JP2011210573A - Separator for nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of manufacturing a nonaqueous secondary battery stably in an assembly process of the battery, when the separator for nonaqueous secondary battery with a heat-resistant porous layer laminated on the base material is used.SOLUTION: The separator for the nonaqueous secondary battery is provided with a polyolefin porous base material and a heat resistant porous layer which is formed by including a heat resistant resin and is laminated on one side or both sides of the porous base material. The ratio of the tensile strength Sin machine direction to the tensile strength Sin machine vertical direction is 2≤S/S≤8.

Description

  The present invention relates to a separator used for a non-aqueous secondary battery. Specifically, the present invention relates to a separator that improves the safety of a non-aqueous secondary battery.

  Non-aqueous secondary batteries typified by lithium ion secondary batteries are widely used as main power sources for portable electronic devices such as mobile phones and notebook computers. In such a lithium ion secondary battery, technological development has been advanced to achieve further higher energy density, higher capacity, and higher output, and this demand is expected to increase further in the future. In order to meet such demands, technology for ensuring a high level of battery safety has become even more important.

  Generally, a microporous film made of polyethylene or polypropylene is used for a separator of a lithium ion secondary battery. This separator has a function called a shutdown function for the purpose of ensuring the safety of the lithium ion secondary battery. This shutdown function refers to a function in which the resistance increases remarkably when the battery temperature rises and reaches a certain temperature. With this shutdown function, when the battery generates heat for some reason, the current can be cut off, further heat generation of the battery can be prevented, and smoke, fire, and explosion can be prevented. Such a shutdown function is based on the operating principle that the material constituting the separator is melted and deformed to close the holes of the separator. Therefore, in the case of a separator made of polyethylene, the shutdown function operates at around 140 ° C. near the melting point of polyethylene, and in the case of polypropylene, this function operates at about 165 ° C. This shutdown function preferably operates at a relatively low temperature from the viewpoint of ensuring the safety of the battery, and polyethylene is generally used for this reason.

  On the other hand, a separator of a lithium ion secondary battery is required to have sufficient heat resistance in addition to a shutdown function. The reason is as follows. In a conventional separator made of only a microporous membrane such as polyethylene, after the shutdown function is activated, the battery continues to be exposed to a temperature higher than the temperature at which the shutdown function is activated, so that the separator is melted (so-called meltdown). End up. This is natural when considering the principle of the shutdown function. As a result of this meltdown, a short circuit occurs inside the battery, and a large amount of heat is generated along with this, so that the battery is exposed to dangers of smoke, ignition, and explosion. For this reason, in addition to the shutdown function, the separator is required to have sufficient heat resistance that does not cause meltdown in the vicinity of the temperature at which the shutdown function operates.

  Here, conventionally, in order to impart both a shutdown function and heat resistance to the separator, a separator having a polyethylene microporous film coated with a porous layer made of a heat-resistant resin such as polyimide or aromatic polyamide has been proposed ( For example, see Patent Documents 1 and 2). In such a separator, the shutdown function operates in the vicinity of the melting point of polyethylene (about 140 ° C.), and the heat-resistant porous layer exhibits sufficient heat resistance, so that no melt down occurs at 180 ° C. or higher.

  However, such a non-aqueous secondary battery separator is wound with a tension when a non-aqueous secondary battery is produced by sandwiching the separator between the positive electrode and the negative electrode. The separator is deformed with respect to the machine direction and the machine vertical direction. And depending on the balance of the deformation of the separator, there is a possibility that the separator may be greatly deformed or damaged, so that the processability in the battery assembling process can be improved and the non-aqueous secondary battery can be more stably manufactured. Technology was desired.

International Publication No. 2008/062727 Pamphlet International Publication No. 2008/156033 Pamphlet

  The present invention provides a technique capable of stably producing a non-aqueous secondary battery in a battery assembly process when a non-aqueous secondary battery separator having a heat-resistant porous layer laminated on a substrate is used. Objective.

As a result of intensive studies to solve the above problems, the present inventors have found that the problem can be solved by the following configuration, and have reached the present invention. That is, the present invention adopts the following configuration.
1. A separator for a non-aqueous secondary battery comprising a polyolefin porous substrate and a heat-resistant porous layer formed by containing a heat-resistant resin and laminated on one or both surfaces of the porous substrate, the ratio of the tensile strength in the machine direction of the separator S _MD and machine vertical tensile strength S _TD is, 2 ≦ S _{MD /} S nonaqueous secondary battery separator, which is a _TD ≦ 8.
2. 2. The separator for a non-aqueous secondary battery according to 1 above, wherein the heat resistant resin is a meta-type wholly aromatic polyamide or para-type wholly aromatic polyamide.
3. 3. The separator for a non-aqueous secondary battery according to 1 or 2 above, wherein the heat-resistant porous layer contains an inorganic filler.
4). 4. The nonaqueous secondary battery according to 3 above, wherein the inorganic filler is at least one selected from metal oxide, metal carbonate, metal sulfate, metal phosphate, and metal hydroxide. Separator for use.

  ADVANTAGE OF THE INVENTION According to this invention, when the separator for non-aqueous secondary batteries by which the heat resistant porous layer was laminated | stacked on the base material is used, the technique which can produce a non-aqueous secondary battery stably in a battery assembly process is provided. be able to. According to the present invention, it is possible to efficiently produce a non-aqueous secondary battery excellent in safety.

Hereinafter, embodiments of the present invention will be sequentially described. In addition, these description and Examples illustrate this invention, and do not restrict | limit the scope of the present invention.
[Separator for non-aqueous secondary battery]
A separator for a non-aqueous secondary battery according to the present invention includes a polyolefin porous substrate and a heat-resistant porous layer formed by including a heat-resistant resin and laminated on one or both surfaces of the porous substrate. a separator for a nonaqueous secondary battery, the ratio of the tensile strength S _TD tensile strength in the machine direction of the separator S _MD and machine vertically, characterized in that it is a _{2 ≦ S MD / S TD ≦} 8 .

According to such a separator for a non-aqueous secondary battery of the present invention, the polyolefin porous substrate can provide a shutdown function, and the heat-resistant porous layer holds the polyolefin even at a temperature higher than the shutdown temperature. Melt down hardly occurs, and safety at high temperatures can be secured. In particular, by the ratio of the tensile strength S _TD of machine direction tensile strength S _MD and machine vertical direction of the separator is _{2 ≦ S MD / S TD ≦} 8, processability property is improved, stable in a battery assembly process In addition, a non-aqueous secondary battery can be produced.

  Here, “process passability” in the present invention means that the nonaqueous secondary battery separator is not deformed or damaged when the nonaqueous secondary battery separator is wound to manufacture the nonaqueous secondary battery. Means. The machine vertical direction means a direction perpendicular to the machine direction. In addition, the machine direction and the machine vertical direction in the separator in a state where the heat-resistant porous layer is composited coincide with the machine direction and the machine vertical direction of the polyolefin porous substrate, respectively.

In the present invention, a separator for a nonaqueous secondary battery, when the tensile strength in the machine direction is S _MD, it S _MD is 5~100N is preferable from the viewpoint of process passing property. Further, when the tensile strength in the machine direction perpendicular to the _{S TD,} it _{S TD} is 2.5~20N is preferable from the viewpoint of process passing property.

Balance of tensile strength is not particularly restricted but a method of controlling the ratio of the tensile strength in the machine direction of the separator S _MD and machine vertical tensile strength S _TD as described above, for example, a polyolefin porous substrate The method etc. which control are mentioned.

The separator for a non-aqueous secondary battery of the present invention preferably has a total film thickness of 30 μm or less from the viewpoint of the energy density of the non-aqueous secondary battery. The Gurley value (JIS P8117) of the separator is preferably 100 to 500 sec / 100 cc from the viewpoint of improving the balance between mechanical strength and membrane resistance. The membrane resistance of the separator is preferably 1.5 to 10 ohm · cm ² from the viewpoint of load characteristics of the non-aqueous secondary battery.

[Polyolefin porous substrate]
The polyolefin porous substrate used in the separator of the present invention is particularly limited as long as it has a large number of pores or voids inside and has a porous structure in which these pores are connected to each other. It is not a thing. Examples of such a substrate include a microporous film, a nonwoven fabric, a paper-like sheet, and other sheets having a three-dimensional network structure. Among these, a microporous membrane is preferable from the viewpoint of handling properties and strength. Further, the polyolefin porous substrate is heated to a predetermined temperature, so that pores and the like are closed, and a shutdown function is exhibited.

  Examples of the polyolefin include polyethylene, polypropylene, and polymethylpentene. Among them, those containing 90% by weight or more of polyethylene are preferable from the viewpoint of obtaining good shutdown characteristics. As the polyethylene, for example, low density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene and the like are preferably used, and particularly, high density polyethylene and ultra high molecular weight polyethylene are suitable. Furthermore, polyethylene comprising a mixture of high density polyethylene and ultra high molecular weight polyethylene is preferred from the viewpoint of strength and moldability.

  The film thickness of the polyolefin porous substrate is preferably 5 to 25 μm from the viewpoint of the energy density, load characteristics, mechanical strength, and handling properties of the non-aqueous secondary battery. The porosity of the polyolefin porous substrate is preferably 30 to 60% from the viewpoints of permeability, mechanical strength, and handling properties. The Gurley value (JIS P8117) of the polyolefin porous substrate is preferably 50 to 500 sec / 100 cc from the viewpoint of obtaining a good balance between mechanical strength and membrane resistance.

In the present invention, the polyolefin porous substrate, _'when a, S _MD' tensile strength in the machine direction S _MD is a 4~100N is preferable from the viewpoint of process passing property. Further, the polyolefin porous substrate, _'when a, S _TD' the tensile strength in the machine direction perpendicular S _TD it is 2~20N is preferable from the viewpoint of process passing property. The polyolefin porous substrate preferably has SMD _′ / _{STD ′} of 2 to 8 in order to control the balance of the tensile strength of the separator within the above-described range.

The ratio of the tensile strength S _{MD 'in} the machine direction of the polyolefin porous base material, a tensile strength S _MD in the machine direction of the non-aqueous secondary battery separator of the present invention which is a composite membrane, 0.9 ≦ S It is preferable that _MD / _{SMD ′} ≦ 1.2. Further, the tensile strength S _{TD 'in} the machine vertical polyolefin porous base material, the ratio of the tensile strength S _TD in the machine direction of the non-aqueous secondary battery separator of the present invention which is a composite membrane, 0.9 ≦ It is preferable that S _TD / S _{TD ′} ≦ 1.2.

[Polyolefin porous substrate manufacturing method]
In the present invention, the method for producing the polyolefin porous substrate is not particularly limited. For example, when a polyolefin microporous film is taken as an example, it can be produced through the following steps (1) to (6).
(1) Preparation of polyolefin solution A solution in which polyolefin is dissolved in a solvent is prepared. At this time, a solution may be prepared by mixing solvents. Examples of the solvent include paraffin, liquid paraffin, paraffin oil, mineral oil, castor oil, tetralin, ethylene glycol, glycerin, decalin, toluene, xylene, diethyltriamine, ethyldiamine, dimethyl sulfoxide, hexane, and the like. The concentration of the polyolefin solution is preferably 1 to 35% by weight, more preferably 10 to 30% by weight.
(2) Extrusion of polyolefin solution The adjusted solution is kneaded with a single screw extruder or a twin screw extruder, and extruded with a T die or an I die at a temperature not lower than the melting point and not higher than the melting point + 60 ° C. A twin screw extruder is preferably used. Then, the extruded solution is passed through a chill roll or a cooling bath to form a gel composition. At this time, it is preferable to rapidly cool below the gelation temperature to cause gelation.
(3) Desolvation treatment Next, the solvent is removed from the gel composition. When a volatile solvent is used, the solvent can also be removed from the gel composition by evaporating by heating or the like, which also serves as a preheating step. In the case of a non-volatile solvent, the solvent can be removed by squeezing out under pressure. The solvent need not be completely removed.
(4) Stretching of the gel-like composition After the solvent removal treatment, the gel-like composition is stretched. Here, a relaxation treatment may be performed before the stretching treatment. In the stretching treatment, the gel-like molded product is heated and biaxially stretched at a predetermined magnification by a normal tenter method, roll method, rolling method, or a combination of these methods. Biaxial stretching may be simultaneous or sequential. Moreover, it can also be set as longitudinal multistage extending | stretching, 3 or 4 steps extending | stretching.
The stretching temperature is preferably 90 ° C. to less than the melting point of the polyolefin, more preferably 100 to 120 ° C. Although a draw ratio changes with thickness of an original fabric, it is preferable to carry out at least 2 times or more in a uniaxial direction, preferably 4 to 20 times. In particular, from the viewpoint of controlling the tensile strength, the draw ratio is preferably 4 to 10 times in the machine direction and 6 to 15 times in the machine vertical direction. After stretching, heat setting is performed as necessary to provide thermal dimensional stability.
(5) Extraction and removal of solvent The stretched gel composition is immersed in an extraction solvent to extract the solvent. Examples of the extraction solvent include hydrocarbons such as pentane, hexane, heptane, cyclohexane, decalin, and tetralin, chlorinated hydrocarbons such as methylene chloride, carbon tetrachloride, and methylene chloride, fluorinated hydrocarbons such as ethane trifluoride, diethyl, and the like. Easily volatile compounds such as ethers and ethers such as dioxane can be used. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin composition, and can be used alone or in combination. Solvent extraction removes the solvent in the microporous membrane to less than 1% by weight.
(6) Annealing of microporous film The microporous film is heat-set by annealing. Annealing is performed at 80 to 150 ° C. In this invention, it is preferable that annealing temperature is 115-135 degreeC from a viewpoint that it has a predetermined | prescribed heat shrinkage rate.

[Heat-resistant porous layer]
In the present invention, examples of the heat-resistant porous layer include microporous film-like, non-woven fabric, paper-like, and other layers having a three-dimensional network-like porous structure. From the viewpoint of being obtained, the layer is preferably a microporous film. Here, the microporous film-like layer has a large number of micropores inside, and has a structure in which these micropores are connected. Gas or liquid can pass from one surface to the other. It says the layer that became.

  The heat-resistant resin used in the present invention is suitably a polymer having a melting point of 200 ° C. or higher, or a polymer having no melting point but having a decomposition temperature of 200 ° C. or higher. Preferable examples of such heat-resistant resins include at least one resin selected from the group consisting of wholly aromatic polyamides, polyimides, polyamideimides, polysulfones, polyketones, polyether ketones, polyether imides, and celluloses. In particular, from the viewpoint of durability, meta-type wholly aromatic polyamide or para-type wholly aromatic polyamide is preferable.

  In the present invention, the heat-resistant porous layer may be formed on both surfaces or one surface of the polyolefin microporous membrane. However, from the viewpoint of handling properties, durability, and the effect of suppressing heat shrinkage, it is preferable to form the heat-resistant porous layer on both surfaces of the substrate. preferable. In order to fix the heat-resistant porous layer on the substrate, a method in which the heat-resistant porous layer is directly formed on the substrate by a coating method is preferable. A technique of adhering the quality layer sheet on the base material using an adhesive or the like, a technique such as heat fusion or pressure bonding can also be employed.

In the present invention, regarding the thickness of the heat resistant porous layer, when the heat resistant porous layer is formed on both surfaces of the substrate, the total thickness of the heat resistant porous layer may be 3 μm or more and 12 μm or less. Preferably, when the heat resistant porous layer is formed only on one side of the substrate, the thickness of the heat resistant porous layer is preferably 3 μm or more and 12 μm or less. The porosity of the heat resistant porous layer is preferably in the range of 30 to 80%. Since the basis weight of the heat-resistant porous layer varies depending on the material used, it cannot be generally stated, but it is preferably approximately ² to 10 g / m ² .

  In the present invention, the heat resistant porous layer preferably contains an inorganic filler. The inorganic filler is not particularly limited, but for example, metal oxides such as alumina, titania, silica and zirconia, metal carbonates such as calcium carbonate, metal sulfates such as barium sulfate, metal phosphates such as calcium phosphate, water It is preferably at least one selected from metal hydroxides such as aluminum oxide and magnesium hydroxide.

  Especially, as an inorganic filler, what produces an endothermic reaction in 200-400 degreeC is preferable. As an inorganic filler which has such a characteristic, the thing which is an inorganic filler which consists of a metal hydroxide, a boron salt compound, or a clay mineral, for example, and produces an endothermic reaction at 200-400 degreeC is mentioned. Specific examples include aluminum hydroxide, magnesium hydroxide, calcium aluminate, dosonite, zinc borate and the like, and these can be used alone or in combination of two or more.

  In the present invention, the average particle diameter of the inorganic filler is preferably in the range of 0.1 to 2 μm from the viewpoint of short circuit resistance at high temperature, moldability, and the like. The content of the inorganic filler in the heat resistant porous layer is preferably 50 to 95% by weight.

  In addition, the inorganic filler in the heat resistant porous layer is present in a state of being trapped by the heat resistant resin when the heat resistant porous layer is in the form of a microporous film, and the heat resistant porous layer is a nonwoven fabric or the like. In such a case, it may be present in the constituent fibers or fixed to the nonwoven fabric surface or the like with a binder such as a resin.

[Method of manufacturing separator for non-aqueous secondary battery]
In the present invention, the method for producing a separator for a non-aqueous secondary battery is not particularly limited as long as the separator of the present invention having the above-described configuration can be produced. For example, it can be produced through the following steps (1) to (5). It is.
(1) Preparation of coating slurry A heat-resistant resin is dissolved in a solvent to prepare a coating slurry. The solvent is not particularly limited as long as it dissolves the heat-resistant resin, but specifically, a polar solvent is preferable, and examples thereof include N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylsulfoxide. Moreover, the said solvent can add the solvent used as a poor solvent with respect to heat resistant resin in addition to these polar solvents. By applying such a poor solvent, a microphase separation structure is induced and the formation of a heat-resistant porous layer is facilitated. As the poor solvent, alcohols are preferable, and polyhydric alcohols such as glycol are particularly preferable. The concentration of the heat resistant resin in the coating slurry is preferably 4 to 9% by weight. Moreover, an inorganic filler is disperse | distributed to this as needed, and it is set as the slurry for coating. In dispersing the inorganic filler in the coating slurry, when the dispersibility of the inorganic filler is not preferable, a method of improving the dispersibility by surface-treating the inorganic filler with a silane coupling agent or the like is also applicable.
(2) Coating of slurry The slurry is coated on at least one surface of the polyolefin microporous membrane. When forming a heat-resistant porous layer on both surfaces of a polyolefin microporous film, it is preferable from a viewpoint of shortening of a process to apply simultaneously on both surfaces of a base material. Examples of the method for coating the slurry for coating include a knife coater method, a gravure coater method, a screen printing method, a Meyer bar method, a die coater method, a reverse roll coater method, an ink jet method, a spray method, and a roll coater method. . Among these, the reverse roll coater method is preferable from the viewpoint of uniformly forming a coating film. When applying simultaneously to both sides of the base material, for example, by passing the base material between a pair of Meyer bars, an excess coating slurry is applied to both sides of the base material, and this is applied to a pair of reverse roll coaters. There is a method of precise measurement by scraping off excess slurry in between.
(3) Solidification of slurry The base material on which the slurry is applied is treated with a coagulating liquid capable of coagulating the heat-resistant resin. By treating the substrate coated with the coating slurry in a coagulating liquid capable of coagulating the heat resistant resin or in a moist heat atmosphere, the heat resistant resin is coagulated to form a heat resistant porous layer. Form. As a method of treating with the coagulating liquid, a method of spraying the coagulating liquid on the substrate coated with the coating slurry, or a method of immersing the substrate in a bath (coagulating bath) containing the coagulating liquid. Alternatively, it may be deposited in an atmosphere of a predetermined humidity and temperature, and then immersed in a coagulation bath to coagulate. Here, when installing a coagulation bath, it is preferable to install it below the coating apparatus. The coagulation liquid is not particularly limited as long as it can coagulate the heat-resistant resin, but water or a solution obtained by mixing an appropriate amount of water with the solvent used in the slurry is preferable. Here, the mixing amount of water is preferably 40 to 80% by weight with respect to the coagulation liquid. When the amount of water is less than 40% by weight, there arises a problem that the time required for solidifying the heat-resistant resin becomes long or the solidification becomes insufficient. On the other hand, when the amount of water is more than 80% by weight, there arises a problem that the cost for solvent recovery becomes high, or the surface that comes into contact with the coagulation liquid is solidified too quickly and the surface is not sufficiently porous.
(4) Removal of coagulating liquid The coagulating liquid is removed by washing with water.
(5) Drying Dry and remove water from the sheet. Although there is no particular limitation on the drying method, the drying temperature is preferably 50 to 80 ° C. When a high drying temperature is applied, a method of contacting with a roll to prevent dimensional change due to heat shrinkage. It is preferable to apply.

[Non-aqueous secondary battery]
In the present invention, the non-aqueous secondary battery is a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, and is characterized by using the separator described above. The type and configuration of the non-aqueous secondary battery to which the separator of the present invention is applied are not limited in any way, but an electrolytic solution is impregnated into a battery element in which a positive electrode, a separator, and a negative electrode are sequentially laminated, and this is applied to the exterior. Any configuration can be applied as long as it has a sealed structure.

  The negative electrode has a structure in which a negative electrode mixture composed of a negative electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the negative electrode active material include materials capable of electrochemically doping lithium, and examples thereof include carbon materials, silicon, aluminum, tin, and wood alloys. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride and carboxymethyl cellulose. As the current collector, a copper foil, a stainless steel foil, a nickel foil, or the like can be used.

The positive electrode has a structure in which a positive electrode mixture composed of a positive electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the positive electrode active material include lithium-containing transition metal oxides. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 Examples include O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _0.5 Ni _0.5 O ₂ , LiAl _0.25 Ni _0.75 O _{2, and the} like. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride. As the current collector, aluminum foil, stainless steel foil, titanium foil, or the like can be used.

The electrolytic solution has a structure in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4 and the} like. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, vinylene carbonate, and the like. These may be used alone or in combination.

  Examples of the exterior material include a metal can or an aluminum laminate pack. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the separator of the present invention can be suitably applied to any shape.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

Each value in this example was determined according to the following method.
[Film thickness]
The film thickness of the polyolefin microporous membrane and the separator for a non-aqueous secondary battery was determined by measuring 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Corporation) and averaging them. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter.
[Weighing]
The basis weight of the non-aqueous secondary battery separator is obtained by cutting a sample into 10 cm × 10 cm and measuring the weight. By dividing this weight by the area, the basis weight which is the weight per 1 m ² was obtained.
[Porosity]
The constituent materials are a, b, c..., N, and the weights of the constituent materials are Wa, Wb, Wc..., Wn (g · cm ² ), and their true densities are da, db, dc. g / cm ³ ), where the film thickness of the layer of interest is t (cm), the porosity ε (%) was obtained from the following equation.
ε = {1− (Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t} × 100
[Tensile strength]
The tensile strength of the polyolefin microporous membrane and the separator for the non-aqueous secondary battery is a sample adjusted to 10 × 100 mm using a tensile tester (A & D, RTC-1225A), load cell load 5 kgf, chuck distance 50 mm Measured with
[Process passability]
The sample adjusted to 10 × 100 mm was wound around a stainless steel rod having a diameter of 1 mm with a tension of 1.5 N so as not to sag. A sample having both the deformation of the sample in the machine direction and the machine vertical direction within 5% was judged as having good process passability (◯), and a sample exceeding 5% was judged as being defective (x).

[Reference Example 1]
Ticona's GUR2126 (weight average molecular weight 4150,000, melting point 141 ° C.) and GURX143 (weight average molecular weight 560,000, melting point 135 ° C.) were used as polyethylene powder. Liquid paraffin (Smoyl P-350, boiling point 480 ° C., Matsumura Oil Research Co., Ltd.) and decalin (Wako Pure) so that GUR2126 and GURX143 become 2: 8 (weight ratio) and the polyethylene concentration becomes 30% by weight. A polyethylene solution was prepared by dissolving in a mixed solvent having a boiling point of 193 ° C. manufactured by Yakuhin Co., Ltd. The composition of the polyethylene solution is polyethylene: liquid paraffin: decalin = 30: 67.5: 2.5 (weight ratio).

  This polyethylene solution was extruded from a die at 148 ° C. and cooled in a water bath to prepare a gel tape (base tape). The base tape was dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes, and the base tape was stretched by biaxial stretching in which longitudinal stretching and lateral stretching were sequentially performed. Here, the longitudinal stretching was 8.5 times, the stretching temperature was 90 ° C., the transverse stretching was 6 times the stretching ratio, and the stretching temperature was 105 ° C. Thereafter, heat setting was performed at 120 ° C. Next, this was immersed in a methylene chloride bath to extract liquid paraffin and decalin. Then, the polyolefin microporous film was obtained by drying at 50 degreeC and annealing at 120 degreeC. The resulting polyolefin microporous membrane had a structure in which fibrillar polyolefins were entangled in a network and constituted pores.

The properties of the resulting microporous polyolefin membrane (thickness, basis weight, porosity, machine direction tensile strength _{S MD ',} the machine vertical tensile strength _{S TD',} the ratio of the tensile strength _{S MD '/ S TD')} The measurement results are shown in Table 1. The following Reference Examples 2 and 3 and Reference Comparative Examples 1 and 2 are similarly shown in Table 1.

[Reference Example 2]
A polyolefin microporous membrane was obtained in the same manner as in Reference Example 1 except that the stretching ratio was 11 times in the longitudinal direction and 5 times in the lateral direction.

[Reference Example 3]
A polyolefin microporous membrane was obtained in the same manner as in Reference Example 1 except that the stretching ratio was 7 times in the longitudinal stretching and 8 times in the lateral stretching.

[Reference Comparative Example 1]
A polyolefin microporous membrane was obtained in the same manner as in Reference Example 1, except that the stretching ratio was 6.2 times in the longitudinal direction and 9 times in the lateral direction.

[Reference Comparative Example 2]
A polyolefin microporous membrane was obtained in the same manner as in Reference Example 1 except that the stretching ratio was 13 times in the longitudinal stretching and 4 times in the lateral stretching.

[Example 1]
The polyolefin microporous membrane obtained in Reference Example 1 was used, and a heat-resistant porous layer made of a heat-resistant resin and an inorganic filler was laminated thereon to produce the non-aqueous secondary battery separator of the present invention.

  Specifically, polymetaphenylene isophthalamide (manufactured by Teijin Techno Products, Conex) was used as the heat resistant resin. This heat resistant resin was dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) in a weight ratio of 50:50. In this polymer solution, magnesium hydroxide as an inorganic filler (Kyowa Chemical Industry Co., Ltd., Kisuma-5P, average particle size: 1.0 μm) was dispersed to prepare a slurry for coating. The concentration of polymetaphenylene isophthalamide in the coating slurry was adjusted to 5.5% by weight, and the weight ratio of polymetaphenylene isophthalamide to inorganic filler was adjusted to 25:75. Then, two Meyer bars were opposed to each other, and an appropriate amount of coating liquid was put between them. Thereafter, the polyolefin microporous film was passed between Mayer bars on which the coating liquid was placed, and the coating liquid was applied to the front and back surfaces of the polyolefin microporous film. Here, the clearance between the Meyer bars was set to 20 μm, and # 6 was used for both the Mayer bars. This was immersed in a coagulating liquid having a weight ratio of water: DMAc: TPG = 50: 25: 25 and 40 ° C., followed by washing and drying. This obtained the separator for non-aqueous secondary batteries in which the heat resistant porous layer was formed in the both surfaces of the polyolefin microporous film.

Characteristics of obtained separator for non-aqueous secondary battery (film thickness, basis weight, porosity, tensile strength S _MD in machine direction, tensile strength S _{TD in} machine vertical direction, ratio of tensile strength S _MD / S _TD , process Table 2 shows the measurement results of the permeability. The following Examples 2 and 3 and Comparative Examples 1 and 2 are similarly shown in Table 2.

[Example 2]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the polyolefin microporous film prepared in Reference Example 2 was used.

[Example 3]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the polyolefin microporous film prepared in Reference Example 3 was used.

[Comparative Example 1]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the polyolefin microporous film prepared in Reference Comparative Example 1 was used.

[Comparative Example 2]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the polyolefin microporous film prepared in Reference Comparative Example 2 was used.

Claims (4)

A non-aqueous secondary battery separator comprising a polyolefin porous substrate, and a heat-resistant porous layer formed by including a heat-resistant resin and laminated on one or both sides of the porous substrate,
The ratio of the tensile strength in the machine direction of the separator S _MD and machine vertical tensile strength S _TD is, 2 ≦ S _{MD /} S nonaqueous secondary battery separator, which is a _TD ≦ 8.   The separator for a non-aqueous secondary battery according to claim 1, wherein the heat resistant resin is a meta-type wholly aromatic polyamide or para-type wholly aromatic polyamide.   The non-aqueous secondary battery separator according to claim 1, wherein the heat-resistant porous layer contains an inorganic filler.   The non-aqueous secondary according to claim 3, wherein the inorganic filler is at least one selected from a metal oxide, a metal carbonate, a metal sulfate, a metal phosphate, and a metal hydroxide. Battery separator.