WO2015190264A1

WO2015190264A1 - Battery separator and production method therefor

Info

Publication number: WO2015190264A1
Application number: PCT/JP2015/064694
Authority: WO
Inventors: 水野　直樹; まさみ菅田; 孝一又野
Original assignee: 東レバッテリーセパレータフィルム株式会社
Priority date: 2014-06-10
Filing date: 2015-05-22
Publication date: 2015-12-17
Also published as: KR102137377B1; JPWO2015190264A1; CN106463679B; JP5876628B1; CN106463679A; KR20170016827A

Abstract

The present invention provides a battery separator on the assumption that battery separators will become increasingly thin and cost less in the future. This battery separator has extremely high peel strength with respect to a modified porous layer, is suitable for high-speed processing in slit processing and battery assembly processing, has excellent shutdown characteristics, and is suitable for a lithium ion battery. The battery separator comprises: a layered polyethylene microporous membrane in which at least two layers of a polyethylene microporous membrane are layered; and a modified porous layer that is present on at least one of the surfaces of the layered polyethylene microporous membrane. The layered polyethylene microporous membrane has a shutdown temperature of 128-135 °C, exhibits an air permeation resistance increase rate of less than 1.5 sec/100 cc air/°C from 30 °C to 105 °C as calculated by converting to a thickness of 20 µm, and comprises 3 to 200 protrusions per cm² that comprise polyethylene and that are present in an irregular manner on at least one outwardly facing surface thereof. The protrusions satisfy 0.5 µm ≤ H (H represents the height of the protrusions) and 5 µm ≤ W ≤ 50 µm (W represents the size of the protrusions). The modified porous layer is layered on the surface of the layered polyethylene microporous membrane that comprises the protrusions. The battery separator also comprises a binder that has a tensile strength of 5 N/mm² or more and inorganic particles.

Description

Battery separator and method for producing the same

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

Thermoplastic resin microporous membranes are widely used as separators and filters. For example, separators for lithium ion secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, polymer batteries, separators for electric double layer capacitors, and reverse osmosis filtration membranes, ultrafiltration membranes for filters And microfiltration membranes. In addition, it is used for moisture permeable waterproof clothing, medical materials, and the like. In particular, as a separator for lithium ion secondary battery, it has ion permeability by impregnation with electrolyte, is excellent in electrical insulation, electrolyte resistance, and oxidation resistance. A polyethylene microporous membrane having a pore blocking effect that blocks ion permeability and suppresses excessive temperature rise is suitably used. However, if the temperature continues to rise after clogging for some reason, a film breakage may occur due to a decrease in the viscosity of the polyethylene constituting the film or a contraction of the film. This phenomenon is not limited to polyethylene, and even when other thermoplastic resins are used, the phenomenon cannot be avoided beyond the melting point of the resin constituting the microporous film.

Lithium-ion battery separators are related to battery characteristics, battery productivity, and battery safety, and include mechanical characteristics, heat resistance, permeability, dimensional stability, pore plugging characteristics (shutdown characteristics), and melt-breaking characteristics (meltdown). Characteristics) and the like are required. Furthermore, in order to improve the cycle characteristics of the battery, it is required to improve the adhesion with the electrode material and to improve the electrolyte permeability to improve the productivity.

Therefore, it has been studied to stack various modified porous layers on a microporous membrane. As the modified porous layer, a polyamide-imide resin, a polyimide resin, a polyamide resin and / or a fluorine-based resin excellent in electrode adhesion, which have both heat resistance and electrolyte solution permeability are preferably used. In addition, a water-soluble or water-dispersible binder capable of laminating a modified porous layer using a relatively simple washing step and drying step is also widely used. The modified porous layer 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 an electrode material, and electrolyte permeability.

Furthermore, the battery separator needs to increase the area that can be filled in the container in order to improve the battery capacity, and it is predicted that the thinning will proceed. However, since microporous membranes are easily deformed in the planar direction as the film thickness is reduced, battery separators in which a modified porous layer is laminated on microporous membranes are modified during processing, in the slitting process, or in the battery assembly process. The porous layer may be peeled off, making it more difficult to ensure safety.

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

In Patent Document 1, polyvinylidene fluoride is applied to a polyethylene microporous film having a thickness of 9 μm, and a part of the polyvinylidene fluoride bites into the pores of the polyethylene porous film appropriately so as to express an anchor effect. A composite microporous membrane having a peel strength (T-type peel strength) at the interface between the porous membrane and the polyvinylidene fluoride coating layer of 1.0 to 5.3 N / 25 mm is disclosed.

In Patent Document 2, a heat-resistant porous layer containing a self-crosslinkable acrylic resin and plate-like boehmite is provided on a corona discharge-treated polyethylene microporous film having a thickness of 16 μm, and a polyethylene microporous film and a heat-resistant porous layer are provided. 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, polyethylene having a viscosity average molecular weight of 200,000, 47.5 parts by mass, 2.5 parts by mass of polypropylene having a viscosity average molecular weight of 400,000, and 50 parts by mass of a composition comprising an antioxidant and liquid paraffin A polyethylene resin solution consisting of 50 parts by mass is extruded from an extruder at 200 ° C., and a gel-like molded product is obtained while being drawn with a cooling roll adjusted to 25 ° C., and then biaxially so as to be 7 × 6.4 times. Stretching to obtain a polyethylene resin porous membrane. A laminated microporous membrane obtained by laminating a coating layer made of polyvinyl alcohol and alumina particles on the surface of the polyethylene resin microporous membrane is disclosed.

In Example 6 of Patent Document 4, a polyethylene resin solution having a weight average molecular weight of 41.5 million, a weight average molecular weight of 560,000, a polyethylene composition of 30% by weight and a mixed solvent of liquid paraffin and decalin of 70% by weight is extruded. Extruded from the machine at 148 ° C., cooled in a water bath to obtain a gel-like molded product, and then biaxially stretched to a size of 5.5 × 11.0 to obtain a polyethylene microporous membrane. A separator for a non-aqueous secondary battery obtained by laminating a coating layer made of meta-type wholly aromatic polyamide and alumina particles on the surface of this polyethylene microporous membrane is disclosed.

In Example 1 of Patent Document 5, 47 parts by mass of homopolymer polyethylene having a viscosity average molecular weight of 700,000, 46 parts by mass of homopolymer polyethylene having a viscosity average molecular weight of 250,000, and 7 parts by mass of polypropylene having a homopolymer of Mv 400,000 Dry blended using a tumbler blender. 1% by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99% by mass of the obtained pure polymer mixture, and again A polyethylene composition that has been dry-blended using a tumbler blender is melt-kneaded and extruded and cast onto a cooling roll controlled to a surface temperature of 25 ° C. to obtain a polyethylene composition in the form of a sheet having a thickness of 2000 μm. A laminated porous membrane obtained by applying an aqueous dispersion of calcined kaolin and latex to a polyethylene microporous membrane obtained by biaxial stretching so as to be × 7 times is disclosed.

Patent Document 6 discloses a separator for a lithium ion secondary battery in which a ceramic layer is laminated on a porous resin base material 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 film by stretching a laminate having a layer to which a low-melting-point resin is added and a layer not containing the layer.

However, in response to the demand for high-speed processing due to cost reduction, which will progress rapidly in the future, and the demand for thinner separators due to higher capacities, these conventional technologies locally improve during slit processing and battery assembly processing. Since the porous layer is peeled off, it is expected that it is difficult to ensure safety. In particular, if the polyethylene microporous membrane serving as a base material becomes thin, it becomes difficult to obtain a sufficient anchoring effect of the modified porous layer on the polyethylene microporous membrane, and thus it becomes more difficult to ensure safety.

JP 2012-037662 A Republished 2010-104127 Japanese Patent No. 4931083 Japanese Patent No. 4460028 JP 2011-000832 A JP 2011-071009 A Special table 2012-521914 gazette

The present invention assumes the case where the battery separator is made thinner and the processing speed is further advanced, and the peel strength between the modified porous layer and the laminated polyethylene microporous film is high. An object of the present invention is to provide a battery separator suitable for high-speed processing, in which a modified porous layer is laminated on a laminated polyethylene microporous membrane suitable for lamination of a modified porous layer.

The peel strength between the laminated polyethylene microporous membrane and the modified porous layer in the separator in the present specification is a value measured by the following method (hereinafter sometimes referred to as 0 ° peel strength).
FIG. 1 schematically shows the state of the side surface of a laminated sample of a laminated polyethylene microporous membrane and a modified porous layer pulled 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 pressure-sensitive adhesive tape, 5 and 5 'are aluminum plates, and the arrows in the figure are tensile directions. Lamination of sample (1) cut to a width of 50 mm x length of 100 mm on a double-sided adhesive tape (4) of the same size on an aluminum plate (5) of size 50 mm x 25 mm and thickness 0.5 mm The surface of the polyethylene microporous membrane (2) is pasted so that 40 mm overlaps from the end of one side of the 25 mm length of the aluminum plate (5), and the protruding part is cut off. Next, a double-sided adhesive tape is attached to one side of an aluminum plate (5 ′) having a length of 100 mm, a width of 15 mm, and a thickness of 0.5 mm. From the end of one side of the aluminum plate (5) on the 25 mm-long sample side. Paste so that 20mm overlaps. Thereafter, the aluminum plate (5) and the aluminum plate (5 ′) are pulled in parallel in opposite directions using a tensile tester at a tensile rate of 10 mm / min, and the strength when the modified porous layer is peeled is measured. If the peel strength is 130 N / 15 mm or more in this evaluation method, the laminated modified porous layer is being conveyed or processed even if the thickness of the laminated polyethylene microporous membrane is 10 μm or less, for example. There is almost no peeling phenomenon.
The T-type peel strength or 180 ° peel strength conventionally used as a peel strength measurement method is the peel force when the coating layer is peeled from the surface of the battery separator vertically or obliquely backward. is there. According to this evaluation method, it is possible to evaluate the abrasion resistance in the slit process and the battery assembly process more practically as compared with these conventional evaluation methods.

In order to solve the above problems, the battery separator of the present invention has the following configuration.
That is,
A battery separator having a laminated polyethylene microporous membrane and a modified porous layer present on at least one surface thereof, wherein the laminated polyethylene microporous membrane comprises at least an A layer and a B layer. The laminate has a shutdown temperature of 128 to 135 ° C., a rate of increase in air permeability resistance from 30 ° C. to 105 ° C. per 20 μm thickness is less than 1.5 sec / 100 cc Air / ° C., and at least one of the surfaces facing the outside is 3 There are irregular projections made of polyethylene of not less than 200 / cm ^{2 and not} more than 200 / cm ² , and the projections are 0.5 μm ≦ H (H is the height of the projection) and 5 μm ≦ W ≦ 50 μm (W is the projection) it viewed in magnitude), the modified porous layer is laminated on a surface having a projection of the laminated microporous polyethylene membrane, and a tensile strength of 5N / mm ² or more A battery separator comprising a binder and inorganic particles.
In the battery separator of the present invention, the laminated polyethylene microporous membrane preferably has a three-layer structure of A layer / B layer / A layer.
Here, the surface facing the outside world means that at least one of the surfaces of each layer constituting the laminated polyolefin microporous membrane faces the side (interface side) in contact with the surface of the other layer, but on the interface side. The other surface that does not face.
In the battery separator of the present invention, the B layer preferably comprises 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 lower than 130 ° C.
In the battery separator 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.
In the battery separator of the present invention, the content of the low melting point resin in the B layer is preferably 20% by mass or more and 35% by mass or less, based on 100% by mass of the entire polyethylene resin of the B layer.
In the battery separator of the present invention, the thickness of the B layer is preferably 3 μm or more and 15 μm or less.
In the battery separator of the present invention, the binder is preferably polyvinyl alcohol or an acrylic resin.
In the battery separator of the present invention, it is preferable that the inorganic particles include at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate and boehmite.
In order to solve the above-described problems, the battery separator manufacturing method of the present invention has the following configuration. That is,
(A) Step of adding a molding solvent to the polyethylene resin constituting the A layer and then melt-kneading to prepare the polyethylene resin solution A (b) Low melting point resin and molding solvent for the polyethylene resin constituting the B layer Step (c) of preparing polyethylene resin solution B by extruding polyethylene resin solutions A and B obtained in steps (a) and (b) from a die, and adding at least one of Step (d) of forming a laminated gel-like molded product by cooling with a cooling roll having a surface from which the molding solvent has been removed by the molding solvent removing means, and stretching the laminated gel-like molded product in the machine direction and the width direction. (E) A step of obtaining a laminated stretched molded product (e) A step of extracting and removing the solvent for lamination molding from the laminated stretched molded product and drying to obtain a laminated porous molded product (f) Laminated porous molded product Heat treating, dissolved obtain a laminated microporous polyethylene membrane step (g) the surface of the laminated polyethylene cooling roll was in contact microporous membrane, tensile strength 5N / mm ² or more binders, inorganic particles and a binder Or the manufacturing method of the separator for batteries including the process of forming a laminated film using the coating liquid containing the solvent which can be disperse | distributed, and drying.
In the method for producing a battery separator of the present invention, the forming solvent removing means in the step (c) is preferably a means for scraping off using a doctor blade.

According to the present invention, a battery separator in which a modified porous layer is laminated on a laminated polyethylene microporous film having excellent adhesion to the modified porous layer, and the modified porous layer does not peel even during high-speed conveyance. Is obtained.

Schematic which shows the measuring method of 0 degree peeling strength. Schematic which shows the spherulite structure and crystal nucleus of polyethylene in a laminated polyethylene microporous membrane. The microscope picture of the ring-shaped trace derived from the spherulite of polyethylene in a laminated polyethylene microporous membrane. Schematic which shows the process of forming a laminated gel-like molding, extruding a polyethylene resin solution from the die | dye installed in the front-end | tip of an extruder, and cooling with a cooling roll.

The laminated polyethylene microporous membrane used in the present invention adjusts a specific polyethylene resin solution and highly controls the cooling rate of the polyethylene resin solution extruded from the extruder via the die, so that the surface has an appropriate amount. It has shape and number of protrusions. In the present invention, when a modified porous layer containing inorganic particles and a binder having a tensile strength of 5 N / mm ² or more is laminated on a laminated polyethylene microporous membrane, the invention is provided between the laminated polyethylene microporous membrane and the modified porous layer. With this, extremely excellent peel strength can be obtained.

The projection referred to in the present invention is essentially different from the projection obtained by adding, for example, inorganic particles to a laminated polyethylene microporous film. The protrusions obtained by adding inorganic particles to the laminated polyethylene microporous membrane are usually extremely small in height, and if it is intended to form protrusions with a height of 0.5 μm or more by the same means, the laminated polyethylene microporous film It is necessary to add particles having a particle size equal to or greater than the thickness of the film. However, when such particles are added, the strength of the laminated polyethylene microporous membrane is lowered, which is not realistic.

The protrusions referred to in the present invention are those in which a part of the surface layer of the laminated polyethylene microporous membrane is grown to a moderately raised shape, and do not deteriorate the basic characteristics of the laminated polyethylene microporous membrane. .

The irregularly scattered projections referred to in the present invention are arranged with regularity or periodicity obtained by passing through an embossing roll before or after the stretching step in the production of a laminated polyethylene microporous membrane. It is clearly different from the protrusion. Press work such as embossing is basically not preferred because it forms protrusions by compressing and tends to cause a decrease in air resistance and electrolyte permeability.

The moderately shaped protrusion as used in the present invention means a protrusion 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 protrusion) and 0.5 μm ≦ H (H is the height of the protrusion). Such a protrusion functions as an anchor when the modified porous layer is laminated on the laminated polyethylene microporous film, and as a result, the battery separator having a large 0 ° peel strength is obtained. On the other hand, the upper limit of the height is not particularly limited, but 3.0 μm is sufficient. The more the protrusions are sufficiently high, the higher the 0 ° peel strength tends to be. That is, the 0 ° peel strength is affected 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 the protrusions is preferably three / cm ^2, more preferably 5 / cm ^2, more preferably is 10 / cm ^2. The upper limit of the number of protrusions is preferably 200 / cm ² , more preferably 150 / cm ² . The lower limit of the height of the protrusion is preferably 0.5 μm, more preferably 0.8 μm, and still more preferably 1.0 μm. In addition, the magnitude | size and height of a processus | protrusion in this invention say the value measured with the measuring method mentioned later.

The increase in the air resistance referred to in the present invention means a difference between the air resistance of the laminated polyethylene microporous membrane and the air resistance of the battery separator, and is preferably 90 seconds / 100 cc Air or less. Preferably it is 80 cc Air, more preferably 50 cc Air.

The outline of the laminated polyethylene microporous membrane, the modified porous layer, and the battery separator of the present invention will be described, but it is naturally 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, and even more preferably 16 μm. The lower limit is preferably 7 μm, more preferably 9 μm. If the thickness of the laminated polyethylene microporous membrane is within the above preferred range, practical membrane strength and pore blocking function can be retained, and the area per unit volume of the battery case is not restricted, and will proceed in the future. It is suitable for increasing the capacity of batteries.

The shutdown temperature of the laminated polyethylene microporous membrane is preferably 128 ° C or higher and lower than 135 ° C. The upper limit is more preferably less than 133 ° C, and even more preferably less than 130 ° C. If the shutdown temperature is lower than 135 ° C., the pores are quickly closed due to heat generation when the battery is abnormal, and the battery reaction is stopped, so that the safety of the battery is increased.

The upper limit of the air resistance of the laminated polyethylene microporous membrane is preferably 300 sec / 100 cc Air, more preferably 200 sec / 100 cc Air, still more preferably 150 sec / 100 cc Air, and the lower limit is preferably 50 sec / 100 cc Air, more preferably 70 sec. / 100 cc Air, more preferably 100 sec / 100 cc Air.

The rate of increase in air resistance of the laminated polyethylene microporous membrane per 20 μm when the temperature is changed from 30 ° C. to 105 ° C. is preferably 1.5 sec / 100 cc Air / ° C. or less, more preferably 1.2 sec / 100 cc Air / ° C. or less, Preferably, it is 1.0 sec / 100 cc Air / ° C. or less. If the rate of increase in air permeability resistance is 1.5 sec / 100 cc Air / ° C. or less, sufficient ion permeability can be secured even when heat is applied during coating or battery production.

The upper limit of the porosity of the laminated polyethylene microporous membrane is preferably 70%, more preferably 60%, and even more preferably 55%. The lower limit is preferably 30%, more preferably 35%, still more preferably 40%. When the air permeability resistance and the porosity are within the above preferred ranges, sufficient battery charge / discharge characteristics, particularly ion permeability (charge / discharge operating voltage) and battery life (closely related to the amount of electrolyte retained) The battery functions sufficiently as a battery. Moreover, since sufficient mechanical strength and insulating properties are obtained, the possibility of a short circuit during charge / discharge is reduced.

The average pore size of the laminated polyethylene microporous membrane greatly affects the pore closing performance, so it is preferably 0.01 to 1.0 μm, more preferably 0.05 to 0.5 μm, still more preferably 0.1 to 0. .3 μm. When the average pore size of the laminated polyethylene microporous membrane is within the above preferred range, the 0 ° peel strength of the modified porous layer sufficient due to the anchor effect of the functional resin is obtained, and when the modified porous layer is laminated, The air resistance is not greatly deteriorated, and the response to the temperature of the hole closing phenomenon is not slowed, and the hole closing temperature due to the heating rate is not shifted to a higher temperature side.

Hereinafter, the polyethylene resin used in the present invention will be described in detail.
[1] Polyethylene resin in the first layer (A layer) The A layer of the present invention is a microporous membrane mainly composed of polyethylene. In order to improve the permeability and puncture strength, the polyethylene content is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass, based on 100% by mass of the entire resin.

The types of polyethylene, high density polyethylene such as density exceeding 0.94 g / cm ^3, density polyethylene in the range density of 0.93 ~ 0.94g / cm ^3, density of from 0.93 g / cm ³ Examples include low low density polyethylene, ultra high molecular weight polyethylene, and linear low density polyethylene. From the viewpoint of strength, it is preferable to contain high-density polyethylene and ultrahigh molecular weight polyethylene.

The ultra high molecular weight polyethylene is not limited to a homopolymer of ethylene but may be a copolymer containing a small amount of other α-olefin. Examples of the α-olefin include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, styrene and the like. In a laminated microporous membrane, especially when it is produced by a coextrusion method, it may be difficult to control the physical property unevenness in the width direction due to a difference in viscosity of each layer, but by using ultrahigh molecular weight polyethylene for the A layer. In addition, since the molecular network of the entire film becomes strong, non-uniform deformation hardly occurs, and a microporous film having excellent uniformity of physical properties can be obtained.

The weight average molecular weight (hereinafter referred to as Mw) of the high density polyethylene is preferably 1 × 10 ⁵ or more, and more preferably 2 × 10 ⁵ or more. The upper limit is preferably 8 × 10 ⁵ for Mw, more preferably 7 × 10 ⁵ for Mw. If Mw is within the above range, the stability of film formation and the finally obtained puncture strength can both be achieved.

The Mw of the ultra high molecular weight polyethylene is preferably 1 × 10 ⁶ or more and less than 4 × 10 ⁶ . By using ultra high molecular weight polyethylene having an Mw of 1 × 10 ⁶ or more and less than 4 × 10 ⁶ , the pores and fibrils can be miniaturized and the puncture strength can be increased. Further, if Mw is 4 × 10 ⁶ or more, the viscosity of the melt becomes too high, so that there may be a problem in the film forming process such that the resin cannot be extruded from the die. Moreover, in this invention, when the viscosity difference with B layer mentioned later becomes high too much, especially in the lamination | stacking by a coextrusion method, each layer may be unable to be extruded uniformly.

The content of ultra high molecular weight polyethylene is 100% by mass with respect to the entire polyethylene resin of the A layer, 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. Within this range, it is easy to obtain both puncture strength and air resistance, and a microporous membrane with less variation in air resistance can be obtained. When the content of the ultrahigh molecular weight polyethylene is within a preferable range, a sufficiently high protrusion can be obtained. When the modified porous layer is laminated by this projection, the projection functions as an anchor, and extremely strong peeling resistance can be obtained with respect to the force applied in parallel to the surface direction of the laminated polyethylene microporous film. Moreover, even when the thickness of the laminated polyethylene microporous film is reduced, sufficient tensile strength can be obtained. The tensile strength is preferably 100 MPa or more. There is no particular upper limit.

The layer A does not substantially contain a low melting point resin. “Substantially free of low melting point resin” means that, for example, the fraction of an elution component of 90 ° C. or less extracted by a cross fractionation chromatograph or the like is preferably 5.0% by mass or less, more preferably 2.5% by mass. % Or less. This is because even if a low-melting point resin is not added intentionally, the polymer has a distribution in molecular weight, and therefore low-molecular components that can have a low melting point are included, so it is difficult to achieve 0% by mass. It is. When the low melting point resin is present in all layers, the air permeability resistance may be easily deteriorated when heated even before shutdown.

The elution component by a cross fractionation chromatograph can be calculated | required as follows, for example.
Measurement device: Cross fractionation chromatograph CFC2 type (manufactured by Polymer ChAR)
Detector: Infrared spectrophotometer IR4 type (manufactured by Polymer ChAR)
・ Detection wavelength: 3.42 μm
Column: “Shodex” (registered trademark) UT806M manufactured by Showa Denko KK
-Column temperature: 140 ° C
Solvent (mobile phase): o-dichlorobenzene Solvent flow rate: 1.0 ml / min Sample concentration: 3.0 mg / ml
・ Temperature drop time: 140 minutes (140 ° C → 0 ° C)
-Elution component amount below 90 ° C: The total extraction amount is the sum of the weights from 0 ° C to 90 ° C among the extraction amounts when fractionating from 0 ° C to 140 ° C every 10 ° C. By dividing, the amount of elution component of 90 ° C. or less is calculated.

[2] Polyethylene resin composition in the second layer (B layer) The B layer of the present invention is a microporous membrane mainly composed of polyethylene. The B layer preferably contains 50% by mass or more of high-density polyethylene from the viewpoint of strength. Further, the weight average molecular weight (hereinafter referred to as Mw) of the high density polyethylene is preferably 1 × 10 ⁵ or more, more preferably 2 × 10 ⁵ or more. The upper limit of Mw is preferably 8 × 10 ⁵ for Mw, more preferably 7 × 10 ⁵ for Mw. If Mw is in the above range, the stability of the film formation and the finally obtained puncture strength can both be achieved.

In the present invention, it is important to add a low melting point resin such as low density polyethylene, linear low density polyethylene, 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, and the characteristics as a battery separator can be improved. Here, the above-mentioned thing is mentioned as an 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, so that it is difficult to produce uneven thickness in the stretching process, and a uniform film thickness distribution can be obtained. Further, since the molecular mobility is good, residual strain hardly remains, and since the molecules are sufficiently relaxed at a low temperature, the pores are hardly clogged due to the residual strain 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 the coextrusion with the A layer, each layer may not be extruded uniformly. Further, in the stretching process at the time of production, the microporous membrane may be broken due to low viscosity.

It is important that the melting point of the low melting point resin is 120 ° C. or higher and lower than 130 ° C. When the melting point is less than 120 ° C., the melting point is too low, so that when the stretching temperature is raised to a temperature at which the laminate can be sufficiently stretched when laminated with the A layer containing ultrahigh molecular weight polyethylene, There is a risk of adverse effects and deterioration of air resistance. On the other hand, when the entire stretching temperature is lowered to prevent the pores from being blocked, the softening of the entire laminate becomes insufficient, and the thickness uniformity expected by adding ultrahigh molecular weight polyethylene in the A layer You may not be able to get the full effect. On the other hand, when the melting point is 130 ° C. or higher, it is difficult to achieve a target low shutdown temperature.

The content of the low melting point resin is 100% by mass with respect to the entire polyethylene resin constituting the B layer, 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% by mass or more, the shutdown temperature can be lowered. Further, when it is 30% by mass or less, breakage of the microporous membrane caused by low viscosity can be suppressed.

Similar to the A layer, from the viewpoint of strength and formation of protrusions, the B layer preferably contains ultrahigh molecular weight polyethylene. The ultra high molecular weight polyethylene may be not only a homopolymer of ethylene but also a copolymer containing a small amount of other α-olefin. The puncture strength can be improved by adding ultrahigh molecular weight polyethylene. The Mw of the ultra high molecular weight polyethylene is preferably 1 × 10 ⁶ or more and less than 4 × 10 ⁶ . By using ultra high molecular weight polyethylene having an Mw of 1 × 10 ⁶ or more and less than 4 × 10 ⁶ , the pores and fibrils can be miniaturized. As a result, the hole is quickly closed by the low melting point resin, and the shutdown temperature can be lowered more effectively.

The content of ultrahigh molecular weight polyethylene is 100% by mass with respect to 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, and even more preferably 30% by mass. Since ultrahigh molecular weight polyethylene has a large difference in molecular mobility with a low melting point resin, if it exceeds 40% by mass, separation from the low melting point resin is likely to proceed during melt-kneading, and the microporous membrane finally obtained May cause poor appearance.

The polyethylene microporous membrane of the present invention has an antioxidant, a heat stabilizer, an antistatic agent, an ultraviolet absorber, an anti-blocking agent and a filling material, as long as both the A layer and the B layer do not impair the effects of the present invention. Various additives such as materials may be included. In particular, it is preferable to add an antioxidant for the purpose of suppressing oxidative deterioration due to the thermal history of the polyethylene resin. Appropriate selection of the type and amount of the antioxidant and heat stabilizer is important for adjusting or enhancing the characteristics of the microporous membrane.

The laminated polyethylene microporous membrane used in the present invention preferably contains substantially no inorganic particles. “Substantially free of inorganic particles” means, for example, a content that is 50 ppm or less, more preferably 10 ppm or less, and even more preferably a detection limit or less when inorganic elements are quantified by fluorescent X-ray analysis. To do. Even if particles are not actively added to the laminated polyethylene microporous membrane, contaminants derived from foreign substances, and dirt attached to the lines and equipment in the manufacturing process of the raw resin or polyolefin microporous membrane peel off, It may be mixed in the film and 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 together with the A layer is preferably in the range of 5 to 200, more preferably 10 to 100. is there. When the range of Mw / Mn is the above preferred range, extrusion of the polyethylene solution is easy. In addition, the polyethylene microporous film can obtain a sufficient number of protrusions on the surface, and even when the thickness of the polyethylene microporous film is reduced, sufficient mechanical strength can be obtained. Mw / Mn is used as a measure of molecular weight distribution. For example, in the case of polyethylene consisting of a single substance, the larger this value, the wider the molecular weight distribution. The Mw / Mn of polyethylene composed of a single substance can be appropriately adjusted by multistage polymerization of polyethylene. Moreover, Mw / Mn of the mixture of polyethylene can be suitably adjusted by adjusting the molecular weight and mixing ratio of each component.

The present inventors consider the mechanism by which protrusions are formed in the present invention as follows. The resin solution of the melted polyethylene resin and the molding solvent is extruded from the die, and at the same time, the crystallization of polyethylene is started. The crystallization speed is increased by contacting the cooling roll and quenching. At this time, a spherulite having a symmetric structure having a crystal nucleus is formed (FIG. 2). When the heat transfer rate between the cooling roll surface and the molten polyethylene resin is relatively low, the crystallization rate is low, and as a result, spherulites having relatively small crystal nuclei are formed. When the heat transfer rate is high, the spherulite has a relatively large crystal nucleus. The crystal nuclei of these spherulites become protrusions during TD (width direction) and / or MD (machine direction) stretching, which is a subsequent process. Spherulites appear as ring-shaped marks on the surface of the laminated polyethylene microporous membrane (FIG. 3).

[3] Method for Producing Laminated Polyethylene Microporous Membrane A laminated polyethylene microporous membrane can be freely selected according to the purpose as long as it satisfies the above various characteristics. Microporous membrane production methods include the foaming method, phase separation method, dissolution recrystallization method, stretch pore opening method, powder sintering method, etc. Among these, in terms of homogenizing fine pores and cost, A separation method is preferred.

As a manufacturing method by the phase separation method, for example, polyethylene and a molding solvent are heated and melt-kneaded, and the obtained molten mixture is extruded from a die and cooled to form a gel-like molded product, and the obtained gel-like molding is obtained. Examples include a method of obtaining a microporous film by stretching the product in at least a uniaxial direction and removing the molding solvent.

A method for producing a laminated polyethylene microporous membrane used in the present invention will be described.
The method for producing a laminated polyethylene microporous membrane of the present invention includes the following steps (a) to (f).
(A) Step of adding a molding solvent to the polyethylene resin composition constituting the A layer and then melt-kneading to prepare a polyethylene resin solution A (b) Adding a molding solvent to the polyethylene resin composition constituting the B layer After adding, melt-kneading and preparing polyethylene resin solution B (c) The polyethylene resin solutions A and B obtained in steps (a) and (b) are extruded from a die, and at least one of them is molded. Step (d) of forming a laminated gel-like molded product by cooling with a cooling roll having a surface from which the molding solvent has been removed by the solvent removal means, and stretching the laminated gel-like molded product in the machine direction and width direction Step of obtaining stretched molded product (e) Step of extracting and removing molding solvent from laminated stretched molded product and drying to obtain laminated porous molded product (f) Heat treatment of laminated porous molded product, Obtaining a Shitsumaku Furthermore, it prior to step (a), during the process (a) ~ (f), or hydrophilic treatment after step (f), also add other steps neutralization treatment. Moreover, a redrawing process can also be provided after a process (f).

Hereinafter, each process is explained in full detail.
(A), (b) Step of adding a molding solvent to the polyethylene resin constituting the A layer and the B layer and then melt-kneading to prepare polyethylene resin solutions A and B. As a molding solvent, polyethylene is sufficient If it can melt | dissolve, it will not specifically limit. For example, nonane, decane, undecane, dodecane, liquid paraffin and other aliphatic or cyclic hydrocarbons, or mineral oil fractions with boiling points corresponding to these, gel-like molded products with a stable solvent content Nonvolatile solvents such as liquid paraffin are preferred for obtaining. The dissolution by heating is performed by a method in which the polyethylene composition is completely dissolved and stirred and uniformly mixed in an extruder. The temperature varies depending on the polymer and solvent to be used when it is dissolved in an extruder or in a solvent while stirring, but it is preferably in the range of 140 to 250 ° C., for example.

The concentration of the polyethylene resin is preferably 15 to 40% by mass, more preferably 25 to 40% by mass, and further preferably 28 to 35% by mass, where the total of the polyethylene resin and the molding solvent is 100% by mass. When the concentration of the polyethylene resin is within the above preferable range, a sufficient number of crystal nuclei for forming protrusions are formed, and a sufficient number of protrusions are formed. In addition, swell and neck-in are suppressed at the die outlet when extruding the polyethylene resin solution, and the moldability and self-supporting property of the extruded product are maintained.

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

The method of melt kneading is not particularly limited, but is usually performed by uniformly kneading in an extruder. This method is suitable for preparing highly concentrated solutions of polyethylene. The melt kneading temperature varies 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., and further preferably 170 ° C. The upper limit is preferably 250 ° C, more preferably 230 ° C, and even more preferably 200 ° C. The molding solvent may be added before the start of kneading, or may be added from the middle of the extruder during kneading and further melt kneaded. In melt kneading, it is preferable to add an antioxidant to prevent oxidation of polyethylene.

From the viewpoint of suppressing the deterioration of the resin, the melt kneading temperature is preferably low, but if it is lower than the above-mentioned temperature, an unmelted product is generated in the extrudate extruded from the die, causing film breakage or the like in the subsequent stretching step. It may be a cause. On the other hand, when the temperature is higher than the above-described temperature, the thermal decomposition of polyethylene becomes severe, and physical properties of the resulting microporous film, such as puncture strength and tensile strength, may be inferior.

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

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

(C) The polyethylene resin solutions A and B obtained in (a) and (b) are extruded from a die, and at least one of them is a cooling roll having a surface from which the molding solvent is removed by the molding solvent removing means. The step of cooling and forming a laminated gel-like molded product The polyethylene resin solutions A and B melt-kneaded by an extruder are pushed up directly from a die or through another extruder and cooled by a cooling roll. To form a laminated gel-like molded product. As a method for obtaining a laminated gel-like molded product, a method for separately laminating gel-shaped molded products to be laminated and then pasting them through a calender roll or the like (sticking method), or supplying a polyethylene solution separately to an extruder is desired. Any method may be used such as a method of melting at a temperature of 5 ° C, joining in a polymer tube or die, coextrusion and laminating, and then forming a laminated gel-like molded product (coextrusion method). From the viewpoint of adhesion, it is preferable to use a coextrusion method.

A gel-like molded product is formed by bringing a polyethylene resin solution extruded from a die into contact with a rotating cooling roll set at a surface temperature of 20 ° C. to 40 ° C. with a refrigerant. The extruded polyethylene resin solution is preferably cooled to 25 ° C. or lower. Here, the cooling rate in the temperature range where crystallization is substantially performed becomes important. For example, the extruded polyethylene resin solution is cooled at a cooling rate of 10 ° C./second or more in a temperature range where crystallization is substantially performed to obtain a gel-like molded product. The cooling rate is preferably 20 ° C./second or more, more preferably 30 ° C./second or more, and further preferably 50 ° C./second or more. By carrying out such cooling, the structure in which the polyethylene phase is microphase-separated by the solvent is fixed, and spherulites having relatively large nuclei are formed on the surface of the gel-like molded product in contact with the cooling roll. Appropriately shaped protrusions can be formed. The cooling rate can be estimated by simulating from the extrusion temperature of the gel-shaped molded product, the thermal conductivity of the gel-shaped molded product, the thickness of the gel-shaped molded product, the molding solvent, the cooling roll, and the heat transfer coefficient of air.

In the present invention, it is important to remove as much as possible the forming solvent adhering to the surface of the cooling roll in contact with the polyethylene resin solution extruded from the die. As shown in FIG. 4, the polyethylene resin solution is cooled by wrapping around a rotating cooling roll to become a gel-like molded product, but the molding solvent adheres to the surface of the cooling roll after the gel-like molded product is pulled apart. Usually, it comes into contact with the polyethylene resin solution again as it is. However, if a large amount of the forming solvent adheres to the surface of the cooling roll, the cooling rate becomes slow due to the heat insulating effect, and it becomes difficult to form protrusions. Therefore, it is important to remove the forming solvent as much as possible before the cooling roll comes into contact with the polyethylene resin solution again.

The method for removing the molding solvent, that is, the method for removing the molding 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-like molded article and passed through the doctor blade. A method is preferably employed in which the molding solvent is scraped off to the extent that the cooling roll surface is invisible until immediately after the gel-like molded product comes into contact. Alternatively, it can be removed by means such as blowing with compressed air, suction, or a combination of these methods. Among them, the method of scraping off using a doctor blade is preferable because it can be carried out relatively easily, and it is more preferable to use a plurality of doctor blades in order to improve the removal efficiency of the forming 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. If it is made of metal, the cooling roll may be scratched. 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 does not only provide a sufficient cooling rate due to the heat insulating effect of the forming solvent, but also causes surface roughness on the gel-like molded product due to condensation on the cooling roll. There is a case.

The thickness of the polyethylene resin solution during extrusion is preferably 1500 μm or less, more preferably 1000 μm or less, and still 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 on the surface on the side of the cooling roll is preferably not slow.

Here, when a laminated gel-like molded product is obtained by the bonding method, if at least one of the polyethylene resin solutions to be the A layer or the B layer is formed as a gel-like molded product under the above cooling conditions. Good. In addition, when bonding together, it is necessary to laminate | stack so that the surface which contacted the cooling roll of the layer formed on the said cooling conditions may become the surface. Further, when a laminated gel-like molded product is obtained by the coextrusion method, the polyethylene resin solution laminated and extruded from the die may be formed as a laminated gel-like molded product under the above cooling conditions.

The laminated polyolefin is a porous laminate comprising at least an A layer and a B layer. The layer structure of the laminated polyethylene may be at least two layers of the A layer and the B layer from the viewpoint of physical properties balance such as shutdown characteristics and strength and permeability, but from the viewpoint of the balance between the front and back of the final film, A three-layer structure of A layer / B layer / A layer or B layer / A layer / B layer is more preferable. 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 the balance between permeability and strength, the surface layer is the A layer, The inner layer is preferably a B layer. On the other hand, from the viewpoint of shutdown, it is preferable that the surface layer is B and the inner layer is A.

The ratio of the B layer is preferably 30% by mass or more and 80% by mass or less with respect to the mass of all layers. The lower limit is more preferably 40% by mass, and the upper limit is more preferably 70% by mass. If the ratio of the B layer is within the above range, the balance between the low shutdown characteristics due to the low melting point component, the stability of the permeability in the usage range of the separator, and the puncture strength can be made good.

The thickness of layer B of the laminated polyethylene microporous membrane is preferably 3 μm or more and 15 μm or less. The upper limit is more preferably 10 μm, further preferably 7 μm, and most preferably 6 μm. The lower limit is more preferably 4 μm. 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) Step of stretching laminated gel-like molded product in MD (machine direction) and TD (width direction) to obtain laminated stretched molded product The laminated gel-like molded product is stretched to obtain a stretched molded product. Stretching is performed by heating the gel-like molded product and performing normal tenter method, roll method, or a combination of these methods at a predetermined magnification in two directions of MD and TD. The stretching may be either simultaneous stretching (simultaneous biaxial stretching) or sequential stretching in MD and TD (machine direction and width direction). In the sequential stretching, the order of MD and TD is not limited, and at least one of MD and TD may be stretched in multiple stages. The draw ratio varies depending on the thickness of the original fabric, but is preferably 9 times or more, more preferably 16 to 400 times in terms of surface magnification. For 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 preferable. When the surface magnification is in the above preferred range, stretching is sufficient and a highly elastic, high strength microporous membrane can be obtained. Moreover, a desired air resistance can be obtained by adjusting the stretching temperature.

The stretching temperature is preferably not higher than the melting point of the low melting point resin added to the B layer. When the melting point is lower than the melting point of the low melting point resin added to the layer B, poor cracking of the hole due to melting of the low melting point resin is prevented, and it becomes possible to efficiently orient the molecular chain by stretching, so that it has good strength. Can be obtained. Moreover, it is preferable that the minimum of extending | stretching temperature is more than the crystal dispersion temperature of the polyethylene resin which comprises A layer. If the stretching temperature is equal to or higher than the crystal dispersion temperature of the polyethylene resin constituting the A layer, the polyethylene resin is sufficiently softened even in the A layer, so that nonuniform deformation that may occur due to insufficient softening is suppressed, and A Since uniform opening by the molecular network formed by the ultrahigh molecular weight polyethylene added to the layer is possible, in addition to good permeability, the physical properties are also uniform. Further, since the stretching tension of the entire laminate can be sufficiently lowered, the film-forming property is improved, and it is difficult to break the film during stretching, and stretching at a high magnification is possible. The crystal dispersion temperature Tcd is determined from the temperature characteristics of dynamic viscoelasticity measured according to ASTM D 4065. Or it may obtain | require from NMR.

(E) A step of extracting and removing the molding solvent from the laminated stretched molded product and drying to obtain a laminated porous molded product. The stretched molded product is treated with a washing solvent to remove the remaining molding solvent, A porous membrane is obtained. Cleaning solvents include hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as ethane trifluoride, and ethers such as diethyl ether and dioxane. Volatile ones can be used. These washing solvents are appropriately selected according to the molding solvent used for dissolving polyethylene, and used alone or in combination. The cleaning method can be performed by a method of immersing and extracting in a cleaning solvent, a method of showering the cleaning solvent, a method of sucking the cleaning solvent from the opposite side of the stretched molded product, or a method of a combination thereof. Washing as described above is performed until the residual solvent in the stretched molded product, which is a stretched molded product, is less than 1% by mass. Thereafter, the cleaning solvent is dried. The cleaning solvent can be dried by heat drying, air drying, or the like.

(F) Step of heat-treating the 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 90 to 150 ° C. When the heat treatment temperature is within the above preferred range, the heat shrinkage rate of the obtained laminated polyethylene microporous membrane can be reduced, and the air resistance can be ensured. The heat treatment time is not particularly limited, but it is usually preferably 1 second to 10 minutes, more preferably 3 seconds to 2 minutes. For the heat treatment, any of a tenter method, a roll method, a rolling method, and a free method can be adopted.

In the heat treatment step, it is preferable to grip in both the MD (machine direction) and TD (width direction) directions and contract in at least one direction of MD and TD. The contraction rate for contracting in at least one direction of MD and TD is preferably 0.01 to 50%, more preferably 3 to 20%. When the shrinkage rate is within the above preferable range, the thermal shrinkage rate at 105 ° C. and 8 hours is improved, and the air resistance is maintained. Further, in order to improve the puncture strength such as the puncture strength, TD or MD may be further performed before the heat treatment, or redrawing of about 5% to 20% in both directions may be performed.

If necessary, the microporous membrane may be hydrophilized. By performing the hydrophilization treatment, for example, when coating a heat-resistant resin layer, the adhesion between the surface of the microporous membrane and the modified porous layer and the uniformity of the coating film can be further improved. The hydrophilic treatment can be performed by monomer grafting, surfactant treatment, corona discharge or the like. Monomer grafting is preferably performed after the crosslinking treatment. The corona discharge treatment can be performed in air, nitrogen, or a mixed atmosphere of carbon dioxide and nitrogen.

Next, the modified porous layer used in the present invention will be described.
The modified porous layer is preferably laminated on the side of the laminated polyethylene microporous membrane having the protrusions. When a modified porous layer is provided on both sides of a laminated polyethylene microporous membrane, the modified porous layer on the side to which parallel stress is more strongly applied by the contact of a roll or a bar in a subsequent process such as a slitting process or a conveying process. Lamination is preferably performed on the side of the laminated polyethylene microporous membrane having the protrusions 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 an electrode material, 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, a battery separator having an extremely excellent 0 ° peel strength can be obtained by the synergistic effect of the protrusions present on the surface of the laminated polyethylene microporous membrane and the tensile strength of the binder. . Moreover, even if a modified porous layer is laminated, the battery separator does not significantly increase the air resistance as compared with the case of a laminated polyethylene microporous membrane alone. This is because sufficient 0 ° peel strength can be obtained without allowing a large amount of binder to penetrate into the pores of the laminated polyethylene microporous membrane.

Tensile strength of the binder is at 5N / mm ² or more, the lower limit is preferably 10 N / mm ^2, more preferably 20 N / mm ^2, more preferably 30 N / mm ^2. There is no particular upper limit, but 100 N / mm ² is sufficient. The tensile strength of the binder refers to a value measured by the method described later.

The use tensile strength of 5N / mm ² or more binders in the present invention, although the tensile strength is not particularly limited as long as 5N / mm ² or more, e.g., polyvinyl alcohol, cellulose ether resins, and acrylic resins . Examples of the cellulose ether resin include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanethyl cellulose, oxyethyl cellulose and the like. As the acrylic resin, a cross-linked acrylic resin is preferable. Commercially available aqueous solutions or aqueous dispersions can also be used. Examples of commercially available products include “POVACOAT” (registered trademark) manufactured by Nisshin Kasei Co., Ltd., “Jurimer” (registered trademark) AT-510, ET-410, FC-60 manufactured by Toa Gosei Co., Ltd. Examples include SEK-301, UW-223SX, UW-550CS manufactured by Taisei Fine Chemical Co., Ltd., WE-301, EC-906EF, CG-8490 manufactured by DIC Corporation. Of these, polyvinyl alcohol and acrylic resins having electrode adhesion, high affinity with non-aqueous electrolytes, suitable heat resistance, and relatively high tensile strength are preferable.

In order to reduce curling of the laminated polyethylene microporous membrane by laminating the modified porous layer, it is important to include inorganic particles in the coating solution for forming the modified porous layer. The coating liquid in this specification contains a binder having a tensile strength of 5 N / mm ² or more, inorganic particles, and a solvent capable of dissolving or dispersing the binder, and is used for forming a modified porous layer. The binder has at least a role of bonding inorganic particles and a role of bonding the laminated polyethylene microporous membrane and the modified porous layer. Examples of the solvent include water, alcohols, acetone, and n-methylpyrrolidone. By adding inorganic particles to the coating solution, the effect of preventing internal short circuit (dendrite prevention effect) due to the growth of the dendritic crystals of the electrode inside the battery, the effect of reducing the heat shrinkage, and the provision of slipperiness are also obtained. be able to. The upper limit of the amount of added particles is preferably 98% by mass, more preferably 95% by mass. The lower limit is preferably 80% by mass, and more preferably 85% by mass. When the amount of particles added is in the above preferred range, the curl reduction effect is sufficient, the ratio of the functional resin to the total volume of the modified porous layer is optimal, and sufficient 0 ° of the modified porous layer is obtained. Peel strength is obtained.

The average particle size of the inorganic particles is preferably 1.5 times or more and 50 times or less, more preferably 2.0 times or more and 20 times or less of the average pore size of the laminated polyethylene microporous membrane. When the average particle size of the particles is within the above-mentioned preferable 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 resistance is maintained, and further, the battery is assembled. In the process, the particles are prevented from falling off and causing a serious defect of the battery.

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. Moreover, you may add a heat resistant crosslinked polymer particle as needed. Examples of the heat-resistant crosslinked polymer particles include crosslinked polystyrene particles, crosslinked acrylic resin particles, and crosslinked methyl methacrylate particles. Examples of the shape of the inorganic particles include a true spherical shape, a substantially spherical shape, a plate shape, a needle shape, and a polyhedral shape, but are not particularly limited.

The solid content concentration of the coating solution is not particularly limited as long as it can be uniformly applied, 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 solution is in the above preferred range, the modified porous layer is prevented from becoming brittle, and a sufficient peel strength of 0 ° of the modified porous layer can be obtained.

The film thickness of the modified porous layer is preferably 1 to 5 μm, more preferably 1 to 4 μm, and still more preferably 1 to 3 μm. When the film thickness of the modified porous layer is within the above preferred range, the battery separator obtained by laminating the modified porous layer can ensure the film breaking strength and insulation when melted / shrinked at the melting point or higher, and A sufficient pore blocking function can be obtained and abnormal reactions can be prevented. Moreover, the winding volume can be suppressed, which is suitable for increasing the battery capacity. In addition, suppressing curling leads to improved productivity in the battery assembly process.

The porosity of the modified porous layer is preferably 30 to 90%, more preferably 40 to 70%. The desired porosity can be obtained by appropriately adjusting the concentration of inorganic particles, the binder concentration, and the like. When the porosity of the modified porous layer is within the above preferred range, the battery separator obtained by laminating the modified porous layer has a low electrical resistance of the membrane, a large current flows easily, and the membrane strength is maintained. The

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, more preferably 7 μm or more. When the total thickness of the battery separator is within the above preferable range, the battery separator obtained by laminating the modified porous layer can ensure sufficient mechanical strength and insulation. In addition, a decrease in capacity can be avoided by reducing the electrode area that can be filled in the container.

The air resistance of the battery separator is one of the most important characteristics, and is preferably 50 to 600 sec / 100 cc Air, more preferably 100 to 500 sec / 100 cc Air, and still more preferably 100 to 400 sec / 100 cc Air. The desired air resistance can be 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 permeability resistance of the battery separator is within the above preferable range, sufficient insulation is obtained, and foreign matter clogging, short circuit and film breakage are prevented. Further, by suppressing the film resistance, charge / discharge characteristics and life characteristics within a practically usable range can be obtained.

Next, a method for laminating the modified porous layer on the laminated polyethylene microporous membrane in the present invention will be described. The method for laminating the modified porous layer on the laminated polyethylene microporous membrane of the present invention includes the following step (g).
(G) A coating liquid 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 on the surface of the laminated polyethylene microporous film in contact with the cooling roll. Step of forming and drying laminated film As a method of laminating the modified porous layer on the laminated polyethylene microporous film, a known method can be used. Specifically, the coating solution is applied to the laminated polyethylene microporous film by a method described later so as to have a predetermined film thickness, and the drying temperature is 40 to 80 ° C. and the drying time is 5 seconds to 60 seconds. It can be obtained by a drying method. In addition, a coating solution in which a binder is soluble and dissolved in a solvent miscible with water is laminated on a predetermined laminated polyethylene microporous film using a coating method described later, placed in a specific humidity environment, and the binder and water It is also possible to use a method in which the solvent to be mixed is phase-separated and the binder is further solidified by adding it to a water bath (coagulation bath).

Examples of methods for applying the coating liquid include 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 coating. Method, die coating method and the like, and these methods can be carried out singly or in combination.

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

The battery separator of the present invention includes a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a secondary battery such as a lithium secondary battery, a lithium polymer secondary battery, and a plastic film capacitor, ceramic Although it can be used as a separator for a capacitor, an electric double layer capacitor, etc., it is particularly preferably used as a separator for a lithium ion secondary battery. Hereinafter, a lithium ion secondary battery will be described as an example.

In a lithium ion secondary battery, a positive electrode and a negative electrode are laminated via a separator, and the separator contains an electrolytic solution (electrolyte). The structure of the electrode is not particularly limited, and may be a known structure. For example, an electrode structure (coin type) in which disc-shaped positive electrodes and negative electrodes are opposed to each other, an electrode structure in which flat plate-like positive electrodes and negative electrodes are alternately stacked (stacked type), and belt-shaped positive electrodes and negative electrodes are stacked. It can be set as a structure such as a wound electrode structure (winding type).

The positive electrode usually has a current collector and a positive electrode active material layer containing a positive electrode active material capable of occluding and releasing lithium ions formed on the surface of the current collector. Examples of the positive electrode active material include transition metal oxides, composite oxides of lithium and transition metals (lithium composite oxides), inorganic compounds such as transition metal sulfides, and the like. Examples of the transition metal include V, Mn, Fe, Co, and Ni. Preferred examples of the lithium composite oxide among the positive electrode active materials include lithium nickelate, lithium cobaltate, lithium manganate, and a layered lithium composite oxide based on an α-NaFeO ₂ type structure.

The negative electrode has a current collector and a negative electrode active material layer including a negative electrode active material formed on the surface of the current collector. Examples of the negative electrode active material include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black. The electrolytic solution can be obtained by dissolving 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 , Examples include LiN (C ₂ F ₅ SO ₂ ) ₂ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , lower aliphatic carboxylic acid lithium salt, LiAlCl _{4 and the} like. These may be used alone or in admixture of two or more. Examples of the organic solvent include organic solvents having a high boiling point and a high dielectric constant such as ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and γ-butyrolactone, and tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane, dimethyl carbonate, diethyl carbonate, and the like. Examples include organic solvents having a low boiling point and a low viscosity. These may be used alone or in admixture of two or more. In particular, a high dielectric constant organic solvent has a high viscosity, and a low viscosity organic solvent has a low dielectric constant. Therefore, it is preferable to use a mixture of both.

When assembling the battery, the separator of the present invention can be impregnated with an electrolytic solution to impart ion permeability to the separator. Usually, the impregnation treatment is performed by immersing the microporous membrane in an electrolytic solution at room temperature. For example, when assembling a cylindrical battery, first, a positive electrode sheet, a separator, and a negative electrode sheet are laminated in this order, and this laminate is wound from one end to form a wound electrode element. Next, a battery can be obtained by inserting this electrode element into a battery can, impregnating with the above electrolyte, and caulking a battery lid also serving as a positive electrode terminal provided with a safety valve via a gasket.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples. In addition, the measured value in an Example is a value measured with the following method.

1. Tensile strength of binder (N / mm ² )
The binder used in the examples and comparative examples is sufficiently dissolved or dispersed in a solvent so that the film thickness after drying is about 100 μm to the dumbbell type for preparing No. 2 type test piece defined in JIS K 7113. The sample sheet obtained by natural drying at 25 ° C. and further vacuum-drying at 25 ° C. for 8 hours (vacuum degree 3 mmHg) to sufficiently remove the solvent was subjected to tensile strength measurement.
Measurement was performed under the following conditions using a tensile tester (Autograph AGS-J, load cell capacity: 1 kN, manufactured by Shimadzu Corporation). The sample film and measurement conditions were as follows. The measurement was performed three times, and the average value was defined as the tensile strength of the binder.
Distance between chucks: 40mm
Test speed: 20 mm / min
Measurement environment: temperature 20 ° C, relative humidity 60%

2. Number of protrusions The number and size of protrusions were measured after stabilizing the light source using a confocal microscope (HD100 manufactured by Lasertec Corporation) placed on a base isolation table.
(procedure)
(1) A 1 cm × 1 cm square frame was drawn with an ultrafine oil pen on the surface of the laminated polyethylene microporous membrane obtained in Examples and Comparative Examples that was in contact with a cooling roll during film formation.
(2) The surface on which the square frame was drawn was placed on the sample stage, and was fixed to the sample stage using an electrostatic contact apparatus attached to the confocal microscope.
(3) Using an objective lens with a magnification of 5 times, a ring-shaped trace derived from a polyethylene spherulite as shown in FIG. 3 is displayed on a monitor as a two-dimensional image (referred to as a REAL screen in this apparatus), and the ring-shaped trace is displayed. The position of the sample stage was adjusted so that the darkest part of was positioned almost at the center of the monitor screen. When two ring-shaped marks were connected, the contact was made. The object of the projection height measurement was such that the major axis of the ring-shaped trace derived from the polyethylene spherulites was 0.2 mm or more. As for the major axis of the ring-shaped mark, the cursor was placed on both ends of the ring in the major axis direction in the two-dimensional image, and the length was read.
(4) Change the objective lens to a 20x lens and focus on the center of the monitor screen (in this device, the center of the monitor screen is displayed brightest), and this height position is used as the reference height (This device is called REF SET).
(5) The measurement range in the height direction was set to 15 μm above and below, with the reference height being 0 μm. Also, the scan time was 120 seconds, the STEP moving distance was 0.1 μm / Step, and the three-dimensional data was captured.
(6) After capturing the three-dimensional data, an image for data processing (referred to as a Z image in the present apparatus) was displayed and smoothing was performed (smoothing condition: filter size 3 × 3, matrix type SMOOTH3-0, number of times once). In addition, horizontal correction was performed on the horizontal correction screen as necessary.
(7) A cursor was placed in a horizontal direction at a position (the brightest part) passing through the highest protrusion in the data processing image, and a cross-sectional profile corresponding to the cursor was displayed on the cross-sectional profile image.
(8) In the cross-sectional profile image, the two cursors were aligned with the inflection points of the sleeves of the protrusions in the vertical direction, and the distance between the cursors was taken as the protrusion size.
(9) In the cross-sectional profile image, align the two cursors in the horizontal direction with the inflection points of the top of the protrusion and the sleeves of the protrusion (if the height of the inflection points of the sleeves of the protrusion is different) The distance between the cursors was the height of the protrusion.
(10) The above operation is repeated within the 1 cm × 1 cm square frame, and the number of protrusions having a size of 5 μm or more and 50 μm or less, a height of 0.5 μm or more and 3.0 μm or less is counted, and the number of protrusions per 1 cm ² is obtained. Further, the average height of the protrusions was obtained.

3. 0 ° peel strength of modified porous layer (N / 15mm)
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 pressure-sensitive adhesive tape, 5 and 5 'are aluminum plates, and the arrows in the figure are tensile directions. A double-sided adhesive tape (NW-K50 manufactured by Nichiban Co., Ltd.) 4 having 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 Sample 1 (battery separator) cut out to a width of 50 mm and a length of 100 mm is pasted on the aluminum plate 5 so that 40 mm overlaps from the edge of one side of the 25 mm length. Attached and cut off the protruding part. Next, a double-sided adhesive tape is attached to one side of an aluminum plate 5 ′ having a length of 100 mm, a width of 15 mm, and a thickness of 0.5 mm, so that 20 mm overlaps from the end of one side of the 25 mm long sample side of the aluminum plate 5. Pasted on. Thereafter, the aluminum plate 5 and the aluminum plate 5 ′ sandwiching the sample are attached to a tensile testing machine (Autograph AGS-J load cell capacity 1 kN, manufactured by Shimadzu Corporation), and the aluminum plate 5 and the aluminum plate 5 ′ are opposite in parallel. The film was pulled in the direction at a pulling speed of 10 mm / min, and the strength when the modified porous layer was peeled was measured. This measurement was performed for any three points with an interval of 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 calculated | required by averaging the measured value of 20 points | pieces using the contact-type film thickness meter (Mitutoyo Corporation light matic series 318). The measurement was performed under the condition of a weight of 0.01 N using a carbide spherical measuring element φ9.5 mm.

5. Average pore diameter The average pore diameter of the laminated polyethylene microporous membrane was measured by the following method. The sample was fixed on the measurement cell using double-sided tape, 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 ten places were selected on the image obtained by SEM measurement, and the average value of the pore diameters at these ten places was taken as the average pore diameter of the sample.

6). Air permeability resistance (sec / 100ccAir)
Using a Gurley Densometer Type B manufactured by Tester Sangyo Co., Ltd., fix the laminated polyethylene microporous membrane or battery separator so that there are no wrinkles between the clamping plate and the adapter plate, and in accordance with JIS P8117 It was measured. The sample was a 10 cm square, the measurement points were a total of 5 points at the center and 4 corners of the sample, and the average value was used as the air resistance. When the length of one side of the sample is less than 10 cm, a value obtained by measuring five points at intervals of 5 cm may be used.
The increase width of the air permeability resistance was obtained from the following formula.
Increasing width of air resistance = (Y) − (X) sec / 100 cc Air
Air permeability resistance of laminated polyethylene microporous membrane (X) sec / 100ccAir
Air permeability resistance of battery separator (Y) sec / 100ccAir

7). Shutdown temperature While heating the laminated polyethylene microporous membrane at a heating rate of 5 ° C / min, the air resistance was measured by the Oken type air resistance meter (Asahi Seiko Co., Ltd., EGO-1T). The temperature at which the air permeation resistance reached the detection limit of 1 × 10 ⁵ seconds / 100 cc Air was determined and used as the shutdown temperature (° C.).

8). Permeability increase rate 7. Of temperature and air resistance P of laminated polyethylene microporous film with thickness T1 (μm) obtained in the shutdown temperature measurement of 3 ° C. from 30 ° C. to 105 ° C. The figure was drawn and the slope Pa (sec / 100 cc Air / ° C.) was calculated by the least square method. The calculated Pa was normalized by the formula: Pb = Pa / T1 × 20 with a film thickness of 20 μm, and the air resistance increase rate Pb (second / 100 cc Air / μm / ° C.) at 30 ° C. to 105 ° C. was calculated.

9. Porosity of laminated polyethylene microporous membrane Prepare a 10 cm square sample, measure the sample volume (cm ³ ) and mass (g), and use the following formula to determine the porosity (%). Calculated.
Porosity = (1−mass / (resin density × sample volume)) × 100

10. Scratch resistance Both ends of the battery were slit while the roll battery separators obtained in Examples and Comparative Examples were wound. Slit processing was performed using a slitter (WA177A model manufactured by Nishimura Seisakusho Co., Ltd.) under conditions of a speed of 20 m / min and a tension of 60 N / 100 mm. During processing, the rolls that contact the coated surface were two hard chrome plating rolls (both free rolls). Next, peeling the modified porous layer having a major axis of 0.5 mm or more using a loupe with a scale (PEAK Co., Ltd. SCALE LUPE × 10) visually while rewinding the slit processed roll battery separator. The defects were counted and evaluated according to the following criteria. The evaluation area was 100 mm wide × 500 m long. (When the width was less than 100 mm, the length was adjusted so that the same evaluation area was obtained.)
Judgment criteria ○ (very good): 5 or less △ (good): 6 to 15 × (defect): 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) method under the following conditions.
・ Measurement device: GPC-150C manufactured by Waters Corporation
Column: “Shodex” (registered trademark) UT806M manufactured by Showa Denko KK
-Column temperature: 135 ° C
Solvent (mobile phase): o-dichlorobenzene Solvent flow rate: 1.0 ml / min Sample concentration: 0.1% by mass (dissolution condition: 135 ° C./1 h)
・ Injection volume: 500μl
-Detector: Differential refractometer manufactured by Waters Corporation-Calibration curve: Prepared from a calibration curve obtained using a monodisperse polystyrene standard sample using a predetermined conversion constant.

12 Melt flow rate (MFR)
According to JIS-K7210, the temperature was 190 ° C. and the load was 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 in a nitrogen gas atmosphere using a differential scanning calorimeter (DSC) DSC 6220 manufactured by SII Nanotechnology Inc. Was the melting point.

Example 1
An antioxidant tetrakis- [methylene was added to 100% by mass of a composition comprising 18% by mass of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and 82% by mass of high density polyethylene (HDPE) having a weight average molecular weight of 350,000. -(3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane) 0.375% by mass was added to obtain a polyethylene composition A (melting point: 135 ° C.). 25% by mass of this polyethylene composition A was charged into a twin screw extruder. 75% by mass of liquid paraffin was supplied from the side feeder of this twin screw extruder, melted and kneaded, and a polyethylene resin solution A was prepared in the extruder.
On the other hand, 17.5 mass% of ultra high molecular weight polyethylene (UHMWPE) with a weight average molecular weight of 2 million, 57.5 mass% of high density polyethylene (HDPE) with a weight average molecular weight of 300,000, MFR of 135 g / 10 min, melting point An antioxidant (tetrakis- [methylene- (3 ′, 5′-di-t) was added to 100% by mass of a composition comprising 25% by mass of linear low-density polyethylene (ethylene / 1-hexene copolymer) at 124 ° C. -Butyl-4'-hydroxyphenyl) propionate] methane) 0.375% by mass of polyethylene composition B (melting point 128 ° C.) was obtained. 25% by mass of this polyethylene composition B was charged into a twin screw extruder. 75% by mass of liquid paraffin was supplied from the side feeder of this twin screw extruder, melted and kneaded, and a polyethylene resin solution B was prepared in the extruder.
The obtained polyethylene resin solutions A and B were co-extruded at 190 ° C. from the laminated die so that the layer configuration was A / B / A and the solution ratio was 1/2/1, and the internal cooling water temperature was 25 ° C. A laminated gel-like molded product was formed while being taken up by a cooling roll having a diameter of 800 mm kept at the same temperature. At this time, one polyester doctor blade is placed between the point where the laminated gel-like molded article is separated from the cooling roll and the point where the laminated polyethylene resin solution extruded from the die contacts the cooling roll. The liquid paraffin adhering to the cooling roll was scraped off in contact with the cooling roll in parallel with the direction. Subsequently, the laminated gel-like molded product was simultaneously biaxially stretched 5 × 5 times while adjusting the temperature so as to obtain a desired air permeability resistance to obtain a stretched molded product. The obtained stretched molded product was washed with methylene chloride to extract and remove the remaining liquid paraffin, and dried to obtain a porous molded product. Thereafter, the microporous film is held in the tenter, and is reduced by 10% only in the TD (width direction) direction, and heat-treated at 123 ° C. for 3 seconds. The thickness is 14 μm, the porosity is 44%, the average pore diameter is 0.45 μm, A laminated polyethylene microporous film having an air resistance of 195 sec / 100 cc Air, a shutdown temperature of 130 ° C., and an air resistance increase rate of 0.8 sec / 100 cc Air / ° C./20 μm was obtained.
Polyvinyl alcohol (average polymerization degree 1700, saponification degree 99% or more), alumina particles having an average particle diameter of 0.5 μm, and ion-exchanged water were blended in a weight ratio of 6:54:40, respectively, and zirconium oxide beads (Toray Industries, Inc. ) “Traceram” (registered trademark) beads, 0.5 mm in diameter) and placed in a polypropylene container, and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho). Subsequently, it filtered with the filter of 5 micrometers of filtration limits, and obtained the coating liquid (a).
A coating liquid (a) is applied by gravure coating to the surface of the laminated polyethylene microporous membrane that was in contact with the cooling roll during film formation, and dried by passing through a hot air drying oven at 50 ° C. for 10 seconds. A battery separator having a final thickness of 16 μm was obtained.

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

Example 3
A battery separator was obtained in the same manner as in Example 2 except that two polyester doctor blades were applied to the cooling roll at an interval of 20 mm.

Example 4
A battery separator was obtained in the same manner as in Example 2 except that three polyester doctor blades were applied to the cooling rolls at intervals of 20 mm.

Example 5
Two-part curable aqueous acrylic urethane resin (solid content concentration 45% by mass) composed of aqueous acrylic polyol and water-dispersible polyisocyanate (curing agent), alumina particles having an average particle size of 0.5 μm, and ion-exchanged water are respectively 10:40: 50 weight ratio, zirconium oxide beads (Toraysemu "Traceram" (registered trademark) beads, diameter 0.5mm) together with polypropylene container, paint shaker (Toyo Seiki Seisakusho) For 6 hours. Subsequently, it filtered with the 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 changed to the coating liquid (b) to obtain a battery separator.

Example 6
Copolymer of polyvinyl alcohol, acrylic acid and methyl methacrylate (“POVACOATR” (registered trademark) manufactured by Nisshin Kasei Co., Ltd.), alumina particles having an average particle size of 0.5 μm, solvent (ion-exchanged water: ethanol = 70: 30) were mixed at a weight ratio of 5:45:50, respectively, and placed in a polypropylene container together with zirconium oxide beads ("Traceram" (registered trademark) beads, diameter 0.5 mm) manufactured by Toray Industries, Inc.) (Toyo Seiki Seisakusho Co., Ltd.) for 6 hours. The solution was filtered through a filter having a filtration limit of 5 μm to obtain a coating solution (c). A modified porous layer was laminated in the same manner as in Example 2 except that the coating liquid (a) was changed to the coating liquid (c) to obtain a battery separator.

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 35 ° C.

Example 8
A battery separator was obtained in the same manner as in Example 2, except that the layer structure was 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 described in Table 1.

Example 13
A battery separator was obtained in the same manner as in Example 2 except that the amount of the low melting point resin contained in the polyethylene composition B was adjusted as shown in Table 1-1.

Example 14
A battery separator was obtained in the same manner as in Example 2 except that the extrusion amounts of the polyethylene resin solutions A and B were adjusted to obtain a laminated polyethylene microporous membrane having a thickness of 9 μm.

Example 15
Alumina particles are replaced with crosslinked polymer particles (polymethyl methacrylate-based crosslinked product particles (“Eposter” (registered trademark) MA1002, manufactured by Nippon Shokubai Co., Ltd., average particle size: 2.5 μm)). Varnish (d) was obtained with a blending ratio of -methyl-2-pyrrolidone of 35:10:55 (weight ratio). 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 (polyvinylidene fluoride (5% N-methylpyrrolidone solution) manufactured by Kureha Chemical Industry Co., Ltd.) and alumina particles having an average particle size of 0.5 μm, N-methyl- 2-pyrrolidone was blended at a weight ratio of 16:34:50, respectively, and placed in a polypropylene container together with zirconium oxide beads ("Traceram" (registered trademark) beads, diameter 0.5 mm) manufactured by Toray Industries, Inc. The mixture was dispersed with a shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.) for 6 hours, and then filtered through a filter having a filtration limit of 5 μm to obtain varnish (e), which was the same as Example 2 except that varnish (e) was used. Thus, a battery separator was obtained.

Example 17
Acrylic emulsion (“Polysol” (registered trademark) AT-731 manufactured by Showa Denko KK, nonvolatile content 47%), alumina particles having an average particle size of 0.5 μm, and ion-exchanged water in a weight ratio of 2:55:43, respectively. Combined, put together with zirconium oxide beads (Toraysemu "Traceram" (registered trademark) beads, diameter 0.5mm) in a polypropylene container and dispersed for 12 hours in a paint shaker (Toyo Seiki Seisakusho) It was. Subsequently, it filtered with the 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 liquid (g) in which the alumina particles were changed to barium sulfate fine particles (average particle size: 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 the ultrahigh molecular weight polyethylene (UHMWPE) and the high density polyethylene (HDPE) of the polyethylene composition A was adjusted as shown in Table 1-1.

Example 21
The blending ratio of ultra high molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) in polyethylene composition A and the ratio of each polyethylene composition A to liquid paraffin were adjusted as shown in Table 1-1. A battery separator was obtained in the same manner as in Example 2 except that the extrusion amounts of the polyethylene solutions A and B were adjusted as described.

Comparative Example 1
Except that only the polyethylene solution A was used to extrude from a single-layer die at 190 ° C. to form a single-layer gel-like molding, and the single-layer gel-like molding obtained instead of the laminated gel-like molding was used. A battery separator was obtained in the same manner as in Example 2.

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 point 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 the ultrahigh molecular weight polyethylene (UHMWPE) and the high density polyethylene (HDPE) of the polyethylene composition A was adjusted as shown in Table 1-1.

Comparative Example 4
The polyethylene resin solution extruded from the die was cooled with a cooling roll, and when the gel-like molded product was obtained, the doctor blade was not used and the liquid paraffin adhering to the cooling roll was not scraped off. Similarly, a battery separator was obtained.

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 kept at 0 ° C. and the doctor blade was not used.

Comparative Example 6
Instead of cooling the polyethylene resin solution extruded from the die with a cooling roll, a battery separator was obtained in the same manner as in Example 2 except that the polyethylene resin solution was immersed in water kept at 25 ° C. for 1 minute.

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 kept at 50 ° C.

Comparative Example 8
In a four-necked flask equipped with a thermometer, cooling tube, and nitrogen gas inlet tube, 1 mol of trimellitic anhydride (TMA), 0.8 mol of o-tolidine diisocyanate (TODI), 2,4-tolylene diisocyanate (TDI) ) 0.2 mol and 0.01 mol of potassium fluoride were charged together with N-methyl-2-pyrrolidone so that the solid concentration was 14%, and stirred at 100 ° C. for 5 hours. A polyamide-imide resin solution was synthesized by diluting with N-methyl-2-pyrrolidone.
A polyamide-imide resin solution, alumina particles having an average particle size of 0.5 μm, and N-methyl-2-pyrrolidone were blended in a weight ratio of 26:34:40, respectively, and zirconium oxide beads (“Traceram” manufactured by Toray Industries, Inc. (registered) (Trademark) beads, 0.5 mm in diameter) were placed in a polypropylene container and dispersed for 6 hours with a paint shaker (Toyo Seiki Seisakusho). Subsequently, it filtered with the filter of 5 micrometers of filtration limits, and obtained the coating liquid (h). The coating liquid (h) was applied to the laminated polyethylene microporous membrane obtained in the same manner as in Example 2 by the gravure coating method in the same manner as in Example 2 to obtain a battery separator.

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

DESCRIPTION OF SYMBOLS 1 Battery separator 2 Laminated polyethylene microporous film 3 Modified porous layer 4 Double-sided adhesive tape 5, 5 'Aluminum plate 6 Polyethylene spherulite crystal nucleus 7 Die 8 Polyethylene resin solution 9 Cooling roll 10 Doctor blade 11 Gel-like molded product

Claims

A battery separator having a laminated polyethylene microporous membrane and a modified porous layer present on at least one surface thereof, wherein the laminated polyethylene microporous membrane comprises at least an A layer and a B layer. A laminated body having a shutdown temperature of 128 to 135 ° C., a rate of increase in air resistance from 30 ° C. to 105 ° C. per 20 μm thickness of less than 1.5 sec / 100 cc Air / ° C., and at least one surface facing the outside world There are irregular projections made of polyethylene of 3 pieces / cm 2 or more and 200 pieces / cm 2 or less, and the projections are 0.5 μm ≦ H (H is the height of the projection) and 5 μm ≦ W ≦ 50 μm (W is it viewed magnitude) of the projections, the modified porous layer is laminated on a surface having a projection of the laminated microporous polyethylene membrane, and a tensile strength of 5N / mm 2 or more Battery separator comprising the binder and the inorganic particles.
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.
3. The battery according to claim 1, wherein the layer B forming the laminated polyethylene microporous membrane comprises 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 lower than 130 ° C. Separator.
The battery separator according to any one of claims 1 to 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 copolymer. .
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, based on 100% by mass of the entire polyethylene resin. The battery separator described in 1.
The battery separator according to any one of claims 1 to 5, wherein the thickness of the B layer is 3 µm or more and 15 µm or less.
The battery separator according to any one of claims 1 to 6, wherein the binder is polyvinyl alcohol or an acrylic resin.
The battery separator according to any one of claims 1 to 7, wherein the inorganic particles include at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate, and boehmite.
The method for producing a battery separator according to any one of claims 1 to 8, comprising the following steps (a) to (g).
(A) Step of adding a molding solvent to the polyethylene resin constituting the A layer and then melt-kneading to prepare the polyethylene resin solution A (b) Low melting point resin and molding solvent for the polyethylene resin constituting the B layer Step (c) of preparing polyethylene resin solution B by extruding polyethylene resin solutions A and B obtained in steps (a) and (b) from a die, and adding at least one of Step (d) of forming a laminated gel-like molded product by cooling with a cooling roll having a surface from which the molding solvent has been removed by the molding solvent removing means, and stretching the laminated gel-like molded product in the machine direction and the width direction, Step (e) of obtaining a laminated stretched molded product (e) Step of extracting the solvent for molding from the laminated stretched molded product and removing the molding solvent and drying to obtain a laminated porous molded product (f) Laminated porous molded product Heat treatment, the surface of the step of obtaining a laminated microporous polyethylene membrane (g) the cooling roll was in contact laminating the microporous polyethylene membrane, the tensile strength of 5N / mm 2 or more binders, dissolved inorganic particles and a binder or The process of forming a laminated film using the coating liquid containing the solvent which can be disperse | distributed, and drying.
The method for producing a battery separator according to claim 9, wherein the forming solvent removing means in the step (c) is means for scraping off using a doctor blade.