by mass), and more preferably (A) / (B) / (C) = 10 to 40% by mass / 20 to 60% by mass. / 10 to 20% by mass (provided that (A) + (B) + (C) = 100% by mass). By containing the inorganic particles (B) in an amount of 20% by mass or more, the heat resistance of the battery against abnormal heat generation can be enhanced, and the safety of the battery can be enhanced. Further, by containing the inorganic particles (B) in an amount of 60% by mass or less, stable film formation can be performed, and productivity of the laminated porous film can be increased.

In addition, the heat-resistant layer (II layer) and the resin composition (II) contain the polypropylene resin (A), the inorganic particles (B), and the vinyl aromatic elastomer (C), so that each material has good properties. Together with the properties, a laminated porous film having excellent heat resistance, being uniformly porous, and having excellent air permeability and ion permeability is formed.
In particular, by simultaneously containing the inorganic particles (B) and the vinyl aromatic elastomer (C), it is possible to obtain a laminated porous film having uniform porosity and heat resistance, each of which is difficult to realize alone.

2-5. Other components In the resin composition (II) forming the heat-resistant layer (II layer), additives such as a heat stabilizer, an antioxidant, an ultraviolet absorber, a light stabilizer, and a crystal are added to such an extent that their properties are not impaired. Various additives such as a nucleating agent, a coloring agent, an antistatic agent, a hydrolysis inhibitor, a lubricant, and a flame retardant may be appropriately blended. Further, other resins may be contained to such an extent that their properties are not impaired.

3. Laminated Structure The laminated porous film of the present invention may have at least two layers, a porous layer (I layer) and a heat-resistant layer (II layer). The laminated structure of the heat-resistant layer (II layer) is not particularly limited.

The presence of at least one porous layer (I layer) allows the laminated porous film of the present invention to have excellent air permeability and mechanical strength.
In addition, the presence of at least one heat-resistant layer (II layer) allows the laminated porous film of the present invention to have excellent air permeability, heat resistance and good electric resistance.
Further, by having at least one layer each of the I layer and the II layer, the present invention has good characteristics and good interlayer adhesion when the I layer and the II layer are in direct contact with each other. Not only has excellent air permeability, but also has excellent stability and productivity at the time of film formation, and has a low electric resistance value with improved ion permeability.

  In addition, the laminated porous film of the present invention may have a layer (III layer) other than the porous layer (I layer) and the heat-resistant layer (II layer) as long as the function is not hindered. Specifically, a configuration in which a strength holding layer, a heat-resistant layer (high melting temperature resin layer), a shutdown layer (low melting temperature resin layer), and the like are stacked is exemplified. The number of layers can be appropriately selected from two layers, three layers, four layers, five layers, six layers, and seven layers. However, from the viewpoint of productivity or economy, a two-layer or three-layer structure is preferable.

  Examples of the laminated structure of the laminated porous film of the present invention include, for example, two types and two layers of I layer / II layer, and two types and three layers of I layer / II layer / I layer and II layer / I layer / II layer. No.

The laminated thickness ratio of the porous layer (I layer) and the heat-resistant layer (II layer) is not particularly limited and may be appropriately adjusted depending on the application and purpose. In the case of a two-layer structure of I layer / II layer, the layer thickness ratio before stretching in the manufacturing method is preferably I layer / II layer = 1 / (0.1 to 10), and 1 / ( 0.2 to 5), more preferably 1 / (0.33 to 3), and particularly preferably 1 / (0.5 to 2).
In the case of a two-layer, three-layer structure of I layer / II layer / I layer, I layer / II layer / I layer = (0.1 to 10) / 1 / (0.1 to 10). Preferably, it is more preferably (0.2-5) / 1 / (0.2-5), further preferably (0.33-3) / 1 / (0.33-3), It is particularly preferable that the ratio is (0.5 to 2) / 1 / (0.5 to 2).
Further, in the case of a two-layer three-layer structure of II layer / I layer / II layer, II layer / I layer / II layer = (0.1 to 10) / 1 / (0.1 to 10). Preferably, it is more preferably (0.2-5) / 1 / (0.2-5), further preferably (0.33-3) / 1 / (0.33-3), It is particularly preferable that the ratio is (0.5 to 2) / 1 / (0.5 to 2).
In any of the layer configurations, if the thickness ratio of the heat-resistant layer (II layer) forming the laminated porous film is such a thickness ratio, unevenness due to a difference in viscosity is unlikely to occur. Excellent stability and stretchability.

4. Next, a method for producing a laminated porous film of the present invention will be described. The following description is an example of a method for producing a laminated porous film of the present invention. The porous film is not limited to a laminated porous film manufactured by such a manufacturing method.

The laminated porous film of the present invention relates to a resin composition (I) containing a polypropylene-based resin (A) and, if necessary, a β-crystal nucleating agent (D) and other components with respect to the porous layer (I layer). And a heat-resistant layer (II layer), a resin composition (II) containing a polypropylene-based resin (A), inorganic particles (B), a vinyl aromatic elastomer (C), and other components as required. ) Are kneaded and melt-molded using an extruder or the like under a temperature condition not lower than the melting point of the polypropylene-based resin (A) and lower than the decomposition temperature, respectively, to obtain a laminated nonporous film-like material, which is stretched. It can be manufactured by processing into a stretched film.
In addition, the method for producing a laminated porous film of the present invention preferably does not include a step of removing an additive with a solvent to make the film porous, that is, it is preferable to make the film porous only by stretching.

4-1. Production of laminated non-porous film The production method of the laminated non-porous film is not particularly limited, and a known method may be used. For example, the resin compositions (I) and (II) are each melted using an extruder. Then, a method of co-extrusion from a T-die and cooling and solidifying with a cast roll may be used. In addition, a method in which a film-like material manufactured by a tubular method is cut open to obtain a planar shape is also applicable.

A more preferred embodiment includes the following production method.
In the extrusion molding, the extrusion temperature is appropriately adjusted depending on the flow properties and moldability of the resin compositions (I) and (II), but is preferably 180 to 370 ° C, more preferably 180 to 300 ° C, and 180 to 240 ° C. Is more preferred. Setting the extrusion temperature to 180 ° C. or higher is preferable because the polypropylene resin (A) is melted, the viscosity of the molten resin is sufficiently low, the moldability is excellent, and the productivity is improved. On the other hand, by setting the extrusion temperature to 370 ° C. or lower, it is possible to suppress deterioration of the resin compositions (I) and (II) and, consequently, a decrease in mechanical strength of the laminated porous film serving as a battery separator.

  The cooling solidification temperature by the cast roll is important in the present invention, and by controlling the cooling solidification temperature, β crystals of the polypropylene resin (A) are generated and grown, and the ratio of β crystals in the laminated nonporous film-like material Can be adjusted. The cooling and solidifying temperature of the cast roll is preferably 80 to 150 ° C, more preferably 90 to 140 ° C, and still more preferably 100 to 130 ° C. By setting the cooling and solidifying temperature to 80 ° C. or higher, the ratio of β crystals in the laminated and nonporous film solidified by cooling can be sufficiently increased, which is preferable. Further, setting the cooling and solidifying temperature to 150 ° C. or lower is preferable because troubles such as the extruded molten resin sticking to and winding around the cast roll hardly occur and the film can be formed efficiently.

  By setting the cast roll in the above temperature range, the β crystal ratio of the polypropylene resin (A) in the laminated nonporous film before stretching is preferably adjusted to 40 to 100%, and more preferably to 50 to 100%. It is more preferably adjusted, and more preferably adjusted to 60 to 100%. By setting the β-crystal ratio of the polypropylene-based resin (A) in the laminated nonporous film before stretching to 40% or more, it is easy to make the film porous by the subsequent stretching operation, and a film having good air permeability is obtained. be able to.

4-2. Stretching process of the laminated non-porous film-like material The stretching method of the obtained laminated non-porous film-like material includes a roll stretching method, a rolling method, a tenter stretching method, a simultaneous biaxial stretching method, and the like. Uniaxial stretching or biaxial stretching is performed by combining two or more.

  Uniaxial stretching may be longitudinal uniaxial stretching or horizontal uniaxial stretching. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. In the case of producing a laminated porous film having high air permeability which is the object of the present invention, stretching conditions can be selected in each stretching step, sequential biaxial stretching in which the porous structure is easily controlled is more preferable, and horizontal stretching after longitudinal stretching is more preferable. Sequential biaxial stretching in which stretching is performed is particularly preferred. The stretching in the machine direction (MD) during extrusion of the laminated nonporous film is called "longitudinal stretching", and the stretching in the direction perpendicular to the machine direction (TD) is called "lateral stretching".

  When sequential biaxial stretching is used, the stretching temperature must be appropriately selected depending on the compositions of the resin compositions (I) and (II) to be used, the crystal melting peak temperature, the crystallinity, and the like. Control of the structure is relatively easy, and it is easy to balance with other physical properties such as mechanical strength and shrinkage.

  The stretching temperature in the longitudinal stretching is generally preferably from 20 to 140 ° C, more preferably from 40 to 120 ° C, and still more preferably from 60 to 110 ° C. It is preferable that the stretching temperature in the longitudinal stretching is 20 ° C. or more, since breakage during stretching is suppressed and uniform stretching is performed. On the other hand, if the stretching temperature in the longitudinal stretching is 140 ° C. or lower, the formation of pores in the polypropylene resin (A), the interfacial separation between the polypropylene resin (A) and the inorganic particles (B), the polypropylene resin (A) Since three types of voids are formed, i.e., interfacial peeling by the vinyl aromatic elastomer (C) and the vinyl aromatic elastomer (C), the voids can be efficiently formed.

  The longitudinal stretching ratio can be arbitrarily selected, but the stretching ratio per uniaxial stretching is preferably 1.1 to 10 times, more preferably 1.5 to 8.0 times, and still more preferably 1.5 to 5.0 times. It is 0 times. By setting the stretching ratio per uniaxial stretching to 1.1 times or more, whitening progresses, suggesting that porosity by stretching has sufficiently occurred. In addition, by setting the stretching ratio per uniaxial stretching to 10 times or less, deformation of pores is suppressed, and a sufficiently whitened laminated porous film can be obtained.

  The transverse stretching temperature is preferably from 100 to 160 ° C, more preferably from 110 to 155 ° C. When the transverse stretching temperature is within the above range, the pores generated during the longitudinal stretching can be enlarged, the porosity of the porous layer can be increased, and sufficient air permeability can be obtained.

  The transverse stretching ratio can be arbitrarily selected, but is preferably 1.1 to 10 times, more preferably 1.5 to 8.0 times, and still more preferably 1.5 to 4.0 times. By stretching at the above-mentioned transverse stretching ratio, it is possible to have sufficient air permeability without deforming the pores generated at the time of longitudinal stretching.

4-3. Heat treatment The laminated porous film obtained as described above is preferably subjected to a heat treatment for the purpose of improving dimensional stability. At this time, the effect of dimensional stability can be expected by setting the heat treatment temperature to preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and further preferably 140 ° C. or higher. On the other hand, the heat treatment temperature is preferably 170 ° C. or lower, more preferably 165 ° C. or lower, and further preferably 160 ° C. or lower. A heat treatment temperature of 170 ° C. or lower is preferable because the heat treatment hardly causes the melting of the polypropylene resin (A) and the porous structure can be maintained. Further, during the heat treatment step, a relaxation treatment of 1 to 20% may be performed as necessary.
After the heat treatment, the film is uniformly cooled and wound up to obtain a wound body of the laminated porous film.

4-4. Others Further, the laminated porous film of the present invention may be subjected to a surface treatment such as corona treatment, plasma treatment, printing, coating, vapor deposition, and further perforation processing after the heat treatment as necessary within a range not to impair the present invention. Can be applied.

5. Physical Properties or Properties of Laminated Porous Film 5-1. Thickness The thickness of the laminated porous film of the present invention is preferably less than 100 μm, more preferably less than 50 μm, even more preferably less than 40 μm. On the other hand, the lower limit is preferably 3 μm or more, more preferably 5 μm or more. When the thickness is less than 100 μm, the electrical resistance of the laminated porous film can be reduced, so that the performance of the power storage device can be sufficiently ensured. Further, when the thickness is 3 μm or more, substantially necessary electric insulation can be obtained, and for example, even when a large voltage is applied, short-circuit is hard to occur and the safety is excellent.

5-2. Air Permeability The laminated porous film of the present invention preferably has an air permeability measured at 25 ° C. in accordance with JIS P8117 (2009) of 100 seconds / 100 ml or less. A laminated porous film having an air permeability of 100 seconds / 100 ml or less can have an excellent electric resistance value. The air permeability of the laminated porous film is more preferably 90 seconds / 100 ml or less, further preferably 80 seconds / 100 ml or less.

The air permeability indicates the difficulty in passing air in the thickness direction of the laminated porous film, and is specifically expressed by the number of seconds required for 100 ml of air to pass through the laminated porous film. Therefore, the smaller the numerical value, the easier it is to pass through, and the larger the numerical value, the harder to pass through. That is, the smaller the value, the better the connectivity in the thickness direction of the laminated porous film, and the larger the value, the poorer the connectivity in the thickness direction of the laminated porous film. The continuity is the degree of connection of the holes in the thickness direction of the laminated porous film.
The air permeability of the laminated porous film is specifically measured by a method described in Examples below.

5-3. Electric resistance value The laminated porous film of the present invention was impregnated with a propylene carbonate: ethyl methyl carbonate = 1: 1 (v / v) solution containing 1 M lithium perchlorate, and measured in thickness direction at 25 ° C. It is preferable that the electric resistance value is 0.7Ω or less. The electric resistance in the thickness direction is more preferably 0.65 Ω or less, and particularly preferably 0.6 Ω or less. The lower limit of the electric resistance in the thickness direction is not particularly limited, but is usually 0.01 Ω or more due to restrictions on material selection.
By setting the electric resistance value in the thickness direction to 0.7Ω or less, it is easy to obtain a large current discharge at a high output of a battery using the laminated porous film of the present invention as a battery separator, and excellent in battery performance. It can be. In order to realize such a low electric resistance value in the laminated porous film, it is necessary to control the porous structure, increase the continuity between the holes, and facilitate the movement of ions. The electric resistance greatly depends on the air permeability. That is, the lower the value of the air permeability, the lower the electric resistance value. However, the air permeability and the electric resistance value are not always in a proportional relationship.

In the present invention, the vinyl aromatic elastomer (C) having a melt flow rate (MFR) of 1 g / 10 minutes or less at a temperature of 230 ° C. and a load of 2.16 kg is used to form pores having a porous structure in a laminated porous film and to form pores. To realize a laminated porous film having a sufficiently low electric resistance value.
The electrical resistance value of the laminated porous film is specifically measured by the method described in the Examples section below.

[battery]
Next, a lithium ion secondary battery accommodating the laminated porous film of the present invention as a battery separator will be described with reference to FIG.

  Both electrodes of the positive electrode plate 21 and the negative electrode plate 22 are spirally wound so as to overlap with each other with the battery separator 10 interposed therebetween, and the outside is stopped with a winding tape to form a wound body.

  The wound body in which the positive electrode plate 21, the battery separator 10, and the negative electrode plate 22 are integrally wound is housed in a bottomed cylindrical battery case, and welded to the positive and negative electrode leads 24 and 25. Next, the following electrolytic solution was injected into the battery can, and after the electrolytic solution sufficiently permeated the battery separator 10 and the like, the positive electrode lid 27 was sealed around the opening rim of the battery can via a gasket 26, and precharge and aging were performed. By performing the above, a cylindrical lithium ion secondary battery 20 is manufactured.

  As the electrolyte, an electrolyte obtained by dissolving a lithium salt in an organic solvent is used. The organic solvent is not particularly limited, for example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, esters such as methyl propionate or butyl acetate, nitriles such as acetonitrile Ethers such as 1,2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolan, tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolan, or sulfolane. These can be used alone or in combination of two or more.

As the negative electrode, one obtained by integrating an alkali metal or a compound containing an alkali metal with a current collecting material such as a stainless steel net is used. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin or magnesium, a compound of an alkali metal and a carbon material, and a low potential alkali metal and a metal oxide. And compounds with sulfides.
When a carbon material is used for the negative electrode, the carbon material may be any material capable of doping and undoping lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, and a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fibers, activated carbon, and the like can be used.

  As the positive electrode, a metal oxide such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, vanadium pentoxide or chromium oxide, or a metal sulfide such as molybdenum disulfide is used as an active material. A mixture obtained by appropriately adding a binder such as a conductive auxiliary agent or polytetrafluoroethylene to these positive electrode active materials, and finishing the molded body using a current collector material such as a stainless steel net as a core material is used. Can be

  EXAMPLES Hereinafter, Examples and Comparative Examples will be shown, and the laminated porous film of the present invention will be described in more detail. However, the present invention is not limited to the following Examples.

[Various evaluation and measurement methods]
<Differential scanning calorimetry (DSC)>
Using a differential scanning calorimeter (DSC-7) manufactured by Perkin Elmer, the laminated porous film was heated from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min, held for 1 minute, and then kept at 240 ° C. After the temperature was lowered to 25 ° C. at a scanning rate of 10 ° C./min, the temperature was maintained for 1 minute, and then the temperature was raised again from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min. The presence or absence of β crystal activity was evaluated based on the following criteria based on whether or not a peak was detected at 145 to 160 ° C., which is the crystal melting peak temperature (Tmβ) derived from the β crystal of the polypropylene resin at the time of the re-heating. .
：: When Tmβ is detected in the range of 145 ° C. to 160 ° C. (with β crystal activity)
×: when Tmβ was not detected in the range of 145 ° C. to 160 ° C. (no β crystal activity)
The β crystal activity was measured under a nitrogen atmosphere with a sample amount of 10 mg.

<Wide-angle X-ray diffraction measurement (XRD)>
As shown in FIG. 2 (A), a sample 32 obtained by cutting a laminated porous film into a 60 mm square and 60 mm square was used to form two aluminum plates (a material: JIS A5052) having a circular hole of 40 mmφ formed in the center. (Size: 60 mm long, 60 mm wide, 1 mm thick) 31, 31, and the periphery was fixed with a clip 33 as shown in FIG.
In a state where the sample 32 of the laminated porous film is constrained between the two aluminum plates 31 and 31, the sample is set to a blower constant temperature incubator (model: DKN602, manufactured by Yamato Scientific Co., Ltd.) having a set temperature of 180 ° C. and a display temperature of 180 ° C. After setting for 3 minutes, the set temperature was changed to 100 ° C., and the temperature was gradually cooled to 100 ° C. over 10 minutes or more. When the display temperature reached 100 ° C., the sample 32 was taken out and cooled in an atmosphere of 25 ° C. for 5 minutes while being restrained between two aluminum plates 31 under the following measurement conditions. Wide-angle X-ray diffraction measurement was performed on a circular portion of 40 mmφ in the center. In FIG. 2B, reference numeral 34 denotes a longitudinal direction of the film, and reference numeral 35 denotes a lateral direction of the film.
・ Wide-angle X-ray diffraction analyzer: manufactured by Mac Science Co., Ltd., model number: XMP18A
・ X-ray source: CuKα ray, output: 40 kV, 200 mA
・ Scanning method: 2θ / θ scan
2θ range: 5 ° to 25 °
Scan interval: 0.05 °
Scanning speed: 5 ° / min
With respect to the obtained diffraction profile, the presence or absence of β crystal activity was evaluated as follows from the peak derived from the (300) plane of β crystal of the polypropylene resin.
：: A peak was detected in the range of 2θ = 16.0 to 16.5 ° (with β-crystal activity)
×: No peak was detected in the range of 2θ = 16.0 to 16.5 ° (no β crystal activity)

<Thickness>
The thickness of the laminated porous film was measured at random at 10 locations in the plane of the laminated porous film with a 1/1000 mm dial gauge, and calculated as an average value.

<Air permeability>
The air permeability of the laminated porous film was measured in an air atmosphere at 25 ° C. in accordance with JIS P8117 (2009). As a measuring device, a digital Oken type air permeability dedicated machine (made by Asahi Seiko Co., Ltd.) was used.

<Electric resistance value>
Under an air atmosphere at 25 ° C., the laminated porous film was cut into 3.5 cm × 3.5 cm squares, placed in a glass petri dish, and propylene carbonate containing 1 M lithium perchlorate as an electrolytic solution: ethyl methyl carbonate = 1 : 1 (v / v) solution (manufactured by Kishida Chemical Co., Ltd.) was introduced to the extent that the laminated porous film was soaked, and the electrolytic solution was impregnated. Thereafter, the laminated porous film was taken out, excess electrolyte was wiped off, and placed at the center of a φ60 mm stainless steel petri dish. A cylindrical weight of 100 g stainless steel having a bottom surface of φ30 mm is slowly placed on this, a terminal is connected to the petri dish and the weight, and the electric resistance value is measured using a HIOKI LCR HiTESTER (manufactured by Hioki Electric Co., model number 3522-50). did. The obtained electric resistance value was evaluated as follows.
：: The electric resistance value is 0.7Ω or less.
×: The electric resistance value exceeds 0.7Ω.

[Film forming raw materials]
<Polypropylene resin (A)>
A-1: polypropylene (Novatech FY6HA, manufactured by Nippon Polypropylene Co., Ltd., MFR: 2.4 g / 10 min, Mw / Mn = 3.2)

<Inorganic particles (B)>
B-1: Alumina (LS235C, manufactured by Nippon Light Metal Company, average particle size 0.53 μm, specific surface area 6.4 m ² / g)
B-2: Alumina (LS710A, manufactured by Nippon Light Metal Co., Ltd., average particle size 0.50 μm, specific surface area 6.9 m ² / g)

<Vinyl aromatic elastomer (C)>
C-1: Styrene-ethylene-propylene block copolymer (grade name: SEPTON1001, styrene content: 35% by mass, MFR: 0.1 g / 10 minutes, manufactured by Kuraray Co., Ltd.)
C-2: Styrene-ethylene-propylene-styrene block copolymer (grade name: SEPTON2007, styrene content: 30% by mass, MFR: 2.7 g / 10 minutes, manufactured by Kuraray Co., Ltd.)

<Β crystal nucleating agent (D)>
D-1; 3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane

[Example 1]
The β crystal nucleating agent (D-1) is compounded in the compounding number shown in Table 1 with respect to 100 parts by mass of the polypropylene resin (A-1), and is charged into a twin-screw extruder and melted at a set temperature of 240 ° C. After mixing, the strands are cooled and solidified in a water tank, the strands are cut with a pelletizer, and pellets of a resin composition (I) forming a porous layer (I layer) made of a polypropylene resin (hereinafter referred to as “pellets (I)”) ). In the same manner, the polypropylene resin (A-1), the inorganic particles (B-1) and the vinyl aromatic elastomer (C-1) are blended in the blending number shown in Table 1, and the heat-resistant layer (II layer) is formed. A pellet of the resin composition (II) to be formed (hereinafter, referred to as “pellet (II)”) was produced.

  The prepared pellets were melt-mixed at 200 ° C. using a single-screw extruder, and then, using a T-die having a lip opening of 1 mm, the polypropylene resin (A-1) and the β crystal nucleating agent (D -1) using a pellet (I), a polypropylene resin (A-1), inorganic particles (B-1), and a pellet (II) of a vinyl aromatic elastomer (C-1) in a middle-layer extruder, Coextrusion molding was performed at an extrusion temperature of 200 ° C., and the mixture was guided to a cast roll at 127 ° C. to obtain a laminated nonporous film. Thereafter, the laminated nonporous film was stretched in the machine direction at a stretch ratio of 4.5 times between rolls set at 105 ° C. using a longitudinal stretching machine. The film after longitudinal stretching was preheated by a film tenter (manufactured by Kyoto Machinery Co., Ltd.) at a preheating temperature of 145 ° C. and a preheating time of 12 seconds, and then stretched 2.0 times in the transverse direction at a stretching temperature of 145 ° C. Heat treatment was performed at ℃ to obtain a laminated porous film. Table 1 summarizes the evaluation results of the obtained laminated porous film.

[Example 2]
In the same manner as in Example 1, the pellets (I) forming the porous layer (I layer) and the pellets (II) forming the heat-resistant layer (II layer) were blended in the blending number shown in Table 1 Produced.
From the produced pellets (I) and (II), molding was performed in the same manner as in Example 1 to obtain a laminated nonporous film. Thereafter, the laminated nonporous film was subjected to longitudinal stretching, transverse stretching, and heat treatment in the same manner as in Example 1. Table 1 summarizes the evaluation results of the obtained laminated porous film.

[Examples 3 to 5]
In the same manner as in Example 1, the pellets (I) forming the porous layer (I layer) and the pellets (II) forming the heat-resistant layer (II layer) were blended in the blending number shown in Table 1 Produced.
From the prepared pellets (I) and (II), the pellets (I) were formed in the middle extruder and the pellets (II) were formed in the front and back layer side extruders to obtain a laminated nonporous film. Thereafter, the laminated nonporous film was subjected to longitudinal stretching, transverse stretching, and heat treatment in the same manner as in Example 1. However, in Examples 3 and 4, the transverse stretching ratio was 3.0 times. Table 1 summarizes the evaluation results of the obtained laminated porous film.

[Comparative Example 1]
In the same manner as in Example 1, the mixture was blended in the blending number shown in Table 1 to prepare a pellet (I) for forming a porous layer (I layer).
The pellets (I) thus produced were molded in the same manner as in Example 1 using a front and back layer side extruder and a middle layer side extruder to obtain a single-layer nonporous film. Thereafter, the single-layer nonporous film was subjected to longitudinal stretching, transverse stretching and heat treatment in the same manner as in Example 1. Table 1 summarizes the evaluation results of the obtained single-layer porous film.

[Comparative Example 2]
In the same manner as in Example 1, the polypropylene resin blended in the blending number shown in Table 1 to form the porous layer (I layer) pellets (I) and the heat-resistant layer (II layer) Pellets (II) containing A-1) and inorganic particles (B-1) but not containing the vinyl aromatic elastomer (C-1) were produced.
From the produced pellets (I) and (II), molding was performed in the same manner as in Example 1 to obtain a laminated nonporous film. Thereafter, the laminated nonporous film was subjected to longitudinal stretching, transverse stretching, and heat treatment in the same manner as in Example 1. Table 1 summarizes the evaluation results of the obtained laminated porous film.

[Comparative Example 3]
In the same manner as in Example 1, the pellets (I) were blended in the blending number shown in Table 1 to form the porous layer (I layer), the polypropylene resin (A-1), and the inorganic particles (B- A pellet (II) containing 1) and forming a heat-resistant layer (II layer) not containing the vinyl aromatic elastomer (C-1) was produced.
From the prepared pellets (I) and (II), the pellets (I) were formed in the middle extruder and the pellets (II) were formed in the front and back layer side extruders to obtain a laminated nonporous film. Thereafter, the laminated nonporous film was subjected to longitudinal stretching, transverse stretching, and heat treatment in the same manner as in Example 1. Table 1 summarizes the evaluation results of the obtained laminated porous film.

[Comparative Example 4]
In the same manner as in Example 1, the polypropylene resin blended in the blending number shown in Table 1 to form the porous layer (I layer) pellets (I) and the heat-resistant layer (II layer) A pellet (II) containing A-1), inorganic particles (B-1), and a vinyl aromatic elastomer (C-2) was produced.
From the produced pellets (I) and (II), molding was performed in the same manner as in Example 1 to obtain a laminated nonporous film. Thereafter, the laminated nonporous film was subjected to longitudinal stretching, transverse stretching, and heat treatment in the same manner as in Example 1. Table 1 summarizes the evaluation results of the obtained laminated porous film.

  Table 1 shows the evaluation results of Examples and Comparative Examples.

  As is clear from Examples 1 to 5, a porous layer (I layer) mainly composed of a polypropylene resin (A), a polypropylene resin (A), inorganic particles (B), a temperature of 230 ° C., and a load of 2 The laminated porous film having a heat-resistant layer (II layer) containing a vinyl aromatic elastomer (C) having a melt flow rate (MFR) of 1 g / 10 min or less at 16 kg is obtained by laminating (I layer) and (II layer) Regardless of the ratio or the number of parts of the vinyl aromatic elastomer (C) added, excellent air permeability was exhibited, and good results were obtained for the electric resistance value.

  On the other hand, the single-layer porous film composed of only the polypropylene-based resin porous layer (I layer) shown in Comparative Example 1 does not contain the inorganic particles (B) or the vinyl aromatic elastomer (C). ) And the addition of the vinyl aromatic elastomer (C) did not produce pores, the air permeability was high, and the electrical resistance was high. In the laminated porous films of Comparative Examples 2 and 3, when the vinyl aromatic elastomer (C) was not contained in the heat-resistant layer (II layer) in the laminated porous film, the vinyl aromatic elastomer (C) was added. Since there is no contribution to the porosity at the time of stretching, it is difficult to obtain continuity between the holes, and a low electric resistance value cannot be obtained. In the laminated porous film of Comparative Example 4, the vinyl aromatic elastomer in the heat-resistant layer (II layer) in the laminated porous film had a melt flow rate (MFR) of 1 g / at a temperature of 230 ° C. and a load of 2.16 kg. Since the time is longer than 10 minutes, stress is not concentrated on the interface between the matrix and the domain, and it does not become a starting point of the opening. Therefore, a sufficiently low electric resistance value cannot be secured.

  The laminated porous film of the present invention is widely used as a power storage device, as a battery device such as a nickel-metal hydride battery, a lithium ion secondary battery, an aluminum electrolytic capacitor, an electric double layer capacitor, and a lithium ion capacitor. Use can be expected. In addition, it can be applied to various uses that require air permeability, such as pads for absorbing body fluids such as disposable diapers, medical materials such as surgical gowns, clothing materials such as jumpers and rainwear, and house waterproofing. It can also be suitably used as materials such as building materials such as materials and heat insulating materials, desiccants, and packaging materials such as disposable warmers.

10 Battery separator (laminated porous film)
Reference Signs List 20 lithium ion secondary battery 21 positive electrode plate 22 negative electrode plate 24 positive electrode lead body 25 negative electrode lead body 26 gasket 27 positive electrode cover

Claims (11)

  From a porous layer (I layer) mainly composed of a polypropylene resin (A) and a resin composition (II) containing a polypropylene resin (A), inorganic particles (B), and a vinyl aromatic elastomer (C). The vinyl aromatic elastomer (C) has a melt flow rate (MFR) of 1 g / 10 min or less at a temperature of 230 ° C. and a load of 2.16 kg. The laminated porous film characterized by the above-mentioned.   The laminated porous film according to claim 1, wherein 1 to 30 parts by mass of the vinyl aromatic elastomer (C) is contained in 100 parts by mass of the resin composition (II).   The laminated porous film according to claim 1, wherein the porous layer (I layer) has β-crystal activity.   The laminated porous film according to any one of claims 1 to 3, wherein the porous layer (I layer) contains a β crystal nucleating agent.   The laminated porous film according to any one of claims 1 to 4, which is a stretched film.   The laminated porous film according to any one of claims 1 to 5, wherein an air permeability measured at 25 ° C in accordance with JIS P8117 (2009) is 100 seconds / 100 ml or less. .   Impregnated with a propylene carbonate: ethyl methyl carbonate = 1: 1 (v / v) solution containing 1 M lithium perchlorate, the electrical resistance in the thickness direction measured at 25 ° C. was 0.7Ω or less. The laminated porous film according to any one of claims 1 to 6, wherein: The vinyl aromatic elastomer (C) is a styrene-ethylene-propylene block copolymer (SEP), a styrene-ethylene-propylene-styrene block copolymer (SEPS), and a styrene-ethylene-butylene-styrene block copolymer The laminated porous film according to any one of claims 1 to 7, further comprising one or more of (SEBS). A battery separator using the laminated porous film according to any one of claims 1 to 8 . A battery using the battery separator according to claim 9 . The method for producing a laminated porous film according to any one of claims 1 to 8 , wherein the polypropylene-based resin composition constituting the I layer and the polypropylene-based resin (A) constituting the II layer A step of preparing a laminated nonporous film by co-extrusion of the resin composition (II) containing the nonaqueous particles, the inorganic particles (B) and the vinyl aromatic elastomer (C); A process of stretching at least uniaxially to make it porous, and not including a step of removing additives with a solvent.

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