KR20170113145A - Separator for batteries and method for producing same - Google Patents

Abstract

The present inventors aim at providing a separator for a battery having both a bending strength at the time of drying and a bending strength at the time of drying, both of which are problems to cope with the spread of a large-sized battery to be carried out in the future (particularly a laminate type battery).
And a porous layer formed on at least one side of the microporous membrane, wherein the porous layer comprises a vinylidene fluoride-hexafluoropropylene copolymer (A) and a polymer (B) containing a vinylidene fluoride unit, And an acrylic resin, wherein the vinylidene fluoride-hexafluoropropylene copolymer (A) contains 0.3 mol% to 3 mol% of a hydrophilic group and a hexafluoropropylene unit, and the vinylidene fluoride-hexafluoropropylene copolymer The polymer (B) has a melting point of 60 占 폚 or more and 145 占 폚 or less and a weight average molecular weight of 100,000 or more and 750,000 or less.

Description

[0001] SEPARATOR FOR BATTERIES AND METHOD FOR PRODUCING SAME [0002]

The present invention relates to a battery separator and a manufacturing method thereof.

BACKGROUND ART [0002] Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are widely used in portable electronic devices such as portable telephones and portable information terminals, and cylindrical batteries, prismatic batteries, laminated batteries and the like are being developed. Generally, these batteries have an electrode body (laminated electrode body) in which an anode electrode and a cathode electrode are laminated via a separator, an electrode body (wound electrode body) surrounded by a spiral shape, and a non- And has a housed configuration.

A conventional separator for a non-aqueous electrolyte secondary cell mainly uses a microporous membrane made of a polyolefin resin, and the pores of the separator are closed at the time of abnormal heat generation of the battery, thereby suppressing current flow and preventing ignition.

In recent years, attempts have been made to improve the battery characteristics by providing a porous layer on one side or both sides of the microporous membrane. For example, there is a separator provided with a porous layer containing fluorine resin or acrylic resin for imparting functions such as electrode adhesiveness (prior arts 1 to 8). In addition, when inorganic particles are added to the porous layer, even when a sharp metal penetrates through the battery due to an accident and causes a short circuit, it is possible to prevent the melting shrinkage of the separator and suppress the spread of the short circuit between the electrodes.

Patent Document 1 discloses an electrode body having a three-layer separator composed of a positive electrode, a negative electrode, polypropylene, polyethylene, and polypropylene, and an adhesive resin layer composed of polyvinylidene fluoride and alumina powder disposed between the electrodes and the separator have.

In Example 1 of Patent Document 2, an NMP solution containing a first polymer (polyvinylidene vinylidene homopolymer) and a second polymer (an acrylonitrile monomer, a 1,3-butadiene-derived monomer, a methacrylic acid monomer, And a polymer containing butyl acrylate monomer) was stirred with a primary mixer to adjust the NMP solution of the binder, and then the adjusted NMP solution and alumina particles were mixed and dispersed to prepare a slurry of polypropylene An organic separator with a porous membrane obtained by applying the composition to a separator.

In the embodiment of Patent Document 3, an NMP solution obtained by dissolving a compounding material composed of a vinylidene fluoride-hexafluoropropylene copolymer (VdF-HFP copolymer) and polymethyl methacrylate was added to an NMP solution in which spherical alumina powder was dispersed , An electrode body obtained by thermally bonding an anode and a cathode to each other via an inorganic fine particle-containing sheet (insulating adhesive layer) obtained by applying a slurry prepared by mixing the above-mentioned mixture to a base PET film and drying the mixture.

In Example 1 of Patent Document 4, a slurry obtained by adding VdF-HFP copolymer and cyanoethylpullulan to acetone, then adding barium titanate powder, and dispersing the mixture with a ball mill, was applied to a polyethylene porous film A separator is described.

In Example 1 of Patent Document 5, VdF-HFP copolymer (HFP unit: 0.6 mol%) and VdF-HFP copolymer (weight average molecular weight: 470,000, HFP unit: 4.8 mol%) were dissolved in dimethylacetamide and tripropylene glycol solution And a porous layer is formed by coating the same on a polyethylene microporous membrane.

In Example 1 of Patent Document 6, PVdF (weight average molecular weight: 500,000) and VdF-HFP copolymer (weight average molecular weight: 400,000, HFP unit: 5 mol%) were dissolved in dimethylacetamide and tripropylene glycol solution, Discloses a separator in which a porous layer is formed by coating a polyethylene microporous membrane.

In Example 1 of Patent Document 7, PVdF (weight average molecular weight: 700,000) and VdF-HFP copolymer (weight average molecular weight: 470,000, HFP unit: 4.8 mol%) were dissolved in dimethylacetamide and tripropylene glycol solution, Discloses a separator in which a porous layer is formed by coating a polyethylene microporous membrane.

In Example 1 of Patent Document 8, PVdF (weight average molecular weight: 350,000) and VdF-HFP polymer (weight average molecular weight: 270,000, HFP copolymerization: 4.8 mol%) were dissolved in dimethylacetamide and tripropylene glycol solution, Discloses a separator in which a porous layer is formed by coating the microporous membrane.

The separator disclosed in Patent Documents 1 to 8 and the layer disposed between the electrode and the separator both contain a polyvinylidene fluoride resin.

Patent Document 1: Japanese Unexamined Patent Publication No. 1999-036981 Patent Document 2: JP-A-2013-206846 Patent Document 3: JP-A-2013-122009 Patent Document 4: Japanese Published Patent Application No. 2013-519206 Patent Document 5: Japanese Patent No. 5282179 Patent Document 6: Japanese Patent No. 5282180 Patent Document 7: Japanese Patent No. 5282181 Patent Document 8: Japanese Patent No. 5342088

In recent years, non-aqueous electrolyte secondary batteries are expected to be developed for use in large-sized applications such as large-size tablets, lawn mowers, electric motorcycles, electric vehicles, hybrid vehicles, small ships and the like.

The wound electrode body is manufactured by winding the positive electrode and the negative electrode around the separator while applying tension to each member. At this time, the anode electrode and the cathode electrode coated on the metal current collector do not substantially expand or contract with respect to the tensile force, but the separator is wrapped around in the machine direction to some extent. If you leave this winding for a while, the separator portion will slowly decrease and return to its original length. As a result, a force in a parallel direction is generated at the interface between the electrode and the separator, so that the wound electrode body (particularly, the electrode body surrounded by a flat surface) is likely to be warped or deformed. Further, these problems are caused by the widening or lengthening of the separator accompanying the enlargement of the battery, and the yield at the time of production is worried. It is expected that the separator is required to have more adhesion with the electrode than ever in order to suppress the warping or deformation of the wound electrode body. In this specification, the bending strength at the drying obtained by the measuring method described later is used as an index for this adhesion.

Further, when the electrode bodies are transported (transported), unless the respective members are sufficiently bonded, the electrodes and the separator are peeled off and can not be transported at a good yield. The problem of adhesiveness at the time of transportation becomes present due to enlargement of the battery, and the yield is worried. Therefore, the separator is expected to have a high peeling force in drying, which is difficult to peel off from the electrode.

Further, particularly in a laminate type battery, it is difficult to apply pressure to a rectangular or cylindrical battery that can apply pressure to an external body, and it is difficult to apply pressure to the external shape due to swelling and shrinkage of the electrode accompanying charge / Free (free) is likely to occur. As a result, the expansion of the battery, the resistance inside the battery, and the cycle performance are lowered. Therefore, the separator needs to have adhesiveness with the electrode in the cell after the electrolyte is injected. In this specification, the bending strength at the time of wetting, which is obtained by the measuring method described later, is used as an index for the adhesion. If the strength is large, improvement in cell characteristics such as suppression of expansion of the battery after repeated charging and discharging is expected.

In the prior art, since there is a trade-off relationship between the bending strength in drying, the peeling force in drying, and the bending strength in wetting, it is extremely difficult to satisfy all physical properties. The present invention aims to provide a separator for a battery which satisfies bending strength during drying, peeling force during drying, and bending strength during wetting in preparation for spreading of a large-sized battery (particularly a laminate battery) to be carried out in the future.

The term "wet bending strength" used herein means adhesion between the separator and the electrode in a state in which the separator contains the electrolyte solution. The bending strength at the time of drying and the peeling force at the time of drying show the adhesion to the interface between the separator and the electrode in a state where the separator does not substantially contain the electrolyte. The term "substantially not contained" means that the electrolytic solution in the separator is 500 ppm or less.

In order to solve the above problems, a separator for a battery and a manufacturing method thereof according to the present invention have the following constitutions. In other words,

(1) A microporous membrane and a porous layer provided on at least one side of the microporous membrane, wherein the porous layer is made of a vinylidene fluoride-hexafluoropropylene copolymer (A) and a polymer containing vinylidene fluoride units (B) and an acrylic resin, wherein the vinylidene fluoride-hexafluoropropylene copolymer (A) contains 0.3 mol% to 3 mol% of a hydrophilic group and a hexafluoropropylene unit, and the vinylidene fluoride-hexafluoropropylene copolymer (B) is a battery separator having a melting point of 60 占 폚 or more and 145 占 폚 or less and a weight average molecular weight of 100,000 or more and 750,000 or less.

(2) In the battery separator of the present invention, it is preferable that the vinylidene fluoride-hexafluoropropylene copolymer (A) has a weight average molecular weight of more than 750,000 and less than 2,000,000.

(3) In the battery separator of the present invention, it is preferable that the porous layer contains particles.

(4) The separator for a battery of the present invention is characterized in that the content of the vinylidene fluoride-hexafluoropropylene copolymer (A) is in the range of 0.1 to 10 parts by weight, based on 100 parts by weight of the vinylidene fluoride-hexafluoropropylene copolymer (A) (B) containing a vinylidene fluoride-hexafluoropropylene copolymer (A), a vinylidene fluoride unit, and an acrylic resin in an amount of not less than 15% by weight and not more than 85% by weight based on the total weight of the acrylic resin And is preferably 4 wt% or more and 40 wt% or less based on the total weight.

(5) In the battery separator of the present invention, it is preferable that the acrylic resin is a copolymer of a monomer having a (meth) acrylate ester and a cyano group.

(6) In the battery separator of the present invention, it is preferable that the acrylic resin is a copolymer containing butyl acrylate.

(7) In the battery separator of the present invention, it is preferable that the acrylic resin is a copolymer of butyl acrylate and acrylonitrile.

(8) In the separator for a battery of the present invention, it is preferable that the content of butyl acrylate in the acrylic resin is 50 mol% to 75 mol%.

(9) In the battery separator of the present invention, it is preferable that the content of the hydrophilic group in the vinylidene fluoride-hexafluoropropylene copolymer (A) is 0.1 mol% to 5 mol%.

(10) It is preferable that the separator for a battery of the present invention has a bending strength of 4 N or more, a bending strength of 5 N or more at the time of drying, and a peel force of 8 N / m at the time of drying.

(11) In the battery separator of the present invention, the content of the particles is preferably 50 wt% or more and 90 wt% or less based on the total weight of the porous layer.

(12) It is preferable that the separator for a battery of the present invention contains at least one kind of particles selected from the group consisting of alumina, titania and boehmite.

(13) In the battery separator of the present invention, it is preferable that the thickness of the porous layer is 0.5 to 3 mu m per side.

(14) In the battery separator of the present invention, it is preferable that the microporous membrane is a polyolefin microporous membrane.

In order to solve the above problems, a method for producing a polyolefin microporous membrane of the present invention has the following constitution. In other words,

(15) In the battery separator of the present invention,

(1) A process for producing a fluorinated resin solution, comprising the steps of: obtaining a fluorinated resin solution in which a vinylidene fluoride-hexafluoropropylene copolymer (A) and a polymer (B) containing vinylidene fluoride units are dissolved in a solvent;

(2) a step of adding an acrylic resin solution in which an acrylic resin is dissolved in a solvent to a fluorine resin solution and mixing them to obtain a coating solution,

(3) a step of applying a coating liquid to a microporous membrane, immersing the coating liquid in a coagulating solution, washing and drying, and wherein the vinylidene fluoride-hexafluoropropylene copolymer (A) has a hydrophilic group and a hexafluoro (B) containing 0.3 mol% to 3 mol% of propylene units and having a melting point of 60 ° C or more and 145 ° C or less and a weight average molecular weight of 100,000 or more and 750,000 or less, The resin is a process for producing a battery separator according to any one of claims 1 to 14, which contains a butyl acrylate unit.

According to the present invention, it is possible to provide a separator for a battery which satisfies bending strength at the time of drying, peeling force at the time of drying, and bending strength at the time of wetting in preparation for spreading of the battery in the future.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front sectional view schematically showing a bending strength test during wetting; Fig.
Fig. 2 is a front sectional view schematically showing a bending strength test during drying. Fig.

Although the outline of the separator for a battery having at least the microporous membrane and the porous layer of the present invention will be described, it is of course not limited to this representative example.

1. Microporous membrane

First, the microporous membrane of the present invention will be described.

In the present invention, the microporous membrane means a membrane having voids connected inside. The microporous membrane is not particularly limited, and a nonwoven fabric or a microporous membrane can be used. Hereinafter, the case where the resin constituting the microporous membrane is a polyolefin resin will be described in detail, but the present invention is not limited thereto.

[1] Polyolefin resin

The polyolefin resin constituting the polyolefin microporous membrane is composed mainly of polyethylene resin or polypropylene resin. The content of the polyethylene resin is preferably 70% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass, based on 100% by mass of the total mass of the polyolefin resin.

Examples of the polyolefin resin include a homopolymer, a two-stage polymer, a copolymer or a mixture thereof obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene and 1-hexene. If necessary, various additives such as an antioxidant and an inorganic filler may be added to the polyolefin resin within a range that does not impair the effects of the present invention.

[2] Process for producing polyolefin microporous membrane

As the method of producing the polyolefin microporous membrane, there is no particular limitation so long as it is possible to produce a polyolefin microporous membrane having desired properties, and conventionally known methods can be used. For example, Japanese Patent No. 2132327 and Japanese Patent No. 3347835 , International Publication No. 2006/137540, and the like can be used. Specifically, it is preferable to include the following steps (1) to (5).

(1) a step of preparing a polyolefin solution by melt kneading the polyolefin resin and a solvent for film formation

(2) a step of extruding the polyolefin solution and cooling to form a gel-like sheet

(3) a first stretching step of stretching the gel sheet

(4) a step of removing the solvent for film formation from the gel sheet after the stretching

(5) a step of drying the sheet after the solvent for film formation is removed

Hereinafter, each step will be described.

(1) Process for preparing polyolefin solution

A suitable solvent for film formation is added to the polyolefin resin, and the mixture is melt-kneaded to prepare a polyolefin solution. As a melt kneading method, for example, a method using a twin-screw extruder described in the specification of Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used. Since the melt-kneading method is known, its explanation is omitted.

In the polyolefin solution, the compounding ratio of the polyolefin resin to the film forming solvent is not particularly limited, but it is preferably 70 to 80 parts by mass of the film forming solvent with respect to 20 to 30 parts by mass of the polyolefin resin. When the ratio of the polyolefin resin is within the above range, it is possible to prevent a swell or a neck-in at the die outlet when the polyolefin solution is extruded, and the moldability and self-supporting property of the extrusion molded article (gel- .

(2) Process for forming a gel sheet

The polyolefin solution is fed from the extruder to the die and extruded into a sheet. A plurality of polyolefin solutions having the same or different compositions may be fed (fed) from an extruder into a single die, and thereafter laminated in layers and extruded into a sheet.

The extrusion method may be either a flat die method or an inflation method. The extrusion temperature is preferably 140 to 250 占 폚, and the extrusion speed is preferably 0.2 to 15 m / min. The film thickness can be controlled by adjusting the extrusion amount of the polyolefin solution. As the extrusion method, for example, the methods disclosed in Japanese Patent Publication No. 2132327 and Japanese Patent Publication No. 3347835 can be used.

The obtained extrusion molding is cooled to form a gel sheet. As a method for forming the gel-like sheet, for example, the methods disclosed in Japanese Patent Publication No. 2132327 and Japanese Patent Publication No. 3347835 can be used. The cooling is preferably carried out at a rate of at least 50 ° C / min up to at least the gelation temperature. The cooling is preferably carried out up to 25 캜. By cooling, the microphase of the polyolefin separated by the solvent for film formation can be immobilized. When the cooling rate is within the above range, the degree of crystallinity is maintained within a suitable range, resulting in a gel-like sheet suitable for stretching. Examples of the cooling method include a method of contacting with a coolant such as cold air or cooling water, a method of bringing the coolant into contact with a cooling roll, and the like.

(3) First drawing step

Next, the obtained gel-like sheet is stretched at least in one axial direction. Since the gel-like sheet contains a solvent for film formation, it can be uniformly stretched. After heating, the gel-like sheet is preferably stretched at a predetermined ratio by a tenter method, a roll method, an inflation method, or a combination thereof. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, either biaxial stretching, continuous stretching, or multistage stretching (for example, a combination of simultaneous biaxial stretching and stretching stretching) may be used.

The drawing magnification (area elongation magnification) in this step is preferably 9 times or more, more preferably 16 times or more, and particularly preferably 25 times or more. The stretching magnifications in the machine direction MD and the width direction TD may be the same or different from each other. The drawing magnification in the present step means the area stretching magnification of the microporous film immediately before being supplied to the next step, based on the microporous membrane immediately before the present step.

The stretching temperature of the present step is preferably within the range of the crystal dispersion temperature (Tcd) to Tcd + 30 占 폚 of the polyolefin resin, and the range of the crystal dispersion temperature (Tcd) + 5 占 폚 to the crystal dispersion temperature (Tcd) + 28 占 폚 , More preferably within the range of Tcd + 10 ° C to + Tcd + 26 ° C. For example, in the case of polyethylene, the stretching temperature is preferably 90 to 140 占 폚, more preferably 100 to 130 占 폚. The crystal dispersion temperature (Tcd) can be obtained by measuring the temperature characteristic of dynamic viscoelasticity according to ASTM D4065.

The elongation as described above causes cleavage between the polyethylene lamellae, and the polyethylene phase is refined to form a large number of fibrils. The fibrils form a three-dimensionally irregularly connected network structure. The stretching improves the mechanical strength and enlarges the pores. However, if the stretching is carried out under appropriate conditions, it becomes possible to control the diameter of the through holes and to have a high porosity even at thinner film thicknesses.

Depending on the desired physical properties, a temperature distribution may be formed in the film thickness direction and stretched, thereby obtaining a microporous membrane excellent in mechanical strength. Details of the method are described in Japanese Patent No. 3347854.

(4) Removal of solvent for film formation

(Cleaning) is performed using a cleaning solvent. Since the polyolefin phase is phase-separated from the film forming solvent phase, when the solvent for film formation is removed, a porous film having holes (pores) communicating irregularly three-dimensionally is formed of fibrils forming a fine three-dimensional network structure . The method of removing the cleaning solvent and the solvent for forming a film using the same is well known, and thus the description thereof is omitted. For example, the method disclosed in Japanese Patent No. 2132327 or Japanese Patent Application Laid-Open No. 2002-256099 can be used.

(5) Drying

The microporous membrane from which the solvent for film formation has been removed is dried by the heat drying method or the air drying method. The drying temperature is preferably not higher than the crystal dispersion temperature (Tcd) of the polyolefin resin, and more preferably 5 ° C or more lower than Tcd. The drying is preferably carried out until 100% by mass (dry weight) of the microporous membrane is reached, and until the residual cleaning solvent becomes 5% by mass or less, more preferably 3% by mass or less. When the residual cleaning solvent is within the above range, porosity of the microporous membrane is maintained when the subsequent microporous membrane stretching step and the heat treatment step are performed, and deterioration of the permeability is suppressed.

2. Porous layer

In the present invention, the porous layer contains a vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer (A), a polymer (B) containing vinylidene fluoride units, and an acrylic resin. Each resin will be described below.

[1] Copolymer of vinylidene fluoride-hexafluoropropylene (VdF-HFP) (A)

The vinylidene fluoride-hexafluoropropylene copolymer (A) used in the present invention contains a hydrophilic group and contains 0.3 mol% to 3 mol% of hexafluoropropylene. The copolymer (A) has high affinity for a non-aqueous electrolyte, high chemical and physical stability, exhibits bending strength at the time of wetting, and can maintain sufficient affinity with an electrolyte even under high temperature use.

Since the vinylidene fluoride-hexafluoropropylene copolymer (A) has a hydrophilic group, it can be strongly adhered to the active material existing on the electrode surface and the binder component in the electrode. This adhesion is presumably due to hydrogen bonding. Examples of the hydrophilic group include a hydroxyl group, a carboxylic acid group, a sulfonic acid group, and salts thereof. In particular, a carboxylic acid group and a carboxylic acid ester are preferable.

In the case of introducing a hydrophilic group into the vinylidene fluoride, for example, in the synthesis of the vinylidene fluoride-hexafluoropropylene copolymer (A), maleic anhydride, maleic acid, maleic acid ester, maleic acid monomethyl ester and the like Is introduced into the main chain by copolymerizing a monomer having a hydrophilic group of the formula (1) or a method of introducing it as a side chain by grafting. The hydrophilic group modification rate can be measured by FT-IR, NMR, quantitative titration, and the like. For example, in the case of a carboxylic acid group, it can be determined from the absorption intensity ratio of C-H stretching vibration and C═O stretching vibration of the carboxyl group based on the homopolymer using FT-IR.

The lower limit of the content of the hydrophilic group in the vinylidene fluoride-hexafluoropropylene copolymer (A) is preferably 0.1 mol% or more, more preferably 0.3 mol% or more, and the upper limit value is preferably 5 mol% More preferably, it is 4 mol% or less. If the content of the hydrophilic group exceeds 5 mol%, the crystallinity of the polymer becomes too low, and the degree of swelling with respect to the electrolytic solution increases, and the bending strength deteriorates in wetting. In the case where the porous layer contains particles, it is possible to suppress dropout of the particles by setting the content of the hydrophilic group within the preferable range.

The lower limit value of the content of hexafluoropropylene in the vinylidene fluoride-hexafluoropropylene copolymer (A) is preferably 0.3 mol% or more, more preferably 0.5 mol% or more, and the upper limit value is 3 mol% or less , And more preferably 2.5 mol% or less. If the content of hexafluoropropylene is less than 0.3 mol%, the crystallinity of the polymer becomes high and the degree of swelling with respect to the electrolytic solution becomes low, so that it is difficult to sufficiently obtain the bending strength at the time of wetting. On the other hand, if it exceeds 3 mol%, the electrolyte swells excessively and the bending strength is lowered in wetting.

The content of the vinylidene fluoride-hexafluoropropylene copolymer (A) is preferably at least 15% by weight, more preferably at least 25% by weight based on the total weight of the copolymer (A) and the polymer (B) And the upper limit value is preferably 85% by weight or less, and more preferably 25% by weight or less.

The lower limit value of the weight average molecular weight of the vinylidene fluoride-hexafluoropropylene copolymer (A) is more than 75,000, preferably 90,000 or more, and the upper limit value is preferably 2,000,000 or less, and more preferably 1,500,000 or less . By setting the weight average molecular weight of the copolymer (A) within the above preferable range, the time for dissolving the copolymer (A) in the solvent is not extremely long, and the production efficiency can be increased. In addition, when the electrolyte solution swells, a suitable gel strength can be maintained, and the bending strength in wetting is improved. On the other hand, the weight average molecular weight as referred to in the present invention is the polystyrene equivalent value obtained by gel permeation chromatography.

The vinylidene fluoride-hexafluoropropylene copolymer (A) can be obtained by a known polymerization method. As a known polymerization method, there may be mentioned, for example, the method exemplified in JP-A-11-130821. Ion exchanged water, maleic acid monomethyl ester, vinylidene fluoride and hexafluoropropylene are placed in an autoclave, suspension polymerization is carried out, and thereafter the polymer slurry is dehydrated, washed with water and then dried to obtain a polymer powder . At this time, methyl cellulose as a suspending agent and diisopropyl peroxycarbonate as a radical initiator can be suitably used.

The vinylidene fluoride-hexafluoropropylene copolymer (A) may be a copolymer obtained by further polymerizing monomers other than monomers having a hydrophilic group within a range that does not impair the properties. Examples of monomers other than monomers having a hydrophilic group include monomers such as tetrafluoroethylene, trifluoroethylene, trichlorethylene and vinyl fluoride.

[2] Polymer (B) containing vinylidene fluoride units [

The polymer (B) containing the vinylidene fluoride unit used in the present invention has a melting point of 60 캜 or more and 145 캜 or less and a weight average molecular weight of 100,000 or more and 750,000 or less, and has high affinity for a nonaqueous electrolyte, The physical stability is high and the bending strength at the time of drying and the peeling force at the time of drying are obtained. In this regard, although the mechanism is not clear, the polymer (B) has fluidity under heating and pressurizing conditions that exhibit bending strength at the time of drying and peeling force at the time of drying, and penetrates into the porous layer of the electrode to become an anchor, The inventors presume that the adhesion between the electrodes is strong. The polymer (B) contributes to the bending strength in drying and the peeling force in drying, and can contribute to prevention of warpage and deformation of the wound electrode body or the laminated electrode body, and improvement of transportability. On the other hand, the polymer (B) containing a vinylidene fluoride unit is a resin different from the vinylidene fluoride-hexafluoropropylene copolymer (A).

The lower limit of the melting point of the polymer (B) containing vinylidene fluoride units is preferably 60 占 폚 or higher, more preferably 80 占 폚 or higher, and the upper limit value is preferably 145 占 폚 or lower, more preferably 140 占 폚 or lower. Here, the melting point is the temperature of the peak top of the endothermic peak at the time of temperature rise measured by differential scanning calorimetry (DSC).

The polymer (B) containing a vinylidene fluoride unit is a resin comprising a copolymer having polyvinylidene fluoride or vinylidene fluoride units. Polymer (B) can be obtained by the suspension polymerization method or the like as in copolymer (A). The melting point of the polymer (B) can be controlled by controlling the crystallinity of a portion composed of vinylidene fluoride units. For example, when the polymer (B) contains a monomer other than vinylidene fluoride unit, the melting point can be adjusted by controlling the ratio of the vinylidene fluoride unit. Monomers other than the vinylidene fluoride unit include monofunctional monomers such as tetrafluoroethylene, trifluoroethylene, trichlorethylene, hexafluoropropylene, vinyl vinyl maleic anhydride, maleic acid, maleic acid ester and maleic acid monomethyl ester. Two or more species may be used. A method of introducing the monomer into the main chain by copolymerization when the polymer (B) is polymerized, and a method of introducing it as a side chain by grafting. Further, the melting point may be adjusted by controlling the ratio of the head-to-head bonding (-CH2-CF2-CF2-CH2-) of the vinylidene fluoride unit.

The lower limit value of the weight average molecular weight of the polymer (B) containing vinylidene fluoride units is preferably 100,000 or more, more preferably 150,000 or more, the upper limit value is preferably 750,000 or less, more preferably 700,000 or less to be.

By setting the melting point and the weight average molecular weight of the polymer (B) containing the vinylidene fluoride unit within the above-described preferable range, the polymer (B) tends to flow under the heating and pressurizing conditions, and the bending strength . When the melting point of the polymer (B) exceeds the upper limit of the above-mentioned preferable range, it is necessary to raise the pressing temperature in the manufacturing process of the winding in order to obtain the bending strength at the time of drying and the peeling force at the time of drying. In this case, the microporous membrane containing polyolefin as a main component may be shrunk. Further, if the weight average molecular weight of the polymer (B) exceeds the upper limit value of the above preferable range, the amount of entanglement of molecular chains increases, and there is a fear that the polymer (B) can not sufficiently flow under the press conditions. When the weight-average molecular weight of the polymer (B) is lower than the lower limit of the above-mentioned preferable range, the amount of the molecular chains to be intertwined is excessively small, so that the strength of the resin becomes weak and the cohesive failure of the porous layer tends to occur.

[3] acrylic resins

Further, since the porous layer contains an acrylic resin, it is possible to improve the bending strength at the time of drying and the peeling force at the time of drying. A separator satisfying the bending strength during drying, the bending strength during wetting and the peeling force at the time of drying can be obtained only by the vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer (A) and the polymer (B) containing the vinylidene fluoride unit I can not get it.

The acrylic resin is preferably a (meth) acrylic acid ester polymer or a copolymer thereof. In the present invention, (meth) acrylic acid ester refers to acrylic acid ester (acrylate) and methacrylic acid ester (methacrylate). Examples of the (meth) acrylic esters include methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, and the like. Particularly, it is preferable to contain butyl acrylate. Butyl acrylate improves the flexibility of the coating film and can suppress the dropout of the particles.

From the viewpoint of adhesion with the electrode, a copolymer of a (meth) acrylic acid ester and a monomer having a cyano group is more preferable as the acrylic resin. Examples of the monomer having a cyano group include an?,? - ethylenically unsaturated monomer having a cyano group, and for example, acrylonitrile or methacrylonitrile is preferable. The acrylic resin is particularly preferably a copolymer of butyl acrylate and acrylonitrile. By controlling the molar ratio, the degree of swelling with respect to the electrolytic solution can be adjusted, and the resin can have appropriate flexibility, and the bending strength Can be improved. The lower limit value of the content of butyl acrylate units in the acrylic resin is preferably 50 mol% or more, more preferably 55 mol% or more, and the upper limit value is preferably 75 mol% or less, more preferably 70 mol% or less to be. By setting the lower limit of the content of butyl acrylate units in the acrylic resin within the above-described preferable range, it is possible to provide the porous layer with appropriate flexibility and to prevent dropping of the porous film. Also, by setting the content of butyl acrylate units in the acrylic resin within the above-described preferable range, the balance between the bending strength during drying, the bending strength during wetting and the peeling force upon drying becomes good.

The acrylic resin can be obtained by a known polymerization method, for example, a method exemplified in JP-A-2013-206846. Ion exchange water, n-butyl acrylate, and acrylonitrile are introduced into an autoclave equipped with a stirrer, and water of a dispersion in which polymer particles obtained by emulsion polymerization are dispersed in water is replaced with N-methyl-2-pyrrolidone Thereby obtaining an acrylic resin solution. Potassium persulfate as a radical polymerization initiator and t-dodecyl mercaptan as a molecular weight regulator may be appropriately used in the polymerization reaction.

The content of the acrylic resin is preferably at least 4% by weight based on the total weight of the vinylidene fluoride-hexafluoropropylene copolymer (A), the polymer (B) containing the vinylidene fluoride unit and the acrylic resin, The upper limit is preferably 40 wt% or less, more preferably 30 wt% or less, further preferably 20 wt% or less. By setting the content of the acrylic resin within the above preferable range, the total amount of the content of the copolymer (A) and the content of the polymer (B) can be set to a certain value or more, so that the oxidation resistance of the porous layer can be maintained.

By setting the content of the vinylidene fluoride-hexafluoropropylene copolymer (A) and the content of the acrylic resin within the above-described preferable range, the porous layer can obtain the bending strength during drying, the bending strength during wetting and the peeling force during drying.

[4] Particles

The porous layer in the present invention may contain particles. By containing particles in the porous layer, the probability of occurrence of a shot between the positive electrode and the negative electrode can be lowered, and an improvement in safety can be expected. Examples of the particles include inorganic particles and organic particles.

Examples of the inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass particles, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, , Molybdenum sulfide, mica, boehmite, magnesium oxide, and the like. Particularly, titanium dioxide, alumina, boehmite and barium sulfate are preferable from the viewpoint of crystal growth property, cost, and availability of the vinylidene fluoride-hexafluoropropylene copolymer.

Examples of the organic particles include crosslinked polystyrene particles, crosslinked acrylic resin particles, and crosslinked methyl methacrylate-based particles.

The content of the particles contained in the porous layer is preferably 90% by weight or less, more preferably 85% by weight or less, and the lower limit value is preferably 50% by weight or more, more preferably 50% By weight, more preferably not less than 60% by weight, still more preferably not less than 65% by weight. When the content of the particles is within the above-mentioned preferable range, a good balance of durability is easily obtained.

When the porous layer contains particles having no adhesive property, the bending strength at the time of wetting, the bending strength at the time of drying and the peeling force at the time of drying tend to decrease. However, even when the porous layer obtained by the resin composition of the present invention contains the particles in the above-mentioned preferable range, the balance between the bending strength in wetting with the electrode, the bending strength in drying and the peeling force in drying is good.

)의 1.5배 이상 50배 이하인 것이 바람직하고, 보다 바람직하게는 2.0배 이상 20배 이하이다. 평균 유량 세공경은, JIS K3832 이나 ASTM F316-86을 따라서 측정되고, 예를 들면, 펌 포로미터(Perm Porometer) (PMI사 제품, CFP-1500A)를 사용하여, 드라이-업(Dry-up), 웨트-업(Wet-up)의 순으로 측정했다. 웨트-업에는 표면장력을 미리 알고 있는 PMI사 제품 갈윅(Galwick)(상품명)로 충분히 적신 미세다공질막에 압력을 가하여, 공기가 관통하기 시작하는 압력으로부터 환산되는 공경을 최대 공경으로 했다. 평균 유량 세공경에 대해서는, 드라이-업 측정에서 압력, 유량 곡선의 1/2의 기울기를 나타내는 곡선과 웨트-업 측정의 곡선이 교차하는 점의 압력으로부터 공경을 환산했다. 압력과 공경의 환산은 하기 수학식을 사용했다.From the viewpoint of particle detachment, the average particle diameter of the particles is the average flow pore diameter of the microporous membrane

), More preferably not less than 2.0 times and not more than 20 times. The average flow rate is measured according to JIS K3832 or ASTM F316-86. For example, the average flow rate is measured by using a Perm Porometer (manufactured by PMI, CFP-1500A) , And wet-up (wet-up). In the wet-up, pressure was applied to the microporous membrane sufficiently wetted with the Galwick (trade name) product of PMI, which had previously known the surface tension, and the pore converted from the pressure at which air began to penetrate was set to the maximum pore size. For the average flow rate, the pore diameter was calculated from the pressure at the point where the curve representing the slope of 1/2 of the pressure and the flow rate curve intersected with the curve of the wet-up measurement in the dry-up measurement. The conversion of pressure and pore size was calculated using the following equation.

? (mN / m) is the surface tension of the liquid, P (Pa) is the pressure, and C is the pressure of the liquid. Was a constant.)

The average particle diameter of the particles is preferably 0.3 to 1.8 mu m, more preferably 0.5 to 1.5 mu m, and still more preferably 0.9 to 1.3 mu m from the viewpoint of slidability with the winding core at the time of cell winding, to be. The average particle diameter of the particles can be measured using a laser diffraction method or a dynamic light scattering method measuring device. For example, particles dispersed in an aqueous solution containing a surfactant using an ultrasonic probe were measured with a particle size distribution analyzer (Microtrack HRA, manufactured by Nikkiso Co., Ltd.) %, The value of the particle diameter (D50) is preferably the average particle diameter. The shape of the particles is not particularly limited, but may be a sphere shape, a substantially spherical shape, a plate shape, or a needle shape.

[5] Physical properties of the porous layer

The thickness of the porous layer is preferably 0.5 to 3 占 퐉, more preferably 1 to 2.5 占 퐉, and still more preferably 1 to 2 占 퐉 per side. When the film thickness per side is 0.5 m or more, the bending strength at the time of wetting, the bending strength at the time of drying and the peeling force at the time of drying can be secured. When the film thickness per side is 3 m or less, the winding volume can be suppressed, which is suitable for increasing the capacity of the battery to be carried out later.

The porosity of the porous layer is preferably 30 to 90%, more preferably 40 to 70%. By setting the porosity of the porous layer within the above-described preferable range, the electrical resistance of the separator can be prevented from rising, allowing a large current to flow, and the film strength can be maintained.

[6] Manufacturing Method of Battery Separator

The method for producing a separator for a battery of the present invention includes the following steps (1) to (3) in order.

(1) a step of obtaining a fluororesin solution in which a vinylidene fluoride-hexafluoropropylene copolymer (A) and a polymer (B) containing a vinylidene fluoride unit are dissolved in a solvent

(2) a step of adding an acrylic resin solution to a fluororesin solution and mixing to obtain a coating solution

(3) coating the coating liquid on the microporous membrane, immersing it in the coagulating liquid, washing and drying

(1) Step of obtaining a fluorine resin solution

The solvent can dissolve the vinylidene fluoride-hexafluoropropylene copolymer (A) and the polymer (B) containing the vinylidene fluoride unit, and can dissolve or disperse the acrylic resin, ) Is not particularly limited. From the viewpoint of solubility and low volatility, the solvent is preferably N-methyl-2-pyrrolidone.

In the case of providing a porous layer containing particles, it is important to adjust a fluororesin solution (also referred to as a dispersion liquid) in which particles are dispersed in advance. (A) and a polymer (B) containing a vinylidene fluoride unit are dissolved in a solvent, particles are added thereto while stirring, and the mixture is stirred for a predetermined time (for example, about 1 hour) Dispersed by preliminary dispersion by stirring with a disperser or the like, and a step of dispersing the particles using a bead mill or a paint shaker (dispersion step) to obtain a fluororesin solution in which aggregation of particles is reduced.

(2) Process for obtaining coating liquid

An acrylic resin solution is added to a fluororesin solution containing a vinylidene fluoride-hexafluoropropylene copolymer (A) and a polymer (B) containing a vinylidene fluoride unit, and the acrylic resin solution is added to a three- (Three-One Motor) to prepare a coating liquid.

The acrylic resin solution is a solution in which an acrylic resin is dissolved or dispersed in a solvent, and the solvent used herein is preferably the same solvent as in the step (1). Particularly, N-methyl-2-pyrrolidone is preferable from the viewpoints of solubility and low volatility. From the viewpoint of operability, it is preferable that the acrylic resin solution is obtained by polymerizing an acrylic resin and then adding a solvent by adding N-methyl-2-pyrrolidone and distilling it.

In the case of providing a porous layer containing particles, it is important to add an acrylic resin solution to a fluororesin solution (dispersion) in which the particles are dispersed. That is, it is important that no acrylic resin is contained in the dispersion step. (B) a vinylidene fluoride-hexafluoropropylene copolymer (A), a polymer (B) containing a vinylidene fluoride unit, and an acrylic resin and particles are simultaneously added to a solvent to prepare a coating liquid. It is presumed that the coating liquid starts to gel gradually due to heat and shearing at the time of dispersing the hydrophilic group and the acrylic resin (especially when containing butyl acrylate), and this is industrially unsuitable. Further, due to the effect of the thickening, it becomes difficult to coat the thin film with the thickness of the porous layer of 3 mu m or less per side. By the steps (1) and (2) in the production method of the present invention, gelation of the coating liquid can be suppressed, thin film coating becomes possible, and storage stability of the coating liquid is improved.

(3) coating the coating liquid on the microporous membrane, immersing it in the coagulating solution, washing and drying

The coating liquid is applied to the microporous membrane, and the applied microporous membrane is immersed in the coagulating solution to form the polymer (B) containing the vinylidene fluoride-hexafluoropropylene copolymer (A), the vinylidene fluoride unit and the acrylic resin Separated, and solidified in a state having a three-dimensional network structure, followed by washing and drying. As a result, a microporous membrane and a separator for a battery having a porous layer on the surface of the microporous membrane can be obtained.

The coating liquid may be applied to the microporous membrane by a known method. Examples of the method include a dip coating method, a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, A Meyer bar coating method, a pipe doctor method, a blade coating method and a die coating method. These methods can be used alone or in combination.

Preferably, the coagulating solution is water, and the polymer (B) containing the vinylidene fluoride-hexafluoropropylene copolymer (A), the vinylidene fluoride unit and the aqueous solution containing 1 to 20% by weight of the good solvent for the acrylic resin By weight, more preferably 5 to 15% by weight. Examples of the good solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide and N, N-dimethylacetamide. The immersion time in the coagulating liquid is preferably 3 seconds or more. The upper limit is not limited, but 10 seconds is sufficient.

Water can be used for cleaning. The drying can be carried out using, for example, hot air at 100 ° C or lower.

The battery separator of the present invention can be used as a separator for batteries such as a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a lithium ion secondary battery, a lithium polymer secondary battery and a lithium- . Particularly, it is preferable to use it as a separator of a lithium ion secondary battery.

[7] Properties of battery separator

The bending strength of the battery separator in wetting is preferably 4 N or more. The upper limit value of the bending strength at the time of wetting is not particularly defined, but 15 N is sufficient. By keeping the ratio within the above-mentioned preferable range, it is possible to suppress the partial glass at the interface between the separator and the electrode, thereby suppressing an increase in the internal resistance of the battery and deterioration of the battery characteristics.

The bending strength of the cell separator during drying is preferably 5 N or more. The upper limit of the bending strength at the time of drying is not particularly specified, but 25 N is sufficient. Within the above-mentioned preferable range, it is expected that warpage and deformation of the wound electrode body can be suppressed.

The separating force for drying the battery separator is preferably 8 N / m or more. The upper limit of the peeling force during drying is not particularly specified, but 40 N / m is sufficient. By making the thickness within the above preferable range, it is expected that the wound electrode body or the laminated electrode body can be transported without being disturbed by the electrode body.

The battery separator satisfies both the bending strength at the time of wetting, the bending strength at the time of drying and the peeling force at the time of drying, and more specifically, the bending strength at the time of wetting is not less than 4 N, the bending strength at the time of drying is not less than 5 N, And the peel force at the time satisfies 8 N / m or more.

EXAMPLES Hereinafter, examples will be specifically described, but the present invention is not limited by these examples. On the other hand, the measurement value in the examples is a value measured by the following method.

1. Bending strength at wet

Generally, when a binder of a fluororesin is used for the positive electrode and a porous layer containing the fluororesin is provided on the separator, adhesion between the fluororesins tends to be ensured due to interdiffusion between the fluororesins. On the other hand, a binder other than the fluororesin is used for the negative electrode, and diffusion of the fluorine resin hardly occurs, so that it is difficult to obtain adhesion of the negative electrode to the separator as compared with the positive electrode. Thus, in this measurement, the adhesion between the separator and the negative electrode was evaluated by using the bending strength described below as an index.

(1) Production of cathode

An aqueous solution containing 1.5 parts by mass of carboxymethylcellulose was added to and mixed with 96.5 parts by mass of artificial graphite, and 2 parts by mass of styrene butadiene latex as a solid component was added and mixed to obtain a slurry containing the negative electrode material mixture. The slurry containing the negative electrode mixture was uniformly applied to both surfaces of a negative electrode current collector made of a copper foil having a thickness of 8 占 퐉 and dried to form a negative electrode layer and then compression molded by a roll press machine, And the density of the negative electrode layer was 1.5 g / cm < 3 >.

(2) Fabrication of test winding

)하여 시험용 권회체를 얻었다. 시험용 권회체는 길이 약 34 ㎜×폭 약 28 ㎜가 되었다.The negative electrode (161 mm in the machine direction × 30 mm in the width direction) prepared above and the separator (160 mm in the machine direction × 34 mm in the width direction) prepared in the examples and comparative examples were superimposed and a metal plate (length 300 mm, width 25 mm, 1 mm) as a winding core, the separator and the negative electrode were wound up so that the separator was inside, and the metal sheet was drawn

) To obtain a test winding. The test winding was about 34 mm in length x about 28 mm in width.

(3) Method of measuring bending strength in wet state

Two test pieces were put in a bag-like laminate film in which three laminate films (length 70 mm, width 65 mm, thickness 0.07 mm) made of polypropylene were stacked and three of the four sides were fused. 500 μL of an electrolytic solution obtained by dissolving LiPF 6 at a rate of 1 mol / L in a solvent mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3: 7 was injected through the opening of the laminate film in a glove box, impregnated into a test winding, One side of the opening was sealed with a sealer.

Next, the test rolled body sealed in the laminated film was sandwiched between two gaskets (thickness 1 mm, 5 cm x 5 cm), followed by pressing with a precision heating pressurizer (CYPT-10, manufactured by Shin-Toko Kagaku Co., Ltd.) Lt; 0 > C and 0.6 MPa for 2 minutes, and then cooled at room temperature. The bending strength at the time of wetting was measured by using a universal testing machine (AGS-J manufactured by Shimadzu Seisakusho Co., Ltd.) with respect to the test winding after being pressurized while being sealed in the laminated film. Details will be described below.

Two aluminum-made L-shaped angles (1 mm in thickness, 10 mm in length and 5 cm in length) were arranged parallel to each other so that the 90 ° portion was on the upper side and the 90 ° portion was set as a fulcrum And fixed at a distance of 15 mm. At the midpoint of the point distance between the two aluminum L-shaped angles, at the midpoint of 7.5 mm, align the midpoint of the side of the test piece in the width direction (about 28 ㎜), so that it does not protrude from the longitudinal side of the L- The body was placed.

)로서 알루미늄제 L자 앵글(두께 1 ㎜, 10 ㎜×10 ㎜, 길이 4 cm)의 길이 방향의 변으로부터 시험용 권회체의 길이 방향의 변(약 34 ㎜)이 튀어나오지 않도록, 또한 평행하게 하여, 시험용 권회체의 폭방향의 변의 중간점에 알루미늄제 L자 앵글에 90° 부분을 맞추고, 90° 부분이 아래가 되도록 알루미늄제 L자 앵글을 만능 시험기의 로드셀(로드셀 용량 50 N)에 고정했다. 3개의 시험용 권회체를 부하 속도 0.5 ㎜/min으로 측정하여 얻어진 최대 시험력의 평균치를 습윤 시 굽힘 강도로 했다.Next,

(About 34 mm) in the longitudinal direction of the test winding from the side of the aluminum L-shaped angle (thickness 1 mm, 10 mm x 10 mm, length 4 cm) , An aluminum L-shaped angle was fixed to a load cell (load cell capacity 50 N) of the universal testing machine so that a 90 ° portion was aligned with the aluminum L-shaped angle at the midpoint between the widthwise sides of the test winding . The average of the maximum test force obtained by measuring the three test windings at a load speed of 0.5 mm / min was defined as the wet bending strength.

2. Bending strength during drying

(1) Production of cathode

The negative electrode having the same bending strength as that of the above-mentioned 1. wet was used.

(2) Fabrication of test winding

The test rolls having the same bending strength as above in the wetting 1 were used.

(3) Method of measuring bending strength in drying

The prepared test specimens were sandwiched between two gaskets (thickness 1 mm, 5 cm x 5 cm), and the specimens were subjected to a heat treatment at 70 DEG C and 0.6 MPa for 2 minutes using a precision heating and pressing apparatus (CYPT-10, manufactured by Shin- The mixture was pressurized and allowed to cool at room temperature. The test specimens were placed in the same manner as in the above-mentioned method for measuring the flexural strength at the time of wetting, and three test specimens were prepared under the following conditions using an universal testing machine (AGS-J manufactured by Shimadzu Seisakusho Co., Ltd.) The average value of the maximum test force obtained by measurement was taken as the bending strength at the time of drying.

Distance between points: 15 mm

Load cell capacity: 50 N

Load speed: 0.5 mm / min

3. Peeling force during drying

(1) Production of cathode

The negative electrode having the same bending strength as that of the above-mentioned 1. wet was used.

(2) Preparation of peel test piece

The negative electrode (70 mm x 15 mm) prepared above and the separator (90 mm in the machine direction x 20 mm in the width direction) prepared in the examples and comparative examples were superposed one on the other and were put into two gaskets (0.5 mm thick and 95 mm x 27 mm thick) And pressurized with a precision heating and pressing apparatus (CYPT-10, manufactured by Shin-Toko Kagaku Co., Ltd.) at 90 DEG C and 8 MPa for 2 minutes, and then cooled at room temperature. A double-sided tape having a width of 1 cm was attached to the negative electrode side of the laminate of the negative electrode and the separator. The other side of the double-sided tape was bonded to an SUS plate (3 mm thick, 150 mm long x 50 mm wide) The SUS plate was stuck so that its longitudinal direction was parallel. This was used as a peel test piece.

(3) Measurement method of peeling force in drying

Using a universal testing machine (manufactured by Shimadzu Seisakusho Co., Ltd., AGS-J), a separator was put on the chuck of the load cell and a 180 degree peel test was carried out at a test speed of 300 mm / min. The value obtained by averaging the measurement values from 20 mm to 70 mm of the stroke during the peeling test was taken as the peeling force of the peeling test piece. A total of three peeling test pieces were measured, and the value obtained by converting the average value of the peeling force in terms of the width was taken as the peeling force (N / m) upon drying.

4. Melting point measurement

A differential scanning calorimetric analyzer (manufactured by Kabushiki Kaisha Kinkelmer Co., Ltd. DSC) was used as a sample for measurement by placing 7 mg of resin in a measuring pan under the following conditions. After the temperature was first raised and cooled, the peak top of the endothermic peak at the second temperature rise was taken as the melting point.

Temperature rise and cooling rate: ± 10 ° C / min

Measuring temperature range: 30 ~ 230 ℃

5. Thickness

Using a contact-type film thickness meter (RIGHT MATIC (registered trademark) series 318 manufactured by Mitsutoyo Co., Ltd.), using a cemented carbide spherical measuring machine? 9.5 mm, 20 points And the average value of the obtained measurement values was taken as the film thickness.

Example

Example 1

[Copolymer (a)]

As the copolymer (A), a copolymer (a) was synthesized as follows. Vinylidene fluoride-hexafluoropropylene copolymer (a) was synthesized by suspension polymerization using vinylidene fluoride, hexafluoropropylene and maleic acid monomethyl ester as starting materials. The obtained copolymer (a) was confirmed by NMR measurement to have a weight average molecular weight of 1,500,000 and a molar ratio of vinylidene fluoride / hexafluoropropylene / maleic acid monomethylester of 98.0 / 1.5 / 0.5.

[Copolymer (b1)]

As the polymer (B), a copolymer (b1) was synthesized as follows. Vinylidene fluoride-hexafluoropropylene copolymer (b1) was synthesized by suspension polymerization using vinylidene fluoride and hexafluoropropylene as starting materials. The obtained copolymer (b1) was confirmed by NMR measurement to have a weight average molecular weight of 300,000 and a molar ratio of vinylidene fluoride / hexafluoropropylene of 93/7.

[Acrylic resin]

Acrylic resin was synthesized by emulsion polymerization using acrylonitrile and n-butyl acrylate as starting materials and then water was substituted with N-methyl-2-pyrrolidone to obtain acrylic resin having a solid content concentration of 5 mass% To obtain a resin solution. The obtained acrylic resin was confirmed to have a Tg of -5 캜 and a molar ratio of acrylonitrile unit / acrylic acid ester unit of 38/62 by NMR measurement.

[Preparation of battery separator]

7.1 parts by mass of the copolymer (a), 21.4 parts by mass of the copolymer (b1) and 359.3 parts by mass of NMP were mixed, and then 70 parts by mass of alumina particles (average particle diameter 1.1 mu m) And preliminarily stirred at 2000 rpm for 1 hour by a disper. Next, using a dyno mill (Shinomaru Enterprise Co., Ltd., Dyno Mill Multilabo (1.46 L vessel, filling rate 80%, 0.5 mm alumina beads)) under conditions of a flow rate of 11 kg / hr and a peripheral speed of 10 m / s To give a dispersion. The acrylic resin solution was mixed with the dispersion and stirred at 500 rpm for 30 minutes with a Srijwo motor equipped with a stirring blade and filtered to obtain a solid content concentration of 20.5% by mass and an alumina particle: copolymer (a): copolymer (b1) Acrylic resin in a weight ratio of 70: 7.1: 21.4: 1.5. A coating solution was applied to both surfaces of a 7 占 퐉 -thick polyethylene microporous membrane by dip coating, immersed in an aqueous solution, washed with pure water, and dried at 50 占 폚 to obtain a battery separator having a thickness of 11 占 퐉.

Example 2

Except that a coating liquid having a solid content concentration of 18.0 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 14.3: 14.2: 1.5 was used, .

Example 3

Except that a coating liquid having a solid content concentration of 15.5 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 21.4: 7.1: 1.5 was used, .

Example 4

Except that a coating liquid having a solid content concentration of 20.5 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 6.8: 20.2: 3.0 was used, .

Example 5

The procedure of Example 1 was repeated except that a coating liquid having a solid content concentration of 18.0 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 13.5: .

Example 6

Except that a coating liquid having a solid content concentration of 15.5 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 20.2: 6.8: 3.0 was used, .

Example 7

Except that a coating liquid having a solid content concentration of 20.5 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 6.4: 19.1: 4.5 was used, .

Example 8

Except that a coating liquid having a solid content concentration of 18.0 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 12.8: 12.7: 4.5 was used, .

Example 9

Except that a coating liquid having a solid content concentration of 19.5 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 19.1: 6.4: 4.5 was used, .

Example 10

Except that a coating liquid having a solid content concentration of 20.5 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 6.0: 18.0: 6.0 was used, .

Example 11

Except that a coating liquid having a solid content concentration of 18.0 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 12.0: 12.0: 6.0 was used, .

Example 12

Except that a coating liquid having a solid content concentration of 15.5 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 70: 18.0: 6.0: 6.0 was used, .

Example 13

Except that a coating liquid having a solid content concentration of 21.0 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 78.8: 9.0: 9.0: 3.2 was used, .

Example 14

Except that a coating liquid having a solid content concentration of 25.0 mass% and an alumina particle: copolymer (a): copolymer (b1): acrylic resin weight ratio of 85.2: 6.3: 6.3: 2.2 was used, .

Example 15

[Copolymer (b2)]

As the polymer (B), a copolymer (b2) was synthesized as follows. Vinylidene fluoride-tetrafluoroethylene copolymer (b2) was synthesized by suspension polymerization using vinylidene fluoride and tetrafluoroethylene as starting materials. The obtained vinylidene fluoride-tetrafluoroethylene copolymer (b2) was confirmed by NMR measurement to have a weight average molecular weight of 280,000 and a molar ratio of vinylidene fluoride / tetrafluoroethylene of 90/10.

[Preparation of battery separator]

(B2): acrylic resin in a weight ratio of 70: 13.5: 13.5: 3.0 (mass%) was obtained by using the copolymer (b2) instead of the copolymer (b1) , A separator for a battery was obtained in the same manner as in Example 1. The results are shown in Table 1.

Example 16

, 45 parts by mass of the copolymer (a), 45 parts by mass of the copolymer (b1) and 1329 parts by mass of NMP were mixed and dissolved. The acrylic resin solution was mixed with this solution, stirred with a three-wheel motor equipped with a stirring blade at 500 rpm for 30 minutes, and filtered to obtain a copolymer having a solid concentration of 6.6% by mass, the copolymer (a) To obtain a coating liquid having a weight ratio of 45.0: 45.0: 10.0. A coating solution was applied to both surfaces of a 7 占 퐉 -thick polyethylene microporous membrane by dip coating, immersed in an aqueous solution, washed with pure water, and dried at 50 占 폚 to obtain a battery separator having a thickness of 11 占 퐉.

Comparative Example 1

30.0 parts by mass of the copolymer (b1) and 334.8 parts by mass of NMP were mixed. Thereafter, 70 parts by mass of alumina particles (average particle diameter 1.1 mu m) was added while stirring with a disperser, Lt; / RTI > Next, using a dyno mill (Shinomaru Enterprise Co., Ltd., Dyno Mill Multilabo (1.46 L vessel, filling rate 80%, 0.5 mm alumina beads)) at a flow rate of 11 kg / hr and a peripheral speed of 10 m / s Under a nitrogen atmosphere to obtain a dispersion. This was filtered to obtain a coating liquid having a solid content concentration of 23.0 mass% and a weight ratio of alumina particle: copolymer (b1) of 70: 30.0. A coating solution was applied to both surfaces of a 7 占 퐉 -thick polyethylene microporous membrane by dip coating, immersed in an aqueous solution, washed with pure water, and dried at 50 占 폚 to obtain a battery separator having a thickness of 11 占 퐉.

Comparative Example 2

7.5 parts by mass of the copolymer (a), 22.5 parts by mass of the copolymer (b1) and 387.8 parts by mass of NMP were mixed, and the mixture was prepared and filtered in the same manner as in Comparative Example 1 to obtain a solid content concentration of 20.5% by mass, (a): copolymer (b1) was 70: 7.5: 22.5. This was coated in the same manner as in Comparative Example 1 to obtain a battery separator.

Comparative Example 3

A separator for a battery was obtained in the same manner as in Comparative Example 2 except that a coating liquid prepared so that the solid content concentration was 18.0 mass% and the alumina particle: copolymer (a): copolymer (b1) weight ratio was 70: 15.0: 15.0.

Comparative Example 4

A separator for a battery was obtained in the same manner as in Comparative Example 2 except that a coating liquid prepared so that the solid content concentration was 15.5 mass% and the alumina particle: copolymer (a): copolymer (b1) weight ratio was 70: 22.5: 7.5.

Comparative Example 5

The same procedure as in Comparative Example 1 was repeated except that 30 parts by mass of the copolymer (a) and 669.2 parts by mass of NMP were mixed. The solid content concentration was 13.0 mass% and the weight ratio of the alumina particle: copolymer (a) was 70: To obtain a coating solution so prepared. This was coated in the same manner as in Comparative Example 1 to obtain a battery separator.

Comparative Example 6

A separator for a battery was obtained in the same manner as in Example 1 except that a coating liquid prepared so that the solid content concentration was 23.0 mass% and the alumina particle: copolymer (b1): acrylic resin weight ratio was 70: 28.5: 1.5.

Comparative Example 7

A separator for a battery was obtained in the same manner as in Example 1 except that a coating liquid prepared so that the solid content concentration was 13.0 mass% and the weight ratio of alumina particles: copolymer (a): acrylic resin was 70: 28.5: 1.5.

Comparative Example 8

A separator for a battery was obtained in the same manner as in Example 1 except that the coating liquid prepared so that the solid content concentration was 23.0 mass% and the alumina particle: copolymer (b1): acrylic resin weight ratio was 70: 27.0: 3.0.

Comparative Example 9

A separator for a battery was obtained in the same manner as in Example 1 except that a coating liquid prepared so that the solid content concentration was 13.0 mass% and the weight ratio of alumina particles: copolymer (a): acrylic resin was 70: 27.0: 3.0.

Comparative Example 10

A separator for a battery was obtained in the same manner as in Example 1 except that a coating liquid prepared so that the solid content concentration was 23.0 mass% and the alumina particle: copolymer (b1): acrylic resin weight ratio was 70: 25.5: 4.5 was used.

Comparative Example 11

A separator for a battery was obtained in the same manner as in Example 1 except that a coating liquid prepared so that the solid content concentration was 23.0 mass% and the alumina particle: copolymer (b1): acrylic resin weight ratio was 70: 24.0: 6.0.

Comparative Example 12

[Copolymer (b3)]

A vinylidene fluoride-tetrafluoroethylene copolymer was synthesized by suspension polymerization using vinylidene fluoride and tetrafluoroethylene as starting materials. The obtained vinylidene fluoride-tetrafluoroethylene copolymer had a weight average molecular weight of 9,500, and a molar ratio of vinylidene fluoride / tetrafluoroethylene of 95/5 was confirmed by NMR measurement.

[Preparation of battery separator]

(B3) was used in place of the copolymer (b1), the solid content concentration was 18.0 mass%, the weight ratio of the alumina particle: copolymer (a): copolymer (b3): acrylic resin was 70: 13.5: , A separator for a battery was obtained in the same manner as in Example 1. The results are shown in Table 1.

Table 1 shows the characteristics of the battery separator obtained in Examples 1 to 16 and Comparative Examples 1 to 12.

[Table 1]

Content (%) of copolymer (A) *: represents the weight% of copolymer (A) based on the total weight of copolymer (A) and polymer (B)

Content (%) of acrylic resin **: It represents the weight percentage of acrylic resin with respect to the total weight of copolymer (A), polymer (B) and acrylic resin.

1: cathode
2: Battery separator
3: Laminated film
4: Aluminum L-shaped angle
5: Inlaid aluminum L-shaped angle

Claims (15)

And a porous layer formed on at least one side of the microporous membrane, wherein the porous layer comprises a vinylidene fluoride-hexafluoropropylene copolymer (A) and a polymer (B) containing a vinylidene fluoride unit, And an acrylic resin, wherein the vinylidene fluoride-hexafluoropropylene copolymer (A) contains 0.3 mol% to 3 mol% of a hydrophilic group and a hexafluoropropylene unit, and the vinylidene fluoride-hexafluoropropylene copolymer The polymer (B) has a melting point of 60 占 폚 or more and 145 占 폚 or less and a weight average molecular weight of 100,000 or more and 750,000 or less. The separator according to claim 1, wherein the vinylidene fluoride-hexafluoropropylene copolymer (A) has a weight average molecular weight of more than 750,000 and not more than 2,000,000. The battery separator according to claim 1 or 2, wherein the porous layer contains particles. 4. The positive resist composition as claimed in any one of claims 1 to 3, wherein the content of the vinylidene fluoride-hexafluoropropylene copolymer (A) is in the range of 0.1 to 10 parts by weight based on 100 parts by weight of the vinylidene fluoride- (A) and a vinylidene fluoride unit (B), wherein the content of the acrylic resin is not less than 15% by weight and not more than 85% by weight based on the total weight of the polymer (B) containing the vinylidene fluoride- Is not less than 4% by weight and not more than 40% by weight based on the total weight of the acrylic resin (B) and the acrylic resin. The battery separator according to any one of claims 1 to 4, wherein the acrylic resin is a copolymer of a (meth) acrylate ester and a monomer having a cyano group. The battery separator according to any one of claims 1 to 4, wherein the acrylic resin is a copolymer containing butyl acrylate. The battery separator according to any one of claims 1 to 4, wherein the acrylic resin is a copolymer of butyl acrylate and acrylonitrile. The battery separator according to claim 6 or 7, wherein the content of butyl acrylate in the acrylic resin is 50 mol% to 75 mol%. The battery separator according to any one of claims 1 to 8, wherein the content of the hydrophilic group in the vinylidene fluoride-hexafluoropropylene copolymer (A) is 0.1 mol% to 5 mol%. The battery separator according to any one of claims 1 to 9, wherein the bending strength in wetting is not less than 4 N, the bending strength in drying is not less than 5 N, and the peeling force in drying is 8 N / m. 11. The battery separator according to any one of claims 3 to 10, wherein the content of the particles is 50% by weight or more and 90% by weight or less based on the total weight of the porous layer. 12. The battery separator according to any one of claims 3 to 11, wherein the particles contain at least one kind selected from the group consisting of alumina, titania, boehmite and barium sulfate. 13. The battery separator according to any one of claims 1 to 12, wherein the thickness of the porous layer is 0.5 to 3 mu m per side. The battery separator according to any one of claims 1 to 13, wherein the microporous membrane is a polyolefin microporous membrane. (1) A process for producing a fluorinated resin solution, comprising the steps of: (1) obtaining a fluorinated resin solution obtained by dissolving a vinylidene fluoride-hexafluoropropylene copolymer (A) and a polymer (B)
(2) a step of adding an acrylic resin solution in which an acrylic resin is dissolved in a solvent to a fluorine resin solution and mixing them to obtain a coating solution,
(3) a step of coating the coating liquid on the microporous membrane, immersing the coating liquid in the coagulating solution, washing and drying, and the vinylidene fluoride-hexafluoropropylene copolymer (A) sequentially contains the hydrophilic group and the hexafluoro (B) containing 0.3 mol% to 3 mol% of propylene units and having a melting point of 60 ° C or more and 145 ° C or less and a weight average molecular weight of 100,000 or more and 750,000 or less, The method for producing a separator for a battery according to any one of claims 1 to 14, wherein the resin contains a butyl acrylate unit.

Images