JP5092253B2 - Battery separator - Google Patents

Description

  The present invention relates to a battery separator.

Porous films are used in various applications such as diapers, medical sheets, and battery separators. In particular, a porous film used as a battery separator is required to be thin and uniform. As a porous film used as a battery separator, 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 are kneaded and formed into a sheet shape. After that, a porous film formed by stretching the sheet is disclosed (see Patent Document 1).

JP 2002-69221 A

  However, when a porous film is produced by the method described in Patent Document 1, when a conventional inorganic filler is used, a thin portion may occur in the obtained porous film. An object of the present invention is to provide a homogeneous battery separator without a thin portion.

  That is, the present invention relates to a sheet comprising a polyolefin resin composition comprising 100 parts by weight of a polyolefin resin and 100 to 400 parts by weight of an inorganic filler having a carbon content of 10 ppm or less based on 100 parts by weight of the polyolefin resin. The battery separator obtained by removing the inorganic filler and then stretching.

The battery separator of the present invention has no thin part and is homogeneous.

  The sheet used in the present invention comprises a polyolefin resin composition containing 100 parts by weight of a polyolefin resin and 100 to 400 parts by weight of an inorganic filler with respect to 100 parts by weight of the polyolefin resin. The inorganic filler content in the polyolefin resin composition is preferably 150 to 350 parts by weight with respect to 100 parts by weight of the polyolefin resin. When the amount of the inorganic filler in the polyolefin resin composition is less than 100 parts by weight, the inorganic filler is removed in a short time when the inorganic filler is removed from the sheet made of the polyolefin resin composition. On the other hand, when the amount exceeds 400 parts by weight, the sheet strength tends to be weak and the handling tends to be difficult.

  The thickness of the sheet comprising the polyolefin resin composition in the present invention is usually 5 to 200 μm, preferably 5 to 100 μm. A sheet having such a thickness can be efficiently removed in a short time when the inorganic filler is removed from the sheet, and stretched when the sheet from which the inorganic filler has been removed is stretched. Cheap.

  The average particle diameter of the inorganic filler used in the present invention is usually from 0.02 to 1 μm, preferably from 0.05 to 0.8 μm, and more preferably from 0.05 to 0.5 μm. A sheet made of a polyolefin resin composition containing an inorganic filler having such an average particle diameter has fewer pinholes (small holes) and thin-walled portions, and is superior in stretchability, and is obtained by stretching the sheet. The battery separator is further excellent in ion permeability. In addition, the average particle diameter of an inorganic filler is an average value of the diameter of the particle | grains recognized in the visual field of 30000 times the magnitude | size using a scanning electron microscope SEM (Hitachi S-4200).

  The inorganic filler used in the present invention is an inorganic filler having a carbon content of 10 ppm or less, preferably 9 ppm or less, more preferably 8 ppm or less. In the present invention, when an inorganic filler having a carbon content of more than 10 ppm is used, the inorganic filler is removed from the sheet comprising the polyolefin resin composition containing the inorganic filler, and then stretched. A thin-walled portion is produced in the battery separator.

  Examples of the inorganic filler used in the present invention include calcium carbonate, magnesium carbonate, barium carbonate, zinc oxide, calcium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and calcium sulfate, which are essentially soluble in acids. Is mentioned. In the present invention, calcium carbonate is used because it is inexpensive, easily available in various particle sizes depending on the application, and easily removed with an acidic aqueous solution when the inorganic filler is removed in a later step. It is preferable to use precipitated calcium carbonate, and more preferable to use precipitated calcium carbonate.

  The inorganic filler used in the present invention is preferably subjected to a surface treatment from the viewpoint of dispersibility in a polyolefin-based resin and stretchability when a sheet containing the inorganic filler is stretched. Examples of the surface treatment agent include higher fatty acids such as palmitic acid, oleic acid, stearic acid, octadecanoic acid, lauric acid, myristic acid, mixtures thereof, and metal salts thereof. In addition to these, a small amount of higher fatty acid esters such as ethyl oleate and ethyl stearate may be used in combination as a surface treatment agent. It is preferable that the surface treatment agent used for the surface treatment of the inorganic filler is about 1 to 10 parts by weight with respect to 100 parts by weight of the inorganic filler.

The carbon contained in the inorganic filler is conductive carbon and is presumed to be contained in the raw material itself or mixed in the inorganic filler manufacturing process. Although the amount of carbon contained in the inorganic filler is extremely small, many of them have a relatively large diameter. In order to obtain an inorganic filler having carbon of 10 ppm or less, for example, an inorganic filler having a small particle diameter obtained by classifying commercially available inorganic fine particles into those having a large particle diameter and those having a small particle diameter can be mentioned. The classification method is not particularly limited, and a dry classifier such as a well-known air classifier, mesh classifier, or cyclone classifier can be used, but an air classifier is preferably used. In wind classification, an inorganic filler is put into a classification rotor, the classification rotor is rotated, and centrifugal force and centripetal force due to airflow are applied to the inorganic fine particles. It is a method of dividing into fine powder. The classification point can be easily changed by changing the air volume and the rotation speed. The classification point is preferably 0.5 to 50 μm, and more preferably 1 to 20 μm. The classification point can be determined by the following equation.
D = c / ν√ (Q / ρ)
Where D: classification point (μm) c: constant, ν: rotational speed (rmp), Q: air volume (m ² / h)
In the above equation, the constant c is a value determined by the apparatus.
It is extremely difficult to remove all the carbon contained in the inorganic filler. In the present invention, even an inorganic filler containing 1 ppm or more of carbon can be used.

  Examples of the polyolefin resin used in the present invention include homopolymers of olefins such as ethylene, propylene, butene, and hexene, copolymers of these monomers, and copolymers of these monomers and non-olefin monomers. Specific examples of the polyolefin resin include low density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), ethylene resin such as high density polyethylene, and propylene resin such as polypropylene and ethylene-propylene copolymer. Examples include poly (4-methylpentene-1), poly (butene-1), and ethylene-vinyl acetate copolymer. Since the shutdown temperature can be about 120 to 150 ° C., the polyolefin resin to be used is preferably an ethylene resin.

  The polyolefin resin used in the present invention preferably contains a polyolefin having a molecular chain length of 2850 nm or more (hereinafter referred to as an ultra-high molecular chain length polyolefin). A battery separator obtained by removing the inorganic filler from a sheet made of a polyolefin resin composition containing the polyolefin resin by using a polyolefin resin containing such an ultra-high molecular chain length polyolefin and then stretching the sheet. Is excellent in strength, and a battery using the battery separator has a low internal resistance. The ultra high molecular chain length polyolefin contained in the polyolefin resin is preferably 10% by weight or more in the polyolefin resin, more preferably 20% by weight or more, and further preferably 30% by weight or more. preferable.

  The polyolefin resin composition used in the present invention preferably contains an olefin wax having a weight average molecular weight of 700 to 6000. Olefinic wax is usually solid at 25 ° C. The polyolefin resin composition containing a wax has improved stretchability, and the resulting porous film has excellent strength. The content of the olefin wax in the polyolefin resin composition is preferably 5 to 100 parts by weight, and preferably 10 to 70 parts by weight with respect to 100 parts by weight of the polyolefin resin contained in the resin composition. Is more preferable.

  Examples of olefin waxes include ethylene resin waxes such as low density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), high density polyethylene, and propylene resin waxes such as polypropylene and ethylene-propylene copolymer. , Poly (4-methylpentene-1), poly (butene-1), and ethylene-vinyl acetate copolymer wax.

  In the present invention, the molecular chain length, weight average molecular chain length, molecular weight, and weight average molecular weight of a polyolefin resin or olefin wax can be measured by GPC (gel permeation chromatography). In addition, the content (% by weight) of the ultra-high molecular chain length polyolefin in the specific polyolefin resin can be obtained by integration of a molecular weight distribution curve obtained by GPC measurement.

The molecular chain length of the polyolefin resin is a molecular chain length in terms of polystyrene as measured by GPC (gel permeation chromatography), and more specifically is a parameter determined by the following procedure. As a mobile phase for GPC measurement, a solvent capable of dissolving both an unknown sample to be measured and standard polystyrene having a known molecular weight is used. First, GPC measurement of a plurality of types of standard polystyrenes having different molecular weights is performed to determine the retention time of each standard polystyrene. The molecular chain length of each standard polystyrene is determined using the polystyrene Q factor, and thereby the molecular chain length of each standard polystyrene and the corresponding retention time are known. The molecular weight, molecular chain length, and Q factor of standard polystyrene are in the following relationship.
Molecular weight = molecular chain length × Q factor Next, GPC measurement of an unknown sample is performed to obtain a retention time-eluting component amount curve. In the standard polystyrene GPC measurement, when the molecular chain length of the standard polystyrene that was the holding time T is L, the “polystyrene converted molecular chain length” of the component that was the holding time T in the GPC measurement of the unknown sample is L. To do. Using this relationship, the polystyrene-reduced molecular chain length distribution of the unknown sample (relation between the polystyrene-reduced molecular chain length and the eluted component amount) is determined from the retention time-eluted component amount curve of the unknown sample.

  In the present invention, the amount of polyolefin having a molecular chain length of 2850 nm or more in the polyolefin resin corresponds to a molecular chain length of 2850 nm or more with respect to the value obtained by integrating the molecular chain length-elution component amount curve obtained by the above method over the entire range. It can be obtained as a ratio of values integrated over the range to be performed.

  The method for producing the polyolefin resin composition in the present invention is not particularly limited, but a material constituting the polyolefin resin composition such as a polyolefin resin or an inorganic filler is mixed with a mixing device such as a roll, a Banbury mixer, a single screw extruder, two A polyolefin resin composition is obtained by mixing using a shaft extruder or the like. When mixing the materials, additives such as an antioxidant, a nonionic surfactant, an ultraviolet absorber, a flame retardant, a fatty acid ester, and a stabilizer may be added as necessary.

  The manufacturing method of the sheet | seat which consists of polyolefin resin composition used by this invention is not specifically limited, It can manufacture by sheet forming methods, such as an inflation process, a calendar process, T-die extrusion process, and a Skyf method. Since a sheet having excellent surface smoothness and high film thickness accuracy can be obtained, it is preferably produced by the following method. In particular, when the polyolefin resin in the polyolefin resin composition contains an ultra high molecular chain length polyolefin, it is preferable to produce a sheet by the following method.

  A preferred method for producing a sheet comprising a polyolefin resin composition is a polyolefin resin composition using a pair of rotational molding tools adjusted to a surface temperature higher than the melting point of the polyolefin resin contained in the polyolefin resin composition. This is a method of rolling a product. The surface temperature of the rotary forming tool is preferably (melting point + 5) ° C. or higher. Further, the upper limit of the surface temperature is preferably (melting point + 20) ° C. or less, and more preferably (melting point + 15) ° 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. The melting point of the polyolefin resin can be determined from the peak temperature in DSC (differential scanning calorimetry). When there are a plurality of peaks, the melting point is the peak temperature having the largest heat of fusion ΔH (J / g). The porous film obtained by removing the inorganic filler from the sheet obtained by such a method and then stretching becomes a battery separator having excellent strength and ion permeability.

  When a polyolefin resin composition is rolled with a pair of rotary molding tools, the polyolefin resin composition discharged in a strand form from an extruder may be directly introduced between the pair of rotary molding tools, and once pelletized. The polyolefin resin composition may be used.

  The battery separator of the present invention can be obtained by a method of stretching after removing the inorganic filler contained in the sheet from the sheet made of the polyolefin resin composition. The battery separator obtained by such a method is excellent in film thickness uniformity. The sheet made of the polyolefin resin composition used in the present invention contains 100 parts by weight of polyolefin resin and 100 to 400 parts by weight of an inorganic filler having a carbon content of 10 ppm or less with respect to 100 parts by weight of the polyolefin resin. It may be a multilayer sheet in which two or more sheets made of a polyolefin resin composition are laminated.

  When removing the inorganic filler from the sheet made of the polyolefin resin composition, a liquid is used. The liquid to be used is appropriately selected according to the type of the inorganic filler in the sheet, but when the inorganic filler is essentially soluble in acid such as calcium carbonate, an acidic aqueous solution may be used. it can. Examples of the method for removing the inorganic filler include a method in which the liquid is showered on the sheet, a method in which the sheet is immersed in a tank containing the liquid, and the like. The method of removing the inorganic filler by the liquid may be batch type or continuous type, but from the viewpoint of productivity, the continuous type is preferable. The method of conveying a sheet | seat and making it pass in a liquid is mentioned. When the liquid is an acidic or alkaline aqueous solution, the sheet from which the inorganic filler has been removed is preferably further washed with water. As the degree of washing, it is usually sufficient to carry out washing to such an extent that dissolved salt or the like does not precipitate. The sheet from which the inorganic filler has been removed is usually dried within a time and temperature range in which the physical properties of the sheet do not change. It is preferable that about 100 to 20000 ppm of the inorganic filler remain in the sheet from which the inorganic filler has been removed. A sheet with a small amount of inorganic filler is stretched by a method described later to form a porous film, and when used as a battery separator, even if the polyolefin resin constituting the porous film melts, a short circuit between the electrodes Expected to prevent the effects. Moreover, as described above, the porous film obtained by stretching a sheet in which a small amount of the inorganic filler remains is superior in air permeability to the case where the inorganic filler is completely removed. The reason for this is not clear, but it is thought that the film is hardly crushed in the film thickness direction due to the trace amount of filler remaining in the film.

  In the case where the inorganic filler is calcium carbonate and an acidic aqueous solution is used when removing calcium carbonate from the sheet, a surfactant, methanol, ethanol, isopropanol, It is preferable to add a small amount of a water-soluble organic solvent such as acetone or N-methylpyrrolidone, but it is preferable to add a surfactant without adding an organic solvent from the viewpoint of the environment. Examples of the surfactant include known nonionic surfactants, cationic surfactants, anionic surfactants, and the like, but nonionic surfactants are preferable. Nonionic surfactants have the advantage that they are difficult to hydrolyze even when the aqueous liquid is strongly alkaline (pH 11 or higher) or strongly acidic (pH 3 or lower). Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene-polyoxypropylene alkyl ether, polyoxyethylene alkylphenyl ether, polyethylene glycol fatty acid ester, polyoxyethylene alkylamine / fatty acid amide, and the like. . The amount of the nonionic surfactant added to the aqueous liquid is 0.05 to 10 from the balance between the effect of increasing the inorganic filler removal rate and the efficiency of removing the surfactant from the film after removing the inorganic filler. It is preferable to set it as weight%.

  The hydrophilic / lipophilic balance (HLB) of the nonionic surfactant used in the present invention is preferably in the range of 3 to 18, more preferably in the range of 5 to 15. HLB is a value indicating a balance between hydrophilicity and hydrophobic strength. If the HLB is too small, the solubility in water tends to be poor. Conversely, if the HLB is too large, the solubility in water is sufficient, but the hydrophobicity is low, so it tends to take time to penetrate into the sheet. is there.

HLB can be calculated by the following Griffin equation.
HLB = ((molecular weight of hydrophilic group in surfactant) / (molecular weight of entire surfactant)) × (100/5)
For surfactant HLB whose HLB cannot be calculated using the Griffin equation, oil is emulsified with the surfactant whose HLB is unknown, and a plurality of surfactants whose HLB is known (those with different HLB values are used) ) By emulsifying the same oil and comparing them. The HLB of the surfactant with the known HLB in which the oil emulsification state is the same as the surfactant with the unknown HLB is defined as the HLB of the surfactant with the unknown HLB.

  A porous film can be produced by stretching a sheet obtained by removing the inorganic filler from the sheet made of the polyolefin resin composition by the method as described above, using a tenter, a roll, an autograph or the like. From the viewpoint of air permeability of the obtained porous film, the draw ratio is preferably 2 to 12 times, and more preferably 4 to 10 times. The stretching temperature is usually a temperature not lower than the softening point and not higher than the melting point of the polyolefin resin, preferably in the range of (melting point-50) ° C. By stretching at a temperature in such a range, a porous film excellent in air permeability and ion permeability and suitable as a battery separator can be obtained. For example, when the polyolefin resin composition to be used is composed of a polyolefin resin mainly composed of polyethylene, the stretching temperature is preferably 80 to 130 ° C, more preferably 90 to 115 ° C. Moreover, it is preferable to heat set after extending | stretching. The heat setting temperature is preferably performed at a temperature lower than the melting point of the polyolefin resin.

  The porous film obtained by the method as described above has no thin part and is uniform, and is suitable for a battery separator.

  A laminated porous film in which a heat-resistant layer is laminated on at least one surface of the porous film obtained by the method as described above can also be used as a battery separator. Hereinafter, the laminated porous film having the above configuration is referred to as a battery laminated separator. The heat-resistant layer is a porous layer composed of a heat-resistant polymer having a thermal decomposition starting temperature of 200 ° C. or higher.

  Examples of the polymer having a thermal decomposition starting temperature of 200 ° C. or higher include oxygen-containing aromatic polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene isophthalate, and nitrogen-containing aromatic polymers described later. Polyethylene terephthalate is obtained by condensation polymerization using ethylene glycol and terephthalic acid as raw materials monomers, polybutylene terephthalate is obtained by condensation polymerization using butylene glycol and terephthalic acid as raw material monomers, polyethylene isophthalate is It can be obtained by condensation polymerization using ethylene glycol and isophthalic acid as raw material monomers. Further, as a raw material monomer, terephthalic acid dichloride may be used instead of terephthalic acid, or isophthalic acid dichloride may be used instead of isophthalic acid.

  The thermal decomposition starting temperature of these polymers is more preferably 220 ° C. or higher, further preferably 300 ° C. or higher. As the polymer constituting the heat-resistant layer, a nitrogen-containing aromatic polymer is preferable from the viewpoint of operability.

  Examples of the nitrogen-containing aromatic polymer include an aromatic polymer containing an amide group, an aromatic polymer containing an amideimide group, an aromatic polymer containing an imide group, an aromatic group containing an ester group and an imide group. Aromatic polymers containing an aromatic polymer, an ester group and an amide group are preferred. Among these, aromatic polyamide (hereinafter sometimes referred to as “aramid”), aromatic polyamideimide, aromatic polyimide, aromatic polyester Amides are more preferred.

  Examples of aramids include meta-oriented aromatic polyamides and para-oriented aromatic polyamides (hereinafter sometimes referred to as “para-aramid”), and para-aramid is preferred because it tends to be porous.

  Here, the 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 (orientated positions extending coaxially or in parallel).

  Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide, poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic amide), poly (para Para-oriented or para-oriented, such as phenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer The para-aramid which has a structure according to is illustrated.

  The number average molecular weight of the nitrogen-containing aromatic polymer is preferably 2000 or more, more preferably 5000 or more, from the viewpoint of the strength of the heat-resistant layer. Moreover, it is preferable that the number average molecular weight of a nitrogen-containing aromatic polymer is 50000 or less from a viewpoint of operativity when forming a heat-resistant layer by the method mentioned later.

  It is preferable that the heat-resistant layer in the battery laminated separator of the present invention further contains an organic powder and / or an inorganic powder. In this case, the porosity of the heat-resistant layer can be controlled by changing the addition amount of the organic powder and / or the inorganic powder. From the viewpoint of maintaining the strength characteristics and smoothness of the heat-resistant layer, the average particle diameter of the primary particles is preferably 1.0 μm or less, and from the viewpoint of operability, the particle diameter of the organic powder and / or inorganic powder is It is preferable that it is 0.01 micrometer or more. From the viewpoint of the strength of the heat-resistant layer, the addition amount of the organic powder and / or inorganic powder is preferably 20% by weight or more and 95% by weight or less, and more preferably 30%, when the total weight of the heat-resistant layer is 100% by weight. % By weight or more and 91% by weight or less. Examples of the shape of the organic powder and / or inorganic powder include a spherical shape and a rod shape, and a spherical shape is preferable.

Examples of the organic powder include, for example, styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate, and the like, or two or more kinds of copolymers, polytetrafluoroethylene, 4 Fluorine-based resins such as fluorinated ethylene-6 fluorinated propylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride; melamine resin; urea resin; polyolefin; powder made of organic matter such as polymethacrylate It is done. The organic powder may be used alone or in combination of two or more. Among these organic powders, polytetrafluoroethylene is preferable from the viewpoint of chemical stability.
Examples of the inorganic powder include powders made of inorganic materials such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, sulfates, and specific examples include alumina, silica, The powder which consists of titanium dioxide or calcium carbonate etc. is mentioned. The inorganic powder may be used alone or in combination of two or more. Among these inorganic powders, alumina is preferable from the viewpoint of chemical stability.

As a method of laminating a heat-resistant layer on a porous film obtained by removing an inorganic filler from a sheet made of a polyolefin-based resin composition and then stretching, the heat-resistant layer is produced separately and then laminated with the porous film. Examples thereof include a method of forming a heat-resistant layer by applying a coating solution containing a heat-resistant polymer on at least one surface of a porous film, and the latter method is preferable from the viewpoint of productivity. Specific examples of a method for forming a heat-resistant layer by applying a coating liquid on at least one surface of a porous film include the following steps.
(A) A coating solution containing a heat resistant polymer is prepared.
(B) The coating solution is applied to at least one surface of the porous film to form a coating film.
(C) The heat-resistant polymer is precipitated from the coating film by means of humidification, solvent removal, or immersion in a solvent that does not dissolve the heat-resistant polymer, 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 coating solution is a solution obtained by dissolving a heat resistant polymer in a polar organic solvent. The polar organic solvent is, for example, a polar amide solvent or a polar urea solvent, and specifically includes N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, tetramethylurea. However, it is not limited to these. From the viewpoint of coating properties, the concentration of the heat resistant polymer in the coating solution is preferably 0.5 to 10% by weight.

  The coating liquid may contain an organic powder and / or an inorganic powder. By forming the heat-resistant layer using such a coating solution, it is possible to form a heat-resistant layer having a uniform film thickness and a fine porosity.

  The average pore diameter measured by the mercury intrusion method of the heat-resistant layer is preferably 3 μm or less, more preferably 1 μm or less. When the average pore diameter exceeds 3 μm, when the laminated porous film is used as a battery separator, there is a problem that short-circuiting easily occurs when carbon powder or a small piece thereof, which is the main component of the positive electrode or negative electrode, falls off. there is a possibility. The heat-resistant layer has a thickness of preferably 1 to 15 μm, more preferably 1 to 10 μm. When the thickness is less than 1 μm, the effect on heat resistance may be insufficient. When the thickness exceeds 15 μm, when the laminated porous film is used as a battery separator, the thickness is too thick and the electric capacity is increased. May be difficult to achieve.

The laminated porous film obtained by the above method has no thin part and is uniform. Moreover, since it is excellent also in heat resistance, intensity | strength, and air permeability (ion permeability), it can be used conveniently as a laminated separator for batteries, especially a laminated separator for lithium ion secondary batteries.

(1) The Gurley value (second / 100 cc) of the Gurley value film was measured with a B-type densometer (manufactured by Toyo Seiki) according to JIS P8117. The measurement was performed at 10 locations per 1 m ² of film.
(2) Film thickness Measured with Mitutoyo VL-50A according to JISK7130. The measurement was performed at 10 locations per 1 m ² of film.

(3) Measurement of molecular chain length and molecular weight by GPC A gel chromatograph Alliance GPC2000 model manufactured by Waters was used. Other conditions are shown below.
Column: TSKgel GMHHR-H (S) HT 30 cm × 2 manufactured by Tosoh Corporation, TSKgel GMH 6 -HTL 30 cm × 2
Mobile phase: o-dichlorobenzene detector: Differential refractometer flow rate: 1.0 mL / min Column temperature: 140 ° C.
Injection volume: 500 μL
After completely dissolving 30 mg of the sample in 20 mL of o-dichlorobenzene at 145 ° C., the solution was filtered through a sintered filter having a pore size of 0.45 μm, and the filtrate was used as a feed solution. The calibration curve was prepared using 16 kinds of standard polystyrenes with known molecular weights.

(4) Measurement of carbon content in inorganic filler After precisely weighing 100 g of inorganic filler, 300 ml of methanol was added and stirred to disperse the inorganic filler. Further, 300 ml of hydrochloric acid (special grade reagent from Wako Pure Chemical Industries, Ltd.) was slowly added while stirring to dissolve the inorganic filler. After confirming that bubbles were not generated, the solution was vacuum filtered using a hydrophilic PTFE filter (pore size: 10 μm; JCW4700, manufactured by Nihon Millipore). 50 ml of methanol and 50 ml of hydrochloric acid were added to the insoluble part remaining on the filter while vacuum filtration to dissolve the undissolved inorganic filler. This operation was repeated three times. Subsequently, the insoluble component remaining on the filter was washed with tetrahydrofuran, methanol, hydrochloric acid, ultrapure water, and methanol in this order. Thereafter, the PTFE filter was vacuum dried in an oven at 80 ° C. for 3 to 4 hours, and then cooled to room temperature in a desiccator. About 5 mg was taken from the dried insoluble component and precisely weighed, and the amount of carbon contained was measured by elemental analysis. For elemental analysis, vario EL manufactured by elemental was used.
(5) Average particle size of inorganic filler The particle size was measured with a scanning electron microscope SEM (S-4200 manufactured by Hitachi) at a magnification of 30000, the diameter of 100 particles was measured, and the average was defined as the average particle size (μm).
(6) 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.
(7) Evaluation of pinholes and thin portions present in porous film About the obtained porous film, the number of pinholes and thin portions per 1 m ² of the film was visually measured. Specifically, the light of the fluorescent lamp is applied from one surface of the porous film, the film is observed from the other surface, and the through hole is a pinhole. The part with much light was judged to be a thin part.

[Example 1]
Commercially available precipitated calcium carbonate (Vigot-10 manufactured by Shiroishi Calcium Co., Ltd.) was classified using Turboflex 100ATP manufactured by Hosokawa Micron Co., Ltd. The classification conditions were a rotor speed of 11000 ppm, an air volume of 4 m ² / min (theoretical classification point 2 μm), and a raw material supply rate of 15 kg / h. As a result of classification, the recovery rate of the obtained fine powder was 85% by weight, the amount of carbon contained in the recovered inorganic filler was 8 ppm, and the average particle size was 0.14 μm.
100 parts by weight of a polyethylene resin (Hi-Zex Million 340M, manufactured by Mitsui Chemicals, Inc., weight average molecular chain length 17000 nm, weight average molecular weight 3 million, melting point 136 ° C.) and 100 parts by weight of the polyethylene resin are classified. The resulting fine powder of 256 parts by weight of calcium carbonate and 44 parts by weight of olefin wax powder (High Wax 110P, manufactured by Mitsui Chemicals, Inc., weight average molecular weight 1000, melting point 110 ° C.) were mixed with a Henschel mixer and then biaxially kneaded. A polyolefin resin composition was obtained by kneading at 230 ° C. in a machine. The polyolefin resin composition was rolled with a pair of rolls having a surface temperature of 150 ° C. and rotating at the same peripheral speed to produce a single layer sheet having a thickness of about 40 μm. Next, the obtained single-layer sheets were pressure-bonded with a pair of rolls having a surface temperature of 150 ° C. to prepare a sheet made of a multilayer polyolefin resin composition. The multilayer sheet had a thickness of 71 μm.
Next, the inorganic filler in the multilayer sheet was removed using the apparatus shown in FIG. The multilayer sheet is conveyed by a roll and immersed in a bath containing a hydrochloric acid aqueous solution (hydrochloric acid 2 to 4 mol / L, nonionic surfactant 0.1 to 0.5% by weight) to remove the inorganic filler, and then the sheet. Was immersed in a bath (b) containing an aqueous sodium hydroxide solution (0.1 to 2 mol / L) for neutralization. Further, the sheet was washed with water in the bath of c, and was finally brought into contact with a roll heated to 50 ° C., dried and wound up. Thereafter, the sheet was stretched 8 times with a tenter (stretching temperature 100 ° C.). Table 1 shows the physical properties of the obtained porous film.

[Comparative Example 1]
Polyolefin-based in the same manner as in Example 1 except that commercially available precipitated calcium carbonate (Vigot-10 manufactured by Shiroishi Calcium Co., Ltd., carbon content: 17 ppm, average particle size: 0.14 μm) was used without classification. A multilayer sheet (81 μm) comprising the resin composition and the polyolefin resin composition was obtained, and the inorganic filler was removed from the sheet, followed by stretching to obtain a porous film. Table 1 shows the physical properties of the obtained porous film.

In an Example, it is a schematic diagram of the apparatus used when removing an inorganic filler from the sheet | seat which consists of polyolefin resin compositions.

Explanation of symbols

a: Acid solution tank
b: Alkaline aqueous solution tank
c: Aquarium
d: Guide roll
e: Drying drum (heating drum)
f: Winder
g: Sheet made of polyolefin resin composition

Claims (3)

From a sheet made of a polyolefin resin composition containing 100 to 400 parts by weight of a polyolefin resin and 100 to 400 parts by weight of an inorganic filler having a carbon content of 10 ppm or less with respect to 100 parts by weight of the polyolefin resin, the inorganic filling A laminated separator for batteries, in which a heat-resistant layer is laminated on a separator for batteries obtained by stretching after removing the agent . The laminated separator for a battery according to claim 1, wherein the inorganic filler has an average particle size of 0.02 to 1 μm . The laminated separator for a battery according to claim 1, wherein the inorganic filler is calcium carbonate .

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