KR20170019345A - Battery separator and production method therefor - Google Patents

Abstract

The present invention is based on the assumption that the separator for a battery is gradually thinned and the cost is progressively reduced in the future so that it has a very high peel strength with the modified porous layer and is excellent in meltdown characteristics suitable for high speed processing in a slit process or a battery assembly process, A battery separator suitable for an ion battery is provided. The present invention provides a separator for a battery having a laminated polyolefin microporous membrane and a modified porous layer present on at least one surface of the laminated polyolefin microporous membrane, wherein the laminated polyolefin microporous membrane is a porous laminate comprising at least an A layer and a B layer, and the temperature is above 165 ℃, air permeability resistance is 300 sec / 100 and ccAir or less, at least on the surface facing the outer space of the side 3 / cm ² or more to 200 / cm ² or less, the protrusion formed of a polyolefin and irregularly presence of , The projections satisfy 0.5 占 퐉? H (H is the height of the projections) and 5 占 퐉? W? 50 占 퐉 (W is the size of the projections), and the modified porous layer is formed on the surface having the projections of the laminated polyolefin microporous membrane Disclosed is a battery separator comprising a binder and inorganic particles which are laminated and have a tensile strength of 5 N / mm ² or more.

Description

TECHNICAL FIELD [0001] The present invention relates to a battery separator,

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

Thermoplastic resin microporous membranes are widely used as an insulator and a filter. For example, the separator may be a lithium ion secondary battery, a nickel-hydrogen battery, a nickel-cadmium battery, a battery separator used for a polymer battery, a separator for an electric double layer capacitor, a reverse osmosis filtration membrane, an ultrafiltration membrane, . In addition, it is used for breathable waterproof medical treatment (clothing) and medical (medical) materials. Particularly, a separator for a lithium ion secondary battery has ion permeability by impregnation with an electrolyte and is excellent in electric insulation property, electrolytic solution resistance and oxidation resistance, and when the battery is abnormally heated, ion permeability is cut off at a temperature of about 120 to 150 캜, A microporous polyethylene film made of polyethylene which also has a hole clogging effect for suppressing a rise in temperature is preferably used. However, if the temperature rise continues even after the occlusion of the hole for any reason, a breakage (rupture) can be caused by viscosity reduction of the polyethylene constituting the film or shrinkage of the film. This phenomenon is not a phenomenon confined to polyethylene but can be avoided at a temperature above the melting point of the resin constituting the microporous film even when other thermoplastic resins are used.

Separators for lithium ion batteries are required to have mechanical properties, heat resistance, transparency, dimensional stability, hole closure characteristics (shutdown characteristics), melt breaking characteristics (meltdown characteristics), and the like, as they relate to battery characteristics, battery productivity and battery safety. In addition, in order to improve the cycle characteristics of the battery, it is required to improve the adhesion with the electrode material, and to improve the permeability of the electrolyte to improve the productivity.

Therefore, up to now, it has been studied to laminate various modified porous layers on a microporous membrane. As the modified porous layer, a polyamideimide resin having heat resistance and electrolyte permeability, a polyimide resin, a polyamide resin and / or a fluororesin having excellent electrode adhesion are preferably used. In addition, a water-soluble or water-dispersible binder capable of laminating the modified porous layer using a relatively simple and easy washing process and drying process is widely used. The modified porous layer in the present invention refers to a layer containing a resin that imparts or enhances at least one or more of functions such as heat resistance, adhesion to an electrode material, electrolyte permeability, and the like.

Further, in order to improve the battery capacity, it is necessary to increase the area of the battery separator that can be filled in the container, and it is predicted that the separator will be thinned. However, since the microporous film is liable to be deformed in the planar direction as the thinning progresses, the battery separator in which the modified porous layer is laminated on the microporous membrane can be peeled off during the slitting process or the battery assembling process during processing , It becomes more difficult to secure safety.

Further, in order to cope with the reduction in cost, it is expected that the speeding up of the above process will progress. Even in such a high-speed processing, high adhesion between the microporous film and the modified porous layer, which have little trouble such as peeling of the modified porous layer, is required. However, in order to improve the adhesion, if the resin contained in the modified porous layer is sufficiently penetrated into the polyolefin microporous film, there is a problem that the rising width of the durability increases.

From the viewpoint of shutdown characteristics, a method of adding a low melting point component to the polyolefin microporous membrane is disclosed. On the other hand, on the other hand, when a resin having a low melting point is added, vacancies are apt to be clogged during production of a microporous membrane or during manufacturing of a battery. Therefore, when the modified porous layer is formed, There was a problem.

In Patent Document 1, polyvinylidene fluoride is applied to a 9 μm-thick polyethylene microporous film, and a part of the polyvinylidene fluoride is appropriately penetrated into the pores of the porous polyethylene membrane to exhibit an anchor effect, Discloses a composite microporous membrane having a peel strength (T-type peel strength) of 1.0 to 5.3 N / 25 mm at a coating layer interface of a polyurethane film and polyvinylidene fluoride.

In Patent Document 2, a heat-resistant porous layer containing a self-crosslinkable acrylic resin and a plate-shaped boehmite is provided on a corona-discharge-treated polyethylene microporous film having a thickness of 16 탆, and a heat- (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, and a polyethylene resin solution comprising 50 parts by mass of a composition comprising an antioxidant and 50 parts by mass of liquid paraffin, Extruded at 200 캜 and taken out with a cooling roll controlled at 25 캜 to obtain a gel-like molded product, followed by biaxial stretching so as to be 7 x 6.4 times to obtain a polyethylene resin porous film. And a laminated micro porous film obtained by laminating a coating layer composed of polyvinyl alcohol and alumina particles on the surface of the polyethylene porous microporous film.

In Example 6 of Patent Document 4, a polyethylene resin solution having a weight average molecular weight of 4,150,000 and a weight average molecular weight of 560,000 and a weight ratio of 1: 9 of 30% by mass and a mixed solvent of liquid paraffin and decalin in a mass ratio of 70% Extruded and cooled in a water bath to obtain a gel-like molded product, followed by biaxial stretching so as to be 5.5 × 11.0 times, thereby obtaining a polyethylene microporous film. Discloses a nonaqueous secondary battery separator obtained by laminating a coating layer composed of meta-type wholly aromatic polyamide and alumina particles on the surface of the polyethylene microporous membrane.

In Example 1 of Patent Document 5, 47 parts by mass of polyethylene, which is a homopolymer having a viscosity average molecular weight of 700,000, 46 parts by mass of polyethylene, which is a homopolymer having a viscosity average molecular weight of 250,000, and 7 parts by mass of polypropylene which is a homopolymer having a viscosity average molecular weight of 400,000, To perform dry blending. 1 mass% of pentaerythritol tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99 mass% of the obtained pure polymer mixture, The polyethylene composition obtained by dry blending using a tumbler blender was melted and kneaded, extruded and cast on a cooling roll controlled at a surface temperature of 25 占 폚 to obtain a sheet-like polyethylene composition having a thickness of 2000 占 퐉, followed by biaxial stretching And then coating (coating) an aqueous dispersion of calcined kaolin and latex on the resulting polyethylene microporous membrane.

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

Patent Document 7 discloses a technique for producing a microporous membrane by stretching a laminate having a layer containing a low melting point resin and a layer not containing a low melting point resin.

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

However, with respect to the demand for the thinning of the separator due to the high-speed processing and the high capacity due to the low cost which will proceed rapidly in the future, these prior art technologies have the problem that the modified porous layer is peeled off locally during slit processing or battery assembly processing, It is expected to be difficult. Particularly, when the polyolefin microporous membrane to be the base material is thinned, it becomes difficult to obtain sufficient anchor effect with respect to the polyolefin microporous membrane of the modified porous layer, so that it becomes more difficult to secure safety.

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

It is an object of the present invention to provide a polyolefin microporous film which is high in peel strength between a modified porous layer and a laminated polyolefin microporous film and which is suitable for high speed processing in a slit process or a battery assembling process on the assumption that the separator for a battery is made thinner, And a modified porous layer laminated on the membrane.

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

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

The T-type peel strength or the peel strength at 180 °, which is conventionally used as a peeling strength measurement method, is a peeling force when peeling the coating layer obliquely backward from the surface of the separator for a battery. According to this evaluation method, the frictional resistance in the slit process or the cell assembly process can be evaluated based on more actuality than the conventional evaluation method.

In order to solve the above problems, a separator for a battery of the present invention has the following constitution.

That is, a separator for a battery having a laminated polyolefin microporous film and a modified porous layer present on at least one surface of the laminated polyolefin microporous film is characterized in that the laminated polyolefin microporous film is a porous laminate comprising at least an A layer and a B layer, Of not less than 165 ° C, a durability of not more than 300 sec / 100 ccAir, and protrusions made of polyolefins of 3 / cm ² to 200 / cm ² or less are irregularly present on the surface facing at least one outer surface, Wherein the protrusions satisfy 0.5 占 퐉? H (H is the height of the protrusions) and 5 占 퐉? W? 50 占 퐉 (W is the size of the protrusions), and the modified porous layer is laminated on the surface having the protrusions of the laminated polyolefin microporous membrane And a separator for a battery comprising a binder and an inorganic particle having a tensile strength of 5 N / mm ² or more.

Here, the surface facing the outside world is a surface on which at least one of the surfaces of the layers constituting the laminated polyolefin microporous film faces the side (interface side) in contact with the surface of the other layer while the other side .

In the battery separator of the present invention, it is preferable that the laminated polyolefin microporous film has a three-layer structure of layer A / layer B / layer A or layer B / layer A / layer B, and polypropylene having a heat of fusion of 90 J / And the like.

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

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

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

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

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

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

(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 poured into a cooling roll Cooling, and forming 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 stretch molded product

(e) a step of extracting the above-mentioned molding solvent from the laminated stretch molding by the solvent for the lamination molding and drying to obtain a laminated porous molded article

(f) heat-treating the laminated porous molded article to obtain a laminated polyolefin microporous membrane

(g) A coating liquid containing a binder capable of dissolving or dispersing a binder, inorganic particles and a binder having a tensile strength of 5 N / mm ² or more on the surface of the laminated polyolefin microporous film to which the cooling roll is in contact is used to form a laminated film Forming, and drying.

The battery separator according to the present invention is preferably a means for scraping off the molding solvent removing means in the step (c) using a doctor blade.

According to the present invention, it is possible to obtain a separator for a battery in which a modified porous layer is laminated on a laminated polyolefin microporous film having excellent adhesion with the modified porous layer, and the modified porous layer is not peeled off even during high-

Fig. 1 is a schematic view showing a measuring method of 0 占 peeling strength.
2 is a schematic view showing the crystal structure and crystal structure of the polyolefin in the laminated polyolefin microporous film.
3 is a photomicrograph of a ring-shaped mark originating from the reclamation of a polyolefin in the laminated polyolefin microporous film.
4 is a schematic view showing a step of extruding a polyolefin resin solution from a die provided at an end of an extruder and cooling the same with a cooling roll to form a laminated gel-like molded product.

The laminated polyolefin microporous film used in the present invention has projections of appropriate shape and number on its surface by adjusting a specific polyolefin resin solution and highly controlling the cooling rate of the extruded polyolefin resin solution from the extruder through a die. The present invention relates to a laminated polyolefin microporous membrane, which has excellent peel strength between a laminated polyolefin microporous membrane and a modified porous layer when the modified porous layer containing inorganic particles and a binder having a tensile strength of 5 N / mm ² or more is laminated on the laminated polyolefin microporous membrane Can be obtained.

The projections mentioned in the present invention are essentially different from the projections obtained by adding, for example, inorganic particles or the like to the laminated polyolefin microporous membrane. The projections obtained by adding the inorganic particles to the laminated polyolefin microporous membrane are usually very small and if the projections having a height of 0.5 탆 or more are formed by the same means, the number of particles having a particle diameter equal to or larger than the thickness of the laminated polyolefin microporous membrane Addition is required. However, when such particles are added, the strength of the laminated polyolefin microporous film is lowered, which is not realistic.

The projections mentioned in the present invention are obtained by growing a part of the surface layer of the laminated polyolefin microporous film with a ridge of an appropriate shape, and do not degrade the basic characteristics of the laminated polyolefin microporous film.

The irregularly scattered protrusions referred to in the present invention means that the laminated polyolefin microporous film has a regularity or periodicity (regularity) obtained by passing through an embossing process roll before or after the stretching process It is clearly different from the protuberance. Pressing such as embossing or the like basically forms protrusions by compressing, which is not preferable because it tends to cause lowering of durability and permeability of the electrolyte solution.

In the present invention, the protrusion having a suitable shape means a protrusion having a size of 5 占 퐉 or more and 50 占 퐉 or less and a height of 0.5 占 퐉 or more. That is, 5 占 퐉? W? 50 占 퐉 (W is the size of the projection) and 0.5 占 퐉? H (H is the height of the projection). These protrusions function as an anchor when the modified porous layer is laminated on the laminated polyolefin microporous membrane, and as a result, the separator for a battery having the above-mentioned 0 DEG peel strength is obtained. On the other hand, the upper limit of the height is not particularly limited, but it is sufficient that the upper limit of the height is about 3.0 탆. The greater the number of protrusions of sufficient height, the greater the 0 DEG peel strength tends to be. That is, the 0 占 peel strength is affected by the number of protrusions having a height of 0.5 占 퐉 or more and the average height thereof. The lower limit value of the number of projections is preferably 3 / cm ² , more preferably 5 / cm ² , even more preferably 10 / cm ² . The upper limit value of the number of projections is preferably 200 pieces / cm ² , more preferably 150 pieces / cm ² . The lower limit of the height of the projection is preferably 0.5 占 퐉, more preferably 0.8 占 퐉, and even more preferably 1.0 占 퐉. The size and height of the projections in the present invention refer to values measured by a measuring method described later.

The rising width of the durability in the present invention means the difference between the durability of the laminated polyolefin microporous membrane and the durability of the battery separator, and is preferably 90 sec / 100 ccAir or less, more preferably 80 ccAir or more Preferably 50 ccAir.

The laminated polyolefin microporous membrane, the modified porous layer, and the separator for a battery of the present invention will be outlined. Of course, the present invention is not limited to these representative examples.

First, the laminated polyolefin microporous film used in the present invention will be described.

The upper limit value of the thickness of the laminated polyolefin microporous film used in the present invention is preferably 25 占 퐉, more preferably 20 占 퐉, and even more preferably 16 占 퐉. The lower limit value is preferably 7 占 퐉, more preferably 9 占 퐉. When the thickness of the laminated polyolefin microporous film is within the above-mentioned preferable range, it is possible to have a practical film strength and a hole clogging function, so that the area per unit area of the battery case is not restricted and is suitable for high capacity of a battery to be advanced in the future.

The melt-down temperature of the polyolefin laminated microporous membrane of the present invention is 165 DEG C or higher, more preferably 170 DEG C or higher. If the meltdown temperature is within the above range, the stability of the battery is improved because the stability of the dimension is high even at a high temperature.

The upper limit of the durability of the laminated 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 More preferably 70 sec / 100 ccAir, even more preferably 100 sec / 100 ccAir.

The upper limit of porosity of the laminated polyolefin microporous membrane is preferably 70%, more preferably 60%, even more preferably 55%. The lower limit value is preferably 30%, more preferably 35%, still more preferably 40%. When the durability and the porosity are within the above preferable range, they are suitable for charging / discharging characteristics of the battery, especially ion permeability (charging / discharging working voltage) and battery life (closely related to the amount of the electrolytic solution) . In addition, since the sufficient mechanical strength and insulating property are obtained, the possibility of occurrence of a short circuit during charging and discharging is reduced.

The average pore diameter of the laminated polyolefin microporous membrane greatly affects the hole closure performance, and is therefore preferably 0.01 to 1.0 mu m, more preferably 0.05 to 0.5 mu m, even more preferably 0.1 to 0.3 mu m. When the average pore diameter of the laminated polyolefin microporous membrane is in the above preferable range, the peeling strength at 0 占 of the fully modified porous layer is obtained by the anchoring effect of the functional resin, and when the modified porous layer is laminated, 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 the higher temperature side.

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

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

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

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, ultrahigh molecular weight polyethylene, and the like. From the viewpoint of strength, it is preferable to contain high-density polyethylene and ultrahigh-molecular-weight polyethylene.

The ultrahigh molecular weight polyethylene may be a homopolymer of ethylene as well as a copolymer containing small amounts of other? -Olefins. Examples of the? -olefin include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate and styrene. When the laminated film is produced by the co-extrusion method, it is difficult to control the physical property irregularity in the width direction due to the viscosity difference of each layer. However, by using the ultra high molecular weight polyethylene in the A layer, So that uneven deformation hardly occurs, and a microporous film excellent in uniformity of physical properties can be obtained.

The weight average molecular weight (hereinafter referred to as Mw) of the high-density polyethylene is preferably at least 1 x 10 ⁵ , and more preferably at least 2 x 10 ⁵ . The upper limit value is preferably 8 × 10 ⁵ , and more preferably 7 × 10 ⁵ . When the Mw is in the above range, both the stability of the film-forming and the finally obtained yield strength can be satisfied.

The Mw of the ultrahigh molecular weight polyethylene is preferably 1 x 10 ⁶ or more and less than 4 x 10 ⁶ . By using the ultrahigh molecular weight polyethylene having an Mw of 1 x 10 < ⁶ > to less than 4 x 10 < ⁶ >, holes and fibrils can be made fine and the piercing strength can be increased. If the Mw is 4 x 10 < ⁶ > or more, the viscosity of the melt becomes excessively high, so that the resin can not be extruded from the die (die).

The content of the ultrahigh molecular weight polyethylene is 100% by mass of the entire polyolefin resin, and the lower limit value thereof is preferably 2% by mass, more preferably 18% by mass. The upper limit value is preferably 45 mass%, more preferably 40 mass%. In this range, it is easy to obtain both of the projecting strength and the specular resistance. If the content of the ultrahigh molecular weight polyethylene is within the above preferable range, a projection having a sufficient height can be obtained. When the modified porous layer is laminated by these protrusions, the protrusions function as an anchors, and very strong peeling resistance can be obtained against a force applied parallel to the plane direction of the polyethylene porous film. Further, even when the thickness of the polyethylene porous film is reduced, a sufficient tensile strength can be obtained. The upper limit value of the tensile strength is not specifically defined, but is preferably 100 MPa or more.

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

The B layer of the present invention is a microporous film containing polyolefin as a main component. The B layer preferably contains 50 mass% or more of high-density polyethylene from the viewpoint of strength. The weight average molecular weight (hereinafter referred to as Mw) of the high-density polyethylene is preferably at least 1 x 10 ⁵ , and more preferably at least 2 x 10 ⁵ . The upper limit value of Mw is preferably 8 × 10 ⁵ , and more preferably 7 × 10 ⁵ . When the Mw is in the above range, both the stability of the film-forming and the finally obtained yield strength can be satisfied.

In the present invention, it is important that the B layer contains polypropylene. When the 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. In addition to the homopolymer, block copolymers and random copolymers can be used as the polypropylene. The block copolymer and random copolymer may contain a copolymer component with an? -Olefin other than propylene, and the other? -Olefin is preferably ethylene.

The Mw of polypropylene is preferably at least 5 x 10 ⁵ , more preferably at least 6.5 x 10 ⁵ , even more preferably at least 8 x 10 ⁵ . When the Mw is within the above range, the dispersibility of polypropylene does not deteriorate at the time of sheet formation, and a film having a uniform film thickness can be obtained. The heat of fusion (DELTA Hm) of the polypropylene is preferably 90 J / g or more, and more preferably 95 J / g. When? Hm is within the above preferable range, good meltdown characteristics can be obtained.

The content of polypropylene is preferably less than 60% by mass based on the total mass of the polyolefin composition. If it is 60% by mass or more, the permeability may be deteriorated. Particularly, when the surface layer is a B layer, the amount of powder generated by dropping polypropylene can be increased when the laminated microporous membrane is slit. If the amount of powder generated due to dropping of polypropylene is large, there is a fear that defects such as pinholes or black spots may occur in the laminated microporous membrane. The lower limit value of the addition amount is preferably not less than 3% by mass, more preferably not less than 10% by mass, and further preferably not less than 20% by mass. When the content of the polypropylene is within the above preferable range, good meltdown characteristics can be obtained.

In addition, from the viewpoint of strength and formation of protrusions, it is also preferable that the B layer also contains ultra-high molecular weight polyolefin. As the ultrahigh molecular weight polyolefin, ultrahigh molecular weight polyethylene or ultra high molecular weight polypropylene as exemplified in the A layer can be used.

The polyolefin microporous membrane of the present invention may contain various additives such as an antioxidant, a heat stabilizer, an antistatic agent, an ultraviolet absorber, an antiblocking agent and a filler in the range of not deteriorating the effect of the present invention in both the A layer and the B layer have. In particular, it is preferable to add an antioxidant for the purpose of suppressing oxidation deterioration due to thermal history of the polyolefin resin. It is important to appropriately select the kind and amount of the antioxidant or heat stabilizer to adjust or enhance the properties of the microporous membrane.

The laminated polyolefin microporous membrane used in the present invention preferably contains substantially no inorganic particles. The phrase " substantially not containing inorganic particles " means, for example, when the inorganic element is quantified by fluorescent X-ray analysis, it is preferably not more than 50 ppm, more preferably not more than 10 ppm, By weight. Contamination components derived from foreign foreign matters and contaminants adhering to the lines or devices in the production process of the raw resin or polyolefin microporous membrane are peeled off without positively adding the particles to the laminated polyolefin microporous film It may be incorporated into the film and may be detected as 50 ppm or less.

The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyolefin resin composition of the layer B is preferably in the range of 5 to 200, more preferably 10 to 100. When the range of Mw / Mn is within the above preferable range, the solution of the polyolefin can be easily extruded. Further, the polyolefin microporous membrane has a sufficient number of projections on the surface thereof, and even when the thickness of the polyolefin microporous membrane is reduced, a sufficient mechanical strength can be obtained. Mw / Mn is used as a measure of the molecular weight distribution. For example, in the case of a single polyolefin, the larger the value is, the larger the molecular weight distribution is. The Mw / Mn of the polyolefin composed of a single material can be suitably adjusted by multi-stage polymerization of polyolefin. The Mw / Mn of the mixture of polyolefins can be appropriately adjusted by adjusting the molecular weight and mixing ratio of each component.

The inventors of the present invention have considered the mechanism by which the projections are formed in the present invention as follows. The resin solution of the molten polyolefin resin and the molding solvent is extruded from the die and at the same time, the crystallization of the polyolefin is started (started), and the crystallization speed is increased by contacting with the cooling roll and quenching. At this time, spherical crystals of 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, and as a result, the crystal having a relatively small crystal nucleus is obtained. When the heat transfer rate is high, the crystal structure is relatively large. These crystal nuclei are protrusions in TD (width direction) and / or MD (machine direction) stretching which is a post-process (post-process). In addition, the moon appears as a ring-shaped mark 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 satisfies the above-mentioned various characteristics, the production method according to the purpose can be freely selected. As a method for producing a microporous film, there are a foaming method, a phase separation method, a dissolution recrystallization method, a stretching method (opening method) and a powder sintering method. Among these methods, a phase separation method is preferable from the viewpoint of uniformization of micropores and cost.

Examples of the production method by the phase separation method include a method in which a polyolefin resin and a molding solvent are heated and melt kneaded, the obtained molten mixture is extruded from a die and cooled to form a gel-like molded product, And a method of obtaining a microporous film by removing the molding solvent.

A method for producing the laminated polyolefin microporous membrane used in the present invention will be described.

The method for producing the laminated polyolefin microporous membrane of the present invention includes the following steps (a) to (f).

(a) a step of adding a molding solvent to the polyolefin resin composition constituting the A layer, followed by melting and kneading to prepare a polyolefin resin solution A

(b) a step of adding a molding solvent to a polyolefin resin composition comprising a polyethylene resin and a polypropylene resin constituting the B layer, followed by melting and kneading to prepare a polyolefin resin solution B

(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 on which a molding solvent is removed by a molding solvent removing means , A step of forming 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 stretch formed product

(e) a step of extracting and removing the molding solvent from the laminated stretch molding and drying to obtain a laminated porous molded article

(f) heat-treating the laminated porous molded article to obtain a laminated polyolefin microporous film.

Further, other steps such as a hydrophilization treatment and a static elimination treatment may be added before the step (a), during the steps (a) to (f), or after the step (f). After the step (f), a re-stretching step may be provided.

Hereinafter, each step will be described in detail.

(a), (b) a step of adding a molding solvent to the polyolefin resin constituting the layers A and B and then 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. Examples thereof include aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, and liquid paraffin, or mineral oil fractions corresponding to the boiling points thereof. However, the solvent content A nonvolatile solvent such as liquid paraffin is preferred for obtaining this stable gel-shaped product. The heating and dissolution is carried out by a method in which the polyolefin composition is completely dissolved and stirred or mixed uniformly in an extruder and dissolved. The temperature varies depending on the polymer and the solvent used in the case of dissolving in an extruder or in a solvent while stirring, but is preferably in the range of 140 to 250 캜, for example.

The concentration of the polyolefin resin is preferably 15 to 40% by mass, more preferably 25 to 40% by mass, still more preferably 28 to 35% by mass, based on 100% by mass of the total of the polyolefin resin and the molding solvent . When the concentration of the polyolefin resin is within the above-described preferable range, the number of crystal nuclei for forming the projections is sufficiently formed, and a sufficient number of projections are formed. Further, swell and neck in are suppressed at the die outlet when the polyolefin resin solution is extruded, and moldability and self-supportability of the extrusion molded article are maintained.

When the resin concentrations of the resin solutions A and B are different, a laminated microporous film having a structure in which the average pore diameter is changed in the film thickness direction (tapered structure) can be obtained. The average pore diameter of the layer formed using the lower concentration resin solution becomes larger than the average pore diameter of the layer formed using the higher concentration resin solution. The concentration of the resin solution A or B can be appropriately selected depending on 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 mu m and the surface layer is a coarse structure layer having a thickness of 1.2 to 5.0 times the dense structure layer, balance between ion permeability and piercing strength can be improved.

The method of melt kneading is not particularly limited, but is usually carried out by kneading uniformly in an extruder. This method is suitable for preparing highly concentrated solutions of polyolefins. The melt kneading temperature differs depending on the polyolefin resin used. For example, since the polyolefin composition has a melting point of about 130 to 140 캜, the lower limit of the melt-kneading temperature is preferably 140 캜, more preferably 160 캜, and most preferably 170 캜. The upper limit value is preferably 250 占 폚, more preferably 230 占 폚, and most preferably 200 占 폚. In the layer B, the polyolefin solution contains polypropylene. In this case, the melt-kneading temperature is preferably 190 to 270 캜.

From the viewpoint of suppressing deterioration of the resin, it is preferable that the melting and kneading temperature be lower. However, if the temperature is lower than the above-mentioned temperature, unmelted matter is generated in the extrudate extruded from the die, There is a case. If the temperature is higher than the above-mentioned temperature, the thermal decomposition of the polyolefin becomes severe, and the physical properties of the resultant microporous film, for example, the protruding strength and the tensile strength may be lowered.

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

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

(c) The polyolefin resin solutions A and B obtained in (a) and (b) were extruded from a die, and at least one of them was cooled with a cooling roll having a surface on which a molding solvent was removed by a molding solvent removing means , A step of forming a laminated gel-like molded product

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 shaped article. As a method for obtaining a laminated gel-like molded product, there are a method (lamination method) in which a gel-like molded material to be laminated is prepared separately and then passed through a calender roll or the like, or a method in which a polyolefin solution is separately supplied to an extruder, (Coextrusion method) in which they are melted in a polymer tube or die, co-extruded and co-extruded and laminated, and thereafter molded into a laminated gel-like molded product, or the like may be used. From the viewpoint of interlayer adhesion, .

The polyolefin resin solution extruded from the die is contacted with a rotating cooling roll set at a surface temperature of 20 占 폚 to 40 占 폚 with a refrigerant to form a gel-like molded product. The extruded polyolefin resin solution is preferably cooled to 25 캜 or lower. Here, the cooling rate in the temperature region in which the crystallization is substantially performed becomes important. For example, the extruded polyolefin resin solution is cooled to obtain a gel-like molded product at a cooling rate of 10 ° C / sec or more in a temperature region where the crystallization is substantially carried out. The cooling rate is preferably 20 ° C / second or more, more preferably 30 ° C / second or more, and even more preferably 50 ° C / second or more. By performing such cooling, the polyolefin phase is immobilized with a microphase-separated structure by a solvent, and a glass having a relatively large nucleus is formed on the surface of the gel-like molded product in contact with the cooling roll, so that a protrusion of a proper shape is formed after stretching can do. The cooling rate can be estimated by simulating the extrusion temperature of the gel-like molded article, the thermal conductivity of the gel-like molded article, the thickness of the gel-like molded article, the molding solvent, the cooling roll, and the heat transfer coefficient of air.

In the present invention, it is important to remove as much as possible the molding solvent adhering to the surface of the cooling roll at a portion in contact with the polyolefin resin solution extruded from the die. As shown in Fig. 4, the polyolefin resin solution is cooled by being wound around a rotating cooling roll to form a gel-like molded product. However, since the molding solvent is adhered to the surface of the cooling roll after the gel-like molded product is separated, And comes into contact with the resin solution. However, if a large amount of molding solvent is adhered to the surface of the cooling roll, the cooling rate becomes gentler due to the adiabatic effect, and protrusions are hardly formed. Therefore, it becomes important to remove the molding solvent as much as possible until the cooling roll again contacts the polyolefin resin solution.

The method for removing the molding solvent, that is, the method for removing the molding solvent from the cooling roll, is not particularly limited, but the doctor blade is placed on the cooling roll so as to be parallel to the width direction of the gel-like molded product. Immediately after passing through the doctor blade, A method of scraping the surface of the cooling roll to the extent that the molding solvent can not be visually observed until it comes into contact is preferably employed. Or may be removed by means such as blowing, sucking, or combining these methods with compressed air. Among them, the method of scraping with a doctor blade is preferable because it is relatively easy to carry out, and it is more preferable to use a plurality of doctor blades than one in view of improving the removal efficiency of a 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 resin or rubber rather than metal. In the case of metal, the cooling roll may be damaged. Examples of the resin-made doctor blade include polyester, polyacetal, and polyolefin.

Even if the temperature of the cooling roll is set to less than 20 캜, not only a sufficient cooling rate can not be obtained due to the heat insulating effect of the molding solvent but also surface roughness is caused in the gel-like molded product by condensation to the cooling roll .

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

Here, when a laminated gel-like molded product is obtained by an attaching method, at least one of the polyolefin resin solutions which become the A layer or the B layer may be formed as a gel-like molded product under the above cooling conditions. When the layers are bonded together, it is necessary to laminate the layer formed by the cooling conditions so that the surface of the layer contacted with the cooling roll becomes the surface. When a laminated gel-like molded product is obtained by a co-extrusion method, a polyolefin resin solution which is laminated and extruded from a die may be formed as a laminated gel-like molded product under the above cooling conditions.

The laminated polyolefin is a porous laminate comprising at least an A layer and a B layer. The layer structure of the laminated polyolefin may be at least two layers of an A layer and a B layer in terms of shutdown characteristics and balance of physical properties such as strength and permeability, but from the viewpoint of balance of front and back of the final film, layer A / layer B / A Layer or a three-layer structure of layer B / layer A / layer B is more preferable. From the viewpoint of adhesion with the modified porous layer, the projections may be formed on either the A layer or the B layer. However, from the viewpoint of balance between permeability and strength, it is preferable that the surface layer is 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 is B and the inner layer is A.

The thickness of the B layer of the laminated polyolefin microporous film is preferably 3 mu m or more and 15 mu m or less. The upper limit value is more preferably 10 mu m, still more preferably 7 mu m, even more preferably 6 mu m. The lower limit value is preferably 4 占 퐉. The thickness of the B layer refers to the total thickness of the respective B layers when the laminated polyolefin microporous membrane has two or more B layers.

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

The laminated gel-like molded product is stretched to obtain a drawn product. The stretching is carried out at a predetermined magnification in two directions, MD and TD, by heating the gel-like molded product and by a conventional tentering method, a roll method, or a combination of these methods. The stretching may be either of simultaneous stretching (simultaneous biaxial stretching) of MD and TD (machine direction and width direction) or continuous stretching. In the sequential stretching, at least one of MD and TD can be stretched in multiple stages regardless of the order of MD and TD. The stretching magnification varies depending on the thickness of the raw material (raw material), but is preferably 9 times or more, and more preferably 16 to 400 times, as the sheet magnification. In the case of simultaneous stretching of MD and TD, stretching at the same MD and TD magnification such as 3x3, 5x5, or 7x7 is preferable. When the surface magnification is within the above-mentioned preferable range, stretching is sufficient and a high-elasticity, high-strength microporous film can be obtained. In addition, the desired durability can be obtained by adjusting the drawing temperature.

The stretching temperature is preferably not higher than the melting point of the polyolefin resin, more preferably in the range of (the crystal dispersion temperature (Tcd) of the polyolefin resin) to (the melting point of the polyolefin resin). When the stretching temperature is not higher than the melting point of the gel-like sheet, melting of the polyolefin resin is prevented, and the molecular chains can be efficiently oriented by stretching. When the stretching temperature is not lower than the crystalline dispersion temperature of the polyolefin resin, softening of the polyolefin resin is sufficient and the stretching tension is low, so that the film forming property becomes good and stretching at a high magnification is possible. The crystal dispersion temperature (Tcd) is determined from the temperature characteristic of dynamic viscoelasticity measured according to ASTM D 4065. Or NMR.

(e) a step of extracting and removing the molding solvent from the laminated stretch molding and drying to obtain a laminated porous molded article

The stretched molded article is treated with a cleaning solvent to remove the remaining molding solvent to obtain a microporous film. 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. Can be used. These cleaning solvents are appropriately selected according to the molding solvent used for dissolving the polyolefin, and used singly or in combination. The cleaning method can be carried out by a method of immersing in a cleaning solvent for extraction, a method for washing the cleaning solvent, a method for sucking the cleaning solvent from the opposite side of the drawn molding, or a combination thereof. The cleaning as described above is carried out until the residual solvent in the drawn molded article, which is a drawn molded article, is less than 1% by mass. Thereafter, the cleaning solvent is dried, but the drying method of the cleaning solvent can be carried out by heat drying, air drying, or the like.

(f) heat-treating the laminated porous molded article to obtain a laminated polyolefin microporous membrane

The dried laminated porous molded article is subjected to heat treatment to obtain a laminated polyolefin micro porous film. The heat treatment temperature is preferably 90 to 150 캜. When the heat treatment temperature is within the above preferable range, the heat shrinkage rate of the resulting laminated polyolefin microporous film can be reduced and the durability of the durability can be ensured. The heat treatment time is not particularly limited, but is usually from 1 second to 10 minutes, more preferably from 3 seconds to 2 minutes or less. The heat treatment can employ both a tenter method, a roll method, a rolling method, and a free method.

In the heat treatment step, it is preferable to grasp both directions of MD (machine direction) and TD (width direction) and shrink it in at least one of MD and TD. MD, and TD is preferably 0.01 to 50%, more preferably 3 to 20%. When the shrinkage percentage is in the above preferable range, the heat shrinkage rate at 105 DEG C for 8 hours is improved, and the durability of the durability is maintained. Further, in order to improve the piercing strength, it is possible to further perform re-stretching of about 5% to 20% in TD, MD, or both directions before the heat treatment.

If necessary, the microporous membrane can be subjected to a hydrophilic treatment. By carrying out the hydrophilization treatment, for example, when the heat resistant resin layer is coated, the adhesion between the surface of the microporous membrane and the modified porous layer and the uniformity of the coating film (coating film) can be further improved. The hydrophilization treatment can be performed by a monomer graft, a surfactant treatment, a corona discharge, or the like. The monomer graft is preferably carried out after the crosslinking treatment. The corona discharge treatment can be performed in air or a mixed atmosphere of nitrogen or carbon dioxide gas and nitrogen.

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

It is preferable that the modified porous layer is laminated on the side of the laminated polyolefin microporous membrane having the projections. When the modified porous layer is provided on both surfaces of the laminated polyolefin microporous membrane, the modified porous layer on the side where the parallel stress is strongly exerted by the contact of the roll or bar in the slitting step, the conveying step, It is preferable to laminate on the side of the surface having the projections of the microporous film because the effect of the present invention is exerted.

The modified porous layer in the present invention means imparting at least one function of heat resistance, adhesion to an electrode material, electrolyte permeability, and the like. 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, it is possible to obtain a separator for a battery having an excellent peeling strength at 0 ° due to a synergistic effect of the protrusions present on the surface of the laminated polyolefin microporous film and the binder. Further, compared with the case of the laminated polyolefin microporous membrane alone, even when the modified porous layers are laminated, the battery separator does not have a large increase in durability. This is because a sufficient 0 DEG peel strength can be obtained even if a large amount of binder is not penetrated into the pores of the laminated polyolefin microporous film.

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

The binder used in the present invention having a tensile strength of 5 N / mm ² or more is not particularly limited as long as it has a tensile strength of 5 N / mm ² or more, and examples thereof include polyvinyl alcohol, cellulose ether resin and acrylic resin . Examples of the cellulose ether resin include carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), carboxyethylcellulose, methylcellulose, ethylcellulose, cyanoethylcellulose, and oxyethylcellulose. As the acrylic resin, a crosslinkable acrylic resin is preferable. A commercially available aqueous solution or aqueous dispersion may also be used. "POVACOAT" (registered trademark) manufactured by Nissin Kasei Co., Ltd., "JURYMER" (registered trademark) AT-510, ET-410 manufactured by Doagosei Kogyo Co., UW-223SX and UW-550CS manufactured by Daicel Chemical Industries, Ltd., WE-301, EC-906EF and CG-8490 manufactured by DIC Co., Ltd. Among them, A polyvinyl alcohol or an acrylic resin having a high affinity with the nonaqueous electrolyte solution, a suitable heat resistance, and a relatively high tensile strength.

In order to reduce the 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 liquid in this specification includes a binder having a tensile strength of 5 N / mm ² or more, inorganic particles and a solvent capable of dissolving or dispersing the binder, and is used for forming a modified porous layer. The binder has a role of binding at least the inorganic particles together and a role of bonding the laminated polyolefin microporous membrane and the modified porous layer. Examples of the solvent include water, alcohols, acetone, and n-methyl pyrrolidone. By adding the inorganic particles to the coating liquid, it is possible to obtain effects such as prevention of an internal short circuit (dendrite prevention effect) caused by growth of the dendritic crystal of the electrode inside the battery, reduction of the heat shrinkage rate, . The upper limit value of the particle addition amount is preferably 98% by mass, more preferably 95% by mass. The lower limit value is preferably 80% by mass, more preferably 85% by mass. When the added amount of the particles is in the above-mentioned preferable range, the curl reduction effect is sufficient, the ratio of the functional resin to the total volume of the modified porous layer is optimum, and the peel strength of the modified porous layer is sufficient at 0 °.

The average particle diameter of the inorganic particles is preferably 1.5 to 50 times, more preferably 2.0 to 20 times the average pore diameter of the laminated polyolefin microporous film. When the average particle diameter of the particles is in the above-mentioned preferable range, the pores of the laminated polyolefin microporous membrane are prevented from climbing in a state where the heat resistant resin and the particles are mixed, and the particles are removed in the battery assembling process, Thereby preventing occurrence of a serious defect of the battery.

Examples of the inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, And boehmite. Further, if necessary, heat-resistant crosslinked polymer particles can be added. Examples of 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, for example, a sphere shape, a substantially spherical shape, a plate shape, a needle shape, or a polyhedral shape, but is not particularly limited.

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

The thickness of the modified porous layer is preferably 1 to 5 mu m, more preferably 1 to 4 mu m, even more preferably 1 to 3 mu m. When the film thickness of the modified porous layer is in the above preferable range, the separator for a battery obtained by laminating the modified porous layer can secure the strength and insulation of the film when melting and shrinking at a melting point or more, The reaction can be prevented. Further, the winding volume can be suppressed, which is suitable for increasing the capacity of the battery. In addition, curl is suppressed, leading to improvement in productivity in a battery assembly process.

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

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

The specular resistance of the battery separator is one of the most important characteristics, and is preferably 50 to 400 sec / 100 ccAir, more preferably 100 to 350 sec / 100 ccAir, still more preferably 100 to 300 sec / 100 ccAir. In order to achieve the desired durability, the porosity of the modified porous layer is adjusted and the degree of penetration of the binder into the laminated polyolefin microporous membrane is adjusted. When the specular resistance of the battery separator is within the above-mentioned preferable range, sufficient insulating property is obtained and foreign matter clogging, short-circuiting and peeling are prevented. In addition, by suppressing the film resistance, charge / discharge characteristics and life characteristics in an actually usable range can be obtained.

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

(g) A coating liquid containing a binder capable of dissolving or dispersing a binder, inorganic particles and a binder having a tensile strength of 5 N / mm ² or more on the surface of the laminated polyolefin microporous film to which the cooling roll is in contact is used to form a laminated film Forming and drying process

As a method for laminating the modified porous layer on the laminated polyolefin microporous membrane, a known method can be used. Specifically, the coating liquid can be obtained by coating the laminated polyolefin microporous film to a predetermined film thickness by a method described later, and then drying under the conditions of a drying temperature of 40 to 80 캜 and a drying time of 5 to 60 seconds. In addition, a coating liquid, which is soluble in a binder and dissolved in a water-miscible solvent, is laminated on a predetermined laminated polyolefin microporous film by a coating method to be described later, and is placed under a specific humidity environment to mix the binder and water A method in which the solvent is phase-separated and further added to a water bath (coagulation bath) to solidify the binder.

Examples of the method for applying the coating liquid include 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 Meyer bar coating method, A coating method and a die coating method, and these methods can be carried out singly or in combination.

The separator for a battery of the present invention is preferably stored in a dry state. However, when it is difficult to keep the separator in an absolutely dry state, it is preferable to carry out a reduced pressure drying treatment at 100 deg.

The separator for a battery of the present invention can be applied to a secondary battery such as a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a lithium secondary battery and a lithium polymer secondary battery, a plastic film capacitor, a ceramic capacitor, , But it is particularly preferable to use it 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 laminated with a separator interposed therebetween, and the separator contains an electrolytic solution (electrolyte). The structure of the electrode is not particularly limited and may be a known structure. For example, an electrode structure (coin type) in which an anode and a cathode are arranged so as to face each other, an electrode structure (stacked type) in which planar anode and cathode are alternately stacked, (Rolled) in which the positive electrode and the negative electrode of the positive electrode and the negative electrode overlap each other and are wound, for example.

The positive electrode usually has a current collector and a positive electrode active material layer including a positive electrode active material capable of absorbing and desorbing lithium ions formed on the surface of the current collector. Examples of the positive electrode active material include transition metal acid compounds, complex oxides of lithium and transition metals (lithium complex oxides), and inorganic compounds such as transition metal sulfides. Examples of the transition metal include V, Mn, Fe, Co, and Ni. Preferable examples of the lithium composite oxide in the cathode active material include lithium nickel oxide, lithium cobaltate, lithium manganese oxide, and a layered lithium composite oxide having a? -NaFeO ₂ type 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 of the current collector. Examples of the negative electrode active material include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black. The electrolytic solution 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 , a lower aliphatic carboxylic acid lithium salt, and LiAlCl ₄ . These may be used alone or in combination of two or more. Examples of the organic solvent include organic solvents having a high boiling point and a high dielectric constant such as ethylene carbonate, propylene carbonate, ethylmethyl carbonate and? -Butyrolactone; organic solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane, dimethyl carbonate , Diethyl carbonate, and other low-boiling point and low-viscosity organic solvents. These may be used alone or in combination of two or more. Particularly, since the organic solvent having a high dielectric constant has a high viscosity and the organic solvent having a low viscosity has a low dielectric constant, it is preferable to use a mixture of both.

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

Example

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by these Examples. The measured values in the examples are values measured by the following methods.

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

The binders used in Examples and Comparative Examples were sufficiently dissolved or dispersed in a solvent capable of dissolving or dispersing them in water so as to have a thickness of about 100 μm after drying in a dumbbell mold for producing a test piece of No. 2 specified in JIS K 7113, And vacuum drying (vacuum degree of 3 mmHg) at 25 DEG C for 8 hours was performed to sufficiently remove the solvent, and the obtained sample sheet was subjected to tensile strength measurement.

Tensile tester (Autograph AGS-J load cell capacity 1 kN, manufactured by Shimadzu Seisakusho Co., Ltd.) under the following conditions. The sample film and measurement conditions were as follows, and the measurement was carried out three times, and the average value was determined as the tensile strength of the binder.

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 microscope (HD100, manufactured by Laser Tech Co., Ltd.) provided on a base plate.

(order)

(1) On the surface of the laminated polyolefin microporous membrane obtained in Examples and Comparative Examples, which had come into contact with the cooling roll at the time of film formation, a square frame of 1 cm x 1 cm was drawn with a micro oil pen.

(2) The square frame was laid on the sample stage with its green side facing up, and fixed tightly to the sample stage using an electrostatic adhesion device attached to a conical microscope.

(3) A ring-shaped mark originating from the reclamation of the polyolefin as shown in Fig. 3 is displayed on a monitor as a two-dimensional image (REAL screen in this embodiment) using an objective lens with a magnification of 5, The position of the sample stage was adjusted so that the dark part was located almost in the center of the monitor screen. If there are two consecutive marks on the ring, the contact point is matched. The height of the protrusion height was determined to be 0.2 mm or more in the long diameter of the ring-shaped mark originating from the earthquake of the polyolefin. The long diameter of the ring-shaped mark was obtained by fitting the cursor to both ends of the ring in the long-diameter direction in the two-dimensional image and reading the length.

(4) The objective lens was changed to a 20x lens and the focus was set at the center of the monitor screen (the center of the monitor screen was brightest in this apparatus), and this height position was set as the reference height (REFSET Quot;).

(5) The measurement range in the height direction was set to 15 占 퐉 with the reference height being 0 占 퐉. In addition, three-dimensional data were collected with a scan time of 120 seconds and a step movement distance of 0.1 占 퐉 / step.

(6) After the three-dimensional data was collected, a smoothing process was performed by displaying an image for data processing (referred to as a Z image in this apparatus) (smoothing condition: filter size 3x3, matrix type SMOOTH3- Once). In addition, horizontal correction was performed on the horizontal correction screen as needed.

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

(8) Profile of the cross section Two cursors in the vertical direction in the image were fitted to the inflection point of both sleeves of the projection, and the distance between both cursors was determined as the projection size.

(9) Profile of the cross section In the image, the two cursors in the horizontal direction should be aligned with the inflection point of both sleeves of the protrusion (the lower one if the inflection points of both sleeves of the protrusion are different) Height.

(10) The above operation is repeated in the square frame of 1 cm x 1 cm to determine the number of projections per 1 cm ² by counting the number of projections having a size of 5 탆 or more and 50 탆 or less and a height of 0.5 탆 or more and 3.0 탆 or less, Further, the height average value of the protrusions was obtained.

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

Fig. 1 schematically shows an evaluation method. 1 is a laminated sample, a dichroic laminated polyolefin microporous membrane, a modified porous layer, a quadriple double-faced adhesive tape, and 5 and 5 'are aluminum plates. A double-faced pressure-sensitive adhesive tape (NW-K50 manufactured by Nichiban K.K.) (4) of the same size was attached to an aluminum plate (5) having a size of 50 mm x 25 mm and a thickness of 0.5 mm. The surface of the laminated polyolefin microporous film 2 of the sample 1 (battery separator) cut into a width of 50 mm and a length of 100 mm was laminated on the aluminum plate 5 so that 40 mm from the end of one side of the 25 mm- I put it on, and cut out the protruding part. Then, a double-faced adhesive tape was affixed to one surface of an aluminum plate 5 'having a length of 100 mm, a width of 15 mm and a thickness of 0.5 mm, and an aluminum plate 5 having a thickness of 20 mm Respectively. Thereafter, the aluminum plate 5 and the aluminum plate 5 'sandwiching the sample were mounted on a tensile tester (Autograph AGS-J load cell capacity 1 kN, manufactured by Shimadzu Seisakusho Co., Ltd.) Each of the aluminum plates 5 'was pulled in parallel in the opposite direction at a tensile speed of 10 mm / min to measure the strength when the modified porous layer was peeled off. This measurement was carried out at arbitrary three points spaced 30 cm or more in the longitudinal direction, and the average value was defined as the 0 degree peel strength of the modified porous layer.

4. Thickness

Was obtained by averaging the measured values at 20 points using a contact type film thickness gauge (Lightmatic series318 manufactured by Mitsutoyo Corporation). The measurement was carried out under the condition of weighted 0.01 N by using a carbide spherical measurer? 9.5 mm.

5. Average hole diameter

The average pore diameter of the laminated polyolefin microporous membrane was measured by the following method. The sample was fixed on the measurement cell using a double-sided tape, platinum or gold was vacuum deposited for several minutes, and the surface of the film was measured by SEM at an appropriate magnification. 10 arbitrary points were selected on the image obtained by the SEM measurement, and the average value of the hole diameters of the 10 holes was selected as the average hole diameter of the sample.

6. Speculative resistance (sec / 100 ccAir)

The laminated polyolefin microporous membrane or separator for a battery was fixed with a clamping plate and an adapter plate so as to prevent wrinkles by using a Jelly type Densometer B type manufactured by Tester Sangyo Kabushiki Kaisha and measured according to JIS P8117. The sample was 10 cm × 10 cm, and the measurement point was the center of the sample and the total of five points at the four corners, and the average value was used as the durability. If the length of one side of the sample is less than 10 cm, the measured value at five points at intervals of 5 cm can be used.

The increase in the durability was obtained from the following equation.

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

The specular resistance of laminated polyolefin microporous membrane (X) sec / 100 ccAir

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

7. Meltdown temperature

A specimen of 10 mm (TD) x 3 mm (MD) was pulled in the longitudinal direction of the specimen at a constant load of 2 gf using a thermomechanical analyzer (TMA / SS6000 manufactured by Seiko Denshi Kogyo Co., Ltd.) , The temperature was raised at a rate of 5 占 폚 / min at room temperature, and the temperature that was broken by melting was set as the meltdown temperature.

8. Heat of fusion of polypropylene (ΔHm)

About 5 mg of the sample was precisely weighed in an aluminum sample pan, and then the mass of the sample pan into which the sample was placed was precisely weighed to obtain the sample mass as a difference from the mass of the sample pan. The sample pan containing the sample was placed in a sample holder of a differential scanning calorimeter (product of PerkinElmer, Inc., DSC-System 7 type) and heated from 40 占 폚 to 190 占 폚 at 10 占 폚 / min under a nitrogen atmosphere Then, heat treatment was performed at 190 占 폚 for 10 minutes. Subsequently, the mixture was cooled to 40 占 폚 at 10 占 폚 / min, maintained at 40 占 폚 for 2 minutes, and then heated to 190 占 폚 at a rate of 10 占 폚 / min. The DSC curve (melting curve) obtained by the heating step was set to a linear base line in the range of 85 to 175 DEG C and the calorie was calculated from the area of the area surrounded by the straight line and the DSC curve, did.

9. Porosity of laminated polyolefin microporous membrane

A sample of 10 cm x 10 cm was prepared and the sample volume (cm ³ ) and mass (g) were measured. From the obtained results, the porosity (%) was calculated using the following equation.

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

10. Wear resistance

Both ends of the separator for roll-type battery obtained in Examples and Comparative Examples were wound while being slit-processed. The slit processing was carried out using a slitter (WA177A model manufactured by Nisshimura Seisakusho Co., Ltd.) at a speed of 20 m / min and a tension of 60 N / 100 mm. During processing, two hard chrome plating rolls (both free rolls) were used for the rolls that contacted the coated surface. Subsequently, while peeling off the slit-processed separator for a rolled cell, the peeling defect of the modified porous layer having a long diameter of 0.5 mm or more was counted using a naked eye and a graduated magnifying glass (PEAK SCALELUPE x 10) with a magnification of 10 times, . The evaluation area was 100 mm in width × 500 m in length (when the width is less than 100 mm, the length was adjusted to obtain the same evaluation area).

Criteria

○ (very good): 5 or less

△ (Good): 6 to 15

× (bad): 16 or more

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

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

Measuring device: Waters Corporation product GPC-150C

Column: "Shodex" (registered trademark) UT806M manufactured by Showa Denko K.K.

· Column temperature: 135 ° C

Solvent (mobile phase): o-Dichlorobenzene

Solvent flow rate: 1.0 ml / min

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

· Injection amount: 500 μl

Detector: Waters Corporation product Differential Refractometer

Calibration curve: The calibration curve was prepared from a calibration curve obtained using a monodisperse polystyrene standard sample using a predetermined conversion constant.

12. Melting Point

Using a differential scanning calorimeter (DSC) DSC6220 available from S-Ai-Nanotechnology Co., Ltd., the peak temperature of the melting peak observed when 5 mg of the resin sample was heated at a heating rate of 20 ° C / did.

Example 1

30 parts by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and 70 parts by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000, tetrakis [methylene-3- , 5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane was added to the polyethylene composition (A). 30 parts by weight of this polyethylene composition (A) was put into a twin-screw extruder. 70 parts by weight of liquid paraffin was supplied from a side feeder of the twin-screw extruder and melt-kneaded to prepare a polyolefin resin solution A in an extruder.

15% by weight of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and 65% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 300,000, a polypropylene having a weight average molecular weight of 530,000 and a heat of fusion of 96 J / g , And 0.375 parts by weight of tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane as an antioxidant were added to 100 parts by weight of a composition To obtain a composition (B). And 25 parts by weight of the polyolefin composition (B) were fed into a twin-screw extruder. 75 parts by weight of liquid paraffin was fed from the side feeder of the twin-screw extruder and melt-kneaded to prepare a polyolefin resin solution B in an extruder.

The obtained polyolefin resin solutions A and B were co-extruded from a multi-layer die at 190 占 폚 so that the layer composition was A / B / A and the solution ratio was 1/1/1, and the internal cooling water temperature was maintained at 25 占 폚, To obtain a laminated gel-like molded product. At this time, one polyester doctor blade was wound around the cooling roll in parallel with the width direction of the gel-like molded product between the layered polyethylene resin solution extruded from the die at the point where the laminated gel- And the liquid paraffin adhered on the cooling roll was scratched 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 drawn molded article. The resulting extrudate was washed with methylene chloride to remove and remove the remaining liquid paraffin and dried to obtain a porous molded article. Thereafter, the porous film was held in a tenter and heat-treated at 125 캜 for 3 seconds to obtain a polyolefin fine particle having a thickness of 20 탆, a porosity of 43%, an average pore diameter of 0.14 탆, a specular resistance of 232 sec / 100 ccAir, A porous film was obtained.

(Average degree of polymerization: 1700, degree of saponification: 99% or more), alumina particles having an average particle diameter of 0.5 탆 and ion-exchanged water were mixed at a weight ratio of 6:54:40, respectively, and zirconium oxide beads (manufactured by Toray Industries, Was put into a container made of polypropylene and dispersed with a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.) for 6 hours. Then, the filtration limit The mixture was filtered through a filter having a size of 5 mu m to obtain a coating liquid (a).

The coating liquid (a) was coated on the surface of the laminated polyethylene microporous membrane that was in contact with the cooling roll at the time of film formation by gravure coating and passed through a hot air drying furnace at 50 ° C for 10 seconds to obtain a battery separator .

Example 2

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

Example 3

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

Example 4

(Solid content concentration: 45% by mass) consisting of an aqueous acrylic polyol and a water-dispersible polyisocyanate (curing agent), alumina particles having an average particle diameter of 0.5 탆 and ion-exchanged water were mixed at a weight ratio of 10:40:50 The mixture was blended with a zirconium oxide bead ("Toray Serum" (registered trademark) bead, 0.5 mm in diameter, manufactured by Toray Industries, Inc.) into a container made of polypropylene, and a paint shaker (B). The same procedure as in Example 1 was carried out except that the coating liquid (a) was changed to the coating liquid (b), and the modified porous layer Were laminated to obtain a battery separator.

Example 5

Polyvinyl alcohol and a copolymer of acrylic acid and methyl methacrylate ("POVACOATR" (registered trademark) manufactured by Nissin Kasei Kabushiki Kaisha), alumina particles having an average particle diameter of 0.5 μm, a solvent (ion-exchanged water: ethanol = 70:30) Were each compounded in a weight ratio of 5:45:50 and placed in a container made of polypropylene together with zirconium oxide beads ("Toray Serum" (registered trademark) beads, 0.5 mm in diameter, manufactured by Toray Industries, Except that the coating liquid (a) was replaced with the coating liquid (c), and the coating liquid (c) was obtained by filtration through a filter having a filtration limit of 5 탆 The modified porous layer was laminated in the same manner as in Example 1 to obtain a battery separator.

Example 6

A separator for a battery was obtained in the same manner as in Example 2 except that the temperature of the cooling water inside the cooling roll was maintained at 35 캜.

Example 7

5% by weight of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and 55% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 300,000 as a polyolefin resin composition (B) And 40 parts by weight of polypropylene having a weight average molecular weight (Mw / J) of 40 parts by weight and 0.375 part by weight of an antioxidant was used, and 70 parts by weight of liquid paraffin was fed to 30 parts by weight of the polyethylene composition (B) Was obtained in the same manner as in Example 1 to obtain a battery separator.

Example 8

To 100 parts by weight of a composition comprising 20% by weight of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and 80% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 300,000, 0.375 , And 70 parts by weight of liquid paraffin was fed to 30 parts by weight of the polyethylene composition (B) to obtain a polyolefin resin solution B, a battery separator was obtained in the same manner as in Example 1.

Example 9

A separator for a battery was obtained in the same manner as in Example 3 except that the extruded amount of the polyolefin solutions A and B was adjusted so that the thickness of the polyolefin laminated porous film was as shown in the table.

Example 10

Except that the blending ratio of the ultra high molecular weight polyethylene and the high density polyethylene of the polyolefin composition (A) and the blending ratio of the high density polyethylene and the polypropylene without using the ultra high molecular weight polyethylene as the polyolefin composition (B) In the same manner, a battery separator was obtained.

Example 11

The alumina particles were changed to crosslinked polymer particles (polymethylmethacrylate crosslinked particles (" epostar " MA1002, manufactured by Nippon Shokubai Co., Ltd., average particle diameter 2.5 mu m)), (D) was obtained in the same manner as in Example 1, except that the varnish (d) was used instead of the varnish (d) A battery separator was obtained.

Example 12

(5% N-methylpyrrolidone solution) and alumina particles having an average particle diameter of 0.5 占 퐉, a fluorine-based resin solution (KF Polymer 占 9300 (manufactured by Kureha Chemical Industries, Methyl-2-pyrrolidone were blended in a weight ratio of 16:34:50, respectively, and mixed with zirconium oxide beads ("Toray Serum" (registered trademark) beads, 0.5 mm in diameter, manufactured by Toray Industries, And the mixture was dispersed for 6 hours in a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Then, the mixture was filtered with a filter having a filtration limit of 5 탆 to obtain a varnish (e) A separator for a battery was obtained in the same manner as in Example 1 except for the above.

Example 13

Acrylic emulsion ("Polysol" (registered trademark) AT-731, nonvolatile matter 47%, manufactured by Showa Denko K.K.), alumina particles having an average particle diameter of 0.5 μm and ion-exchanged water were 2:55:43 And the mixture was put into a container made of polypropylene together with zirconium oxide beads ("Toray Serum" (registered trademark) beads, 0.5 mm in diameter, manufactured by Toray Industries, Inc.), and the mixture was dispersed in a paint shaker (available from TOYO SEIKI SEISAKUSHO Co., Show product) for 12 hours. Subsequently, the solution was filtered with a filter having a filtration limit of 5 탆 to obtain a coating liquid (f). The coating liquid (f) was applied to the laminated polyethylene microporous film of Example 1 in the same manner as in Example 1 to obtain a battery separator.

Example 14

A separator for a battery was obtained in the same manner as in Example 1 except that the coating liquid (g) in which the alumina particles were changed to barium sulfate fine particles (average particle diameter 0.3 탆) was used.

Comparative Example 1

A separator for a battery was obtained in the same manner as in Example 1 except that the polyethylene solution A was extruded from a single-layer die at 190 占 폚 to form a single-layer gel-like molded product and a single-

Comparative Example 2

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

Comparative Example 3

A separator for a battery was obtained in the same manner as in Example 1 except that the blending ratio, the addition amount, and the resin concentration were changed as shown in the table as the polyolefin resin compositions (A) and (B).

Comparative Example 4

Except that the polyethylene resin solution extruded from the die was cooled with a cooling roll and the liquid paraffin adhered on the cooling roll was not scratched without using a doctor blade to obtain a gel molded product, .

Comparative Example 5

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

Comparative Example 6

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

Comparative Example 7

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

Comparative Example 8

1 mol of trimellitic anhydride (TMA), 0.8 mol of o-tolylidine diisocyanate (TODI), 2 mol of 2,4-tolylene (TMA), and 4 mol of toluene were added to a 4-neck flask equipped with a thermometer, 0.2 mol of diisocyanate (TDI) and 0.01 mol of potassium fluoride were charged together with N-methyl-2-pyrrolidone so that the solid content concentration became 14%, and after stirring at 100 DEG C for 5 hours, the solid content concentration became 14% And diluted with N-methyl-2-pyrrolidone to synthesize a polyamideimide resin solution.

Polyamide-imide resin solution, alumina particles having an average particle diameter of 0.5 mu m and N-methyl-2-pyrrolidone were blended in a weight ratio of 26:34:40, respectively, and zirconium oxide beads (Toray Serum (Registered trademark) beads, 0.5 mm in diameter) were dispersed in a polypropylene container and dispersed for 6 hours using a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Then, filtration with a filter having a filtration limit of 5 탆 The coating liquid (h) was applied to the laminated polyethylene microporous film obtained in the same manner as in Example 1 by the same method as in Example 1 by gravure coating, to obtain a battery separator.

Table 1 shows the production conditions of Examples 1 to 14 and Comparative Examples 1 to 8. Table 2 shows the characteristics of the resulting laminated polyolefin microporous film and battery separator.

[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 Crystalline nuclei of polyethylene
7 die
8 Polyethylene resin solution
9 Cooling roll
10 Doctor Blades
11 Gel form

Claims (7)

A battery separator comprising a laminated polyolefin microporous film and a modified porous layer existing on at least one surface of the laminated polyolefin microporous film, wherein the laminated polyolefin microporous film is a porous laminated body comprising at least an A layer and a B layer and having a meltdown temperature of 165 ° C. or higher, a durability of not higher than 300 sec / 100 ccAir, and at least one outer surface facing the outer surface, irregularities of polyolefins of 3 / cm ² to 200 / cm ² or less are irregularly present, Satisfies 0.5 占 퐉? H (H is the height of the projections) and 5 占 퐉? W? 50 占 퐉 (W is the size of the projections), and the modified porous layer is laminated on the surface having the projections of the laminated polyolefin microporous film , And a binder and an inorganic particle having a tensile strength of 5 N / mm ² or more. The method according to claim 1,
Wherein the laminated polyolefin microporous film comprises a polypropylene having a three-layer structure of layer A / layer B / layer A, or layer B / layer A / B and a layer B having a heat of fusion of 90 J / g or more. Battery separator. 3. The method according to claim 1 or 2,
And the thickness of the B layer is not less than 3 占 퐉 and not more than 15 占 퐉. 4. The method according to any one of claims 1 to 3,
Wherein the binder comprises polyvinyl alcohol or an acrylic resin. 5. The method according to any one of claims 1 to 4,
Wherein the inorganic particles comprise at least one kind selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate and boehmite. A method for producing a separator for a battery according to any one of claims 1 to 5, comprising the following steps (a) to (g)
(a) a step of adding a molding solvent to a polyolefin resin constituting the A layer, followed by melt kneading to prepare a polyolefin resin solution A,
(b) a step of adding a molding solvent to a polyolefin resin comprising a polyethylene resin and a polypropylene resin constituting the B layer, followed by melt kneading to prepare a polyolefin resin solution B,
(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 poured into a cooling roll A step of forming a laminated gel-like molded product by cooling,
(d) a step of stretching the laminated gel-like molded product in the machine direction and the width direction to obtain a laminated stretch molded product,
(e) a step of extracting and removing the molding solvent from the laminated stretch molding material and drying the solvent to obtain a laminated porous molded article,
(f) heat-treating the laminated porous molded article to obtain a laminated polyolefin microporous film,
(g) A coating liquid containing a binder capable of dissolving or dispersing a binder, inorganic particles and a binder having a tensile strength of 5 N / mm ² or more on the surface of the laminated polyolefin microporous film to which the cooling roll is in contact is used to form a laminated film Forming, and drying. The method according to claim 6,
Wherein the means for removing the molding solvent in the step (c) is a means for scraping off with a doctor blade.

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