KR102137377B1 - Battery separator and production method therefor - Google Patents

Abstract

The present invention assumes the case where the battery separator is gradually thinned and lowered in cost in the future, the peel strength with the modified porous layer is very high, suitable for high-speed processing in a slit process or a battery assembly process, excellent shutdown characteristics, lithium A battery separator suitable for an ion battery is provided. The present invention is a separator for a battery having a laminated polyethylene microporous membrane in which at least two layers of polyethylene microporous membranes are laminated and a modified porous layer present on at least one surface thereof, wherein the laminated polyethylene microporous membrane has a shutdown temperature of 128 to 135°C, The rate of increase in the air permeation resistance at 30°C to 105°C in terms of thickness of 20 μm is less than 1.5 sec/100 ccAir/°C, and at least 3 pieces/cm ² or more and 200 pieces/cm ² or less polyethylene The protrusions formed irregularly, and the protrusions satisfy 0.5 μm ≤ H (H is the height of the protrusions) and 5 μm ≤ W ≤ 50 μm (W is the size of the protrusions), and the modified porous layer is the laminated polyethylene fine A battery separator comprising a binder and inorganic particles having a tensile strength of 5 N/mm ² or more, which are laminated on a surface having a projection of a porous membrane.

Description

Battery separator and manufacturing method therefor{BATTERY SEPARATOR AND PRODUCTION METHOD THEREFOR}

The present invention relates to a separator for a battery having at least a laminated polyethylene microporous membrane and a modified porous layer suitable for lamination of a modified porous layer. It is a battery separator useful as a separator for a lithium ion battery.

Thermoplastic resin microporous membranes are widely used as separators and filters. Examples of the separator include a lithium ion secondary battery, a nickel-hydrogen battery, a nickel-cadmium battery, a battery separator used in a polymer battery, an electric double layer capacitor separator, and a reverse osmosis filtration membrane, an ultrafiltration membrane, and a precision filtration membrane as filters. Can. It is also used for moisture-permeable, waterproof medical and medical materials. Particularly, as a separator for a lithium ion secondary battery, it has ion permeability by electrolytic solution impregnation, excellent electrical insulation, electrolyte resistance, and oxidation resistance. When the battery is heated up abnormally, the ion permeability is blocked at a temperature of about 120 to 150°C, resulting in excessive temperature increase. A microporous membrane made of polyethylene, which also has a hole-blocking effect that suppresses it, is preferably used. However, when the temperature rise continues even after the hole is closed for some reason, there is a case that a film is broken due to a decrease in the viscosity of the polyethylene constituting the film or shrinkage of the film. This phenomenon is not limited to polyethylene, and even when another thermoplastic resin is used, it cannot be avoided beyond the melting point of the resin constituting the microporous membrane.

The separator for a lithium ion battery is related to battery characteristics, battery productivity, and battery safety, and mechanical characteristics, heat resistance, permeability, dimensional stability, hole occlusion characteristics (shutdown characteristics), and melt rupture characteristics (meltdown characteristics) are required. Moreover, in order to improve the cycle characteristics of the battery, it is required to improve the adhesion to the electrode material, and to improve the permeability of the electrolyte to improve productivity.

Therefore, it has been studied to stack various modified porous layers on the microporous membrane. As the modified porous layer, polyamideimide resin, polyimide resin, polyamide resin, and/or fluorine-based resin having excellent 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 and easy 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.

Moreover, in order to improve the battery capacity, the battery separator needs to increase the area that can be filled in the container, and it is predicted that thinning will proceed. However, since the microporous membrane tends to be deformed in the planar direction when the thinning progresses, the separator for a battery in which the modified porous layer is laminated on the microporous membrane may be peeled off during processing or in a slit process or a battery assembly process, It becomes more difficult to ensure safety.

In addition, in order to cope with the reduction in cost, it is expected that the speed of the battery assembly process will proceed. Even in such high-speed processing, high adhesion between the microporous membrane and the modified porous layer is required, which has less trouble such as peeling of the modified porous layer. However, in order to improve the adhesion, if the resin contained in the modified porous layer is sufficiently penetrated into the polyethylene microporous membrane, there is a problem that the increase in the air permeation resistance increases.

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

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

In Example 1 of Patent Document 3, a polyethylene resin solution comprising 47.5 parts by weight of polyethylene with a viscosity average molecular weight of 200,000, 2.5 parts by mass of polypropylene with a viscosity average molecular weight of 400,000, and 50 parts by mass of a composition composed of an antioxidant and 50 parts by mass of liquid paraffin. Extruded from the extruder at 200°C, and taken out with a cooling roll temperature-controlled to 25°C to obtain a gel-like molded product, and then biaxially stretched to 7x6.4 times to obtain a porous polyethylene resin film. A laminated microporous membrane obtained by laminating a coating layer made of polyvinyl alcohol and alumina particles on the surface of this polyethylene resin microporous membrane is disclosed.

In Example 6 of Patent Document 4, a polyethylene resin solution of 30% by mass of a polyethylene composition with a weight average molecular weight of 4.15 million, a weight average molecular weight of 560,000, and a weight ratio of 1:9 and 70% by mass of a mixed solvent of liquid paraffin and decalin is 148°C from an extruder. Extruded from, cooled in a water bath to obtain a gel-like molding, and then biaxially stretched to be 5.5×11.0 times to obtain a polyethylene microporous membrane. Disclosed is a separator for a non-aqueous secondary battery obtained by laminating a coating layer composed of meta-type wholly aromatic polyamide and alumina particles on the surface of this polyethylene microporous membrane.

In Example 1 of Patent Document 5, 47 parts by mass of polyethylene, which is a homopolymer of viscosity average molecular weight of 700,000, 46 parts by mass of polyethylene, which is a homopolymer of viscosity average molecular weight of 250,000, and 7 parts by mass of polypropylene, which is a homopolymer of Mv 40, are used as tumble blenders. And dry blended. 1 mass% of pentaerythritol-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 polyethylene composition having a thickness of 2000 μm, and then biaxially stretched to be 7×7 times. Laminated porous membranes obtained by coating an aqueous dispersion of calcined kaolin and latex on a polyethylene microporous membrane obtained by performing the above are disclosed.

Patent Document 6 discloses a separator for a lithium ion secondary battery in which a ceramic layer is laminated on a porous resin substrate having a porous polyethylene layer as an inner layer and a porous polypropylene layer as an outer layer.

Patent Document 7 discloses a technique for producing a microporous membrane by stretching a laminate having a layer to which a low-melting-point resin is added and a layer not including it.

However, with respect to the demand for high-speed processing due to low cost and thinning of the separator due to high capacity, which will be rapidly progressed in the future, these conventional techniques will secure the safety because the modified porous layer will be peeled locally during slit processing or battery assembly processing. It is expected to be difficult to do. In particular, when the polyethylene microporous membrane serving as a base material becomes thinner, it becomes difficult to obtain a sufficient anchor effect for the polyethylene microporous membrane of the modified porous layer, and thus it becomes more difficult to ensure safety.

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 Patent Document 6: Japanese Patent Publication No. 2011-071009 Patent Document 7: Japanese Publication Patent Publication No. 2012-521914

The present invention assumes a case where the thinning of the battery separator and the high-speed processing are progressing in the future, and has a high peel strength between the modified porous layer and the laminated polyethylene microporous membrane, and is suitable for high-speed processing in a slit process or a battery assembly process. It is to provide a separator for batteries in which a modified porous layer is laminated on a laminated polyethylene microporous membrane suitable for lamination of porous layers.

The peel strength between the laminated polyethylene microporous membrane and the modified porous layer in the separator referred to in this specification is a value measured by the following method (hereinafter sometimes referred to as 0° peel strength).

Fig. 1 schematically shows a side surface state of a laminated sample of a laminated polyethylene microporous membrane and a modified porous layer in a stretched state by a tensile tester (not shown). 1 is a laminated sample, 2 is a laminated polyethylene microporous membrane, 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 the tensile direction. A laminated polyethylene microporous membrane of a sample (1) with a double-sided adhesive tape (4) of the same size attached to an aluminum plate (5) having a size of 50 mm x 25 mm and a thickness of 0.5 mm, and cut thereon to a width of 50 mm x 100 mm in length. The surface of (2) is attached so that 40 mm overlaps at the end of one side of the 25 mm length of the aluminum plate 5, and the protruding portion is cut 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 Glued so that they overlap. Thereafter, the aluminum plate 5 and the aluminum plate 5'are pulled at a tensile speed of 10 mm/min using a tensile tester in opposite directions in parallel 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 laminated polyethylene microporous membrane is, for example, 10 μm or less, the phenomenon that the laminated modified porous layer peels off during transportation or processing is It rarely happens.

The T-type peel strength conventionally used as a method for measuring the peel strength or the peel strength at 180° is the peel force when the coating layer is peeled off at an angle perpendicular or perpendicular to the surface of the battery separator. 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 battery separator of the present invention has the following configuration.

In other words,

A separator for batteries having a laminated polyethylene microporous membrane and a modified porous layer present on at least one surface thereof, wherein the laminated polyethylene microporous membrane is a porous laminate comprising at least A and B layers, and has a shutdown temperature of 128 to 135°C. and Fig rate of 1.5 dumping resistance at 30 ℃ to 105 ℃ per 20 ㎛ thickness sec / 100 ccAir / ℃ less, and at least one surface in contact with the outside world (外界) of the side 3 / cm ² or more to 200 / cm ² The protrusions made of polyethylene below are irregular, and the protrusions satisfy 0.5 μm ≤ H (H is the height of the protrusions) and 5 μm ≤ W ≤ 50 μm (W is the size of the protrusions), and the modified porous layer is It is a separator for batteries comprising a binder and inorganic particles having a tensile strength of 5 N/mm ² or more while being laminated on a surface having a projection of the laminated polyethylene microporous membrane.

In the battery separator of the present invention, it is preferable that the laminated polyethylene microporous membrane has a three-layer structure of A layer/B layer/A layer.

Here, the surface in contact with the external system means at least one surface of each layer constituting the laminated polyolefin microporous membrane facing the other side (interface side), but not the interface side. .

In the separator for a battery of the present invention, it is preferable that the B layer contains a low melting point resin having a melt flow rate of 25 to 150 g/10 min and a melting point of 120°C or higher and less than 130°C.

In the separator for a battery of the present invention, it is preferable that the low-melting point resin is a low-density polyethylene or a linear low-density polyethylene ethylene/α-olefin copolymer.

It is preferable that the content of the low-melting-point resin in the said B layer of the battery separator of this invention is 20 mass% or more and 35 mass% or less with the whole polyethylene resin of layer B being 100 mass %.

It is preferable that the thickness of the said B layer is 3 micrometers or more and 15 micrometers or less in the battery separator of this invention.

In the separator for a battery of the present invention, it is preferable that the binder is polyvinyl alcohol or an acrylic resin.

The separator for a battery of the present invention preferably contains at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate, and boehmite.

In order to solve the above problems, the method for manufacturing the battery separator of the present invention has the following configuration. In other words,

(a) After adding a molding solvent to the polyethylene resin constituting the layer A, melt-kneading to prepare a polyethylene resin solution A

(b) After adding a low-melting-point resin and a molding solvent to the polyethylene resin constituting the layer B, melt-kneading to prepare a polyethylene resin solution B

(c) The polyethylene resin solutions A and B obtained in steps (a) and (b) are extruded from the die, and at least one of them is a cooling roll having a surface on which the molding solvent is removed by means of removing the molding solvent. Cooling to form a layered gel-like molding

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

(e) a step of extracting and removing the solvent for forming the laminate from the layered stretched molded product and drying it to obtain a laminated porous molded product.

(f) Process of heat-treating a laminated porous molded product to obtain a laminated polyethylene microporous membrane.

(g) On the surface of the laminated polyethylene microporous membrane that the cooling roll was in contact with, the laminated film was coated with a coating solution containing a binder having a tensile strength of 5 N/mm ² or more, an inorganic particle, and a solvent capable of dissolving or dispersing the binder. The manufacturing method of the battery separator which includes the process of forming and drying.

In the manufacturing method of the battery separator of the present invention, it is preferable that the means for removing the molding solvent in the step (c) is a means for scraping out using a doctor blade.

ADVANTAGE OF THE INVENTION According to this invention, the separator for batteries which does not generate|occur|produce peeling of a modified porous layer even in high-speed conveyance which laminate|stacks a modified porous layer on the laminated polyethylene microporous membrane which has excellent adhesiveness with a modified porous layer can be obtained.

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

The laminated polyethylene microporous membrane used in the present invention has a suitable shape and number of projections on the surface by adjusting a specific polyethylene resin solution and controlling the cooling rate of the extruded polyethylene resin solution via a die from the extruder. The present invention provides a very good peel strength between the laminated polyethylene microporous membrane and the modified porous layer when the modified porous layer comprising inorganic particles and a binder having a tensile strength of 5 N/mm ² or more is laminated to the laminated polyethylene microporous membrane. Can be obtained.

The projections referred to in the present invention are essentially different from projections obtained by adding, for example, inorganic particles to a laminated polyethylene microporous membrane. The projections obtained by adding inorganic particles to the layered polyethylene microporous membrane are usually very small in height, and if it is desired to form projections of 0.5 µm or more in height by the same means, particles having a particle diameter equal to or greater than the thickness of the layered polyethylene microporous membrane are used. Addition becomes necessary. However, the addition of such particles decreases the strength of the laminated polyethylene microporous membrane, which is not realistic.

The projection referred to in the present invention means that a part of the surface layer of the laminated polyethylene microporous membrane is grown with an appropriately shaped bump, and does not degrade the basic properties of the laminated polyethylene microporous membrane.

Irregularly interspersed projections referred to in the present invention are clearly different from regular or periodic projections obtained by passing an embossing roll before or after the stretching step in the production of a laminated polyethylene microporous membrane. Do. Press processing, such as embossing, is basically not preferable since it forms protrusions by compression, and air permeation resistance and electrolytic solution permeability are easily reduced.

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). Such a projection functions as an anchor when laminating a modified porous layer on a laminated polyethylene microporous membrane, and as a result, a battery separator having a large 0° peel strength as described above is obtained. Meanwhile, the upper limit of the height is not particularly limited, but about 3.0 µm is sufficient. The more protrusions of sufficient height, the higher the 0° peel strength 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 , 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. On the other hand, the size and height of the projection in the present invention refers 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 laminated polyethylene microporous membrane and the air permeation resistance between the battery separator, and preferably 90 seconds/100 ccAir or less, more preferably 80 ccAir, more More preferably 50 ccAir.

The outline of the laminated polyethylene microporous membrane, the modified porous layer, and the battery separator of the present invention will be described, but of course not limited to this representative example.

First, the laminated polyethylene microporous membrane used in the present invention will be described.

The upper limit of the thickness of the laminated polyethylene microporous membrane used in the present invention is preferably 25 µm, more preferably 20 µm, even more preferably 16 µm. The lower limit is preferably 7 μm, and more preferably 9 μm. If the thickness of the layered polyethylene microporous membrane is in the above-mentioned preferred range, it is possible to retain practical film strength and hole blocking function, and the area per unit volume of the battery case is not limited, and is suitable for high capacity of the battery to be advanced in the future.

The shutdown temperature of the laminated polyethylene microporous membrane is preferably 128°C or higher and less than 135°C. The upper limit is more preferably less than 133°C, even more preferably less than 130°C. When the shutdown temperature is less than 135°C, pores are quickly blocked by heat generation in the event of an abnormality of the battery, and the battery reaction is stopped, so that the safety of the battery increases.

The upper limit of the air permeation resistance of the laminated polyethylene microporous 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 preferably 50 sec/100 ccAir. And more preferably 70 sec/100 ccAir, even more preferably 100 sec/100 ccAir.

The rate of increase in the air permeation resistance of the laminated polyethylene microporous membrane per 20 μm at 30°C to 105°C is preferably 1.5 sec/100 ccAir/°C or less, more preferably 1.2 sec/100 ccAir/°C or less, even more preferably It is 1.0 sec/100 ccAir/℃ or less. When the rate of increase in air permeability is 1.5 sec/100 ccAir/°C or less, sufficient ion permeability can be ensured even when heat is applied during coating or battery manufacturing.

The upper limit of the porosity of the laminated polyethylene microporous 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 and discharge characteristics, particularly ion permeability (charge/discharge operating voltage) and battery life (closely related to the amount of electrolyte), function as a battery. Exerts enough. In addition, since sufficient mechanical strength and insulating properties are obtained, the possibility of a short circuit occurring during charging and discharging is lowered.

Since the average pore diameter of the layered polyethylene microporous membrane greatly affects the hole occlusion performance, it 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. If the average pore diameter of the laminated polyethylene microporous membrane is in the above-mentioned preferred range, the peel strength of 0° of the sufficient modified porous layer is obtained by the anchor effect of the functional resin, and the air permeation resistance is large when laminating the modified porous layer. It does not deteriorate, and the response to the temperature of the hole occlusion phenomenon is not slowed down, and the hole occlusion temperature according to the heating rate does not move to the higher temperature side.

Hereinafter, the polyethylene resin used in the present invention will be described in detail.

[1] Polyethylene resin in the first layer (layer A)

The layer A of the present invention is a microporous membrane composed mainly of polyethylene. In order to improve the permeability and puncture strength, the content of polyethylene is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass of the entire resin. %to be.

The kinds of polyethylene high density, such as density exceeds 0.94 g / cm ³ of polyethylene, the density of a density in the range of 0.93 ~ 0.94 g / cm ³ of polyethylene and a density of 0.93 g / cm low density polyethylene, ultra high molecular weight polyethylene than ³ , Linear low-density polyethylene, and the like. From the viewpoint of strength, it is preferable to contain high density polyethylene and ultra high molecular weight polyethylene.

The ultra high molecular weight polyethylene may be a homopolymer of ethylene, as well as a copolymer containing a small amount of other α-olefins. Examples of α-olefins include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, and styrene. In the case of the laminated microporous membrane, it is difficult to control physical property non-uniformity in the width direction due to the difference in viscosity of each layer, especially when manufactured by coextrusion, but by using ultra high molecular weight polyethylene in the A layer, the molecular network of the entire membrane is used. Since it becomes hard, non-uniform deformation is unlikely to occur, and a microporous membrane excellent in uniformity of physical properties can be obtained.

The weight average molecular weight of the high-density polyethylene (hereinafter referred to as Mw) is preferably 1×10 ⁵ or more, and more preferably 2×10 ⁵ or more. As for the upper limit, Mw is preferably 8×10 ⁵ , more preferably Mw is 7×10 ⁵ . When Mw is in the above range, the film-forming stability and finally the protruding strength can be achieved.

It is preferable that Mw of ultra high molecular weight polyethylene is 1×10 ⁶ or more and less than 4×10 ⁶ . By using ultra-high molecular weight polyethylene having a Mw of 1×10 ⁶ or more and less than 4×10 ⁶ , holes and fibrils can be refined, and it becomes possible to increase the stiffness. Moreover, when Mw is 4x10<^6> or more, since the viscosity of a melt is too high, a defect may arise in a film forming process, such as being unable to extrude a resin from a die (die). Moreover, in this invention, when the viscosity difference with the B layer mentioned later becomes too high, it may be impossible to extrude each layer uniformly, especially in lamination by a co-extrusion method.

The content of the ultra high molecular weight polyethylene is 100% by mass of the entire polyethylene resin in the layer A, and the lower limit is preferably 15% by mass, more preferably 18% by mass. The upper limit is preferably 45% by mass, more preferably 40% by mass. If it is within this range, it is easy to obtain a balance between the projecting strength and the air permeation resistance, and a microporous membrane with little variation in air permeation resistance can be obtained. If the content of ultra high molecular weight polyethylene is within a preferred range, protrusions of sufficient height are obtained. When the modified porous layer is stacked by these projections, the projections function as anchors, and it is possible to obtain very strong peel resistance against the force applied in parallel in the plane direction of the laminated polyethylene microporous membrane. Further, even when the thickness of the laminated polyethylene microporous membrane is thinned, sufficient tensile strength can be obtained. The tensile strength is preferably 100 MPa or more. No upper limit is specified.

The layer A contains substantially no low melting point resin. The phrase "substantially does not contain a low-melting point resin" means that the fraction of the eluting component at 90°C or lower extracted by cross fractionation chromatography or the like is preferably 5.0% by mass or less, more preferably It means that it is 2.5 mass% or less. This is because, even if a low-melting point resin is not intentionally added, since the polymer has a distribution in molecular weight, a low-molecular component that can be a low-melting point is included, making it difficult to make it 0% by mass. If the low-melting-point resin is present over the entire layer, even before shutdown, there is a case that air permeation resistance tends to deteriorate when heated.

The elution component by cross fractionation chromatography can be determined, for example, as follows.

Measurement device: Cross fractionation chromatography CFC2 type (manufactured by Polymer ChAR)

Detector: Infrared spectrophotometer IR4 type (manufactured by Polymer ChAR)

Detection wavelength: 3.42 μm

Column: Showa Denko Corporation "Shodex" (registered trademark) UT806M

Column temperature: 140℃

Solvent (mobile phase): o-dichlorobenzene

Solvent flow rate: 1.0 ml/min

Sample concentration: 3.0 mg/ml

Cooling time: 140 minutes (140℃→0℃)

Elution component content of 90°C or lower: Elution of 90°C or lower by dividing the weights from 0°C to 90°C in each extraction amount by dividing the total weight from 0°C to 140°C in 10°C increments every 10°C Calculate the amount of ingredients.

[2] Polyethylene resin composition in the second layer (layer B)

The layer B of the present invention is a microporous membrane composed mainly of polyethylene. It is preferable that the layer B contains 50% by mass or more of high-density polyethylene from the viewpoint of strength. The high-density polyethylene preferably has a weight average molecular weight (hereinafter referred to as Mw) of 1×10 ⁵ or more, and more preferably 2×10 ⁵ or more. As for the upper limit of Mw, Mw is preferably 8×10 ⁵ , more preferably Mw is 7×10 ⁵ . When Mw is within the above range, the stability of the film forming and finally the protruding strength can be achieved.

In the present invention, it is important to add a low-melting point resin such as low-density polyethylene, straight-chain low-density polyethylene, and ethylene/α olefin copolymer to the B layer. By adding any of these, the B layer can be provided with a shutdown function at a low temperature, thereby improving characteristics as a battery separator. Here, the above-mentioned thing is mentioned as alpha-olefin.

It is important that the melt flow rate (MFR) of the low melting point resin is 25 g/10 min or more. The lower limit is preferably 50 g/10 min, more preferably 100 g/min. If the MFR is 25 g/10 min or more, the fluidity is good, and thus it is difficult to produce a nonuniformity in thickness during the stretching process, so that a uniform thickness distribution can be achieved. In addition, since the molecular mobility is good, residual deformation is difficult to remain, and since the molecule is sufficiently relaxed at a low temperature, clogging of holes due to residual deformation is unlikely to occur at a temperature lower than the melting point. Therefore, an increase in air permeability can be suppressed in the range of 30°C to 105°C. The upper limit is preferably 180 g/min, more preferably 150 g/min. When the MFR is 180 g/min or more, the viscosity of the melt is too low, and therefore, in coextrusion with the A layer, each layer may not be extruded uniformly. In addition, in the stretching step at the time of production, the microporous membrane may be broken because the viscosity is low.

It is important that the melting point of the low melting point resin is 120°C or more and less than 130°C. When the melting point is less than 120°C, since the melting point is too low, when the stretching temperature is raised to a temperature at which the laminate can be sufficiently stretched during lamination with A layer containing ultra-high molecular weight polyethylene, it adversely affects the hole formation of the B layer. There is a possibility that speculative resistance may deteriorate. On the other hand, when the overall stretching temperature is lowered to prevent clogging of the pores, softening as the entire laminate is insufficient, and there is a concern that the effect of expected thickness uniformity cannot be sufficiently obtained by adding ultra high molecular weight polyethylene in the A layer. On the other hand, when the melting point is 130°C or higher, it becomes difficult to achieve the targeted low shutdown temperature.

The content of the low-melting point resin is 100% by mass of the entire polyethylene resin constituting the layer B, and the lower limit is preferably 20% by mass, more preferably 25% by mass. The upper limit is preferably 35% by mass, more preferably 30% by mass. If it is 20 mass% or more, the shutdown temperature can be made low. Moreover, when it is 30 mass% or less, the fracture|rupture of the microporous membrane which arises because a viscosity is low can be suppressed.

Like the layer A, from the viewpoint of strength and protrusion formation, the layer B also preferably contains ultra high molecular weight polyethylene. The ultra high molecular weight polyethylene may be a homopolymer of ethylene, as well as a copolymer containing a small amount of other α-olefins. By adding ultra high molecular weight polyethylene, it is possible to improve the protruding strength. The Mw of the ultra high molecular weight polyethylene is preferably 1×10 ⁶ or more and less than 4×10 ⁶ . By using ultrahigh molecular weight polyethylene having a Mw of 1×10 ⁶ or more and less than 4×10 ⁶ , it becomes possible to refine the pores and fibrils. Thereby, the clogging of the hole by the low-melting-point resin is quick, and it becomes possible to lower the shutdown temperature more effectively.

The content of the ultra high molecular weight polyethylene is 100% by mass of the entire polyethylene resin, and the lower limit is preferably 10% by mass, more preferably 18% by mass. The upper limit is more preferably 40% by mass, even more preferably 30% by mass. Since ultra-high molecular weight polyethylene has a large difference in molecular mobility with a low-melting resin, if it exceeds 40% by mass, it is easy to separate from the low-melting resin during melt-kneading, possibly causing poor appearance of the finally obtained microporous membrane. There is this.

The polyethylene microporous membrane of the present invention may contain various additives such as antioxidants, heat stabilizers or antistatic agents, ultraviolet absorbers, and additional blocking inhibitors or fillers, in a range that does not impair the effects of the present invention in both the A and B layers. Can. In particular, it is preferable to add an antioxidant for the purpose of suppressing oxidation deterioration due to the thermal history of the polyethylene resin. Proper selection of the type and addition amount of the antioxidant or thermal stabilizer is important as adjustment or enhancement of the properties of the microporous membrane.

It is preferable that the laminated polyethylene microporous membrane used in the present invention does not substantially contain inorganic particles. "Substantially free of inorganic particles" is, for example, when the inorganic element is quantified by fluorescence X-ray analysis, preferably 50 ppm or less, more preferably 10 ppm or less, even more preferably below the detection limit It means the content to be. Even if the particles are not actively added to the layered polyethylene microporous membrane, contamination components derived from foreign substances, raw material resin, or dirt adhering to the line or device in the manufacturing process of the polyolefin microporous membrane are peeled off and mixed into the membrane. There is a possibility that it may be detected at 50 ppm or less.

The ratio (Mw/Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polyethylene resin composition of the B layer and the A layer is preferably in the range of 5 to 200, more preferably 10 to 100. . If the range of Mw/Mn is the above preferred range, extrusion of a solution of polyethylene is easy. In addition, a sufficient number of protrusions are obtained on the surface of the polyethylene microporous membrane, and even when the thickness of the polyethylene microporous membrane is thinned, sufficient mechanical strength is obtained. Mw/Mn is used as a measure of the molecular weight distribution. For example, 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. In addition, Mw/Mn of the mixture of polyethylene can be appropriately adjusted by adjusting the molecular weight and mixing ratio of each component.

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 melted polyethylene resin and the molding solvent is extruded from the die and crystallization of polyethylene is started, and the crystallization rate is increased by rapid cooling by contact with a cooling roll. At this time, a spherical crystal of a symmetric structure having 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 post-processing TD (width direction) and/or MD (machine direction) stretching. In addition, the Chinese New Year appears as ring marks on the surface of the laminated polyethylene microporous membrane (Fig. 3).

[3] Manufacturing method of laminated polyethylene microporous membrane

The laminated polyethylene microporous membrane is free to select a manufacturing method according to the purpose as long as it satisfies the above-mentioned various characteristics. As a method for producing a microporous 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 micropores and cost.

As a production method by a phase separation method, for example, polyethylene and a molding solvent are heat-melted and kneaded, the obtained molten mixture is extruded from a die, cooled to form a gel-like molded article, and stretched in at least one axis direction to the obtained gel-like molded article. And a method for obtaining a microporous membrane by removing the solvent for molding.

The manufacturing method of the laminated polyethylene microporous membrane used for this invention is demonstrated.

The method of manufacturing the multilayer polyethylene microporous membrane of the present invention includes the steps (a) to (f) below.

(a) After adding a molding solvent to the polyethylene resin composition constituting the layer A, melt-kneading to prepare a polyethylene resin solution A

(b) After adding a molding solvent to the polyethylene resin composition constituting the layer B, melt-kneading to prepare a polyethylene resin solution B

(c) The polyethylene resin solutions A and B obtained in steps (a) and (b) are extruded from the die, and at least one of them is cooled by a cooling roll having a surface from which the forming solvent is removed by means of removing the forming solvent. To form a laminated gel-like molded product

(d) Process of stretching laminated gel-like molded product in machine direction and width direction to obtain laminated stretched product

(e) Process of extracting and removing the molding solvent from the laminated stretched molding and drying it to obtain a laminated porous molded article

(f) Process of heat-treating a laminated porous molded product to obtain a laminated polyethylene microporous membrane.

In addition, other steps, such as hydrophilization treatment and charging treatment, may be added before step (a), during steps (a) to (f), or after step (f). Moreover, a re-stretching process can also be provided after process (f).

Hereinafter, each process will be described in detail.

(a), (b) A step of adding a molding solvent to the polyethylene resins constituting the layers A and B, followed by melt-kneading to prepare polyethylene resin solutions A and B.

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 a gel-like molding having a stable solvent content In order to obtain a non-volatile solvent such as liquid paraffin is preferred. The heating and dissolving is performed by a method of dissolving the polyethylene composition by mixing in a stirring or extruder at a temperature at which the polyethylene composition is completely dissolved. When the temperature is dissolved while stirring in an extruder or in a solvent, it varies depending on the polymer and solvent used, but, for example, a range of 140 to 250°C is preferable.

The concentration of the polyethylene resin is preferably 15 to 40% by mass, more preferably 25 to 40% by mass, and even more preferably 28 to 35% by mass, with the total amount of the polyethylene resin and the molding solvent as 100% by mass. . 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, and a sufficient number of projections is formed. In addition, swelling or necking is suppressed at the exit of the die when extruding the polyethylene resin solution, thereby maintaining moldability and self-supporting properties of the extruded body.

When the resin concentrations of the resin solutions A and B are varied, a laminated microporous membrane having a structure in which the average pore diameter is changed in the film thickness direction (inclined structure) can be obtained. The average pore diameter of the layer formed using the resin solution having a lower concentration becomes larger than the average pore diameter of the layer formed using the resin solution having a higher concentration. Which concentration of the resin solution A or B is to be increased can be appropriately selected depending on the physical properties required for the laminated microporous membrane. For example, if the inner layer is a dense structure layer having a thickness of 0.01 to 0.05 µm, and the surface layer is a coarse structure layer having a thickness of 1.2 to 5.0 times that of the dense structure layer, the balance between ion permeability and protruding strength can be improved.

Although the method of melt-kneading is not particularly limited, it is usually carried out by uniformly kneading in an extruder. This method is suitable for preparing a high concentration solution of polyethylene. The melt kneading temperature is different depending on the polyethylene resin used. For example, since the polyethylene composition has a melting point of about 130 to 140°C, the lower limit of the melt-kneading temperature is preferably 140°C, more preferably 160°C, even more preferably 170°C. The upper limit is preferably 250°C, more preferably 230°C, even more preferably 200°C. The molding solvent may be added before the start of kneading, or may be further melt-kneaded by adding it from the middle of the extruder during kneading. In melt kneading, it is preferable to add an antioxidant to prevent the oxidation of polyethylene.

From the viewpoint of suppressing the deterioration of the resin, the melt kneading temperature is preferably lower, but if it is lower than the above-mentioned temperature, a non-melting material is generated in the extruded product extruded from the die, causing a breakage or the like in the subsequent stretching process. There is. Moreover, when it is higher than the above-mentioned temperature, the thermal decomposition of polyethylene becomes severe, and the physical properties of the resulting microporous membrane, for example, puncture strength, tensile strength, etc., may be inferior.

The ratio (L/D) of the screw length (L) and the diameter (D) of the twin-screw extruder is preferably 20 to 100 from the viewpoint of obtaining good kneading and dispersibility and distribution of the resin. The lower limit is more preferably 35. The upper limit is more preferably 70. When L/D is 20 or more, melt kneading becomes sufficient. When L/D is 100 or less, the residence time of the polyethylene solution is not excessively increased. From the viewpoint of obtaining good dispersibility and dispersibility while preventing deterioration of the resin to be kneaded, it is preferable that the inner diameter of the cylinder of the twin-screw extruder is 40 to 100 mm.

In order to obtain good dispersion of polyethylene in the extrudate and to obtain excellent thickness uniformity of the microporous membrane, it is preferable to set the screw rotation speed (Ns) of the twin-screw extruder to 150 rpm or more. The ratio of the extrusion amount Q (kg/h) of the polyethylene solution to Ns (rpm), Q/Ns is preferably 0.64 kg/h/rpm or less, and more preferably 0.35 kg/h/rpm or less.

(c) The polyethylene resin solutions A and B obtained in (a) and (b) were extruded from the die, and at least one of them was cooled by a cooling roll having a surface from which the solvent for molding was removed by a solvent removing means for molding, Process to form a laminated gel-like molding

The polyethylene resin solutions A and B melt-kneaded with an extruder are extruded directly or through another extruder from a die and cooled with a cooling roll to form a laminated gel-like molding. As a method for obtaining a laminated gel-like molding, after producing the gel-like molding to be laminated separately, a method of pasting through a calender roll or the like (gluing method), or separately supplying a polyethylene solution to an extruder to obtain a desired temperature And melted in a polymer tube or die, coextruded and laminated, and thereafter, any method such as a laminated gel-like molding (coextrusion method) may be used, but from the viewpoint of interlayer adhesion, the coextrusion method is used. It is preferred.

A gel-like molding is formed by contacting a polyethylene resin solution extruded from the die with a rotating cooling roll 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. Here, the cooling rate in the temperature region where crystallization is substantially performed becomes important. For example, by cooling the extruded polyethylene resin solution at a cooling rate of 10° C./sec or more in a temperature region where crystallization is substantially performed, a gel-like molding is obtained. 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 separated into a microphase by a solvent is fixed, and a sphere having a relatively large nucleus is formed on the surface of the gel-like molded product that is in contact with the cooling roll to form a protrusion having an appropriate shape after stretching. can do. The cooling rate can be estimated by simulating from the extrusion temperature of the gel-like molding, the thermal conductivity of the gel-like molding, the thickness of the gel-like molding, the solvent for molding, the cooling roll, and the heat transfer rate of the air.

In the present invention, it is important to remove as much of the molding solvent adhering to the surface of the cooling roll of the portion in contact with the polyethylene resin solution extruded from the die as possible. 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, but a molding solvent is attached to the surface of the cooling roll after the gel-like molded article is separated, and is normally returned to its original state. It comes into contact with the polyethylene resin solution. 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 contacts the polyethylene resin solution again.

The forming solvent removing means, that is, the method for removing the forming solvent from the cooling roll is not particularly limited, but the doctor blade is placed on the cooling roll so as to be parallel to the width direction of the gel forming article, and the gel forming article is immediately after passing through the doctor blade. A method of scraping the molding solvent to the surface of the cooling roll until contact cannot be visually observed is preferably employed. Alternatively, it may be removed by means of blowing with compressed air, suctioning, or a combination of these methods. Among them, the 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 from the viewpoint of improving 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. In the case of metal, there is a fear that the cooling roll is damaged. 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 thermal insulation effect of the molding solvent, but also causes surface roughening of the gel-like molded article by condensation on the cooling roll. .

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

Here, when a laminated gel-like molded article is obtained by the pasting method, at least one of the polyethylene resin solutions serving as the A or B layer may be formed as a gel-like molded article under the above cooling conditions. In addition, when bonding, it is necessary to laminate such that the surface contacting the cooling roll of the layer formed by the above cooling conditions becomes a surface. In addition, when a laminated gel-like molded article is obtained by a co-extrusion method, a polyethylene resin solution laminated and extruded from the die may be formed as a laminated gel-like molded article under the above cooling conditions.

The laminated polyolefin is a porous laminate comprising at least A and B layers. The layer structure of the laminated polyethylene may be at least two layers of the A layer and the B layer in terms of physical properties such as shutdown characteristics and strength and permeability, but from the viewpoint of the balance between the front and back of the final film, the layer A/B layer/A It is more preferable to have a three-layer structure of a layer or a layer B/A layer/B layer. In terms of adhesion to the modified porous layer, the protrusions may be formed on either the A layer or the B layer, but from the viewpoint of balance between permeability and strength, it is preferable to use the surface layer as the A layer and the inner layer as the B layer. On the other hand, from the viewpoint of shutdown, it is preferable to make the surface layer B and the inner layer A.

The proportion of the B layer is preferably 30% by mass or more and 80% by mass or less with respect to the mass of the entire layer. The lower limit is more preferably 40% by mass, and the upper limit is more preferably 70% by mass. When the proportion of the B layer is within the above range, a balance between low shutdown characteristics due to the low melting point component, stability of permeability in the range of use of the separator, and protruding strength can be made into a good range.

The thickness of the layer B of the layered polyethylene microporous membrane is preferably 3 µm or more and 15 µm or less. The upper limit is more preferably 10 μm, even more preferably 7 μm, and most preferably 6 μm. Moreover, 4 micrometers is more preferable as a lower limit. The thickness of the B layer refers to the total thickness of each B layer when the laminated polyethylene microporous membrane has two or more B layers.

(d) Process of stretching laminated gel-like molding in MD (machine direction) and TD (width direction) to obtain laminated stretched molding

The laminated gel-like molding is stretched to obtain a stretched molding. Stretching is performed by heating the gel-like molded product and performing a predetermined magnification in two directions of MD and TD by a conventional tenter method, a roll method, or a combination of these methods. The stretching may be either simultaneous stretching of MD and TD (machine direction and width direction) (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. In addition, although the stretching magnification differs depending on the thickness of the raw material, 9 times or more is preferable as the surface magnification, and more preferably 16 to 400 times. If simultaneous stretching of MD and TD, stretching at the same magnification of MD and TD, such as 3×3, 5×5, or 7×7, is preferred. If the surface magnification is within the above-mentioned preferred range, stretching is sufficient to obtain a high-elasticity and high-strength microporous membrane. In addition, desired air permeability resistance can be obtained by adjusting the stretching temperature.

It is preferable that the stretching temperature is equal to or less than the melting point of the low melting point resin added to the B layer. When the melting point of the low-melting-point resin added to the layer B is lower than or equal to the melting point of the low-melting-point resin, defects in cleavage of the pores are prevented, and it is possible to efficiently orient the molecular chain by stretching, so that good strength can be obtained. have. Moreover, it is preferable that the lower limit of extending|stretching temperature is more than the crystal dispersion temperature of the polyethylene resin which comprises A layer. When the stretching temperature is equal to or higher than the crystal dispersion temperature of the polyethylene resin constituting the layer A, since the softening of the polyethylene resin is sufficient even in the layer A, uneven deformation that may occur due to insufficient softening is suppressed, and ultrahigh molecular weight added to the layer A Since uniform pores can be made by the molecular network formed of polyethylene, the permeability is improved, and the uniformity of physical properties is also improved. In addition, since it is possible to sufficiently reduce the stretching tension of the entire laminate, film forming properties are improved, and it is difficult to be ruptured during stretching, so that stretching at a high magnification becomes possible. The crystal dispersion temperature Tcd is obtained from the temperature characteristics of dynamic viscoelasticity measured according to ASTM D 4065. Alternatively, it may be obtained from NMR.

(e) Process of extracting and removing the molding solvent from the laminated stretched molding and drying it to obtain a laminated porous molded article

The stretched molded article is treated with a cleaning solvent to remove the remaining molding solvent to obtain a microporous membrane. Examples of the cleaning solvent include those of hydrocarbons such as pentane, hexane, and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, and fluorinated hydrocarbons such as ethane trifluoride, and ethers such as diethyl ether and dioxane. Can be used. These cleaning solvents are appropriately selected depending on the molding solvent used for dissolving polyethylene, and used alone or in combination. The washing method can be carried out by a method of extracting by immersing in a washing solvent, a method of washing the washing solvent, a method of sucking the washing solvent from the opposite side of the stretched molding, 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 mass. 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.

(f) Process of heat-treating a laminated porous molded product to obtain a laminated polyethylene microporous membrane.

The laminated porous molded product obtained by drying is heat-treated to obtain a laminated polyethylene microporous membrane. The heat treatment temperature is preferably carried out at 90 ~ 150 ℃. If the heat treatment temperature is within the above-mentioned preferred range, the heat shrinkage rate of the obtained multilayer polyethylene microporous membrane can be reduced to ensure air permeation resistance. The heat treatment time is not particularly limited, but is usually 1 second or more and 10 minutes or less, and more preferably 3 seconds to 2 minutes or less. The heat treatment may adopt a tenter method, a roll method, a rolling method, or a free method.

In the heat treatment process, it is preferable to grip in both directions of MD (machine direction) and TD (width direction) and contract in at least one of MD and TD. The contraction rate of shrinking in MD and TD in at least one direction is preferably 0.01 to 50%, and more preferably 3 to 20%. If the shrinkage ratio is within the above-mentioned preferred range, the thermal shrinkage at 105°C and 8 hr is improved, and the air permeation resistance is maintained. In addition, in order to improve the protruding strength, re-stretching of about 5% to 20% may be additionally performed in TD, MD, or both directions before heat treatment.

If necessary, hydrophilization treatment can be performed on the microporous membrane. By performing the hydrophilization treatment, for example, when coating the heat-resistant resin layer, the adhesion between the microporous membrane surface and the modified porous layer and uniformity of the coating membrane can be further improved. The hydrophilization treatment can be performed by monomer graft, surfactant treatment, corona discharge, or the like. It is preferable that the monomer graft is performed after the crosslinking treatment. Corona discharge treatment can be carried out in air or nitrogen or a mixed atmosphere of carbon dioxide and nitrogen.

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

It is a preferred form that the modified porous layer is laminated on the side of the surface having the projection of the laminated polyethylene microporous membrane. When a modified porous layer is provided on both sides of a laminated polyethylene microporous membrane, in a post process such as a slit process or a conveying process, the modified porous layer on the side where parallel stress is more strongly caused by contact with a roll or bar, etc. is laminated. It is preferable to laminate the polyethylene microporous membrane on the side having projections because the effect of the present invention is exhibited.

The modified porous layer referred to in the present invention imparts or improves at least one function such as heat resistance, adhesion to electrode materials, and electrolyte permeability. The modified porous layer 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, it is possible to obtain a battery separator having excellent 0° peel strength due to protrusions present on the surface of the laminated polyethylene microporous membrane and the anti-tensile effect of the binder. In addition, compared with the case of the laminated polyethylene microporous membrane alone, even if the modified porous layer is laminated, the battery separator does not significantly increase the air permeation resistance. This is because sufficient 0° peel strength is obtained even if many binders do not penetrate into the pores of the laminated polyethylene microporous membrane.

The tensile strength of the binder is 5 N/mm ² or more, and the lower limit is preferably 10 N/mm ² , more preferably 20 N/mm ² , even more preferably 30 N/mm ² . The upper limit is not specified, but 100 N/mm ² Enough is enough. The tensile strength of the binder refers to a value measured by a method described later.

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

In order to reduce the curl of the laminated polyethylene microporous membrane by laminating the modified porous layer, it is important to include inorganic particles in 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 binder has a role of at least bonding inorganic particles and a role of bonding a laminated polyethylene microporous membrane and a modified porous layer. Examples of the solvent include water, alcohols, acetone or N-methyl-2-pyrrolidone. By adding inorganic particles to the coating liquid, it is also possible to obtain an effect of 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 providing slipperiness. . The upper limit of the amount of particles added is preferably 98% by mass, more preferably 95% by mass. The lower limit is preferably 80% by mass, more preferably 85% by mass. If the particle addition amount 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, the peel strength of 0° sufficient with the modified porous layer is obtained.

The average particle diameter of the inorganic particles is preferably 1.5 times or more and 50 times or less, and more preferably 2.0 times or more and 20 times or less, than the average pore diameter of the laminated polyethylene microporous membrane. If the average particle diameter of the particles is within the above-mentioned preferred range, the pores of the laminated polyethylene microporous membrane are blocked in a state where the heat-resistant resin and the particles are mixed, and as a result, the air permeation resistance is maintained. To prevent causing serious defects.

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. Further, heat-resistant crosslinked polymer particles can 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.

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

The thickness of the modified porous layer is preferably 1 to 5 μm, more preferably 1 to 4 μm, even more preferably 1 to 3 μm. If the film thickness of the modified porous layer is within the above-mentioned preferred range, the separator for batteries obtained by laminating the modified porous layer can secure the breaking strength and insulation properties when melting and shrinking at a melting point or higher, and a sufficient hole occlusion function is obtained, which is ideal. The reaction can be prevented. In addition, it is possible to suppress the cold volume, which is suitable for high capacity of the battery. Moreover, suppressing curls leads to productivity improvement in the battery assembly process.

The porosity of the modified porous layer is preferably 30 to 90%, more preferably 40 to 70%. In order to achieve the desired porosity, it is obtained by appropriately adjusting the concentration of the inorganic particles, the concentration of the binder, and the like. When the porosity of the modified porous layer is within the above-mentioned preferred range, the battery separator obtained by laminating the modified porous layer has a low electrical resistance of the film, so that a large current is easy to flow, and the film strength is maintained.

The upper limit of the total film thickness of the battery separator 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 overall film thickness of the battery separator is within the above-mentioned preferred range, the battery separator obtained by laminating the modified porous layer can ensure sufficient mechanical strength and insulation. Further, a decrease in capacity can be avoided by reducing the area of the electrode that can be filled in the container.

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

Next, a method of laminating the modified porous layer on the laminated polyethylene microporous membrane in the present invention will be described. The method of laminating the modified porous layer on the laminated polyethylene microporous membrane of the present invention includes the following (g) process.

(g) On the surface of the laminated polyethylene microporous membrane that the cooling roll was in contact with, the laminated film was coated with a coating solution containing a binder having a tensile strength of 5 N/mm ² or more, an inorganic particle, and a solvent capable of dissolving or dispersing the binder. Process of forming and drying

As a method of laminating the modified porous layer on the laminated polyethylene microporous membrane, a known method can be used. Specifically, the coating solution may be obtained by coating the laminated polyethylene microporous membrane by a method described later 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. In addition, the binder is soluble, and at the same time, a coating solution dissolved in a solvent that is miscible with water is laminated to a predetermined laminated polyethylene microporous membrane using a coating method described below, placed under a specific humidity environment, and mixed with the binder and water. A method of separating the solvent and further solidifying the binder by introducing it into a water bath (coagulation bath) can also be used.

As a method of applying the coating liquid, for example, 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 method, blade And a coating method and a die coating method, and these methods can be performed alone or in combination.

It is preferable to store the separator for a battery of the present invention in a dry state, but when it is difficult to store in a dry state, it is preferable to carry out a vacuum drying treatment at 100°C or less immediately before use.

The battery separator of the present invention includes a secondary battery such as a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a lithium secondary battery, a lithium polymer secondary battery, and a plastic film capacitor, ceramic capacitor, and electric double layer capacitor. Although it can be used as a separator, etc., 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 with the separator interposed therebetween, 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) in which the anode and the cathode of the disk shape face each other (coin type), the electrode structure (lamination type) in which the anode and the cathode on the flat plate are alternately stacked (stacked type), the object (帶狀) ), and may have a structure such as an electrode structure (winding type) in which the anode and the cathode are wound.

The positive electrode usually 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 transition metal oxides, complex oxides of lithium and transition metals (lithium complex oxides), and inorganic compounds such as transition metal sulfides. 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 layered lithium composite oxides based on α-NaFeO ₂ type structures.

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 is 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( And C ₂ F ₅ SO ₂ ) ₂ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , lower aliphatic carboxylic acid lithium salts, and LiAlCl ₄ . 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 mix and use both.

When assembling the battery, the separator of the present invention can be impregnated with an electrolyte to impart ion permeability to the separator. Usually, the impregnation treatment is performed by immersing the microporous membrane in the electrolyte at room temperature. For example, when assembling a cylindrical battery, first, a positive electrode sheet, a separator, 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. Then, the electrode element is inserted into the battery can, and the electrolyte is impregnated, and the battery cap can also be obtained by caulking the battery cover serving as the positive electrode terminal provided with the safety valve through a gasket.

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 binders used in Examples and Comparative Examples were sufficiently dissolved or dispersed in a soluble solvent, and put into a dumbbell type for producing test piece No. 2 specified in JIS K 7113 so that the film thickness after drying was about 100 µm and dried naturally at 25°C. The sample sheet obtained by further removing the solvent by performing vacuum drying (vacuum degree 3 mmHg) at 25° C. for 8 hours was further used for tensile strength measurement.

It measured under the following conditions using the tensile tester (Autograph AGS-J load cell capacity 1 kN manufactured by Shimadzu Corporation). 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.

Distance between chucks: 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 (HD100 manufactured by Laser Tech Co., Ltd.) installed on an isolator.

(order)

(1) The laminated polyethylene microporous membrane obtained in Examples and Comparative Examples was drawn with an ultrafine oil-based pen with a 1 cm×1 cm square frame on the surface that was in contact with the cooling roll at the time of film formation.

(2) The square molded surface was placed on the sample stage with the drawn side up, and was fixed to the sample stage using an electrostatic adhesion device provided with a confocal microscope.

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

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

(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 collected with a scan time of 120 seconds and a STEP travel distance of 0.1 µm/Step.

(6) After collecting the 3D data, an image for data processing (referred to as a Z-image in this apparatus) was displayed to perform smoothing processing (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 in the vertical direction to the inflection points of both sleeves of the protrusions, and the distance between the two cursors was defined as the size of the protrusions.

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

(10) The above operation was repeated within a square frame of 1 cm×1 cm, the number of protrusions of 5 µm or more and 50 µm or less, and 0.5 µm or more and 3.0 µm or less in height was calculated to obtain the number of protrusions per 1 cm ² . , Further, the average height of the projections was obtained.

3. 0° peel strength of modified porous layer (N/15 mm)

Fig. 1 schematically shows the evaluation method. 1 is a laminated sample, 2 is a laminated polyethylene microporous membrane, 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 the tensile direction. A double-sided pressure-sensitive adhesive tape (NW-K50 manufactured by Nichiban Co., Ltd.) 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 laminated polyethylene microporous membrane 2 of the sample 1 (battery separator) cut to a width of 50 mm x a length of 100 mm overlaps 40 mm from one end of the 25 mm length of the aluminum plate 5 And cut off the protruding part. 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 (Autograph AGS-J load cell capacity of 1 kN manufactured by Shimadzu Corporation), and the aluminum plate 5 was mounted. Each of the aluminum plates 5'was pulled in parallel in the opposite direction at a tensile speed of 10 mm/min to measure the strength when the modified porous layer was peeled off. This measurement was performed on any three points separated by 30 cm or more in the longitudinal direction, and the average value was taken as the 0° peel strength of the modified porous layer.

4. Film thickness

It was calculated|required by averaging the measured value of 20 points using the contact-type film thickness meter (currently, Lightmatic series318 manufactured by Mitsubiyo Corporation). Using an ultra-oral surface measuring instrument, Φ9.5 mm, the measurement was performed under the condition of a weight of 0.01 N.

5. Average hole diameter

The average pore diameter of the laminated polyethylene microporous 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 locations were selected on the image obtained by SEM measurement, and the average value of the pore diameters of these 10 locations 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 Co., Ltd., the laminated polyethylene microporous membrane or battery separator 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×10 cm, and the measurement point was a total of 5 points at the center and four corners of the sample, and the average value was used as the speculative resistance. And, when the length of one side of the sample does not reach 10 cm, the value measured at 5 points at 5 cm intervals may be used.

The increase in speculation resistance was obtained by the following equation.

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

Air permeability of laminated polyethylene microporous membrane (X) sec/100 ccAir

Battery separator speculative resistance (Y) sec/100 ccAir

7. Shutdown temperature

While heating the laminated polyethylene microporous membrane at a heating rate of 5°C/min, the air permeation resistance was measured by an Oken Type air permeation resistance meter (EGO-1T manufactured by Asahi Seiko Co., Ltd.). , The temperature at which the air resistance reached the detection limit of 1×10 ⁵ sec/100 ccAir was determined as the shutdown temperature (°C).

8. Speculation resistance increase rate

From the data of temperature and air permeation resistance P of the layered polyethylene microporous membrane having a thickness T1 (μm) obtained by the shutdown temperature measurement of 7. above, the correlation between the temperature at 30°C and 105°C and the air permeation resistance P ( A phase was prepared, and the slope Pa (sec/100 ccAir/°C) was calculated by the least squares method. The calculated Pa is normalized with the formula: Pb=Pa/T1×20 with a film thickness of 20 μm, and the rate of increase in air permeation resistance at 30° C. to 105° C. Pb (sec/100 ccAir/μm/° C.) is calculated. did.

9. Porosity of laminated polyethylene microporous 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

10. Friction resistance

Both ends were slit while winding the separator for roll-shaped batteries obtained in Examples and Comparative Examples. 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 (type WA177A manufactured by Kabushiki Kaisha Nishimura Seisakusho). During processing, the rolls contacting the coated surface were two hard chrome plated rolls (all free rolls). Then, while rewinding the slit-processed separator for roll-shaped batteries, the peeling defects of the modified porous layer having a diameter of 0.5 mm or more were counted by using a loupe (SCALE LUPE×10 manufactured by PEAK) with a visual observation and a magnification of 10 times. , It evaluated by the following criteria. The evaluation area was 100 mm wide and 500 m long (when the width did not reach 100 mm, the length was adjusted to make the same evaluation area).

Criteria

(Very good): 5 or less

△ (Good): 6~15

× (bad): 16 or more

11. Weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn)

Mw and Mw/Mn were determined by gel permeation chromatography (GPC) under the following conditions.

Measurement device: GPC-150C manufactured by Waters Corporation

Column: Showa Denko Corporation "Showdex" (registered trademark) UT806M

Column temperature: 135℃

Solvent (mobile phase): o-dichlorobenzene

Solvent flow rate: 1.0 ml/min

Sample concentration: 0.1% by mass (dissolution conditions: 135°C/1h)

·Injection amount: 500 μl

Detector: Waters Corporation's Differential Refractometer

-Calibration curve: It was produced using a predetermined conversion constant from a calibration curve obtained using a monodisperse polystyrene standard sample.

12. Melt Flow Rate (MFR)

In accordance with JIS-K7210, the temperature was measured at 190°C and a load of 2.16 g.

13. Melting point

The peak temperature of the melting peak observed when 5 mg of a resin sample is heated at a heating rate of 20° C./min under a nitrogen gas atmosphere using a differential scanning calorimeter (DSC) DSC6220 manufactured by S.I.Nano Technology Co., Ltd. As was.

Example 1

An antioxidant (tetrakis-[methylene-(3') was added to 100% by mass of a composition consisting of 18% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and 82% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000. ,5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane) 0.375% by mass of polyethylene composition A (melting point 135°C) was obtained. 25 mass% of this polyethylene composition A was put into a twin screw extruder. 75 mass% of liquid paraffin was supplied from the side feeder of this twin-screw extruder, melt-kneaded, and polyethylene resin solution A was prepared in the extruder.

On the other hand, 17.5 mass% of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and 57.5 mass% of high density polyethylene (HDPE) having a weight average molecular weight of 300,000, MFR is 135 g/10 min, and linear low density with a melting point of 124°C. Antioxidant (tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)) in 100% by mass of a composition consisting of 25% by mass of polyethylene (ethylene/1-hexene copolymer) Propionate]methane) Polyethylene composition B (melting point 128°C) to which 0.375 mass% was added was obtained. 25 mass% of this polyethylene composition B was put into a twin screw extruder. 75 mass% of liquid paraffin was supplied from the side feeder of this twin screw extruder, melt-kneaded, and polyethylene resin solution B was prepared in the extruder.

The obtained polyethylene resin solutions A and B were co-extruded from the lamination die at 190°C so that the layer constitution was A/B/A and the solution ratio was 1/2/1, and the internal cooling water temperature was maintained at 25°C with a diameter of 800 mm. A laminated gel-like molded product was formed while being drawn with a cooling roll of. At this time, between the point where the laminated gel-like molding falls from the cooling roll and the point where the laminated polyethylene resin solution extruded from the die and the cooling roll come into contact, a doctor blade made of polyester is cooled in parallel to the width direction of the laminated gel-like molding. The liquid paraffin attached on the cooling roll was scraped off. Subsequently, this laminated gel-like molded article was simultaneously biaxially stretched 5x5 times while controlling the temperature so as to achieve the desired air permeability, thereby obtaining a stretched molded article. The obtained stretched molding was washed with methylene chloride to remove and remove the remaining liquid paraffin, and dried to obtain a porous molding. Thereafter, the microporous membrane was kept in the tenter, the width was reduced by 10% only in the TD (width direction) direction, and heat-treated at 123°C for 3 seconds to achieve a thickness of 14 µm, a porosity of 44%, an average pore diameter of 0.45 µm, and speculation A laminated polyethylene microporous membrane having a resistivity of 195 sec/100 ccAir, a shutdown temperature of 130°C, and an air permeation resistance increase rate of 0.8 sec/100 ccAir/°C/20 μm was obtained.

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 Industries, Ltd.) The product "torayceram" (registered trademark) beads, 0.5 mm in diameter, were placed in a container made of polypropylene and dispersed for 6 hours with a paint shaker (manufactured by Toyoce Chemical Co., Ltd.). Subsequently, it filtered with a filter of 5 micrometers of filtration limits, and obtained the coating liquid (a).

A coating liquid (a) was applied to the surface of the laminated polyethylene microporous membrane, which was in contact with the cooling roll at the time of film formation, by gravure coating, dried by passing through a hot-air drying furnace at 50° C. for 10 seconds, and a separator for a battery having a final thickness of 16 μm Got

Example 2

A battery separator was obtained in the same manner as in Example 1 except that the blending ratio of ultra high molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) of the polyethylene composition A was adjusted as shown in Table 1.

Example 3

A battery separator was obtained in the same manner as in Example 2 except that two doctor blades made of polyester were placed on a cooling roll at intervals of 20 mm.

Example 4

A battery separator was obtained in the same manner as in Example 2 except that three doctor blades made of polyester were placed on a cooling roll at intervals of 20 mm each.

Example 5

A two-component curable aqueous acrylic urethane resin (solid content concentration: 45% by mass) composed of an aqueous acrylic polyol and a water-dispersible polyisocyanate (curing agent), alumina particles having an average particle diameter of 0.5 µm, and ion-exchanged water in a weight ratio of 10:40:50, respectively. Mixed with zirconium oxide beads ("Toray Serum" (registered trademark) beads, 0.5 mm in diameter) with zirconium oxide beads, and placed in a polypropylene container, paint shaker (manufactured by Toyo Seiki Seisakusho) ) For 6 hours. Subsequently, it filtered with a filter of 5 micrometers of filtration limits, and obtained the coating liquid (b). A modified porous layer was laminated in the same manner as in Example 2 except that the coating liquid (a) was replaced with the coating liquid (b) to obtain a battery separator.

Example 6

Copolymer of polyvinyl alcohol, acrylic acid and methyl methacrylate ("POVACOAT®" (registered trademark, manufactured by Nisshin Chemical Co., Ltd.)), alumina particles having an average particle diameter of 0.5 µm, solvent (ion-exchanged water: ethanol = 70: 30) are blended in a weight ratio of 5:45:50, respectively, placed in a polypropylene container with zirconium oxide beads ("Toray Serum" (trademark) beads manufactured by Toray Industries, Inc.), 0.5 mm in diameter, and painted. It was dispersed for 6 hours with a shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Filtration was performed with a filter having a 5 µm limit to obtain a coating liquid (c). A modified porous layer was stacked in the same manner as in Example 2 except that the coating solution (a) was replaced with the coating solution (c) to obtain a battery separator.

Example 7

A battery separator was obtained in the same manner as in Example 2 except that the temperature of the internal cooling water in the cooling roll was maintained at 35°C.

Example 8

A battery separator was obtained in the same manner as in Example 2 except that the layer configuration was coextruded so that the ratio of B/A/B and the solution ratio was 1/2/1.

Examples 9-12

A battery separator was obtained in the same manner as in Example 2 except that the low-melting-point resin contained in the polyethylene composition B was changed as shown in Table 1.

Example 13

A battery separator was obtained in the same manner as in Example 2 except that the addition amount of the low-melting-point resin contained in the polyethylene composition B was adjusted as shown in Table 1.

Example 14

Extrusion amounts of the polyethylene resin solutions A and B were adjusted, and a separator for batteries was obtained in the same manner as in Example 2 except that a laminated polyethylene microporous membrane having a thickness of 9 µm was obtained.

Example 15

The alumina particles were replaced with crosslinked polymer particles (polymethacrylic acid methyl-based crosslinked particles ("EPOSTAR" (registered trademark) MA1002, manufactured by Kabuki Chemical Co., Ltd., average particle diameter 2.5 µm)) and crosslinked polymer Varnish (d) was obtained by setting the mixing ratio of the particles and N-methyl-2-pyrrolidone to 35:10:55 (weight ratio), respectively. A battery separator was obtained in the same manner as in Example 2 except that the varnish (d) was used.

Example 16

Fluorine resin solution ("KF Polymer" (registered trademark) #9300 (a polyvinylidene fluoride solution (5% N-methyl-2-pyrrolidone solution) manufactured by Kureha Chemical Co., Ltd.) and alumina having an average particle diameter of 0.5 mu m Particles and N-methyl-2-pyrrolidone were mixed at a weight ratio of 16:34:50, respectively, and zirconium oxide beads ("Toray Serum" (registered trademark) beads manufactured by Toray Industries, 0.5 mm in diameter) Together, they were placed in a polypropylene container and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.) Then, filtered with a filter having a filtration limit of 5 μm to obtain a varnish (e). A battery separator was obtained in the same manner as in Example 2 except for using ).

Example 17

Acrylic emulsion ("Polysol" (registered trademark) AT-731 manufactured by Showa Denko Co., Ltd., 47% non-volatile content), alumina particles having an average particle diameter of 0.5 µm, and ion-exchanged water, respectively 2:55: Blended in a weight ratio of 43, put in a container made of polypropylene with zirconium oxide beads ("Toray Serum" (registered trademark) beads manufactured by Toray Industries, Inc., 0.5 mm in diameter), and a paint shaker (Kyodo Corporation) It was dispersed for 12 hours with Seisakusho). Subsequently, it filtered with a filter of 5 micrometers of filtration limits, and obtained the coating liquid (f). The coating liquid (f) was applied to the laminated polyethylene microporous membrane of Example 2 in the same manner as in Example 2 to obtain a battery separator.

Example 18

A battery separator was obtained in the same manner as in Example 2 except that the coating solution (g) in which the alumina particles were replaced with barium sulfate fine particles (average particle diameter of 0.3 µm) was used.

Example 19

A battery separator was obtained in the same manner as in Example 2 except that the layer configuration was A/B/A and the solution ratio was 1.5/2/1.5.

Example 20

A battery separator was obtained in the same manner as in Example 2 except that the blending ratio of ultra high molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) of the polyethylene composition A was adjusted as shown in Table 1.

Example 21

The blending ratio of ultra high molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) of the polyethylene composition A, and the ratio of each polyethylene composition A and liquid paraffin were adjusted as shown in Table 1, and the polyethylene solution A and the thickness were as shown in Table 3. A battery separator was obtained in the same manner as in Example 2 except that the extrusion amount of B was adjusted.

Comparative Example 1

A battery separator was obtained in the same manner as in Example 2 except that only the polyethylene solution A was used, and it was extruded from a single-layer die at 190°C to form a single-layer gel-like molding, and a single-layer gel-like molding obtained in place of the laminated gel-like molding was used.

Comparative Example 2

A battery separator was obtained in the same manner as in Example 2, except that an ethylene·1-hexene copolymer having an MFR of 3.2 g/10 min was used as the low-melting resin contained in the polyethylene composition B.

Comparative Example 3

A battery separator was obtained in the same manner as in Example 1 except that the blending ratio of ultra high molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) of the polyethylene composition A was adjusted as shown in Table 1.

Comparative Example 4

Cooling the polyethylene resin solution extruded from the die with a cooling roll, the same procedure as in Example 2 was carried out except that a doctor blade was not used to obtain a gel-like molding, and the liquid paraffin attached to the cooling roll was not scraped off. Got.

Comparative Example 5

A battery separator was obtained in the same manner as in Example 2, 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 6

A battery separator was obtained in the same manner as in Example 2, except that the polyethylene resin solution extruded from the die was immersed in water kept at 25°C for 1 minute instead of being cooled by a cooling roll.

Comparative Example 7

A battery separator was obtained in the same manner as in Example 2 except that the internal cooling water temperature of the cooling roll was maintained at 50°C.

Comparative Example 8

1 mole of trimellitic anhydride (TMA), 0.8 mole of o-tolidine diisocyanate (TODI), 2, 4-tolylene in a 4-necked flask with a thermometer, cooling tube, and nitrogen gas introduction tube 0.2 mol of diisocyanate (TDI) and 0.01 mol of potassium fluoride are injected together with N-methyl-2-pyrrolidone so that the solid content becomes 14%, and stirred at 100° C. for 5 hours, so that the solid content becomes 14%. A polyamideimide resin solution was synthesized by dilution with N-methyl-2-pyrrolidone.

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 26:34:40, respectively, and zirconium oxide beads (manufactured by Toray Industries, Inc.) 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 filtered with a filter of 5 micrometers of filtration limits, and obtained the coating liquid (h). The coating liquid (h) was applied in the same manner as in Example 2 to the laminated polyethylene microporous membrane obtained in the same manner as in Example 2 by the gravure coating method to obtain a battery separator.

The manufacturing conditions of Examples 1 to 21 and Comparative Examples 1 to 8 are shown in Table 1 and Table 2. In addition, Table 3 shows the properties of the resulting laminated polyethylene microporous membrane and battery separator.

Level A Level B UHMWPE HDPE Resin concentration UHMWPE HDPE Low melting point resin Resin concentration Amount added Amount added Amount added Amount added ingredient Melting point MFR Amount added (Wt%) (Wt%) (Parts by weight) (Wt%) (Wt%) - (℃) (g/10 min) (Wt%) (Wt%) Example 1 18 82 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 2 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 3 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 4 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 5 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 6 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 7 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 8 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 9 30 70 25 17.5 57.5 Ethylene·1-butene copolymer 121 55 25 25 Example 10 30 70 25 17.5 57.5 Low density polyethylene 122 28 25 25 Example 11 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 123 50 25 25 Example 12 30 70 25 17.5 57.5 Ethylene·1-octene copolymer 125 136 25 25 Example 13 30 70 25 17.5 55.0 Ethylene·1-hexene copolymer 124 135 27.5 25 Example 14 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 15 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 16 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 17 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 18 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 19 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 20 2 98 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Example 21 40 60 30 30.0 50.0 Ethylene·1-hexene copolymer 124 135 25 25 Comparative Example 1 30 70 25 - - - - - - - Comparative Example 2 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 123 3.2 25 25 Comparative Example 3 0 100 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Comparative Example 4 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Comparative Example 5 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Comparative Example 6 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25 Comparative Example 7 30 70 25 17.5 57.5 Ethylene1-hexene copolymer 124 135 25 25 Comparative Example 8 30 70 25 17.5 57.5 Ethylene·1-hexene copolymer 124 135 25 25

Layer composition Layer thickness ratio Cooling roll temperature Scraping solvent for molding Coating liquid Tensile strength of binder (℃) (Number of blades) (N/mm ² ) Example 1 A/B/A 1/2/1 25 One a 8 Example 2 A/B/A 1/2/1 25 One a 8 Example 3 A/B/A 1/2/1 25 2 a 8 Example 4 A/B/A 1/2/1 25 3 a 8 Example 5 A/B/A 1/2/1 25 One b 20 Example 6 A/B/A 1/2/1 25 One c 31 Example 7 A/B/A 1/2/1 35 One a 8 Example 8 B/A/B 1/2/1 25 One a 8 Example 9 A/B/A 1/2/1 25 One a 8 Example 10 A/B/A 1/2/1 25 One a 8 Example 11 A/B/A 1/2/1 25 One a 8 Example 12 A/B/A 1/2/1 25 One a 8 Example 13 A/B/A 1/2/1 25 One a 8 Example 14 A/B/A 1/2/1 25 One a 8 Example 15 A/B/A 1/2/1 25 One d 8 Example 16 A/B/A 1/2/1 25 One e 5 Example 17 A/B/A 1/2/1 25 One f 25 Example 18 A/B/A 1/2/1 25 One g 8 Example 19 A/B/A 1.5/2/1.5 25 One a 8 Example 20 A/B/A 1/2/1 25 One a 8 Example 21 A/B/A 1/2/1 25 One a 8 Comparative Example 1 A - 25 One a 8 Comparative Example 2 A/B/A 1/2/1 25 One a 8 Comparative Example 3 A/B/A 1/2/1 25 One a 8 Comparative Example 4 A/B/A 1/2/1 25 0 a 8 Comparative Example 5 A/B/A 1/2/1 0 0 a 8 Comparative Example 6 A/B/A 1/2/1 25℃
(Bathing) - a 8 Comparative Example 7 A/B/A 1/2/1 50 One a 8 Comparative Example 8 A/B/A 1/2/1 25 One h 2

Characteristics Thickness of laminated polyethylene microporous membrane Shutdown temperature Speculation resistance increase rate Air permeation resistance of laminated polyethylene microporous membrane (X) Air permeability of battery separator (Y) Speculation resistance rise [(Y)-(X)] Number of projections Average projection height 0° peel strength Friction resistance (㎛) (℃) (sec/100 ccAir/℃/20㎛) (sec/100 ccAir) (sec/100 ccAir) (sec/100 ccAir) (Pcs/cm ² ) (㎛) (N/15 mm) Example 1 14 130 0.8 195 243 48 41 0.7 155 ○ Example 2 14 128 0.9 169 223 54 66 0.6 158 ○ Example 3 14 128 0.9 168 218 50 70 0.7 161 ○ Example 4 14 128 0.9 167 218 51 73 0.7 162 ○ Example 5 14 128 0.9 169 223 54 66 0.6 172 ○ Example 6 14 128 0.9 169 223 54 66 0.6 185 ○ Example 7 14 127 0.8 162 215 53 67 0.6 158 ○ Example 8 14 126 1.1 179 243 64 40 1.0 164 ○ Example 9 14 128 1.4 169 247 78 66 0.7 161 ○ Example 10 14 128 1.5 195 281 86 66 0.7 161 ○ Example 11 14 129 1.4 176 253 77 66 0.7 161 ○ Example 12 14 131 0.9 164 214 50 66 0.7 161 ○ Example 13 14 132 0.9 168 222 54 66 0.7 161 ○ Example 14 9 128 0.9 110 165 55 72 0.6 159 ○ Example 15 14 128 0.9 169 223 54 66 0.6 158 ○ Example 16 14 128 0.9 169 223 54 66 0.6 132 ○ Example 17 14 128 0.9 169 223 54 66 0.6 175 ○ Example 18 14 128 0.9 169 223 54 66 0.6 154 ○ Example 19 14 128 0.9 169 223 54 64 0.6 152 ○ Example 20 14 128 1.0 152 218 66 8 1.7 177 ○ Example 21 7 128 0.9 167 218 51 100 0.5 145 ○ Comparative Example 1 14 137 1.1 198 261 63 66 0.6 158 ○ Comparative Example 2 14 128 1.7 382 481 99 66 0.7 161 ○ Comparative Example 3 14 128 1.7 380 476 96 0 - 98 × Comparative Example 4 14 128 0.9 168 221 53 0 - 97 × Comparative Example 5 14 128 0.9 171 224 53 0 - 98 × Comparative Example 6 14 128 0.9 173 226 53 2 0.3 118 △ Comparative Example 7 14 128 0.9 175 227 52 0 - 97 × Comparative Example 8 14 128 0.9 169 223 54 66 0.6 127 △

1 Battery separator
2 laminated polyethylene microporous membrane
3 modified porous layer
4 double sided adhesive tape
5, 5'aluminum plate
6 Crystalline nucleus of polyethylene Lunar New Year
7 die
8 Polyethylene resin solution
9 cooling rolls
10 Doctor Blade
11 Gel-like molding

Claims (10)

A separator for a battery having a laminated polyethylene microporous membrane and a modified porous layer present on at least one surface thereof, wherein the multilayer polyethylene microporous membrane is a porous laminate comprising at least A and B layers, and has a shutdown temperature of 128 to 135°C. , Polyethylene of 3/cm ² or more and 200/cm ² or less on the surface in contact with at least one extraterrestrial, with a rate of increase in air permeation resistance at 30°C to 105°C per 20 μm of thickness less than 1.5 sec/100 ccAir/°C Irregular projections consisting of, and the projections satisfy 0.5 ㎛ ≤ H (H is the height of the projection) and 5 ㎛ ≤ W ≤ 50 ㎛ (W is the size of the projection), the modified porous layer is the laminated polyethylene A battery separator comprising a binder and inorganic particles having a tensile strength of 5 N/mm ² or more while being laminated on a surface having a projection of a microporous membrane. The battery separator according to claim 1, wherein the laminated polyethylene microporous membrane has a three-layer structure of A layer/B layer/A layer. The battery separator according to claim 1, comprising a low melting point resin having a melt flow rate of 25 to 150 g/10 min and a melting point of 120°C or more and less than 130°C in the layer B forming the laminated polyethylene microporous membrane. The battery separator according to claim 3, wherein the low-melting point resin is at least one selected from the group consisting of low-density polyethylene, linear low-density polyethylene, and ethylene/α-olefin copolymers. The battery separator according to claim 3, wherein the content of the low-melting point resin in the layer B forming the laminated polyethylene microporous membrane is 20% by mass or more and 35% by mass or less with the entire polyethylene resin as 100% by mass. The battery separator according to claim 1, wherein the layer B has a thickness of 3 μm or more and 15 μm or less. The battery separator according to claim 1, wherein the binder is polyvinyl alcohol or an acrylic resin. The battery separator according to claim 1, wherein the inorganic particles include at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate, and boehmite. The manufacturing method of the battery separator in any one of Claims 1-8 containing the following processes (a)-(g).
(a) After adding a molding solvent to the polyethylene resin constituting the layer A, melt-kneading to prepare a polyethylene resin solution A
(b) After adding a low-melting-point resin and a molding solvent to the polyethylene resin constituting the layer B, melt-kneading to prepare a polyethylene resin solution B
(c) The polyethylene resin solutions A and B obtained in steps (a) and (b) are extruded from the die, and at least one of them is a cooling roll having a surface on which the molding solvent is removed by means of removing the molding solvent. Cooling to form a layered gel-like molding
(d) a step of stretching the laminated gel-like molding in the machine direction and in the width direction to obtain a laminated stretched molding.
(e) Process of extracting and removing the molding solvent from the laminated stretched molding and drying it to obtain a laminated porous molded article.
(f) Process of heat-treating a laminated porous molded product to obtain a laminated polyethylene microporous membrane.
(g) On the surface of the laminated polyethylene microporous membrane that the cooling roll was in contact with, the laminated film was coated with a coating solution containing a binder having a tensile strength of 5 N/mm ² or more, an inorganic particle, and a solvent capable of dissolving or dispersing the binder. The process of forming and drying. The method for manufacturing a battery separator according to claim 9, wherein the solvent removing means for molding in the step (c) is a means for scraping using a doctor blade.

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