JP5874781B2 - Resin composition, sheet, and porous film - Google Patents

Description

The present invention relates to a resin composition, a sheet obtained by molding the resin composition, and a porous film obtained by stretching the sheet.

The porous film is used for various applications such as sanitary materials, medical materials, and battery separators. In particular, when a porous film is used as a battery separator such as a lithium ion secondary battery, high piercing strength is required.
A composition comprising a high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, a thermoplastic resin having a weight average molecular weight of 2 × 10 ⁴ or less, and fine particles as a method for producing a porous film having excellent puncture strength Is kneaded and formed into a sheet shape, and then a method for producing a porous film by stretching the sheet is known (see Patent Document 1).
However, in the case where a homogeneous porous film is produced for a long time using the above-described composition, it is necessary to strictly control the kneading conditions, and therefore a composition having better workability has been demanded.

JP 2002-69221 A

An object of the present invention is to provide a resin composition having an excellent balance between processability during film production and the piercing strength of the obtained film, a sheet obtained using the resin composition, a porous film, and a battery using the same It is providing a separator for a battery and a battery.

That is, the present invention relates to [1] to [6].
[1] A resin composition comprising a filler, a high molecular weight polyolefin, and a polyolefin wax having a weight average molecular weight of 700 to 6000, wherein the weight of the ultrahigh molecular weight polyolefin contained in the resin composition is W1, and the weight average molecular weight is 700. The resin composition which satisfy | fills following formula (1) when the polyolefin wax weight of -6000 is set to W2, and the intrinsic viscosity of the said ultra high molecular weight polyolefin is set to [(eta)].
[Η] × 4.3−21 <{W2 / (W1 + W2)} × 100 <[η] × 4.3−8 Formula (1)
[2] Sheet obtained by molding the resin composition of [1] [3] A porous film obtained by stretching the sheet of [2].
[4] A laminated porous film obtained by laminating the porous film of [3] above and a porous heat-resistant layer.
[5] A battery separator comprising the porous film according to [3] or the laminated porous film according to [4].
[6] A battery comprising the battery separator according to [5].

  ADVANTAGE OF THE INVENTION According to this invention, the resin composition which is excellent in the balance of the workability at the time of film manufacture, and the piercing strength of the film obtained, the sheet | seat obtained using this resin composition, a porous film, and a battery using the same Separators and batteries can be provided.

The present invention is a resin composition comprising a filler, a high molecular weight polyolefin, and a polyolefin wax having a weight average molecular weight of 700 to 6000, wherein the weight of the high molecular weight polyolefin contained in the resin composition is W1, and the weight average molecular weight is 700. It is a resin composition satisfying the following formula (1) when the weight of the polyolefin wax of ˜6000 is W2 and the intrinsic viscosity of the high molecular weight polyolefin is [η].
[Η] × 4.3−21 <{W2 / (W1 + W2)} × 100 <[η] × 4.3−8 Formula (1)
The resin composition of the present invention satisfying the above formula (1) is excellent in the balance between processability during film production and the piercing strength of the obtained film.

The high molecular weight polyolefin in the present invention preferably has an intrinsic viscosity [η] of 4 to 30 from the viewpoint of the balance between the piercing strength of the obtained porous film and the workability during film production, and is preferably 5 to 15. More preferably. Examples of the high molecular weight polyolefin include a high molecular weight homopolymer or copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. Among these, high molecular weight polyethylene mainly composed of ethylene-derived structural units is preferable.

The intrinsic viscosity of the high molecular weight polyolefin is an intrinsic viscosity obtained by measuring in accordance with JISK7130 at 135 ° C. with a Ubbelohde viscometer using tetralin as a solvent.

The polyolefin wax in the present invention is a wax having a weight average molecular weight of 700 to 6000. The weight average molecular weight of the polyolefin wax is a weight average molecular weight in terms of polystyrene determined by GPC measurement. For example, GPC measurement is performed at 140 ° C. using o-dichlorobenzene as a solvent.
Polyolefin waxes include polyethylene resins such as ethylene homopolymers and ethylene-α-olefin copolymers, polypropylene resins such as propylene homopolymers and propylene-α-olefin copolymers, and poly (4-methylpentene-1 ), Poly (butene-1), ethylene-vinyl acetate copolymer, and the like.
It is preferable to select a polyolefin wax excellent in compatibility with the high molecular weight polyolefin, for example, it is preferable to use a high molecular weight polyethylene as the high molecular weight polyolefin, and a polyethylene wax, particularly an ethylene-α-olefin copolymer wax, as the polyolefin wax. .

When the high molecular weight polyolefin and the polyolefin wax in the present invention are mixed together with the filler within the range satisfying the above formula (1), it is easy to process into a sheet or film, and the obtained sheet or film has a high piercing strength. . Depending on the intrinsic viscosity of the high molecular weight polyolefin, by adding an appropriate amount of polyolefin wax, the molecular mobility of the composition can be maintained moderately, so that good processability is obtained, and at the same time, the intrinsic viscosity of the high molecular weight polyolefin and It is considered that sufficient puncture strength can be obtained from the ratio. That is, [η] × 4.3-21 ≧ {W2 / (W1 + W2)} × 100
When satisfying, although a high puncture strength is obtained when it is made into a sheet or film, it becomes a resin composition inferior in workability,
{W2 / (W1 + W2)} × 100 ≧ [η] × 4.3-8
When satisfy | filling, although it is excellent in workability, when it is set as a sheet | seat or a film, it will be inferior to puncture strength.

As the filler in the present invention, inorganic or organic fine particles generally called a filler are used. Inorganic fine particles include calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, oxidation Magnesium, titanium oxide, alumina, mica, zeolite, glass powder, zinc oxide and the like are used. Of these, calcium carbonate and barium sulfate with low water content are particularly preferred. As the organic fine particles, known resin particles are used. As the resin, a polymer such as styrene, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, methyl acrylate, or the like obtained by polymerization alone or in combination of two or more types. Polycondensation resins such as coalescence, melamine and urea are preferred.

  The filler may be removed before or after the sheet is stretched. In that case, it is preferable that the filler is water-soluble because it can be easily removed with an aqueous solution such as neutral, acidic or alkaline. Examples of the water-soluble filler include talc, clay, kaolin, diatomaceous earth, calcium carbonate, magnesium carbonate, barium carbonate, magnesium sulfate, calcium oxide, calcium oxide, magnesium hydroxide, calcium hydroxide, and zinc oxide among the aforementioned fine particles. And silica. Among these, calcium carbonate is preferable.

The average particle size of the filler is preferably 0.01 to 3 μm, more preferably 0.02 to 1 μm, and most preferably 0.05 to 0.5 μm. When the average particle size is 3 μm or less, a film having better piercing strength can be obtained. When the average particle size is 0.01 μm or more, it becomes easy to highly disperse in the high molecular weight polyolefin and the polyolefin wax. It becomes easy to perforate.

The filler used in the present invention has been subjected to a surface treatment from the viewpoints of improving dispersibility with high molecular weight polyolefin and polyolefin wax, facilitating interfacial peeling from the resin, and preventing external moisture absorption. Is preferred. Examples of the surface treatment agent include higher fatty acids such as stearic acid and lauric acid, and metal salts thereof.

  The filler content in the resin composition of the present invention is preferably 15 to 150 parts by volume with respect to 100 parts by volume when the total volume of the high molecular weight polyolefin and the polyolefin wax is 100 parts by volume. More preferably, it is 25-100 volume parts. If it is 15 parts by volume or more, it can be sufficiently opened by stretching to obtain a good porous film, and if it is 150 parts by volume or less, a resin ratio is high, so that a porous film having excellent puncture strength is obtained. be able to.

The resin composition of the present invention may be added with additives (antistatic agents, plasticizers, lubricants, antioxidants, nucleating agents, etc.) that are generally used as long as they do not impair the purpose of the present invention. May be.

  The method for producing the polyolefin resin composition of the present invention is not particularly limited, but the raw material high molecular weight polyolefin, polyolefin wax, filler, and additives as necessary are kneaded in a kneading apparatus having high shearing force. Can be obtained. Specifically, a roll, a Banbury mixer, a single screw extruder, a twin screw extruder, etc. are illustrated.

  The method for producing the sheet by molding the resin composition of the present invention is not particularly limited, and examples thereof include inflation processing, calendar processing, T-die extrusion processing, and Skyf method. Since a sheet with higher film thickness accuracy can be obtained, it is preferable to produce the sheet by the following method.

A preferable production method of the sheet is a method of rolling the resin composition using a pair of rotational molding tools adjusted to a surface temperature higher than the melting point of the high molecular weight polyolefin contained in the resin composition. The surface temperature of the rotary forming tool is preferably (melting point + 5) ° C. or higher. The upper limit of the surface temperature is preferably (melting point + 30) ° C. or less, and more preferably (melting point + 20) ° C. or less. Examples of the pair of rotary forming tools include a roll and a belt. The peripheral speeds of the two rotary forming tools do not necessarily have to be exactly the same peripheral speed, and the difference between them may be about ± 5% or less. By producing a porous film using a sheet obtained by such a method, a porous film excellent in strength, ion permeation, air permeability and the like can be obtained. Moreover, you may use what laminated | stacked the sheet | seat of the single layer obtained by the above methods for manufacture of a porous film.

  When the resin composition is roll-formed with a pair of rotational molding tools, the resin composition discharged in a strand form from an extruder may be directly introduced between the pair of rotational molding tools, and the resin composition once pelletized May be used.

  Although the method of extending | stretching the sheet | seat obtained by shape | molding a resin composition and making it a porous film is not specifically limited, It can extend | stretch using well-known apparatuses, such as a tenter, a roll, and an autograph. Further, the stretching may be performed in a uniaxial direction or a biaxial direction, and the stretching may be performed in one step or in multiple steps. In order to cause interface peeling between the resin and the filler, the draw ratio is preferably 2 to 12 times, and more preferably 4 to 10 times. The stretching temperature is usually from a softening point to a melting point of the high molecular weight polyolefin and preferably from 80 ° C to 120 ° C. By stretching at such a temperature, the film hardly breaks during stretching, and the high-molecular-weight polyolefin hardly melts, so that the holes generated by the interface peeling between the resin and the filler are difficult to close. In addition, after stretching, a heat setting treatment may be performed as necessary to stabilize the shape of the holes.

  After removing at least a part of the filler from the sheet obtained by molding the resin composition, it may be stretched by the method described above to produce a porous film. Or after extending | stretching the sheet | seat obtained by shape | molding a resin composition by the above-mentioned method, you may remove a at least one part filler and manufacture a porous film. Examples of the method for removing the filler include a method of immersing the sheet or the stretched film in a liquid capable of dissolving the filler.

  In the present invention, a porous heat-resistant layer can be laminated on at least one surface of the porous film obtained by the method as described above. A laminated porous film having such a heat-resistant layer is excellent in uniformity of film thickness, heat resistance, strength, and ion permeability, and therefore suitable for use as a separator for non-aqueous electrolyte batteries, particularly as a separator for lithium secondary batteries. can do.

  The heat-resistant resin constituting the heat-resistant layer is preferably a polymer containing a nitrogen atom in the main chain, and particularly preferably contains an aromatic ring from the viewpoint of heat resistance. For example, aromatic polyaramid (hereinafter sometimes referred to as “aramid”), aromatic polyimide (hereinafter sometimes referred to as “polyimide”), aromatic polyamideimide, and the like can be given. Examples of aramids include meta-oriented aromatic polyamides and para-oriented aromatic polyamides (hereinafter sometimes referred to as “para-aramids”), and it is easy to form a porous heat-resistant layer having a uniform film thickness and excellent air permeability. To para-aramid.

  Para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4,4′-biphenylene). , 1,5-naphthalene, 2,6-naphthalene, and the like, which are substantially composed of repeating units bonded in the opposite direction (orientation positions extending coaxially or in parallel). Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly ( (Paraphenylene 2,6-naphthalene dicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer, etc. Para-aramid having a similar structure is exemplified.

When providing a heat-resistant layer, a heat-resistant resin is usually dissolved in a solvent and used as a coating solution. When the heat-resistant resin is para-aramid, a polar amide solvent or a polar urea solvent can be used as the solvent. Specifically, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl Examples include, but are not limited to, -2-pyrrolidone and tetramethylurea.
From the viewpoint of coatability, the heat resistant resin is preferably a heat resistant resin having an intrinsic viscosity of 1.0 to 2.8 dl / g, and more preferably a heat resistant resin having an intrinsic viscosity of 1.7 to 2.5 dl / g. . The intrinsic viscosity here is a value measured by dissolving the heat-resistant resin once deposited and making it into a heat-resistant resin sulfuric acid solution. From the viewpoint of coating properties, the heat-resistant resin concentration in the coating solution is preferably 0.5 to 10% by weight.

  When para-aramid is used as the heat-resistant resin, it is preferable to add an alkali metal or alkaline earth metal chloride during the para-aramid polymerization for the purpose of improving the solubility of para-aramid in a solvent. Specific examples include, but are not limited to lithium chloride or calcium chloride. The amount of the chloride added to the polymerization system is preferably 0.5 to 6.0 mol, more preferably 1.0 to 4.0 mol, per 1.0 mol of the amide group produced by condensation polymerization. If the chloride is 0.5 mol or more, the resulting para-aramid is sufficiently soluble, and if it is 6.0 mol or less, the chloride does not remain dissolved in the solvent. In general, the alkali metal or alkaline earth metal chloride is often 2% by weight or more and the solubility of para-aramid is often sufficient. At 10% by weight or less, the alkali metal or alkaline earth metal chloride is polar. In many cases, it is completely dissolved without being dissolved in a polar organic solvent such as an amide solvent or a polar urea solvent.

  The polyimide used in the present invention is preferably a wholly aromatic polyimide produced by condensation polymerization of an aromatic dianhydride and a diamine. Specific examples of the dianhydride include pyromellitic dianhydride, 2,2′-bis (3,4-dicarboxyphenylphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetra. Examples thereof include carboxylic dianhydrides. Specific examples of the diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, 1,5-naphthalene. Although diamine etc. are mentioned, this invention is not limited to these. In the present invention, a polyimide soluble in a solvent can be suitably used. An example of such a polyimide is a polyimide that is a condensation polymer of 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride and an aromatic diamine. As a polar organic solvent for dissolving polyimide, dimethyl sulfoxide, cresol, o-chlorophenol, and the like can be suitably used in addition to those exemplified as a solvent for dissolving aramid.

In the present invention, the coating solution used for forming the heat-resistant layer particularly preferably contains ceramic powder. By forming a heat-resistant layer using a coating solution in which ceramic powder is added to a solution having an arbitrary heat-resistant resin concentration, it is possible to form a heat-resistant layer having a uniform film thickness and a fine porosity. The air permeability can be controlled by the amount of ceramic powder added. In the ceramic powder of the present invention, the average particle diameter of the primary particles is preferably 1.0 μm or less, more preferably 0.5 μm or less, from the viewpoint of the strength of the porous film and the smoothness of the heat-resistant layer surface. More preferably, it is 0.1 μm or less.
The content of the ceramic powder is preferably 1% by weight to 95% by weight or less in the porous film, and more preferably 5% by weight to 50% by weight. When the content is 1% by weight or more, sufficient porosity is obtained, so that the ion permeability is excellent. When the content is 95% by weight or less, sufficient film strength is obtained, so that handling is excellent. The shape of the ceramic powder to be used is not particularly limited, and can be spherical or random.

  Examples of the ceramic powder in the present invention include ceramic powders made of electrically insulating metal oxides, metal nitrides, metal carbides, and the like. For example, powders of alumina, silica, titanium dioxide, zirconium oxide and the like are preferably used. The above ceramic powders may be used alone, or two or more kinds thereof may be mixed, or the same or different ceramic powders having different particle diameters may be arbitrarily mixed and used.

As a method of laminating a heat-resistant layer on a porous film obtained by using a resin composition containing a high-molecular-weight polyolefin, a polyolefin wax and a filler, a method of separately producing a heat-resistant layer and laminating the porous film later, porous Although the method of apply | coating the coating liquid containing ceramic powder and a heat resistant resin to the at least single side | surface of a film and forming a heat resistant layer is mentioned, The latter method is preferable from a viewpoint of productivity. Specifically, the latter method includes a method including the following steps.
(A) In a polar organic solvent solution containing 100 parts by weight of a heat resistant resin, a slurry-like coating liquid in which 1 to 500 parts by weight of ceramic powder is dispersed with respect to 100 parts by weight of the heat resistant resin is prepared. (B) The coating liquid is porous. Coating is performed on at least one surface of the quality film to form a coating film.
(C) The heat resistant resin is deposited from the coating film by means of humidification, solvent removal, or immersion in a solvent that does not dissolve the heat resistant resin, and then dried as necessary.
The coating liquid is preferably applied continuously by a coating apparatus described in JP-A-2001-316006 and a method described in JP-A-2001-23602.

  The porous film of the present invention is excellent in permeability at the use temperature and can be quickly shut down at a low temperature when the use temperature is exceeded, and is suitable as a separator for non-aqueous batteries. Moreover, the laminated porous film obtained by laminating the heat-resistant layer on the porous film of the present invention is excellent in heat resistance, strength and ion permeability, and is preferably used as a separator for non-aqueous batteries, particularly a separator for lithium secondary batteries. Can do.

The battery separator according to the present invention includes the porous film or the laminated porous film. The membrane resistance of the porous film or laminated porous film used for the battery separator is preferably 5 or less from the viewpoint of ion permeability. In addition, since there is little shrinkage | contraction when heat | fever is applied, it is preferable to include the said laminated porous film from a viewpoint of the improvement of safety | security.

When the battery separator of the present invention includes the porous film of the present invention, the porosity of the porous film is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. If the porosity is less than 30% by volume, the amount of electrolyte retained may be reduced, and if it exceeds 80%, the strength may be insufficient and the shutdown function may be reduced. Moreover, 5-50 micrometers is preferable, as for the thickness of a porous film, 10-50 micrometers is more preferable, More preferably, it is 10-30 micrometers. If the thickness is too thin, the shutdown function may be insufficient, or the battery may be short-circuited during winding, and if it is too thick, high electrical capacity may not be achieved. The pore diameter of the porous film is preferably 0.1 μm or less, and more preferably 0.08 μm or less. By reducing the pore diameter, a porous film having a small membrane resistance value is obtained even with the same air permeability.

When the battery separator of the present invention includes the laminated porous film of the present invention, among the laminated porous films, preferred porosity and pore diameter of the porous film are the same as those of the porous film. However, the film thickness is preferably 5 to 50 μm, more preferably 10 to 50 μm, and still more preferably 10 to 30 μm as the whole laminated porous film.
Of the laminated porous film, the porosity of the heat-resistant layer is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. If the porosity is too small, the amount of electrolyte retained tends to be small, and if it is too large, the strength of the heat-resistant layer tends to be insufficient. The film thickness of the heat-resistant layer is preferably 0.5 μm to 10 μm, more preferably 1 μm to 5 μm. If the film thickness is too thin, the heat-resistant layer tends not to be able to suppress shrinkage during heating, and if the film thickness is too thick, the load characteristics tend to deteriorate when the battery is used.

The battery of the present invention includes the battery separator of the present invention. In the following, components other than the battery separator will be described by taking, as an example, the case where the battery of the present invention is a non-aqueous electrolyte secondary battery such as a lithium battery, but is not limited thereto.

As the non-aqueous electrolyte solution, for example, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used. Examples of lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , One or a mixture of two or more of lower aliphatic carboxylic acid lithium salts, LiAlCl _{4 and the} like can be mentioned. The lithium salt is selected from the group consisting of LiPF ₆ containing fluorine, LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) ₃ among these. It is preferable to use one containing at least one selected from the above.

Examples of the organic solvent used in the nonaqueous electrolyte solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di ( Carbonates such as methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2-methyl Ethers such as tetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetate Amides such as amide; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or those obtained by introducing a fluorine substituent into the above organic solvent Usually, a mixture of two or more of these is used.

Among these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate or cyclic carbonate and ether is more preferable. The mixed solvent of cyclic carbonate and non-cyclic carbonate has a wide operating temperature range, excellent load characteristics, and is hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material. In addition, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable. As the positive electrode sheet, a sheet in which a mixture containing a positive electrode active material, a conductive material, and a binder is supported on a current collector is usually used. Specifically, as the positive electrode active material, a material containing a material that can be doped / undoped with lithium ions, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder can be used. Examples of the material that can be doped / undoped with lithium ions include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni. Among these, in view of high average discharge potential, lithium based on a layered lithium composite oxide based on an α-NaFeO2 type structure such as lithium nickelate and lithium cobaltate and a spinel type structure such as lithium manganese spinel is preferable. A composite oxide is mentioned.

The lithium composite oxide may contain various additive elements, particularly at least selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Ag, Mg, Al, Ga, In, and Sn. Composite nickel acid containing a metal such that the at least one metal is 0.1 to 20 mol% with respect to the sum of the number of moles of one metal and the number of moles of Ni in lithium nickelate Lithium is preferable because cycle characteristics in use at a high capacity are improved.

As the thermoplastic resin as the binder, polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether Copolymer, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, thermoplastic polyimide, polyethylene, polypropylene and the like.

Examples of the carbonaceous material as the conductive agent include natural graphite, artificial graphite, cokes, and carbon black. As the conductive material, each may be used alone, or for example, a composite conductive material system in which artificial graphite and carbon black are mixed and used may be selected.

As the negative electrode sheet, for example, a material capable of doping and dedoping lithium ions, lithium metal, or a lithium alloy can be used. Materials that can be doped / undoped with lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds, and lower potential than the positive electrode. And chalcogen compounds such as oxides and sulfides for doping and dedoping lithium ions. As a carbonaceous material, a carbonaceous material mainly composed of graphite materials such as natural graphite and artificial graphite, because it has a high potential flatness and a low average discharge potential, so that a large energy density can be obtained when combined with a positive electrode. Is preferred.

As the negative electrode current collector, Cu, Ni, stainless steel, or the like can be used. In particular, in a lithium secondary battery, Cu is preferable because it is difficult to form an alloy with lithium and it can be easily processed into a thin film. As a method of supporting the mixture containing the negative electrode active material on the negative electrode current collector, a method of pressure molding, or a method of pasting into a paste using a solvent or the like and applying pressure to the current collector by pressing after drying Is mentioned.

The shape of the battery of the present invention is not particularly limited, and may be any of a paper type, a coin type, a cylindrical type, a rectangular shape, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

(1) Film thickness Measured with Mitutoyo VL-50A according to JISK7130.

(2) Puncture strength The maximum stress (gf) when the porous film was fixed with a 12 mmφ washer and the pin was punctured at 200 mm / min was defined as the puncture strength of the film. A pin with a pin diameter of 1 mmΦ and a tip of 0.5R was used.

(3) Melt index (MI)
Measurement was performed in accordance with JISK7130 using a melt indexer manufactured by Takara Industries. The measurement temperature was 240 ° C., the office diameter was 3.3 mmφ, and the composition was measured with a load of 21.6 kg. The higher the MI value, the better the workability.

(4) Intrinsic viscosity Measured according to JISK7367-1. Tetralin was used as a solvent, and measurement was performed at 135 ° C. with an Ubbelohde viscometer.

Example 1
20.9 g (= W1) of high molecular weight polyethylene powder having an intrinsic viscosity [η] of 7.7 (Hi-Zex Million 145M, Mitsui Chemicals), polyethylene wax powder (High Wax 110P, Mitsui Chemicals, weight average molecular weight 1000) 3 0.7 g (= W2), calcium carbonate (010AS, manufactured by Maruo Calcium) 39.6 g, antioxidant (Irg1010, manufactured by Ciba Specialty Chemicals) 0.17 g, (P168, manufactured by Ciba Specialty Chemicals) 0.05 g and 0.47 g of sodium stearate were mixed in powder form, then kneaded for 3 minutes at 200 ° C. and 60 rpm in a lab plast mill (R-60H type), and then kneaded for 3 minutes at 230 ° C. and 100 rpm. It was taken out as a uniform kneaded product.
The obtained kneaded material was processed into a sheet having a thickness of about 150 μm by a hot press set at 230 ° C., and then solidified by a cooling press. The obtained sheet was washed with hydrochloric acid containing a surfactant to dissolve calcium carbonate to form a porous sheet, and then washed with water and dried. The obtained porous sheet was uniaxially stretched 5 times using an autograph (AGS-G, Shimadzu Corporation) to obtain a stretched film. The stretching was performed at 105 ° C. and a stretching speed of 200 mm / min. Table 1 shows the puncture strength of the stretched film.

Example 2
A kneaded product and a stretched film were obtained in the same manner as in Example 1 except that high molecular weight polyethylene having an intrinsic viscosity [η] of 7.5 (GUR4012, manufactured by Ticona) was used. The evaluation results are shown in Table 1.

Comparative Example 1
17.2 g (= W1) of high molecular weight polyethylene powder (GUR4032, manufactured by Ticona) having an intrinsic viscosity [η] of 14.1, 7.4 g of polyethylene wax powder (High Wax 110P, manufactured by Mitsui Chemicals, weight average molecular weight 1000) A kneaded product and a stretched film were obtained in the same manner as in Example 1 except that (= W2) was used. The evaluation results are shown in Table 1.

Comparative Example 2
19.7 g (= W1) of high molecular weight polyethylene powder (GUR4113, manufactured by Ticona) having an intrinsic viscosity [η] of 10.2 and 4.9 g of polyethylene wax powder (High Wax 110P, manufactured by Mitsui Chemicals, weight average molecular weight 1000) A kneaded product and a stretched film were obtained in the same manner as in Example 1 except that (= W2) was used. The evaluation results are shown in Table 1.

Claims (13)

A sheet comprising a high molecular weight polyolefin and a polyolefin wax having a weight average molecular weight of 700 to 6000, wherein the weight of the high molecular weight polyolefin contained in the sheet is W1, and the weight of the polyolefin wax having a weight average molecular weight of 700 to 6000 is W2. when the intrinsic viscosity of the high molecular weight polyolefin and [η], [η] is from 5 to 7.7, and meets the following formula (1), and {W2 / (W1 + W2) } × 100 is 15 or less Is a sheet.
[Η] × 4.3−21 <{W2 / (W1 + W2)} × 100 <[η] × 4.3−8 Formula (1) A porous film comprising a high molecular weight polyolefin and a polyolefin wax having a weight average molecular weight of 700 to 6000, wherein the weight of the high molecular weight polyolefin contained in the porous film is W1, and the weight of the polyolefin wax having a weight average molecular weight of 700 to 6000 was a W2, when the intrinsic viscosity of the high molecular weight polyolefin and [η], [η] is from 5 to 7.7, and meets the following formula (1), and {W2 / (W1 + W2) } × A porous film in which 100 is 15 or less .
[Η] × 4.3−21 <{W2 / (W1 + W2)} × 100 <[η] × 4.3−8 Formula (1) A laminated porous film obtained by laminating the porous film according to claim 2 and a porous heat-resistant layer. A battery separator comprising the porous film according to claim 2 or the laminated porous film according to claim 3. A battery comprising the battery separator according to claim 4. A resin composition comprising a filler, a high molecular weight polyethylene, and a polyolefin wax having a weight average molecular weight of 700 to 6000, wherein the weight of the high molecular weight polyethylene contained in the resin composition is W1, and a polyolefin having a weight average molecular weight of 700 to 6000 When the wax weight is W2 and the intrinsic viscosity of the high molecular weight polyethylene is [η], [η] is 5 to 7.
It is 7, and meets the following formula (1), and {W2 / (W1 + W2) } × 100 is a resin composition is 15 or less.
[Η] × 4.3−21 <{W2 / (W1 + W2)} × 100 <[η] × 4.3−8 Formula (1) A sheet obtained by molding the resin composition according to claim 6 . A porous film obtained by stretching the sheet according to claim 7 . The porous film obtained by extending | stretching after removing at least one part filler from the sheet | seat of Claim 7 . The porous film obtained by extending | stretching the sheet | seat of Claim 7 , and removing at least one part filler. A laminated porous film obtained by laminating the porous film according to claim 8 and a porous heat-resistant layer. The battery separator containing the porous film in any one of Claims 8-10 , or the laminated porous film of Claim 11. A battery comprising the battery separator according to claim 12 .