JP5235487B2 - Method for producing inorganic particle-containing microporous membrane - Google Patents

Description

  The present invention relates to a method for producing an inorganic particle-containing microporous membrane and a storage battery separator comprising the inorganic particle-containing microporous membrane.

Microporous membranes have various pore diameters, pore shapes, and numbers of pores, and are used in a wide range of fields because of their characteristics that can be manifested by their unique structures. In storage batteries such as lithium ion secondary batteries and electric double layer capacitors, a porous film holding an electrolytic solution called a separator having a function of preventing contact between positive and negative electrodes and transmitting ions is provided between the positive and negative electrodes. . In recent years, with the intensification of performance competition for lithium ion secondary batteries, demands for polyolefin microporous membranes used as separators have become severe and widespread.
Under such circumstances, for example, Patent Document 1 discloses that an inorganic filler such as barium sulfate or calcium carbonate is 50 to 400 parts by mass, solid at 25 ° C. and has a boiling point with respect to 100 parts by mass of high-density polyethylene. A porous film containing 1 to 30 parts by mass of a normal temperature solid plasticizer at 140 ° C. or higher is disclosed.

JP 2005-343930 A

Here, with the recent increase in battery assembly speed, further improvement in the strength of the microporous membrane is required. By improving the strength, the film breakage at the time of battery assembly is reduced, and the yield is improved. Recently, in order to increase the capacity of batteries, it has been studied to reduce the thickness of the separator, and further improvement in strength is desired.
However, all of the conventional microporous membranes still have room for improvement in terms of tensile strength and tensile modulus of the microporous membrane. An object of the present invention is to provide a method for producing a microporous membrane having good tensile strength and good tensile modulus.

  As a result of repeated studies, the present inventors have melt-kneaded a resin composition containing a polyolefin resin, inorganic particles, and a plasticizer to form a sheet, and extracted the plasticizer to obtain a microporous film containing inorganic particles. In adopting a so-called wet method for producing a microporous membrane, it has been found that by using a specific plasticizer in combination, a microporous membrane having excellent tensile strength and tensile elastic modulus can be obtained, and the present invention has been achieved. It was.

That is, the present invention is as follows.
[1]
A method for producing a microporous membrane containing inorganic particles, in which a resin composition containing a polyolefin resin, inorganic particles and a plasticizer is melt-kneaded, formed into a sheet and biaxially stretched, and then the plasticizer is extracted to obtain a microporous membrane Because
The proportion of the inorganic particles in the total amount of polyolefin resin, inorganic particles, and plasticizer is 20
A plasticizer (I) having an SP value of 7.5 or more and less than 8.5, and a plasticizer (II) having an SP value of 8.5 or more and less than 9.9. mixed plasticizers der is, the production method of the inorganic particles-containing microporous membrane remaining ratio of the inorganic particles occupying in the microporous film after the plasticizer extraction and wherein 30 to 60% by mass Rukoto including.
[ 2 ]
The production method according to [ 1 ], wherein a proportion of the plasticizer (I) in the mixed plasticizer is 60 to 90% by mass.
[ 3 ]
The manufacturing method as described in [ 1 ] whose ratio which the said plasticizer (I) accounts in the said mixed plasticizer is 20-55 mass%.
[ 4 ]
The manufacturing method according to any one of claims [1] to [ 3 ], wherein the inorganic particles are silicon oxide. [ 5 ]
A storage battery separator comprising an inorganic particle-containing microporous membrane obtained by the production method according to any one of [1] to [ 4 ].

  The present invention can provide a method for producing a microporous membrane having good tensile strength and good tensile elastic modulus.

The best mode for carrying out the present invention (hereinafter abbreviated as “embodiment”) will be described in detail below. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.
The manufacturing method of the present embodiment is a method comprising melt-kneading a resin composition containing a polyolefin resin, inorganic particles, and a plasticizer to form a sheet, and extracting the plasticizer to obtain a microporous film. A method for producing a film, wherein the plasticizer is an plasticizer (I) having an SP value of 7.5 or more and less than 8.5, and a plasticizer (II) having an SP value of 8.5 or more and less than 9.9 And a mixture (mixed plasticizer).

The polyolefin resin refers to a polyolefin resin used for ordinary extrusion, injection, inflation, blow molding and the like, and includes ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Homopolymers and copolymers such as, multistage polymers and the like can be used. In addition, polyolefins selected from the group of these homopolymers, copolymers, and multistage polymers can be used alone or in combination. Representative examples of the polymer include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, polybutene, ethylene propylene rubber, and the like. These can be used alone or in combination. When the microporous membrane of the present embodiment is used as a storage battery separator, it is particularly preferable that the polyolefin resin contains high-density polyethylene from the viewpoint of realizing good fuse characteristics and good puncture strength.
Here, the proportion of the high-density polyethylene in the polyolefin resin is preferably 10 to 70% by mass, more preferably 15 to 65% by mass.

  The polyolefin resin or the microporous membrane preferably has a viscosity average molecular weight of 50,000 or more and less than 10 million. A viscosity average molecular weight of 50,000 or more is preferable because the melt tension at the time of melt molding is increased and the moldability is easily improved, and sufficient entanglement is easily imparted and the strength is easily increased. If the viscosity average molecular weight is less than 10 million, it tends to be easy to obtain uniform melt-kneading and is preferable because it tends to be excellent in sheet formability, particularly thickness stability. A more preferable viscosity region is 100,000 or more and less than 2 million, and further 500,000 or more and less than 1 million. If it is less than 2 million, melt kneading at a high polymer concentration tends to be easy and productivity improvement can be expected, and heat shrinkage tends to be reduced, which is preferable. For example, instead of using a polyolefin having a viscosity average molecular weight of less than 2 million alone, a mixture of polyethylene having a viscosity average molecular weight of 2 million and 270,000 may be used, and the viscosity average molecular weight of the mixture may be less than 2 million.

From the viewpoint of heat resistance, the polyolefin resin preferably contains polypropylene. In particular, it is preferable to use a mixture of high-density polyethylene and polypropylene from the viewpoint of improving both high puncture strength and heat resistance.
As a ratio for which a polypropylene accounts in the said polyolefin resin, Preferably it is 1-50 mass%, More preferably, it is 5-40 mass%, More preferably, it is 20-30 mass%. Setting the proportion to 1% by mass or more is preferable from the viewpoint of obtaining good heat resistance, and setting it to 50% by mass or less improves the stretchability and realizes high puncture strength of the microporous membrane. To preferred.

The plasticizer is preferably a non-volatile solvent capable of forming a uniform solution above the melting point of the polyolefin resin when mixed with the polyolefin resin. Moreover, it is preferably a liquid at normal temperature.
As a plasticizer (plasticizer (I)) having an SP value of 7.5 or more and less than 8.5, for example, liquid paraffin (abbreviated as “LP”, SP value 8.4), process oil, etc. Examples thereof include hydrocarbon oils such as mineral oil, xylene, and decalin. These can be used alone or in combination of two or more.
On the other hand, as a plasticizer (plasticizer (II)) having an SP value of 8.5 or more and less than 9.9, for example, dibutyl phthalate (“DBP”) may be abbreviated as SP value 9.4, melting point − 35 ° C.), di-2-ethylhexyl phthalate (may be abbreviated as “DOP”, SP value 8.9, melting point −55 ° C.) and the like, and dioctyl sebacate (“DOS”). A sebacic acid ester such as SP value 8.6, melting point −62 ° C., adipic acid ester such as dioctyl adipate (“DOA”, SP value 8.6, melting point −70 ° C.), Trioctyl trimellitic acid (sometimes abbreviated as “TOTM”, SP value 9.5, melting point −30 ° C.) and other trimellitic acid esters, trioctyl phosphate, (sometimes abbreviated as “TOP”, SP value) 9. , And phosphate with a melting point of -70 ° C.) and the like. These can be used alone or in combination of two or more.

  In particular, when the polyolefin resin is polyethylene, the combination of liquid paraffin and di-2-ethylhexyl phthalate is highly compatible with the mixture of polyethylene and inorganic particles, and the polyethylene and inorganic particles are plasticized during stretching. Since the interfacial peeling with the agent is unlikely to occur, uniform stretching is easy to implement, and is therefore preferable from the viewpoint of realizing a microporous film having high strength and high elastic modulus.

In the combination of the plasticizer (I) and the plasticizer (II), the proportion of the plasticizer (I) in the mixed plasticizer is preferably 10 to 90% by mass, more preferably 20 to 80%. % By mass. When the said mass fraction is 10 mass% or more, since there exists a tendency for dispersion | distribution of polyolefin resin and an inorganic particle to be performed, it is preferable. On the other hand, the content of 90% by mass or less is preferable because aggregation of inorganic particles hardly occurs and uniform stretching tends to be performed.
Here, from the viewpoint of improving the puncture strength of the obtained microporous membrane, the proportion of the plasticizer (I) in the mixed plasticizer is preferably 60 to 90% by mass, and more preferably 60 to 90%. 80% by mass.
On the other hand, from the viewpoint of improving the tensile elastic modulus of the obtained microporous membrane, the proportion of the plasticizer (I) in the mixed plasticizer is preferably 20 to 55% by mass, more preferably 25 to 50%. % By mass.

  The “SP value” as used in the present embodiment is a solubility parameter: a method described in Saburo Akiyama et al., Polymer Blends, page 125 to (published by CMC, 1981), Journal of Applied Chemistry 3rd by Small. It is a value calculated by the method of Volume 71-(1953).

In the manufacturing method of the present embodiment, inorganic particles are further blended with the above-described polyolefin resin and plasticizer. The inorganic particles are preferably inert to the polyolefin resin.
As the inorganic particles, inorganic particles having an electrical resistivity at room temperature of 10 ⁻² Ω · cm or more are preferable. More preferably, it is 10 ¹⁴ Ω · cm or more. The use of inorganic particles having an electrical resistivity of 10 ⁻² Ω · cm or more is preferable from the viewpoint of improving the electronic insulation between the electrodes when the microporous film is used as a separator for an electricity storage device.

More specifically, the inorganic particles are preferably oxides and nitrides such as silicon, aluminum, titanium, and magnesium, and carbonates and sulfates such as calcium and barium. These can be used alone or in combination of two or more. Silicon oxide is excellent in terms of weight reduction and cost reduction. In addition, aluminum oxide is excellent in chemical resistance, and particularly excellent in that it has low reactivity with hydrofluoric acid that may occur when used as a separator for nonaqueous batteries. Titanium oxide is excellent in that a highly permeable microporous film can be easily obtained.
Moreover, the inorganic particle which performed the surface treatment suitably can be used. For example, when producing microporous membranes for filtration applications using aqueous solvents and separators for aqueous electrolyte storage devices, hydrophilic particles are suitable, and separators for nonaqueous electrolyte storage devices are manufactured. In this case, inorganic particles that have been subjected to hydrophobic treatment are suitable.

The shape of the inorganic particles may be any shape such as a spherical shape, a rod shape, a needle shape, or a plate shape. From the viewpoint of heat resistance, a spherical shape, a rod shape, and a needle shape are preferable. The structure of the inorganic particles may be, for example, a porous structure, a layered structure, or a nonporous structure. A non-porous structure is preferred. The non-porous structure is a structure that does not substantially have an internal surface area inside the primary particles, that is, has substantially no fine pores in the primary particles themselves. The particles having substantially no fine pores in the primary particles themselves are particles having a porosity (P / S) in the range of 0.1 to 3.0. P / S is the ratio of the specific surface area P to the surface area S per unit weight calculated from the primary particle diameter D (unit: μm) and the density d (unit: g / cm ³ ) of the substance constituting the particles. is there. When the particles are spherical, the surface area per particle is πD ² × 10 ⁻¹² (unit: m ² ), and the weight of one particle is (πD ³ d / 6) × 10 ⁻¹² (unit). : G), the surface area S per unit weight is S = 6 / (Dd) (unit: m ² / g). The specific surface area P is obtained from a nitrogen adsorption isotherm at −196 ° C. based on the BET equation. When such particles are used, for example, when used as a separator for a non-aqueous electrolyte battery, there is a tendency that performance deterioration such as capacity reduction is difficult to occur. The reason is not clear, but if it does not substantially have fine pores inside the primary particles, it is easy to remove adsorbed water etc. in the normal drying process, so it is difficult to cause capacity reduction due to moisture mixing. Guessed. Furthermore, when particles having a nonporous structure are used for a microporous membrane containing a polyolefin resin, a microporous membrane excellent in heat resistance tends to be obtained.

  The particle size of the inorganic particles is preferably 1 nm or more and less than 200 nm, more preferably 6 nm or more and less than 100 nm, still more preferably 10 nm or more and less than 60 nm. The particle size can be measured with a scanning electron microscope or a transmission electron microscope. When the particle size is less than 200 nm, even when stretching or the like is performed, peeling between the polyolefin and the particles is difficult to occur, so that generation of macrovoids tends to be suppressed and high strength tends to be obtained. Further, since the particles are dispersed and fused in the polyolefin, the heat resistance tends to be excellent.

  The proportion of the inorganic particles in the total amount of the polyolefin resin, the inorganic particles, and the plasticizer is preferably 6% by mass or more and 55% by mass or less. More preferably, it is 7 mass% or more and 50 mass% or less, More preferably, it is 7 mass% or more and less than 45 mass%. When the content is 6% by mass or more, a microporous film having excellent heat resistance can be easily obtained in a microporous film containing a polyolefin resin. If it is 55 mass% or less, high intensity | strength will be easy to be obtained. Further, when used as a battery separator, the capacity is hardly lowered during high-temperature storage, and the reliability is excellent. In particular, when the content is 20% by mass or less, the tendency becomes remarkable, which is preferable.

  In addition, the polyolefin resin, if necessary, antioxidants such as phenolic, phosphorus and sulfur, metal soaps such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, Additives such as antifogging agents and coloring pigments can be mixed and used.

The manufacturing method of the present embodiment includes, for example, the following steps (1) to (4):
(1) a step of melt-kneading a resin composition containing a polyolefin resin, a plasticizer (I), a plasticizer (II), and inorganic particles;
(2) A step of forming a sheet from the melt-kneaded product obtained by the step (1) and cooling and solidifying it,
(3) A step of stretching the sheet obtained by the step (2) at least in a uniaxial direction with a surface magnification of 20 times or more and less than 100 times,
(4) A step of extracting a plasticizer from the stretched product obtained in the step (3) to produce a microporous membrane,
including.

In the step (1), the ratio of the plasticizer used is a ratio that enables uniform melt-kneading, is a ratio sufficient to form a sheet-like microporous membrane precursor, and is produced. It is preferable that it is a grade which does not impair property.
The proportion of the plasticizer in the total amount of the polyolefin resin, the plasticizer, and the inorganic particles is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass. When the plasticizer has a mass fraction of 80% by mass or less, the melt tension at the time of melt molding is hardly insufficient and the moldability tends to be improved, which is preferable. On the other hand, when the mass fraction is 30% by mass or more, it is preferable because the film becomes thinner in the thickness direction as the draw ratio increases and a thin film can be obtained. Further, since the plasticizing effect is sufficient, the crystalline folded lamellar crystals can be efficiently stretched. Even when stretched at a high magnification, the polyolefin chain is not broken and the pore structure is uniform and fine, and the strength is likely to increase.
A method of melt-kneading a polyolefin resin, inorganic particles, and a plasticizer is performed by introducing the mixture into a resin kneading apparatus such as an extruder or a kneader, and introducing a plasticizer at an arbitrary ratio while the resin is heated and melted. A method of obtaining a uniform solution by kneading a composition comprising inorganic particles and a plasticizer is preferred.

The step (2) is a step of manufacturing the microporous membrane precursor by transferring the melt-kneaded material, forming it into a sheet, and cooling and solidifying it. The process involves extruding a uniform solution of polyolefin resin, inorganic particles, and plasticizer into a sheet form through a T-die, etc., and contacting with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin. Preferably it is done. As the heat conductor used for cooling and solidification, metal, water, air, plasticizer itself, or the like can be used. In particular, a method of cooling by contacting with a metal roll has the highest heat conduction efficiency and is preferable. Further, it is more preferable that the metal roll is sandwiched between the rolls because the heat conduction efficiency is further increased, the sheet is oriented and the film strength is increased, and the surface smoothness of the sheet is also improved.
The die lip interval when extruding into a sheet form from a T die is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm. A die lip spacing of 400 μm or more is preferable because it reduces the meander and the like, has less influence on the film quality such as streaks and defects, and prevents film breakage in the subsequent stretching process. A thickness of 3000 μm or less is preferable because the cooling rate is high and uneven cooling can be prevented and the thickness stability can be maintained.

  In the step (3), the stretching direction is at least uniaxial stretching. When the film is stretched at a high magnification in the biaxial direction, it has a stable structure that is difficult to tear because of molecular orientation in the plane direction, and a high puncture strength is obtained. The stretching method may be simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, multiple stretching, etc., either alone or in combination, but if the stretching method is simultaneous biaxial stretching, the piercing strength is increased. And from the viewpoint of uniform film thickness. The term “simultaneous biaxial stretching” as used herein refers to stretching in the machine direction (or length direction, hereinafter abbreviated as “MD direction”) and TD direction (width direction, hereinafter abbreviated as “TD direction”). Is a method in which stretching is performed simultaneously, and the deformation rate in each direction may be different. Sequential biaxial stretching is a technique in which stretching in the MD direction or TD direction is performed independently. When stretching is performed in the MD direction or TD direction, the other direction is unconstrained or fixed. It is in a state of being fixed to the length.

The draw ratio is preferably in the range of 20 times to less than 100 times, more preferably 20 times to 80 times, and still more preferably 25 times to 50 times in terms of surface magnification.
The stretching ratio in each axial direction is preferably 4 to 10 times in the MD direction, preferably 4 to 10 times in the TD direction, 5 to 8 times in the MD direction, and 5 to 8 times in the TD direction. The range of is more preferable. When the total area magnification is 20 times or more, sufficient puncture strength can be imparted to the film, and when it is less than 100 times, film breakage is prevented and high productivity is obtained, which is preferable. When the film is stretched 4 times or more in the MD direction and 4 times or more in the TD direction, it is preferable because a product with small film thickness unevenness is easily obtained in both the MD direction and the TD direction. Ten times or less is preferable because the winding property tends to be excellent.

  Further, the stretching temperature is preferably a melting point temperature of polyolefin of −50 ° C. or higher and lower than the melting point temperature, more preferably a melting point temperature of polyolefin of −30 ° C. or higher, and a melting point temperature of −2 ° C. or lower, The melting point temperature is more preferably −3 ° C. or lower. When the melting point temperature of the polyolefin is −50 ° C. or higher, interfacial peeling between the polyolefin and the inorganic particles or between the polyolefin and the plasticizer hardly occurs, and the heat resistance tends to be excellent. Less than the melting point temperature of polyolefin is preferable because high puncture strength can be easily obtained and uneven stretching can be reduced. For example, when high density polyethylene is used, 110 ° C. or higher and 132 ° C. or lower is preferable. When a plurality of polyolefins are mixed and used, the melting point of the polyolefin having the larger heat of fusion may be used as a reference.

The step (4) may be performed before the step (3), but is preferably performed after the step (3) from the viewpoint of high piercing strength.
The method of extracting the plasticizer may be either a batch type or a continuous type. However, the plasticizer is extracted by immersing the microporous membrane in an extraction solvent and sufficiently dried, so that the plasticizer is substantially removed from the microporous membrane. It is preferable to remove. In order to suppress shrinkage of the microporous membrane, it is preferable to constrain the end of the microporous membrane during a series of steps of immersion and drying.
The residual amount of plasticizer in the microporous membrane after extraction is preferably less than 1% by mass.
Moreover, the residual ratio of the inorganic particles in the microporous membrane after extraction is preferably 15 to 85% by mass, more preferably 30 to 60% by mass.

  The extraction solvent is a poor solvent for the polyolefin resin and inorganic particles and a good solvent for the plasticizer, and it is desirable that the boiling point is lower than the melting point of the polyolefin microporous membrane. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane, halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane, and non-chlorine-based solvents such as hydrofluoroether and hydrofluorocarbon. Examples thereof include halogenated solvents, alcohols such as ethanol and isopropanol, ethers such as diethyl ether and tetrahydrofuran, and ketones such as acetone and methyl ethyl ketone.

In addition, when further extending | stretching after the process of (4), it is preferable that the draw ratio after extraction of a plasticizer shall be less than 4 times as a surface magnification, and more preferably less than 3 times. A surface magnification of less than 4 is preferable because generation of macrovoids and reduction in puncture strength can be suppressed.
In addition, it is preferable to carry out a heat treatment step such as heat setting or heat relaxation after the stretching because of the effect of further suppressing the shrinkage of the microporous membrane.
Furthermore, it is also possible to carry out post-treatments such as a hydrophilic treatment with a surfactant or the like, or a crosslinking treatment with ionizing radiation or the like within a range that does not impair the advantages of the present embodiment.

The final film thickness of the produced microporous film is preferably in the range of 2 μm to 100 μm, more preferably in the range of 5 μm to 80 μm, and still more preferably in the range of 10 μm to 50 μm. When the film thickness is 2 μm or more, the mechanical strength is sufficient, and when the film thickness is 100 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the capacity of the battery.
The porosity is preferably in the range of 25% to 90%, more preferably 40% to 80%, and still more preferably 50% to 80%. When the porosity is 25% or more, the permeability is hardly lowered, while when the porosity is 90% or less, there is little possibility of self-discharge when used as a battery separator, which is preferable. The porosity can be adjusted by adjusting the stretching temperature and stretching ratio in the step (3) and / or adjusting the temperature and the like in the step (5).

The air permeability of the produced microporous membrane is preferably in the range of 10 seconds to 1000 seconds, more preferably 20 seconds to 500 seconds, and still more preferably 40 seconds to 400 seconds. When the air permeability is 10 seconds or more, self-discharge is small when used as a battery separator, and when it is 1000 seconds or less, good charge / discharge characteristics are obtained, which is preferable. In addition, the said air permeability can be adjusted with the method etc. which adjust the temperature etc. of the process of said (5).
The puncture strength is preferably 1.2 N / 20 μm or more and 20 N / 20 μm or less, more preferably 2.0 N / 20 μm or more and 10 N / 20 μm or less, and further preferably 2.4 N / 20 μm or more and 6.0 N / 20 μm or less. . When the pin puncture strength is 1.2 N / 20 μm or more, when used as a battery separator, when wound together with the electrode, defects such as film breakage hardly occur and excellent winding property, and at 20 N / 20 μm or less, good heat resistance Is preferable. The piercing strength can be adjusted by a method of adjusting the polyethylene molecular weight, the ratio of the polyolefin resin, the stretching temperature and the stretching ratio in the step (3), and the like.

The tensile fracture strength of the produced microporous membrane is preferably in the range of 10 MPa to 200 MPa, more preferably 20 MPa to 150 MPa, and still more preferably 40 MPa to 130 MPa. When the tensile breaking strength is 10 MPa or more, when used as a battery separator, when wound together with the electrode, defects such as a film breakage hardly occur, and excellent winding resistance is obtained at 200 MPa or less. preferable. The tensile strength at break can be adjusted by a method of adjusting the polyethylene molecular weight, the ratio of the polyolefin resin, the stretching temperature and the stretching ratio in the step (3), and the like.
The tensile modulus is preferably in the range of 10 MPa to 600 MPa, more preferably 20 MPa to 550 MPa, and still more preferably 40 MPa to 500 MPa. When the tensile elastic modulus is 10 MPa or more, when used as a battery separator, when wound together with the electrode, defects such as a film breakage hardly occur and excellent winding properties. When the tensile elastic modulus is 600 MPa or less, there are problems such as winding tightening after winding. It is preferable because it hardly occurs. The tensile elastic modulus can be adjusted by a method of adjusting the polyethylene molecular weight, the ratio of the polyolefin resin, the stretching temperature and the stretching ratio in the step (3), and the like.

As mentioned above, according to this Embodiment, the manufacturing method of a microporous film which is excellent in tensile strength and a tensile elasticity modulus is provided. The high tensile strength and high tensile elastic modulus of the manufactured microporous membrane can improve the handleability at the time of winding, and thus can improve the productivity of the battery.
The microporous membrane obtained by the present embodiment is suitable as a separator for batteries, particularly for storage batteries such as non-aqueous electrolyte batteries.

  Next, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist. In addition, the physical property in an Example was measured with the following method.

(1) Viscosity average molecular weight (Mv)
Based on ASTM-D4020, the intrinsic viscosity [η] at 135 ° C. in a decalin solvent is determined. Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 ⁻⁴ Mv ^0.67

(2) Film thickness The film thickness was measured at a room temperature of 23 ± 2 ° C. using a micro thickness gauge manufactured by Toyo Seiki, KBM (trademark).

(3) Porosity A sample of 10 cm × 10 cm square was cut out from the microporous membrane, its volume (cm ³ ) and mass (g) were determined, and calculated from these and the film density (g / cm ³ ) using the following formula: did.
Porosity (%) = (volume-mass / density of mixed composition) / volume × 100
In addition, the value calculated | required by calculation from the density and mixing ratio of each used polyolefin resin and an inorganic particle was used for the density of a mixed composition.

(4) Air permeability It measured with the Gurley type air permeability meter (made by Toyo Seiki) based on JIS P-8117.

(5) Puncture strength Using Kato Tech, trademark, KES-G5 handy compression tester, a puncture test is performed under the conditions of a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm / sec. (N).

(6) Tensile modulus (MPa), tensile strength at break (MPa)
Based on JIS K7127, it measured about MD and TD sample (shape; width 10mm x length 100mm) using the tensile tester by Shimadzu Corporation, and autograph AG-A type (trademark). In addition, the sample had a chuck spacing of 50 mm.
The tensile elongation at break (%) was obtained by dividing the amount of elongation (mm) up to rupture by the distance between chucks (50 mm) and multiplying by 100.
The tensile strength at break (MPa) was determined by dividing the strength at break by the cross-sectional area of the sample before the test. The measurement was performed at a temperature of 23 ± 2 ° C., a chuck pressure of 0.30 MPa, and a tensile speed of 200 mm / min.
The tensile elastic modulus was evaluated by an inclination between 1 to 4% in elongation.

[Example 1]
28 parts by mass of ultra high molecular weight polyethylene “UH-850” (trademark manufactured by Asahi Kasei Chemicals Co., Ltd.) with a viscosity average molecular weight (Mv) of 2 million, high density polyethylene “SH-800” (trademark Asahi Kasei Chemicals Co., Ltd.) with a Mv of 270,000 Made of alumina (AluC) (trademark, manufactured by Degussa, hydrophobic treatment not performed, specific gravity 3.2 g / cm ³ ) 30 parts by mass, plasticizer with DOP and LP 150 parts by mass of the mixture (DOP / LP = 50/50 in mass ratio), 0 as pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant What was added at a ratio of 3 parts by mass was heated and mixed using a plast mill manufactured by Toyo Seiki Seisakusho. The heating and mixing were performed for 10 minutes with the temperature of the plastmill set to 200 ° C. and the rotation speed set to 50 rpm. The molten mixture was taken out from the plastmill and cooled, and the obtained solidified product was sandwiched between metal plates via a polyimide film, and compressed at 10 MPa using a hot press set at 200 ° C. to prepare a sheet having a thickness of 1000 μm. . The obtained sheet was simultaneously biaxially stretched 7 times in the longitudinal direction and 7 times in the transverse direction at 115 ° C. using a biaxial stretching machine manufactured by Iwamoto Seisakusho. Next, the plasticizer was removed in methylene chloride with the four sides fixed with a stainless steel frame, and then dried at room temperature to obtain a microporous membrane. Table 1 shows the film forming conditions and film characteristics.

Example 2 , Reference Examples 3 to 4, Example 5, Reference Examples 6 to 7 and Comparative Examples 1 to 9 were carried out in the same manner as Example 1 under the conditions described in Table 1. did. The results are shown in Table 1.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the inorganic particle containing microporous film which is excellent in tensile strength and a tensile elasticity modulus can be provided.

Claims (5)

A method for producing a microporous membrane containing inorganic particles, in which a resin composition containing a polyolefin resin, inorganic particles and a plasticizer is melt-kneaded, formed into a sheet and biaxially stretched, and then the plasticizer is extracted to obtain a microporous membrane Because
The proportion of the inorganic particles in the total amount of polyolefin resin, inorganic particles, and plasticizer is 20% by mass or less, and the plasticizer has a SP value of 7.5 or more and less than 8.5 (I ) and, Ri mixed plasticizer der containing a plasticizer SP value is less than 8.5 or more 9.9 (II), the residual ratio of the inorganic particles occupying in the microporous film after the plasticizer extraction 30 method of producing an inorganic particle-containing microporous membrane, wherein 60% by mass Rukoto. The manufacturing method according to claim 1, wherein a proportion of the plasticizer (I) in the mixed plasticizer is 60 to 90% by mass. The manufacturing method according to claim 1, wherein a proportion of the plasticizer (I) in the mixed plasticizer is 20 to 55 mass%. The method according to any one of claims 1 to 3 , wherein the inorganic particles are silicon oxide. The storage battery separator which consists of an inorganic particle containing microporous film obtained by the manufacturing method in any one of Claims 1-4 .