KR102316033B1 - Battery separator and production method therefor - Google Patents

Abstract

In the present invention, assuming that the battery separator is progressively thinner and lower in cost in the future, the peel strength from the modified porous layer is very high, and the meltdown property is excellent, suitable for high-speed processing in the slit process or battery assembly process, and lithium A battery separator suitable for an ion battery is provided. The present invention relates to a battery separator having a multilayer polyolefin microporous membrane and a modified porous layer present on at least one surface thereof, wherein the multilayer polyolefin microporous membrane comprises at least an A layer and a B layer. The temperature is 165 ° C. or higher, the air permeation resistance is 300 sec/100 ccAir or less, and at least 3/cm ² or more and 200/cm ² or less protrusions made of polyolefin are irregularly present on the surface facing the outside. , the protrusion satisfies 0.5 µm≤H (H is the height of the protrusion) and 5 µm≤W≤50 µm (W is the size of the protrusion), and the modified porous layer is on the surface having the protrusions of the multilayer polyolefin microporous membrane A battery separator comprising a binder and inorganic particles having a tensile strength of 5 N/mm ^{2 or more while being laminated is disclosed.}

Description

Battery separator and manufacturing method thereof

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

Thermoplastic resin microporous membranes are widely used as insulating materials, filters, and the like. For example, as a separator, a battery separator used for a lithium ion secondary battery, a nickel-hydrogen battery, a nickel-cadmium battery, and a polymer battery, a separator for an electric double layer capacitor, a reverse osmosis membrane, an ultrafiltration membrane, a microfiltration membrane etc. are mentioned as a filter. can In addition, it is used for moisture-permeable waterproof clothing (衣料), medical materials (醫療用), etc. In particular, as a separator for lithium ion secondary batteries, it has ion permeability by being impregnated with an electrolyte, and has excellent electrical insulation, electrolyte resistance, and oxidation resistance. A polyethylene microporous membrane which also has the pore blocking effect which suppresses temperature rise is used preferably. However, if the temperature continues to rise even after the pores are blocked for some reason, the film may break due to a decrease in the viscosity of polyethylene constituting the film or shrinkage of the film. This phenomenon is not limited to polyethylene and is unavoidable above the melting point of the resin constituting the microporous membrane even when other thermoplastic resins are used.

Lithium ion battery separators are related to battery characteristics, battery productivity, and battery safety, and mechanical properties, heat resistance, permeability, dimensional stability, hole occlusion properties (shutdown properties), melt rupture properties (meltdown properties), etc. are required. In addition, in order to improve the cycle characteristics of the battery, it is required to improve the adhesion to the electrode material, and to improve the electrolyte permeability to improve the productivity.

Therefore, laminating various modified porous layers on a microporous membrane has been studied so far. As the modified porous layer, a polyamide-imide resin, polyimide resin, polyamide resin, and/or a fluorine-based resin excellent in electrode adhesion, which have both heat resistance and electrolyte permeability, are preferably used. In addition, a water-soluble or water-dispersible binder capable of laminating a modified porous layer using a relatively simple and easy water washing process and drying process is also widely used. In addition, the modified porous layer as used in this invention means the layer containing resin which provides or improves at least one or more functions, such as heat resistance, adhesiveness with an electrode material, and electrolyte solution permeability.

Furthermore, for the battery separator to increase the battery capacity, it is necessary to increase the area which can be filled in a container, and it is predicted that thin film formation will progress. However, since the microporous membrane tends to deform in the planar direction as thinning progresses, the battery separator in which the modified porous layer is laminated on the microporous membrane may be peeled off during processing, in the slit process or in the battery assembly process, , it becomes more difficult to ensure safety.

In addition, in order to cope with cost reduction, it is expected that the process will be accelerated. Even in such high-speed processing, high adhesion between the modified porous layer and the microporous membrane with few troubles such as peeling of the modified porous layer is required. However, if the resin contained in the modified porous layer is sufficiently permeated into the polyolefin microporous membrane in order to improve the adhesion, there is a problem in that the increase in the air permeability resistance becomes large.

From the viewpoint of shutdown characteristics, methods such as adding a low-melting-point component to a polyolefin microporous film are disclosed. However, on the other hand, when a resin with a low melting point is added, the pores are easily clogged during the manufacture of the microporous membrane or during the manufacture of the battery. There was a problem.

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

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

In Example 1 of Patent Document 3, 47.5 parts by mass of polyethylene having a viscosity average molecular weight of 200,000, 2.5 parts by mass of polypropylene having a viscosity average molecular weight of 400,000, 50 parts by mass of a composition comprising an antioxidant, and 50 parts by mass of liquid paraffin, a polyethylene resin solution consisting of an extruder extruded at 200 ° C., and taken with a cooling roll temperature controlled at 25 ° C. to obtain a gel-like molded product, and then biaxially stretched to 7 x 6.4 times 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 containing 30% by mass of a polyethylene composition having a weight average molecular weight of 4.15 million, a weight average molecular weight of 560,000, and a weight ratio of 1:9 and a mixed solvent of liquid paraffin and decalin of 70% by mass was fed from an extruder at 148° C. Extrusion and cooling in a water bath to obtain a gel-like molded product, followed by biaxial stretching so as to be 5.5 × 11.0 times, to obtain a polyethylene microporous membrane. A separator for non-aqueous secondary batteries obtained by laminating a coating layer made of meta-type wholly aromatic polyamide and alumina particles on the surface of the polyethylene microporous membrane is disclosed.

In Example 1 of Patent Document 5, 47 parts by mass of polyethylene, which is a homopolymer with a viscosity average molecular weight of 700,000, 46 parts by mass of polyethylene, which is a homopolymer with a viscosity average molecular weight of 250,000, and 7 parts by mass of polypropylene, which is a homopolymer with a viscosity average molecular weight of 400,000, were mixed with a tumbler blender was dry blended using To 99% by mass of the obtained pure polymer mixture, 1% by mass of pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant, and again A polyethylene composition dry-blended using a tumbler blender is melt-kneaded, extruded on a cooling roll controlled at a surface temperature of 25° C., and cast to obtain a sheet-like polyethylene composition having a thickness of 2000 μm, and then biaxially stretched to 7×7 times. A laminated porous membrane obtained by coating an aqueous dispersion of calcined kaolin and latex on a polyethylene microporous membrane obtained by performing the

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

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

Patent Document 8 discloses a separator for a nonaqueous electrolyte battery in which heat resistance at high temperature is improved by laminating an inorganic filler-containing layer on a polyolefin microporous film containing a small amount of polypropylene.

However, in response to the demand for thin film separators due to high-speed processing due to cost reduction and high capacity, which will be rapidly progressing in the future, in these conventional techniques, the modified porous layer is peeled off locally during slit processing or battery assembly processing, so securing safety is difficult. expected to be difficult. In particular, when the polyolefin microporous membrane used as the base material becomes thin, it becomes difficult to obtain a sufficient anchor effect of the modified porous layer to the polyolefin microporous membrane, and therefore, it becomes even more difficult to ensure safety.

Patent Document 1: Japanese Patent Application Laid-Open No. 2012-043762 Patent Document 2: Japanese Republished Patent Publication No. 2010-104127 Patent Document 3: Japanese Patent Publication No. 4931083 Patent Document 4: Japanese Patent Publication No. 4460028 Patent Document 5: Japanese Patent Application Laid-Open No. 2011-000832 Patent Document 6: Japanese Patent Application Laid-Open No. 2011-071009 Patent Document 7: Japanese Patent Publication No. 2012-521914 Patent Document 8: Japanese Patent Publication No. 4789274

The present invention assumes that the thin film and high-speed processing of the battery separator will gradually progress in the future, and the peel strength of the modified porous layer and the laminated polyolefin microporous membrane is high, and the polyolefin microporous material is suitable for high-speed processing in the slit process or battery assembly process. To provide a battery separator in which a modified porous layer is laminated on a membrane.

The peel strength of the laminated polyolefin microporous membrane and the modified porous layer in the separator as used herein is a value measured by the following method (hereinafter, sometimes referred to as 0° peel strength).

In FIG. 1, the side state of the laminated sample of the laminated polyolefin microporous membrane and the modified porous layer in a state pulled by a tensile tester (not shown) is schematically shown. Reference numeral 1 denotes a laminated sample, a divalent laminated polyolefin microporous membrane, 3 a modified porous layer, a tetravalent double-sided adhesive tape, and 5 and 5' an aluminum plate, and arrows in the figure indicate the tensile direction. A laminated polyolefin microporous membrane of the sample (1) cut out to a width of 50 mm x a length of 100 mm on the double-sided adhesive tape (4) of the same size on an aluminum plate (5) having a size of 50 mm × 25 mm and a thickness of 0.5 mm The surface of (2) is attached so that 40 mm overlaps at the end of one side of the 25 mm length of the aluminum plate 5, and the protruding part is cut out. 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, and 20 mm from the end of one side of the 25 mm long sample side of the aluminum plate 5 paste so that they overlap. 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 off is measured. If the peel strength is 130 N/15 mm or more in this evaluation method, even if the thickness of the laminated polyolefin microporous film is, for example, 10 µm or less, the phenomenon that the laminated modified porous layer is peeled off during transport or processing is almost doesn't happen

The T-type peel strength or peel strength at 180 degrees conventionally used as a measurement method of peel strength is the peel force when peeling back perpendicular|vertical or perpendicular|vertical with respect to the surface of a battery separator obliquely backward. According to this evaluation method, compared with these conventional evaluation methods, the friction resistance in a slit process and a battery assembly process can be evaluated more based on actual.

In order to solve the said subject, the separator for batteries of this invention has the following structures.

That is, in a battery separator having a multilayer polyolefin microporous membrane and a modified porous layer present on at least one surface thereof, the multilayer polyolefin microporous membrane is a porous layered product comprising at least an A layer and a B layer, a meltdown temperature is 165 ° C. or higher, air permeation resistance is 300 sec/100 ccAir or less, and at least 3/cm ² or more and 200/cm ² or less protrusions made of polyolefin on the surface facing the outside are irregularly present, The protrusions satisfy 0.5 μm≤H (H is the height of the protrusions) and 5 μm≤W≤50 μm (W is the size of the protrusions), and the modified porous layer is laminated on the surface having the protrusions of the multilayer polyolefin microporous membrane At the same time, it is a battery separator comprising a binder and inorganic particles having a ^{tensile strength of 5 N/mm 2 or more.}

Here, the surface facing the outside means that at least one surface of the surfaces of each layer constituting the multilayer polyolefin microporous membrane faces the side (interface side) in contact with the surface of the other layer, but the other side does not face the interface side refers to the surface of

In the battery separator of the present invention, it is preferable that the laminated polyolefin microporous membrane has a three-layer structure of A layer/B layer/A layer, or B layer/A layer/B layer, and polypropylene having a heat of fusion in layer B of 90 J/g or more It is more preferable to include

In the battery separator of the present invention, the thickness of the layer B is preferably 3 µm or more and 15 µm or less.

In the battery separator of the present invention, the binder preferably contains polyvinyl alcohol or an acrylic resin.

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

In order to solve the said subject, the manufacturing method of the separator for batteries of this invention has the following structures. in other words,

(a) The step of adding a molding solvent to the polyolefin resin constituting the layer A, followed by melt-kneading to prepare the polyolefin resin solution A

(b) A step of preparing a polyolefin resin solution B by adding a molding solvent to a polyolefin resin comprising a polyethylene resin and a polypropylene resin constituting the B layer, followed by melt-kneading

(c) extruding the polyolefin resin solutions A and B obtained in the steps (a) and (b) from a die, and at least one of them is used as a cooling roll having a surface from which the molding solvent is removed by a molding solvent removing means. Cooling to form a laminated gel-like molded article

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

(e) a step of extracting and removing the solvent for lamination molding from the laminated and stretched molded product, and drying it to obtain a laminated porous molded product

(f) heat-treating the laminated porous molding to obtain a laminated polyolefin microporous film

(g) On the surface of the multilayer polyolefin microporous membrane in contact with the cooling roll, a ^{binder having a tensile strength of 5 N/mm 2} or more, inorganic particles, and a coating solution containing a solvent capable of dissolving or dispersing the binder, the laminated film forming and drying process.

In the manufacturing method of the battery separator of this invention, it is preferable that the solvent removal means for shaping|molding in the said (c) process is a means for scraping using a doctor blade.

According to the present invention, a separator for batteries in which the modified porous layer is laminated on a multilayer polyolefin microporous membrane having excellent adhesion with the modified porous layer, the modified porous layer does not peel off even during high-speed conveyance is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the measuring method of 0 degree peeling strength.
2 is a schematic diagram showing the spheroid structure and crystal nuclei of polyolefin in a multilayer polyolefin microporous membrane.
Fig. 3 is a photomicrograph of ring-shaped marks derived from spheroids of polyolefin in the laminated polyolefin microporous membrane.
Fig. 4 is a schematic view showing a step of extruding a polyolefin resin solution from a die provided at the end of the extruder, and forming a laminated gel-like molding while cooling with a cooling roll.

The laminated polyolefin microporous membrane used in the present invention has an appropriate shape and number of protrusions on the surface by adjusting a specific polyolefin resin solution and highly controlling the cooling rate of the polyolefin resin solution extruded from the extruder through the die. The present invention provides very good peel strength between the multilayer polyolefin microporous membrane and the modified porous layer when a modified porous layer comprising inorganic particles and a binder having a tensile strength of 5 N/mm ^{2 or more is laminated on the multilayer polyolefin microporous membrane.} can be obtained

The protrusion as used in the present invention is essentially different from a protrusion obtained by adding inorganic particles or the like to the laminated polyolefin microporous membrane. The protrusions obtained by adding inorganic particles to the multilayer polyolefin microporous membrane are usually very small in height, and if a protrusion of 0.5 μm or more in height is formed by the same means, particles having a particle diameter equal to or larger than the thickness of the multilayer polyolefin microporous membrane. addition is necessary However, the addition of such particles lowers the strength of the laminated polyolefin microporous membrane, which is not practical.

The protrusion as used in the present invention means that a part of the surface layer of the multilayer polyolefin microporous membrane is grown to have an appropriate shape of ridges, and the basic properties of the multilayer polyolefin microporous membrane are not reduced.

The irregularly dispersed projections as used in the present invention refer to regularity or periodicity obtained by passing an embossing roll before or after the stretching step during the production of the multilayer polyolefin microporous membrane. It is clearly different from the protrusion. Press working, such as embossing, basically forms projections by compression, and since it is easy to generate the fall of the air permeation resistance and electrolyte solution permeability, it is unpreferable.

Protrusions of suitable shape as used in the present invention mean protrusions 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 ㎛ ≤ W ≤ 50 ㎛ (W is the size of the protrusion), while 0.5 ㎛ ≤ H (H is the height of the protrusion). These projections function as anchors when laminating the modified porous layer on the laminated polyolefin microporous membrane, and as a result, the battery separator having a large 0° peel strength described above is obtained. In addition, although the upper limit of a height is not specifically limited, About 3.0 micrometers is sufficient. The 0 degree peel strength tends to become high, so that there are many protrusions of sufficient height. That is, the 0° peel strength is affected by the number of protrusions of 0.5 µm or more in height and their average height. The lower limit of the number of projections ^{is preferably 3 pieces/cm 2} , more preferably 5 pieces/cm ² , and still more preferably 10 pieces/cm ² . The upper limit of the number of the projections was 200 / cm ² are preferred, and more preferably 150 / cm ^2. As for the lower limit of the height of a processus|protrusion, 0.5 micrometer is preferable, More preferably, it is 0.8 micrometer, More preferably, it is 1.0 micrometer. In addition, the size and height of the projections in the present invention refer to values measured by a measuring method to be described later.

The increase in air permeation resistance as used in the present invention means the difference between the air permeability resistance of the laminated polyolefin microporous membrane and the air permeation resistance of the battery separator, preferably 90 sec/100 ccAir or less, more preferably 80 ccAir, further Preferably it is 50 ccAir.

The outline of the laminated polyolefin microporous membrane, the modified porous layer, and the battery separator of the present invention will be described, but of course, it is not limited to these representative examples.

First, the laminated polyolefin microporous membrane used for this invention is demonstrated.

As for the upper limit of the thickness of the laminated polyolefin microporous membrane used for this invention, 25 micrometers is preferable, More preferably, it is 20 micrometers, More preferably, it is 16 micrometers. As for a lower limit, 7 micrometers is preferable, More preferably, it is 9 micrometers. If the thickness of the multilayer polyolefin microporous membrane is within the above preferred range, practical membrane strength and hole blocking function can be maintained, so that the area per unit volume of the battery case is not restricted, and it is suitable for high-capacity batteries in the future.

The meltdown temperature of the multilayer microporous film made of polyolefin of the present invention is 165°C or higher, more preferably 170°C or higher. If the meltdown temperature is within the above range, the stability of the battery is increased because dimensional stability is high even at a high temperature.

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

The upper limit of the porosity of the multilayer polyolefin microporous membrane is preferably 70%, more preferably 60%, still more preferably 55%. The lower limit is preferably 30%, more preferably 35%, still more preferably 40%. When the air permeation resistance and the porosity are within the above preferred ranges, it is suitable for the charge/discharge characteristics of the battery, particularly the ion permeability (charge/discharge operating voltage) and the life of the battery (closely related to the holding amount of the electrolyte), and functions as a battery perform enough Moreover, since sufficient mechanical strength and insulation are acquired, the possibility that a short circuit will generate|occur|produce at the time of charging/discharging becomes low.

Since the average pore diameter of the laminated polyolefin microporous membrane greatly affects the pore occlusion performance, it is preferably 0.01 to 1.0 m, more preferably 0.05 to 0.5 m, still more preferably 0.1 to 0.3 m. When the average pore diameter of the laminated polyolefin 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 the air permeability resistance is large when the modified porous layer is laminated. It does not deteriorate, and the response to the temperature of the hole-occlusion phenomenon does not become gentle, and the hole-occlusion temperature according to the temperature increase rate does not shift to a higher temperature side.

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

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

The polyolefin microporous membrane constituting the layer A of the present invention has polyethylene as a main component. In order to improve the permeability and puncture strength, the content of polyethylene is preferably 80 mass % or more, more preferably 90 mass % or more, still more preferably 100 mass % with the total polyolefin resin being 100 mass %. %am.

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

The ultra-high molecular weight polyethylene may be a homopolymer of ethylene as well as a copolymer containing small amounts of other α-olefins. Examples of the α-olefin include propylene, butene-1, hexene-1, pentene-1, 4-methyl pentene-1, octene, vinyl acetate, methyl methacrylate, and styrene. In a laminated film, especially when it is produced by a co-extrusion method, it may be difficult to control non-uniformity of physical properties in the width direction due to the difference in viscosity of each layer. is hardened, so it is difficult to generate non-uniform deformation, and it is possible to obtain a microporous membrane excellent in uniformity of physical properties.

As for the weight average molecular weight (henceforth Mw) of a high density polyethylene, 1x10 ⁵ or more is preferable, More preferably, it is 2x10 ⁵ or more. As for the upper limit, Mw is ^{preferably 8×10 5} , and more preferably Mw is 7×10 ⁵ . When Mw is the said range, stability of film forming and the puncture strength finally obtained can be compatible.

Mw of the ultra-high molecular weight polyethylene is preferably ^{1×10 6} or more and less than 4×10 ^{6 .} By using the ultra-high molecular weight polyethylene having Mw of 1×10 ⁶ or more and less than 4×10 ⁶ , pores and fibrils can be miniaturized, and it becomes possible to increase the puncture strength. Moreover, when Mw is ^4x10<6> or more, since the viscosity of a melt|molten material becomes high too much, a defect may come out in a film forming process, such as being unable to extrude resin from a nozzle|cap|die (die).

As for content of ultra high molecular weight polyethylene, the whole polyolefin resin shall be 100 mass %, 2 mass % is preferable and, as for a lower limit, 2 mass % is preferable, More preferably, it is 18 mass %. As for an upper limit, 45 mass % is preferable, More preferably, it is 40 mass %. If it is this range, it will become easy to obtain coexistence of puncture intensity|strength and air permeation resistance. When the content of ultra-high molecular weight polyethylene is within the preferable range, protrusions of sufficient height are obtained. When the modified porous layer is laminated with these projections, the projections function as anchors, and very strong peel resistance can be obtained with respect to a force applied parallel to the surface direction of the polyethylene porous membrane. Further, even when the thickness of the polyethylene porous membrane is reduced, sufficient tensile strength can be obtained. Although the tensile strength does not specifically set an upper limit, 100 MPa or more is preferable.

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

Layer B of the present invention is a microporous membrane containing polyolefin as a main component. It is preferable that layer B contains 50 mass % or more of high-density polyethylene from a viewpoint of intensity|strength. Moreover, as for the weight average molecular weight (henceforth Mw) of a high density polyethylene, 1x10 ⁵ or more is preferable, More preferably, it is 2x10 ⁵ or more. As for the upper limit of Mw, Mw is ^{preferably 8x10 5} , More preferably, Mw is 7x10 ⁵ . When Mw is the said range, stability of film forming and the puncture strength finally obtained can be compatible.

In the present invention, it is important that the layer B contains polypropylene. When polypropylene is added, the meltdown temperature can be further improved when the polyolefin microporous membrane of the present invention is used as a battery separator. As for the kind of polypropylene, in addition to a homopolymer, a block copolymer and a random copolymer can also be used. The block copolymer and random copolymer may contain a copolymer component with an ?-olefin other than propylene, and ethylene is preferable as the other ?-olefin.

Mw of polypropylene ^{is preferably 5×10 5} or more, more preferably 6.5×10 ⁵ or more, and still more preferably 8×10 ⁵ or more. When Mw is within the above range, the dispersibility of polypropylene does not deteriorate at the time of sheet formation, and a film with a uniform film thickness can be obtained. Further, the heat of fusion (?Hm) of polypropylene is preferably 90 J/g or more, more preferably 95 J/g. When ΔHm is within the above preferred range, good meltdown characteristics can be obtained.

As for content of polypropylene, less than 60 mass % is preferable with respect to the total mass of a polyolefin composition. When it is 60 mass % or more, there exists a possibility that permeability may deteriorate. In particular, in the case where the surface layer is the B layer, the amount of powder generated by the polypropylene drop-off when the laminated microporous film is slit may increase. If there is a large amount of powder generated due to dropping of polypropylene, there is a possibility that defects such as pinholes or black spots may occur in the laminated microporous film. As a lower limit of the addition amount, 3 mass % or more is preferable, More preferably, it is 10 mass %, More preferably, it is 20 mass % or more. When content of polypropylene is in the said preferable range, favorable meltdown characteristic can be acquired.

In addition, from the viewpoints of strength and projection formation, it is preferable that the layer B also contains an ultra-high molecular weight polyolefin. Examples of the ultra-high molecular weight polyolefin include ultra-high molecular weight polyethylene and ultra-high molecular weight polypropylene as exemplified in the layer A.

The polyolefin microporous membrane of the present invention can contain various additives such as antioxidants, heat stabilizers and antistatic agents, ultraviolet absorbers, and further anti-blocking agents and fillers in both the A and B layers within the range that does not impair the effects of the present invention. have. In particular, it is preferable to add an antioxidant for the purpose of suppressing the oxidative deterioration due to the thermal history of the polyolefin resin. Appropriate selection of the type and amount of the antioxidant or heat stabilizer is important for adjusting or enhancing the properties of the microporous membrane.

It is preferable that the laminated polyolefin microporous membrane used for this invention does not contain an inorganic particle substantially. "Substantially free of inorganic particles" means, for example, when quantifying inorganic elements by fluorescence X-ray analysis, preferably 50 ppm or less, more preferably 10 ppm or less, still more preferably below the detection limit. means the amount of Even if particles are not actively added to the laminated polyolefin microporous membrane, contamination components derived from foreign substances and contaminants adhering to lines and devices in the manufacturing process of raw material resin or polyolefin microporous membrane are peeled off. It may mix in a film|membrane and may be detected at 50 ppm or less.

The inside of the range (Mw/Mn) of the weight average molecular weight (Mw) of the polyolefin resin composition of B layer and the number average molecular weight (Mn) together with A-layer (Mw/Mn) is preferable, More preferably, it is 10-100. If the range of Mw/Mn is the said preferable range, extrusion of the solution of polyolefin is easy. In addition, a sufficient number of projections are obtained on the surface of the polyolefin microporous membrane, and also when the thickness of the polyolefin microporous membrane is reduced, sufficient mechanical strength is obtained. Mw/Mn is used as a measure of molecular weight distribution. For example, in the case of a polyolefin composed of a single material, the larger the value, the wider the molecular weight distribution. The Mw/Mn of the polyolefin composed of a single substance can be appropriately adjusted by multistage polymerization of the polyolefin. In addition, Mw/Mn of the mixture of polyolefin can be suitably adjusted by adjusting the molecular weight and mixing ratio of each component.

The present inventors think about the mechanism by which the processus|protrusion is formed as mentioned in this invention as follows. When the molten polyolefin resin and the resin solution of the molding solvent are extruded from the die, crystallization of the polyolefin is started, and the crystallization rate is increased by being rapidly cooled in contact with a cooling roll. At this time, spherical crystals having a symmetrical structure having crystal nuclei are formed (FIG. 2). When the heat transfer rate between the surface of the cooling roll and the molten polyolefin resin is relatively small, the crystallization rate is small, resulting in spheroids having relatively small crystal nuclei. When the heat transfer rate is large, it becomes a spheroid having relatively large crystal nuclei. The crystal nuclei of these spheroids become protrusions at the time of TD (width direction) and/or MD (machine direction) stretching, which is a post-process. In addition, spheroids appear as ring-shaped marks on the surface of the laminated polyolefin microporous membrane (Fig. 3).

[3] Manufacturing method of laminated polyolefin microporous membrane

As long as the laminated polyolefin microporous membrane is within the range satisfying the various characteristics described above, a manufacturing method according to the purpose can be freely selected. As a method for producing a microporous membrane, there are a foaming method, a phase separation method, a dissolution recrystallization method, a stretch pore method, a powder sintering method, and the like, and among these methods, the phase separation method is preferable from the viewpoint of uniformity of micropores and cost.

As a manufacturing method by a phase separation method, for example, a polyolefin resin and a molding solvent are heated, melt-kneaded, and the resulting molten mixture is extruded from a die and cooled to form a gel-like molded product, and the resulting gel-like molded product is stretched in at least uniaxial direction. and a method of obtaining a microporous membrane by removing the solvent for molding.

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

The manufacturing method of the laminated polyolefin microporous membrane of this invention includes the process of the following (a)-(f).

(a) The process of adding the solvent for shaping|molding to the polyolefin resin composition which comprises A-layer, then melt-kneading and preparing the polyolefin resin solution A

(b) A step of preparing a polyolefin resin solution B by adding a molding solvent to a polyolefin resin composition containing a polyethylene resin and a polypropylene resin constituting the B layer, followed by melt-kneading

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

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

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

(f) A step of heat-treating the laminated porous molding to obtain a laminated polyolefin microporous film.

In addition, you may add other processes, such as a hydrophilization treatment and an antistatic treatment, before a process (a), during a process (a)-(f), or after a process (f). Moreover, a re-stretching process can also be provided after a process (f).

Hereinafter, each process will be described in detail.

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

The molding solvent is not particularly limited as long as it can sufficiently dissolve the polyolefin. For example, aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, and liquid paraffin, or mineral oil fractions having boiling points corresponding to these are mentioned, but solvent content A nonvolatile solvent such as liquid paraffin is preferable to obtain this stable gel-like article. Heat dissolution is performed by stirring or uniformly mixing and dissolving in an extruder at a temperature at which the polyolefin composition is completely dissolved. The temperature varies depending on the polymer and solvent to be used when dissolving while stirring in the extruder or in the solvent, but is preferably in the range of 140 to 250°C, for example.

The concentration of the polyolefin resin is 100% by mass of the total of the polyolefin resin and the molding solvent, preferably 15 to 40% by mass, more preferably 25 to 40% by mass, still more preferably 28 to 35% by mass. . When the concentration of the polyolefin resin is in the above preferred range, the number of crystal nuclei for forming the projections is sufficiently formed, and a sufficient number of the projections is formed. Moreover, a swell and a neck-in are suppressed at the die outlet at the time of extruding a polyolefin resin solution, and the moldability and self-supporting property of an extruded object are maintained.

When the resin concentrations of the resin solutions A and B are different, it is possible to obtain a laminated microporous membrane having a structure (slanted structure) in which the average pore diameter is changed in the film thickness direction. The average pore diameter of the layer formed using the resin solution with a lower density|concentration becomes larger than the average pore diameter of the layer formed using the resin solution with a higher density|concentration. The concentration of either resin solution A or B can be appropriately selected according to the physical properties required for the laminated microporous membrane. For example, when the inner layer is a dense structure layer having a thickness of 0.01 to 0.05 µm and the surface layer is a coarse structure layer having a thickness of 1.2 to 5.0 times that of the dense structure layer, a good balance between ion permeability and puncture strength can be achieved.

Although the method of melt-kneading is not specifically limited, Usually, it carries out by kneading|mixing uniformly in an extruder. This method is suitable for preparing a high concentration solution of polyolefin. The melt-kneading temperature differs depending on the polyolefin resin to be used. For example, since the polyolefin composition has a melting point of about 130 to 140°C, the lower limit of the melt-kneading temperature is preferably 140°C, even more preferably 160°C, and most preferably 170°C. As for an upper limit, 250 degreeC is preferable, More preferably, it is 230 degreeC, Most preferably, it is 200 degreeC. Moreover, in B layer, although polypropylene is included in a polyolefin solution, 190-270 degreeC of melt-kneading temperature in that case is preferable.

From the viewpoint of suppressing deterioration of the resin, the melt-kneading temperature is preferably lower, but if it is lower than the above-mentioned temperature, an unmelted material is generated in the extrudate extruded from the die, which may cause film breakage in the subsequent stretching process. There are cases. In addition, when the temperature is higher than the above-mentioned temperature, the thermal decomposition of the polyolefin becomes severe, and the physical properties of the resulting microporous membrane, for example, puncture strength, tensile strength, etc. may be deteriorated.

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

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

(c) extruding the polyolefin resin solutions A and B obtained in (a) and (b) from a die, and cooling at least one of them with a cooling roll having a surface from which the molding solvent is removed by a molding solvent removing means , a process of forming a laminated gel-like molding

The polyolefin resin solutions A and B melt-kneaded with an extruder are extruded from a die directly or through another extruder, and cooled with a cooling roll to form a laminated gel-like molding. As a method of obtaining a laminated gel-like molding, the gel-like molding to be laminated is separately prepared and then pasted through a calender roll or the like (laminating method), or a polyolefin solution is separately supplied to an extruder to a desired temperature. Melting in a polymer tube or die, coextrusion, lamination, and then forming a laminated gel-like molded product (coextrusion method) may be used. However, from the viewpoint of interlayer adhesion, coextrusion method is used it is preferable

A gel-like molding is formed by bringing the polyolefin resin solution extruded from the die into contact with a rotating cooling roll set at a surface temperature of 20°C to 40°C as a refrigerant. It is preferable to cool the extruded polyolefin resin solution to 25 degrees C or less. Here, the cooling rate in the temperature region where crystallization is substantially performed becomes important. For example, the extruded polyolefin resin solution is cooled at a cooling rate of 10° C./sec or more in a temperature region where crystallization is substantially performed to obtain a gel-like molding. The cooling rate is preferably 20°C/sec or more, more preferably 30°C/sec or more, and still more preferably 50°C/sec or more. By carrying out such cooling, the structure in which the polyolefin phase is separated into microphases by the solvent is fixed, and spheroids having relatively large nuclei are formed on the surface of the gel-formed product in contact with the cooling roll, and protrusions of an appropriate shape are formed after stretching. can do. The cooling rate can be estimated by simulating from the extrusion temperature of the gel molding, the thermal conductivity of the gel molding, the thickness of the gel molding, the molding solvent, the cooling roll, and the heat transfer rate of air.

In the present invention, it is important to remove as much as possible the molding solvent adhering to the surface of the cooling roll at the portion in contact with the polyolefin resin solution extruded from the die. As shown in Fig. 4, the polyolefin resin solution is cooled by winding it on a rotating cooling roll to form a gel-like molded product, but the molding solvent is adhered to the surface of the cooling roll after the gel-like molded product is separated. come into contact with the resin solution. However, when a large amount of the molding solvent adheres to the surface of the cooling roll, the cooling rate becomes slow due to the heat insulating effect, and the projection becomes difficult to form. Therefore, it becomes important to remove the molding solvent as much as possible until the cooling roll comes into contact with the polyolefin resin solution again.

The molding solvent removing means, that is, the method of 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-shaped molding, and the gel-shaped molding is removed immediately after passing through the doctor blade. The method of scraping off to such an extent that the solvent for shaping|molding cannot visually recognize on the surface of a cooling roll until it contacts is employ|adopted preferably. Alternatively, it may be removed by blowing with compressed air, suctioning, or a combination of these methods. Among them, the scraping method 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 rather than one from the viewpoint of improving the removal efficiency of the molding solvent.

The material of the doctor blade is not particularly limited as long as it is resistant to the molding solvent, but it is preferably made of resin or rubber rather than metal. When it is made of metal, there exists a possibility of damaging a cooling roll. Examples of the resin doctor blade include polyester, polyacetal, and polyolefin.

Even if the temperature of the cooling roll is set to less than 20 ° C, a sufficient cooling rate cannot be obtained only by this due to the heat insulating effect of the molding solvent, and condensation on the cooling roll may cause surface roughness in the gel-like molding. .

As for the thickness of the polyolefin resin solution at the time of extrusion, 1500 micrometers or less are preferable, More preferably, it is 1000 micrometers or less, More preferably, it is 800 micrometers or less. When the thickness of the polyolefin resin solution at the time of extrusion is in the said range, the cooling rate of the surface by the side of a cooling roll does not become gentle, but it is preferable.

Here, when a laminated gel-formed article is obtained by the pasting method, at least one of the polyolefin resin solutions serving as the A-layer or the B-layer may be formed as a gel-formed article under the cooling conditions described above. And when laminating|stacking, it is necessary to laminate|stack so that the surface which contacted the cooling roll of the layer formed by the said cooling condition may become a surface. In addition, when obtaining a laminated gel-formed article by a co-extrusion method, the polyolefin resin solution laminated|stacked and extruded from a die|dye should just be formed as a laminated|multilayer gel-formed article under the said cooling conditions.

The laminated polyolefin is a porous laminate comprising at least an A layer and a B layer. The layer configuration of the laminated polyolefin may be at least two layers of the A layer and the B layer from the viewpoint of the balance of shutdown characteristics, strength and permeability, etc. of physical properties, but from the viewpoint of the balance of the front and back of the final film, A layer / B layer / A It is more preferable to set it as three-layer structure of a layer or B-layer/A-layer/B-layer. From the viewpoint of adhesion to the modified porous layer, the projections may be formed on either the A layer or the B layer, but from the viewpoint of the balance between the permeability and the strength, the surface layer is preferably the A layer and the inner layer is the B layer. On the other hand, from the viewpoint of shutdown, it is preferable that the surface layer be B and the inner layer be A.

As for the thickness of layer B of the laminated polyolefin microporous membrane, 3 micrometers or more and 15 micrometers or less are preferable. As for an upper limit, 10 micrometers is more preferable, More preferably, it is 7 micrometers, More preferably, it is 6 micrometers. Moreover, as for a lower limit, 4 micrometers is preferable. The thickness of the layer B refers to the total thickness of each layer B when the multilayer polyolefin microporous membrane has two or more layers of the B layer.

(d) A step of stretching the laminated gel-like molded product in MD (machine direction) and TD (width direction) to obtain a laminated stretched molded product

The laminated gel-like molded article is stretched to obtain a stretched molded article. Stretching is performed by heating the gel-like molded product, and at a predetermined magnification in two directions, MD and TD, by a conventional tenter method, a roll method, or a combination of these methods. 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, at least one of MD and TD may be stretched in multiple stages regardless of the order of MD and TD. Moreover, although a draw ratio changes with the thickness of a raw material (raw material), 9 times or more in surface magnification is preferable, More preferably, it is 16 to 400 times. In the case of simultaneous stretching of MD and TD, stretching at the same magnification in MD and TD such as 3×3, 5×5, or 7×7 is preferable. If the surface magnification is within the above preferred range, stretching is sufficient to obtain a microporous membrane with high elasticity and high strength. Moreover, desired air permeation resistance can be obtained by adjusting extending|stretching temperature.

It is preferable that extending|stretching temperature shall be below melting|fusing point of polyolefin resin, More preferably, it is the range of (crystal dispersion temperature (Tcd) of polyolefin resin) - (melting|fusing point of polyolefin resin). Melting of polyolefin resin is prevented as extending|stretching temperature is below melting|fusing point of a gelatinous sheet, and it becomes possible to orientate a molecular chain efficiently by extending|stretching. In addition, when the stretching temperature is equal to or higher than the crystal dispersion temperature of the polyolefin resin, the polyolefin resin is sufficiently softened and the stretching tension is low, so that the film formability becomes good, and it is difficult to break a film during stretching, and stretching at a high magnification becomes possible. The crystal dispersion temperature (Tcd) is obtained from the temperature characteristic of dynamic viscoelasticity measured according to ASTM D 4065. Alternatively, it may be obtained from NMR.

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

The stretched and stretched molding is treated with a cleaning solvent to remove the remaining molding solvent, thereby obtaining a microporous membrane. Examples of the cleaning solvent include hydrocarbons such as pentane, hexane, and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as trifluoroethane, and ethers such as diethyl ether and dioxane. Available. These cleaning solvents are appropriately selected according to the molding solvent used for dissolving the polyolefin, and used alone or in combination. The cleaning method can be carried out by a method of extraction by immersion in a cleaning solvent, a method of rinsing off the cleaning solvent, a method of sucking the cleaning solvent from the opposite side of the stretched article, or a method by a combination thereof, and the like. Washing as described above is performed until the residual solvent in the stretch-molded article, which is the stretch-molded article, becomes less than 1% by mass. Thereafter, the cleaning solvent is dried, but the drying method of the cleaning solvent can be carried out by a method such as heat drying or air drying.

(f) heat-treating the laminated porous molding to obtain a laminated polyolefin microporous film

The laminated porous molded product obtained by drying is subjected to heat treatment to obtain a laminated polyolefin microporous film. The heat treatment temperature is preferably carried out at 90 to 150 ℃. When the heat treatment temperature is in the above preferred range, the thermal contraction rate of the obtained multilayer polyolefin microporous membrane can be reduced, and air permeation resistance can be ensured. Although the heat processing time is not specifically limited, Usually, 1 second or more and 10 minutes or less are preferable, More preferably, it is performed in 3 second - 2 minutes or less. For the heat treatment, all of a tenter method, a roll method, a rolling method, and a free method may be employed.

In a heat treatment process, it is preferable to hold|grind with respect to both directions of MD (machine direction) and TD (width direction), and to shrink in at least one direction among MD and TD. As for the shrinkage rate of shrinkage in at least one direction among MD and TD, 0.01 to 50% is preferable, More preferably, it is 3 to 20%. When the shrinkage rate is in the above-mentioned preferred range, the heat shrinkage rate at 105°C and 8 hr is improved, and the air permeability resistance is maintained. In addition, in order to improve the puncture strength, re-stretching of about 5% to 20% in TD, MD, or both directions may be additionally performed before heat treatment.

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

Next, the modified porous layer used for this invention is demonstrated.

The modified porous layer is preferably laminated on the protrusion side of the laminated polyolefin microporous membrane. When the modified porous layer is provided on both surfaces of the multilayer polyolefin microporous membrane, the modified porous layer on the side to which a parallel stress is more strongly applied by contact with a roll or bar in a subsequent step such as a slit process or a conveying process is laminated polyolefin It is preferable to laminate the microporous membrane on the protrusion side because the effect of the present invention is exhibited.

The modified porous layer as used in the present invention provides or improves at least one function such as heat resistance, adhesion to electrode material, and electrolyte permeability. The modified porous layer includes inorganic particles and a binder having a ^{tensile strength of 5 N/mm 2 or more.} By using a binder having a tensile strength of 5 N/mm ² or more, a battery separator having very excellent 0° peel strength is obtained due to the protrusion existing on the surface of the multilayer polyolefin microporous membrane and the effect of increasing the tensile strength of the binder. Moreover, compared with the case of a laminated polyolefin microporous membrane alone, even if a modified porous layer is laminated|stacked, the air permeation resistance does not rise significantly in the battery separator. This is because sufficient 0° peel strength can be obtained even if a large amount of binder does not permeate into the pores of the multilayer polyolefin microporous membrane.

The tensile strength of the binder is 5 N/mm ² or more, and the lower limit is ^{preferably 10 N/mm 2} , more preferably 20 N/mm ² , and still more preferably 30 N/mm ² . The upper limit is not particularly set, but 100 N/mm ² That's enough. The tensile strength of the binder refers to a value measured by a method described later.

The binder having a tensile strength of 5 N/mm ² or more used in the present invention is not particularly limited as long as the tensile strength is 5 N/mm ² or more, and examples thereof include polyvinyl alcohol, cellulose ether-based resin, and acrylic resin. . Examples of the cellulose ether-based resin include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanoethyl cellulose, and oxyethyl cellulose. As the acrylic resin, a crosslinked acrylic resin is preferable. In addition, a commercially available aqueous solution or aqueous dispersion can also be used. As commercially available ones, for example, Nisshin Kasei Co., Ltd. "POVACOAT" (registered trademark), Toagosei Co., Ltd. "JURYMER" (registered trademark) AT-510, ET-410, FC- 60, SEK-301, Daisei Fine Chemicals Co., Ltd. UW-223SX, UW-550CS, DIC Corporation WE-301, EC-906EF, CG-8490, etc. Especially, electrode adhesiveness Polyvinyl alcohol and acrylic resin having high affinity with non-aqueous electrolyte, suitable for heat resistance, and relatively large tensile strength are preferable.

In order to reduce curl of the laminated polyolefin microporous film by laminating the modified porous layer, it is important to include inorganic particles in the coating liquid for forming the modified porous layer. The coating solution in the present specification includes a ^{binder having a tensile strength of 5 N/mm 2} or more, inorganic particles, and a solvent capable of dissolving or dispersing the binder, and is used to form the modified porous layer. The binder has at least a role for binding inorganic particles to each other and a role for binding the laminated polyolefin microporous membrane and the modified porous layer to each other. As a solvent, water, alcohol, acetone, n-methylpyrrolidone, etc. are mentioned, for example. By adding inorganic particles to the coating solution, effects such as prevention of internal short circuit caused by growth of dendrites of electrodes inside the battery (dendritic prevention effect), reduction of thermal contraction rate, and imparting of slidability can also be obtained. . As for the upper limit of the particle|grain addition amount, 98 mass % is preferable, More preferably, it is 95 mass %. As for a lower limit, 80 mass % is preferable, More preferably, it is 85 mass %. When the amount of particles added is within the above preferred range, the effect of reducing curl is sufficient, the ratio of the functional resin to the total volume of the modified porous layer is optimal, and the peeling strength of 0° sufficient for the modified porous layer is obtained.

As for the average particle diameter of an inorganic particle, 1.5 times or more and 50 times or less of the average pore diameter of a laminated polyolefin microporous membrane are preferable, More preferably, they are 2.0 times or more and 20 times or less. If the average particle diameter of the particles is within the above preferred range, the increase in air permeation resistance due to blocking the pores of the laminated polyolefin microporous membrane in a state where the heat-resistant resin and the particles are mixed is prevented, and further, the particles fall off in the battery assembly process, Avoid causing serious battery failure.

Examples of inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, mica, boehmite and the like. In addition, heat-resistant cross-linked polymer particles may be added if necessary. Examples of the heat-resistant crosslinked polymer particles include crosslinked polystyrene particles, crosslinked acrylic resin particles, and crosslinked methyl methacrylate particles. The shape of the inorganic particles may be a true spherical shape, a substantially spherical shape, a plate shape, a needle shape, or a polyhedral shape, but is not particularly limited.

Although it will not restrict|limit especially as long as the solid content concentration of a coating liquid can apply|coat uniformly, 50 mass % or more and 98 mass % or less are preferable, and 80 mass % or more and 95 mass % or less are more preferable. When the solid content concentration of the coating liquid is in the above preferred range, the modified porous layer is prevented from weakening, and a sufficient peel strength of 0° of the modified porous layer is obtained.

As for the film thickness of a modified porous layer, 1-5 micrometers is preferable, More preferably, it is 1-4 micrometers, More preferably, it is 1-3 micrometers. If 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 film breaking strength and insulation when melted and contracted above the melting point, and a sufficient hole blocking function is obtained. reaction can be prevented. Moreover, the winding volume can be suppressed and it is suitable for the capacity increase of a battery. Furthermore, by suppressing curl, it leads to productivity improvement in a battery assembly process.

The porosity of the modified porous layer is preferably 30 to 90%, more preferably 40 to 70%. In order to set it as a desired porosity, it is obtained by adjusting the density|concentration of an inorganic particle, binder density|concentration, etc. suitably. When the porosity of the modified porous layer is in the above-mentioned 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.

As for the upper limit of the total film thickness of the separator for batteries obtained by laminating|stacking a modified porous layer, 25 micrometers is preferable, More preferably, it is 20 micrometers. As for a lower limit, 6 micrometers or more are preferable, More preferably, it is 7 micrometers or more. When the total film thickness of the battery separator is in the above preferred range, the battery separator obtained by laminating the modified porous layer can ensure sufficient mechanical strength and insulation. In addition, a decrease in the capacity can be avoided by reducing the electrode area that can be filled in the container.

The air permeation resistance of the battery separator is one of the most important characteristics, preferably 50 to 400 sec/100 ccAir, more preferably 100 to 350 sec/100 ccAir, and even more preferably 100 to 300 sec/100 ccAir. In order to set it as a desired air permeation resistance, it is obtained by adjusting the porosity of a modified porous layer, and adjusting the degree of penetration into the laminated polyolefin microporous membrane of a binder. If the air permeation resistance of the battery separator is in the above preferred range, sufficient insulation is obtained, and foreign matter clogging, short circuit, and film breakage are prevented. In addition, by suppressing the film resistance, charge/discharge characteristics and lifespan characteristics within a practically usable range are obtained.

Next, the method of laminating|stacking a modified porous layer on the laminated polyolefin microporous membrane in this invention is demonstrated. The method of laminating the modified porous layer on the laminated polyolefin microporous membrane of the present invention includes the following step (g).

(g) On the surface of the multilayer polyolefin microporous membrane in contact with the cooling roll, a ^{binder having a tensile strength of 5 N/mm 2} or more, inorganic particles, and a coating solution containing a solvent capable of dissolving or dispersing the binder, the laminated film forming and drying process

A well-known method can be used for the method of laminating|stacking a modified porous layer on a laminated polyolefin microporous membrane. Specifically, it can be obtained by coating the coating solution on the laminated polyolefin microporous membrane to a predetermined film thickness by the method described later and drying it under the conditions of a drying temperature of 40 to 80° C. and a drying time of 5 seconds to 60 seconds. In addition, a coating solution dissolved in a solvent that is capable of dissolving the binder and miscible with water is laminated on a predetermined multilayer polyolefin microporous membrane using the coating method described later, placed under a specific humidity environment, and the binder and water are mixed. A method in which the solvent is phase-separated and further introduced into a water bath (coagulation bath) to solidify the binder may also be used.

As a method of applying the coating liquid, for example, a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a Mayer bar coating method, a pipe doctor method, a blade coating method and die coating method, etc. are mentioned, and these methods can be performed individually or in combination.

The battery separator of the present invention is preferably stored in a dry state, but when storage in a dry state is difficult, it is preferable to perform a reduced pressure drying treatment at 100° C. or less immediately before use.

The battery separator of the present invention is a secondary battery such as a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a lithium secondary battery, and a lithium polymer secondary battery, and a plastic film capacitor, a ceramic capacitor, an electric double layer capacitor Although it can use as a separator of these etc., it is especially preferable to use as a separator of a lithium ion secondary battery. A lithium ion secondary battery will be described below as an example.

In a lithium ion secondary battery, a positive electrode and a negative electrode are stacked with a separator interposed therebetween, and the separator contains an electrolyte solution (electrolyte). The structure of the electrode is not particularly limited and may be a known structure. For example, a disk-shaped electrode structure (coin type) in which anodes and cathodes are arranged to face each other, an electrode structure in which flat anodes and cathodes are alternately stacked (stacked type), and a target (帶狀) ) in which the anode and the cathode are overlapped and wound, and it can be set as a structure such as an electrode structure (wound type).

The positive electrode has a positive electrode active material layer comprising a current collector and a positive electrode active material capable of occluding and releasing lithium ions formed on the surface thereof. Examples of the positive electrode active material include inorganic compounds such as a transition metal compound, a composite oxide of lithium and a transition metal (lithium composite oxide), and a transition metal sulfide. Examples of the transition metal include V, Mn, Fe, Co, and Ni. Preferred examples of the lithium composite oxide in the positive electrode active material include lithium nickelate, lithium cobaltate, lithium manganate, and a layered lithium composite oxide having an _{α-NaFeO 2 structure as a matrix.}

The negative electrode has a current collector and a negative electrode active material layer including a negative electrode active material formed on the surface thereof. Examples of the negative electrode active material include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black. The electrolyte solution is obtained by dissolving a lithium salt in an organic solvent. Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiN ( C ₂ F ₅ SO ₂ ) ₂ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , lower aliphatic carboxylic acid lithium salt, LiAlCl ₄ , and the like. These may be used independently and may mix and use 2 or more types. Examples of the organic solvent include organic solvents having a high boiling point and high dielectric constant such as ethylene carbonate, propylene carbonate, ethylmethyl carbonate, and γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane, and dimethyl carbonate. , and organic solvents of low boiling point and low viscosity, such as diethyl carbonate. These may be used independently and may mix and use 2 or more types. In particular, an organic solvent having a high dielectric constant has a high viscosity and a low viscosity organic solvent has a low dielectric constant, so it is preferable to use a mixture of both.

When assembling a battery, the separator of the present invention can be impregnated with an electrolyte solution to impart ion permeability to the separator. Usually, the impregnation treatment is performed by immersing the microporous membrane in an electrolyte 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 obtain a wound electrode element. Then, the battery can be obtained by inserting this electrode element into a battery can, impregnating it with the electrolyte solution, and caulking the battery lid that also serves as a positive terminal with a safety valve through a gasket.

Example

Hereinafter, although an Example is shown and demonstrated concretely, this invention is not limited in any way by these Examples. In addition, the measured value in an Example is the value measured by the following method.

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

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

It measured under the following conditions using the tensile tester (Autograph AGS-J load cell capacity|capacitance of 1 kN by Shimadzu Corporation Corporation). The sample film and measurement conditions were as follows, and the measurement was performed three times, and the average value was made into the tensile strength of the binder.

Distance between chucks: 40 mm

Test speed: 20 mm/min

Measurement environment: temperature 20℃, relative humidity 60%

2. Number of projections

The number and size of the projections were measured after stabilizing the light source using a confocal (confocal) microscope (HD100 manufactured by Lasertech Co., Ltd.) installed on an isolator.

(order)

(1) A 1 cm x 1 cm square frame was drawn with an ultrafine oil pen on the surface that was in contact with the cooling roll at the time of forming the laminated polyolefin microporous membranes obtained in Examples and Comparative Examples.

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

(3) Using an objective lens with a magnification of 5 times, the ring-shaped traces derived from the spherical crystals of polyolefin as shown in Fig. 3 are displayed on the monitor as a two-dimensional image (referred to as a REAL screen in this device), so that the most color of the ring-shaped marks is The position of the sample stage was adjusted so that the dark part was almost in the center of the monitor screen. In the case where two ring-shaped marks were continuous, they were aligned with the contact point. The object of the projection height measurement was to have a long diameter of 0.2 mm or more of the ring-shaped traces derived from the spherical crystals of the polyolefin. The length of the long diameter of the ring-shaped mark was read by placing a cursor at both ends of the ring in the longitudinal direction in the two-dimensional image.

(4) Change the objective lens to a 20x lens, focus on the central part of the monitor screen (in this device, the central part of the monitor screen is displayed the brightest), and this height position was used as the reference height (referred to as REFSET in this device) called).

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

(6) After three-dimensional data collection, an image for data processing (referred to as a Z image in this apparatus) was displayed, and smoothing was performed (smoothing conditions: filter size 3×3, matrix type SMOOTH3-Ø, 1 recovery). In addition, horizontal correction was performed on the horizontal correction screen as needed.

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

(8) In the cross-sectional profile image, two cursors were vertically aligned with the inflection points of both sleeves of the projection, and the distance between the cursors was defined as the size of the projection.

(9) Align the two cursors in the horizontal direction with the vertex of the protrusion and the inflection point of both sleeves of the protrusion in the cross-sectional profile image (if the heights of the inflection points of both sleeves of the protrusion are different, the lower one) and determine the distance between the two cursors. made in height

(10) Repeat the above operation in the 1 cm × 1 cm square frame, count the number of projections with a size of 5 μm or more and 50 μm or less and a height of 0.5 μm or more and 3.0 μm or less to obtain the number of projections per ^{cm 2 ,} Furthermore, the average value of the height of the processus|protrusion was calculated|required.

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

1 schematically shows an evaluation method. Reference numeral 1 denotes a laminated sample, a divalent laminated polyolefin microporous membrane, 3 a modified porous layer, a tetravalent double-sided adhesive tape, and 5 and 5' an aluminum plate, and arrows in the figure indicate the tensile direction. A double-sided adhesive tape (NW-K50 manufactured by Nichiban Corporation) 4 of the same size was attached to an aluminum plate 5 having a size of 50 mm×25 mm and a thickness of 0.5 mm. On it, the surface of the laminated polyolefin microporous membrane 2 of the sample 1 (separator for batteries) cut to a width of 50 mm x a length of 100 mm is overlapped by 40 mm from the end of one side of the 25 mm length of the aluminum plate 5. I glued it on and cut off the protruding part. Then, 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, and 20 mm from the end of one side of the sample side with a length of 25 mm to the aluminum plate 5 are pasted so that they overlap. Thereafter, the aluminum plate (5) and the aluminum plate (5') sandwiched with the sample were mounted on a tensile tester (Autograph AGS-J load cell capacity of 1 kN manufactured by Shimadzu Corporation), and the aluminum plate (5) and Each of the aluminum plates 5' was pulled in parallel in opposite directions at a tensile rate of 10 mm/min, and the strength when the modified porous layer was peeled off was measured. This measurement was performed for three arbitrary points spaced apart by 30 cm or more in the longitudinal direction, and the average value was taken as the 0° peel strength of the modified porous layer.

4. Film thickness

It was calculated|required by averaging the measured values of 20 points|pieces using the contact-type film thickness meter (Mitsutoyo Co., Ltd. lightmatic series318). Measurements were made under the condition of a weight of 0.01 N by using a carbide-spherical surface measuring device φ9.5 mm.

5. Average hole diameter

The average pore diameter of the laminated polyolefin microporous membrane was measured by the following method. A sample was fixed on the cell for measurement using a double-sided tape, and platinum or gold|metal|money was vacuum-deposited for several minutes, and the surface of the film|membrane was SEM-measured with appropriate magnification. On the image obtained by SEM measurement, ten arbitrary places were selected, and the average value of the pore diameters of those ten places was made into the average pore diameter of the sample.

6. Air resistance (sec/100 ccAir)

Using a Gurley-type densometer type B manufactured by Tester Sangyo Co., Ltd., a laminated polyolefin microporous membrane or a battery separator was fixed so as not to wrinkle between the clamping plate and the adapter plate, and measurements were made in accordance with JIS P8117. The sample was 10 cm x 10 cm, and the measurement point was made into a total of 5 points of the center part and four corners of the sample, and the average value was used as air permeation resistance. In addition, when the length of one side of the sample is less than 10 cm, the values measured at 5 points at intervals of 5 cm can be used.

The increase in speculative resistance was obtained by the following formula.

Rise of Speculative Resistance = (Y)-(X) sec/100 ccAir

Air permeation resistance of laminated polyolefin microporous membrane (X) sec/100 ccAir

Permeation resistance of battery separator (Y) sec/100 ccAir

7. Meltdown temperature

Using a thermomechanical analysis device (manufactured by Seiko Denshi Kogyo Co., Ltd., TMA/SS6000), a 10 mm (TD) × 3 mm (MD) specimen was pulled in the longitudinal direction of the specimen with a constant load of 2 gf. , the temperature was raised from room temperature at a rate of 5°C/min, and the temperature at which the film was ruptured by melting was defined as the meltdown temperature.

8. Heat of fusion of polypropylene (ΔHm)

About 5 mg of a sample was placed in a previously precisely weighed aluminum sample pan, and then the mass of the sample pan into which the sample was placed was precisely weighed, and the difference from the sample pan mass was defined as the sample mass. The sample pan containing the sample was placed in a sample holder of a scanning differential calorimeter (manufactured by PerkinElmer, Inc., DSC-System 7 type), and heated at 10°C/min from 40°C to 190°C under a nitrogen atmosphere. Then, heat treatment was performed at 190° C./10 minutes. Then, after cooling at 10 degreeC/min to 40 degreeC and hold|maintaining at 40 degreeC for 2 minutes, it heated up to 190 degreeC at the temperature increase rate of 10 degreeC/min. For the DSC curve (melting curve) obtained in the temperature increase process, a straight baseline is set in the range of 85 to 175° C. did.

9. Porosity of Laminated Polyolefin Microporous Membrane

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

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

10. Friction resistance

Both ends were slitted while winding the separator for roll-shaped batteries obtained by the Example and the comparative example. The slit processing was performed using a slitter (type WA177A manufactured by Nishimura Seisakusho Co., Ltd.) under the conditions of a speed of 20 m/min and a tension of 60 N/100 mm. During processing, the rolls in contact with the coating surface were two hard chrome plating rolls (both free rolls). Next, while rewinding the slitted roll-shaped battery separator, visually and using a magnifying glass with a scale of 10 times magnification (PEAK SCALELUPE×10), the peeling defects of the modified porous layer having a long diameter of 0.5 mm or more were counted, and the following determination was made. evaluated on the basis of The evaluation area was 100 mm wide x 500 m long (when the width was less than 100 mm, the length was adjusted so that the evaluation area was the same).

Criteria

○ (very good): 5 or less

△ (Good): 6 to 15

× (defective): 16 or more

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

Mw and Mw/Mn were calculated|required by the gel permeation chromatography (GPC) method under the following conditions.

・Measuring device: Waters Corporation GPC-150C

・Column: Showa Denko Co., Ltd. product "Shodex" (registered trademark) UT806M

·Column temperature: 135℃

·Solvent (mobile phase): o-dichlorobenzene

·Solvent flow rate: 1.0 ml/min

-Sample concentration: 0.1 mass % (dissolution condition: 135 degreeC/1h)

・Injection amount: 500 μl

Detector: Differential Refractometer manufactured by Waters Corporation

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

12. Melting Point

Using a differential scanning calorimeter (DSC) DSC6220 manufactured by SI Nanotechnology Co., Ltd., 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 is taken as the melting point. did.

Example 1

To 100 parts by weight of a composition comprising 30% by weight of ultra-high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and 70% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000, tetrakis [methylene-3-(3) A polyethylene composition (A) to which 0.375 parts by weight of ,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane was added was obtained. 30 parts by weight of this polyethylene composition (A) was put into a twin-screw extruder. 70 weight part of liquid paraffin was supplied from the side feeder of this twin screw extruder, it melt-kneaded, and the polyolefin resin solution A was prepared in the extruder.

On the other hand, 15% by weight of ultra-high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million, 65% by weight of high-density polyethylene (HDPE) having a weight average molecular weight of 300,000, polypropylene having a weight average molecular weight of 530,000 and a heat of fusion of 96 J/g Polyolefin obtained by adding 0.375 parts by weight of tetrakis[methylene-3-(3,5-di-tertbutyl-4-hydroxyphenyl)-propionate]methane as antioxidant to 100 parts by weight of a composition comprising 20% by weight A composition (B) was obtained. 25 parts by weight of this polyolefin composition (B) was put into a twin-screw extruder. 75 weight part of liquid paraffin was supplied from the side feeder of this twin screw extruder, it melt-kneaded, and the polyolefin resin solution B was prepared in the extruder.

The obtained polyolefin resin solutions A and B were co-extruded from a multilayer die at 190°C so that the layer structure was A/B/A and the solution ratio was 1/1/1, and the internal cooling water temperature was maintained at 25°C, 800 mm in diameter A laminated gel-like molded article was formed while taking it up with a cooling roll of At this time, between the point where the laminated gel-like molding is separated from the cooling roll and the point where the laminated polyethylene resin solution extruded from the die and the cooling roll come into contact, one polyester doctor blade is applied to the cooling roll parallel to the width direction of the gel-like molding. The liquid paraffin adhering to the cooling roll was scraped off. Subsequently, this laminated gel-like molded product was subjected to simultaneous biaxial stretching at a temperature of 115° C. at 5×5 times to obtain a stretched molded product. The obtained stretched article was washed with methylene chloride to extract and remove residual liquid paraffin, and dried to obtain a porous molded article. Thereafter, the porous membrane is maintained in a tenter, heat-treated at 125° C. for 3 seconds, and a polyolefin fine having a thickness of 20 μm, a porosity of 43%, an average pore diameter of 0.14 μm, an air resistance of 232 sec/100 ccAir, and a meltdown temperature of 178° C. A porous membrane was obtained.

Polyvinyl alcohol (average degree of polymerization 1700, saponification degree 99% or more), alumina particles having an average particle diameter of 0.5 μm, and ion-exchanged water were each blended in a weight ratio of 6:54:40, and zirconium oxide beads (manufactured by Toray Corporation) It was put in a polypropylene container together with "Torayceram" (registered trademark) beads, 0.5 mm in diameter) and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho, Ltd.). Then, the filtration limit It filtered with a 5 micrometer filter, and obtained the coating liquid (a).

The coating liquid (a) is applied by a gravure coating method to the surface of the multilayer polyethylene microporous membrane in contact with the cooling roll at the time of film formation, dried by passing it through a hot air drying furnace at 50° C. for 10 seconds, and a final thickness of 22 μm battery separator got

Example 2

A battery separator was obtained in the same manner as in Example 1 except that two polyester doctor blades were applied to the cooling roll at intervals of 20 mm.

Example 3

A battery separator was obtained in the same manner as in Example 1 except that three polyester doctor blades were applied to the cooling roll at intervals of 20 mm each.

Example 4

Two-component curable aqueous acrylic urethane resin (solid content concentration: 45% by mass) consisting of aqueous acrylic polyol and water-dispersible polyisocyanate (curing agent), alumina particles having an average particle diameter of 0.5 μm, and ion-exchanged water were mixed in a weight ratio of 10:40:50, respectively. Blend, put in a polypropylene container together with zirconium oxide beads (“Toray Serum” (registered trademark) beads manufactured by Toray Corporation, 0.5 mm in diameter), and use a paint shaker (manufactured by Toyo Seiki Seisakusho) Disperse for 6 hours.Then, filtration with a filter having a filtration limit of 5 μm to obtain a coating solution (b).The modified porous layer is the same as in Example 1 except that the coating solution (a) is replaced with a coating solution (b). was laminated to obtain a battery separator.

Example 5

Copolymer of polyvinyl alcohol, acrylic acid, and methyl methacrylate ("POVACOATR" (registered trademark) manufactured by Nisshin Kasei Co., Ltd.), alumina particles having an average particle diameter of 0.5 µm, solvent (ion-exchanged water: ethanol = 70:30) was mixed in a weight ratio of 5:45:50, put in a polypropylene container together with zirconium oxide beads (“Toray Serum” (registered trademark) beads manufactured by Toray Corporation, 0.5 mm in diameter), and put in a paint shaker (proper or not) Disperse for 6 hours with Toyo Seiki Seisakusho Co., Ltd.) Filtered with a filter with a filtration limit of 5 µm to obtain a coating solution (c).Except that the coating solution (a) was replaced with a coating solution (c) The modified porous layer was laminated|stacked similarly to Example 1, and the separator for batteries was obtained.

Example 6

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 7

As the polyolefin resin composition (B), 5 wt% of ultra-high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and 55 wt% of high density polyethylene (HDPE) having a weight average molecular weight of 300,000, a weight average molecular weight of 530,000, and a heat of fusion of 96 Using a composition in which 0.375 parts by weight of antioxidant is added to 100 parts by weight of a composition composed of 40% by weight of polypropylene of J/g, and 70 parts by weight of liquid paraffin with respect to 30 parts by weight of polyethylene composition (B), polyolefin resin solution B A battery separator was obtained in the same manner as in Example 1 except that .

Example 8

As the polyolefin resin composition (A), to 100 parts by weight of a composition comprising 20% by weight of ultra-high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and 80% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 300,000, antioxidant 0.375 weight A battery separator was obtained in the same manner as in Example 1 except that the polyolefin resin solution B was obtained by supplying 70 parts by weight of liquid paraffin with respect to 30 parts by weight of the polyethylene composition (B) using the composition in which parts were added.

Example 9

A battery separator was obtained in the same manner as in Example 3 except that the extrusion amounts of the polyolefin solutions A and B were adjusted so that the thickness of the polyolefin laminated porous membrane was as described in the table.

Example 10

Example 1, except that the blending ratio of ultra-high molecular weight polyethylene and high density polyethylene in the polyolefin composition (A), and that ultra-high molecular weight polyethylene is not used in the polyolefin composition (B) and the blending ratio of high density polyethylene and polypropylene are as shown in the table In the same manner, a battery separator was obtained.

Example 11

Alumina particles are replaced with crosslinked polymer particles (polymethyl methacrylate-based crosslinked particles (“epostar” (registered trademark) MA1002, manufactured by Nippon Shokubai, Inc., average particle diameter of 2.5 µm)), crosslinked polymer The mixing ratio of particles and N-methyl-2-pyrrolidone was 35:10:55 (weight ratio) to obtain a varnish (d), except that the varnish (d) was used in the same manner as in Example 1, A battery separator was obtained.

Example 12

Fluorine resin solution (Kureha Chemical Co., Ltd. "KF Polymer" (registered trademark) #9300 (polyvinylidene fluoride (5% N-methylpyrrolidone solution) and alumina particles having an average particle diameter of 0.5 µm, N- Methyl-2-pyrrolidone was blended in a weight ratio of 16:34:50, respectively, and together with zirconium oxide beads (“Toray Serum” (registered trademark) beads manufactured by Toray Corporation, 0.5 mm in diameter), polypropylene Put in a container and disperse for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.) Then, filtered through a filter with a filtration limit of 5 µm to obtain varnish (e). Except for that, it carried out similarly to Example 1, and obtained the separator for batteries.

Example 13

Acrylic emulsion (Showa Denko Co., Ltd. "Polysol" (registered trademark) AT-731, non-volatile content 47%), alumina particles with an average particle diameter of 0.5 µm, and ion-exchanged water were mixed at 2:55:43, respectively. was mixed in a weight ratio of , and put in a polypropylene container together with zirconium oxide beads (“Toray Serum” (registered trademark) beads manufactured by Toray Corporation, 0.5 mm in diameter), and put in a paint shaker (Toyo Seiki Seisaku Co., Ltd.) show product) for 12 hours. Then, it filtered with a filter with a filtration limit of 5 micrometers, and obtained the coating liquid (f). The coating liquid (f) was applied to the laminated polyethylene microporous membrane of Example 1 in the same manner as in Example 1 to obtain a battery separator.

Example 14

A battery separator was obtained in the same manner as in Example 1 except that the coating liquid (g) in which the alumina particles were replaced with barium sulfate fine particles (average particle diameter of 0.3 µm) was used.

Comparative Example 1

A battery separator was obtained in the same manner as in Example 1 except that, using only polyethylene solution A, it was extruded from a single-layer die at 190° C. to form a single-layer gel-formed article, and the obtained single-layer gel-formed article was used instead of the laminated gel-shaped article.

Comparative Example 2

A battery separator was obtained in the same manner as in Example 8 except that polypropylene having a weight average molecular weight of 490,000 and a heat of fusion of 70 J/g was used as the polypropylene used for the polyolefin solution B.

Comparative Example 3

As polyolefin resin compositions (A) and (B), the battery separator was obtained like Example 1 except having made the compounding ratio, addition amount, and resin concentration as the table|surface.

Comparative Example 4

The polyethylene resin solution extruded from the die was cooled with a cooling roll, and a doctor blade was not used to obtain a gel-like molded product, and the liquid paraffin adhering on the cooling roll was not scraped off in the same manner as in Example 1, except that the battery separator got

Comparative Example 5

A battery separator was obtained in the same manner as in Example 1 except that the internal cooling water temperature of the cooling roll was maintained at 0° C. and no doctor blade was used.

Comparative Example 6

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

Comparative Example 7

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

Comparative Example 8

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

A polyamideimide resin solution, alumina particles having an average particle diameter of 0.5 μm, and N-methyl-2-pyrrolidone were each blended in a weight ratio of 26:34:40, and zirconium oxide beads (“Toray Serum manufactured by Toray Corporation”) ” (registered trademark) beads, 0.5 mm in diameter), put in a polypropylene container, and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Then, filtration with a filter having a filtration limit of 5 µm Thus, a coating solution (h) was obtained.The coating solution (h) was applied to the multilayer polyethylene microporous membrane obtained in the same manner as in Example 1 in the same manner as in Example 1 by a gravure coating method to obtain a battery separator.

Table 1 shows the manufacturing conditions of Examples 1-14 and Comparative Examples 1-8. In addition, Table 2 shows the characteristics of the obtained laminated polyolefin microporous membrane and the separator for batteries.

[Table 1]

[Table 2]

1 Battery separator
2 Laminated Polyethylene Microporous Membrane
3 modified porous layer
4 Double-sided adhesive tape
5, 5' aluminum plate
6 Polyethylene spherulite nuclei
7 die
8 Polyethylene resin solution
9 cooling rolls
10 Doctor Blade
11 Gel-like moldings

Claims (7)

A battery separator having a multilayer polyolefin microporous membrane and a modified porous layer present on at least one surface thereof, wherein the multilayer polyolefin microporous membrane is a porous layered product comprising at least an A layer and a B layer, and a meltdown temperature of 165 ℃ or higher, the air permeability resistance is 300 sec/100 ccAir or less, and at least 3/cm ² or more and 200/cm ² or less protrusions made of polyolefin on the surface facing the outside are not periodic and irregularly present and the protrusion satisfies 0.5 µm≤H (H is the height of the protrusion) and 5 µm≤W≤50 µm (W is the size of the protrusion), and the modified porous layer is a surface having protrusions of the multilayer polyolefin microporous membrane A battery separator, comprising: a binder laminated thereon and having a tensile strength of 5 N/mm ^{2 or more, and inorganic particles.} According to claim 1,
The laminated polyolefin microporous membrane has a three-layer structure of A layer / B layer / A layer, or B layer / A layer / B layer, characterized in that the B layer comprises polypropylene having a heat of fusion of 90 J / g or more, battery separator. 3. The method of claim 1 or 2,
The battery separator whose thickness of B-layer is 3 micrometers or more and 15 micrometers or less. 3. The method of claim 1 or 2,
A battery separator, wherein the binder contains polyvinyl alcohol or an acrylic resin. 3. The method of claim 1 or 2,
A battery separator, wherein the inorganic particles contain at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate, and boehmite. A method for producing a battery separator according to claim 1 or 2, comprising the steps (a) to (g) below;
(a) the step of adding a molding solvent to the polyolefin resin constituting the layer A, followed by melt-kneading to prepare the polyolefin resin solution A;
(b) adding a molding solvent to a polyolefin resin containing a polyethylene resin and a polypropylene resin constituting the B layer, followed by melt-kneading to prepare a polyolefin resin solution B;
(c) extruding the polyolefin resin solutions A and B obtained in the steps (a) and (b) from a die, and at least one of them is used as a cooling roll having a surface from which the molding solvent is removed by a molding solvent removing means. cooling to form a laminated gel-like molding;
(d) stretching the laminated gel-like molded product in the machine direction and the width direction to obtain 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 it to obtain a laminated porous molded product;
(f) heat-treating the laminated porous molding to obtain a laminated polyolefin microporous film;
(g) On the surface of the multilayer polyolefin microporous membrane in contact with the cooling roll, a ^{binder having a tensile strength of 5 N/mm 2} or more, inorganic particles, and a coating solution containing a solvent capable of dissolving or dispersing the binder, the laminated film forming and drying process. 7. The method of claim 6,
The method for manufacturing a battery separator, wherein the means for removing the solvent for molding in the step (c) is a means for scraping using a doctor blade.

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