KR20160091917A - Laminated porous film, and production method therefor - Google Patents

Abstract

A multilayer porous film of the present invention has a very high peel strength between a polyolefin porous film and a modified porous layer and is suitable for high-speed processing, and a laminated porous film used as a separator for a battery.
[MEANS FOR SOLVING PROBLEMS] The projection of a polyolefin 5 ㎛≤W≤50 ㎛ (W is the size of the projections) and 0.5 ㎛≤H satisfy the (H is the height of the projections), per side 3 / cm ² or more on both sides 200 Cm ² or less and a film thickness of 25 탆 or less on one side of the modified porous layer A and the opposite side of the modified porous layer B on the other side of the polyolefin porous film, A laminated porous film comprising a binder having a tensile strength of 5 N / mm ² or more and inorganic particles.

Description

TECHNICAL FIELD [0001] The present invention relates to a laminated porous film and a method for manufacturing the laminated porous film,

The present invention relates to a laminated porous film having a modified polyolefin porous film and a modified porous layer suitable for lamination of the modified porous layer and a method for producing the same. The laminated porous film of the present invention is a battery separator useful as a separator for a lithium ion battery.

BACKGROUND ART [0002] Microporous membranes made of a thermoplastic resin are widely used as separation membranes for materials, selective permeable membranes, and separation membranes. For example, various filters such as a lithium ion secondary battery, a nickel-hydrogen battery, a nickel-cadmium battery, a battery separator used for a polymer battery, a separator for an electric double layer capacitor, a reverse osmosis filtration membrane, an ultrafiltration membrane and a microfiltration membrane, Medical (clothing), and medical (medical) materials. Particularly, as a separator for a lithium ion secondary battery, a separator having an ion permeability by impregnation with an electrolyte is excellent in electric insulation, and has a pore closing effect for suppressing an excessive increase in temperature by shutting off the current at a temperature of about 120 to 150 ° C A porous polyethylene-made membrane is preferably used. However, when the temperature continues to rise after the pore closure for some reason, a film rupture may occur due to shrinkage of the film. This phenomenon is not a phenomenon confined to a polyethylene microporous membrane but can be inevitable at a temperature above the melting point of the resin constituting the porous membrane even in the case of a microporous membrane using another thermoplastic resin.

Particularly, separators for lithium ion batteries are deeply related to battery characteristics, battery productivity and battery safety, and are required to have mechanical properties, heat resistance, permeability, dimensional stability, shut-off characteristics (shutdown characteristics) . Further, in order to improve the cycle characteristics of the battery, it is required to improve the adhesion between the separator and the electrode material, and to improve the permeability of the electrolyte to improve the productivity.

Therefore, up to now, studies have been made to laminate a modified porous layer on a polyolefin porous film. As the resin contained in the modified porous layer, a polyamideimide resin having heat resistance and electrolyte permeability, a polyimide resin, a polyamide resin, and a fluorine resin having excellent electrode adhesion are preferably used. Further, a water-soluble or water-dispersible binder capable of laminating the modified porous layer using a relatively simple water washing step and a drying step is widely used.

The modified porous layer in the present invention refers to a layer containing a resin that imparts or enhances at least one or more of functions such as heat resistance, adhesion with an electrode material, electrolyte permeability, and the like.

In Patent Document 1, polyvinylidene fluoride is applied to a porous polyethylene membrane having a thickness of 9 탆, and a part of polyvinylidene fluoride penetrates pores of the porous membrane made of polyethylene appropriately to exhibit an anchor effect, (T-type peel strength) at the interface between the porous film and the coating layer of polyvinylidene fluoride is 1.0 to 5.3 N / 25 mm.

In Patent Document 2, a heat-resistant porous layer including a self-crosslinkable acrylic resin and a plate-shaped boehmite is provided on a corona-discharge-treated polyethylene porous film having a thickness of 16 탆, and a porous polyethylene- (T-type peel strength) of 1.1 to 3.0 N / 10 mm is disclosed.

In Example 1 of Patent Document 3, 47.5 parts by mass of polyethylene having a viscosity average molecular weight of 200,000, 2.5 parts by mass of polypropylene having a viscosity average molecular weight of 400,000, 50 parts by mass of a composition comprising an antioxidant and 50 parts by mass of a liquid paraffin Is extruded from an extruder at 200 ° C and taken in a cooling roll controlled at 25 ° C to obtain a gel-like molded product, followed by biaxial stretching so as to be 7 × 6.4 times to obtain a polyolefin resin porous film. Then, a multilayer porous film obtained by laminating a coating layer composed of polyvinyl alcohol and alumina particles on the surface of the polyolefin resin porous film is disclosed.

In Example 6 of Patent Document 4, a polyethylene resin solution having a weight average molecular weight of 4,155,000, a weight average molecular weight of 560,000, a weight ratio of 1: 9 of 30% by weight of a polyethylene composition and a mixed solvent of liquid paraffin and decalin in an amount of 70% , And the mixture was cooled in a water bath to obtain a gel-like shaped product, followed by biaxial stretching so as to be 5.5 x 11.0 times to obtain a polyethylene porous film. Next, a separator for a non-aqueous secondary battery is obtained by further laminating a coating layer composed of meta-type wholly aromatic polyamide and alumina particles on the surface of the polyethylene porous film.

In Example 1 of Patent Document 5, 47 parts by mass of polyethylene of homopolymer having Mv (viscosity average molecular weight) of 700,000, 46 parts by mass of polyethylene of homopolymer having Mv of 250,000 and 7 parts by mass of polypropylene of homopolymer having Mv of 400,000 Followed by dry blending using a tumbler blender. 1 mass% of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99 mass% of the obtained pure polymer mixture, The polyethylene composition obtained by dry blending using a tumbler blender was melted and kneaded, extruded and cast on a cooling roll controlled at a surface temperature of 25 占 폚 to obtain a sheet-shaped polyolefin composition having a thickness of 2000 占 퐉, Discloses a multilayer porous film obtained by coating an aqueous dispersion of fired kaolin and latex on a polyethylene porous film obtained by stretching.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2012-043762 Patent Document 2: Japanese Laid-Open Patent Publication No. 2010-104127 Patent Document 3: Japanese Patent Publication No. 4931083 Patent Document 4: Japanese Patent Publication No. 4460028 Patent Document 5: Japanese Laid-Open Patent Publication No. 2011-000832

In order to improve the battery capacity in the future, it is necessary to increase the area that can be filled in the container not only in the electrode sheet but also in the separator, and it is predicted that further thinning will proceed. However, as the porous film becomes thinner, it is liable to be deformed in the planar direction, so that the modified porous layer laminated on the porous film of the thin film may be peeled off during processing, slitting process or battery assembling process.

Further, in order to cope with the reduction in cost, the battery assembly process is expected to be accelerated. In order to obtain a separator having less trouble such as peeling of the modified porous layer even in high-speed processing, high adhesion that can withstand high-speed processing is required between the porous polyolefin film and the modified porous layer. However, if the resin contained in the modified porous layer is sufficiently permeated into the polyolefin porous film in order to improve the adhesion, there is a problem that the rising width of the durability increases.

In the prior art, since the modified porous layer is locally peeled off during the slit processing or the cell assembly processing in order to meet the demand for the high-speed processing accompanied with the high cost, the high capacity processing and the thinning of the separator to proceed rapidly in the future, It is expected to be difficult. In particular, when the polyolefin resin porous film is thinned, it becomes difficult to obtain sufficient anchor effect with respect to the polyolefin resin porous film of the modified porous layer, so that it becomes more difficult to secure safety.

The inventors of the present invention have found that the separator for a battery is excellent in the peeling strength with the modified porous layer and is suitable for the lamination of the modified porous layer suitable for the high speed processing in the slit process or the battery assembly process A multilayer porous film having a polyolefin porous film and a modified porous layer, and the laminated porous film used as a separator for a battery.

The peel strength referred to in the present specification means the 0 degree peel strength between the polyolefin porous film and the modified porous layer, and is a value measured by the following method (hereinafter sometimes referred to as 0 degree peel strength).

Fig. 1 schematically shows a side view of a laminated sample of a polyolefin porous film and a modified porous layer in a state of being stretched by a tensile tester (not shown). 1 is a laminated sample, 2 is a polyolefin porous film, 3 is a modified porous layer, 4 is a double-sided adhesive tape, and 5 and 5 'are aluminum plates. A double-faced pressure-sensitive adhesive tape 4 of the same size was attached to an aluminum plate 5 having a size of 50 mm x 25 mm and a thickness of 0.5 mm and a sample 1 (laminated porous film) having a width of 50 mm and a length of 100 mm cut thereon The surface of the polyolefin porous film 2 is laminated so that 40 mm is overlapped from the end of one side of the 25 mm length of the aluminum plate 5, and the outgoing portion is cut out. Then, a double-faced adhesive tape was affixed to one side of an aluminum plate 5 'having a length of 100 mm, a width of 15 mm and a thickness of 0.5 mm, and a double-sided adhesive tape was attached to one side of the aluminum plate 5 . Thereafter, the aluminum plate 5 and the aluminum plate 5 'are pulled in parallel to each other in the opposite direction using a tensile tester at a tensile speed of 10 mm / min to measure the strength when the modified porous layer is peeled off. When the peel strength is 130 N / 15 mm or more in this evaluation method, even when the thickness of the polyolefin porous film is equal to or less than 10 탆, the laminated modified porous layer hardly peels off during transportation or processing.

The T-type peel strength or the peel strength at 180 DEG which is conventionally used as the peeling strength measurement method is the peeling strength when peeling off the coating layer from the polyethylene porous membrane to the obliquely backward direction perpendicular or perpendicular to the surface of the porous polyethylene- It is power. According to the present evaluation method, the friction resistance in the slit process or the cell assembly process can be evaluated based on actuality, as compared with the conventional evaluation methods.

In order to solve the above problems, the laminated porous film of the present invention has the following constitution. In other words,

A projection of a polyolefin 5 ㎛≤W≤50 ㎛ (W is the size of the projections) and 0.5 ㎛≤H satisfy the (H is the height of the projections), per side on both sides 3 / cm ² or more to 200 / cm ² And a modified porous layer A laminated on one side of the porous polyolefin membrane A and the modified porous layer B on the opposite side of the polyolefin porous membrane with a film thickness of not more than 25 μm and at least the modified porous layer A has a tensile strength of 5 N / mm < ² > or more and inorganic particles.

The laminated porous film of the present invention is preferably a binder in which the tensile strength is not less than 5 N / mm ² is polyvinyl alcohol or acrylic resin.

The laminated porous film of the present invention preferably contains at least one kind of inorganic particles selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate, mica and boehmite.

The thickness of the polyolefin porous film of the laminated porous film of the present invention is preferably 20 m or less.

The thickness of the polyolefin porous film of the laminated porous film of the present invention is preferably 16 占 퐉 or less.

The laminated porous film of the present invention is preferably used as a battery separator.

In order to solve the above problems, a method for producing a multilayer porous film of the present invention has the following constitution. In other words,

(a) a step of adding a molding solvent to a polyolefin resin and then melt-kneading to prepare a polyolefin resin solution

(b) a step of extruding the polyolefin resin solution from a T-die and cooling the polyolefin resin solution on both sides of a polyolefin resin solution extruded into a film with a cooling roll having a surface from which a solvent for formation has been removed to form a gel-

(c) a step of stretching the gel-like molded product in the machine direction and the width direction to obtain a drawn product

(d) a step of removing the molding solvent from the drawn molded article and drying to obtain a porous molded article

(e) heat-treating the porous formed article to obtain a polyolefin porous film

(f) A laminate film is formed on at least one surface of the polyolefin porous film using a coating liquid containing a binder having a tensile strength of 5 N / mm ² or more, a solvent capable of dissolving or dispersing the binder, and inorganic particles, followed by drying fair.

In the method for producing a laminated porous film of the present invention, it is preferable that the means for removing the molding solvent is a doctor blade.

In addition, in the present specification, the modified porous layer A and the modified porous layer B may be abbreviated simply as a modified porous layer.

According to the present invention, it is possible to obtain a laminated porous film having a highly porous polyolefin porous film and a modified porous layer having excellent adhesion with the modified porous layer, and a separator for a battery which does not cause peeling even during high-speed transportation using the laminated porous film.

Fig. 1 is a schematic view showing a measuring method of 0 占 peeling strength.
2 is a schematic view showing a spherical structure and crystal nuclei of polyethylene in a polyethylene porous film.
3 is a microphotograph of a ring-shaped trace originating from the reclamation of polyethylene in a polyethylene porous film.
4 is a schematic view showing a step of forming a gel-like molded product by extruding a polyethylene resin solution from a T-shaped die provided at a tip end of an extruder and cooling it with a cooling roll.

The polyolefin porous film used in the present invention is a polyolefin porous film which is obtained by adjusting a specific polyolefin resin solution and highly controlling the cooling rate of a polyolefin resin solution extruded through a T- It is membrane. In addition, when the modified porous layer containing inorganic particles and a binder having a tensile strength of 5 N / mm ² or more is laminated on the polyolefin porous film, a very excellent peel strength can be obtained between the polyolefin porous film and the modified porous layer .

The projections mentioned in the present invention are essentially different from the projections obtained by adding, for example, inorganic particles or the like to the polyolefin porous film. The projections obtained by adding inorganic particles to the polyolefin porous film are usually very small. In order to form protrusions 0.5 mu m or more in height by the same means, it is necessary to add particles having a particle size equal to or larger than the thickness of the polyolefin porous film . However, when such particles are added, the strength of the polyolefin porous film deteriorates, which is not realistic.

The projections referred to in the present invention are obtained by growing a part of the polyolefin porous film with a ridge of a proper shape and do not degrade the basic characteristics of the polyolefin porous film.

In addition, the irregular scattering in the present invention is clearly different from the regular or periodic arrangement obtained by passing through the embossing roll before or after the stretching process in the production of the polyolefin porous film. Pressing such as embossing or the like basically forms protrusions by compressing portions other than the projections, which is undesirable because it tends to lower the permeation resistance and the electrolyte permeability.

In the present invention, a protrusion having an appropriate shape means a protrusion having a size of 5 mu m or more and 50 mu m or less and a height of 0.5 mu m or more. That is, 5 占 퐉? W? 50 占 퐉 (W is the size of the projection) and 0.5 占 퐉? H (H is the height of the projection). These projections function as an anchor when the modified porous layer is laminated on the porous film, and as a result, the laminated porous film having the large 0 ° peel strength can be obtained. On the other hand, the upper limit of the height is not particularly limited, but it is sufficient that the upper limit of the height is about 3.0 탆. The greater the number of protrusions of sufficient height, the greater the 0 DEG peel strength described above. That is, the 0 占 peel strength is affected by the number of protrusions having a height of 0.5 占 퐉 or more and the average height thereof. The lower limit of the number of projections is preferably 3 / cm ² , more preferably 5 / cm ² , even more preferably 10 / cm ² . The upper limit of the number of projections is preferably 200 / cm ² , and more preferably 150 / cm ² . The lower limit of the height of the projection is preferably 0.5 占 퐉, more preferably 0.8 占 퐉, and even more preferably 1.0 占 퐉.

In addition, the size and height of the projections in the present invention refer to values measured by a measuring method described later.

The rising width of the durability in the present invention means the difference between the durability of the polyolefin porous film and the durability of the laminated porous film laminated with the modified porous layer, preferably 100 sec / 100 ccAir or less.

The outline of the laminated porous film having the polyolefin porous film and the modified porous layer of the present invention and the laminated porous film used as the battery separator will be described, but the present invention is not limited thereto.

1. Polyolefin porous film

First, the polyolefin porous film of the present invention will be described.

The thickness of the polyolefin porous film of the present invention is preferably 25 占 퐉 or less, more preferably 20 占 퐉, and still more preferably 16 占 퐉. The lower limit is 7 占 퐉, preferably 9 占 퐉. When the thickness of the polyolefin porous film is within the above-mentioned preferable range, it is possible to have a practical film strength and a pore-closing function, and the area per unit area of the battery case is not restricted,

The upper limit of the permeation resistance of the polyolefin porous membrane is preferably 300 sec / 100 ccAir, more preferably 200 sec / 100 ccAir, even more preferably 150 sec / 100 ccAir, and the lower limit is 50 sec / 100 ccAir More preferably 70 sec / 100 ccAir, even more preferably 100 sec / 100 ccAir.

The upper limit of the porosity of the polyolefin porous film is preferably 70%, more preferably 60%, still more preferably 55%. The lower limit is preferably 30%, more preferably 35%, even more preferably 40%. When the durability and the porosity are within the above preferable range, sufficient charge / discharge characteristics of the battery, especially ion permeability (charge / discharge operation voltage) and battery life (closely related to the amount of electrolyte retained) And sufficient mechanical strength and insulating property are obtained, thereby reducing the possibility of short-circuiting during charging and discharging.

The average pore diameter of the polyolefin porous film is preferably 0.01 to 1.0 占 퐉, more preferably 0.05 to 0.5 占 퐉, and even more preferably 0.1 to 0.3 占 퐉 in order to greatly affect the pore-closing performance. When the average pore diameter of the polyolefin porous film is within the above preferable range, the peeling strength of the modified porous layer can be obtained at 0 ° due to the anchoring effect of the functional resin, and when the modified porous layer is laminated, And the response to the temperature of the pore closure phenomenon does not become gentle and the pore closure temperature due to the temperature rise rate does not move to the higher temperature side.

The polyolefin porous film needs to have the function of closing the pores at the time of abnormality in the charge-discharge reaction. Therefore, the melting point (softening point) of the constituting resin is 70 to 150 캜, more preferably 80 to 140 캜, and even more preferably 100 to 130 캜. When the melting point of the resin to be constituted is within the above-mentioned preferable range, the pore-closing function is exhibited at the time of normal use and the battery can not be used, and the pore-closing function is exhibited at the time of the abnormal reaction.

The polyolefin resin constituting the polyolefin porous film is preferably polyethylene or polypropylene. It may also be a single substance or a mixture of two or more different polyolefin resins, for example a mixture of polyethylene and polypropylene, or a copolymer of different olefins. This is because, in addition to the basic properties such as electrical insulation and ion permeability, a pore-closure effect is provided that cuts off the current at the time of abnormally increasing the battery temperature and suppresses excessive temperature rise. Among them, polyethylene is particularly preferable from the standpoint of excellent pore-closure performance.

Hereinafter, the polyolefin resin used in the present invention will be described in detail by taking polyethylene as an example.

Examples of the polyethylene include ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene. The polymerization catalyst is not particularly limited, and examples thereof include a Ziegler-Natta catalyst, a Phillips catalyst and a metallocene catalyst. These polyethylene may be not only homopolymers of ethylene but also copolymers containing small amounts of other? -Olefins. As the? -Olefins other than ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (meth) acrylic acid, esters of (meth) acrylic acid, .

The polyethylene may be a single material, but it is preferably a mixture of two or more kinds of polyethylene. As the polyethylene mixture, a mixture containing two or more kinds of ultrahigh molecular weight polyethylene having different weight average molecular weights (Mw) may be used, or a mixture of high density polyethylene, medium density polyethylene or low density polyethylene may be used. Further, a mixture of two or more kinds of polyethylenes selected from the group consisting of ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene may be used.

As the polyethylene mixture, a mixture of ultrahigh molecular weight polyethylene having a weight average molecular weight (Mw) of 5 10 ⁵ or more and polyethylene having Mw of 1 10 ⁴ or more and less than 5 10 ⁵ is preferable. The Mw of the ultrahigh molecular weight polyethylene is preferably 5 × 10 ⁵ to 1 × 10 ⁷ , more preferably 1 × 10 ⁶ to 15 × 10 ⁶ , and even more preferably 1 × 10 ⁶ to 5 × 10 ⁶ . High density polyethylene, medium density polyethylene and low density polyethylene can be used as the polyethylene having Mw of 1 x 10 ⁴ or more and less than 5 x 10 ⁵ , but it is particularly preferable to use high density polyethylene. As the polyethylene having an Mw of 1 x 10 ⁴ or more and less than 5 x 10 ^5, two or more materials having different Mws may be used, or two or more materials having different densities may be used. By setting the upper limit of Mw of the polyethylene mixture to 15 x 10 < ⁶ > or less, melt extrusion can be facilitated.

In the present invention, the upper limit of the content of the ultrahigh molecular weight polyethylene is preferably 40 wt%, more preferably 30 wt%, even more preferably 10 wt%, and the lower limit is preferably 1 wt% By weight, more preferably 2% by weight, and even more preferably 5% by weight.

If the content of the ultrahigh molecular weight polyethylene is within the preferable range, a projection having a sufficient height can be obtained. By this protrusion, when the modified porous layer is laminated, the protrusion functions as an anchor, and very strong peeling resistance can be obtained against a force applied parallel to the plane direction of the polyethylene porous film. Further, sufficient tensile strength can be obtained even when the thickness of the polyethylene porous film is reduced. The tensile strength is preferably 100 MPa or more. The upper limit is not specifically defined.

The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polyethylene resin preferably have a non-molecular weight distribution (Mw / Mn) in the range of 5 to 200, more preferably 10 to 100. When the range of Mw / Mn is within the above preferable range, the polyethylene resin solution can be easily extruded and a sufficient number of projections can be obtained. Further, when the thickness of the polyethylene porous film is made thin, sufficient mechanical strength can be obtained. Mw / Mn is used as a measure of the molecular weight distribution, that is, in the case of polyethylene made of a single substance, the larger this value is, the larger the width of the molecular weight distribution is. The Mw / Mn of the polyethylene made of a single material can be suitably adjusted by the multi-terminal polymerization of polyethylene. The Mw / Mn of the polyethylene mixture can be appropriately adjusted by adjusting the molecular weight and the mixing ratio of each component.

The polyethylene porous film may be a monolayer film or a layer composed of two or more layers having different molecular weights or average pore diameters. In the case of a layer constitution comprising two or more layers, it is preferable that the molecular weight and the molecular weight distribution of the polyethylene resin in at least one outermost layer satisfy the above-mentioned. As long as the polyethylene porous film satisfies the above-described various characteristics, the manufacturing method according to the purpose can be freely selected.

2. Process for producing polyolefin porous film

As the method of producing the polyolefin porous film, there are a foaming method, a phase separation method, a dissolution recrystallization method, a stretching method (opening method) and a powder sintering method. Among them, the phase separation method is preferable from the viewpoint of uniformization of micropores and cost.

As a production method by the phase separation method, for example, a method in which polyethylene and a molding solvent are heated and melt kneaded, the obtained molten mixture is extruded and cooled in a T-die to form a gel-like molded product, Followed by stretching and removing the molding solvent to obtain a porous film.

As a method for producing a multilayer film composed of two or more layers, for example, polyethylene constituting the a layer and the b layer is melted and kneaded with a molding solvent, and the obtained molten mixture is fed to one T-die in each extruder, A method in which a gel sheet constituting the component is integrated and pneumatically delivered, and a method in which a gel sheet constituting each layer is superimposed and heat-sealed. The coextrusion method is more preferable because it is easy to obtain a high interlaminar bond strength, easily forms a communication hole between the layers, easily maintains high permeability, and is excellent in productivity.

The method for producing the porous polyolefin membrane used in the present invention will be described in detail.

The method for producing the porous polyolefin membrane used in the present invention includes the following steps (a) to (e).

(a) a step of adding a molding solvent to a polyolefin resin and then melt-kneading to prepare a polyolefin resin solution

(b) a step of extruding the polyethylene solution from a T-die and cooling the polyolefin resin solution on both sides of the polyolefin resin solution extruded into a film with a cooling roll having a surface on which the molding solvent is removed to form a gel-

(c) a step of stretching the gel-like molded product in the machine direction (MD) and the transverse direction (TD) to obtain a drawn product

(d) a step of removing the molding solvent from the drawn molded article and drying to obtain a porous molded article

(e) heat-treating the porous article to obtain a polyolefin porous film.

After the steps (a) to (e), a corona treatment step or the like may be provided if necessary.

An example of using a polyethylene resin as the polyolefin resin for each step will be described below.

(a) preparing a polyethylene resin solution

After a molding solvent is added to the polyethylene resin, the polyethylene resin solution is prepared by melting and kneading.

The molding solvent is not particularly limited as long as it can sufficiently dissolve polyethylene. For example, aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, liquid paraffin and the like, or mineral oil fractions corresponding to the boiling point, and the like, Non-volatile solvents, such as liquid paraffin, are preferred for obtaining moldings. The heat dissolution is carried out by stirring or mixing the mixture at a temperature at which the polyethylene composition is completely dissolved or by homogeneously mixing in an extruder. The temperature varies depending on the polymer and the solvent used in the case of dissolving in an extruder or in a solvent while stirring, but is preferably in the range of 140 to 250 ° C, for example.

The concentration of the polyethylene resin is 25 to 40 parts by weight, preferably 28 to 35 parts by weight, based on 100 parts by weight of the total of the polyethylene resin and the molding solvent. When the concentration of the polyethylene resin is within the above preferable range, the number of crystal nuclei for forming the projections is sufficiently formed, and a sufficient number of projections are formed. Further, swelling and neck in are suppressed at the exit of the T-die when the polyethylene resin solution is extruded, and moldability and self-supportability of the extrusion molded article are maintained.

The melt-kneading method is not particularly limited, but is usually carried out by homogeneously kneading in an extruder. This method is suitable for preparing high concentration solutions of polyethylene as described above. The melting temperature is preferably in the range of the melting point of polyethylene + 10 ° C to + 100 ° C. In general, the melting temperature is preferably in the range of 160 to 230 占 폚, more preferably in the range of 170 to 200 占 폚. Here, the melting point refers to a value obtained by differential scanning calorimetry (DSC) according to JIS K7121. The molding solvent may be added before the start of the kneading, or may be added during the kneading in the middle of the extruder to melt and knead the mixture, but it is preferably added before the start of the kneading to prepare a solution. At the time of melt kneading, it is preferable to add an antioxidant to prevent the oxidation of polyethylene.

(b) a step of forming a gel-like molded product

The melt-kneaded polyethylene resin solution is extruded from a T-die and cooled with a cooling roll having a surface on which a molding solvent is removed by a molding solvent removing means to form a gel-like molded product. The extrusion in the T-die is carried out by melt-kneading the polyethylene resin solution directly in the extruder or through another extruder. As the T-shaped die, a T-shaped die for a sheet having a generally rectangular barrel shape is used.

Next, a gel-like molded product is formed by contacting both surfaces of a polyethylene resin solution extruded into a film form in a T-die to a pair of rotating cooling rolls set at a surface temperature of 20 DEG C to 40 DEG C as a refrigerant. The extruded polyethylene resin solution is preferably cooled to 25 ° C or lower.

In the present invention, it is important to control the cooling rate in the temperature region where the crystallization substantially takes place in the formation of the projections.

The inventors of the present invention have devised the following mechanism for forming the projections in the present invention. The resin solution of the melted polyethylene resin and the molding solvent is extruded from the T-die, and at the same time, the crystallization of the polyethylene starts, and the crystallization speed is increased by contacting with the cooling roll and quenching. At this time, a symmetrical structure having crystal nuclei is formed (Fig. 2). When the heat transfer rate between the surface of the cooling roll and the molten polyethylene resin is relatively small, the crystallization rate is small, and as a result, the crystal having a relatively small crystal nucleus is obtained. When the heat transfer rate is high, the crystal structure is relatively large. These crystal nuclei are projections in the subsequent process of TD (width direction) and / or MD (machine direction) stretching. In addition, the moon appears as a ring-shaped trace on the surface of the polyethylene porous film (Fig. 3).

In the present invention, for example, the extruded polyethylene resin solution is cooled at a cooling rate in a temperature range where the surface of the polyethylene resin solution is substantially crystallized at 10 DEG C / sec or more to obtain a gel-like shaped article. The cooling rate is preferably 20 DEG C / sec or more, more preferably 30 DEG C / sec or more, and even more preferably 50 DEG C / sec or more. By carrying out such cooling, a structure in which a polyethylene phase is micro-phase-separated by a solvent is immobilized, and a glass having a relatively large core is formed on the surface of a gel-like molded article in contact with the cooling roll, . The cooling rate on the cooling roll can be estimated by simulating from the thermal conductivity of the polyolefin resin solution, the thickness, the solvent for molding, and the heat transfer coefficient of the cooling roll and air.

In the present invention, in order to control the cooling rate, it is important to remove as much as possible the molding solvent adhering to the surface of the cooling roll in a portion in contact with the polyethylene resin solution extruded from the T-die. That is, as shown in Fig. 4, the polyethylene resin solution is cooled by being wound around a rotating cooling roll to become a gel-like molded product. The molding resin is adhered to the surface of the cooling roll after being separated from the gel- And is brought into contact with the polyethylene resin solution as it is. However, if a molding solvent is adhered to the surface of the cooling roll much, the cooling rate becomes gentle due to the adiabatic effect, and it is difficult to form a projection. Therefore, it is important to remove the molding solvent as much as possible until the cooling roll is again brought into contact with the polyethylene resin solution.

The method for removing the molding solvent from the cooling roll (also referred to as a means for removing the molding solvent) is not particularly limited, but the doctor blade is placed on the cooling roll so as to be parallel to the width direction of the gel-like molding, A method of scraping the molding solvent to such an extent that the molding solvent can not be visually observed on the surface of the cooling roll until the gel-like molded product is contacted is preferably employed. Or may be removed by such means as blowing with compressed air, sucking, or combining these methods. Among them, a method of scraping using a doctor blade is preferable because it is relatively easy to carry out, and it is more preferable to use a plurality of doctor blades than one, in order to improve the removal efficiency of a molding solvent.

The material of the doctor blade is not particularly limited as long as it is resistant to a molding solvent, but resin or rubber rather than a metal is preferable. In the case of metal, there is a possibility that the cooling roll may be wound. Examples of the resin-made doctor blade include polyester, polyacetal, and polyethylene.

Even if the temperature of the cooling roll is set at less than 20 ° C, this alone can not provide a sufficient cooling rate due to the heat insulating effect of the molding solvent, and the surface of the gel-like molded product is roughened by the condensation attached to the cooling roll .

The cooling rolls are two cooling rolls disposed on both sides of the polyethylene resin solution, and it is preferable that the diameter of each roll is different. In addition, the heights of the installation positions of the rotary shafts of the two cooling rolls differ from the height of the mounting position of the polyethylene resin solution of the T-die. It is preferable that the height of the installation position of the rotary shaft of the cooling roll having a small diameter is closer to the position of the ejection outlet arrangement of the polyethylene resin solution of the T-die than the cooling roll having a large diameter. This is to minimize the distance from the arrangement position of the discharge port of the polyethylene resin solution of the T-die to the grounding position of the polyethylene resin solution on the cooling roll having a large diameter. For example, by arranging as shown in Fig. 4, it becomes possible to set the cooling rate in the temperature region where the polyethylene resin solution extruded from the T-die is substantially crystallized to 10 DEG C / sec or more.

The thickness of the polyethylene resin solution at the time of extrusion is preferably 1500 占 퐉 or less, more preferably 1000 占 퐉 or less, and even more preferably 800 占 퐉 or less. When the thickness of the polyethylene resin solution at the time of extrusion is within the above range, the cooling rate on the side of the cooling roll side is not gentle, which is preferable.

(c) Step of obtaining a drawn molded article

Next, this gel-like molded product is stretched in the machine direction (MD) and the transverse direction (TD) to obtain a stretch formed product. The stretching is performed at a predetermined magnification in two directions of MD and TD by heating the gel-like molded product and by a conventional tentering method, a roll method, or a combination of these methods. The stretching may be either MD and TD simultaneous stretching (simultaneous biaxial stretching) or continuous stretching. In the continuous stretching, at least one of MD and TD can be stretched in multiple stages irrespective of the order of MD and TD. The stretching temperature is the melting point of the polyolefin composition + 10 DEG C or less. Although the drawing magnification varies depending on the thickness of the fabric, it is preferably 9 times or more, and more preferably 16 to 400 times as large as the surface magnification. In the case of MD and TD simultaneous stretching (simultaneous biaxial stretching), stretching at the same MD and TD magnifications such as 3x3, 5x5 and 7x7 is preferable. If the plane magnification is within the above-mentioned preferable range, stretching is sufficient and a porous film having high elasticity and high strength can be obtained. Further, the desired durability can be obtained by adjusting the drawing temperature.

(d) a step of obtaining a porous formed article

The stretched molded product is treated with a cleaning solvent to remove the remaining molding solvent to obtain a porous film. As the cleaning solvent, those having easy volatility such as hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as trifluoroethane, and ethers such as diethyl ether and dioxane can be used . These cleaning solvents are appropriately selected depending on the molding solvent used for dissolving the polyethylene, and used singly or in combination. The cleaning method can be carried out by a method of dipping in a cleaning solvent to extract, a method of spraying a cleaning solvent, a method of suctioning a cleaning solvent from the opposite side of a drawn molding, or a combination thereof. The cleaning as described above is carried out until the residual solvent in the drawn product, which is a drawn product, is less than 1% by weight. Thereafter, the cleaning solvent is dried, and the drying method of the cleaning solvent can be carried out by heat drying, air drying, or the like.

(e) Step of obtaining a polyethylene porous film

The dried porous molded product is heat-treated to obtain a polyethylene porous film. The heat treatment can employ a tenter method, a roll method, a rolling method, and a free method. The heat treatment is preferably carried out within a temperature range of 90 to 150 ° C. When the heat treatment temperature is within the above preferable range, the heat shrinkage rate and the durability of the obtained polyolefin porous film are sufficiently secured. The residence time of the heat treatment process is not particularly limited, but is usually from 1 second to 10 minutes, preferably from 3 seconds to 2 minutes or less.

Further, in the heat treatment step, it is preferable to shrink in at least one of MD and TD while fixing both the machine direction (MD) and the width direction (TD), from the viewpoint of heat shrinkage. MD, and TD is preferably 0.01 to 50%, more preferably 3 to 20%.

After the steps (a) to (e), a function imparting step such as a corona treatment step or a hydrophilization step may be provided as occasion demands.

3. Modified Porous Layer

Next, the modified porous layer used in the present invention will be described.

The laminated porous film in the present invention is a laminated porous film obtained by laminating the modified porous layer A on one side of the polyolefin porous film and the modified porous layer B on the opposite side.

The modified porous layer A and the modified porous layer B may be the same porous layer or may be different. However, it is important that at least the modified porous layer A contains inorganic particles and a binder having a tensile strength of 5 N / mm ² or more. In the case where only the modified porous layer A contains inorganic particles and a binder having a tensile strength of 5 N / mm ² or more, it is preferable to carry out a modification to the side subjected to more stress by contact with a roll or a bar in a subsequent step such as a slit step, It is preferable to laminate the porous layer A because the effect of the present invention is exhibited.

The modified porous layer referred to in the present invention means imparting or enhancing at least one of functions such as heat resistance, adhesion to an electrode material, and electrolyte permeability. At least the modified porous layer A includes inorganic particles and a binder having a tensile strength of 5 N / mm ² or more. By using a binder having a tensile strength of 5 N / mm ² or more, it is possible to obtain a multilayer porous film having a very high 0 ° peel strength by a synergistic effect of the protrusions existing on the surface of the polyolefin porous film and the binder thereof . In addition, compared with the durability of the polyolefin porous film, the durability of the laminated porous film of the present invention does not increase significantly. This is because a sufficient 0 DEG peel strength can be obtained even if a large amount of binder is not penetrated into the pores of the polyolefin porous film.

The lower limit of the tensile strength of the binder is preferably 10 N / mm ² , more preferably 20 N / mm ² , even more preferably 30 N / mm ² . The upper limit is not specifically defined, but 100 N / mm ² is sufficient. The tensile strength of the binder refers to a value measured by the method described later.

The binder used in the present invention having a tensile strength of 5 N / mm ² or more is not particularly limited as far as the tensile strength is 5 N / mm ² or more, and examples thereof include polyvinyl alcohol, cellulose ether resin and acrylic resin . Examples of the cellulose ether resin include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyan ethyl cellulose and oxyethyl cellulose. . A commercially available aqueous solution or aqueous dispersion may also be used. For example, "POVACOAT" (registered trademark) of Nisshin Kasei, "JURYMER" (registered trademark) AT-510, ET-410 of Toagosei Kogyo Co., UW-223SX and UW-550CS manufactured by Taisei Fine Chemical Co., Ltd., WE-301, EC-906EF and CG-8490 manufactured by DIC Co., . Of these, polyvinyl alcohol and acrylic resins having an electrode adhesiveness, a high compatibility with a non-aqueous electrolyte, a suitable heat resistance, and a relatively high tensile strength are preferable.

The binder used for the modified porous layer B may be the same as or different from the modified porous layer A. For example, in the case of imparting excellent heat resistance, a heat-resistant resin such as a polyamide-imide resin, a polyimide resin, or a polyamide resin is used, and in the case of giving an electrode adhesion, a fluorine resin such as polyvinylidene fluoride or a derivative thereof .

In order to reduce the curl of the laminated porous film, it is important to add inorganic particles to the coating liquid for forming the modified porous layer. The coating liquid in this specification includes a binder having a tensile strength of 5 N / mm ² or more, inorganic particles and a solvent capable of dissolving or dispersing the binder, and is used for forming a modified porous layer.

The upper limit of the addition amount of the inorganic particles is preferably 98% by weight, more preferably 95% by weight. The lower limit is preferably 80% by weight, more preferably 85% by weight. When the addition amount of the inorganic particles is within the above-described preferable range, the curl reduction effect is sufficient, the ratio of the functional resin to the total volume of the modified porous layer is optimal, and sufficient 0 DEG peel strength of the modified porous layer can be obtained.

Examples of the inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, , And boehmite. Further, if necessary, heat-resistant crosslinked polymer particles may be added. Examples of heat-resistant crosslinked polymer particles include crosslinked polystyrene particles, crosslinked acrylic resin particles, crosslinked methyl methacrylate particles and the like.

The shape of the inorganic particles may be, for example, a sphere shape, a substantially spherical shape, a plate shape, a needle shape, or a polyhedral shape, but is not particularly limited.

The average particle diameter of these inorganic particles is preferably 1.5 times or more and 50 times or less the average pore diameter of the polyolefin porous film. More preferably 2.0 times or more and 20 times or less. If the average particle diameter of the particles is in the above-mentioned preferable range, the pores of the polyolefin porous film are not blocked in a state in which the heat resistant resin and the particles are mixed, and consequently the pore resistance is maintained, Thereby preventing the occurrence of serious defects.

The binder has a role of binding at least the inorganic particles together and a role of bonding the polyolefin porous film and the modified porous layer. Examples of the solvent include water, alcohols, acetone, and n-methyl pyrrolidone. By adding the inorganic particles to the coating liquid, effects such as prevention of an internal short circuit (dendrite prevention effect) caused by the growth of the dendritic crystal of the electrode in the battery, reduction in heat shrinkage, and provision of slipperiness can be obtained.

The solid content concentration of the coating liquid is not particularly limited as long as it can be uniformly applied, but is preferably 50 wt% or more and 98 wt% or less, more preferably 80 wt% or more and 95 wt% or less. When the solid concentration of the coating liquid is within the above-mentioned preferable range, the modified porous layer is prevented from weakening, and a sufficient peeling strength of the modified porous layer can be obtained at 0 °.

The thickness of the modified porous layer is preferably 1 to 5 占 퐉, more preferably 1 to 4 占 퐉, still more preferably 1 to 3 占 퐉. When the film thickness of the modified porous layer is in the above-mentioned preferable range, the laminated porous film obtained by laminating the modified porous layers can secure the strength and insulation of the film when melted and shrunk at the melting point or more, An adverse reaction can be prevented. Further, the winding volume can be suppressed, which is suitable for increasing the capacity of the battery. Further, curl is suppressed, leading to improvement of productivity in a battery assembling process. The thicknesses of the modified porous layers A and B may be the same or different, but the difference in film thickness is preferably 0.5 占 퐉 or less, and more preferably 0.3 占 퐉 or less.

The porosity of the modified porous layer is preferably 30 to 90%, more preferably 40 to 70% in view of the battery characteristics. The desired porosity can be obtained by appropriately adjusting the concentration of the inorganic particles, the binder concentration, and the like.

The upper limit of the film thickness of the laminated porous film obtained by laminating the modified porous layer is preferably 25 占 퐉, more preferably 20 占 퐉. The lower limit is preferably 6 占 퐉 or more, more preferably 7 占 퐉 or more. When the film thickness of the laminated porous film is within the above preferable range, the laminated porous film obtained by laminating the modified porous layers can secure sufficient mechanical strength and insulation. In addition, the reduction of the capacity can be avoided by reducing the electrode area that can be filled in the container.

The durability of the laminated porous membrane is one of the most important characteristics. It is preferably 50 to 600 sec / 100 ccAir, more preferably 100 to 500 sec / 100 ccAir, even more preferably 100 to 400 sec / 100 ccAir. In order to achieve the desired durability, it is possible to adjust the porosity of the modified porous layer to adjust the degree of penetration of the binder into the porous polyolefin film. When the laminated porous film has the above-mentioned preferable range of the durability, sufficient insulating property can be obtained and clogging, short-circuiting and peeling can be prevented. In addition, by suppressing the film resistance, charge / discharge characteristics and life characteristics in a practically usable range can be obtained.

4. A method of laminating a modified porous layer on a polyolefin porous film

Next, a method of laminating the modified porous layer on the polyolefin porous film of the present invention will be described.

As a method of laminating the modified porous layer on the polyolefin porous film, a known method can be used. Specifically, the coating liquid can be obtained by coating the polyolefin porous film to a predetermined film thickness by a method described below, followed by drying under the conditions of a drying temperature of 40 to 80 DEG C and a drying time of 5 seconds for 60 seconds. In addition, a coating liquid obtained by dissolving a binder in a solvent which is melted while mixing with water is laminated to a predetermined polyolefin porous film by using a coating method to be described later, and the mixture is placed under a specific humidity environment to separate the binder and water- And then putting it in a water bath (coagulation bath) to coagulate the binder.

Examples of the method for applying the coating liquid include a dipping method, a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, Method, a blade coating method and a die coating method, and these methods can be carried out singly or in combination.

It is preferable that the laminated porous film of the present invention is stored in a dry state. However, when it is difficult to keep in a completely dried state, it is preferable to carry out a reduced pressure drying treatment at 100 deg.

The laminated porous film of the present invention can be applied to a secondary battery such as a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a lithium secondary battery and a lithium polymer secondary battery, a plastic film capacitor, An electric double layer capacitor or the like, but it is particularly preferably used as a separator of a lithium ion secondary battery. Hereinafter, a lithium ion secondary battery will be described as an example.

In a lithium ion secondary battery, a positive electrode and a negative electrode are laminated via a separator, and the separator contains an electrolyte (electrolyte). The structure of the electrode is not particularly limited and may be a known structure. For example, an electrode structure (coin type) in which disc-shaped positive electrodes and negative electrodes are arranged facing each other, an electrode structure (laminate type) in which planar type positive electrodes and cathodes are alternately stacked, an electrode structure in which belt- Shaped), and the like.

The anode usually has a current collector and a cathode active material layer including a cathode active material capable of intercalating and deintercalating lithium ions formed on the surface of the current collector. Examples of the positive electrode active material include transition metal oxides, complex oxides of lithium and transition metals (lithium complex oxides), and inorganic compounds such as transition metal sulfides. Examples of the transition metal include V, Mn, Fe, Co, and Ni. Preferable examples of the lithium composite oxide in the cathode active material include lithium nickel oxide, lithium cobaltate, lithium manganese oxide, and layered lithium composite oxide having a? -NaFeO ₂ type structure as a matrix.

The negative electrode has a current collector layer and a negative electrode active material layer including a negative electrode active material formed on the current collector surface. Examples of the negative electrode active material include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black. The electrolytic solution can be obtained by dissolving the lithium salt in an organic solvent. Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiN C ₂ F ₅ SO ₂ ) ₂ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , lower aliphatic carboxylic acid lithium salt and LiAlC ₁₄ . These may be used alone or in combination of two or more. Examples of the organic solvent include organic solvents having a high boiling point and high dielectric constant such as ethylene carbonate, propylene carbonate, ethylmethyl carbonate and? -Butyrolactone; organic solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane, dimethyl carbonate , Diethyl carbonate, and other low-boiling point and low-viscosity organic solvents. These may be used alone or in combination of two or more. Particularly, since an organic solvent having a high dielectric constant has a high viscosity and an organic solvent having a low viscosity has a low dielectric constant, it is preferable to use a mixture of two.

When the battery is assembled, the separator of the present invention can be impregnated with an electrolyte to impart ion permeability to the separator. Typically, the impregnation treatment is carried out by immersing the microporous membrane in an electrolytic solution at normal temperature. For example, when assembling a cylindrical battery, first, a positive electrode sheet, a separator (composite porous film) and a negative electrode sheet are laminated in this order, and the laminate is wound at one end to form a wound electrode element. Subsequently, the electrode element is inserted into the battery can to impregnate the electrolyte, and the battery lid serving as a positive electrode terminal having a safety valve again is caulked through a gasket to obtain a battery.

Example

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited by these examples. In addition, the measurement value in the examples is a value measured by the following method.

1. Tensile strength of binder (N / mm ² )

The binder used in the examples and the comparative examples was sufficiently dissolved or dispersed in a solvent for dissolving or dispersing in water so that the film thickness after drying was about 100 탆 in a dumbbell mold for producing a test piece of No. 2 specified in JIS K7113 and naturally dried at 25 캜, Vacuum drying (vacuum degree of 3 mmHg) was performed at 25 캜 for 8 hours to sufficiently remove the solvent, and the obtained sample sheet was provided for tensile strength measurement. The tensile tester (manufactured by Shimadzu Corporation, Autograph AGS-J load cell capacity 1 kN) was used and measured under the following conditions. The sample film and measurement conditions were as follows, and the measurement was carried out three times, and the average value was determined as the tensile strength of the binder.

Chuck distance: 40 mm

Test speed: 20 mm / min

Measurement environment: temperature 20 ℃, relative humidity 60%

2. Number of projections

The number and size of the projections were measured after stabilizing the light source using a confocal microscope (HD100, manufactured by Lasertec) installed on an earthquake-proof stand.

(order)

(1) A square frame of 1 cm x 1 cm was drawn on an arbitrary one side (referred to as A side) of the separator for a battery obtained in Examples and Comparative Examples with a microfluidic pen.

(2) The square rim was placed on the sample stage with the green side facing up, and tightly fixed to the sample stage using an electrostatic adhesion apparatus attached with a conforction microscope.

(3) Using an objective lens with a magnification of 5 times, a ring-shaped trace originating from the earth of polyethylene as shown in Fig. 3 is displayed on a monitor as a two-dimensional image (REAL screen in this embodiment) We adjusted the position of the sample stage so that the part is almost in the center of the monitor screen. When two traces of ring traces are consecutive, they are fitted to the contact point. The height of the protrusion was measured to be 0.2 mm or more in the long diameter of the ring-shaped trace derived from the above-mentioned polyethylene. The long diameter of the ring-shaped trace was obtained by aligning the cursor with both ends of the ring in the long-diameter direction in the two-dimensional image.

(4) Change the objective lens to a 20x lens to focus on the center of the monitor screen (the center of the monitor screen is brightest in this unit) and set this height as the reference height. box).

(5) The measurement range in the height direction was set to 15 占 퐉 with the reference height being 0 占 퐉. Further, the scanning time was 120 seconds and the step movement distance was 0.1 占 퐉 / step, thereby capturing the three-dimensional data.

(6) After capturing the three-dimensional data, a data processing image (Z image in the present apparatus) was displayed and subjected to smoothing processing (smoothing condition: filter size 3x3, matrix type SMOOTH3_0, number of times once). In addition, horizontal correction was performed on the horizontal correction screen as needed.

(7) A cross-sectional profile corresponding to the cursor was placed on the cross-sectional profile image at a position (the brightest portion) passing through the highest projection in the data processing image in the horizontal direction.

(8) Section profile In the image, two cursors are vertically aligned with the inflection point of both sleeves of the projection, and the distance between both cursors is defined as the projection size.

(9) Section profile In the image, align the two cursors in the horizontal direction with the inflection point of both sleeves of the protrusion (the lower one if the inflection points of both sleeves of the protrusion are different) Height.

(10) The above operation is repeated in the square frame of 1 cm x 1 cm to count the number of projections having a size of 5 mu m or more and 50 mu m or less and a height of 0.5 mu m or more and 3.0 mu m or less to obtain the number of projections per 1 cm ² , And the height average value of the protrusions was determined to be the average protrusion height of the A side. The same operation was performed on the surface opposite to the surface A (referred to as the surface B) to determine the number of projections on the surface B and the average height of the projections.

3. Peel strength at 0 ° of the modified porous layer

To measure an arbitrary plane (for example, plane A), the modified porous layer on the opposite plane (plane B) was peeled off with an adhesive tape in advance, and one surface of the polyolefin porous film was exposed to provide a sample.

Fig. 1 schematically shows an evaluation method. 1 is a laminated sample, 2 is a polyolefin porous film, 3 is a modified porous layer, 4 is a double-sided adhesive tape, and 5 and 5 'are aluminum plates. A double-faced adhesive tape (NW-K50, manufactured by Nichiban Co., Ltd.) 4 was attached to an aluminum plate 5 having a size of 50 mm x 25 mm and a thickness of 0.5 mm. And the surface of the polyolefin porous film 2 of the sample 1 (battery separator) cut out into a width of 50 mm and a length of 100 mm was laminated on the aluminum plate 5 so that 40 mm was overlapped on the end of one side of the 25 mm length I cut out the part that came out. Then, a double-faced adhesive tape was affixed to one side of an aluminum plate 5 'having a length of 100 mm, a width of 15 mm and a thickness of 0.5 mm, and a double-sided adhesive tape was attached to one side of the aluminum plate 5 Respectively. Thereafter, the aluminum plate 5 and the aluminum plate 5 'sandwiching the sample were mounted on a tensile tester (Autograph AGS-J 1kN, manufactured by Shimadzu Seisakusho Co., Ltd.) 5 ') were stretched parallel to each other in the opposite direction at a tensile speed of 10 mm / min to measure the strength when the modified porous layer was peeled off. This measurement was carried out at arbitrary three points spaced 30 cm or more in the longitudinal direction, and the average value was defined as the peel strength at 0 DEG of the modified porous layer of the A side. Similarly, the peel strength at 0 DEG of the modified porous layer was determined for the B side.

4. Thickness

Contact type film thickness meter [Film thickness meter; Quot ;, manufactured by Mitutoyo Co., Ltd., Lightmatic series318). The measurement was carried out under the condition of 0.01 N by weight using a tapered (superhard spherical) tester 9 9.5 mm.

5. Average pore diameter

The average pore diameter of the polyolefin porous film was measured by the following method. The sample was fixed on the measuring cell using a double-sided tape, platinum or gold was vacuum-deposited for a few minutes, and the surface of the film was subjected to SEM measurement at an appropriate magnification. 10 arbitrary portions were selected on the image obtained by the SEM measurement, and the average value of the pore diameters of the ten portions was determined as the average pore diameter of the sample.

6. Speculative resistance (sec / 100 ccAir)

The polyolefin porous film or the laminated porous film was fixed with a clamping plate and an adapter plate so as not to be wrinkled by using a Jelly type Densometer B type manufactured by TESTER SANGYO Co., Ltd. and measured according to JIS P8117. The sample was 10 cm × 10 cm, and the measurement point was the center of the sample and 5 points of the four corners. In addition, if the length of one side of the sample is less than 10 cm, the measured value at five points at intervals of 5 cm can be used. The rise of the durability was obtained by the following equation.

Increase in speculative resistance = (Y) - (X) sec / 100 ccAir

Air permeability of polyolefin porous membrane (X) sec / 100 ccAir

Insulation resistance of laminated porous membrane (Y) sec / 100 ccAir

7. Porosity of polyolefin porous membrane

The porosity (%) was calculated from the results obtained by measuring a sample volume (cm ³ ) and mass (g) of a sample of 10 cm × 10 cm and using the following equation.

Porosity = (1-mass / (resin density x sample volume)) x 100

8. Friction resistance

The rolled laminated porous films obtained in Examples and Comparative Examples were slit at both ends while winding was started. The slit processing was carried out at a speed of 20 m / min and a tension of 60 N / 100 mm using a slitter (product of NISHIMURA WORKS, model WA177A). During processing, two hard chrome plating rolls (both free rolls) were used for the rolls that contacted the coated surface. Subsequently, the peeling defect of the modified porous layer having a long diameter of 0.5 mm or more was counted by using a magnifying glass with a scale (Scale LUPE x 10, manufactured by PEAK) with a naked eye and an enlargement ratio of 10 times while reeling the slit-processed rolled laminated porous film, Were evaluated according to the following criteria. The evaluation area was 100 mm wide × 500 m long (when the width was less than 100 mm, the length was adjusted to obtain the same evaluation area).

Criteria

○ (very good): 5 or less

△ (Good): 6 to 15

X (bad): 16 or more

Example 1

To 100 parts by weight of a composition (Mw / Mn = 16.0) composed of 2% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and 98% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000, 0.375 parts by weight To obtain an added polyethylene composition (melting point 135 캜). 30 parts by weight of this polyethylene composition was fed into a twin-screw extruder. 70 parts by weight of liquid paraffin was fed from a side feeder of the twin-screw extruder and melt-kneaded to prepare a polyethylene resin solution in the extruder. Subsequently, the polyethylene resin solution was extruded at 190 DEG C and extruded thickness of 825 mu m in a T-die provided at the tip of the extruder, and the polyethylene resin solution extruded into a film was placed on both sides thereof (see Fig. 4) And a gel-like molded product was formed while taking the inside cooling water temperature with two cooling rolls maintained at 25 占 폚. At this time, in each of the cooling rolls, between the point where the gel-like molded product is separated from the cooling roll and the point where the polyethylene resin solution extruded from the T-die comes into contact with the cooling roll, a single polyester- So that the liquid paraffin adhered to the cooling roll was scraped off. Subsequently, the gel-like molded product was subjected to simultaneous biaxial stretching at 5 × 5 times while adjusting the temperature so as to have a desired speculative resistance, thereby obtaining a drawn product. The resulting drawn product was washed with methylene chloride to remove residual liquid paraffin and dried to obtain a porous molded article. Thereafter, the porous film was held in the tenter, the width was reduced by 10% only in the TD (width direction) direction, and heat treatment was performed at 90 for 3 seconds to form a film having a thickness of 16 탆, a porosity of 45%, an average pore diameter of 0.15 탆, sec / 100 ccAir of a polyethylene porous film.

(Combination (coating) of coating liquid A)

Alumina particles having an average particle size of 0.5 mu m and ion-exchanged water were blended in a weight ratio of 6:54:40, respectively, and a zirconium oxide bead (TORAY (Manufactured by Toyo Seiki Seisaku-sho) with a paint shaker in a container made of polypropylene together with "Torei Serum" (registered trademark) beads, 0.5 mm in diameter, manufactured by Toyo Seiki Seisaku-sho, And dispersed for 6 hours. Subsequently, the solution was filtered with a filter having a filtration limit of 5 탆 to obtain a coating liquid (a).

(Combination of coating liquid B)

1 mol of trimellitic anhydride (TMA), 0.8 mol of o-tolylidine diisocyanate (TODI) and 0.2 mol of 2,4-tolylene diisocyanate (TDI) were placed in a four-necked flask equipped with a thermometer, And 0.01 mol of potassium fluoride were added together with N-methyl-2-pyrrolidone so that the solid concentration became 14%, and the mixture was stirred at 100 ° C for 5 hours. Then, N-methyl- And diluted with water to synthesize a polyamideimide resin solution. The polyamide-imide resin thus obtained had an inherent viscosity of 1.35 dl / g and a glass transition temperature of 320 ° C.

Polyamide-imide resin solution, alumina particles having an average particle diameter of 0.5 占 퐉 and N-methyl-2-pyrrolidone were blended in a weight ratio of 26:34:40, respectively, and zirconium oxide beads (manufactured by Toray Industries, (Registered trademark) beads, 0.5 mm in diameter] in a polypropylene container and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Subsequently, the solution was filtered with a filter having a filtration limit of 5 탆 to obtain a coating liquid (b). The coating liquid (a) was dried on one surface (referred to as A side) of the polyethylene porous film by a gravure coating method and then applied to a thickness of 2 mu m and dried by passing through a hot air drying furnace at 50 DEG C for 10 seconds. Subsequently, a 2.5 탆 -thick layer was applied to the opposite surface (referred to as B-side), and after passing through a humidification zone at 25 캜 and an absolute humidity of 12 g / m ³ for 5 seconds, N-methyl- And immersed in an aqueous solution containing 5% by weight of pyrrolidone for 10 seconds. After washing with pure water, it was dried by passing through a hot-air drying furnace at 70 ° C to obtain a laminated porous film having a final thickness of 20.5 탆.

Example 2

(Weight% ratio) of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and high density polyethylene (HDPE) having a weight average molecular weight of 350,000 was changed to 10:90 (weight% ratio), a laminated porous film .

Example 3

(Weight% ratio) of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and high density polyethylene (HDPE) having a weight average molecular weight of 350,000 was changed to 20:80 (weight% ratio), a laminated porous film .

Example 4

(Weight% ratio) of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and high density polyethylene (HDPE) having a weight average molecular weight of 350,000 was changed to 30:70 (weight% ratio), a laminated porous film .

Example 5

A multilayer porous film was produced in the same manner as in Example 1 except that the blending ratio of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and high density polyethylene (HDPE) having a weight average molecular weight of 350,000 was changed to 40:60 (weight% .

Example 6

A laminated porous film was obtained in the same manner as in Example 1, except that two cooling rolls were made of two polyester doctor blades at intervals of 20 mm.

Example 7

A laminated porous film was obtained in the same manner as in Example 1, except that both of the two cooling rolls and the three doctor blade made of polyester were each placed on a cooling roll at intervals of 20 mm.

Example 8

2-L curing type aqueous acrylic urethane resin (solid content concentration: 45% by mass) consisting of aqueous acrylic polyol and water-dispersible polyisocyanate (curing agent) Alumina particles having an average particle size of 0.5 탆 and ion-exchanged water were mixed in a weight ratio of 10:40:50 (Manufactured by Toyo Seiki Seisakusho Co., Ltd.) into a container made of polypropylene together with zirconium oxide beads ("Torei Serum" (registered trademark) beads, 0.5 mm in diameter, manufactured by Toray Industries, Time-dispersed. Subsequently, the solution was filtered with a filter having a filtration limit of 5 占 퐉 to obtain a coating liquid (c). Modified porous layers were laminated on both surfaces in the same manner as in Example 1 except that the coating liquid (a) was changed to the coating liquid (c) to obtain a laminated porous film having a final thickness of 20.5 占 퐉.

Example 9

Alumina particles having an average particle size of 0.5 占 퐉, a solvent (ion-exchanged water: ethanol = 70: 30), a copolymer of polyvinyl alcohol and acrylic acid and methyl methacrylate (manufactured by Nissin Kasei Kabushiki Kaisha, "POVACOAT" Were mixed in a weight ratio of 5:45:50, and the mixture was placed in a container made of polypropylene together with zirconium oxide beads ("Torei Serum" (registered trademark) beads, 0.5 mm in diameter, manufactured by Toray Industries, Manufactured by Toyo Seiki Seisakusho Co., Ltd.) for 6 hours. Subsequently, the solution was filtered with a filter having a filtration limit of 5 탆 to obtain a coating liquid (d). The same procedure as in Example 1 was carried out except that the coating liquid (a) was changed to the coating liquid (d), and the modified porous layers were laminated on both sides to obtain a laminated porous film having a final thickness of 20.5 占 퐉.

Example 10

A polyvinylidene fluoride resin solution (melting point 175, 12% N-methylpyrrolidone solution), KF Polymer # 1120 (manufactured by KUREHA KABUSHIKI KAISHA) and alumina particles having an average particle size of 0.5 mu m, N -Methyl-2-pyrrolidone were blended in a weight ratio of 14:19:67, respectively, and mixed with zirconium oxide beads ("Torei Serum" (registered trademark) beads, 0.5 mm in diameter, manufactured by Toray Industries, And the mixture was dispersed in a container for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Then, the mixture was filtered with a filter having a filtration limit of 5 탆 to prepare a varnish (e). The same procedure as in Example 1 was carried out except that the coating liquid (b) was changed to the coating liquid (e), and the modified porous layers were laminated on both sides to obtain a laminated porous film having a final thickness of 20.5 占 퐉.

Example 11

A laminated porous film was obtained in the same manner as in Example 1 except that the temperature of the cooling water inside the cooling roll was maintained at 35 캜.

Example 12

A laminated porous film having a final thickness of 24.5 占 퐉 was obtained in the same manner as in Example 1 except that a polyethylene porous film having a thickness of 20 占 퐉 was obtained by adjusting the extrusion amount of the polyethylene resin solution.

Example 13

A laminated porous film having a final thickness of 16.5 占 퐉 was obtained in the same manner as in Example 1 except that a polyethylene porous film having a thickness of 12 占 퐉 was obtained by adjusting the extrusion amount of the polyethylene resin solution.

Example 14

A laminated porous film having a final thickness of 13.5 占 퐉 was obtained in the same manner as in Example 1 except that a polyethylene porous film having a thickness of 9 占 퐉 was obtained by adjusting the extrusion amount of the polyethylene resin solution.

Example 15

26 parts by weight of a polyethylene composition was charged into a twin-screw extruder and 74 parts by weight of liquid paraffin was supplied from a side feeder of the twin-screw extruder to melt-knead the mixture, thereby obtaining a laminated porous film.

Example 16

35 parts by weight of a polyethylene composition was fed into a twin-screw extruder and 65 parts by weight of liquid paraffin was supplied from a side feeder of the twin-screw extruder to melt-knead the mixture to obtain a laminated porous film.

Example 17

The coating liquid (f) was prepared by changing the alumina particles to titanium oxide particles (average particle diameter of 0.38 mu m) in the coating liquid (a). A laminated porous film was obtained in the same manner as in Example 1 except that the coating liquid (f) was used instead of the coating liquid (a).

Example 18

In the coating liquid (a), a coating liquid (g) in which alumina particles were changed to plate-shaped boehmite fine particles (average particle diameter of 1.0 mu m) was combined. A laminated porous film was obtained in the same manner as in Example 1 except that the coating liquid (g) was used instead of the coating liquid (a).

Example 19

A laminated porous film was obtained in the same manner as in Example 1 except that the coating liquid (a) was used on both sides.

Comparative Example 1

Except that the polyethylene resin solution extruded from the T-die was cooled with two cooling rolls to obtain a gel-like molded product, and neither of the two cooling rolls used a doctor blade and the floating paraffin adhered on the cooling roll was not scratched 1, a laminated porous film was obtained.

Comparative Example 2

Except that a polyethylene composition (melting point 135 ° C) to which 0.375 parts by weight of an antioxidant was added was used in 100 parts by weight of a composition (Mw / Mn = 16.0) composed of 100% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000 A laminated porous film was obtained in the same manner as in Example 1.

Comparative Example 3

A laminated porous film was obtained in the same manner as in Example 1 except that the temperature of the internal cooling water of the cooling roll was maintained at 0 캜 and no doctor blade was used.

Comparative Example 4

A laminated porous film was obtained in the same manner as in Example 1, except that the polyethylene resin solution extruded from the T-die was immersed in water held at 25 캜 for one minute instead of cooling with a cooling roll.

Comparative Example 5

50 parts by weight of the polyethylene composition used in Example 1 was fed into a twin-screw extruder, and 50 parts by weight of liquid paraffin was supplied from a side feeder of the twin-screw extruder and melted and kneaded to prepare a polyethylene resin solution in an extruder. However, it was impossible to extrude into a uniform film.

Comparative Example 6

A laminated porous film was obtained in the same manner as in Example 1 except that the temperature of the cooling water inside the cooling roll was maintained at 50 캜.

Comparative Example 7

1 mol of trimellitic anhydride (TMA), 0.8 mol of o-tolylidine diisocyanate (TODI) and 0.2 mol of 2,4-tolylene diisocyanate (TDI) were placed in a four-necked flask equipped with a thermometer, And 0.01 mol of potassium fluoride were added together with N-methyl-2-pyrrolidone so that the solid concentration became 14%, and the mixture was stirred at 100 ° C for 5 hours. Then, N-methyl- And diluted with water to synthesize a polyamideimide resin solution.

Polyamide-imide resin solution, alumina particles having an average particle diameter of 0.5 mu m and N-methyl-2-pyrrolidone were blended in a weight ratio of 13:47:40, respectively, and zirconium oxide beads (manufactured by Toray Industries, (Registered trademark) bead ", 0.5 mm in diameter) was placed in a polypropylene container and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Subsequently, the solution was filtered with a filter having a filtration limit of 5 탆 to obtain a coating liquid (h). A laminated porous film having a final thickness of 20.5 占 퐉 was obtained in the same manner as in Example 1 except that the coating liquid (a) was changed to the coating liquid (h).

The production conditions of Examples 1 to 19 and Comparative Examples 1 to 7 are shown in Table 1.

UHMWPE HDPE Suzy
density Cooling roll
Temperature Scrubbing solvent for molding Coating liquid Tensile strength of A-side binder (wt%) (wt%) (Parts by weight) (° C) (Number of blades) A side B side (N / mm2) Example 1 2 98 30 25 One a b 8 Example 2 10 90 30 25 One a b 8 Example 3 20 80 30 25 One a b 8 Example 4 30 70 30 25 One a b 8 Example 5 40 60 30 25 One a b 8 Example 6 2 98 30 25 2 a b 8 Example 7 2 98 30 25 3 a b 8 Example 8 2 98 30 25 One c b 20 Example 9 2 98 30 25 One d b 31 Example 10 2 98 30 25 One a e 8 Example 11 2 98 30 35 One a b 8 Example 12 2 98 30 25 One a b 8 Example 13 2 98 30 25 One a b 8 Example 14 2 98 30 25 One a b 8 Example 15 2 98 26 25 One a b 8 Example 16 2 98 35 25 One a b 8 Example 17 2 98 30 25 One f b 8 Example 18 2 98 30 25 One g b 8 Example 19 2 98 30 25 One a a 8 Comparative Example 1 2 98 30 25 0 a b 8 Comparative Example 2 0 100 30 25 One a b 8 Comparative Example 3 2 98 30 0 0 a b 8 Comparative Example 4 2 98 30 25 ℃
(Watering) - a b 8 Comparative Example 5 2 98 50 - - - - - Comparative Example 6 2 98 30 50 One a b 6 Comparative Example 7 2 98 30 25 One h b 2

The properties of the polyolefin porous film and the laminated porous film obtained in Examples 1 to 19 and Comparative Examples 1 to 7 are shown in Table 2.

All characteristics The thickness of the polyolefin porous film Air resistance of polyolefin porous membrane
(X) The durability of laminated porous membrane
(Y) Increase in speculative resistance
[(Y) - (X)] (탆) (sec / 100 ccAir) (sec / 10 < 0 > ccAir) (sec / 10 < 0 > ccAir) Example 1 16 240 290 50 Example 2 16 252 293 41 Example 3 16 260 298 38 Example 4 16 273 306 33 Example 5 16 95 136 41 Example 6 16 240 290 50 Example 7 16 240 292 52 Example 8 16 240 289 49 Example 9 16 240 290 50 Example 10 16 240 290 50 Example 11 16 240 334 94 Example 12 20 250 305 55 Example 13 12 170 219 49 Example 14 9 220 263 43 Example 15 16 228 271 43 Example 16 16 250 298 48 Example 17 16 245 295 50 Example 18 16 243 301 58 Example 19 16 240 290 50 Comparative Example 1 16 239 289 50 Comparative Example 2 16 238 283 45 Comparative Example 3 16 240 283 43 Comparative Example 4 16 241 301 60 Comparative Example 5 - - - - Comparative Example 6 16 241 295 54 Comparative Example 7 16 240 288 48 All characteristics Number of projections on A side The average height of the projection on the A side Number of projections on side B The average height of the projections on the B side A-side
0 ° peel strength B-side
0 ° peel strength My Friction (Pieces / cm ² ) (탆) (Pieces / cm ² ) (탆) (N / 15 mm) (N / 15 mm) Example 1 14 2.8 13 2.6 180 118 ○ Example 2 17 1.1 16 1.0 177 117 ○ Example 3 19 0.8 18 0.7 173 114 ○ Example 4 42 0.6 40 0.6 177 117 ○ Example 5 126 0.5 120 0.5 156 103 ○ Example 6 16 2.9 15 2.8 189 125 ○ Example 7 17 2.9 16 2.8 194 127 ○ Example 8 14 2.8 13 2.7 186 123 ○ Example 9 14 2.8 13 2.7 203 117 ○ Example 10 14 2.8 13 2.6 181 114 ○ Example 11 12 2.6 11 2.5 177 117 ○ Example 12 12 2.9 11 2.7 177 118 ○ Example 13 18 1.0 17 0.9 174 113 ○ Example 14 20 0.6 19 0.5 165 120 ○ Example 15 11 2.5 10 2.4 177 108 ○ Example 16 19 2.9 18 2.8 183 120 ○ Example 17 14 2.8 13 2.7 165 118 ○ Example 18 14 2.8 13 2.7 188 118 ○ Example 19 14 2.8 13 2.6 180 179 ○ Comparative Example 1 0 - 0 - 98 93 X Comparative Example 2 0 - 0 - 97 92 X Comparative Example 3 0 - 0 - 95 90 X Comparative Example 4 2 0.6 One 0.5 99 97 △ Comparative Example 5 - - - - - - - Comparative Example 6 0 - - - 95 90 X Comparative Example 7 14 2.8 13 2.6 99 118 △

1 laminated porous film
2 polyolefin porous film
3 modified porous layer
4 Double-sided adhesive tape
5 Aluminum plate
5 'aluminum plate
6 Crystalline nuclei of polyethylene
7 T Die
8 polyolefin resin solution
9 Cooling roll
9 'cooling roll
10 Doctor Blades
11 Gel form

Claims (8)

A projection of a polyolefin 5 ㎛≤W≤50 ㎛ (W is the size of the projections) and 0.5 ㎛≤H satisfy the (H is the height of the projections), per side on both sides 3 / cm ² or more to 200 / cm ² And a modified porous layer A laminated on one side of the porous polyolefin membrane A and the modified porous layer B on the opposite side of the polyolefin porous membrane with a film thickness of not more than 25 μm and at least the modified porous layer A has a tensile strength of 5 N / mm < ² > or more and inorganic particles. The laminated porous film according to claim 1, wherein the binder having a tensile strength of 5 N / mm ² or more is polyvinyl alcohol or acrylic resin. The laminated porous film according to claim 1 or 2, wherein the inorganic particles comprise at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate, mica and boehmite. The laminated porous film according to any one of claims 1 to 3, wherein the thickness of the polyolefin porous film is 20 占 퐉 or less. The laminated porous film according to any one of claims 1 to 3, wherein the thickness of the polyolefin porous film is 16 占 퐉 or less. The laminated porous film according to any one of claims 1 to 5, which is used as a battery separator. (a) a step of adding a molding solvent to a polyolefin resin and then melt-kneading to prepare a polyolefin resin solution
(b) a step of extruding the polyolefin resin solution from a T-die and cooling the polyolefin resin solution placed on both sides of the extruded polyolefin resin solution into a film with a cooling roll having a surface from which the polyolefin resin solution has been removed to form a gel-
(c) a step of stretching the gel-like molded product in the machine direction and the width direction to obtain a drawn product
(d) a step of removing the molding solvent from the drawn molded article and drying to obtain a porous molded article
(e) heat-treating the porous formed article to obtain a polyolefin porous film
(f) A laminate film is formed on at least one surface of the polyolefin porous film using a coating liquid containing a binder having a tensile strength of 5 N / mm ² or more, a solvent capable of dissolving or dispersing the binder, and inorganic particles, followed by drying Comprising the steps of:
A process for producing a multilayer porous film according to any one of claims 1 to 6 The method for producing a laminated porous film according to claim 7, wherein the means for removing the molding solvent in the step (b) is a doctor blade.

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