JP2012011751A - Laminated porous film and method for production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated porous film suitable for a separator, excellent in planarity, safety, cycle characteristics and easy to produce batteries, and to provide a method for production of the film.SOLUTION: The laminated porous film includes an external layer A comprising a porous film, and a layer B laminated adjacently to the inner side of the layer A and comprising the porous film of substantially the same film as that of the layer A. The porosity ratio of the layer A to the layer B, (porosity of layer A)/(that of layer B) is >0.90 but ≤1.1, and a melting point difference between the layers A and B is ≥0°C but ≤5°C. The thickness difference between the layers A and B, (layer A thickness)-(layer B thickness) is ≥-20 μm.

Description

  The present invention relates to a laminated porous film and a method for producing the same.

  The porous film is used as a packaging film, a microfiltration membrane, a battery separator, a capacitor separator, a fuel cell material, and the like. The battery separator is particularly used as a lithium ion secondary battery separator. In recent years, lithium ion secondary batteries have been applied to small electronic devices such as mobile phones and laptop computers, as well as electric vehicles and small electric motorcycles. In particular, high safety, cycle performance, and ease of battery creation are required for automotive applications where the market will continue to expand rapidly worldwide. To meet these requirements, separators are required. Therefore, it is necessary to reduce the variation in physical properties in the plane to the utmost limit, and there is a demand for a separator having excellent flatness without uneven thickness.

As a technique for imparting such flatness, Patent Document 1 describes a method of producing a three-layer porous film by a coextrusion method. This document discloses a technique in which the surface layer is mainly made of polypropylene and the intermediate layer is mainly made of polyethylene.
Patent Document 2 discloses a film made of a resin composition containing at least a polyethylene resin, a polypropylene resin having a melt tension of 3.0 gf or more, and a filler, and starting from the filler by stretching. A porous film characterized by pores is described, and it is disclosed that this film is excellent in thickness accuracy.
Patent Document 3 discloses a method of obtaining a microporous film having a thickness unevenness accuracy of about 5 to 10% by superimposing cast films and stretching them in a stacked state. .
In Patent Document 4, as a method for producing a porous film, in a method of cleaving a resin / filler interface by stretching a layer made of a thermoplastic resin such as polyolefin and a filler, the layer is formed. As an intermediate layer, an outer layer of a thermoplastic resin such as polyamide that is not thermally fused to the thermoplastic resin is coextruded on both sides to obtain a laminated sheet, and stretched before and / or after the outer layer of the laminated sheet is peeled off. The method for producing a porous film characterized in that the ratio of MFR of the surface layer resin to the intermediate layer resin is in the range of 1:30 to 30: 1, the moldability to the sheet is the best, It describes that a film having a good surface condition and thickness accuracy can be obtained.
Patent Document 5 discloses a film having a small difference in melt viscosity or a difference in melting point between adjacent layers in a multilayer microporous film.

JP 09-219184 A JP 2006-016550 A JP 2004-051648 A Japanese Patent Laid-Open No. 06-100719 JP 2010-036355 A

However, all of the separators described in Patent Documents 1 to 5 have room for improvement from the viewpoint of flatness.
In view of the above circumstances, an object of the present invention is to provide a laminated porous film and a method for producing the same, which are suitable as a separator having excellent flatness, safety, cycleability, and ease of battery production.

  As a result of intensive studies on the above problems, the present inventors have focused on the characteristics of the surface layer and the inner layer of the laminated porous film, adjusted the porosity ratio of the surface layer and the inner layer, and the melting point difference to a specific range, and The inventors have found that the thickness difference between the surface layer and the inner layer is within a specific range, whereby the uneven thickness of the film can be solved, and the present invention has been completed.

That is, the present invention is as follows.
[1]
A laminated porous film comprising an outer A layer comprising a porous film and a B layer laminated adjacent to the inner side of the A layer and comprising a porous film substantially the same type as the A layer,
The porosity ratio of the A layer and the B layer is 0.90 or more and 1.1 or less as (the porosity of the A layer) / (the porosity of the B layer),
The melting point difference between the A layer and the B layer is 0 ° C. or more and 5 ° C. or less,
A laminated porous film in which a thickness difference between the A layer and the B layer is −20 μm or more as (A layer thickness) − (B layer thickness).
[2]
The laminated porous film according to [1], wherein the A layer is laminated adjacent to both surfaces of the B layer, and has a three-layer configuration of A layer / B layer / A layer.
[3]
[1] or [2] is a method for producing a laminated porous film according to the following steps (1) and (2):
(Step 1) Resin composition A forming (A layer) and resin composition B forming (B layer) are both extruded in a molten state from a die, and (A layer) and (B layer) are laminated. A laminated film forming step of forming the laminated film,
(Step 2) After the laminated film forming step, a laminated porous film forming step in which both the (A layer) and (B layer) are microporous.
Have
In the film state in which the die divides the molten resin stream extruded from one extruder into two or more resin streams, and each molten resin stream spreads in the coat hanger part in the die, each film In a die to form a multi-layered state and extrude out of the die through a lip opening.
[4]
The die is
A distributor for dividing the molten resin stream into two or more resin streams;
Expanding each of the divided resin flows in a coat hanger shape in the cross direction of the flow, and further forming a sheet shape;
A stacking portion in which the resin flow formed in the sheet shape is stacked in a die to form a multilayer state,
[3] The production method according to [3].
[5]
The separator for nonaqueous electrolyte secondary batteries containing the laminated porous film as described in [1] or [2].

  ADVANTAGE OF THE INVENTION According to this invention, the lamination | stacking porous film suitable as a separator excellent in planarity, safety, cycling property, and the ease of battery preparation and its manufacturing method are provided.

Side surface sectional drawing of the die | dye used in the Example is shown. The upper surface sectional drawing of the die | dye used in the Example is shown.

  Hereinafter, a mode for carrying out the present invention (hereinafter abbreviated as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

The laminated porous film of the present embodiment includes an outer A layer composed of a porous film, and a B layer laminated adjacent to the inner side of the A layer and composed of a porous film substantially the same type as the A layer. Including laminated porous film,
The porosity ratio of the A layer and the B layer is 0.90 or more and 1.1 or less as (the porosity of the A layer) / (the porosity of the B layer),
The melting point difference between the A layer and the B layer is 0 ° C. or more and 5 ° C. or less,
In the laminated porous film, the difference in thickness between the A layer and the B layer is −20 μm or more as (A layer thickness) − (B layer thickness).

  The laminated porous film of the present embodiment is a laminated porous film in which two or more layers of substantially the same kind of porous film are stacked. When the layers adjacent to each other are A layer and B layer, A layer / B The porosity ratio of the layers is in the range of 0.90 <porosity ratio ≦ 1.1, and the difference in melting point mp of the resin constituting the A layer B layer is 0 ° C. ≦ mp difference ≦ 5 ° C. The difference in thickness of the B layer is adjusted to -20 μm or more as (the thickness of the A layer) − (the thickness of the B layer), and these functions synergistically to provide excellent planarity as a separator and battery safety. , Cycleability, and ease of battery creation. Hereinafter, each physical property of the laminated porous film of the present embodiment will be described.

  In the laminated porous film of the present embodiment, two or more layers of substantially the same kind of porous film are stacked. When two or more layers of porous films are stacked, the uneven thickness phase of each layer is different, so the uneven thickness of the stacked films is averaged and improved. Here, “substantially the same kind” means that the ratio of the porosity of layer A / layer B is 0.90 <porosity ratio <1.1 when the layers adjacent to each other are layer A and layer B. The difference between the melting points mp of the resins constituting the A layer and the B layer is 0 ° C. ≦ mp difference ≦ 5 ° C. Further, the thickness difference between the A layer and the B layer is (the thickness of the A layer) − (the B layer) Thickness) of −20 μm or more.

  If the porosity ratio of the A layer and the B layer is in the range of 0.90 <porosity ratio ≦ 1.1, uneven thickness is improved. In addition, the position of the A layer and the B layer refers to the layers adjacent to each other at one layer interface. For example, in the case of a five-layer film, there are four interfaces. There are also four layers. In the case of a two-layer film, either may be the A layer. The porosity ratio is more preferably 0.95 <porosity ratio ≦ 1.05, and if it is in the above range, the uneven thickness tends to be further improved. The porosity ratio is more preferably 0.97 <porosity ratio ≦ 1.02, and in the above range, the uneven thickness is further improved, and in the case of coextrusion molding, the number of extruders Can be reduced, and the economy tends to be excellent.

  The laminated porous film of the present embodiment basically has a three-layer configuration of A layer / A layer / B layer / A layer with the A layer as the outermost layer, and the layer ratio can take various combinations. The relationship between A) and B layer thickness (thickness B) satisfies the condition of (thickness A) − (thickness B) ≧ −20 μm. For example, when the total layer thickness is 20 μm, 2/18/2 μm (thickness difference −16 μm), 5/10/5 μm (thickness difference −5 μm), 6/7/6 μm (thickness difference—1 μm), 8/4 / If it is 8 μm (thickness difference 4 μm) or the like and the thickness relationship is within the above range, the uneven thickness is improved. More preferably, the thickness difference between the A layer and the B layer is (thickness A) − (thickness B) ≧ −5 μm, and if the thickness is within the above range, the uneven thickness tends to be further improved. The thickness difference between the A layer and the B layer is more preferably (thickness A) − (thickness B) ≧ −1 μm. Since the surface layer is relatively thick within the above range, the interface between the layers at the time of merging in coextrusion. Disturbance is improved, and extrusion at high speed tends to be possible.

  The laminated porous film of the present embodiment preferably has a film thickness of 5 to 50 μm. The film thickness is preferably 7 to 35 μm, more preferably 9 to 25 μm. When the film thickness of the laminated porous film is within the above range, the battery capacity and safety tend to be easily balanced.

  The air permeability of the laminated porous film of the present embodiment is preferably 30 seconds / 100 cc or more from the viewpoint of mechanical strength and self-discharge, and preferably 400 seconds / 100 cc or less from the viewpoint of battery cycle characteristics and rate characteristics. is there. The air permeability is more preferably 70 seconds / 100 cc or more and 230 seconds / 100 cc or less, and further preferably 100 seconds / 100 cc or more and 230 seconds / 100 cc or less. Here, the air permeability refers to a value measured with a Gurley air permeability meter “G-B2” (trademark, manufactured by Toyo Seiki Seisakusho Co., Ltd.) in accordance with JIS P-8117. In addition, as a method of adjusting the air permeability to the above range, although it depends on the production method of the porous film, in the case of the “wet method” in which a resin and a plasticizer are used as raw materials and the plasticizer is extracted and made porous after film formation The method of adjusting the mixing ratio of resin and a plasticizer, the method of adjusting the draw ratio and temperature in a film forming process, or the draw ratio and temperature in a heat setting process, etc. are mentioned. In addition, using a crystalline resin without using a plasticizer, the interface of the amorphous part between lamellae and the interface of the resin and an inorganic filler such as calcium carbonate are cleaved by longitudinal stretching at low temperature to make it porous. In the case of the “dry method”, a method of controlling the crystallization of the lamella by adjusting the draft ratio and the stretching speed can be mentioned.

  The puncture strength of the laminated porous film of the present embodiment is preferably 150 g or more, more preferably 300 g or more, and even more preferably 500 g or more, from the viewpoint of strength during battery assembly. Here, the puncture strength is obtained by conducting a puncture test using a handy compression tester “KES-G5” (trade name, manufactured by Kato Tech Co., Ltd.) under the conditions of a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm / sec. This is the calculated value. Moreover, as a method for adjusting the puncture strength to the above range, for example, a method of changing the orientation state of the porous film can be mentioned. Specifically, in either case of the wet method or the dry method, the draw ratio and the temperature are adjusted. The method of adjusting is mentioned. Another method is to use a high-strength resin as the raw material resin itself. For example, in the case of polyolefin, mixing ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more, preferably 1,000,000 or more. Etc.

  In the laminated porous film of the present embodiment, the average pore diameter D of all layers is preferably 0.02 μm or more and 0.1 μm or less. When the average pore diameter D is within the above range, it is preferable from the viewpoint of achieving both ion permeability and fine short-circuit prevention. The average pore diameter D is more preferably 0.03 μm or more from the viewpoints of ion permeability and electrolyte absorbability, and more preferably 0.09 μm or less from the viewpoint of prevention of slight short circuit. Here, the average pore diameter of all layers can be determined by the measurement method described in Examples described later. In addition, as a method for adjusting the average pore diameter to the above range, in the case of a wet method, a method of adjusting a combination of a resin and a plasticizer and using a resin that has a larger dispersion diameter of the plasticizer, Examples include a method using a poor poor solvent, and examples of the film forming conditions include a method of adjusting a stretching ratio in the stretching step. Further, the average pore diameter DA of the A layer and the average pore diameter DB of the B layer are not particularly limited, but from the viewpoint of reducing the electric resistance, the difference between DA and DB is preferably within 0.03 μm.

  The laminated porous film of the present embodiment preferably has a porosity in the range of 25 to 69%. If the porosity is within the above range, the balance between membrane strength and permeability tends to be better. In particular, the balance of self-discharge suppression effect, prevention of fine short-circuiting, and cycle characteristics when used as a separator for a secondary battery or the like is good. Furthermore, the porosity is preferably 30 to 59% from the viewpoint of film strength, and preferably 30 to 49% from the viewpoint of suppressing fine short-circuiting. Here, the porosity can be obtained by the measurement method described in Examples described later. Examples of the method for adjusting the porosity to the above range include a method for adjusting the mixing ratio of the raw material resin and the plasticizer in the case of the wet method, and a method for adjusting the draw ratio in the case of the dry method.

  Further, the difference of (porosity A) − (porosity B) is preferably in the range of −3 to 3%. In this range, in the coextrusion which is a preferred embodiment in the method for producing a laminated porous film described later, the merging in the die of (A layer) (B layer) becomes good, and the film of the film such as interlayer disturbance There is a tendency to be able to mold well without causing a phenomenon that adversely affects homogeneity.

The laminated porous film of the present embodiment has an F value defined by the following formula (1) when the curvature is T (−), the average pore diameter is D (μm), and the porosity is P (%). However, it is preferable to satisfy 0.25 ≦ F ≦ 0.9.
F = T / (D * P) (1)
When the F value is within the above range, the liquid absorbency is improved, and it becomes easy to adjust the liquid absorbency index (H30) to 7 mm or more, and as a result, the pouring property of the electrolyte during battery production is improved. There is a tendency. As apparent from the definition, the F value is a parameter related to the permeation resistance of the membrane. The F value is preferably 0.9 or less, more preferably 0.8 or less, from the viewpoints of liquid absorbency, cycleability and ion permeability. On the other hand, if the F value is too small, the strength of the film tends to decrease, so it is preferably 0.25 or more, more preferably 0.4 or more.

  The laminated porous film of the present embodiment may be subjected to a hydrophilization treatment or a corona treatment for increasing the affinity for the electrolytic solution. If the F value is within the above range, the liquid absorption is possible even without the hydrophilization treatment. There is a tendency to improve the performance.

  In order to adjust the F value within the above-mentioned preferable range, the average pore diameter, porosity, and curvature of the laminated porous film are adjusted by a known method, and of course, the specific porosity described above (layer A) It is also possible to adjust by using a laminated porous film comprising (B layer).

  The range of the curvature of the laminated porous film of the present embodiment is preferably 1.0 to 3.0, and if it is within this range, the cycleability tends to be improved. The range of the curvature is more preferably 1.5 to 2.5. Here, the curvature can be obtained by the measurement method described in Examples described later. In addition, as a method for adjusting the curvature to the above range, in the case of a wet method, a method for adjusting stretching conditions such as a stretching ratio and a stretching temperature, a method for appropriately selecting a combination of a resin and a plasticizer, and the like can be given. It is done.

  Examples of the layer structure of the laminated porous film of the present embodiment include, but are not particularly limited to, two layers, three layers, or more multilayers. For example, in the case of three layers, (A layer) / ( B layer) / (A layer) is preferred. Further, the laminated porous film may have a multi-layer structure of more than three layers of four layers, five layers, seven layers, nine layers, and several tens of layers.

  Each layer of the laminated porous film of the present embodiment is usually composed of a resin composition containing a thermoplastic resin. The resin composition preferably contains a polyolefin as a main component from the viewpoints of moldability and solvent resistance to the electrolytic solution. Examples of the polyolefin include polyethylene, polypropylene, and polybutene-1. The term “main component” means that the proportion of the specific component in the matrix component containing the specific component is preferably 50% by mass or more, more preferably 80% by mass or more, and 100% by mass. It means you may.

  Examples of resins other than polyolefin include engineering plastic resins such as polyphenylene ether, polyamides such as nylon 6, nylon 6-12, and aramid resin, polyimide resins, polyester resins such as PET and PBT, polycarbonate resins, and polyvinylidene fluoride. Fluorine resin such as (PVDF), copolymer of ethylene and vinyl alcohol, copolymer of C2-C12 α-olefin and carbon monoxide and hydrogenated product thereof, hydrogenated product of styrenic polymer, and styrene Copolymers of α-olefins and hydrogenated products thereof, copolymers of styrene and aliphatic monounsaturated fatty acids, acrylic acid and derivatives thereof, copolymers of styrene and conjugated diene unsaturated monomers Polymers and thermoplastic resins selected from these hydrogenated materials are used.

  Examples of the polyethylene include high density polyethylene, ultra high molecular weight polyethylene, linear low density polyethylene, high pressure method low density polyethylene, and mixtures thereof. Among these, from the viewpoint of reducing thermal shrinkage when used as a separator, linear high-density polyethylene, ultrahigh molecular weight polyethylene, or a mixture thereof by ion polymerization is preferable. The ultra-high molecular weight polyethylene here refers to those having a viscosity average molecular weight of 500,000 or more. The proportion of ultra high molecular weight polyethylene in the total polyethylene is preferably 5 to 50% by mass, and more preferably 9 to 40% by mass from the viewpoint of dispersibility.

  The viscosity average molecular weight (Mv) of polyethylene (when using plural types of polyethylene, the total viscosity average molecular weight) is preferably 200,000 or more, more preferably from the viewpoint of improving the strength of the laminated porous film. Is over 300,000. The upper limit of the viscosity average molecular weight (Mv) is preferably 10 million or less, more preferably 5 million or less, from the viewpoints of extrusion moldability and stretchability.

  The molecular weight distribution (Mw / Mn) of polyethylene is preferable from the viewpoint of improving the kneadability when mixing and kneading inorganic fillers, etc., and suppressing the occurrence of granular defects in which the inorganic filler is secondary agglomerated. Is 6 or more, more preferably 8 or more.

  Examples of polypropylene include propylene homopolymers such as isotactic polypropylene (IPP), syndiotactic polypropylene, and atactic polypropylene, and propylene and comonomer such as ethylene, butene, and α-olefin having 5 or more carbon atoms. Examples thereof include a random copolymer (RPP), a block copolymer (BPP), and a terpolymer obtained by copolymerization. Among these, IPP having high crystallinity is preferable when it is desired to impart heat resistance, and RPP or BPP that is easily stretched is desirable when imparting strength.

  The viscosity average molecular weight (Mv) of polypropylene is easy to melt and knead. As a result, when it is used as a film, it tends to improve fish-eye defects, and is preferably 1 million or less, more preferably 700,000 or less. More preferably, it is 600,000 or less.

  Also preferred is a resin composition obtained by blending 0.5-30% by mass of polypropylene, BPP, or RPP with reduced stereoregularity using a metallocene catalyst or the like with respect to IPP. Thereby, the permeability tends to be improved when a microporous film mainly composed of polypropylene is formed by a wet method to be described later.

  Polybutene-1 resin and polymethylpentene-1 resin can also be used, and those having a melt index (MI) of about 0.1 to 10 g / 10 minutes are preferably used.

  In this Embodiment, you may mix an inorganic filler with the resin composition of each layer. Examples of the inorganic filler that can be used include alumina (for example, α-alumina), silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, and other oxide ceramics; silicon nitride, nitriding Nitride ceramics such as titanium and boron nitride; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, candy Ceramics such as sight, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; glass fiber etc. may be used, and these may be used alone or in combination. Also good. As a ratio for which an inorganic filler accounts in the resin composition of each layer, Preferably it is 10-90 mass%, More preferably, it is 20-55 mass%.

  The particle size of the inorganic filler is not particularly limited, but various types can be used depending on the purpose. For example, in order to improve wettability with an organic solvent, when using a hydrophobic filler or the like, a material having a relatively small average particle diameter, for example, 5 nm to 1 μm, preferably, in order to improve the dispersibility in the resin and the surface area. Is about 5 to 100 nm. On the other hand, when particles having an average particle diameter of 1 μm to 10 μm are used, the strength of the film can be improved. The average particle diameter of the inorganic filler is more preferably 1.5 μm to 5 μm, and if it is within this range, uneven thickness during film formation tends to be suppressed.

  In the laminated porous film of the present embodiment, for example, various additives such as an antioxidant, a crystal nucleating agent, a dispersion aid, and an antistatic agent may be blended as necessary.

  Examples of the antioxidant include phenolic antioxidants such as “Irganox 1010”, “Irganox 1076”, and “BHT” (both are trademarks, manufactured by Ciba Specialty Chemicals), phosphorus-based and sulfur-based antioxidants. A secondary antioxidant, a hindered amine weathering agent, and the like can be used alone or in accordance with the purpose. As the antioxidant, a combination of a phenolic antioxidant and a phosphorus antioxidant is particularly preferably used. Specifically, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butylhydroxyphenyl) propionate 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butylhydroxybenzyl) benzene, tris (2,4-di-t-butylphenyl) phosphite, tetrakis (2 , 4-di-t-butylphenyl) -4,4′-biphenylene phosphite is preferred. In addition, 6- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-t-butyldibenzo [d, f] [1,3, 2] Dioxyphosphine and the like are also suitable. The blending amount of the antioxidant is preferably 100 ppm to 10000 ppm with respect to the resin constituting the laminated porous film, and the ratio is preferably 1/3 to 3/1 in the case of the combined use of phenolic / phosphorus. It is.

  In the present embodiment, when polypropylene is used as the resin constituting the laminated porous film, it is preferable to use a crystal nucleating agent in order to control its crystallinity and control the formation of micropores. It is preferable when manufacturing a membrane. Although it does not specifically limit as a kind of crystal nucleating agent, Carboxylic acid metal salts, such as general benzyl sorbitol type | system | group, a phosphoric acid metal salt, aluminum t-butylbenzoate, etc. are mentioned. Specific examples thereof include bis (p-ethylbenzylidene) sorbitol, bis (4-methylbenzylidene) sorbitol, bis (3,4-dimethylbenzylidene) sorbitol, bisbenzylidenesorbitol, and the like. The compounding amount of the crystal nucleating agent is preferably 100 ppm or more based on the amount of polypropylene, from the viewpoint that crystallization proceeds rapidly and moldability is easy, although it depends on the desired crystallization conditions. From the viewpoint of preventing excessive bleeding due to the crystal nucleating agent, it is preferably 10,000 ppm or less. A more preferable amount of the crystal nucleating agent is 100 to 2,000 ppm with respect to polypropylene. In the production method of microporous membranes using ordinary plasticizers, when liquid paraffin or phthalate ester plasticizers are used, polyethylene tends to exhibit permeability, but polypropylene has pores compared to polyethylene. It tends to be small and inferior in permeability. As a means for eliminating the permeability of this polypropylene, a method of adjusting the pores to an appropriate size is effective, but the phase separation rate is adjusted by using the above-mentioned crystal nucleating agent, and an appropriate pore structure can be formed. It becomes easy.

  In addition, as a dispersion aid for polypropylene and polyethylene, for example, a hydrogenated styrene-butadiene elastomer, an elastomer copolymerized with ethylene and propylene, or the like is used as necessary. Although the compounding quantity of these adjuvants is not specifically limited, Preferably 1-10 mass parts is used with respect to 100 mass parts of total amounts of a polypropylene and polyethylene.

  Furthermore, as antistatic agents, amines such as alkyldiethanolamine and hydroxyalkylethanolamine, amine esters such as stearyl diethanolamine monofatty acid ester, alkyloamides such as lauric acid diethanolamide and stearic acid diethanolamide, glycerin and diglycerin These mono-fatty acid esters, anionic antistatic agents such as alkylbenzene sulfonic acids, polyoxyethylene alkyl ethers and the like may be used alone or in combination. The blending amount of these antistatic agents is not particularly limited, but is preferably about 500 to 10,000 ppm with respect to the resin constituting the laminated porous film.

The production method of the laminated porous film of the present embodiment may be a known method such as a co-extrusion method, a method of laminating each layer individually and then laminating, but preferably the following (Step 1) and (Step 2). ).
(Step 1) Resin composition A forming (A layer) and resin composition B forming (B layer) are both extruded in a molten state from a die, and (A layer) and (B layer) are laminated. A laminated film forming step of forming the laminated film,
(Step 2) A laminated porous film forming step in which both the (A layer) and the (B layer) are microporous after the laminated film forming step.
Here, about the process 1, the resin composition which comprises a 3rd layer other than (A layer) (B layer) may be included.

An example of (Step 1) will be described below.
For example, when the resin composition A and the resin composition B are kneaded by separate extruders, as a method of kneading the resin composition A or B, a raw material resin and a plasticizer depending on the case may be used in advance as a Henschel mixer or tumbler. Through a step of pre-kneading with a mixer or the like, the kneaded product is put into an extruder, and a plasticizer is introduced to a predetermined amount at an arbitrary ratio as necessary while being heated and melted in the extruder, and further kneaded. A method is mentioned. Such a method tends to be able to obtain a sheet having a better dispersibility of the resin composition, and is preferable from the viewpoint that each layer can be stretched without breaking even at a high magnification. (Step 2) is a step of forming a laminated porous film by adding a plasticizer and an inorganic filler to the resin composition A and the resin composition B, respectively, and extracting the plasticizer and the inorganic filler after film formation (wet method). In this case, a plasticizer or an inorganic filler may be added to the resin composition A and the resin composition B. In the case where (Step 2) is a step of opening using a crystal interface between the resin composition A and the resin composition B or an interface between the inorganic filler and the resin composition (dry method), the resin composition Opening can be carried out without adding a plasticizer to A and the resin composition B.

  In (Step 1), a more preferred embodiment is a case in which the resin composition having the same composition is used for both the A layer and the B layer, and the die is further used for 2 molten resin streams extruded from one extruder. Divide into two or more resin flows, and each molten resin flow is spread in the coat hanger part in the die, and each film is stacked in the die to form a multi-layer state and pushed out of the die from the lip port. It is a manufacturing method including that. In this case, since a multilayer film can be obtained with one extruder, it tends to be excellent in terms of prevention of thermal deterioration and economy.

More preferably, the die has a distribution unit 1 that divides the molten resin flow into two or more resin flows, and each divided molten resin flow spreads in a coat hanger shape in the cross direction of the flow, and further in a sheet shape It has the expansion part 2 to shape | mold, and the integration | stacking part 3 which makes the resin flow shape | molded by the sheet form integrate in a die | dye, and makes it a multilayer state. The multilayer film that is in a multilayer state at the stacking portion 3 is discharged out of the die from the extrusion die lip port 4.
1 shows a side sectional view of the die, and FIG. 2 shows a top sectional view (XX sectional view of FIG. 1).

  The laminated porous film in the present embodiment is suitably used as a separator for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. In addition, it can be used as various separation membranes.

  The method for stacking the laminated porous film of the present embodiment is not particularly limited, and may be a co-extrusion method using a plurality of ordinary extruders and one die, or the method described in JP-T 2009-543711. It may be used. In addition, a production apparatus called a super nanolayer manufactured by Clawren may be used, but as described above, the molten resin stream extruded from one extruder is divided into two or more resin streams, and each In the film state in which the molten resin flow spreads on the coat hanger portion in the die, the respective films are stacked in the die to form a multilayer state, and the manufacturing method of extruding out of the die from the lip port is preferable. In this case, the apparatus is simple and the manufacturing cost can be reduced. Furthermore, according to this method, in addition to the simplicity of the apparatus, the merging of the layers is performed after the resin spreads in the same manner as in the multi-manifold type coextrusion die, so that it is excellent in uneven thickness and flow. Since the path is simple, there is an advantage that there is little generation of deteriorated gel due to resin retention or the like.

  When the resin composition A and the resin composition B contain a plasticizer, the resin component concentration in the resin composition A is preferably 25 to 50% by mass, and the resin component concentration in the resin composition B is preferably 30 to 55% by mass. (The resin component concentration may be abbreviated as “PC” (polymer concentration).) The difference (PCB−PCA) between the PC of (B layer) and the PC of (A layer) is preferably 3 to 20 mass. %. Setting the PC difference in the above range is preferable from the viewpoint of adjusting the physical properties of the laminated porous film to a specific range in the present embodiment.

  As the melt extruder used in the above (Step 1), it is preferable to use a twin-screw extruder, which can impart a strong shear, thereby further improving dispersibility. More preferably, L / D of the screw of a twin screw extruder is about 20-70, More preferably, it is 25-55. The screw may be provided with a full flight portion and generally a kneading portion such as a kneading disk or a rotor.

  It is preferable to use a coextrusion die in the step (1) for obtaining a laminated film. In the case of a T die, a coat hanger type multi-manifold die in which the molten resin is spread in a film shape inside the die and then the layers are joined together Is particularly preferable from the viewpoint of thickness control. However, it is also possible to use a feed block die or a crosshead die. In the case of a circular die, a spiral die, and in the case of a multilayer film having five or more layers, a stack die is preferable from the viewpoint of preventing thermal deterioration, and is particularly preferable when it is desired to increase the adhesive strength between layers.

  In the above (Step 1), the resin composition A and the resin composition B are both extruded in a molten state, and the two are stacked and laminated preferably in the die, but laminated outside the die. May be.

  The die attached to the tip of the extruder is not particularly limited, but a circular die, a T die, or the like is used. When using an inorganic filler or a resin composition that easily deteriorates, measures that prevent wear and adhesion caused by it, for example, Teflon (registered trademark) processing, ceramic processing on the flow path and lip Nickel processing, molybdenum processing, and hard chrome coating are preferably used.

  In (Step 1), when the resin composition A and the resin composition B are both extruded in a molten state, the melt viscosity A at the extrusion temperature of the resin composition A and the extrusion temperature of the resin composition B As a ratio with melt viscosity B, melt viscosity A / melt viscosity B is preferably 1/5 to 5/1, more preferably 1/2 to 2/1. Setting the ratio in the above range is preferable from the viewpoint of suppressing interface disturbance at the time of resin merging and suppressing uneven thickness.

  The molten resin extruded from the die is introduced into, for example, a casting apparatus, but may be formed by bank molding or bankless molding. The thick original fabric obtained in the casting process can be used as the original fabric before stretching. Thereafter, the film is stretched for imparting a high mechanical strength and a balance between physical and longitudinal properties. In this case, the stretching method may be longitudinal uniaxial stretching, lateral uniaxial stretching, etc., but biaxial stretching is preferable, and simultaneous biaxial is more preferable. Stretching and sequential biaxial stretching. In the case of sequential biaxial stretching, longitudinal stretching may be performed first or lateral stretching may be performed first. The stretching temperature varies depending on the resin composition used, but is generally a temperature in the range between the Vicat softening point and the melting point of the main resin. From the viewpoint of film strength, the draw ratio is preferably in the range of 3 to 200 times, preferably 20 to 60 times in terms of area magnification.

  (Step 2) is a laminated porous film forming step in which both the (A layer) and (B layer) are microporous after the laminated film forming step, and as described above, is performed by a wet method or a dry method. The extraction of the plasticizer and the inorganic filler may be performed by immersing the film in an extraction solvent and then sufficiently drying the film. When extracting only the plasticizer, the extraction solvent is preferably a poor solvent for the polyolefin and the inorganic filler and a good solvent for the plasticizer, and the boiling point is preferably lower than the melting point of the polyolefin. Further, from the viewpoint of dispersibility with the resin when it is mixed with the resin for extrusion moldability, the molecular weight of the extraction solvent is preferably about 100 to 900 on average. Examples of such extraction solvents include chlorinated solvents such as methylene chloride and 1,1,1-trichloroethane; ketones such as methyl ethyl ketone and acetone; hydrofluorocarbons, hydrofluoroethers, cyclic hydrofluorocarbons, perocarbons, perfluoros. Halogenous organic solvents such as ether; ethers such as diethyl ether and tetrahydrofuran; hydrocarbons such as n-hexane and cyclohexane; alcohols such as methanol and isopropyl alcohol. Among the above, methylene chloride is particularly preferable. Two or more of these extraction solvents may be used. The extraction step may be before or after the stretching step, or may be multistage extraction using a plurality of extraction tanks. Examples of the extraction solvent for the inorganic filler include alkaline water.

  Moreover, you may add the heat setting by heating extending | stretching as needed for adjustment of film | membrane physical properties, such as a film thickness and an air permeability, or prevention of the thermal contraction of a film. Examples of the stretching after extraction of the plasticizer and the inorganic filler include uniaxial stretching, simultaneous biaxial stretching, and sequential biaxial stretching, and simultaneous biaxial stretching and sequential biaxial stretching are preferable. The stretching temperature varies depending on the resin composition used, but is generally a temperature in the range between the Vicat softening point and the melting point of the main resin. The draw ratio is preferably more than 1 time and 10 times or less in terms of area magnification.

  Further, when heat treatment for dimensional stabilization is performed, from the viewpoint of reducing film shrinkage in a high temperature atmosphere, for example, using a biaxial stretching machine, a uniaxial stretching machine, or both, 100 ° C. or more and 150 ° C. or less. Heat treatment can be performed. Preferably, it is carried out by relaxing the magnification and / or stress in the width direction, the length direction, or both directions at a temperature below the melting point of the main resin. The relaxation rate in this case is preferably in the range of 0 to 30% in the vertical direction and 5 to 30% in the horizontal direction. This heat treatment may be performed continuously with heat setting by heat treatment or may not be performed continuously.

  The laminated porous film thus obtained may be appropriately subjected to corona treatment or electron beam crosslinking treatment, or may be coated with an inorganic layer or an organic layer.

  The laminated porous film of the present embodiment preferably has a three-dimensional network structure in which pores are three-dimensionally complicated. The three-dimensional network structure means a structure in which the surface has a vein shape and the film structure of a cross section from an arbitrary three-dimensional coordinate axis direction is a sponge shape. Leaf vein is a state in which fibrils form a network structure. These can be confirmed by observing the surface and cross section with a scanning electron microscope. The fibril diameter of the three-dimensional network structure is preferably 0.01 μm or more and 0.3 μm or less, and this can also be observed with a scanning electron microscope.

  In addition, about the various parameters mentioned above, unless otherwise indicated, it measures according to the measuring method in the Example mentioned later.

  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 physical property in an Example was measured with the following method. Judgment was performed on necessary items, and ◎ and ○ were accepted and × was rejected.

(1) Melting point (mp) (° C)
Measured by DSC method. Heat from normal temperature to 200 ° C. at a temperature increase rate of 10 ° C./min, wait for 5 minutes, then decrease to 50 ° C. at a temperature decrease rate of 10 ° C./min. The temperature indicated by the peak with the maximum melting energy among the rapid heating peaks observed during the second heating was defined as mp (° C.).

(2) Thickness of each layer and total layer thickness (μm)
The thickness of each layer constituting the laminate was measured by cross-sectional observation with a general scanning electron microscope (S4100, manufactured by Hitachi, Ltd.).
The total thickness of each layer was defined as the total layer thickness.

(3) Porosity (%)
The weight per unit area W (g / cm ² ) and the average density ρ (g / cm ³ ) of the components (resin and additive) constituting the microporous membrane were calculated from the mass of the 100 mm square microporous membrane sample. The following formula was calculated from the thickness d (cm).
Porosity = (W / (d * ρ)) * 100 (%)
In addition, the ratio of the porosity of each layer (the porosity of the A layer / the porosity of the B layer)
For example, in the case of a three-layer film of A layer / B layer / A layer, when peelable, it was peeled and determined by the above method. In the case of a wet method, peeling may not be possible, but in this case, the volume concentration P (A layer PA, B layer PB, etc.) of the charged solvent in each layer, thickness D (A layer thickness DA, B layer thickness) by cross-sectional observation by SEM DB, etc.) was measured, and the porosity of the A layer was VA, the porosity of the B layer was VB, and the following two equations were solved simultaneously.
Formula 1 ... all layer porosity = (PA * DA * number of layers 2 + PB * DB * number of layers 1) / total layer thickness Formula 2 ... (VA / VB) = (PA / PB)

(4) Air permeability (sec / 100cc)
Based on JIS P-8117, it was measured with a Gurley type air permeability meter “G-B2” (trademark, manufactured by Toyo Seiki Seisakusho Co., Ltd.).
In addition, the value in a table | surface is the air permeability of 20 micrometers conversion calculated by the proportional calculation on the basis of total thickness.

(5) Puncture strength (g)
Using a handy compression tester “KES-G5” (trade name, manufactured by Kato Tech Co., Ltd.), the puncture test was performed under the conditions of a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm / sec.
In addition, the value in a table | surface is the puncture intensity | strength of 20 micrometers conversion calculated by the proportional calculation on the basis of total thickness.

(6) Average pore diameter (μm), curvature, F value It is known that the fluid inside the capillary follows the Knudsen flow when the mean free path of the fluid is larger than the pore diameter of the capillary, and the Poiseuille flow when it is small. ing. Therefore, it is assumed that the air flow in the measurement of the permeability of the microporous membrane follows the Knudsen flow, and the water flow in the measurement of the permeability of the microporous membrane follows the Poiseuille flow.
In this case, the average pore diameter D (μm) and the curvature T (dimensionless) are the air permeation rate constant Rgas (m ³ / (m ² · sec · Pa)) and the water permeation rate constant Rliq (m ³ / (M ² · sec · Pa)), air molecular velocity ν (m / sec), water viscosity η (Pa · sec), standard pressure Ps (= 101325 Pa), porosity ε (%), film thickness L ( [mu] m) using the following formula.
D = 2ν × (Rliq / Rgas) × (16η / 3Ps) × 106
T = (D × (ε / 100) × ν / (3L × Ps × Rgas)) 1/2
Here, Rgas is obtained from the air permeability (sec) using the following equation.
Rgas = 0.0001 / (air permeability × (6.424 × 10 ⁻⁴ ) × (0.01276 × 101325))
Rliq is obtained from the water permeability (cm ³ / (cm ² · sec · Pa)) using the following equation.
Rliq = water permeability / 100
In addition, water permeability is calculated | required as follows. A microporous membrane previously immersed in alcohol is set in a stainless steel permeation cell having a diameter of 41 mm, and after the alcohol in the membrane is washed with water, water is allowed to permeate at a differential pressure of about 50000 Pa, and 120 seconds have elapsed. The water permeation amount per unit time, unit pressure, and unit area was calculated from the water permeation amount (cm ³ ) at the time, and this was taken as the water permeability.
Ν is a gas constant R (= 8.314), an absolute temperature T (K), a circumference ratio π, and an average molecular weight M of air (= 2.896 × 10 ⁻² kg / mol), using the following formula. Desired.
ν = ((8R × T) / (π × M)) 1/2
Further, the F value is defined by the following formula (1) when the curvature is T (−), the average pore diameter is D (μm), and the porosity is P (%).
F = T / (D * P) (1)

(7) Liquid absorbency (Liquid absorbency index H30 (mm))
The laminated porous film was sampled in a strip shape of MD 100 mm and TD 10 mm, and the upper part 5 mm of the strip was fixed to a stand or the like so that the MD direction was vertical. At this time, the lower 95 mm of the strip was suspended vertically and floated in the air. Under the condition of 23 ° C., the plate was immersed in the following electrolyte simulation reagent from the lower end of the strip to 10 mm, and the height of the solution rising after 30 minutes was measured based on the immersion time (liquid absorbency index H30 (Mm)). The liquid height can be easily determined by changing the color of the porous film from white to translucent. The determination was performed as follows. The immersion in the reagent was performed in a glass bottle to avoid the influence of wind and the like.
Electrolytic solution simulation reagent: Mixed at a ratio of ethylene carbonate / propylene carbonate / dimethyl ether = 3/1/6.
A: Increased by 9 mm or more.
A: Less than 9 mm and increased by 7 mm or more.
X: It rose only less than 7 mm.

(8) Flatness (uneven thickness characteristics)
In the width direction of the formed film, measure the thickness with a contact-type continuous thickness measuring device (ANRITSU K310D manufactured by Anritsu Electric Co., Ltd.), read the peak height relative to the baseline on the chart in units of 1μ, and calculate this value. I evaluated it. In addition, when two or more peaks were expressed, it was set as the total value of each peak.
Evaluation: Criteria (total peak height)
◎ (very good) ... less than 0.1 µm ○ (no problem) ... 0.1 µm or more, less than 0.3 µm x (bad) ... 0.3 µm or more

(9) Safety (withstand voltage)
A 50mm * 50mm film sample is sandwiched between electrodes with a Φ35mm with a clean surface, a voltage is applied to the electrode, and the voltage is measured when a 0.5mA current flows and sparks. It was used as an index. This measurement was measured at least 15 times in the plane of the sample film, and the average value was recorded. An average value of 1.8 KV or more was rated as ◎, 1.0 KV or more as ◯, and less than 1.0 KV as x.

(10) Cyclicity After producing an electrode and an electrolytic solution as shown below, an evaluation battery was produced using the electrode and the electrolytic solution, and its cycle characteristics were evaluated.
(I) Production of positive electrode 100 parts by mass of lithium cobalt composite oxide LiCoO ₂ as a positive electrode active material, 2.5 parts by mass of flake graphite and acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) 3 as a binder A slurry was prepared by dispersing 5 parts by mass in N-methylpyrrolidone (NMP). This slurry was applied to both surfaces of a 20 μm thick aluminum foil serving as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material coating amount of the positive electrode was 250 g / m ² and the active material bulk density was 3.00 g / cm ³ . This was cut in accordance with the battery width to form a strip.
(Ii) Production of negative electrode As a negative electrode active material, 90 parts by mass of graphitized mesophase pitch carbon fiber (MCF) and 10 parts by mass of flake graphite, 1.4 parts by mass of ammonium salt of carboxymethyl cellulose as a binder and styrene-butadiene A slurry was prepared by dispersing 1.8 parts by mass of polymer latex in purified water. This slurry was applied to both sides of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material application amount of the negative electrode was 106 g / m ² , and the active material bulk density was 1.35 g / cm ³ . This was cut in accordance with the battery width to form a strip.
(Iii) Preparation of Nonaqueous Electrolyte Solution It was prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 mol / liter.
(Iv) Production of battery for evaluation Electrode plate laminate by winding microporous membrane separator to be evaluated, strip-shaped positive electrode, and strip-shaped negative electrode in a spiral shape by overlapping the strip-shaped negative electrode, separator, strip-shaped positive electrode and separator in this order. Was made. After pressing this electrode plate laminate into a flat shape, it is housed in an aluminum container, the aluminum lead is led out from the positive electrode current collector and the nickel lead is led out from the negative electrode current collector to the bottom of the container. The battery wound body was fabricated by welding to a battery.
(V) Cycleability The above-described non-aqueous electrolyte solution was injected into the battery roll for evaluation produced as described above and sealed to produce a lithium ion battery.
The battery was charged to a charge end voltage of 4.2 V with a charge current of 1 A under a temperature of 25 ° C., and discharged to a discharge end voltage of 3 V with a charge current of 1 A. Charging / discharging was repeated as one cycle, and the capacity retention after 500 cycles with respect to the initial capacity was expressed as cycle characteristics and evaluated as follows. The capacity retention is ◎: 90% or more, ◯: less than 90%, 60% or more, and x: less than 60%.

(11) Viscosity average molecular weight Mv
Based on ASTM-D4020, the intrinsic viscosity [η] at 135 ° C. in a decalin solvent was determined. Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 ⁻⁴ Mv 0.67
For polypropylene, Mv was calculated by the following formula.
[Η] = 1.10 × 10 ⁻⁴ Mv0.80
(12) Ease of battery creation (battery winding / separator winding)

In the cylindrical battery production process, the positive electrode, the negative electrode, the conductive foil and the separator are generally rolled and then inserted into the cylindrical battery can. However, in a separator with uneven thickness, slack, or bend, the winding diameter and end face are In some cases, the battery can not be inserted into the battery can, or even if it can be inserted, the end face may protrude from the battery can and the battery may not be created. Such a tendency can be grasped by the winding shape when the separator is wound around the winding core, that is, the local variation of the winding diameter and the disturbance of the end face. Therefore, here, the ease of battery production (battery winding / separator winding shape) was evaluated as follows.
The separator was cut to a width of 60 mm and wound 200 m into an ABS resin tube having an inner diameter of 3 inches to obtain a reel. At this time, a reel having a uniform end face and a winding diameter within the reel of less than 0.5 mm across the width direction is marked with ◯, and the end face is non-uniform or the winding diameter difference within the reel is 0.5 mm or more. Was marked with x.

[Example 1]
The manufacture example of the lamination | stacking porous film which has 3 layer structure of (A layer) / (B layer) / (A layer) is shown. The raw material resins used in the examples are shown in Table 1.
In Table 1, HD1 is a high-density polyethylene having a viscosity average molecular weight (MV) of 300,000 (manufactured by Asahi Kasei Corporation, SH810), and HD2 is a high-density polyethylene having an MV of 300,000 (manufactured by Asahi Kasei Corporation, F184). , LD is a low density polyethylene (Made by Asahi Kasei Co., Ltd., F1920) with a MV of 100,000, UH is an ultra high molecular weight polyethylene (Made by Asahi Kasei Co., Ltd., UHMWPE prototype) with a MV of PP, An isotactic homopolypropylene having a MV of 500,000 (PB170A manufactured by Sun Allomer) is shown. Moreover, talc (SK-C2 manufactured by Katsumitsuyama Co., Ltd.) was used as the inorganic filler.
The raw material resin (resin component) was blended at the blending ratio (parts by mass) shown in Table 1. 0.5 parts by mass of bis (P-ethylbenzylidene) sorbitol as a nucleating agent and tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4) as an antioxidant with respect to 100 parts by mass of the raw material resin '-Hydroxyphenyl) propionate] 0.3 parts by mass of methane and 10 parts by mass of liquid paraffin (kinematic viscosity at 37.8 ° C., density of 868 kg / m ³ ) as a plasticizer were blended. These raw materials were stirred with a Henschel mixer to prepare the raw materials.
Next, the raw material of the (A) layer and the raw material of the (B) layer were put into separate twin-screw extruders (caliber 41 mm, L / D = 49). Liquid paraffin was injected into the middle part of the cylinders of both extruders so as to be 68% by mass in the (A) layer and 62% by mass in the (B) layer.
The amount of extrusion of both surface layers ((A) layer) and intermediate layer ((B) layer) is adjusted so that the thickness ratio of the (A) layer and the (B) layer becomes the thickness ratio shown in Table 2 at the die outlet. Set to.
A 250 mesh screen was disposed between the extruder and the die. The die used was a T-die capable of multi-manifold coextrusion. In the die, the surface layer was divided into approximately equal parts and stacked on both sides of the intermediate layer. The melted film raw material coming out of the die was cooled and solidified with a cast roll.
The sheet was stretched by a simultaneous biaxial stretching machine at 120 ° C. under an area magnification of 49 times (length 7 times * width 7 times), immersed in methylene chloride, extracted by liquid paraffin, dried, and further dried. Using a tenter stretching machine, the film was stretched 1.5 times in the transverse direction at 125 ° C., and the stretched sheet was relaxed in the 14% width direction at 130 ° C. and subjected to heat treatment. As a result, a microporous film of 20 μm (surface layer / intermediate layer / surface layer = 7 μm / 6 μm / 7 μm) was obtained in all layers having a three-layer structure. Table 2 shows the physical properties of the obtained microporous membrane.

[Examples 2-6, Example 15, Comparative Examples 1-2]
A laminated porous film was molded and evaluated in the same manner as in Example 1 while changing each layer configuration and structure factor described in Table 2. The amount of liquid paraffin added was in the range of 40% by mass to 80% by mass although it was different in each example. The simultaneous biaxial stretching machine was stretched at an area magnification of 45 times within a range of 115 ° C to 125 ° C. Liquid paraffin is extracted and dried, then dried, and further stretched 1.1 to 2.0 times in the transverse direction at 120 to 130 ° C. by a tenter stretching machine, and this stretched sheet is relaxed in the width direction by 7% at 130 ° C. The heat treatment was performed. Table 2 shows the physical properties of the obtained microporous membrane.

[Example 7]
A laminated porous film was molded and evaluated in the same manner as in Example 6 except that a two-type five-layer coextrusion die was used and the layer configuration was changed to A / B / A / B / A.

[Examples 8 to 14]
A laminated porous film was molded and evaluated by the same method as in Example 1 using one extruder and the one-type three-layer die shown in FIGS. The amount of liquid paraffin added was in the range of 40% by mass to 80% by mass although it was different in each example. The simultaneous biaxial stretching machine was stretched at an area magnification of 49 times within a range of 115 ° C to 125 ° C. The liquid paraffin is extracted and dried, then dried, and further stretched 1.1 to 2.0 times in the transverse direction under the conditions of 120 to 130 ° C. by a tenter stretching machine, and this stretched sheet is relaxed in the width direction by 14% at 130 ° C. The heat treatment was performed. Table 2 shows the physical properties of the obtained microporous membrane.
As shown in Table 2, the microporous membrane of this example is particularly excellent in flatness (uneven wall thickness), and is excellent in safety, cycleability, and ease of battery production. This effect reduces the safety and cycleability in the plane of the film by improving the flatness of the laminated porous film by optimizing the porosity ratio, melting point difference, and thickness difference of the A layer and B layer. It is presumed that the existence of defective parts to be caused is significantly reduced.

[Comparative Example 3]
A laminated porous film was molded and evaluated in the same manner as in Example 10 except that one extruder and a single-layer die were used. Table 2 shows the physical properties of the obtained microporous membrane.

  According to the present invention, a laminated porous film having excellent flatness can be obtained. Further, the application of the present invention can provide a separator excellent in safety, output performance, and ease of battery production. Further, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery (LIB) can be provided.

Claims (5)

A laminated porous film comprising an outer A layer comprising a porous film and a B layer laminated adjacent to the inner side of the A layer and comprising a porous film substantially the same type as the A layer,
The porosity ratio of the A layer and the B layer is 0.90 or more and 1.1 or less as (the porosity of the A layer) / (the porosity of the B layer),
The melting point difference between the A layer and the B layer is 0 ° C. or more and 5 ° C. or less,
A laminated porous film in which a thickness difference between the A layer and the B layer is −20 μm or more as (A layer thickness) − (B layer thickness).   The laminated porous film according to claim 1, wherein the A layer is laminated adjacent to both surfaces of the B layer, and has a three-layer configuration of A layer / B layer / A layer. It is a manufacturing method of the lamination | stacking porous film of Claim 1 or 2, Comprising: Each process of the following (1) and (2),
(Step 1) Resin composition A forming (A layer) and resin composition B forming (B layer) are both extruded in a molten state from a die, and (A layer) and (B layer) are laminated. A laminated film forming step of forming the laminated film,
(Step 2) After the laminated film forming step, a laminated porous film forming step in which both the (A layer) and (B layer) are microporous.
Have
In the film state in which the die divides the molten resin stream extruded from one extruder into two or more resin streams, and each molten resin stream spreads in the coat hanger part in the die, each film In a die to form a multi-layered state and extrude out of the die through a lip opening. The die is
A distributor for dividing the molten resin stream into two or more resin streams;
Expanding each of the divided resin flows in a coat hanger shape in the cross direction of the flow, and further forming a sheet shape;
A stacking portion in which the resin flow formed in the sheet shape is stacked in a die to form a multilayer state,
The manufacturing method of Claim 3 which has these.   The separator for nonaqueous electrolyte secondary batteries containing the lamination | stacking porous film of Claim 1 or 2.