KR102102120B1 - Laminated porous film and separator for electrical energy storage device - Google Patents

Abstract

Providing a laminated porous film that achieves excellent battery performance, heat resistance, and low cost, and is suitable for separators for high-quality power storage devices. The laminated porous film of the present invention is characterized in that a porous layer is formed on at least one side of the substrate, and the porous layer includes inorganic particles (A), at least two types of water-soluble polymers (B), and resins (C).

Description

Separator for laminated porous film and power storage device {LAMINATED POROUS FILM AND SEPARATOR FOR ELECTRICAL ENERGY STORAGE DEVICE}

The present invention relates to a laminated porous film usable for a separator for an electrical storage device having excellent electrical properties and safety. More specifically, the present invention relates to a laminated porous film suitable for use as a separator for power storage devices because it has excellent safety by forming a porous layer on a porous film, has excellent film properties, high battery performance, and is of high quality.

Porous films made of polyolefins, etc., are widely used for separator applications of lithium ion secondary batteries, in addition to electrical insulation and ion permeability, and also excellent in mechanical properties. Large hole diameter reduction, thin film formation, and high porosity have been studied (for example, see Patent Document 1 and Patent Document 2). However, there is a problem in that the porous film made by this method alone lacks heat resistance and dimensional stability, and cannot prevent the penetration of foreign matter mixed in the battery.

Further, a method has been proposed in which a layer made of inorganic particles is laminated on a porous film made of an olefin resin to improve heat resistance (for example, see Patent Documents 3 to 5), but the moisture content contained in the porous film is high. When used as a separator for a lithium-ion secondary battery, there was a problem that the moisture contained in the lithium and the reaction material deteriorated, resulting in deterioration of battery performance. Therefore, as a method of reducing the moisture of the porous film, a method of hydrophobizing inorganic particles has been proposed (for example, see Patent Document 6), but there is a fear that the hydrophobization treatment agent may degrade battery performance. In addition, although a method of performing dehydration treatment at a high temperature using a resin having high heat resistance as a substrate for a separator has been proposed (for example, see Patent Document 7), the resin is expensive in raw material or complicated in porosity. There was a problem that one thing led to high cost.

Japanese Patent Publication No. Hei 11-302434 International Publication No. 2005/61599 International Publication No. 2008/149986 Japanese Patent Publication 2008-123996 Japanese Patent Publication No. 2004-227972 International Publication No. 2008/029922 Japanese Patent Publication No. 2011-233482

The problem of the present invention is to solve the above problems. That is, the object of the present invention is to achieve excellent battery performance, heat resistance, and low cost by improving water content and improving coating properties by containing at least two types of water-soluble polymers in the porous layer, and further improving the quality of the separator for power storage devices. It is to provide a laminated porous film suitable as a dragon.

The present invention for achieving the above object is a porous layer is formed on at least one side of the substrate, the porous layer is a laminated porous film comprising inorganic particles (A), at least two kinds of water-soluble polymer (B) and resin (C) It is characterized by.

(Effects of the Invention)

Since the laminated porous film of the present invention contains at least two types of water-soluble polymers (B) in the porous layer, it is possible to attain low water content and provide excellent coating properties, thereby providing excellent battery performance, heat resistance, and cost reduction. It is possible to provide a laminated porous film which is high quality and is suitable for separators for power storage devices.

In the present invention, the laminated porous film refers to a laminated film in which a porous layer is formed on at least one side of a substrate. The porous layer contains inorganic particles (A), at least two types of water-soluble polymers (B), and resins (C).

In the present invention, the substrate used for the laminated porous film is a porous sheet shape having air permeability for laminating a porous layer. Specifically, a nonwoven fabric, various woven fabrics, a porous film, etc. are mentioned. As the substrate used in the present invention, a porous film made of a resin is preferable because of its excellent productivity and processability.

In the present invention, the porous film is a microporous membrane that penetrates both surfaces of the film and has a large number of fine through holes having air permeability. It is preferable that the main component of this porous film is resin (D). In the present invention, the main component of the porous film means 80% by mass or more of the raw materials constituting the porous film.

As the resin (D), an olefin-based resin, a fluorine-based resin, an imide-based resin, a urethane-based resin, an acrylic-based resin, etc. can be used, but the olefin-based resin is excellent in terms of ease of processing and low cost, and has a high ionic conductivity. Is preferred.

As the olefin-based resin, a single polyolefin resin such as polyethylene, polypropylene, polybutene-1, and poly-4-methylpentene-1, a mixture of these resins, and a resin obtained by random copolymerization or block copolymerization of monomers can be used.

The porous film used as the base material of the laminated porous film of the present invention preferably has a melting point of 110 ° C or higher from the viewpoint of heat resistance. When the melting point is less than 110 ° C, when the porous layer is laminated on the porous film, the porous film may be dimensionally changed. The melting point of a porous film refers to the melting point of course when it shows a single melting point, but when the porous film has a plurality of melting points, such as a mixture of olefinic resins, the melting point appears on the hottest side. Is called the melting point of the porous film. In addition, from the viewpoint of planarity and heat resistance of the substrate in the coating step of forming the porous layer described later, the melting point of the porous film is more preferably 130 ° C or higher, and even more preferably 150 ° C or higher. In addition, when the porous film exhibits a plurality of melting points as described above, it is preferable that all of them are within the above range.

As the above-mentioned resin (D), it is preferable to use the polypropylene resin of the kind described later from the viewpoint of achieving both the above-mentioned heat resistance viewpoint and the processability for forming the through hole in the thickness direction of the film.

It is preferable that the porous film used for the base material in the present invention has the ability to form β crystals. When the porous film has the ability to form β crystals, the porous film can be produced by porosity of the film by the β crystal method described later. Since the porous film obtained by the β crystal method has excellent productivity and has a pore diameter (surface pore diameter) of a surface suitable for expressing high adhesion due to the anchor effect when the porous layer is laminated, it is suitable as a substrate for a laminated porous film. Can be used.

In the present invention, the beta crystal method refers to a method of forming a through hole in a film by stretching after sheeting a resin having a beta crystal forming ability.

In the present invention, a method for imparting β crystal forming ability to a resin used for a porous film can be achieved by containing a nucleating agent (β crystal nucleating agent) capable of selectively forming β crystals among the crystalline species of the resin. As the β-crystal nucleating agent of the polypropylene resin, various pigment-based compounds, amide-based compounds, and the like can be mentioned. In particular, amide-based compounds disclosed in Japanese Patent Laid-Open No. 5-310665 can be preferably used. As content of (beta) crystal nucleating agent, when the whole polypropylene resin is 100 parts by mass, it is preferably 0.05 to 0.5 parts by mass, and more preferably 0.1 to 0.3 parts by mass.

In the present invention, the ability to form β crystals indicates the proportion of β crystals present in the polypropylene resin under certain conditions, measured under the following conditions, and is a value indicating how much the ability to form β crystals exists. For the measurement of β crystal forming ability, 5 mg of polypropylene resin or polypropylene film was heated (first run) from room temperature to 240 ° C. at 10 ° C./min under a nitrogen atmosphere using a differential scanning calorimeter, and maintained at 10 ° C. for 30 minutes. Cool down to 10 ° C / min. Regarding the melting peak observed when the temperature is raised (second run) at 10 ° C / min after holding for 5 minutes, the melting peak where the peak exists in the temperature range of 145 to 157 ° C is the melting peak of β-crystal, peaking at 158 ° C or higher When the fusion heat observed is the melting peak of the α crystal, respectively, the heat of fusion is determined, and when the heat of fusion of the α crystal is ΔHα and the heat of fusion of the β crystal is ΔHβ, the value calculated by the following formula is called β crystal forming ability.

β crystal forming capacity (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100

In the present invention, the ability to form β crystals of the polypropylene resin constituting (comprising) the porous film used for the substrate has a high porosity and a suitable air permeability, and when the porous layer is laminated, the porous layer and the porous film adhere to each other. It is preferable that it is 40 to 90% from the viewpoint of forming a suitable surface pore diameter. When the beta crystal forming ability is less than 40%, the amount of beta crystals at the time of film production is small, so the number of pores formed in the film is reduced using the transition to the α crystal, and as a result, only a film having low permeability may be obtained. Moreover, when the beta crystal forming ability exceeds 90%, a coarse hole may be formed and may not have a function as a separator for an electrical storage device. In order to make the β crystal forming ability within the range of 40 to 90%, it is preferable to use a polypropylene resin having a high Isotactic Index and to add the β crystal nucleating agent. It is more preferable that it is 45-80% as a (beta) crystal forming ability.

In the present invention, the polypropylene resin constituting the porous film has an isotactic polypropylene resin in which melt flow rate (hereinafter referred to as MFR, measurement condition is 230 ° C., 2.16 kg) is in the range of 2 to 30 g / 10 min. It is preferred. When the MFR is out of the above-described preferred range, it may be difficult to obtain a stretched film. More preferably, MFR is 3 to 20 g / 10 minutes.

The isotactic polypropylene resin preferably has an isotactic index of 90 to 99.9%. If the isotactic index is less than 90%, the crystallinity of the resin is low, and it is sometimes difficult to achieve high air permeability. As the isotactic polypropylene resin, commercially available resins can be used.

Homo polypropylene resin can be used for the porous film, and from the viewpoint of stability, film-forming properties, and uniformity of physical properties in the film forming process, polypropylene contains 5% by mass of an olefin component such as ethylene, butene, hexene, and octene. You may use the copolymer copolymerized in the following range. Moreover, as a form of introduction of the comonomer into polypropylene, it may be random copolymerization or block copolymerization.

Moreover, it is preferable from the viewpoint of improving film forming property that the said polypropylene resin contains the high-melting-tension polypropylene in 0.5-5 mass% of range. The high-melting-tension polypropylene is a polypropylene resin that increases the tension in a molten state by mixing a component having a high molecular weight component or a branched structure in a polypropylene resin or copolymerizing a long-chain branching component with polypropylene. It is preferable to use a polypropylene resin in which the components are copolymerized. The high-melting-tension polypropylene is commercially available, and for example, polypropylene resins PF814, PF633, and PF611 manufactured by Basell, polypropylene resin WB130HMS manufactured by Borealis, and polypropylene resins D114 and D206 manufactured by Dow can be used.

As the polypropylene resin constituting the porous film, the efficiency of forming pores during stretching is increased, and the air permeability is improved by expanding the pore diameter, so that the mixture containing 1 to 10% by mass of ethylene / α-olefin copolymer in the homo polypropylene resin This is preferred. Here, examples of the ethylene / α-olefin copolymer include linear low-density polyethylene and ultra-low-density polyethylene, and among them, an ethylene-octene-1 copolymer obtained by copolymerizing octene-1 can be preferably used. As the ethylene-octene-1 copolymer, commercially available resins such as "Engage (registered trademark)" manufactured by Dow Chemical (type names: 8411, 8452, 8100, etc.) can be used.

In the present invention, it is preferable that the porous film used for the substrate is stretched in at least one axial direction. When an unstretched film is used, the porosity and mechanical strength of the film may be insufficient. As a method of stretching the porous film in at least one axial direction, it is preferable to stretch at a predetermined magnification by a tenter method, a roll method, an inflation method, or a combination of these after heating. The stretching may be uniaxial stretching or biaxial stretching. In the case of biaxial stretching, any of simultaneous biaxial stretching, sequential stretching and multistage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching) may be used, but sequential biaxial stretching is preferred from the viewpoint of productivity.

In the present invention, the porous film used for the base material may contain various additives such as antioxidants, thermal stabilizers, antistatic agents, lubricants made of inorganic or organic particles, and blocking inhibitors, fillers, and incompatible polymers. Particularly, when an olefinic resin is used as a main component of the porous film, it is preferable to contain 0.01 to 0.5 parts by mass of an antioxidant with respect to 100 parts by mass of the olefinic resin for the purpose of suppressing oxidation deterioration due to the thermal history of the olefinic resin.

In the present invention, it is preferable that the air permeation resistance of the porous film used for the substrate of the laminated porous film is 50 to 500 seconds / 100 ml. If the air permeation resistance is less than 50 seconds / 100 ml, it may be difficult to maintain insulation when a separator is used. Moreover, when it exceeds 500 seconds / 100 ml, when it is used as a base material for a laminated porous film, the air permeation resistance of the laminated porous film is large, and the battery characteristics when used as a separator tend to deteriorate. The air permeation resistance of the porous film is more preferably 80 to 400 seconds / 100 ml, more preferably 100 to 300 seconds / 100 ml.

The porous film used in the present invention preferably has a porosity of 50% or more and less than 85%, and more preferably 65% or more and less than 80%. If it is less than 50%, the number of pores on the surface decreases, so that when the porous layer is laminated, the adhesion to the porous film may be insufficient. When it is 85% or more, it may be insufficient from the viewpoint of the separator characteristics and strength. The porosity of the porous film can be obtained from the specific gravity (ρ) of the porous film and the specific gravity (a) of the resin (D) by the following equation.

Porosity (%) = [(a-ρ) / a] × 100

As a method for controlling the air permeation resistance and porosity to such a preferable range, when a polypropylene resin is used for the resin (D), it can be achieved by using a resin in which the ethylene / α-olefin copolymer is mixed at a specific ratio described above. . Moreover, it can achieve effectively by employing the specific biaxial stretching conditions mentioned later.

For the porous film used in the present invention, the number of holes having a pore diameter of 0.01 μm or more and less than 0.5 μm (N _A ) and the number of holes having a pore diameter of 0.5 μm or more and less than 10 μm (N _B ) with respect to the surface hole diameter (N _B ) It is preferable that the value of (N _A ) / (N _B ) which is the ratio of is 0.1 to 4, and more preferably 0.4 to 3. By setting it as the said range, the fall of air permeation resistance can be suppressed and adhesiveness of a porous layer and a porous film can be improved. When the value of (N _A ) / (N _B ) is less than 0.1, the porous film may have excessively large openings with large pore diameters, so that the coating liquid excessively enters the openings at the time of application, so that the air permeability may decrease. In addition, when the value of (N _A ) / (N _B ) exceeds 4, the proportion of pores with small pore diameters on the surface of the porous film is too large. Since some parts are difficult to enter the opening portion, sufficient adhesiveness may not be exhibited, or the air permeability may decrease due to the closing of the hole.

As a method of controlling the surface pore size to such a preferable range, it can be achieved by stretching and porosity of the polypropylene resin to which the above-mentioned β crystal nucleating agent is added.

The surface pore size of the porous film can be confirmed by taking a surface image using a scanning electron microscope and performing image analysis.

The laminated porous film of the present invention forms a porous layer on at least one side of the porous film obtained as described above. It is preferable to perform surface treatment for easy adhesion, such as corona discharge treatment, on the surface of the porous film for the purpose of improving the adhesion between the porous film and the porous layer before formation of the porous layer. Examples of the surface treatment include corona discharge treatment in air, oxygen atmosphere, nitrogen atmosphere, plasma treatment, and the like, but simple corona discharge treatment is preferred.

In the laminated porous film of the present invention, a porous layer including inorganic particles (A) is formed. It is preferable that this inorganic particle (A) is a main component in a porous layer. In the present invention, the main component of the porous layer means that 50% by mass or more of the composition constituting the porous layer is inorganic particles (A). By having the above-mentioned porous layer, it is possible to express heat resistance at a high temperature, which cannot be achieved with a porous film alone. The porous layer will be described in detail below.

The inorganic particles (A) used for the porous layer are preferably particles whose particle shape is maintained at least up to 200 ° C. That the shape is maintained means that the aspect ratio of the inorganic particles (A) at room temperature and the average particle diameter do not change even at 200 ° C. More preferably, the shape is maintained up to 300 ° C, and more preferably, the shape is maintained up to 330 ° C. That is, it is preferable that the phase transition accompanying the melting point, softening point, thermal decomposition temperature, or volume change of the inorganic particles A does not occur to the above temperature. Specifically, as an inorganic particle (A) that does not exhibit a melting point and maintains its shape until at least 330 ° C, oxides such as alumina, boehmite, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, etc. Nitride ceramics such as ceramics, silicon nitride, titanium nitride and boron nitride, silicon carbide, calcium carbonate, aluminum sulfate, potassium titanate, talc, kaolin clay, kaolinite, halosite, pyrophyllite, montmorillonite, sericite, mica, Amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, and the like. In the present invention, the particles of these compounds may be used alone, or a plurality of them may be mixed and used. Among these, the inorganic particles (A) are preferably calcium carbonate, alumina, boehmite, and silica from the viewpoint of electrochemical stability, and calcium carbonate is more preferable from the viewpoint of dispersibility and adhesion to the resin (C).

The average particle diameter of the inorganic particles (A) used in the porous layer is preferably 0.05 to 15 µm, and more preferably 0.1 to 10 µm, from the viewpoint of compatibility between the air permeability and the mechanical properties of the porous layer. When the average particle diameter is less than 0.05 µm, the inorganic particles (A) enter the inside of the porous film from the pore surface of the porous film, and the air permeation resistance of the porous film increases or the surface area of the particles becomes large, so that it becomes easy to aggregate and the porous layer Since it becomes a coarse projection when it is provided on the surface, the quality of the laminated porous film may be deteriorated. On the other hand, when the average particle size exceeds 15 µm, it may be difficult to control the thickness of the porous layer. In addition, the average particle diameter of the inorganic particle (A) means the value obtained by measuring the inorganic particle in a laminated porous film.

In the present invention, the aspect ratio of the inorganic particles (A) in the porous layer (the long diameter of the particles / the short diameter of the particles) is preferably 1.5 or more and 10 or less, more preferably 2 or more and 8 or less, and more preferably 2 or more and 6 or less desirable. By using the particles having the aspect ratio in the above range, it is possible to effectively suppress a decrease in air permeation resistance when laminating a porous layer on a porous film. When the aspect ratio is less than 1.5, the filling rate of the particles increases, so that the decrease in air permeation resistance may easily occur. In addition, when the aspect ratio is larger than 10, the flexibility of the porous layer is impaired, and cracks may easily enter when the laminated porous film is bent. The aspect ratio of the inorganic particles (A) can be evaluated by a method described later by observation of a scanning electron microscope of the laminated porous film.

The ratio of the inorganic particles (A) contained in the porous layer in the laminated porous film of the present invention is preferably 50% by mass or more and less than 95% by mass, and 60% by mass or less and less than 90% by mass in the composition forming the porous layer It is more preferable. When the proportion of the inorganic particles (A) is 95% by mass or more, the amount of the resin (C) to be described later with respect to the inorganic particles (A) decreases, so that the inorganic particles (A) cannot be sufficiently adhered to each other and the heat resistance decreases. There are cases. In addition, when the proportion of the inorganic particles (A) is lower than 50% by mass, the heat resistance of the porous layer is not sufficiently expressed and shrinkage becomes remarkable when it is a laminated porous film, or the resin (C) closes the hollow in the porous layer. As a result, there is a case that a decrease in speculation resistance may occur. The proportion of the inorganic particles (A) contained in the porous layer of the laminated porous film of the present invention is peeled off and recovered from the laminated porous film, and this is analyzed by powder X-ray analysis to identify inorganic particle types, followed by combustion analysis. It can be calculated | required by calculating content of an inorganic element from the mass after removing the organic component of a porous layer by.

The thickness of the porous layer of the laminated porous film of the present invention (the coating thickness when formed by application (thickness after application and drying)) is preferably 1 to 30 µm from the viewpoint of heat resistance and mechanical properties, more preferably 1 to 20 μm, more preferably 1 to 10 μm, particularly preferably 1 to 6 μm. When the thickness is less than 1 µm, sufficient heat resistance may not be obtained, or elasticity as a laminated porous film may be weak, and wrinkles and necking may occur when the carrier is applied with tension in the assembly process of the battery as a separator. In addition, when the thickness exceeds 30 µm, when the porous layer is formed on the porous film, the wet thickness (thickness in the wet state before drying) becomes thicker when applied to the laminated porous film due to a decrease in drying efficiency. Cracking and peeling are liable to occur when the water content of is increased or when the laminated porous film is bent. As a method of controlling the thickness in such a preferred range, it can be achieved by controlling the discharge amount, conveyance speed, and the like of the coating liquid when the coating method described later is used. The thickness of the porous layer can be confirmed by a method described later.

The porous layer of the laminated porous film of the present invention contains at least two types of water-soluble polymers (B). Since the drying efficiency in the drying process at the time of application can be effectively improved by including two or more types of the water-soluble polymer (B), a low water content can be expressed without using a special process. Moreover, since the stability of the coating liquid which forms a porous layer can be improved by including two or more types of water-soluble polymers (B), it becomes possible to suppress defects in application when laminating a porous layer on a porous film. From the above effects, it is possible to manufacture a laminated porous film having excellent electrochemical stability, high quality and low cost.

It is preferable that the water-soluble polymer (B) used for the porous layer of the laminated porous film of the present invention is a material having an effect of adjusting the viscosity of the coating liquid for forming the porous layer on the surface of the porous film to be within a range that can be applied.

As the water-soluble polymer (B) used for the porous layer in the laminated porous film of the present invention, vinyl alcohol-based polymers (for example, ethylene vinyl alcohol (EVA), polyvinyl alcohol (PVA), polyvinyl butyral (PVB)) Etc.], polyalkylvinyl ether, carboxyvinyl polymer, water-soluble acrylic resin, water-soluble styrene-based resin, vinylpyrrolidone-based resin [for example, polyvinylpyrrolidone (PVP), etc.], cellulose-based compounds and derivatives thereof [Example] For example, carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), etc. are mentioned, and it is preferable to include at least two types of water-soluble polymers selected from these. Especially, it is preferable to select at least 2 types from a vinyl alcohol type polymer, a water-soluble acrylic resin, and a cellulose type compound from a viewpoint of electrochemical stability, and it is preferable to select at least 2 types from a cellulose type compound especially from a heat resistance viewpoint.

One of the water-soluble polymers (B) used for the porous layer of the laminated porous film of the present invention has a side chain of the polymer skeleton because the dispersant effect (effect of promoting dispersion and maintaining dispersion stability) of the inorganic particles (A) is obtained. It is preferable that it is a water-soluble polymer (B1) containing at least one functional group selected from the group consisting of an amino group, a carbonyl group, a carboxyl group, a sulfonyl group and a phosphoric acid group as a functional group at the terminal of the. The side chain of the polymer skeleton refers to a molecular chain having one or more carbons branched from the repeating unit (main chain) of the polymer constituting the water-soluble polymer. As the functional group at the end of the side chain of the polymer skeleton, it is particularly preferable to include an amino group and a carboxyl group from the viewpoint of having high adsorption property to the surface of the inorganic particles (A).

In addition, as long as the water-soluble polymer (B1) includes the above-described functional group, functional groups such as hydroxyl groups, alkyl groups, and halogen groups exemplified in the description of the water-soluble polymer (B2) described later may be included.

As the water-soluble polymer (B1) used for the porous layer of the laminated porous film of the present invention, acrylic acid / sulfonic acid monomer copolymer salts, polyacrylamides, polyethyleneimines, polystyrenesulfonic acid salts, polyamidines, carboxymethylcellulose (CMC), Carboxymethylethyl cellulose, carboxymethylhydroxyethylcellulose, etc. are mentioned. Among them, carboxymethylcellulose (CMC), carboxymethylethylcellulose, and carboxymethylhydroxyethylcellulose are preferred from the viewpoint of heat resistance, and from the viewpoint of electrochemical stability. From carboxymethylcellulose (CMC) is preferred.

In addition, the other one of the water-soluble polymers (B) used for the porous layer of the laminated porous film of the present invention includes at least one functional group selected from the group consisting of hydroxyl groups, alkyl groups and halogen groups at the ends of the side chains of the polymer skeleton. It is preferable that it is a water-soluble polymer (B2). By including only these functional groups, adsorption and dehydration of the ends of the side chains and water can be facilitated, and the water content of the porous layer can be reduced. Among these, a water-soluble polymer (B2) containing only a hydroxyl group or an alkyl group as a functional group is particularly preferable, since it has good solubility in a coating liquid forming a porous layer and is difficult to form a non-dissolved lysate.

Examples of the water-soluble polymer (B2) used for the porous layer of the laminated porous film of the present invention include polyvinyl alcohol, ethylene vinyl alcohol, polyvinyl butyral, polyalkyl vinyl ether, hydroxyethyl cellulose (HEC), and butyl methyl cellulose. , Hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, alkylhydroxyethylcellulose, etc. are preferred, and hydroxyethylcellulose (HEC) is preferred from the viewpoints of electrochemical stability and heat resistance.

In the laminated porous film of the present invention, the water-soluble polymer (B1) and the water-soluble polymer (B2) contained in the porous layer are preferably selected from cellulose-based compounds. Since the cellulose-based compound does not have or has a high crystal melting point, if the water-soluble polymer (B1) and the water-soluble polymer (B2) used are cellulose-based compounds, it becomes possible to impart sufficient heat resistance to the laminated porous film. When the water-soluble polymer (B1) or water-soluble polymer (B2) to be used is other than a cellulose-based compound, heat resistance may not be obtained because the heat resistance of the water-soluble polymer (B) itself is insufficient. Among them, the cellulose-based compound used for the water-soluble polymer (B1) and the water-soluble polymer (B2) is preferably the aforementioned cellulose.

The water-soluble polymer contained in the porous layer of the laminated porous film of the present invention can be confirmed by composition analysis of the porous layer of the laminated porous film.

The water-soluble polymer (B) used for the porous layer of the laminated porous film of the present invention can be defined with a preferable molecular weight range by measuring the viscosity when it is used as a 1% by mass aqueous solution as described later. The viscosity of the 1% by mass aqueous solution is an index indicating the molecular weight of the water-soluble polymer (B), and the higher the viscosity, the higher the molecular weight.

In the laminated porous film of the present invention, the viscosity of the 1% by mass aqueous solution of the water-soluble polymer (B1) used for the porous layer is preferably 5 mPa · s or more and 3,000 mPa · s or less, and more preferably 10 mPa · s or more and 2,500 mPa · s or less Preferably, 10 mPa · s or more and 900 mPa · s or less are more preferable. By setting the viscosity in the above range, the water-soluble polymer (B1) can be quickly dissolved in a solvent of a coating liquid and then adsorbed on the inorganic particles (A). If the viscosity of the 1 mass% aqueous solution of the water-soluble polymer (B1) is less than 5 mPa · s, the heat resistance may be lowered when the porous layer is formed. In addition, since the solubility in the coating liquid decreases when it exceeds 3,000 mPa · s, the non-harmful places aggregated while adsorbing to the inorganic particles (A), and the aggregate adhesion of the lumps (inorganic particles (A) and water-soluble polymers (B1)) Water. In order to set the viscosity of the water-soluble polymer (B1) to the above range, it can be achieved by using a low-molecular weight water-soluble polymer (B1). The viscosity of the water-soluble polymer (B1) is evaluated under a condition of 25 ° C. and 60 revolutions using a 1 mass% aqueous solution using a B-type viscometer.

In addition, in the laminated porous film of the present invention, the viscosity of the 1% by mass aqueous solution of the water-soluble polymer (B2) used for the porous layer is preferably 1,000 mPa · s or more and 5,000 mPa · s or less, and 2,000 mPa · s or more and 4,000 mPa · s or less is more preferable. Since the water-soluble polymer (B2) has low adsorption property to the inorganic particles (A) and is difficult to form coarse aggregates, it is preferable to select the water-soluble polymer (B2) exhibiting the viscosity in the above range in order to set the viscosity of the coating liquid to a suitable range for application. desirable. In addition, heat resistance and flexibility when forming a porous layer can be imparted by using a water-soluble polymer (B2) exhibiting viscosity in the above range. When the viscosity of the 1% by mass aqueous solution is less than 1,000 mPa · s, when used in combination with a water-soluble polymer (B1), the viscosity of the coating liquid cannot be controlled within a range suitable for application, or the flexibility as a porous layer decreases and the laminated porous film When bent, cracks or peeling may occur. Moreover, when it exceeds 5,000 mPa * s, dispersibility of the water-soluble polymer (B2) in a coating liquid will fall, and mixing unevenness may arise at the time of coating, which may cause defects. In order to set the viscosity of the water-soluble polymer (B2) to the above range, it can be achieved by using a high-molecular weight water-soluble polymer (B2). The viscosity of the water-soluble polymer (B2) is measured under a condition of 25 ° C. and 30 revolutions with a 1 mass% aqueous solution using a B-type viscometer.

When the mass percentage of the weight percentage of the water-soluble polymer (B1) in the porous layer in the laminated porous film of the present invention, C _b1, the water-soluble polymer (B2) have been called C _b2, more than the value of C _b1 / C _b2 0.2 8 or less It is preferable to mix the water-soluble polymer (B1) and the water-soluble polymer (B2) at a ratio. Since the water content in the laminated porous film can be effectively reduced and the stability of the coating liquid for forming the porous layer can be maintained by setting the value of C _b1 / C _b2 to 0.2 or less, 8 or more, defects caused by denaturation of the coating liquid It can be suppressed can improve the quality of the laminated porous film. The value of C _b1 / C _b2 is preferably 0.3 or more and 6 or less, and more preferably 0.5 or more and 3 or less. When the value of C _b1 / C _b2 is less than 0.2, the proportion of the water-soluble polymer (B1) contributing to the dispersion stability of the coating liquid is small, so that aggregation of the inorganic particles (A) tends to occur, and defects such as coarse projections when a porous layer is formed There are cases that cause. In addition, when the value of C _b1 / C _b2 exceeds 8, the water content may increase by increasing the number of water-soluble polymers (B1) in the composition of the porous layer.

In addition, for the water-soluble polymer (B1) and the water-soluble polymer (B2) included in the porous layer of the laminated porous film of the present invention, when a plurality of water-soluble polymers (B1) are used, the water-soluble polymer (B1) belonging to the water-soluble polymer (B1) to the mass percentage of the total by C _b1, and the water-soluble polymer (B2) weight percentage of the total of the water-soluble polymer (B2) belonging to the water-soluble polymer (B2) when using a plurality of types C _b2 aforementioned C _b1 / C _b2 by a Calculate

The water-soluble polymer (B) contained in the porous layer of the laminated porous film of the present invention includes a water-soluble polymer that does not belong to either the water-soluble polymer (B1) or the water-soluble polymer (B2), as long as it does not impair the performance of the laminated porous film. You may do it.

In the present invention, the total amount of the water-soluble polymer (B), that is, the water-soluble polymer (B1) and the water-soluble polymer (B2), and the total amount of the water-soluble polymer that does not belong to either when used, is 0.5 to 100 parts by mass of the inorganic particles (A) It is preferable that it is -10 parts by mass, and more preferably 2-7 parts by mass. By setting it as the said range, the effect of the addition of a water-soluble polymer (B) can be exhibited without impairing physical properties, such as air permeation resistance. If the total amount of the water-soluble polymer (B) is less than 0.5 parts by mass with respect to 100 parts by mass of the inorganic particles (A), the viscosity of the coating liquid cannot be within a suitable range for application, and cising or coating may occur during application to form a porous layer. It may cause defects such as stripes. In addition, when the total amount exceeds 10 parts by mass, the water-soluble polymer (B) may close the pores of the porous layer, causing a decrease in air permeation resistance.

The mixing ratio of at least two or more water-soluble polymers (B) of the porous layer of the laminated porous film of the present invention or the total amount in the porous layer is measured by the amount of the solvent in the porous layer when the composition included in the coating liquid is clear. It can be calculated from the composition contained in and the amount of residual solvent. When the prescription is not clear, it can be confirmed by analyzing the composition of the porous layer of the laminated porous film.

The moisture content of the laminated porous film of the present invention is preferably 0.1 ppm or more and 3,000 ppm or less. Here, the water content refers to the mass percentage of moisture contained in the laminated porous film. Moisture contained in the laminated porous film reacts with lithium metal to generate halogen acids such as hydrogen fluoride (HF) or hydrogen when used as a separator for a lithium ion secondary battery, so the moisture content of the laminated porous film is within the above range. It is possible to effectively suppress deterioration of battery performance and deterioration of the separator. It is practically difficult to make the moisture content in the laminated porous film less than 0.1 ppm. In addition, when the water content exceeds 3,000 ppm, the cycle characteristics of the battery may decrease. The water content is preferably 0.1 ppm or more and 2,000 ppm or less, and more preferably 0.1 ppm or more and 1,500 ppm or less. As a method of making the water content into the above range, it can be achieved by using the specific water-soluble polymer (B) described above for the porous layer of the laminated porous film. The moisture content of the laminated porous film can be confirmed by a method described later.

The resin (C) used for the porous layer in the laminated porous film of the present invention is a material capable of binding between different materials (for example, between inorganic particles (A), between inorganic particles (A)-substrate, etc.) Says

Ethylene-acrylic acid such as polyvinylidene fluoride (PVDF), acrylic (excluding water-soluble acrylic resin), and ethylene-ethyl acrylate copolymer (EEA) are used as the resin (C) used for the porous layer of the laminated porous film of the present invention. And copolymers, fluorine-based rubbers, styrene-butadiene rubbers (SBR), crosslinked acrylic resins, polyurethanes, epoxy resins, modified polyolefins, silicon alkoxides, zirconium compounds, colloidal silica, and oxirane ring-containing compounds. In particular, a compound dispersible or soluble in water is preferably used as the resin (C). As the resin (C), one of the above-described examples may be used alone, or two or more of them may be used in combination.

In the laminated porous film of the present invention, it is preferable that other materials (for example, inorganic particles (A), inorganic particles (A)-substrates, etc.) are bound by melting of the resin (C). When the resin (C) is bound by melting, since the molten resin (C) enters a part of the pores of the inorganic particles (A) and the surface opening of the porous film, the anchor effect is expressed to show a strong binding force, and thus the porous layer It is possible to suppress the dropping of the inorganic particles (A) and the separation of the porous layer from the porous film. The binding property between the different materials (inorganic particles (A), inorganic particles (A) to base materials, etc.) by the resin (C) can be evaluated by the rate of change (K) of the friction coefficient (μk) or peel strength. have. The details of the evaluation method will be described later.

In the laminated porous film of the present invention, the rate of change (K) of the friction coefficient (μk) when the film running test is performed by bringing the surface of the porous layer into contact with the roll is preferably less than 500%, more preferably less than 300%. Do. The friction coefficient (μk) is calculated from the following formula by running the laminated porous film in a tape runability tester.

μk = 2 / πln (T2 / T1)

Here, T1 is the inlet tension and T2 is the outlet tension.

The rate of change (K) (%) of the friction coefficient (μk) is calculated by substituting the following equations for the friction coefficients (μk ₁ , μk ₅₀ ) for the first and 50th film runs.

Rate of change (K) (%) = [Friction coefficient for the _50th run (μk ₅₀ ) / Friction coefficient for the first run (μk ₁ )] × 100

When the rate of change (K) is 500% or more, dropping of the inorganic particles (A) occurs during film travel, and white powder may be generated. When the laminated porous film is used as a separator, the drop of the inorganic particles (A) may cause defects such as yield or foreign matter mixing in the battery assembly process.

It can be achieved by using a resin (C) in order to make the rate of change (K) a desirable range.

The binding property between the porous layer and the porous film of the laminated porous film of the present invention can be evaluated as the peel strength when the laminated porous film is peeled from the porous layer / porous film interface.

This peel strength is an index of the binding force between the porous film and the porous layer, and the higher the peel strength, the higher the binding force between the inorganic particles (A) -substrate by the resin (C) and the inorganic particles (A) in the porous layer. . Peel strength can be evaluated by the method described below.

It is preferable that the laminated porous film of the present invention can be peeled at the porous layer / porous film interface. The peel strength when peeling at the porous layer / porous film interface is preferably 10 to 500 g / 25 mm width, more preferably 20 to 300 g / 25 mm width. When the peel strength is less than 10 g / 25 mm, the porous layer is liable to peel from the laminated porous film, and when the laminated porous film is used as a separator, partial peeling may occur in the cutting and slit process. When the peeling strength exceeds 500 g / 25 mm width, the adhesion between the porous film and the porous layer is too strong when the battery using the laminated porous film as a separator heats up, so it is difficult to maintain the shape of the porous layer by shrinking and melting the porous film. It may be dark.

In order to make peel strength into a preferable range, it can be achieved by making the surface pore size into a preferable range and / or by using a resin (C).

In the present invention, in order to bind the inorganic particles (A) between the inorganic particles (A) and the inorganic particles (A) -substrate by fusion of the resin (C), it is preferable to use a resin having a melting point or softening point lower than that of the porous film as the resin (C). desirable.

The melting point or softening point of the resin (C) used for the porous layer of the laminated porous film of the present invention is preferably 70 to 120 ° C, more preferably 80 to 110 ° C. When the melting point or softening point is lower than 70 ° C, when the resin (C) is added to the porous layer and used, the heat resistance of the laminated porous film may decrease. In addition, when the melting point or softening point is higher than 120 ° C., shrinkage of the porous film is required because processing at a high temperature is necessary when melt-bonding the inorganic particles (A) and the inorganic particles (A) -substrate with the resin (C). In some cases, characteristics such as air permeation resistance and planarity may be deteriorated. The melting point or softening point of the resin (C) can be confirmed by a method described later.

The mixing ratio of the resin (C) used in the porous layer of the porous film of the present invention in the porous layer is preferably 1 to 30 parts by mass, and preferably 1 to 20 parts by mass, based on 100 parts by mass of the inorganic particles (A) from the viewpoint of adhesiveness. It is more preferable, and 5-15 parts by mass is more preferable. When the blending ratio of the resin (C) is less than 1 part by mass, the adhesion between the inorganic particles (A) and between the inorganic particles (A) and the substrate is insufficient, and the inorganic particles (A) may fall off or peel off of the porous layer. Moreover, since the hole in a porous layer is closed when it exceeds 30 mass parts, air permeability may fall.

The porous layer of the laminated porous film of the present invention contains a carboxyl group and / or a hydroxyl group in the molecular structure of the resin (C) from the viewpoint of improving the binding property between the inorganic particles (A) and the inorganic particles (A) -substrate. It is preferred. The wettability of the interface to be bound can be improved by including the functional group, and stronger binding properties can be expressed.

Examples of the resin (C) containing a carboxyl group and / or a hydroxyl group in the molecular structure include an acrylate copolymer or a modified polyolefin having an unsaturated carboxylic acid skeleton. Among the above, from the viewpoint of laminating and bonding the inorganic particles (A) and the inorganic particles (A) -substrate by fusion of the resin (C), and also maintaining the properties of the porous film, the layer of the porous layer is resin ( As C), it is preferable to use a modified polyolefin.

When the modified polyolefin is included as the resin (C) in the porous layer of the laminated porous film of the present invention, the modified polyolefin is preferably composed of an olefin skeleton and an unsaturated carboxylic acid skeleton. Examples of the olefin skeleton include olefins having 2 to 6 carbon atoms such as propylene, ethylene, isobutylene, 1-butene, 1-pentene, and 1-hexene, and the unsaturated carboxylic acid skeleton includes at least one carboxyl group or acid in the molecule. A compound having an anhydride group is preferred, and in addition to acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, crotonic acid, etc., half esters of unsaturated dicarboxylic acids, half amides, etc. Can be lifted.

In the present invention, when an olefin-based resin is used as a main component of the porous film, olefin has a high surface tension, so that the surface is easy to bounce and may cause defects such as clumping or streaks when applying a coating liquid forming a porous layer. , By including the olefin-based resin as the resin (C), the fusion is good, and aggregation can be suppressed. However, when the same olefinic resin is used for the porous film and the resin (C), the porous film itself is deformed at the melting point or softening point temperature for melt-bonding the resin (C) in the coating process of forming the porous layer on the porous film, and thus is air permeable. This may worsen or lose flatness. In the present invention, the melting point of the porous film and the melting point or softening point temperature of the resin (C) are within the above-mentioned range, and by drying at a temperature range to be described later, it is excellent in defect quality such as clumping and stripes, and furthermore, the porous film and the porous layer It is preferable because it is possible to obtain a laminated porous film having excellent adhesion and good flatness.

The porous layer of the laminated porous film of the present invention can contain thermoplastic resin particles having a melting point of 120 to 160 ° C from the viewpoint of providing shutdown properties to the laminated porous film. When the laminated porous film is used as a separator, the shut-down property refers to a property of blocking the flow of ions by closing the through-hole of the laminated porous film by the components contained in the film during abnormal heating of the battery. If the melting point of the thermoplastic resin particles is less than 120 ° C, a malfunction occurs in which the through-holes of the film are blocked and shut down at a low temperature of about 120 ° C, where the environment of use is no problem for other materials of the power storage device. On the other hand, if the melting point exceeds 160 ° C, the self-heating reaction may start in the power storage device before shutdown. In the case of the cobalt-based positive electrode which is frequently used in lithium ion batteries, since the shutdown function is preferably performed at 125 to 150 ° C from the viewpoint of the thermal stability of the positive electrode, the melting point of the thermoplastic resin particles is more preferably 125 to 150 ° C, It is desirable to change the melting point in consideration of the thermal stability of. In addition, when the thermoplastic resin particles have a plurality of melting points, the melting point of the highest temperature may be within the above range.

When the thermoplastic resin particles are contained in the porous layer of the laminated porous film of the present invention, the melting point is not particularly limited as long as it is composed of a thermoplastic resin that falls within the above range, but thermoplastic resin particles made of an olefin resin are preferred. Thermoplastic resin particles made of olefin resins such as polyethylene, polyethylene copolymer, polypropylene, and polypropylene copolymer are preferred. The average particle size of the thermoplastic resin particles is preferably 0.5 to 5 μm, and more preferably 0.8 to 3 μm.

When the thermoplastic resin particles are contained in the porous layer of the laminated porous film of the present invention, the proportion in the porous layer is preferably 10 to 40% by mass, more preferably 15 to 35% by mass. When it is less than 10% by mass, when the laminated porous film is used as a separator, there is a case that the pores in the porous layer cannot be sufficiently blocked during heat generation, so that shutdown properties may not be exhibited. Moreover, when it exceeds 40 mass%, the heat resistance at the time of using a laminated porous film as a separator may fall.

In the laminated porous film of the present invention, the coating liquid forming the porous layer is combined by dispersing the components forming the porous layer in a solvent. The solvent used for the coating liquid can be used as long as it is a solvent that can stably disperse without reacting with the component forming the porous layer. From the viewpoint of ease of drying after application as a coating liquid, and between the inorganic particles (A) and the adhesion between the inorganic particles (A) and the porous film, and the effect on the porous film, the melting point of the resin (C) or It is preferably a solvent having a boiling point of not less than the softening point to 120 ° C. As the solvent of the coating liquid forming the porous layer, an alcohol-based solvent having a boiling point of about 60 to 120 ° C., water, and a mixed solution of the alcohol-based solvent and water can be suitably used.

In the present invention, a method of mixing the composition with a dispersing device may be mentioned as a combination method of the coating liquid used for the porous layer of the laminated porous film. As a specific example of the mixing device, a ball mill, a bead mill, a jet mill, a homogenizer, an ultrasonic disperser, etc. can be used, but any method may be used.

As a method of forming a porous layer in the laminated porous film of the present invention, a coating liquid containing other compositions, such as inorganic particles (A), at least two water-soluble polymers (B), resins (C), and solvents, is applied. The method is preferably employed. As the coating method, any method that is generally performed may be used, but for example, the porous film is formed by a coating method such as a reverse coating method, a bar coating method, a gravure coating method, a rod coating method, a die coating method, or a spray coating method. It may be applied to, dried and formed into a porous layer. Moreover, when preparing a coating liquid, you may add a dispersing agent etc. suitably in order to prevent the localization of the inorganic particle (A) in a porous layer.

In the laminated porous film of the present invention, the viscosity of the coating liquid used to form the porous layer is preferably 30 mPa · s or more and 500 mPa · s or less, more preferably 50 mPa · s or more and 300 mPa · s or less, more preferably 70 mPa S to 200 mPa · s. When the viscosity of the coating liquid is less than 30 mPa · s, the fluidity of the coating liquid is high at the time of formation of the coating film, and thus defects such as agglomeration may be exhibited. In addition, when the thickness exceeds 500 mPa · s, the fluidity of the coating liquid at the time of forming the coating film is low, so that control of the thickness at the time of coating becomes difficult or uneven coating may occur. The viscosity of the coating liquid forming the porous layer can be controlled in the above range by the addition amount of inorganic particles (A), water-soluble polymer (B1), water-soluble polymer (B2), and the like. In addition, the viscosity of the coating liquid is measured under a condition of 25 ° C. and a natural frequency of 30 Hz with a tuning-fork vibrational viscometer.

The drying temperature in the coating step of forming the porous layer in the laminated porous film of the present invention is a resin (C) from the viewpoint of melt-bonding the resin (C) or suppressing heat shrinkage of the laminated porous film and maintaining planarity. The melting point or softening point of is more than -120 ° C is preferred, and the melting point or softening point of resin (C) + 5 ° C to 120 ° C is more preferable. When the melting point or softening point of the resin (C) is lower than that, the resin (C) does not melt or soften, so that the binding property is poor, or the moisture content of the porous layer is high, which may cause problems when used as a battery separator. Moreover, when it exceeds 120 degreeC, a shrinkage of a porous film may arise in the drying process of application | coating, and the flatness may fall.

In the present invention, it is preferable that the air permeation resistance of the laminated porous film is 50 to 500 seconds / 100 ml. When the air permeation resistance is less than 50 seconds / 100 ml, the insulation between the electrodes may not be sufficiently maintained. Moreover, when it exceeds 500 second / 100 ml, the output characteristics of the battery may fall when a laminated porous film is used as a separator. Although the air permeation resistance of the laminated porous film depends on the application, it is preferably 80 to 490 seconds / 100 ml, more preferably 150 to 390 seconds / 100 ml. As a method for setting the air permeation resistance of the laminated porous film to the above range, it can be achieved by containing the inorganic particles (A) having an aspect ratio of 2 or more in the porous layer. The air permeation resistance of the laminated porous film can be confirmed by a method described later.

The thermal shrinkage of the film in the longitudinal direction and the width direction at 150 ° C of the laminated porous film of the present invention is preferably 0 to 3%, more preferably 0 to 2%. If the heat shrinkage ratio of the film in the longitudinal direction and the width direction at 150 ° C is greater than 3%, it may easily shrink due to heat generated when used as a separator for a battery, causing a short circuit. Moreover, when it is less than 0%, when used as a separator of a battery, it may affect the dimensional stability of the battery itself, and a problem may occur. In order to set the thermal contraction rate of the film in the longitudinal direction and the width direction at 150 ° C to the above range, the porous layer contains the specific water-soluble polymer (B) described above and the specific inorganic particles (A) described above. Effective use can be achieved. The heat resistance of the laminated porous film can be confirmed by a method described later.

Hereinafter, a porous film constituting the laminated porous film of the present invention and a method for manufacturing the laminated porous film will be described in detail. In addition, the manufacturing method of the laminated porous film of this invention is not limited to this. For the porous film, the composition of the polypropylene porous film by the β crystal method, the porous layer is composed of inorganic particles (A), calcium carbonate, water-soluble polymer (B), carboxymethylcellulose (B1), hydroxyethyl cellulose (B2), and resin ( It will be described as an example using a modified polyethylene emulsion in C).

As a polypropylene resin, 94.7 mass% of commercial homo polypropylene resin of MFR 8 g / 10 min, 5 parts by mass of ultra low density polyethylene resin of melt index 18 g / 10 min, N, N'-dicyclohexyl-2,6-naphthalendy 0.3 mass% of carboxyamide is mixed, and a raw material mixed in a predetermined ratio in advance using a twin-screw extruder is prepared. At this time, the melting temperature is preferably 270 to 300 ° C.

Subsequently, the mixed raw material is supplied to a single-screw melt extruder, and melt extrusion is performed at 200 to 230 ° C. Then, after removing foreign matter or denatured polymer from the filter installed in the middle of the polymer tube, it is discharged from the T die onto the casting drum to obtain an unstretched sheet. At this time, it is preferable that the casting drum has a surface temperature of 105 to 130 ° C from the viewpoint of highly controlling the ability to form β crystals of the casting film. In addition, since the molding of the end portion of the sheet affects the stretchability of the back, it is preferable to spray the spot air at the end portion to make it close to the drum. In addition, the polymer may be closely adhered to the casting drum by a method of spraying air using an air knife on the entire surface from the state of adhesion to the drum on the entire sheet, or by using an electrostatic application method.

Subsequently, the obtained unstretched sheet is biaxially oriented to form voids in the film. As a method of biaxially oriented, a film is stretched in the longitudinal direction and then stretched in the width direction, or a sequential biaxial stretching method in which the film is stretched in the width direction and then stretched in the longitudinal direction, or at the same time stretching the film in the longitudinal direction and the width direction almost simultaneously 2 Although a axial stretching method or the like can be used, it is preferable to adopt a sequential biaxial stretching method in that it is easy to obtain a high-permeability film, and it is particularly preferable to stretch in the longitudinal direction and then in the width direction.

As the specific stretching conditions, first, the temperature at which the unstretched sheet is stretched in the longitudinal direction is controlled. As a method of temperature control, a method using a temperature-controlled rotary roll, a method using a hot air oven, or the like can be employed. It is preferable to adopt a temperature of 90 to 140 ° C, more preferably 110 to 135 ° C, as the stretching temperature in the longitudinal direction. The stretching ratio is 3 to 6 times, more preferably 4 to 5.5 times. Subsequently, after cooling once, the film end is gripped and introduced into the stenter stretching machine. Then, it is preferably heated to 130 to 155 ° C to stretch 2 to 12 times, more preferably 4 to 10 times in the width direction. Moreover, it is preferable to perform at 300-5,000% / min as a lateral stretch speed at this time, and it is more preferable if it is 500-3,000% / min. Subsequently, heat setting is performed in the stenter as it is, but the temperature is preferably lateral stretching temperature or higher and 165 ° C or lower. In addition, it may be performed while relaxing in the longitudinal direction and / or the width direction of the film at the time of heat setting, and it is particularly preferable from the viewpoint of thermal dimension stability that the relaxation rate in the width direction is 5 to 35%.

Subsequently, on the porous film thus obtained, a coating solution containing inorganic particles (A), at least two kinds of water-soluble polymers (B), and resins (C) is applied and dried to form a porous layer.

Specifically, for example, 15% by mass of calcium carbonate (average particle size: 3 µm) as inorganic particles (A), and a modified polyethylene emulsion in which an unsaturated carboxylic acid skeleton is introduced as resin (C) (solid content concentration: 20% by mass) 7.5 Coating solution by mixing mass%, 0.3 mass% of carboxymethyl cellulose as water-soluble polymer (B1), 0.4 mass% of hydroxyethyl cellulose as water-soluble polymer (B2), 10 mass% of isopropyl alcohol, and 66.80 mass% of ion-exchanged water Is prepared.

After stirring this coating solution for 4 hours, it is coated on a porous film by a coating method using a die coater, and dried at 100 ° C. for 1 minute to obtain a porous layer having a lamination thickness of 1 to 30 μm.

Since the laminated porous film of the present invention has excellent output characteristics, planarity, and air permeability, it can be suitably used as a separator for power storage devices.

Here, examples of power storage devices include various batteries, in particular non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries, electric double layer capacitors such as lithium ion capacitors, and the like. Since such a power storage device can be repeatedly used by charging and discharging, it can be used as a power supply device such as an industrial device, a household appliance, an electric vehicle, or a hybrid electric vehicle. The power storage device using the laminated porous film of the present invention as a separator can be suitably used in industrial equipment or power supplies for automobiles because of the excellent characteristics of the separator.

(Example)

Hereinafter, the present invention will be described in detail by examples. In addition, the characteristic was measured and evaluated by the following method.

(1) The ability to form β crystals of porous films and laminated porous films

The resin constituting the porous film, laminated porous film, or 5 mg of the porous film itself was taken as a sample and collected in an aluminum pan, and measured using a differential scanning calorimeter (RDC220 manufactured by Seiko Denshi High School). First, under a nitrogen atmosphere, the temperature was raised from room temperature to 280 ° C at 10 ° C / min (first run), held for 10 minutes, and then cooled to 30 ° C at 10 ° C / min. After holding for 5 minutes, the melting peak which exists in the temperature range of 145 to 157 ° C for the melting peak observed when the temperature is raised (second run) at 10 ° C / min again is the melting peak of β crystal, peaking at 158 ° C or higher Is the melting peak of the α crystal, and the respective heat of fusion is obtained from the area of the area enclosed by the baseline and the peak drawn with respect to the flat portion on the high temperature side, and the heat of fusion of the α crystal is ΔHα and β crystal When the heat of fusion was set to ΔHβ, the value calculated by the following formula was taken as the β crystal forming ability. In addition, the heat of fusion was corrected using indium.

β crystal forming capacity (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100

(2) The thickness of the laminated porous film, porous film, and porous layer

Ion etching for 10 minutes under the condition of reduced pressure of 10 ^-3 Torr, voltage of 0.25 전류, current of 12.5 스 using a sputtering device so that the laminated porous film fixed to the sample table of the scanning electron microscope can be observed in a section in the longitudinal direction of the film. After performing the treatment and cutting the cross section, gold sputtering was performed on the surface in the same apparatus, and the magnification was observed at a magnification of 3,000 using a scanning electron microscope.

The thickness of the laminated porous film, the porous film, and the porous layer was measured from the image obtained by observation. For the sample used for the thickness measurement, a total of 10 locations at random locations are selected at least 5 cm apart in the longitudinal direction, and the average of the measured values of 10 samples is the thickness of the laminated porous film (la) of the sample and the porous film. The thickness (lb) and the porous layer thickness (lc) were used.

(3) Surface pore diameter and surface pore diameter ratio of porous film

The surface of the porous film fixed to the sample stage of the scanning electron microscope was sputtered using a sputtering device, and observed at a magnification of 10,000 times using a scanning electron microscope. About the obtained observation image, the maximum length and minimum length in the shape of the pore part by the hole of the surface were calculated | required using the image analysis apparatus, and the average value was made into the hole diameter of the hole. In the above operation, the hole diameter was determined for 100 holes in the observation image.

The number of holes having a hole diameter of 0.01 µm or more and less than 0.5 µm is (N _A ), and the number of holes having a hole diameter of 0.5 µm or more and less than 10 µm is (N _B ). The ratio of the surface pore size of the sample was calculated.

Surface hole diameter ratio = (N _A ) / (N _B )

(4) Porosity of porous film

The porous film was cut to a size of 50 mm x 40 mm to obtain a sample. The specific gravity was measured using an electronic hydrometer (SD-120L manufactured by Mirage Boeki Co., Ltd.) in an atmosphere of 23 ° C at room temperature and 65% relative humidity. The measurement was performed three times, and the average value was taken as the specific gravity (ρ) of the film.

Subsequently, the measured film was heat-pressed at 280 ° C and 5 MPa, and then quenched with water at 25 ° C to prepare a sheet in which voids were completely eliminated. The specific gravity of this sheet was similarly measured by the method described above, and the average value was taken as the specific gravity (d) of the resin. In addition, in Example 1 described later, the specific gravity (d) of the resin (D) was 0.94. The specific gravity (d) of the resin (D) in Examples 2 to 8 and Comparative Examples 1 to 5 was 0.91. The porosity (Pa) was calculated by the following equation from the specific gravity of the porous film and the specific gravity of the resin.

Porosity (Pa) (%) = [(d-ρ) / d] × 100

(5) Air permeation resistance of porous film and laminated porous film

A. Air permeation resistance of laminated porous film

A square of 150 mm in length on one side of the laminated porous film was cut out as a sample, and a permeation time of 100 ml of air at 23 ° C. and 65% relative humidity was randomized using a Gurley tester of type B of JIS P 8117 (2009). The location was measured. The average value of the three permeation times was defined as the air permeation resistance of the laminated porous film.

B. Air permeation resistance of porous film

After attaching a 65 mm wide PP tape (Sumitomo 3M Co., Ltd., 313D) to the porous layer side of the laminated porous film used in A, it was peeled off to remove the porous layer from the laminated porous film.

About the part where the porous layer of the sample was removed, the permeation time of 100 ml of air at 23 ° C. and 65% relative humidity was measured at any three locations using a Gurley tester of type B of JIS P 8117 (2009). The average value of the permeation time at three locations was defined as the air permeation resistance of the porous film.

(6) Aspect ratio of inorganic particles (A) in the porous layer

The laminated porous film fixed to the sample stage of the scanning electron microscope was ionized for 10 minutes under conditions of reduced pressure of 10 ^-3 Torr, voltage of 0.25 ㎸, and current of 12.5 하여 using a sputtering device so that a cross section in the longitudinal direction of the film could be observed. After the cross-section was cut by performing an etching treatment, observation was performed at a magnification of 1,000 times using a scanning electron microscope SEM, and microscopic X-ray analysis (EDX) was applied to the element specific to inorganic particles (A). About the analysis and mapping, the shape of the inorganic particles was imaged from the mapping diagram. About the obtained image, the long-diameter and short-diameter of the particle | grains were calculated | required using image analysis software, and the value was inserted into the following formula, and it was set as the aspect ratio of the particle | grains in a porous layer. The aspect ratio was calculated for 100 particles, and the average was taken as the aspect ratio of inorganic particles (A) in the porous layer.

Aspect ratio = long diameter of particles / short diameter of particles

(7) Heat resistance

The laminated porous film was cut into rectangles of 150 mm × 10 mm and 10 mm × 150 mm in the longitudinal and width directions, respectively, to prepare samples. Samples were drawn at intervals of 100 mm, and 3 g of weight were suspended and installed in a hot air oven heated to 150 ° C. for 1 hour to perform heat treatment. After the heat treatment, it was left to cool and the distance between the marked lines was measured, and the heat shrinkage ratio in the longitudinal direction and the width direction was calculated from the change in the distance between the marked lines before and after heating, and used as an index of dimensional stability. For the measurement, each of the five points was measured in the longitudinal direction and the width direction, and the average value was used as each measurement value. In the evaluation, in the absolute values of the measured values in the longitudinal direction and in the width direction, values in the direction in which the shrinkage rate is large were evaluated based on the following criteria.

A: 0% or more but less than 2%

B: 2% or more but less than 3%

C: 3% or more

(8) Rate of change of friction coefficient (μk) (K)

The laminated porous film was slit into a tape shape having a width of 1 cm using a tape runability tester TBT-300 (manufactured by Yokohama Systems Kenkyusho), and was run in an atmosphere of 23 ° C and 50% RH to obtain a coefficient of friction (μk). . The sample was set so that the porous layer side contacted the guide. The guide diameter is 6 mmφ, the guide material is SUS27 (surface roughness 0.2S), the winding angle is 90 °, the traveling speed is 3.3 cm / sec, and repeats 1 to 50 times. From the rate of change (K) (%) of the friction coefficient calculated by applying the friction coefficient (μk ₁ ) at the first repetition number and the friction coefficient at the 50 repetition number (μk ₅₀ ) obtained by this measurement to the following test, The film runability by was evaluated by the following criteria, and A and B were set as pass.

Rate of change of friction coefficient (K) (%) =

[Friction coefficient at _50th iteration (μk ₅₀ ) / Friction coefficient at 1st iteration (μk ₁ )] × 100

A: Change rate is less than 300%

B: Change rate of 300% or more and less than 500%

C: The rate of change is 500% or more.

(9) flaws

The surface on which the porous layer of the laminated porous film having a width of 130 mm in the film width direction was formed was visually observed using a transmission light source over 10 m with respect to the film length direction, and defects were evaluated. In the visual observation, the presence or absence of a portion where the porous layer is not formed (omission of coating), the number of portions where the porous layer is formed but thinned compared to the surroundings, and the number of the porous layer formed, but compared to the surroundings The number of darkened parts (coarse projections) was counted and evaluated based on the following criteria.

AA: No flaws

A: 1 or more defects less than 3 defects

B: 3 or more defects, less than 5 defects

C: There are 5 or more defects or 1 or more omissions.

(10) Water content of the laminated porous film

A laminated porous film 0.5 for 24 hours in a constant temperature and humidity chamber at a temperature of 20 ° C and a relative humidity of 60% using a Culfisher moisture measuring device ("AQ7" manufactured by Hiranuma Sangyo Co., Ltd.) and a moisture vaporization device ("EV6" manufactured by Hiranuma Sangyo). The water content contained in g was determined. When the heating furnace of the water vaporizing device with nitrogen gas flowing 0.2 to 0.3 L / min is heated to 200 ° C, and the measurement sample weighed on the sample stage of the water vaporizing device is set and held for 15 minutes, the amount of water drawn out from the measurement sample The concentration was measured, and the water content (mass%) was determined.

(11) Battery characteristics (cycle characteristics)

A positive electrode having a thickness of 40 µm was punched into a circular shape of 15.9 mm in diameter with a lithium cobalt oxide (LiCoO ₂ ) manufactured by Housen Co., Ltd. Further, a graphite negative electrode having a thickness of 50 µm manufactured by Housen Co., Ltd. was punched into a circle having a diameter of 16.2 mm. Next, the laminated porous film or porous film was punched to a diameter of 24 mm. It is stacked in the order of the negative electrode, the laminated porous film or the porous film, and the positive electrode from the bottom so that the positive electrode active material and the negative electrode active material face to each other, and is stored in a stainless metal container with a lid [Houssen Co., Ltd., HS cell, spring pressure 1Kgf] did. The container and the lid are insulated, the container is in contact with the copper foil of the negative electrode, and the lid is in contact with the aluminum foil of the positive electrode. An electrolyte solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate: dimethyl carbonate = 3: 7 (volume ratio) as a solute to a concentration of 1 mol / L was injected into this container, and then sealed to prepare a battery.

The produced battery was charged 4 times at a constant current to 4.2V at 3 ° C in an atmosphere of 25 ° C, and then charged 4 times at constant voltage to 0.03㎃ at 4.2V, and then discharged to 2.7V at 3㎃ 4 times, and then to 3㎃. After constant current charging up to 4.2 V, constant voltage charging up to 0.03 mA at 4.2 V and discharge capacity 1 when discharged to 2.7 V at 3 mA were measured. In addition, after measuring the discharge capacity 1, the operation of charging at 9 ° C for 20 minutes under an atmosphere of 25 ° C. and discharging to 2.7V at 3 ° C was repeated 50 times. The discharge capacity 50 at the 50th charge / discharge was measured, and the cycle characteristics obtained by the calculation formula of [(discharge capacity 50 / discharge capacity 1) × 100] were evaluated based on the following criteria. In addition, the number of tests was measured 10, and it evaluated by the average value.

A: 90% or more

B: 70% or more and less than 90%

C: less than 70% or more than one less than 20%.

(12) The presence or absence of melting of the binder [resin (C)] in the porous layer

After fixing the porous layer side of the laminated porous film to the SEM die sheet, the gold sputtering was performed using a sputtering device, and an observation image was taken at a magnification of 70,000 times using a scanning electron microscope SEM. In the obtained observation image, the presence or absence of a particle-like substance was evaluated about the part which is not an inorganic particle.

A: No particulate matter

B: Particulate matter is present.

(13) Peel strength

The laminated porous film was sampled in a rectangular shape of 200 mm in the film length direction and 25 mm in the film width direction, and one end A was peeled off with a tape or the like, and then peeled by hand up to 100 mm, and the peeled two stages A It is fixed to the chuck of a tensile tester ("AG-100A" manufactured by Shimadzu Corporation) according to JIS K-7127 (1999) to read the load when peeling at a speed of 100 mm / min, and to determine the fracture mode of the peeling point. Visual confirmation. Five points were measured on the above sample, and the average was evaluated based on the following criteria.

A: The peel strength is 10 to 500 g / 25 mm wide, and peeling occurs at the interface between the porous layer and the porous film.

B: The peel strength was outside the range of 10 to 500 g / 25 mm width, or the peel strength was in the range of 10 to 500 g / 25 mm width, but fracture occurred in the layer of the porous layer or fracture in the layer of the porous film.

(14) viscosity of coating liquid

Using a tuning-fork vibration type viscometer ("SV-1A" manufactured by A & T Co., Ltd.), the viscosity of 2 ml of the coating liquid at a circulating water temperature of 25 deg. The average value of three viscosities was taken as the viscosity of the coating liquid.

(Example 1)

High density polyethylene (density 0.95, viscosity average molecular weight 250,000) as resin (D) 99.4% by mass, and tetrakis- [methylene- (3 ', 5'-di-t-butyl4'-hydroxyphenyl) as antioxidant Propionate] Methane 0.6% by mass was mixed and fed to the extruder using a feeder. In addition, the liquid paraffin was injected into the extruder using a side feeder so as to be 100 parts by mass relative to 100 parts by mass of the resin (D), and the conditions were 200 ° C and 200 rpm using a twin-screw extruder having a diameter of 25 mm and L / D = 48. After melt-kneading in, it was extruded from a T-die attached to the tip of the extruder.

Immediately cooled and solidified in a cast roll cooled to 25 ° C, an unstretched sheet having a thickness of 1.2 mm was formed. The unstretched sheet was stretched 7 × 7 times at 120 ° C. with a simultaneous biaxial stretching machine, immersed in methylene chloride to extract and remove the liquid paraffin, and dried, and then 1.5 in the transverse direction at a temperature of 125 ° C. by a tenter stretching machine. After stretching twice, the film was relaxed at 130 ° C in the 7% width direction to perform heat treatment to obtain a porous film 1 having a thickness of 18 μm. The porous film thus obtained had an air permeation resistance of 200 seconds / 100 ml and a porosity of 40%.

Subsequently, the composition for forming the porous layer was metered and mixed with the prescription shown in Table 1-2 to prepare a coating solution for forming the porous layer. This was coated on one side of the porous film (the surface contacting the drum during melt extrusion, hereinafter referred to as the D surface) using a die coater so that the lamination thickness after drying was 7 µm, and dried at 100 ° C. for 1 minute. A porous layer was formed to produce a laminated porous film.

(Examples 2 to 12)

Polypropylene (Sumitomo Kagaku Co., Ltd., FLX80E4) as a raw material for the porous film is 94.45% by mass. Dow Chemical, an ethylene-octene-1 copolymer, "Engage (trademark)" 8411 (Melt index: 18g / 10 min, hereinafter referred to as PE-1 only) is added to 5% by mass, and the β crystal nucleating agent N, N'-dicyclohexyl-2,6-naphthalenedicarboxamide [cinniponica (Nu-100 Co., Ltd., hereinafter referred to simply as β crystal nucleating agent) 0.3% by mass, and also the antioxidant, Chiba Specialty Chemicals "IRGANOX (registered trademark)" 1010, "IRGAFOS (registered trademark)" 168, The raw materials are supplied to a twin-screw extruder from a weighing hopper to be mixed at a rate of 0.15 and 0.1 mass%, respectively, melt-kneaded at 300 ° C, discharged from a die in a strand shape, cooled and solidified in a water tank at 25 ° C, and cut into chip shapes. It was used as a raw material for chips.

This chip is supplied to a single-screw extruder, melt-extruded at 220 ° C, and foreign matter is removed with a 25 µm cut sintered filter, and then discharged from a T die to a casting drum with a surface temperature controlled at 120 ° C to contact the drum for 15 seconds. Casting was performed to obtain an unstretched sheet having a thickness of 200 μm and a width of 250 mm. Subsequently, preheating was performed using a ceramic roll heated to 120 ° C, and stretched 4.5 times in the longitudinal direction of the film. After cooling, the end was gripped with a clip and then introduced into a tenter drawing machine, and stretched 6 times at 145 ° C. As it is, heat treatment was performed at 155 ° C. for 6 seconds while applying a relaxation of 16% in the width direction to obtain a porous film 2 having a thickness of 18 μm. The porous film thus obtained had an air permeability of 200 seconds / 100 ml and a porosity of 70%.

Subsequently, the composition for forming the porous layer was metered and mixed by the prescription shown in Table 1-2, and the porous layer was formed on the porous film in the same manner as in Example 1 to obtain a laminated porous film. In addition, in Example 11 and Example 12, a porous layer was formed by drying the coating solution at 60 ° C and 130 ° C for 1 minute, respectively, to form a porous layer.

(Comparative Example 1)

In Example 2, the porous film before forming the porous layer was evaluated as it is.

(Comparative Examples 2 to 5)

The composition for forming the porous layer was metered and mixed with the prescription shown in Table 2-2 to prepare a coating solution for forming the porous layer. This was the same as in Example 1 on the one side of the porous film 2 prepared in Example 2, and a coating solution was applied so that the laminated thickness after drying was 7 µm using a die coater and dried at 100 ° C. for 1 minute to form a porous layer. The laminated porous film was produced.

(Composition used for coating solution)

Inorganic particles (A)

Calcium carbonate Shiraishi Calcium Co., Ltd. "PC", average particle diameter 3.0 µm, aspect ratio 4

Silica Denki Kagaku Kogyo Co., Ltd. "SFP-30", average particle diameter 0.7 µm, aspect ratio 1

Water-soluble polymer (B1)

Carboxymethylcellulose A (CMC A) Daicel FineChem Co., Ltd. "CMC Daicel 1220"

Carboxymethylcellulose B (CMC B) Daicel FineChem Co., Ltd. "CMC Daicel 2200"

・ "AS58" manufactured by Nippon Shokubai Co., Ltd.

Polyacrylamide Arakawa Kagaku Kogyo Co., Ltd. "Polytron 117"

Water-soluble polymer (B2)

Hydroxyethylcellulose A (HEC A) Daicel Finechem Co., Ltd. "HEC EP-850"

Hydroxyethylcellulose B (HEC B) Daicel Finechem Co., Ltd. "HEC EE-820"

Polyvinyl alcohol Nippon Kosei Kagaku High School Co., Ltd. "Koseran L3266"

Resin (C)

Modified polyethylene water dispersion (modified PE) "Chemipal S-100" manufactured by Mitsui Kagaku Co., Ltd., 20% by mass water dilution

Styrene-butadiene rubber water dispersion (SBR) "TRD2001" manufactured by JSR Corporation, 20% by mass dilution of solid content

The evaluation results for the samples of Examples 1 to 12 and Comparative Examples 1 to 5 are shown in Tables 1-3 and Table 2-3. In Example 1 and Example 4, the peel strength was slightly weak due to the influence of the substrate or particles, and the evaluation was B. With respect to Example 8, due to the influence of the binder (resin (C)) used, the binding to the substrate was slightly weak, and the peel strength was evaluated B. In Example 9, since the amount of the binder (resin (C)) was small, the binding with the substrate was slightly weak, and the peel strength was evaluated B. For Example 10, the peel strength was evaluated as evaluation B because the binding between the porous layer and the porous film was strong and fracture occurred in the layer of the porous film. For Example 11, since the drying temperature was low, fracture occurred in the layer of the porous layer, and the peel strength was evaluated as B. With respect to Example 12, the peeling strength was weak due to deformation of the substrate because the drying temperature was high, and evaluation B was obtained.

(Table 1-1)

(Table 1-2)

(Table 1-3)

(Table 2-1)

(Table 2-2)

(Table 2-3)

(Industrial availability)

Since the laminated porous film of the present invention is capable of achieving heat resistance, low water content and high quality, it has excellent safety and battery performance, and is also inexpensive, and can be suitably used as a storage device, particularly a separator for lithium ion batteries that are nonaqueous electrolyte secondary batteries. have.

Claims (12)

A porous layer is formed on at least one side of a substrate made of an olefin-based porous film, and the porous layer comprises:
Inorganic particles (A) whose particle shape is maintained at least up to 200 ° C.,
A water-soluble polymer (B1) containing at least one functional group selected from the group consisting of an amino group, a carbonyl group, a carboxyl group, a sulfonyl group and a phosphoric acid group at the end of the side chain of the polymer skeleton, and a hydroxyl group, an alkyl group and a halogen group at the end of the side chain of the polymer skeleton A water-soluble polymer (B) containing at least one water-soluble polymer (B2) containing only at least one functional group selected from the group consisting of,
Contains at least one resin (C) selected from polyvinylidene fluoride (PVDF), acrylic (excluding water-soluble acrylic resin), fluorine-based rubber, styrene-butadiene rubber (SBR), polyurethane, epoxy resin, and modified polyolefin. ,
When the contents of the water-soluble polymer (B1) and the water-soluble polymer (B2) in the porous layer are C _b1 and C _{b2 in} order, respectively, the value of C _b1 / C _b2 is 0.2 to 8, wherein the laminated porous film. According to claim 1,
The laminated porous film, characterized in that the water-soluble polymer (B1) and the water-soluble polymer (B2) are both cellulose-based compounds. According to claim 1,
The laminated porous film, wherein the resin (C) is a modified polyolefin. According to claim 1,
A laminated porous film, characterized in that the porosity of the substrate is 50% or more and less than 85%. According to claim 1,
The laminated porous film, characterized in that the substrate has the ability to form β crystals. A separator for an electrical storage device, characterized by comprising the laminated porous film according to any one of claims 1 to 5. The electrical storage device characterized by using the laminated porous film as described in any one of Claims 1-5 as a separator. A coating liquid for forming the porous layer of the laminated porous film according to any one of claims 1 to 5,
Inorganic particles (A) whose particle shape is maintained at least up to 200 ° C.,
A water-soluble polymer (B1) containing at least one functional group selected from the group consisting of an amino group, a carbonyl group, a carboxyl group, a sulfonyl group and a phosphoric acid group at the end of the side chain of the polymer skeleton, and a hydroxyl group, an alkyl group and a halogen group at the end of the side chain of the polymer skeleton A water-soluble polymer (B) containing at least one water-soluble polymer (B2) containing only at least one functional group selected from the group consisting of,
Contains at least one resin (C) selected from polyvinylidene fluoride (PVDF), acrylic (excluding water-soluble acrylic resin), fluorine-based rubber, styrene-butadiene rubber (SBR), polyurethane, epoxy resin, and modified polyolefin. ,
When the contents of the water-soluble polymer (B1) and the water-soluble polymer (B2) in the porous layer are C _b1 and C _{b2 in} order, respectively, the value of C _b1 / C _b2 is 0.2 to 8, which is a porous porous laminated film. Coating liquid for forming a layer. A method for producing a laminated porous film, comprising applying a coating liquid for forming the porous layer of the laminated porous film according to claim 8 onto a substrate, followed by drying to form a porous layer. delete delete delete