JP5311361B2 - Porous film, battery separator and battery - Google Patents

Description

  The present invention relates to a porous film, and can be used as packaging, sanitary, livestock, agricultural, architectural, medical, separation membrane, light diffusion plate, battery separator, and particularly as a separator for non-aqueous electrolytic battery. It can be used suitably.

Polymer porous film with many fine communication holes is used for separation membranes used for the production of ultrapure water, production of chemicals, water treatment, waterproof and moisture permeable films used for clothing and sanitary materials, batteries, etc. It is used in various fields such as battery separators.
Conventional small secondary batteries are widely used as power sources for portable electronic devices such as OA, FA, home appliances, communication devices, etc. Furthermore, when equipped with devices, they have good volumetric efficiency, making the devices smaller and lighter. Therefore, portable devices using lithium ion secondary batteries are increasing.
On the other hand, large secondary batteries are being researched and developed in many fields related to environmental issues such as load leveling, uninterruptible power supply (UPS), and electric vehicles, and have large capacity, high output, and high voltage. The use of lithium ion secondary batteries, which are a kind of non-aqueous electrolyte secondary battery, is expanding from the viewpoint of excellent long-term storage.

The working voltage of a lithium ion secondary battery is usually designed with an upper limit of 4.1 to 4.2V. At such a high voltage, the aqueous solution causes electrolysis and cannot be used as an electrolyte. Therefore, a so-called non-aqueous electrolyte using an organic solvent is used as an electrolyte that can withstand a high voltage.
As the solvent for the nonaqueous electrolyte, a high dielectric constant organic solvent capable of causing more lithium ions to be present is used, and organic carbonates such as polypropylene carbonate and ethylene carbonate are used as the high dielectric constant organic solvent. Yes. Further, as a supporting electrolyte that becomes a lithium ion source in a solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the solvent and used.

Since many combustible substances are used in the constituent materials of lithium ion secondary batteries, various measures are taken to prevent accidents such as ignition even if misused. In particular, since the separator is interposed between the positive electrode and the negative electrode in direct contact, insulation is required from the viewpoint of prevention of internal short circuit, and in order to provide air permeability and a function of diffusing and holding the electrolyte as a lithium ion passage, When the temperature is abnormally high (140 to 160 ° C.), the separator is melted, the micropores are closed, the ion conduction inside the battery is cut off, and it is required to have a shutdown function that can prevent the subsequent temperature rise inside the battery. The
From this viewpoint, a microporous film made of polyolefin resin is used as a separator. However, if the temperature continues to rise inside the battery for some reason after shutdown and exceeds the heat resistance temperature of the separator, the separator melts and the isolation between the electrodes is significantly reduced, which may cause a short circuit in the battery. There is.

In order to solve the above problems, an inorganic-containing porous membrane separator having excellent heat resistance made of a kneaded product made of polyolefin resin and inorganic powder or inorganic fiber is provided in JP-A-10-50287 (Patent Document 1). ing.
However, when manufacturing a porous film for a separator using polyolefin resin and inorganic powder as raw materials, primary processing for mixing the polyethylene resin and inorganic powder with a plasticizer and forming the mixture into a sheet, the sheet After performing secondary processing to provide pores by stretching, rolling, etc., it is necessary to extract and remove the plasticizer that is blended with an organic solvent. In this extraction process, a large amount of organic solvent is used. There is a problem that the number of processes increases and productivity is poor.

JP 2001-164015 A (Patent Document 2) provides a porous film made of a polypropylene resin, a filler, and an amide plasticizer.
However, polypropylene has a high melting point and is difficult to block at an abnormally high temperature, and a shutdown function cannot be expected. Therefore, although it can be used as a separator for a large-capacity battery system, it is not currently used as a separator for consumer batteries.
In addition, since polypropylene is used, it is difficult to form a film with uniform permeability, it is very easy to tear, and it is difficult and stable when winding the positive electrode, separator, and negative electrode in a spiral shape using a winding core. Battery cannot be manufactured.

Furthermore, JP-A-2003-82139 (Patent Document 3) includes a high-density polyethylene resin, a filler made of calcium carbonate, and the like, and a plasticizer of a low molecular weight compound such as an aliphatic hydrocarbon having a molecular weight of 200 to 500 or a higher alcohol. There is provided a porous film formed by forming a sheet from the kneaded product of the resin composition and stretching the sheet.
However, as a result of further trial by the inventor at the production machine level, it is difficult to manufacture continuously, and the thickness accuracy cannot be obtained by controlling the target accuracy. As a cause, in particular, when biaxial stretching is performed, there is a problem that only high-density polyethylene has poor spreadability. If the spreadability is not good, the separator made of the porous film to be produced has a low thickness accuracy and does not have a uniform thickness. In that case, when winding the positive electrode, separator and negative electrode in a spiral shape using a cylindrical, rhombus or flat core, etc., it cannot be stored in a predetermined size and cannot be accommodated in a battery can, There has been a problem that poor entrainment is likely to occur. Furthermore, even if it can be accommodated, pressure may be locally applied and a short circuit may occur.

Furthermore, since the separator made of any porous film of Patent Documents 1 to 3 has a low tensile strength of the olefin resin, the battery cannot be assembled at a high speed in a stable state at the time of winding, and the separator The separator is easily stretched, and the air permeability is changed so that the battery characteristics as designed cannot be obtained. Further, when the separator becomes thin due to elongation, there is a problem that the insulating property is lowered.
Japanese Patent Laid-Open No. 10-50287 JP 2001-164015 A JP 2003-82139 A

The present invention has been made in view of the above problems. In particular, the present invention provides a porous film that has excellent molding stability, has strength and tensile strength, is not easily torn in the winding process as a separator, is not easily stretched, and has good continuous productivity. To do. Further, it provided with a shutdown function at abnormally high temperature, and an object of the invention to provide a porous film suitable as a battery separator capable of the spreadability well thickness precision high rather uniform thickness.

As a result of intensive studies, the present inventors have found that a porous film or battery separator that can solve the above problems can be produced by stretching a composition comprising at least a polyethylene resin, polypropylene having a high melt tension and melting point , and a filler. The inventors have found that the battery using the same has good battery characteristics.

Based on the above findings, the present invention provides a polyethylene resin (A) having a density of 0.94 g / cm ³ or more, a melt tension of 3.0 gf or more, and a melting point of 20 ° C. or more than the melting point of the polyethylene resin (A). a resin component comprising a polypropylene resin (B) is a high rather and 140 ° C. or more ethylene-propylene copolymer, a film made of a resin composition comprising three components of the filler (C), the filler by stretching (C A porous film is provided, which is provided with pores starting from).

  By using the polyethylene resin (A) having a melting point different by 20 ° C. or more as the resin component and the polypropylene resin (B) having a melt tension of 3.0 gf or more as the resin component, when used as a battery separator, The temperature at which pinholes are generated is raised without increasing the (shutdown temperature) so much that a more safe separator can be provided.

With high-density polyethylene resin as the port Riechiren resin (A), the strength by a high density polyethylene resin itself, to increase the rigidity, also can be difficult to tear when a thin film, definitive during processing handling And the shutdown function can be enhanced.

The reason why the density of the high-density polyethylene resin is 0.940 g / cm ³ or more is to provide required strength and rigidity that do not easily tear even if the thickness is about 5 to 40 μm, for example. More preferably 0.950 g / cm ³ or more, the upper limit is 0.970 g / cm ^3. This high density polyethylene resin has a melt flow rate of 1 g / 10 min or less, preferably 0.6 g / 10 min or less, more preferably 0.1 g / 10 min or less. When the melt flow rate is greater than 1 g / 10 min, it becomes difficult to stretch 3 times or more, and the strength of the resulting porous film decreases. The lower limit is 0.01 g / 10 minutes.

Specifically, the high-density polyethylene resin is preferably a homopolymer polyethylene or a copolymer polyethylene having an α-olefin comonomer content of 2 mol% or less, and more preferably a homopolymer polyethylene. There is no restriction | limiting in particular in the kind of alpha-olefin comonomer. More preferably, 0.95 g / cm ³ or more is preferable from the viewpoint of the rigidity of the film.
The polymerization catalyst for polyethylene is not particularly limited, and any of a Ziegler type catalyst, a Philips type catalyst, a Kaminsky type catalyst or the like may be used. As a method for polymerizing polyethylene, there are one-stage polymerization, two-stage polymerization, or more multistage polymerization, and any method of polyethylene can be used.

As described above, the polypropylene resin (B) needs to have a melt tension of 3.0 gf or more. Preferably it is 5.0 gf or more, More preferably, it is 7.0 gf or more, Most preferably, it is 11-16 gf. The higher the melt tension, the better the upper limit is not limited, but it is about 20 gf.
As described above, melt tension is the addition of more polypropylene resin 3.0 g f, particularly molding stability of the film is greatly improved. Conversely, when the melt tension of the added polypropylene resin is less than 3.0 gf, the molding becomes unstable as compared with the case where a polypropylene resin having a melt tension of 3.0 gf or more is added. The accuracy becomes worse. Melt tension above 3.0 gf, the temperature of the melting point is with ethylene propylene copolymer is 140 ° C. or higher.
The melt tension was measured by setting a melt tension meter manufactured by Toyo Seiki Co., Ltd. at 190 ° C. Melt tension of the present invention, the speed 1.5 m / min take-off by using the melt tension meter, extrusion rate is a value measured at 4.5 mm / min.

  The blending ratio of the polyethylene resin (A) and the polypropylene resin (B) is selected depending on the types of the resins (A) and (B) and the use or physical properties of the obtained porous film, and the resin (A) 100 mass. The resin (B) is 1 to 100 parts by mass, preferably 1 to 50 parts by mass with respect to parts. In this way, the resin (B) having a melting point of 20 ° C. or higher is set to the same amount as that of the low melting point resin (A), preferably 50 parts by mass or less.

  The average particle size of the filler (C) is, for example, about 0.1 to 25 μm, preferably 0.3 μm or more, and more preferably about 0.5 μm. When the average particle size is less than 0.1 μm, the dispersibility decreases due to the aggregation of the fillers, causing stretching unevenness, and the contact area of the interface between the thermoplastic resin and the filling split increases, resulting in stretching. Interfacial peeling is difficult and porosity is likely to be difficult. On the other hand, if the average particle size exceeds 25 μm, it becomes difficult to make the film thin and uniform, and the mechanical strength of the film is remarkably lowered.

As the filler, any of inorganic and organic yarn fillers can be used, and one kind or a combination of two or more kinds can be used.
Examples of inorganic fillers include carbonates such as calcium carbonate, magnesium carbonate and barium carbonate, sulfates such as calcium sulfate, magnesium sulfate and barium sulfate, chlorides such as sodium chloride, calcium chloride and magnesium chloride, calcium oxide, In addition to oxides such as magnesium oxide, zinc oxide, titanium oxide, and silica, silicates such as talc, clay, and mica can be used. Among these, barium sulfate and calcium carbonate are preferable.

  The inorganic filler may be hydrophobized by coating the surface of the inorganic filler with a surface treatment agent in order to improve dispersibility in the resin. Examples of the surface treatment agent include higher fatty acids such as stearic acid and lauric acid, and metal salts thereof.

As the organic filler, resin particles higher than the melting point of the thermoplastic resin mainly composed of high-density polyethylene are preferable so that the filler does not melt at the stretching temperature, and crosslinked resin particles having a gel content of about 4 to 10%. Is more preferable.
Examples of organic fillers include ultra high molecular weight polyethylene, polystyrene, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polypropylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, poly Examples thereof include thermoplastic resins such as etherimide, melamine, and benzoguanamine, and thermosetting resins. Among these, cross-linked polystyrene and the like are particularly preferable.

The filler (C) is filled in a relatively large amount of 50 to 400 parts by weight with respect to a total of 100 parts by mass of the resins (A) and (B), and the amount of the filler (C) is small or Since the strength is relatively low as compared with the case where no filler is blended, it is important to sufficiently control the thickness and thickness accuracy. When the blending amount is 50 to 400 parts by mass, when the amount is less than 50 parts by weight, the desired good air permeability is hardly expressed, and the appearance and the texture are liable to deteriorate. On the other hand, when the amount exceeds 400 parts by weight, not only the process failure such as resin burning is likely to occur during film forming, but also the film strength is greatly reduced.
More preferably, the filler (C) is most preferably 50 to 300 parts by mass, and most preferably 100 to 200 parts by mass with respect to a total of 100 parts by mass of the resin components (A) and (B).

  The resins (A) and (B) and the filler (C) are essential components of the film. Furthermore, the purpose of improving the dispersibility of the filler (C) in the resin component when these raw materials are mixed and melted. Thus, a plasticizer (D) may be blended as necessary.

The kind and addition amount of the plasticizer (D) affect the moldability, stretchability, appearance, texture and the like of the film. The plasticizer is preferably a liquid or solid having a melting point of 25 ° C. or higher and lower than 140 ° C. and having a boiling point of 140 ° C. or higher.
When the melting point is not 25 ° C. or higher, the rigidity of the film is lowered, so there is no problem in applications that do not require film stiffness. However, when it is used as a porous film that requires film stiffness, such as a battery separator, handling in the battery assembly process becomes difficult. Here, the melting point is defined as having a clear endothermic peak as measured by DSC or having a kinematic viscosity of 100,000 mm2 / SEC or more.
On the other hand, if the plasticizer has a boiling point of 140 ° C. or higher, if the boiling point is lower than 140 ° C., the plasticizer volatilizes when the resin is heated at the time of stretching and large voids are generated, resulting in a porous structure having fine pores. This is because it cannot be formed as a conductive film. In addition, if the temperature becomes high for some reason after being accommodated as a separator in the battery, the plasticizer may gasify and the battery may burst, which is not preferable.
When the boiling point is 140 ° C. or higher, that is, below 140 ° C., the liquid or solid means that the boiling point is clearly 140 ° C. or higher in the atmosphere, or the weight after heating at 140 ° C. for 1 hour is based on the weight before heating It is defined as not decreasing more than 10%.

As the plasticizer in the present invention, the following plasticizers are used as long as the melting point is 25 ° C. or higher and the boiling point is 140 ° C. or higher.
Ester compound, amide compound long chain fatty acid, long chain alcohol, paraffin wax, amine compound, epoxy compound, ether compound, mineral oil, paraffin wax, long chain fatty acid salt long chain amine, liquid silicone, fluorine oil, liquid polyethers, liquid Examples include polybutenes, liquid polybutadienes, carboxylic acids, sulfonates, carboxylic acid compounds, fluorine compounds, and compounds having a sulfone bond.
Specifically, “Plastic compounding agent” (published by Taiseisha Co., Ltd., published on November 30, 1987, second edition) is described in the items of plasticizers P29 to P64. The plasticizers listed in Table 6 of ~ P54 can be used.
One plasticizer may be used alone, or two or more plasticizers may be combined.

Examples of the ester compound include tetraglycerin tristearate, glycerin tristearate, stearyl stearate, and distearyl carbonate. More preferred are esters or amides composed of saturated fatty acids, and still more preferred are plasticizers mainly composed of ethylene carbonate.
Examples of the amide compound include ethylene bis stearamide and hexamethylene bis stearamide.
Examples of the amine compound include dihydrodiethyl stearylamine and laurylamine.
Examples of the amine salt include stearyl dimethyl betaine or lauryl trimethyl ammonium chloride.
Examples of the long chain alcohol include stearyl alcohol, oleyl alcohol, and dodecylphenol.
Examples of the epoxy compound include epoxy soybean oil.
Examples of the ether compound include triethylene glycol.
Examples of the mineral oil include kerosene and naphthenic oil.
Examples of the carboxylate include calcium stearate and sodium oleate.
Examples of the sulfonate include sodium dodecylbenzenesulfonate.
Examples of the carboxylic acid compound include stearic acid or oleic acid, or derivatives thereof (excluding salts).
Examples of the compound having a sulfone bond include sulfolane and dipropylsulfonic acid.

  As a plasticizer used by this invention, the ester compound or amide compound which consists of saturated fatty acids is more preferable. In particular, in the present invention, a plasticizer mainly composed of ethylene carbonate is preferable as the plasticizer.

The blending ratio of the plasticizer is preferably 1 to 30 parts by mass with respect to 100 parts by mass of the polyethylene resin. A more preferable blending ratio is 1 to 20 parts by mass with respect to 100 parts by mass of the resin.
If the blending ratio of the plasticizer is less than 1 part by mass, the desired good stretchability is hardly expressed, and the appearance and the texture are liable to deteriorate. On the other hand, when the blending ratio of the plasticizer exceeds 30 parts by mass, it is easy to cause problems on the process such as resin burning during film forming.

  Furthermore, in the porous film of the present invention, additives generally blended in the resin composition, for example, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents. In addition, an antistatic agent, a slip agent, a colorant, and the like may be blended within a range that does not impair the characteristics of the porous film.

The porous film of the present invention, as described above, by molding the melt-kneaded product of the resin composition as a film, and set only the pores starting from the filler by stretching the molded film. When the porous film is used as a battery separator, the average thickness is 5 μm or more and 40 μm or less, and the maximum and minimum thicknesses are less than ± 25% of the average thickness, that is, the thickness fluctuation is less than ± 25%. Yes.
When the average thickness is less than 5 μm, the film tends to be torn, and when it exceeds 40 μm, the battery area becomes smaller and the battery capacity becomes smaller when wound into a predetermined battery can as a battery separator. Preferably it is 30 micrometers or less.
Further, the maximum value and the minimum value of the thickness are preferably ± 25% or less of the average thickness, and more preferably ± 20% or less. When the thickness fluctuation exceeds ± 25% of the average thickness, a partial pressure is applied when wound, and the insulating property is lowered when used as a battery separator.

  In addition, the average thickness of the said porous film is a value obtained by measuring 30 places unspecified in a surface with a 1/1000 mm dial gauge, and calculating the average. Moreover, the maximum value of the thickness refers to the largest value among the measured values at the 30 locations, and the minimum value of the thickness refers to the smallest value among the measured values at the 30 locations. The thickness fluctuation is a value calculated by the formula: {(maximum thickness or minimum thickness−average thickness) / average thickness} × 100 (%).

  The thickness of the porous film depends on the type or blending amount of the polyethylene resin (A), thermoplastic elastomer (B), filler (B) and plasticizer (D), and stretching conditions (stretching ratio, stretching temperature, etc.). It can be adjusted freely.

The porous film of the present invention is produced, for example, by the following method.
First, each component is mixed with a powder mixer such as a Henschel mixer, a super mixer, or a tumbler mixer. At this time, it is preferable that the polyethylene and the thermoplastic resin be in the form of powder or pellets, the filler is the powder, the plasticizer is the powder, and the stretching aid is in the form of a pellet.
Next, the mixture is heated and kneaded with a uniaxial or biaxial kneader or a kneader. Thereafter, it may be pelletized and transferred to a film forming step, or may be directly formed by a molding machine without being pelletized. The pellets may be temporarily stored in equipment or containers for storing raw materials such as silos and hopper flexible containers.

  In the present invention, the moisture content of the pellets is usually 1000 ppm or less, preferably 700 ppm or less, and melt-molded to form a film. This is because if the moisture content of the pellet is larger than 1000 ppm, gel and pinball are extremely generated, which is not preferable. On the other hand, when the molten mixture is directly taken to the film forming process without pelletization, vacuum degassing or open degassing is performed in the middle from the melt kneading process to the film forming process so that the moisture content of the molten mixture is 1000 ppm or less. Preferably it is done.

  Thereafter, a film (raw sheet) is obtained by melting and forming a film using an extruder or the like under a temperature condition that is higher than the melting point of polyethylene and polypropylene, preferably higher than the melting point + 20 ° C. and lower than the decomposition temperature. Specific examples of the film forming method include T-die molding, calendar molding, and press molding. The thickness of the film (raw fabric sheet) formed in this way can be selected as appropriate as long as the stretchability and the like are not impaired, but is preferably in the range of 0.02 to 2 mm.

The molded resin film (raw fabric sheet) is stretched in at least a uniaxial direction (uniaxial stretching) by a method such as roll stretching, tenter stretching, simultaneous biaxial stretching, and rolling, preferably in the film longitudinal direction (longitudinal direction). Is stretched (biaxial stretching) in the biaxial direction in the transverse direction. Such stretching treatment is preferably performed in the vicinity of the softening point of the resin (measured according to JIS K6760). A number of pores can be provided by peeling the interface between the resin and the filler by the above stretching. In addition, in order to stabilize an aperture diameter, you may heat-process after extending | stretching.
The stretching ratio in the stretching step may be appropriately selected in accordance with the film breakage during stretching, the air permeability of the obtained film, the hardness of the film, or the like. Specifically, in uniaxial stretching or biaxial stretching, at least one direction in the longitudinal and transverse directions is stretched 1.5 times or more, preferably 2 times or more.

The pores formed by stretching the porous film have a three-dimensional network shape and are communicated with the opening on both sides of the film to form a battery separator. Gas or water vapor can be transmitted and liquid droplets cannot be transmitted. . Specifically, the pore diameter is set to 0.3 μm or less, water droplets of 100 to 3000 μm are not transmitted, and water vapor of about 0.0004 μm can be transmitted.
More specifically, the porous film of the present invention preferably has an air permeability of 50 to 500 (sec / 100 cc), more preferably 100 to 500 (sec / 100 cc), More preferably, it is 300 (sec / 100 cc).
When the air permeability is 50 to 500 (sec / 100 cc), if it is less than 50 (sec / 100 cc), the impregnation / retention property of the electrolyte is lowered and the capacity of the secondary battery is lowered, or the cycle property is reduced. May decrease. On the other hand, if the air permeability exceeds 500 (sec / 100 cc), the ion conductivity becomes low, and sufficient battery characteristics cannot be obtained when used as a separator for a nonaqueous electrolyte battery.
In addition, the said air permeability (Gurley value) has measured the air permeability (sec / 100cc) based on JISP8117.

When the porous form of the present invention is used as a battery separator, the porous form of the present invention is usually interposed between a positive electrode and a negative electrode and wound into a spiral shape and stored in a battery can.
In the present invention, the entrainment defect rate at this time is set to 5% or less, the handling property is good in the battery assembling process, the occurrence rate of defective products is reduced, and it is more suitable for industrial production. In addition, the entrainment defect rate is measured by the method described in Examples described later.
Furthermore, the film of the present invention does not become longer than 10 mm with respect to the initial specified length, that is, it can suppress elongation, and as a result, can be maintained at a required thickness without causing a short circuit between electrodes, and has excellent entrainment characteristics. It becomes.

  Furthermore, the non-aqueous electrolyte battery containing the separator made of the porous film of the present invention closes the fine holes opened in the separator when in a high temperature (140 to 160 ° C.) state from the viewpoint of safety, As a result, there is a need for a shutdown function that blocks ion conduction inside the battery and prevents subsequent temperature rise inside the battery. As an index of this function, the non-aqueous electrolyte battery of the present invention has an insulation failure rate after temperature rise of less than 5%. In addition, the insulation defect rate after temperature rising is measured by the method as described in the Example mentioned later.

As described above, since the porous film of the present invention contains a polyethylene resin, it can exhibit an excellent shutdown function in a high temperature state when used in a non-aqueous electrolyte battery separator. Furthermore, since the porous film of the present invention is blended with polypropylene having a high melt tension, the spreadability is good, the thickness accuracy is increased during stretching, and a film having a uniform thickness can be obtained.
Therefore, when the battery separator is interposed between the positive electrode plate and the negative electrode plate and wound in a spiral shape and accommodated in the battery can, it is possible to prevent the separator from being locally loaded, thereby preventing the separator from being damaged. Insulating properties can be reliably maintained. And since the thickness of the separator is made as thin as 40 μm or less, the filling amount of the positive electrode plate and the negative electrode plate into the battery can can be increased, and the battery capacity can be increased.

Furthermore, since the porous film of the present invention has the required strength and rigidity and has a small elongation, it is difficult to tear when wound as a separator, and it is easy to wind up and increase productivity, and even after winding. The insulation between the electrodes can be increased with a required thickness.
In addition, a stretching method is employed to provide a fine pore structure that maintains appropriate air permeability, and the manufacturing cost can be reduced.
Moreover, the physical properties of the porous film of the present invention can be freely adjusted by the blending amount and type of resin, filler and plasticizer, and stretching conditions (stretching ratio, stretching temperature, etc.). Therefore, a porous film having desired physical properties according to the application can be obtained by variously changing the conditions.

Hereinafter, the present invention will be specifically described based on examples.
FIG. 1 is a schematic cross-sectional view of a porous film. The porous film 1 includes three-dimensional network-like pores 1a, and the pores 1a communicate with both surfaces 1b and 1c of the porous film. The temperament is in the range of 50 to 500 [sec / 100 cc].
The thickness of the porous film 1a is 5 to 40 μm, and the thickness fluctuation is less than ± 25% of the average thickness.

The porous film uses, as a resin component, a high density polyethylene having a density of 0.95 g / cm ³ or more and a melt flow rate of 1.5 g / 10 min or less and a polypropylene having a melt tension of 3.0 gf or more, using barium sulfate particle size 0.1~25μm as a filler, with a melting point as a plasticizer is 25 ° C. or higher and a boiling point of 140 ° C. or higher, propylene carbonate kinematic viscosity at 25 ° C. of less than 100,000 mm ² / S, Bed Ji Ren carbonate, .gamma. butyrolactone, are used .gamma.-valerolactone or Jimechirusu sulfo Kishido.

  The blending ratio of the resin is 1 to 50 masses of polypropylene with respect to 100 mass parts of high density polyethylene. The filler is 50 to 400 parts by mass and the plasticizer is 1 to 30 parts by mass with respect to 100 parts by mass in total of high-density polyethylene and polypropylene.

The above raw materials are mixed and kneaded to disperse the filler in the resin. The kneaded material is heated and melted at a required temperature, and then molded with a T-die to form a film. The thickness of the obtained film is 0.02 to 2 mm.
This film is stretched by 1.5 times or more in any one of the longitudinal and transverse length directions with a biaxial stretching machine. Specifically, the film is stretched at a stretch ratio of 4 to 4.5 times in the longitudinal direction (longitudinal direction), and then stretched at a stretch ratio of 4 to 4.5 times in the direction perpendicular to the longitudinal direction (transverse direction). .
The film 10 in which the filler 12 is dispersed in the resin 11 made of high-density polyethylene and polypropylene as shown in FIG. Peeling occurs at the interface, and the porous film 1 is obtained using the peeled portion as the pore 1a. In that case, the thickness of the porous film 1 is 5-40 micrometers as above-mentioned, and the fluctuation | variation of thickness is less than +/- 25%.
The porous film 1 is obtained as a continuous material by continuously biaxially stretching a film 10 made of a continuous material, and is wound in a coil shape.

In the present embodiment, the obtained porous film 1 is cut into a required length to form a separator 1 ′ for a nonaqueous electrolyte battery.
The separator 1 ′ is housed inside the cylindrical lithium secondary battery 20 shown in FIG. 3 by being interposed between the positive electrode plate 21 and the negative electrode plate 22 and spirally wound.

The lithium secondary battery containing the porous film of the present invention as a separator will be described in detail.
As the electrolyte, for example, an electrolyte in which a lithium salt is used as an electrolyte and is dissolved in an organic solvent is used. As the organic solvent, is not particularly limited, for example, propylene carbonate, ethylene carbonate, blanking Ji Ren carbonate, .gamma. butyrolactone, .gamma.-valerolactone, dimethyl carbonate, methyl propionate, esters such as acetic Bed Chill Nitrites such as acetonitrile, ethers such as 1,2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyl-1,3-dioxolane news alone such Sulf O orchids, or a mixed solvent of two or more can be used.

As the negative electrode, a material in which an alkali metal or a compound containing an alkali metal is integrated with a current collecting material such as a stainless copper net is used. At that time, examples of the alkali metal include lithium, sodium, and potassium.
Examples of the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin and magnesium, a compound of an alkali metal and a carbon material, a low potential alkali metal and a metal oxide, and the like. And compounds with sulfides.
When a carbon material is used for the negative electrode, the carbon material may be any material that can be doped and dedoped with lithium ions. For example, graphite, pyrolytic carbons, cokes, glassy carbons, and firing organic polymer compounds Bodies, mesocarbon microbeads, carbon fibers, activated carbon, and the like can be used.

  As the positive electrode, for example, a metal oxide such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, vanadium pentoxide, or chromium oxide, or a metal nitride such as molybdenum disulfide is used as an active material. Used. A mixture obtained by appropriately adding a conductive additive or a binder such as polytetrafluoroethylene to these positive electrode active materials and using a current collector material such as a stainless steel net as a core material is used.

In the battery used for measuring the insulation failure rate of the separator made of the porous film of the present invention to be described later, the electrolyte is 1.4 parts of L1PF6 in a mixed solvent of 2 parts by weight of methyl ethyl carbonate with respect to 1 part by weight of ethylene carbonate. The dissolved electrolyte is adjusted at a mole / liter ratio.
The negative electrode plate 22 was made into a slurry by mixing a carbon material having an average particle diameter of 10 μm with a solution in which vinylidene fluoride was dissolved in N-methylpyrrolidone. This negative electrode mixture slurry was passed through a 70-mesh net to remove large particles, and then uniformly applied to both sides of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm and dried. A belt-shaped negative electrode plate is formed by compression molding and cutting with a machine.
The positive electrode plate 21 is prepared by adding and mixing lithium graphite oxide (LiCoO ₂ ) as a conductive additive in a weight ratio of 90: 5 and mixing this mixture and polyvinylidene fluoride in N-methylpyrrolidone. Were mixed into a slurry. This positive electrode mixture slurry was passed through a 70 mesh net to remove a large one, and then uniformly applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm and dried. After compression molding, it is cut into a strip-like positive electrode plate.

  Both electrodes of the positive electrode plate 21 and the negative electrode plate 22 are wound in a spiral shape so as to overlap each other via the separator 1 ′, and the outside is stopped by a winding tape to form a wound body. When wound in this spiral shape, the separator 1 ′ has a thickness of 5 to 30 μm.

  A wound body in which the positive electrode plate 21, the separator 1 ′ and the negative electrode plate 22 are integrally wound is filled in a bottomed cylindrical battery case and welded to the positive and negative electrode lead bodies 24 and 25. The wound positive electrode plate 21, separator 1 ′ and negative electrode plate 21 are accommodated in a battery case, and then the electrolyte is injected into the battery can so that the electrolyte sufficiently permeates the separator 1 ′ and the like. A positive electrode lid 27 is sealed around the periphery of the opening via a gasket 26, and precharging and aging are performed to produce a cylindrical secondary lithium battery.

  Since the separator made of the porous film 1 has insulating properties, it prevents a short circuit between the positive electrode plate 21 and the negative electrode plate 22 that are in direct contact with both surfaces, and lithium ions permeate the pores 1a but do not allow liquid to permeate. Therefore, the electrolyte can be diffused and retained.

Example consisting of porous film of the present invention, as a comparative example, to produce a film consisting of the raw material and compounding ratios shown in Table 1 below, to prepare a porous film by stretching the film, the air permeability time, shutdown temperature, rupture temperature, winding-out write-failure rate (tearing easiness) to measure the insulation failure rate after heating.

"Example 1"
High-density polyethylene [Sumitomo Mitsui Polyolefin Co., Ltd. 7000FP, density 0.954 g / cm ³ , melt flow rate 0.04 g / 10 min] 100 parts by mass, polypropylene [Dow Chemical Co., Ltd. Inspire 114 density 0.90 g / cm ³ , Melt flow rate 0.4 g / 10 min, melt tension 11.1 gf] 8 parts by mass, filler barium sulfate [B-55, manufactured by Sakai Chemical Co., Ltd.] 176 parts by weight, plasticizer [Hicaster Wax Toyokuni Seiyaku HCOP , Melting point 86 ° C., weight loss rate after heating at 140 ° C. for 1 hour is 2.4%] blended as 9 parts by weight, compounded, then T-die molded at 200 ° C. to obtain a raw sheet . The thickness of the original fabric sheet was 80 μm on average.
Next, the obtained raw sheet is stretched 4.5 times in the longitudinal direction (MD) of the sheet at 60 ° C. to produce a porous film having an average thickness of 22 μm, a thickness accuracy of ± 12%, and an air permeability of 410 sec / 100 cc. did.

"Example 2"
The same composition as in Example 1 was blended and compounded, and then T-die molding was performed at a temperature of 200 ° C. to obtain an original sheet. The thickness of the original fabric sheet was 150 μm on average.
Next, the obtained raw fabric sheet was stretched 4.0 times in the longitudinal direction (MD) of the sheet at 60 ° C., and then stretched 3.5 times in the orthogonal TD direction, and the thickness average after stretching was 18 μm, thickness A porous film having an accuracy of ± 10% and an air permeability of 150 sec / 100 cc was produced.

"Example 3"
High-density polyethylene [Sumitomo Mitsui Polyolefin Co., Ltd. 7000FP, density 0.954 g / cm ³ , melt flow rate 0.04 g / 10 min] 100 parts by mass, polypropylene [CHISSO Corporation NEWSTREN SH9000 density 0.90 g / cm ³ , melt Flow rate 0.3 g / 10 min, melt tension 15.2 gf] 10 parts by mass, as filler, barium sulfate [B-55, manufactured by Sakai Chemical Co., Ltd.] 115 parts by weight, as plasticizer [HICASTER wax HCOP manufactured by Toyokuni Seiyaku Co., Ltd., The melting point was 86 ° C., 140 ° C., and the weight reduction rate after heating for 1 hour was 2.4%. Blending was carried out at 5 parts by weight, and then T-die molding was performed at a temperature of 200 ° C. to obtain a raw sheet. The thickness of the original fabric sheet was 130 μm on average.
Next, the obtained raw sheet is stretched 3.5 times in the longitudinal direction (MD) of the sheet at 60 ° C., and then 2.8 times in the TD direction. The thickness average is 22 μm, the thickness accuracy is ± 7%, and the transparent A porous film having a tempering of 260 sec / 100 cc was produced.

“Comparative Example 1”
High-density polyethylene [HY430P manufactured by Nippon Polychem Co., Ltd., density: 0.955 g / cm ³ , melt flow rate: 0.8 g / 10 min] to 100 parts by mass, barium sulfate [B-55, manufactured by Sakai Chemical Co., Ltd.] 150 parts by weight , Glycerin tristilate as a plasticizer [manufactured by Wako Pure Chemical Industries, Ltd., reagent melting point: 72 ° C., weight loss rate after heating at 140 ° C. for 1 hour: 1.1%] Then, T-die molding was performed at a temperature of 200 ° C. to obtain a raw sheet. The thickness of the original fabric sheet was 100 μm on average.
Next, the obtained raw sheet is stretched 5.0 times in the longitudinal direction (MD) of the sheet at 80 ° C. to produce a porous film having a thickness average of 16 μm, a thickness accuracy of ± 10%, and an air permeability of 190 sec / 100 cc. did.

“Comparative Example 2”
High-density polyethylene [Sumitomo Mitsui Polyolefin Co., Ltd. 7000FP, density 0.954 g / cm ^3, a melt flow rate 0.04 g / 10min] 100 parts by weight, polypropylene peak Len [manufactured by Japan Polychem Corporation EG7F density 0.90 g / ^cm 3, Melt flow rate 1.3 g / 10 min, melt tension 2.65 gf] 10 parts by mass, 137 parts by weight of barium sulfate [B-55, manufactured by Sakai Chemical Co., Ltd.] as a filler, and HCOP manufactured by Hicaster Wax Toyokusei Seiyaku Co., Ltd. , Melting point 86 ° C., weight loss rate after heating at 140 ° C. for 1 hour is 2.4%] blended as 9 parts by weight, compounded, then T-die molded at 200 ° C. to obtain a raw sheet . The thickness of the original fabric sheet was 120 μm on average.
Next, the obtained raw sheet is stretched 4.5 times in the longitudinal direction (MD) of the sheet at 60 ° C., and then 3.5 times in the TD direction. The thickness average is 16 μm, and the thickness accuracy is ± 21%. A porous film having an air permeability of 260 sec / 100 cc was produced.

The thickness of the porous film was determined by measuring 30 in-plane thicknesses with a 1/1000 mm dial gauge unspecified, and calculating the average value.
Thickness accuracy (thickness runout) is calculated based on the following equation based on the following equation from the maximum value (maximum thickness), the minimum value (minimum thickness) and the calculated average value among the 30 measured values measured by the above measurement method. Calculated. Of the values calculated by the following equation, the one with the larger absolute value is described.
(Maximum thickness-average thickness) / average thickness x 100 (%)
(Minimum thickness-average thickness) / average thickness x 100 (%)
For the air permeability, the air permeability (seconds / 100 cc) was measured in accordance with JIS P 8117.

  The porous films of Examples 1 to 3 and Comparative Examples 1 and 2 were used as battery separators, and the entanglement failure rate, the insulation insulating rate after temperature rise, the shutdown temperature, and the membrane breaking temperature when mounted on the battery were measured.

(Measurement of entrainment defect rate)
Using a positive electrode plate and a negative electrode plate having a length of 50 cm and a width of 59 mm, using two separators made of the porous films of the above examples and comparative examples, the two separators, the positive electrode plate, and the negative electrode plate are alternately stacked. Metal core with 3.92 N / cm applied to the plate, 3.92 N / cm applied to the negative electrode plate, 0.29 N / cm applied to the separator, and a slit 4 mm in diameter and sandwiching two separators. Was wound around the core so as to wind it. After completion, the metal core was pulled out.
100 of the above-mentioned entrained electrode groups were made, and the number of the separators that were torn was confirmed. The number of separators that were torn was set to x, and the winding failure rate was set to x%.

(Insulation after temperature rise)
The above-mentioned 100 electrode groups were heated at a rate of 10 ° C./min, put in an oven at 60 ° C. for 1 hour, measured the insulation resistance between the positive and negative electrodes, counted as 1 MΩ or less, and expressed in%. When this ratio is large, the initial failure rate as a battery increases.

(Shutdown temperature)
The porous film was sandwiched between aluminum plates with holes of 100 mmφ, left in an oven for 2 minutes, and the air permeability was measured. The oven temperature of 3000 seconds / 100 cc or higher was taken as the shutdown temperature. If this temperature is higher than 140 ° C., when incorporated in a battery, the permeability of the porous film does not drop even if the temperature rises abnormally during charge and discharge, and there is a risk of smoke and fire.

(Bearing temperature)
Cut out the porous film at 80 mm square. The cut out 80 mm square film is sandwiched between two 80 mm square aluminum plates with a 40 mmφ hole in the center, and the aluminum plate is fixed with clips. Open the oven set at 200 ° C and lower the temperature to 100 ° C, then put the film sandwiched between aluminum plates into the oven and close the door. The film was observed, and the display temperature when pinholes occurred was defined as the film breaking temperature.

As shown in Table 1, the porous films of Examples 1-3, the insulation failure rate after Atsushi Nobori is not more than 1% Comparative Example 1, 5% not blended polypropylene pin Ren, polypropylene Pi Ren In Comparative Example 2 where the melt tension was as low as 2.65 gf, it was 3%. In addition, the winding failure rate was 2 to 5% in Examples 1 to 3, and the failure rate could be kept low, but in Comparative Example 1, it was as high as 15% and in Comparative Example 2 was also 8%. The handling at the time was worse. The film breaking temperature was also low at 145 ° C. in Comparative Example 1, and the separator was easily broken during abnormal heating. In contrast, Examples 1 to 3 were confirmed to have heat resistance of 177 to 181 ° C.

  The porous film according to the present invention can be used for various applications such as packaging, hygiene, livestock, agriculture, construction, medical, separation membrane, light diffusion plate, battery separator, etc. It can be suitably used as an electrolyte battery separator, and a good nonaqueous electrolyte battery can be obtained.

It is a cross-sectional schematic diagram of the said porous film. It is explanatory drawing which shows the method in which the hole by extending | stretching is formed. It is a partially broken perspective view which shows the separator in a battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous film 1a Hole 1 'Separator 10 Film 11 Resin 12 Filler 20 Battery 21 Positive electrode plate 22 Negative electrode plate

Claims (10)

Density polyethylene resin (A) is 0.94 g / cm ³ or more, the melt tension of not less than 3.0 gf, the melting point is above the high rather and 140 ° C. 20 ° C. or higher than the melting point of the polyethylene resin (A) ethylene-propylene A film made of a resin composition comprising a resin component comprising a polypropylene resin (B) as a copolymer and three components of a filler (C), and provided with pores starting from the filler (C) by stretching. A porous film characterized by being made. The porous film according to claim 1, wherein the polypropylene resin (B) is 1 to 50 parts by mass with respect to 100 parts by mass of the polyethylene resin (A) . Porous film of the filler (C) is placing serial to claim 1 or claim 2 which is an inorganic filler. The filler (C) is calcium carbonate and / or barium sulfate having an average particle size of 0.1 to 50 μm, and the filler (C) is added to 100 parts by mass of the resin (A) and the resin (B) in total. The porous film according to any one of claims 1 to 3, wherein 50 to 400 parts by mass are blended . The porous film according to any one of claims 1 to 4, wherein a plasticizer (D) is added . The plasticizer (D) is liquid or solid at 0 ° C., and the plasticizer (D) is added in an amount of 1 part by mass or more and 30 parts by mass with respect to 100 parts by mass in total of the polyethylene resin (A) and the polypropylene resin (B). The porous film according to claim 5 , which is added in an amount of not more than part by mass . The porous film according to claim 5 or 6, wherein the plasticizer (D) is a plasticizer having a melting point of 25 ° C or higher and lower than 140 ° C that is liquid or solid and has a boiling point of 140 ° C or higher . The porous film according to any one of claims 1 to 7, wherein the stretching is uniaxial stretching or biaxial stretching and is stretched 1.5 times or more in at least one direction . It consists of the porous film of any one of Claim 1 thru | or 8, It is 5-40 micrometers in average thickness, The thickness of the maximum value of thickness and the minimum value is ± 25% or less of average thickness. A battery separator comprising a porous film as a constituent element . A battery using the battery separator according to claim 9.

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