KR102131009B1 - Laminated porous film, and production method therefor - Google Patents

Abstract

[Problem] The laminated porous membrane of the present invention provides a laminated porous membrane suitable for high-speed processing and a laminated porous membrane used as a separator for batteries, which has a very high peel strength between the polyolefin porous membrane and the modified porous layer.
[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 A layered porous membrane in which a modified porous layer A and a modified porous layer B are stacked on one side of a polyolefin porous membrane having an irregular thickness of less than or equal to ² cm/cm ² and having a film thickness of 25 μm or less, wherein at least the modified porous layer A is A laminated porous membrane comprising a binder and inorganic particles having a tensile strength of 5 N/mm ² or more.

Description

Laminated porous membrane and manufacturing method therefor {LAMINATED POROUS FILM, AND PRODUCTION METHOD THEREFOR}

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

Microporous membranes made of thermoplastic resins are widely used as separators for materials, selective permeable membranes, and separators. For example, separators for batteries used in lithium ion secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, polymer batteries, separators for electric double layer capacitors, various filters such as reverse osmosis filtration membranes, ultrafiltration membranes, precision filtration membranes, moisture-permeable waterproof Medical materials, medical materials, and the like. In particular, as a separator for a lithium ion secondary battery, it has ion permeability by electrolytic impregnation, has excellent electrical insulation, and has a pore closing effect to suppress excessive heating by blocking a current at a temperature of about 120 to 150°C when the battery is abnormally heated. A porous membrane made of polyethylene is preferably used. However, when the temperature rise continues even after the pores are closed for any reason, there is a case where a breakage occurs due to shrinkage of the membrane. This phenomenon is not limited to a polyethylene microporous membrane, and even in the case of a microporous membrane using another thermoplastic resin, it cannot be avoided beyond the melting point of the resin constituting the porous membrane.

In particular, separators for lithium ion batteries are closely related to battery characteristics, battery productivity, and battery safety, and mechanical characteristics, heat resistance, permeability, dimensional stability, pore closing characteristics (shutdown characteristics), and melt rupture characteristics (meltdown characteristics) are required. . In addition, in order to improve the cycle characteristics of the battery, it is required to improve the adhesion between the separator and the electrode material or to improve the permeability of the electrolyte to improve productivity.

Therefore, studies have been made so far to laminate the modified porous layer on the polyolefin porous membrane. As the resin contained in the modified porous layer, polyamide-imide resin, polyimide resin, polyamide resin, and fluorine-based resin excellent in electrode adhesion, which have both heat resistance and electrolyte permeability, are preferably used. In addition, a water-soluble or water-dispersible binder capable of laminating a modified porous layer using a relatively simple washing and drying process is also widely used.

In addition, the modified porous layer referred to in the present invention refers to a layer containing a resin that imparts or improves at least one function such as heat resistance, adhesion to electrode materials, and electrolyte permeability.

In patent document 1, polyvinylidene fluoride is coated on a porous membrane made of polyethylene having a thickness of 9 µm, and a part of polyvinylidene fluoride penetrates into pores of a polyethylene porous membrane and exhibits an anchor effect, thereby making polyethylene. A composite porous membrane having a peel strength (T-type peel strength) of 1.0 to 5.3 N/25 mm at the interface between the porous membrane and the coating layer of polyvinylidene fluoride is disclosed.

In Patent Document 2, a porous membrane made of a self-crosslinking acrylic resin and plate-like boehmite is installed on a porous membrane made of corona discharge-treated polyethylene having a thickness of 16 µm, at 180° of a porous membrane made of polyethylene and a heat-resistant porous layer. Separators having a peel strength (T-type peel strength) of 1.1 to 3.0 N/10 mm are disclosed.

In Example 1 of Patent Document 3, a polyethylene resin solution composed of 47.5 parts by weight 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 composed of an antioxidant, and 50 parts by mass of liquid paraffin Was extruded at 200° C. in an extruder, and taken out with a cooling roll temperature controlled at 25° C. to obtain a gel-like molding, and then biaxially stretched to 7×6.4 times to obtain a porous polyolefin resin film. Subsequently, a multilayer porous membrane obtained by laminating a coating layer made of polyvinyl alcohol and alumina particles on the surface of the polyolefin resin porous membrane is disclosed.

In Example 6 of Patent Document 4, a polyethylene resin solution having a weight average molecular weight of 415 million and a weight average molecular weight of 560,000, a weight ratio of 30% by weight of a polyethylene composition and 70% by weight of a mixed solvent of liquid paraffin and decalin is 148°C in an extruder. Extruded by, and cooled in a water bath to obtain a gel-like molding, followed by biaxial stretching to 5.5×11.0 times to obtain a polyethylene porous membrane. Subsequently, a separator for a non-aqueous secondary battery obtained by further laminating a coating layer composed of meta-type wholly aromatic polyamide and alumina particles on the surface of this polyethylene porous membrane is disclosed.

In Example 1 of Patent Document 5, 47 parts by weight of polyethylene of a homopolymer having an Mv (viscosity average molecular weight) of 700,000, 46 parts by weight of polyethylene of a homopolymer having an Mv of 250,000, and 7 parts by weight of polypropylene of a homopolymer having an Mv of 400,000. Dry blending was performed using a tumbler blender. 1 mass% of pentaerythryl-tetrakis-[3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99 mass% of the obtained net polymer mixture, and again The polyethylene composition dry-blended using a tumbler blender is melt-kneaded, extruded and cast on a cooling roll controlled at a surface temperature of 25° C. to obtain a sheet-like polyolefin composition having a thickness of 2000 μm, and then biaxially to be 7×7 times. A multi-layered porous membrane obtained by coating an aqueous dispersion of calcined kaolin and latex on a polyethylene porous membrane obtained by stretching is disclosed.

Patent Document 1: Japanese Patent Application Publication No. 2012-043762 Patent Literature 2: Japanese 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 Patent Application Publication No. 2011-000832

In the future, in order to improve the battery capacity, it is necessary to increase the area that can be filled in the container in the separator as well as in the electrode sheet, and it is predicted that further thinning will proceed. However, as the porous membrane is thinned, it tends to deform in the planar direction, so that the modified porous layer laminated on the porous membrane of the thin film may be peeled off during processing, in a slit process, or in a battery assembly process, thereby making safety more difficult.

In addition, in order to cope with cost reduction, it is expected that the battery assembly process will be accelerated. High-speed processing also requires high adhesion to withstand high-speed processing between the polyolefin porous membrane and the modified porous layer in order to obtain a separator with less trouble such as peeling of the modified porous layer. However, if the resin contained in the modified porous layer is sufficiently penetrated into the polyolefin porous membrane in order to improve the adhesion, there is a problem that the increase in the air permeation resistance increases.

Regarding the demands for rapid cost reduction, high-capacity processing, and thinning of separators to be rapidly progressed in the future, in the prior art, since the modified porous layer is locally peeled during slit processing or battery assembly processing, it is more secure to secure safety. It is expected to be difficult. Particularly, when the porous polyolefin resin film becomes thinner, it becomes difficult to obtain a sufficient anchor effect for the polyolefin resin porous film of the modified porous layer, making it more difficult to secure safety.

The present inventors assume that the battery separator is further thinned and lowered in cost in the future, and the peel strength with the modified porous layer is very high, suitable for high-speed processing in the slit process or the battery assembly process, suitable for lamination of the modified porous layer It aims to provide the laminated porous membrane which has a polyolefin porous membrane and a modified porous layer, and the said laminated porous membrane used as a battery separator.

The peel strength in this specification means the 0° peel strength between the polyolefin porous membrane and the modified porous layer, and is a value measured by the following method (hereinafter, sometimes referred to as 0° 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 porous polyolefin film, 3 is a modified porous layer, 4 is a double-sided adhesive tape, 5 and 5'are aluminum plates, and the arrow in the drawing is a tensile direction. A double-sided 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 membrane) cut into a width of 50 mm x length of 100 mm was placed thereon. The surface of the polyolefin porous membrane 2 is pasted so that 40 mm overlaps at the end of one side of the 25 mm length of the aluminum plate 5, and the portion that comes out is cut off. Subsequently, a double-sided adhesive tape was attached to one side of the aluminum plate 5'having a length of 100 mm, a width of 15 mm, and a thickness of 0.5 mm, and 20 mm from the end of one side of the sample side of the 25 mm length of the aluminum plate 5 Glued so that they overlap. Thereafter, the aluminum plate 5 and the aluminum plate 5'are stretched in parallel in the opposite direction using a tensile tester at a tensile rate of 10 mm/min to measure the strength when the modified porous layer is peeled off. If the peel strength in this evaluation method is 130 N/15 mm or more, even if the thickness of the polyolefin porous film is equal to or less than 10 µm, the phenomenon that the layered modified porous layer peels off during transportation or processing hardly occurs.

The T-type peel strength, which has been conventionally used as a method for measuring peel strength, or peel strength at 180°, is peeling when the coating layer is detached from the polyethylene porous membrane at an angle perpendicular or perpendicular to the surface of the polyethylene porous membrane. Power. According to this evaluation method, the frictional resistance in a slit process or a battery assembly process can be evaluated more practically than these conventional evaluation methods.

In order to solve the above problems, the laminated porous membrane of the present invention has the following configuration. 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 Laminated porous membrane in which the modified porous layer A and the modified porous layer B are stacked on one side of the polyolefin porous membrane having an irregularly scattered film thickness of 25 µm or less, wherein at least the modified porous layer A has a tensile strength of 5 It is a laminated porous membrane containing N/mm ² or more binder and inorganic particles.

In the laminated porous membrane of the present invention, it is preferable that the binder having a tensile strength of 5 N/mm ² or more is polyvinyl alcohol or an acrylic resin.

The laminated porous membrane of the present invention preferably includes at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate, mica, and boehmite.

The laminated porous membrane of the present invention preferably has a polyolefin porous membrane having a thickness of 20 µm or less.

The laminated porous membrane of the present invention preferably has a polyolefin porous membrane having a thickness of 16 µm or less.

It is preferable to use the laminated porous membrane of this invention as a battery separator.

In order to solve the above problems, the method for producing a laminated porous membrane of the present invention has the following configuration. In other words,

(a) After adding a molding solvent to the polyolefin resin, melt-kneading to prepare a polyolefin resin solution

(b) Process of extruding the polyolefin resin solution in a T-type die and cooling it with a cooling roll having a surface on which the forming solvent is removed on both sides of the polyolefin resin solution extruded into a film to form a gel-like molded product.

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

(d) Process for removing the molding solvent from the stretched molding and drying to obtain a porous molding

(e) Process of heat-treating the porous molded product to obtain a polyolefin porous membrane

(f) forming a laminated film using at least one surface of the porous polyolefin membrane, a binder having a tensile strength of 5 N/mm ² or more, a solvent capable of dissolving or dispersing the binder, and a coating liquid containing inorganic particles, and drying the layered film. fair.

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

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

ADVANTAGE OF THE INVENTION According to this invention, the laminated porous membrane which has the polyolefin porous membrane which has excellent adhesiveness with a modified porous layer and a modified porous layer, and the separator for batteries which do not peel off even at high-speed conveyance using the laminated porous membrane can be obtained.

1 is a schematic view showing a method of measuring a 0° peel strength.
Fig. 2 is a schematic view showing a spherical crystal structure and crystal nuclei of polyethylene in a polyethylene porous membrane.
Fig. 3 is a photomicrograph of a ring-like trace originating in the Lunar New Year of polyethylene in a polyethylene porous membrane.
4 is a schematic view showing a process of extruding a polyethylene resin solution from a T-shaped die installed at the tip of an extruder and forming a gel-like molded product while cooling with a cooling roll.

The polyolefin porous membrane used in the present invention is obtained by adjusting a specific polyolefin resin solution and highly controlling the cooling rate of the polyolefin resin solution extruded via a T-die in an extruder, the polyolefin porous material having a suitable shape and number of protrusions on the surface. It's just. In addition, when a 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 membrane, very excellent peel strength can be obtained between the polyolefin porous membrane and the modified porous layer. .

The projection referred to in the present invention is essentially different from the projection obtained by adding, for example, inorganic particles to the polyolefin porous membrane. The protrusions obtained by adding inorganic particles to the polyolefin porous membrane are usually very small in height, and in order to form protrusions of 0.5 µm or more in height by the same means, it is necessary to add particles having a particle diameter equal to or greater than the thickness of the polyolefin porous membrane. . However, the addition of such particles decreases the strength of the polyolefin porous membrane, which is not practical.

The projection referred to in the present invention is a part of a polyolefin porous membrane grown by a suitable shape of ridge, and does not degrade the basic properties of the polyolefin porous membrane.

In addition, irregular scattering referred to in the present invention is clearly different from regular or periodic arrangements obtained by passing an embossing roll before or after the stretching step in the production of a polyolefin porous membrane. Press processing, such as embossing, is basically not preferable because compression is formed by compressing portions other than the projections, and air permeation resistance and electrolytic solution permeability are likely to decrease.

The projections of a suitable shape referred to in the present invention mean projections having a size of 5 µm or more and 50 µm or less, and a height of 0.5 µm or more. That is, 5 µm ≤ W ≤ 50 µm (W is the size of the protrusions) and 0.5 µm ≤ H (H is the height of the protrusions). These projections function as anchors when the modified porous layer is laminated on the porous membrane, and as a result, a laminated porous membrane having a large 0° peel strength can be obtained. Meanwhile, the upper limit of the height is not particularly limited, but about 3.0 µm is sufficient. The more the protrusions of sufficient height exist, the higher the 0° peel strength described above tends to be. That is, the 0° peel strength is influenced by the number of protrusions having a height of 0.5 µm or more and the average height thereof. The lower limit of the number of protrusions is preferably 3/cm ² , more preferably 5/cm ² , and even more preferably 10/cm ² . The upper limit of the number of protrusions is preferably 200 pieces/cm ² , more preferably 150 pieces/cm ² . The lower limit of the height of the projections is preferably 0.5 μm, more preferably 0.8 μm, even more preferably 1.0 μm.

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

The rising width of the air permeation resistance referred to in the present invention means the difference between the air permeation resistance of the polyolefin porous film and the air permeation resistance of the laminated porous film on which the modified porous layer is laminated, and is preferably 100 sec/100 ccAir or less.

The laminated porous membrane having the polyolefin porous membrane and the modified porous layer of the present invention and the laminated porous membrane used as a battery separator will be outlined, but of course not limited to this representative example.

1. Polyolefin porous membrane

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

The thickness of the polyolefin porous membrane of the present invention is preferably 25 µm or less, and a more preferable upper limit is 20 µm, even more preferably 16 µm. The lower limit is 7 μm, preferably 9 μm. If the thickness of the polyolefin porous membrane is within the above-mentioned preferred range, it is possible to retain practical membrane strength and pore closing function, and the area per unit volume of the battery case is not limited, which is suitable for high capacity of the battery to be advanced in the future.

The upper limit of the air 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 Preferred, more preferably 70 sec/100 ccAir, even more preferably 100 sec/100 ccAir.

The upper limit of the porosity of the polyolefin porous membrane is preferably 70%, more preferably 60%, even more preferably 55%. The lower limit is preferably 30%, more preferably 35%, even more preferably 40%. If the air permeation resistance and porosity are within the above-mentioned preferred range, sufficient battery charge/discharge characteristics, particularly ion permeability (charge/discharge operating voltage) and battery life (closely related to the amount of electrolyte retention), are sufficient to function as a battery. Can be sufficiently exhibited, and by obtaining sufficient mechanical strength and insulation, the possibility of a short circuit during charging and discharging is reduced.

The average pore diameter of the polyolefin porous membrane is preferably 0.01 to 1.0 µm, more preferably 0.05 to 0.5 µm, and even more preferably 0.1 to 0.3 µm because it greatly affects the pore closing performance. If the average pore diameter of the polyolefin porous membrane is in the above-mentioned preferred range, the peel strength of the 0° of the sufficient modified porous layer can be obtained due to the anchor effect of the functional resin, and when the modified porous layer is laminated, the air permeation resistance deteriorates significantly. In addition, the response to the temperature of the pore closing phenomenon is not slowed, and the pore closing temperature due to the heating rate does not move to the higher temperature side.

The polyolefin porous membrane needs to have a function of closing the pores in the event of an abnormal charge-discharge reaction. Therefore, the melting point (softening point) of the resin constituting is 70 to 150°C, more preferably 80 to 140°C, and even more preferably 100 to 130°C. If the melting point of the resin constituting the above-described preferred range, the pore closing function is expressed during normal use, the battery cannot be used, and the pore closing function is expressed during an abnormal reaction to ensure safety.

As the polyolefin resin constituting the polyolefin porous membrane, polyethylene or polypropylene is preferable. Further, it may be a single substance or a mixture of two or more different polyolefin resins, for example, a mixture of polyethylene and polypropylene, or may be a copolymer of different olefins. This is because, in addition to basic characteristics such as electrical insulation and ion permeability, it has a pore closing effect that suppresses excessive temperature by blocking current when the battery is abnormally heated. Among them, polyethylene is particularly preferable from the viewpoint of excellent pore closing performance.

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

Polyethylene may include ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, and low density polyethylene. Also, the polymerization catalyst is not particularly limited, and examples include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. These polyethylenes may be not only homopolymers of ethylene, but also copolymers containing small amounts of other α-olefins. As α-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, styrene, and the like are preferred. .

Polyethylene may be a single product, but is preferably a mixture of two or more polyethylenes. As the polyethylene mixture, a mixture containing two or more ultrahigh molecular weight polyethylenes 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. In addition, a mixture of two or more polyethylenes selected from the group consisting of ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene can also be used.

As the polyethylene mixture, a mixture of ultra high 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 to 5×10 ^{5 or} less is preferable. Mw of ultra high molecular weight polyethylene is preferably 5×10 ⁵ ~1×10 ⁷ , more preferably 1×10 ⁶ ~15×10 ⁶ , and even more preferably 1×10 ⁶ ~5×10 ⁶ . As polyethylene having a Mw of 1×10 ⁴ or more and less than 5×10 ⁵ , high-density polyethylene, medium-density polyethylene, and low-density polyethylene can all be used, but it is particularly preferable to use high-density polyethylene. As the polyethylene having a Mw of 1×10 ⁴ or more and less than 5×10 ^5, two or more types having different Mws may be used, or two or more types having different densities may be used. Melt extrusion can be facilitated by setting the upper limit of the Mw of the polyethylene mixture to 15×10 ⁶ or less.

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

If the content of the ultrahigh molecular weight polyethylene is within a preferred range, protrusions of sufficient height can be obtained. With this projection, when the modified porous layer is laminated, the projection functions as an anchor, and very strong peel resistance can be obtained against the force applied in parallel in the plane direction of the polyethylene porous membrane. In addition, sufficient tensile strength can be obtained even when the polyethylene porous membrane is thinned. It is preferable that the tensile strength is 100 MPa or more. No upper limit is specified.

The non-molecular weight distribution (Mw/Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polyethylene resin is preferably in the range of 5 to 200, more preferably in the range of 10 to 100. When the range of Mw/Mn is the above-mentioned preferred range, extrusion of the polyethylene resin solution is easy, and a sufficient number of projections can be obtained. In addition, sufficient mechanical strength can be obtained when the thickness of the polyethylene porous membrane is thinned. Mw/Mn is used as a measure of molecular weight distribution, that is, in the case of polyethylene composed of a single substance, the larger the value, the greater the width of the molecular weight distribution. The Mw/Mn of polyethylene composed of a single substance can be appropriately adjusted by multistage polymerization of polyethylene. Moreover, Mw/Mn of a polyethylene mixture can be appropriately adjusted by adjusting the molecular weight or mixing ratio of each component.

The polyethylene porous membrane may be a monolayer membrane, or may be a layered structure composed of two or more layers having different molecular weights or average pore diameters. In the case of a layer structure composed of two or more layers, it is preferable that the molecular weight and molecular weight distribution of the polyethylene resin of at least one outermost layer satisfy the above. If the polyethylene porous membrane is within a range that satisfies the above various characteristics, a manufacturing method according to the purpose can be freely selected.

2. Manufacturing method of polyolefin porous membrane

As a method for producing a polyolefin porous membrane, there are a foaming method, a phase separation method, a dissolving recrystallization method, a stretching opening method, a powder sintering method, etc. Among these, a phase separation method is preferable from the viewpoint of uniformity of fine pores and cost.

As a production method by a phase separation method, for example, polyethylene and a molding solvent are heat-melted and kneaded, and the obtained molten mixture is extruded and cooled in a T-type die to form a gel-like molded product, and at least uniaxially with respect to the obtained gel-like molded product. And a method of obtaining a porous membrane by stretching and removing the solvent for molding.

As a method for manufacturing a multilayer film composed of two or more layers, for example, each of the polyethylenes constituting the layers a and b is melt-kneaded with a molding solvent, and the obtained melt mixture is supplied to one T-type die in each extruder. The gel sheet constituting the components can be produced by any one of a method of co-extrusion and a method of superimposing and heat-sealing a gel sheet constituting each layer. The coextrusion method is more preferable because it is easy to obtain a high interlayer adhesive strength, and it is easy to form a communication hole between the layers, so it is easy to maintain high permeability and excellent productivity.

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

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

(a) After adding a molding solvent to the polyolefin resin, melt-kneading to prepare a polyolefin resin solution

(B) a process of extruding the polyethylene solution in a T-shaped die and cooling it with a cooling roll having a surface on which the molding solvent disposed on both sides of the polyolefin resin solution extruded into a film is removed to form a gel-like molding.

(c) a step of stretching the gel-like molding in the machine direction (MD) and in the width direction (TD) to obtain a stretched molding.

(d) Process for removing the molding solvent from the stretched molding and drying to obtain a porous molding

(e) Process of heat-treating the porous molded product to obtain a polyolefin porous membrane.

In addition, after the steps (a) to (e), a corona treatment step or the like may be provided as necessary.

For each step, an example in which a polyethylene resin is used as the polyolefin resin is described below.

(a) Process for preparing polyethylene resin solution

After adding a molding solvent to the polyethylene resin, melt-kneading to prepare a polyethylene resin solution.

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, and liquid paraffin, or mineral oil fractions corresponding to these boiling points may be mentioned, but the gel content is stable in solvent content. In order to obtain a molded product, a non-volatile solvent such as liquid paraffin is preferred. The heating and dissolving is performed by stirring or uniformly mixing in a extruder to a temperature at which the polyethylene composition is completely dissolved. The temperature varies depending on the polymer and solvent used when dissolved while stirring in an extruder or in a solvent, 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, with the total of the polyethylene resin and the solvent for molding as 100 parts by weight, preferably 28 to 35 parts by weight. When the concentration of the polyethylene resin is within the above-mentioned preferred range, the number of crystal nuclei for forming the projections is sufficiently formed to form a sufficient number of projections. In addition, swelling or neck in is suppressed at the exit of the T-type die when extruding the polyethylene resin solution, thereby maintaining the moldability and self-supporting properties of the extruded body.

Although it does not specifically limit as a melt-kneading method, Usually, it is performed by kneading uniformly in an extruder. This method is suitable for preparing a high concentration solution of polyethylene as described above. The melting temperature is preferably in the range of +10°C to +100°C of the melting point of polyethylene. In general, the melting temperature is preferably in the range of 160 to 230°C, more preferably in the range of 170 to 200°C. 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 kneading, or may be further melt-kneaded by adding it in the middle of the extruder during kneading. In melt kneading, it is preferable to add an antioxidant to prevent the oxidation of polyethylene.

(b) Process of forming a gel-like molding

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

Next, a gel-like molded article is formed by contacting both surfaces of a polyethylene resin solution extruded in a film form from a T-type die to a rotating pair of cooling rolls set at a surface temperature of 20°C to 40°C with a refrigerant. It is preferable to cool the extruded polyethylene resin solution to 25°C or lower.

In the present invention, it is important to control the cooling rate in the temperature region where crystallization is substantially effected in forming the projections.

About the mechanism in which the projection formed in the present invention is formed, the present inventors think as follows. The resin solution of the molten polyethylene resin and the molding solvent is extruded from the T-type die, and crystallization of the polyethylene starts, and the crystallization rate increases by rapid cooling by contact with a cooling roll. At this time, a spherical crystal having a symmetrical structure with crystal nuclei is formed (FIG. 2). When the heat transfer rate between the cooling roll surface and the molten polyethylene resin is relatively small, the crystallization rate is small, and as a result, it becomes a sphere having relatively small crystal nuclei. When the heat transfer rate is large, it is a crystal ball having relatively large crystal nuclei. The crystal nuclei of these Lunar New Years become projections during the subsequent process of TD (width direction) and/or MD (machine direction) stretching. In addition, the Chinese New Year appears as a ring-shaped trace on the surface of the polyethylene porous membrane (Fig. 3).

In the present invention, for example, the cooling rate in the temperature range where the surface of the polyethylene resin solution is substantially crystallized is 10° C./sec or more, and the extruded polyethylene resin solution is cooled to obtain a gel-like molding. The cooling rate is preferably 20° C./sec or more, more preferably 30° C./sec or more, even more preferably 50° C./sec or more. By performing such cooling, a structure in which the polyethylene phase is microphase separated by a solvent is fixed, and a sphere having a relatively large nucleus is formed on the surface of the gel-like molded article in contact with the cooling roll, to form a protrusion having a suitable shape after stretching. Can. The cooling rate on the cooling roll can be estimated by simulating from the thermal conductivity, thickness of the polyolefin resin solution, the molding solvent, and the heat transfer rate 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 the portion in contact with the polyethylene resin solution extruded from the T-shaped die. That is, as shown in Fig. 4, the polyethylene resin solution is cooled by being wound on a rotating cooling roll to form a gel-like molded article, and a molding solvent is attached to the surface of the cooling roll after being removed as a gel-like molded article. As it is, it comes into contact with the polyethylene resin solution again. However, if a lot of molding solvent adheres to the surface of the cooling roll, the cooling rate becomes slow due to the heat insulation effect, and projections are difficult to form. Therefore, it is important to remove the molding solvent as much as possible until the cooling roll comes into contact with the polyethylene resin solution again.

The method for removing the forming solvent from the cooling roll (also referred to as a removing means for forming solvent) is not particularly limited, but the doctor blade is placed on the cooling roll to be parallel to the width direction of the gel-formed article, and immediately after passing through the doctor blade. A method of scraping the solvent for molding onto the surface of the cooling roll until it contacts the gel-like molded article is preferably employed. Alternatively, it may be removed by means of blowing with compressed air, sucking, or combining these methods. Among them, a method of scraping using a doctor blade is preferable because it can be performed relatively easily, and it is more preferable to use a plurality of doctor blades than one in order to improve the removal efficiency of the molding solvent.

The material of the doctor blade is not particularly limited as long as it is resistant to the molding solvent, but is preferably made of resin or rubber rather than metal. This is because there is a fear of damaging the cooling roll in the case of metal. Examples of the resin doctor blade include polyester, polyacetal, and polyethylene.

Even if the temperature of the cooling roll is set to less than 20°C, this alone not only does not provide a sufficient cooling rate due to the heat insulating effect of the molding solvent, but also causes the surface of the gel-like molded article to become rough by attaching condensation to the cooling roll. It may occur.

The cooling rolls are two cooling rolls arranged on both sides of the polyethylene resin solution, and the diameter of each roll is preferably different. Moreover, the height of the installation position of the rotating shaft of two cooling rolls differs with respect to the height of the installation position of the discharge port of the polyethylene resin solution of a T-shaped die. It is preferable that the height of the installation position of the rotating shaft of the small diameter cooling roll is closer to the placement position of the polyethylene resin solution outlet of the T-type die than the large diameter cooling roll. This is to make the distance from the placement position of the discharge port of the polyethylene resin solution of the T-shaped die to the ground position of the polyethylene resin solution onto a large-diameter cooling roll as small as possible. For example, by arranging as shown in Fig. 4, it becomes possible to make the cooling rate in the temperature range in which the polyethylene resin solution extruded from the T-type die is substantially crystallized to 10°C/sec or more.

The thickness of the polyethylene resin solution during extrusion is preferably 1500 µm or less, more preferably 1000 µm or less, even more preferably 800 µm or less. When the thickness of the polyethylene resin solution during extrusion is within the above range, the cooling rate of the surface on the cooling roll side is not slowed, and it is preferable.

(c) Process to obtain stretched article

Next, this gel-like molding is stretched in the machine direction (MD) and the width direction (TD) to make a stretched molding. Stretching is performed by heating the gel-like molded product and performing a predetermined magnification in both directions of MD and TD by a conventional tenter method, a roll method, or a combination of these methods. The stretching may be either MD and TD simultaneous stretching (simultaneous biaxial stretching) or sequential stretching. In the sequential stretching, at least one of MD and TD can be stretched in multiple stages regardless of the order of MD and TD. The stretching temperature is below the melting point of the polyolefin composition + 10°C. The draw ratio varies depending on the thickness of the fabric, but it is preferably 9 times or more, and more preferably 16 to 400 times, with a surface magnification. In the case of MD and TD simultaneous stretching (simultaneous biaxial stretching), stretching at the same magnification of MD and TD such as 3×3, 5×5 and 7×7 is preferred. If the surface magnification is within the above-mentioned preferred range, stretching is sufficient to obtain a high elasticity, high strength porous membrane. Further, a desired air permeability resistance can be obtained by adjusting the stretching temperature.

(d) Process for obtaining porous molded article

The stretched molded article is treated with a cleaning solvent to remove residual molding solvent to obtain a porous membrane. 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, and fluorinated hydrocarbons such as ethane trifluoride, ethers such as diethyl ether and dioxane can be used. . These cleaning solvents are appropriately selected depending on the molding solvent used for dissolving polyethylene, and used alone or in combination. The cleaning method may be performed by a method of extracting by immersing in a cleaning solvent, a method of spraying the cleaning solvent, a method of sucking the cleaning solvent from the opposite side of the stretched article, or a combination thereof. The cleaning as described above is performed until the residual solvent in the stretched molding which is the stretched molding becomes less than 1% by weight. Thereafter, the cleaning solvent is dried, and the drying method of the cleaning solvent may be performed by a method such as heat drying and air drying.

(e) Process for obtaining polyethylene porous membrane

The porous molded product obtained by drying is heat-treated to obtain a polyethylene porous membrane. The heat treatment can adopt a tenter method, a roll method, a rolling method, or a free method. The heat treatment is preferably performed within a temperature range of 90 to 150°C. If the heat treatment temperature is within the above-mentioned preferred range, the heat shrinkage rate reduction and air permeation resistance of the obtained polyolefin porous membrane are sufficiently secured. The residence time of the heat treatment process is not particularly limited, but is usually performed in 1 second or more and 10 minutes or less, preferably in 3 seconds to 2 minutes or less.

In the heat treatment step, it is preferable to shrink in at least one of MD and TD while fixing both directions in the machine direction MD and the width direction TD from the viewpoint of heat shrinkage. The contraction rate of contracting in at least one of MD and TD is preferably 0.01 to 50%, more preferably 3 to 20%.

In addition, after the steps (a) to (e), a function imparting step such as a corona treatment step or a hydrophilization step may be provided as necessary.

3. Modified porous layer

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

The laminated porous membrane in the present invention is a laminated porous membrane in which a modified porous layer A and a modified porous layer B are laminated on one side of the polyolefin porous membrane.

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. When 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 modified on the side that is more strongly stressed by contact with a roll or bar in a subsequent process such as a slit process or a conveying process. Laminating the porous layer A is preferable because the effect of the present invention is exhibited.

The modified porous layer referred to in the present invention is to impart or improve at least one of functions such as heat resistance, adhesion to electrode materials, and electrolyte permeability. At least the modified porous layer A contains 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, a laminated porous membrane having excellent 0° peel strength can be obtained due to a synergistic effect of protrusions on the surface of the polyolefin porous membrane and the tensile strength of the binder. . Further, compared with the air permeability of the polyolefin porous membrane, the layered porous membrane of the present invention does not significantly increase the air permeability. This is because a sufficient 0° peel strength can be obtained without permeating many binders into the pores of the polyolefin porous membrane.

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 particularly determined, but 100 N/mm ² is sufficient. The tensile strength of the binder refers to a value measured by a method described later.

As a tensile strength of 5 N / mm ² or more binder used in the present invention, when the tensile strength of 5 N / mm ² or higher is not particularly limited, and examples thereof include polyvinyl alcohol, cellulose ether based resin, acrylic resin, etc. . Examples of the cellulose ether-based resins include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanoethyl cellulose, and oxyethyl cellulose, and acrylic resins are crosslinked acrylic resins. Is preferred. Further, commercially available aqueous solutions or aqueous dispersions can also be used. As commercially available products, for example, "POVACOAT" manufactured by Nisshin Kasei (registered trademark), "JURYMER" manufactured by Toagosei (registered trademark) AT-510, ET-410 , FC-60, SEK-301, Daisei Fine Chemical Co., Ltd. products UW-223SX, UW-550CS, DIC Co., Ltd. WE-301, EC-906EF, CG-8490, etc. . Among them, polyvinyl alcohol and acrylic resins having electrode adhesion, high affinity with a non-aqueous electrolyte, and also having adequate heat resistance and relatively high tensile strength are preferred.

The binder used for the modified porous layer B may be the same as the modified porous layer A, but may be different. For example, when providing excellent heat resistance, heat-resistant resins such as polyamideimide resin, polyimide resin, and polyamide resin are used, and when providing electrode adhesion, fluorine-based resins such as polyvinylidene fluoride and derivatives thereof Etc. can be used.

In order to reduce the curl of the laminated porous membrane, it is important to add inorganic particles to the coating liquid for forming the modified porous layer. The coating liquid in the present 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 to form 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, and more preferably 85% by weight. When the amount of the inorganic particles added is within the above-mentioned preferred range, the curl reduction effect is sufficient, and the ratio of the functional resin to the total volume of the modified porous layer is optimal, and at the same time, sufficient 0° 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, mica , Boehmite, and the like. In addition, heat-resistant crosslinked polymer particles may be added as necessary. Examples of the heat-resistant crosslinked polymer particles include crosslinked polystyrene particles, crosslinked acrylic resin particles, and crosslinked methyl methacrylate particles.

The shape of the inorganic particles may include a spherical shape, a substantially spherical shape, a plate shape, a needle shape, and a polyhedron shape, but is not particularly limited.

It is preferable that the average particle diameter of these inorganic particles is 1.5 times or more and 50 times or less of the average pore diameter of the polyolefin porous membrane. More preferably, it is 2.0 times or more and 20 times or less. When the average particle diameter of the particles is within the above-mentioned preferred range, the pores of the polyolefin porous membrane are not blocked while the heat-resistant resin and the particles are mixed, and as a result, the air permeation resistance is maintained, and the particles are eliminated in the battery assembly process to remove the battery. Avoid causing serious defects.

The binder has a role of at least bonding inorganic particles and a role of bonding a polyolefin porous membrane and a modified porous layer. Examples of the solvent include water, alcohols, acetone or n-methylpyrrolidone. By adding the inorganic particles to the coating liquid, effects such as preventing an internal short circuit (dendrite preventing effect) due to growth of dendritic crystals of the electrode inside the battery (dendrite preventing effect), reducing heat shrinkage, and imparting slippage can also be obtained.

The solid content concentration of the coating liquid is not particularly limited as long as it can be applied uniformly, but is preferably 50% by weight or more and 98% by weight or less, and more preferably 80% by weight or more and 95% by weight or less. When the solid content concentration of the coating solution is within the above-mentioned preferred range, it is possible to prevent the modified porous layer from weakening and obtain a sufficient peeling strength of 0° of the modified porous layer.

The thickness of the modified porous layer is preferably 1 to 5 μm, more preferably 1 to 4 μm, and even more preferably 1 to 3 μm. If the film thickness of the modified porous layer is within the above-mentioned preferred range, the laminated porous film obtained by laminating the modified porous layer can secure the breaking strength and insulation when melted and contracted at a melting point or higher, and also obtain a sufficient pore closing function. Adverse reactions can be prevented. In addition, it is possible to suppress the cold volume, which is suitable for high capacity of the battery. Furthermore, suppressing curls leads to productivity improvement in the battery assembly process. The film 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 μm or less, and even more preferably 0.3 μm or less.

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

The upper limit of the film thickness of the laminated porous membrane obtained by laminating the modified porous layer is preferably 25 µm, more preferably 20 µm. The lower limit is preferably 6 µm or more, and more preferably 7 µm or more. If the film thickness of the laminated porous film is within the above-mentioned preferred range, the laminated porous film obtained by laminating the modified porous layer can ensure sufficient mechanical strength and insulation. In addition, a decrease in capacity can be avoided by reducing the area of the electrode that can be filled in the container.

The air permeability of the laminated porous membrane is one of the most important properties, preferably 50 to 600 sec/100 ccAir, more preferably 100 to 500 sec/100 ccAir, and even more preferably 100 to 400 sec/100 ccAir. To achieve the desired air permeability, it can be obtained by adjusting the porosity of the modified porous layer and adjusting the degree of penetration of the binder into the polyolefin porous membrane. If the air permeation resistance of the laminated porous membrane is within the above-mentioned preferred range, sufficient insulating properties can be obtained, and clogging of foreign substances, short circuit, and rupture are prevented. In addition, by suppressing the film resistance, it is possible to obtain charge/discharge characteristics and life characteristics in a practically usable range.

4. Method of laminating a modified porous layer on a polyolefin porous membrane

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

As a method of laminating the modified porous layer on the polyolefin porous membrane, a known method can be used. Specifically, the coating solution can be obtained by coating the polyolefin porous film with a method described later so as to have a predetermined film thickness, and drying under conditions of a drying temperature of 40 to 80°C and a drying time of 5 seconds to 60 seconds. Further, a coating solution dissolved in a solvent that is miscible with water while the binder is melted is laminated on a predetermined polyolefin porous membrane using a coating method described later, and placed under a specific humidity environment to phase-separate the solvent for mixing the binder and water, It is also possible to use a method of solidifying the binder by adding it to a water bath (coagulation bath) again.

As a method of applying the coating liquid, for example, dipping method, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, Mayer bar coating method, pipe doctor Methods, blade coating methods, die coating methods, and the like, and these methods can be performed alone or in combination.

The laminated porous membrane of the present invention is preferably stored in a dry state, but when it is difficult to store in a completely dried state, it is preferable to perform a vacuum drying treatment at 100°C or lower immediately before use.

The laminated porous membrane of the present invention includes secondary batteries such as nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, lithium secondary batteries, lithium polymer secondary batteries, plastic film capacitors, ceramic capacitors, Although it can be used as a separator, such as an electric double layer capacitor, it is particularly preferable to use it as a separator of a lithium ion secondary battery. The lithium ion secondary battery will be described below as an example.

In the lithium ion secondary battery, the positive electrode and the negative electrode are stacked 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, the electrode structure (coin type) installed with the disc type anode and cathode facing each other (coin type), the electrode structure in which the plate type anode and the cathode are alternately stacked (stacked), and the electrode structure in which the belt type anode and the cathode are superimposed and wound (volume) Gray).

The positive electrode typically has a positive electrode active material layer including a current collector and a positive electrode active material capable of storing and releasing lithium ions formed on the surface. Examples of the positive electrode active material include a transition metal oxide, a composite oxide of lithium and a transition metal (lithium composite oxide), and inorganic compounds such as a transition metal sulfide. V, Mn, Fe, Co, Ni, etc. are mentioned as a transition metal. Preferred examples of the lithium composite oxide among the positive electrode active materials include lithium nickel oxide, lithium cobalt oxide, lithium manganate, and a layered lithium composite oxide based on an α-NaFeO ₂ structure.

The negative electrode has a negative electrode active material layer including a current collector and a negative electrode active material formed on its surface. Examples of the negative electrode active material include carbonaceous materials such as natural graphite, artificial graphite, coke, and carbon black. The electrolytic solution can be obtained by dissolving a lithium salt in an organic solvent. Lithium salts 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, LiAlC ₁₄ and the like. These may be used alone or in combination of two or more. Examples of the organic solvent include high boiling point and high dielectric constant organic solvents such as ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and γ-butyrolactone; tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane, and dimethyl carbonate , Low boiling point and low viscosity organic solvents such as diethyl carbonate. These may be used alone or in combination of two or more. In particular, since the organic solvent having a high dielectric constant has a high viscosity and the organic solvent having a low viscosity has a low dielectric constant, it is preferable to use a mixture of the two.

When assembling the battery, the separator of the present invention can be impregnated with an electrolyte to impart ion permeability to the separator. Typically, the impregnation treatment is performed by immersing the microporous membrane in an electrolyte at room temperature. For example, when assembling a cylindrical battery, first, a positive electrode sheet, a separator (composite porous membrane) and a negative electrode sheet are stacked in this order, and the stacked body is wound at one end to form a wound electrode element. Subsequently, this electrode element is inserted into a battery can, so as to impregnate the electrolyte solution, and a battery lid can be obtained by caulking the battery cover serving as the positive electrode terminal provided with a safety valve through a gasket again.

Example

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

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

The binder used in Examples and Comparative Examples was sufficiently dissolved or dispersed in a soluble solvent, and put into a dumbbell type for producing test piece No. 2 specified in JIS K7113 so that the film thickness after drying was about 100 µm and dried naturally at 25° C., Again, vacuum drying (vacuum 3 mmHg) was performed at 25° C. for 8 hours to sufficiently remove the solvent to provide a sample sheet obtained for tensile strength measurement. It measured under the following conditions using the tensile tester (Shimadzu Corporation, Autograph AGS-J load cell capacity 1 kN). The sample film and the measurement conditions are as follows, three measurements were performed, and the average value was taken as the tensile strength of the binder.

Interchuck distance: 40 mm

Test speed: 20 mm/min

Measurement environment: air 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 (confocal) microscope (Lasertec manufactured by HD100, Inc.) installed on an earthquake proofing table.

(order)

(1) A square border of 1 cm x 1 cm was drawn with an ultrafine oil pen on any one side (called A side) of the battery separators obtained in Examples and Comparative Examples.

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

(3) Using an objective lens with a magnification of 5x, a ring-like trace originating in the Lunar New Year shown in Fig. 3 is displayed on a monitor as a two-dimensional image (referred to as a REAL screen in this device), and the darkest color of the ring-like trace is darkened. The sample stage position was adjusted so that the portion was almost centered on the monitor screen. In the case of two consecutive ring-shaped traces, they were matched to the contact point. The object of the projection height measurement was that the long diameter of the ring-like traces originating from the above-mentioned polyethylene was determined to be 0.2 mm or more. The long diameter of the ring-shaped trace was read from the two-dimensional image by aligning the cursors on both ends of the ring in the long diameter direction.

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

(5) The measurement range in the height direction was set to 15 µm above and below with the reference height set at 0 µm. In addition, three-dimensional data was captured with a scan time of 120 seconds and a STEP movement distance of 0.1 µm/Step.

(6) After capturing the three-dimensional data, an image for data processing (referred to as a Z-picture in this apparatus) was displayed, and a smoothing process was performed (smoothing condition: filter size 3×3, matrix type SMOOTH3_0, recovery once). In addition, horizontal correction was performed on the horizontal correction screen as needed.

(7) A cursor was placed in the horizontal direction at the position (lightest part) passing through the highest projection in the data processing image, and the cross-sectional profile corresponding to the cursor was displayed on the cross-sectional profile image.

(8) In the cross-sectional profile image, two cursors were aligned to the inflection points of both sleeves of the projections in the vertical direction, and the distance between both cursors was taken as the size of the projections.

(9) In the cross-sectional profile image, align the two cursors in the horizontal direction to the vertex of the projection and the inflection point of both sleeves of the projection (if the heights of the inflection points of both sleeves of the projection are different, the lower side), the distance between the two cursors I made it high.

(10) The above operation was repeated in a square frame of 1 cm x 1 cm, the number of protrusions having a size of 5 µm or more and 50 µm or less, and a height of 0.5 µm or more and 3.0 µm or less was counted to obtain the number of protrusions on the A side per 1 cm ² . In addition, the average height of the projections was obtained to be the average projection height of the A-plane. The same operation was performed on the A side and the opposite side (referred to as B side) to obtain the number of protrusions on the B side and the average protrusion height.

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

In order to measure an arbitrary surface (for example, A surface), the modified porous layer on the opposite surface (B surface) was previously peeled off with an adhesive tape to expose one surface of the polyolefin porous film to provide a sample.

Fig. 1 schematically shows the 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, 5 and 5'are aluminum plates, and arrows in the drawing are tensile directions. A double-sided pressure-sensitive adhesive tape (manufactured by Nichiban Corporation, NW-K50) (4) of the same size was attached to an aluminum plate 5 having a size of 50 mm×25 mm and a thickness of 0.5 mm. The surface of the polyolefin porous membrane 2 of the sample 1 (battery separator) cut to a width of 50 mm x a length of 100 mm was pasted so that 40 mm overlapped at one end of the 25 mm length of the aluminum plate 5 , Cut out the part that came out. Subsequently, a double-sided adhesive tape was attached to one side of the aluminum plate 5'having a length of 100 mm, a width of 15 mm, and a thickness of 0.5 mm, and 20 mm from the end of one side of the sample side of the 25 mm length of the aluminum plate 5 Attached so that they overlap. Subsequently, the aluminum plate 5 and the aluminum plate 5'sandwiched with the sample were mounted on a tensile tester (manufactured by Shimadzu Corporation, Autograph AGS-J 1kN), and the aluminum plate 5 and aluminum plate ( Each of 5') was stretched in parallel in the opposite direction at a tensile rate of 10 mm/min to measure the strength when the modified porous layer was peeled off. This measurement was performed on any three points separated by 30 cm or more in the longitudinal direction, and the average value was taken as the peel strength of 0° of the modified porous layer on the A side. The peel strength of 0° of the modified porous layer was similarly determined for the B surface.

4. Film thickness

Contact type film thickness meter [膜厚計; It was calculated|required by averaging the measured value of 20 points using Mitutoyo Corporation, Lightmatic series318. The measurement was carried out under a condition of 0.01 N weighted using a cemented carbide measuring instrument Φ9.5 mm.

5. Average pore diameter

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

6. Speculation resistance (sec/100 ccAir)

Using a Gurley densometer B type manufactured by TESTER SANGYO, a polyolefin porous film or a laminated porous film was fixed to prevent wrinkles between the clamping plate and the adapter plate, and measured according to JIS P8117. The sample was set to 10 cm x 10 cm, and the measurement point was a total of 5 points at the center of the sample and 4 corners, and the average value was used as the speculation resistance. In addition, if the length of one side of the sample is less than 10 cm, the value measured at 5 points at 5 cm intervals may be used. The rising width of the speculative resistance was determined by the following equation.

Rise of speculation resistance = (Y)-(X) sec/100 ccAir

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

Air permeability of laminated porous membrane (Y) sec/100 ccAir

7. Porosity of porous polyolefin membrane

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

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

8. Friction resistance

Both ends were slit while winding the rolled laminated porous membrane obtained in Examples and Comparative Examples. The slit processing was performed under a condition of a speed of 20 m/min and a tension of 60 N/100 mm using a slitter (manufactured by NISHIMURA WORKS, WA177A type). During processing, two hard chrome plated rolls (all free rolls) were in contact with the coated surface. Subsequently, while rewinding the rolled laminated porous membrane after the slit processing, the peeling defects of the modified porous layer having a long diameter of 0.5 mm or more were counted using a magnifying glass with a scale of 10 times and a magnification with a magnification (PECA, SCALE LUPE×10). It evaluated by the following judgment criteria. The evaluation area was 100 mm in width and 500 m in length (if the width was less than 100 mm, the length was adjusted to make the same evaluation area).

Criteria

○ (very good): 5 or less

△ (good): 6 to 15

X (poor): 16 or more

Example 1

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 million and 98% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000 (0.375 parts by weight of antioxidant) The added polyethylene composition (melting point 135°C) was obtained. 30 parts by weight of this polyethylene composition was put into a twin screw extruder. From the side feeder of this twin-screw extruder, 70 parts by weight of liquid paraffin was supplied and melt-kneaded to prepare a polyethylene resin solution in the extruder. Subsequently, the polyethylene resin solution was extruded from a T-shaped die installed at the tip of the extruder to 190°C and an extrusion thickness of 825 µm, and the polyethylene resin solution extruded in the form of a film was placed on both sides thereof (see Fig. 4) and the cooling roll was rolled. A gel-like molded article was formed while drawing with two cooling rolls maintaining the internal cooling water temperature at 25°C. At this time, in each cooling roll, a doctor blade made of polyester is formed between a point where the gel-like molding is separated from the cooling roll and a point where the cooling roll rolls with the polyethylene resin solution extruded from the T-type die. The liquid paraffin adhered on the cooling roll was scraped out so as to be in contact with the cooling roll in parallel to the width direction of. Subsequently, while simultaneously adjusting the temperature of the gel-like molding to a desired air permeation resistance, simultaneous biaxial stretching was performed at 5×5 times to obtain a stretched molding. The obtained stretched molding was washed with methylene chloride to remove the remaining liquid paraffin, and dried to obtain a porous molding. Thereafter, the porous membrane was kept in the tenter, the width was reduced by 10% in the TD (width direction) direction, and heat treated for 3 seconds at 90 to give a thickness of 16 µm, a porosity of 45%, an average pore diameter of 0.15 µm, and a permeation resistance of 240. A polyethylene porous membrane of sec/100 ccAir was obtained.

(Combination of coating solution A)

Polyvinyl alcohol (average degree of polymerization 1700, saponification degree of 99% or more), alumina particles having an average particle diameter of 0.5 µm, and ion-exchanged water were mixed at a weight ratio of 6:54:40, respectively, and zirconium oxide beads (Toray (TORAY) ) With a plastic shaker (Toyo Seiki Seisaku-sho), put it in a polypropylene container with a "Toray Serum" (registered trademark) bead, 0.5 mm diameter] Disperse for 6 hours. Subsequently, it was filtered with a filter having a filtration limit of 5 μm to obtain a coating solution (a).

(Combination of coating liquid B)

1 mol of trimellitic anhydride (TMA), 0.8 mol of o-tolidine diisocyanate (TODI), 0.2 mol of 2, 4-tolylene diisocyanate (TDI) in a 4-neck flask equipped with a thermometer, cooling tube, and nitrogen gas introduction tube , Potassium fluoride 0.01 mol with N-methyl-2-pyrrolidone so that the solid content becomes 14%, and stirred at 100° C. for 5 hours, then N-methyl-2-pyrrolid so that the solid content becomes 14%. Dilution with money synthesized a polyamideimide resin solution. The logarithmic viscosity of the obtained polyamideimide resin was 1.35 dl/g, and the glass transition temperature was 320°C.

Polyamideimide resin solution, alumina particles having an average particle diameter of 0.5 µm, and N-methyl-2-pyrrolidone were mixed in a weight ratio of 26:34:40, respectively, and zirconium oxide beads [manufactured by Toray Industries, Ltd.," Toray Serum "(Registered trademark) beads, 0.5 mm in diameter] were placed in a polypropylene container and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Subsequently, it was filtered through a filter having a filtration limit of 5 μm to obtain a coating solution (b). After drying the coating liquid (a) on one side of the polyethylene porous membrane (referred to as the A side) by a gravure coating method, it was coated with a thickness of 2 μm, and dried by passing through a hot air drying furnace at 50° C. for 10 seconds. Subsequently, after drying on the opposite side (referred to as B side) and applying 2.5 µm in thickness, a humidity zone of 25°C and absolute humidity of 12 g/m ³ was passed for 5 seconds, and then N-methyl-2- It was immersed in an aqueous solution containing 5% by weight of pyrrolidone for 10 seconds. Then, after washing with pure water, drying was performed by passing through a hot-air drying furnace at 70° C. to obtain a laminated porous membrane having a final thickness of 20.5 μm.

Example 2

A laminated porous membrane was prepared in the same manner as in Example 1, except that the mixing ratio of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and high density polyethylene (HDPE) having a weight average molecular weight of 350,000 was changed to 10:90 (weight percent ratio). Got.

Example 3

A laminated porous membrane was prepared in the same manner as in Example 1, except that the mixing ratio of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and high density polyethylene (HDPE) having a weight average molecular weight of 350,000 was changed to 20:80 (weight percent ratio). Got.

Example 4

A laminated porous membrane was prepared in the same manner as in Example 1, except that the mixing ratio of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and high density polyethylene (HDPE) having a weight average molecular weight of 350,000 was changed to 30:70 (weight percent ratio). Got.

Example 5

A laminated porous membrane was prepared in the same manner as in Example 1, except that the mixing ratio of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and high density polyethylene (HDPE) having a weight average molecular weight of 350,000 was changed to 40:60 (weight percent ratio). Got.

Example 6

In both cooling rolls, a laminated porous membrane was obtained in the same manner as in Example 1 except that two doctor blades made of polyester were placed on the cooling roll at intervals of 20 mm.

Example 7

In both cooling rolls, a laminated porous membrane was obtained in the same manner as in Example 1 except that three doctor blades made of polyester were applied to the cooling rolls at intervals of 20 mm each.

Example 8

Aqueous acrylic polyol and water-dispersible polyisocyanate (curing agent), a two-liquid curable aqueous acrylic urethane resin (solid content concentration: 45% by mass), alumina particles having an average particle diameter of 0.5 µm, and ion-exchanged water are mixed at a weight ratio of 10:40:50, respectively. Then, place it in a polypropylene container with zirconium oxide beads (made by Toray Corporation, "Toray Serum" (registered trademark) beads, diameter of 0.5 mm) as a paint shaker (manufactured by Toyo Seiki Seisakusho, Ltd.) 6 Time was dispersed. Subsequently, it was filtered through a filter having a filtration limit of 5 μm to obtain a coating liquid (c). A modified porous layer was laminated on both sides in the same manner as in Example 1, except that the coating solution (a) was replaced with the coating solution (c) to obtain a laminated porous film having a final thickness of 20.5 µm.

Example 9

Copolymer of polyvinyl alcohol, acrylic acid, and methyl methacrylate [Nisshin Kasei Co., Ltd., "POVACOAT" (registered trademark)), alumina particles having an average particle diameter of 0.5 mu m, solvent (ion-exchanged water: ethanol = 70:30) 5:45:50 in a weight ratio of each, and put in a container made of polypropylene with a zirconium oxide bead [Toray Serum Co., Ltd., "Toray Serum" (trademark) beads, diameter 0.5 mm]. It was dispersed for 6 hours with Shiki Kaisha Toyo Seiki Seisakusho). Subsequently, it was filtered through a filter having a filtration limit of 5 μm to obtain a coating solution (d). The coating solution (a) was applied in the same manner as in Example 1 except that the coating solution (d) was changed, and a modified porous layer was laminated on both surfaces to obtain a laminated porous film having a final thickness of 20.5 μm.

Example 10

KF Polymer #1120 (Kureha Chemical Co., Ltd. product, polyvinylidene fluoride resin solution (melting point 175, 12% N-methylpyrrolidone solution)) and alumina particles having an average particle diameter of 0.5 μm, N -Methyl-2-pyrrolidone was blended in a weight ratio of 14:19:67, respectively, and polypropylene together with zirconium oxide beads (Toray Industries, Ltd., "Toray Serum" (trademark) beads, diameter 0.5 mm). It was put in my container and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Subsequently, the varnish (e) was combined by filtration with a filter having a filtration limit of 5 μm. The coating solution (b) was applied in the same manner as in Example 1 except that the coating solution (e) was changed, and a modified porous layer was laminated on both sides to obtain a laminated porous film having a final thickness of 20.5 µm.

Example 11

A laminated porous membrane was obtained in the same manner as in Example 1 except that the temperature of the internal cooling water in the cooling roll was maintained at 35°C.

Example 12

The laminated porous membrane having a final thickness of 24.5 µm was obtained in the same manner as in Example 1, except that a polyethylene porous membrane having a thickness of 20 µm was obtained by adjusting the extrusion amount of the polyethylene resin solution.

Example 13

The laminated porous membrane having a final thickness of 16.5 µm was obtained in the same manner as in Example 1, except that a polyethylene porous membrane having a thickness of 12 µm was obtained by adjusting the extrusion amount of the polyethylene resin solution.

Example 14

By adjusting the extrusion amount of the polyethylene resin solution to obtain a polyethylene porous membrane having a thickness of 9 µm, the same procedure as in Example 1 was carried out to obtain a laminated porous membrane having a final thickness of 13.5 µm.

Example 15

A laminated porous membrane was obtained in the same manner as in Example 1, except that 26 parts by weight of the polyethylene composition was put into a twin screw extruder, and 74 parts by weight of liquid paraffin was supplied from the side feeder of the twin screw extruder to melt-knead it.

Example 16

A laminated porous membrane was obtained in the same manner as in Example 1, except that 35 parts by weight of the polyethylene composition was put 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 and knead it.

Example 17

In the coating solution (a), the coating solution (f) in which the alumina particles were replaced with titanium oxide particles (average particle diameter of 0.38 µm) was combined. A laminated porous membrane 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), the coating liquid (g) in which the alumina particles were replaced with plate-like boehmite fine particles (average particle diameter of 1.0 µm) was combined. A laminated porous membrane 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 membrane was obtained in the same manner as in Example 1 except that both sides used the coating liquid (a).

Comparative Example 1

When the polyethylene resin solution extruded from the T-type die was cooled with two cooling rolls to obtain a gel-like molding, both cooling rolls did not use a doctor blade, except that the liquid paraffin attached on the cooling roll was not scraped off. In the same manner as in 1, a laminated porous membrane was obtained.

Comparative Example 2

Except for using a polyethylene composition (melting point 135° C.) in which a polyethylene composition is added with 100 parts by weight of a high-density polyethylene (HDPE) having a weight average molecular weight of 350,000 (Mw/Mn=16.0) and 0.375 parts by weight of an antioxidant. A laminated porous membrane was obtained in the same manner as in Example 1.

Comparative Example 3

A laminated porous membrane was obtained in the same manner as in Example 1 except that the internal cooling water temperature of the cooling roll was maintained at 0°C, and a doctor blade was not used.

Comparative Example 4

A laminated porous membrane was obtained in the same manner as in Example 1, except that the polyethylene resin solution extruded from the T-type die was immersed in water kept at 25°C for 1 minute instead of being cooled with a cooling roll.

Comparative Example 5

50 parts by weight of the polyethylene composition used in Example 1 was introduced into a twin-screw extruder, 50 parts by weight of liquid paraffin was supplied from a side feeder of a twin-screw extruder, and melt-kneaded to prepare a polyethylene resin solution in the extruder to extrude the T-die. Tried, but could not be extruded into a uniform film.

Comparative Example 6

A laminated porous membrane was obtained in the same manner as in Example 1 except that the internal cooling water temperature of the cooling roll was maintained at 50°C.

Comparative Example 7

1 mol of trimellitic anhydride (TMA), 0.8 mol of o-tolidine diisocyanate (TODI), 0.2 mol of 2, 4-tolylene diisocyanate (TDI) in a 4-neck flask equipped with a thermometer, cooling tube, and nitrogen gas introduction tube , Potassium fluoride 0.01 mol with N-methyl-2-pyrrolidone so that the solid content becomes 14%, and stirred at 100° C. for 5 hours, then N-methyl-2-pyrrolid so that the solid content becomes 14%. Dilution with money synthesized a polyamideimide resin solution.

The polyamideimide resin solution, alumina particles having an average particle diameter of 0.5 µm, and N-methyl-2-pyrrolidone were mixed in a weight ratio of 13:47:40, respectively, and zirconium oxide beads [manufactured by Toray Industries, Ltd.," Toray Serum (Registered trademark) beads", 0.5 mm in diameter] in a polypropylene container and dispersed with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.) for 6 hours. Subsequently, it was filtered through a filter having a filtration limit of 5 μm to obtain a coating solution (h). A laminated porous membrane having a final thickness of 20.5 µm was obtained in the same manner as in Example 1 except that the coating liquid (a) was replaced with the coating liquid (h).

Table 1 shows the production conditions of Examples 1 to 19 and Comparative Examples 1 to 7.

UHMWPE HDPE Suzy
density Cooling roll
Temperature Scraping solvent for molding Coating liquid Tensile strength of A side binder (wt%) (wt%) (Parts by weight) (℃) (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℃
(Bathing) - 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

Table 2 shows the properties of the polyolefin porous membrane and the laminated porous membrane obtained in Examples 1 to 19 and Comparative Examples 1 to 7.

Characteristics Polyolefin porous membrane thickness Air permeability of polyolefin porous membrane
(X) Air permeation resistance of laminated porous membrane
(Y) Rise of speculation resistance
[(Y)-(X)] (㎛) (sec/100 ccAir) (sec/10O ccAir) (sec/10O 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 Characteristics Number of protrusions on side A Average projection height of side A Number of projections on the B side Average projection height of B side A side
0° peel strength B side
0° peel strength Friction resistance (Pcs/cm ² ) (㎛) (Pcs/cm ² ) (㎛) (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 membrane
2 Polyolefin porous membrane
3 modified porous layer
4 double sided adhesive tape
5 aluminum plate
5'aluminum plate
6 Crystalline nucleus of polyethylene Lunar New Year
7 T type die
8 Polyolefin resin solution
9 cooling rolls
9'cooling roll
10 Doctor Blade
11 Gel-like molding

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 Laminated porous membrane in which the modified porous layer A and the modified porous layer B are stacked on one side of the polyolefin porous membrane having an irregularly scattered film thickness of 25 µm or less, wherein at least the modified porous layer A has a tensile strength of 5 N/mm ² or more binder and inorganic particles,
The polyolefin porous membrane contains 1 to 40% by weight of ultra-high molecular weight polyethylene having a weight average molecular weight of 5x10 ⁵ or more,
The size (W) of the protrusion is a distance between the inflection points of both sleeves of the protrusion in the cross-sectional profile image of the protrusion, the laminated porous membrane. The laminated porous membrane according to claim 1, wherein the binder having a tensile strength of 5 N/mm ² or more is polyvinyl alcohol or an acrylic resin. The laminated porous membrane according to claim 1, wherein the inorganic particles include at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate, mica, and boehmite. The laminated porous membrane according to claim 1, wherein the porous polyolefin membrane has a thickness of 20 µm or less. The laminated porous membrane according to claim 4, wherein the porous polyolefin membrane has a thickness of 16 µm or less. The laminated porous membrane according to claim 1, which is used as a battery separator. (a) After adding a molding solvent to the polyolefin resin, melt-kneading to prepare a polyolefin resin solution
(b) process of extruding the polyolefin resin solution in a T-type die and cooling it with a cooling roll having a surface on which the polyolefin resin solution is disposed on both sides of the polyolefin resin solution extruded into a film to form a gel-like molding.
(c) a step of stretching the gel-like molded product in a machine direction and a width direction to obtain a stretched product.
(d) Process for removing the molding solvent from the stretched molding and drying to obtain a porous molding
(e) Process of heat-treating the porous molded product to obtain a polyolefin porous membrane
(f) forming a laminated film using at least one surface of the porous polyolefin membrane, a binder having a tensile strength of 5 N/mm ² or more, a solvent capable of dissolving or dispersing the binder, and a coating liquid containing inorganic particles, and drying the layered film. Including the process,
The internal cooling water temperature of the cooling roll has a range of 20 ℃ to 40 ℃
The manufacturing method of the laminated porous membrane as described in any one of Claims 1-6. The method for producing a laminated porous membrane according to claim 7, wherein the removing means for the molding solvent in the step (b) is a doctor blade.

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