JP2016038934A - Method of manufacturing separator for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method that can perform high-speed processing while suppressing occurrence of coating streaks even when reduction of the thickness of a battery separator is promoted in a method of manufacturing a separator for a battery in which reformed porous layers are laminated on both the surfaces of a porous membrane formed of polyolefin resin.SOLUTION: A method of manufacturing a separator for a battery in which reformed porous layers are laminated on both the surfaces of a polyolefin porous membrane 1 contains a step of coating both the surfaces with coating liquid at the same time, a solidifying step, a cleaning step and a drying step. A slur preventing device 9 is brought into contact with the gap between a coating device 10 for coating both the surfaces at the same time and a solidification tank.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a method for manufacturing a battery separator. In particular, it is useful as a method for producing a battery separator having a modified porous layer.

  Thermoplastic resin microporous membranes are widely used as separators and filters. For example, separators for lithium ion secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, or polymer batteries for separators, separators for electric double layer capacitors, filters for reverse osmosis filtration membranes, ultrafiltration Examples thereof include a membrane and a microfiltration membrane. In addition, it is used for moisture-permeable and waterproof clothing, medical materials, and the like. In particular, as a separator for a lithium ion secondary battery, it has ion permeability by impregnation with an electrolytic solution, is excellent in electrical insulation, electrolytic solution resistance and oxidation resistance, and has a temperature of about 120 to 150 ° C. during abnormal battery temperature rise. In polyethylene, a porous film made of polyethylene is also preferably used, which has a pore blocking effect that blocks ion permeation and suppresses excessive temperature rise. However, if the temperature continues to rise after clogging for some reason, a film breakage may occur due to a decrease in viscosity of the polyethylene constituting the film or a contraction of the film. This phenomenon is not limited to polyethylene, and even when other thermoplastic resins are used, the phenomenon cannot be avoided beyond the melting point of the resin constituting the porous film.

  Lithium-ion battery separators are deeply involved in battery characteristics, battery productivity, and battery safety. Excellent mechanical characteristics, heat resistance, permeability, dimensional stability, pore clogging characteristics (shutdown characteristics), melt film breaking characteristics (Melt down characteristic) etc. are required. Furthermore, in order to improve the cycle characteristics of the battery, it is required to improve the electrolyte permeability in order to improve the adhesion with the electrode material and the productivity. Therefore, a separator in which various modified porous layers are laminated on a porous membrane has been studied so far. For the modified porous layer, polyamideimide resin, polyimide resin, aromatic polyamide resin, fluorine resin having excellent electrode adhesion, etc. having both heat resistance and electrolyte solution permeability are suitably used. The modified porous layer in the present invention refers to a layer containing a resin that imparts or improves at least one function such as heat resistance, adhesion to an electrode material, and electrolyte permeability.

  In order to reduce the cost of the battery separator, it is expected that the processing speed (conveyance speed) will be further increased in the porous film forming process and the modified porous layer stacking process. Moreover, in order to improve battery capacity, it is necessary to increase not only the electrode sheet but also the separator, the area that can be filled in the container, and it is expected that the separator will become thinner.

Various studies have been made to solve the above problems.
In Example 1 of Patent Document 1, a fluororesin solution is applied to both surfaces of a polyethylene microporous membrane, and then entered into a coagulation tank, washed with water and dried to obtain a separator for a non-aqueous secondary battery.

  In Example 1 of Patent Document 2, a fluororesin solution is placed in a tank in which two Meyer bars are arranged in parallel at the bottom, and a polypropylene microporous film enters the tank from the top of the tank at a conveyance speed of 3 m / min. The fluorine-based solution is applied to both sides by passing between two Meyer bars, and then is allowed to enter the coagulation tank without being brought into contact with other devices, washed with water and dried to obtain a composite porous membrane. ing.

  In Example 2 of Patent Document 3, a meta-type wholly aromatic polyamide resin solution containing alumina particles is placed in a tank in which two Meyer bars are arranged in parallel at the bottom, and a polyethylene microporous membrane is placed from the top of the tank into the tank. The resin solution was applied to both sides by entering at a conveyance speed of 20 m / min and passing between two Meyer bars, then after passing through the pre-coagulation device, entering the coagulation tank, washing with water and drying, A battery separator has been obtained.

  In the future, the transport speed during coating will tend to be increased, and soft materials such as polyolefin porous membranes used for battery separators are more likely to blur during transport as the transport speed increases. . This tendency becomes more prominent as the thickness of the polyolefin porous membrane serving as the substrate decreases.

  In the coating methods of Patent Document 1 and Patent Document 2, for example, when the conveyance speed is 30 m / min or more, a coating streak may occur in the longitudinal direction due to blurring of a polyolefin porous film serving as a base material. As the speed increases, the clearance between the two Meyer bars needs to be reduced in order to adjust the coating amount, and therefore, coating stripes are more likely to occur.

Japanese Patent No. 4988973 JP 2011-012266 A JP 2010-149011 A

  Assuming that lithium-ion secondary batteries will continue to cost more and more in the future, the present inventors have provided a method for producing a battery separator in which a modified porous layer is laminated on both sides of a porous film made of a polyolefin resin. It is an object of the present invention to provide a production method that is less likely to cause coating streaks even when battery separators are made thinner and that can be processed at high speed. The above-mentioned problem is a problem peculiar to battery separators that are not observed in a coating process of a general thermoplastic resin film having relatively high rigidity. In addition, the coating streaks referred to in this specification are streaks extending in the conveying direction of the polyolefin porous membrane that can be visually detected, and the length is approximately 5 to 100 cm, and a plurality of strips are spaced at intervals of 1 to 50 mm in the coating width direction. Or streak-like defects over the entire coating width.

In order to solve the above-described problems, the battery separator manufacturing method of the present invention has the following configuration. That is,
1. A method for producing a battery separator in which a modified porous layer is formed on the surface of a polyolefin porous membrane,
(1) a step of simultaneously applying a coating solution obtained by dissolving a resin in a solvent on both surfaces of the polyolefin porous membrane;
(2) a step of solidifying the resin component in the applied coating liquid;
(3) a cleaning step;
(4) including a step of drying,
Between the said process (1) and the said process (2), the process of making the coated polyolefin porous membrane contact an anti-blur apparatus, and the conveyance speed of (1)-(4) is 30 m / min or more A method for producing a battery separator.
2. 2. The method for producing a battery separator as described in 1 above, wherein the polyolefin porous membrane has a thickness of 25 μm or less.
3. 3. The method for producing a battery separator as described in 1 or 2 above, wherein the resin is a fluorine resin or a polyamideimide resin.
4). The manufacturing method of the battery separator as described in any one of the above 1-3, wherein the coating liquid contains inorganic particles or crosslinked organic particles.

  According to the production method of the present invention, a battery separator having high productivity and excellent appearance quality in which a modified porous layer is laminated on both surfaces can be obtained.

An example of an apparatus (coating apparatus A) used when coating with a blade in the present invention is shown. An example of an apparatus (coating apparatus B) used when coating with a die in the present invention is shown. An example of an apparatus (coating apparatus C) used when coating by the dipping method in the present invention is shown. An example (Y-shaped jig) of an anti-shake device is shown. In the present invention, an example of a combination of an apparatus used when coating with a blade and an anti-blur apparatus (Y-shaped jig) will be described.

  Although the manufacturing method of the battery separator which has a modified porous layer on both surfaces of the polyolefin porous membrane of this invention is demonstrated below, naturally it is not limited to this representative example.

First, the polyolefin porous membrane of the present invention will be described.
The upper limit of the thickness of the polyolefin porous membrane of the present invention is preferably 25 μm, more preferably 20 μm, and still more preferably 16 μm. The lower limit is preferably 3 μm, more preferably 5 μm. If the thickness of the polyolefin porous membrane is within the above preferred range, practical membrane strength and pore blocking function can be retained, and the area per unit volume of the battery case is not restricted, and will proceed in the future. Suitable for increasing the capacity of brazing batteries.

  The upper limit value of the air permeability resistance of the polyolefin porous membrane is preferably 300 sec / 100 cc Air, more preferably 200 sec / 100 cc Air, still more preferably 150 sec / 100 cc Air, and the lower limit is preferably 50 sec / 100 cc Air, more preferably 70 sec / 100 cc Air. More preferably, it is 100 sec / 100 cc Air.

  The upper limit of the porosity of the polyolefin porous membrane is preferably 70%, more preferably 60%, and even more preferably 55%. The lower limit is preferably 30%, more preferably 35%, still more preferably 40%. When the air permeability resistance and the porosity are within the above preferred ranges, sufficient battery charge / discharge characteristics, particularly ion permeability (charge / discharge operating voltage) and battery life (closely related to the amount of electrolyte retained) The battery function can be fully exhibited. Moreover, since mechanical strength and insulation are obtained, the possibility of a short circuit during charging / discharging can be reduced.

  Since the average pore diameter of the polyolefin porous membrane greatly affects the pore closing performance, it is preferably 0.01 to 1.0 μm, more preferably 0.05 to 0.5 μm, still more preferably 0.1 to 0.3 μm. is there. When the average pore size of the polyolefin porous membrane is within the above preferred range, an appropriate peel strength of the modified porous layer can be obtained due to the anchor effect of the functional resin. In addition, when the modified porous layer is laminated, the air resistance is prevented from deteriorating significantly, and the response to the temperature of the pore clogging phenomenon is not slowed down. There is no shift to.

  As polyolefin resin which comprises a polyolefin porous membrane, polyethylene and polypropylene are preferred. Further, it may be a single substance or a mixture of two or more different polyolefin resins, for example, a mixture of polyethylene and polypropylene, or a copolymer of different olefins. In addition to basic characteristics such as electrical insulation and ion permeability, the separator obtained by using a polyolefin resin should have a pore blocking effect that cuts off the current and suppresses excessive temperature rise when the battery temperature rises abnormally. Can do. Among these, polyethylene is particularly preferable from the viewpoint of pore closing performance.

  Hereinafter, polyethylene will be described in detail as an example of the polyolefin resin used in the invention. Examples of the polyethylene include ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, and low density polyethylene. The polymerization catalyst is not particularly limited, and examples thereof include a Ziegler-Natta catalyst, a Phillips catalyst, and a metallocene catalyst. These polyethylenes may be not only ethylene homopolymers but also copolymers containing a small amount of other α-olefins. Examples of α-olefins other than ethylene include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (meth) acrylic acid, esters of (meth) acrylic acid, styrene, etc. Is preferred. Polyethylene may be a single substance, but is preferably a mixture of two or more kinds of polyethylene. As the polyethylene mixture, a mixture of two or more types of ultrahigh molecular weight polyethylenes having different weight average molecular weights (Mw) may be used, as well as a mixture of high density polyethylene, medium density polyethylene and low density polyethylene, or ultra high molecular weight polyethylene. A mixture of two or more polyethylenes selected from the group consisting of high-density polyethylene, medium-density polyethylene, and low-density polyethylene may be used.

As the polyethylene mixture, a mixture composed of ultrahigh molecular weight polyethylene having Mw of 5 × 10 ⁵ or more and polyethylene having Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ is preferable. The Mw of the ultra high molecular weight polyethylene is preferably 5 × 10 ⁵ to 1 × 10 ⁷ , more preferably 1 × 10 ⁶ to 15 × 10 ⁶ , and particularly preferably 1 × 10 ^{6 to} 5 × 10 ^6. . As the polyethylene having an Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , any of high density polyethylene, medium density polyethylene and low density polyethylene can be used, and it is particularly preferable to use high density polyethylene. As polyethylene with Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , two or more types having different Mw may be used, or two or more types having different densities may be used. By setting the upper limit of Mw of the polyethylene mixture to 15 × 10 ⁶ or less, melt extrusion can be facilitated.

  In the present invention, the content of the ultra high molecular weight polyethylene is preferably 40% by weight, more preferably 30% by weight, still more preferably 10% by weight, and the lower limit is preferably 1% by weight, more preferably. 2% by weight, more preferably 5% by weight. When the content of ultrahigh molecular weight polyethylene is within the above preferred range, sufficient tensile strength can be obtained even when the thickness of the polyethylene porous membrane is reduced. The tensile strength is preferably 100 MPa or more, and the upper limit is not particularly defined.

  The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) ((Mw / Mn) molecular weight distribution) of the polyethylene resin is preferably in the range of 5 to 200, and more preferably 10 to 100. When the range of Mw / Mn is within the above preferred range, the polyethylene resin can be easily extruded, and sufficient mechanical strength can be obtained when the thickness of the polyethylene porous membrane is reduced. Mw / Mn is used as a measure of molecular weight distribution, that is, in the case of polyethylene consisting of a single substance, the larger this value, the wider the molecular weight distribution. The Mw / Mn of polyethylene composed of a single substance can be appropriately adjusted by multistage polymerization of polyethylene. Moreover, Mw / Mn of the mixture of polyethylene can be suitably adjusted by adjusting the molecular weight and mixing ratio of each component.

  As long as the polyethylene porous membrane is within a range that satisfies the above-mentioned various characteristics, a production method according to the purpose can be freely selected. There are foaming methods, phase separation methods, dissolution recrystallization methods, stretched pore opening methods, powder sintering methods, etc., among these porous membrane production methods. Among these, phase separation is performed in terms of uniform micropores and cost. The method is preferred.

  As a manufacturing method by the phase separation method, for example, polyethylene and a molding solvent are heated and melt-kneaded, and the obtained molten mixture is extruded from a die and cooled to form a gel-like molded product, and the obtained gel-like molding is obtained. Examples include a method of obtaining a porous film by stretching the product in at least a uniaxial direction and removing the molding solvent.

  The polyethylene porous membrane may be a single-layer membrane or a layer configuration composed of two or more layers having different molecular weights or average pore diameters. Moreover, in the case of the layer structure which consists of two or more layers, the laminated body of the layer containing polyolefin resin other than a polyethylene porous layer and polyethylene may be sufficient.

  As a method for producing a multilayer film composed of two or more layers, for example, each of the polyethylene constituting the a layer and the b layer is melt kneaded with a molding solvent, and the obtained molten mixture is supplied from an extruder to one die. Either a method of integrating and coextrusion of the gel sheets constituting each component, or a method of heat-sealing the gel sheets constituting each layer by overlapping them can be produced. The coextrusion method is preferred because it is easy to obtain the adhesive strength between layers, and it is easy to form communication holes between layers, so that high permeability is easily maintained and productivity is excellent. In the case of a layer structure composed of two or more layers, it is preferable that the molecular weight and molecular weight distribution of at least one outermost polyethylene resin satisfy the above.

  The polyethylene porous film needs to have a function of blocking pores when the charge / discharge reaction is abnormal. Therefore, the melting point (softening point) of the constituent resin is 70 to 150 ° C, more preferably 80 to 140 ° C, and still more preferably 100 to 130 ° C. When the melting point of the constituent resin is within the above-mentioned preferable range, it is possible to ensure safety by exhibiting the pore closing function during an abnormal reaction without exhibiting the pore closing function during normal use.

Next, a method for laminating the modified porous layer used in the present invention will be described.
The method for producing a battery separator of the present invention comprises a step of simultaneously applying both surfaces of a polyolefin porous membrane with a coating solution in which a resin such as a fluorine-based resin or a polyamide-imide resin is soluble and is miscible with water, It includes a coagulation step, a washing step, and a drying step, and is characterized in that an anti-blur device is brought into contact between a coating apparatus that performs double-side coating and a coagulation tank. As used herein, simultaneous double-sided coating includes a method of coating one side at a time within 10 seconds, and simultaneously coagulating, washing, and drying both sides. Moreover, as a coating apparatus which coats both surfaces simultaneously, a coating apparatus as shown in FIGS. 1-3 is mentioned, for example.

  FIG. 1 shows a method of coating both surfaces using a blade. The coating amount can be adjusted by the clearance between the polyolefin porous membrane and the blade tip. In this case, it is preferable that the blade tip is not square but has a round shape in the thickness direction of the blade. If the blade tip is square, coating stripes are likely to occur when it comes into contact with the polyolefin porous membrane during coating.

  FIG. 2 shows a coating method using a die. The two dies disposed opposite to both surfaces of the polyolefin porous membrane slightly shift the coating position, and the die coated on the upstream side has a coating surface of the polyolefin porous membrane as shown in FIG. It is preferable to install a backup roll on the opposite side. It is also preferable to install an anti-blur device immediately after the downstream die.

  Fig. 3 shows that the coating liquid is put into a tank with two straight bars arranged in parallel at the bottom of the tank, and the polyolefin porous membrane enters the tank from above the tank, and two straight bars arranged in parallel with the tank bottom. It is a method of applying by passing between. The coating amount can be adjusted by the clearance between the two straight bars. The straight bar used here is preferably a straight bar having a smooth surface. If the straight bar has irregularities, coating streaks are likely to occur when it comes into contact with the polyolefin porous membrane during coating. The diameter of the straight bar is preferably 5 to 50 mm with good coatability. In addition to the above, a method may be used in which gravure rolls are disposed on both sides of the polyolefin porous membrane and coating is performed on both sides, and the present invention is not limited thereto.

  The anti-blur device is not particularly limited as long as it is installed between the coating device and the coagulation tank and can reduce the blur of the polyolefin porous membrane during coating. Examples thereof include a method of bringing a Y-shaped jig as shown in FIG. 4 into contact with both ends of the porous film immediately after coating, and a method of holding both ends of the porous film immediately after coating with a pinch roll. When using a Y-shaped jig, it is preferable that the Y-shaped jig is installed obliquely as shown in FIG. 5, and the coating liquid adhering to the Y-shaped jig is discharged so as not to return to the porous film.

  The position of the anti-shake device is closer to the coating device, and it is easier to obtain the anti-shake effect, and the coating end point (in the case of two front and rear coating devices, the rear side coating end point) is 50 mm to 500 mm. Located within range. The coating end point is, for example, the position of the blade tip of the coating apparatus in the case of FIG. 1, the position of the rear die tip in the case of FIG. 2, and the straight rod and the polyolefin porous membrane in the case of FIG. Refers to the position of the contact. The position of the anti-shake device has an upper limit value of 400 mm, more preferably 300 mm, and a lower limit value of 80 mm, more preferably 100 mm. In addition, you may provide a humidification process as needed other than the said anti-shake apparatus between a coating device and a coagulation tank. The shake of the polyolefin porous membrane at the time of coating here means the vibration of the polyolefin porous membrane due to the mechanical vibration of the conveying device including the unwinding device and the winding device.

  By immersing the porous film coated with the coating liquid in an aqueous solution (coagulating liquid) in a coagulation tank, the coated resin component, or the resin component and the inorganic particles are solidified into a three-dimensional network. The aqueous solution is an aqueous solution containing 1 to 20% by weight, more preferably 5 to 15% by weight, of a good solvent described later with respect to the resin component constituting the modified porous layer. The immersion time in the coagulation tank is preferably 3 seconds or longer. If it is less than 3 seconds, the resin component may not be sufficiently solidified. The upper limit is not limited, but 10 seconds is sufficient. Furthermore, the final battery separator can be obtained through a washing step using water and a drying step using hot air of 100 ° C. or less.

  In the cleaning step for removing the solvent, the cleaning efficiency can be further increased by a general method such as heating, ultrasonic irradiation or bubbling. Specifically, a method of extruding the solution inside the porous layer with air or an inert gas, a method of physically squeezing out the solution inside the membrane with a guide roll, and the like can be mentioned.

  The conveyance speed in the production method of the present invention is 30 m / min or more. According to the present invention, even when the conveyance speed is 30 m / min or more, the occurrence of coating streaks can be greatly suppressed. The conveyance speed is preferably 40 m / min or more, more preferably 50 m / min or more from the viewpoint of productivity.

  The modified porous layer is preferably laminated on both sides of the porous film serving as the substrate. The curling can be reduced by laminating on both sides, thereby preventing a reduction in productivity in the electrode pair assembly process. Further, when improving the adhesion with the electrode material, the adhesion can be improved on both the positive electrode side and the negative electrode side, and when improving the heat resistance, a significant heat shrinkage preventing effect can be obtained.

Next, the modified porous layer used in the present invention will be described.
The resin constituting the modified porous layer is not particularly limited as long as it can provide adhesion with an electrode material and a function of suppressing heat shrinkage (heat resistance). For example, polyamideimide resin having excellent heat resistance, excellent A fluorine resin having electrode adhesion is preferred. These resins may be used alone or in combination with other materials.

Hereinafter, the polyamide-imide resin and the fluorine-based resin will be described in detail as examples.
(1) Polyamideimide resin In general, polyamideimide resin is synthesized by an ordinary method such as an acid chloride method using trimellitic acid chloride and diamine or a diisocyanate method using trimellitic anhydride and diisocyanate. From the viewpoint, the diisocyanate method is preferable.

  Examples of the acid component used for the synthesis of the polyamide-imide resin include trimellitic anhydride (chloride). A part of the acid component can be replaced with another polybasic acid or an anhydride thereof. For example, tetracarboxylic acids such as pyromellitic acid, biphenyltetracarboxylic acid, biphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic acid, biphenylethertetracarboxylic acid, ethylene glycol bistrimellitate, propylene glycol bistrimellitate and their anhydrides, Aliphatic dicarboxylic acids such as oxalic acid, adipic acid, malonic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), dicarboxypoly (styrene-butadiene), 1,4 -Cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 4,4'-dicyclohexylmethanedicarboxylic acid, alicyclic dicarboxylic acids such as dimer acid, terephthalic acid, Le acid, diphenyl sulfone dicarboxylic acid, diphenylether dicarboxylic acid, and aromatic dicarboxylic acids such as naphthalene dicarboxylic acid. Among these, 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid are preferable from the viewpoint of the resistance to electrolytic solution, and dimer acid, dicarboxypolybutadiene having a molecular weight of 1000 or more and dicarboxypoly (acrylonitrile) from the shutdown characteristics. Butadiene) and dicarboxypoly (styrene-butadiene) are preferred.

  In addition, a urethane group can be introduced into the molecule by replacing part of the trimellitic acid compound with glycol. Examples of glycols include alkylene glycols such as ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, and hexanediol, polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, and one or more of the above dicarboxylic acids. And polyesters having terminal hydroxyl groups synthesized from one or two or more of the above-mentioned glycols. Among these, polyethylene glycol and polyesters having terminal hydroxyl groups are preferred because of the shutdown effect. Moreover, these number average molecular weights are preferably 500 or more, and more preferably 1000 or more. The upper limit is not particularly limited, but is preferably less than 8000.

  When replacing a part of the acid component with at least one of the group consisting of dimer acid, polyalkylene ether, polyester and butadiene rubber containing any of carboxyl group, hydroxyl group and amino group at the end, 1 to 60 mol% is preferably replaced.

  As the diamine (diisocyanate) component used for the synthesis of the polyamide-imide resin, those having o-tolidine and tolylenediamine as components are preferable. Aliphatic components such as ethylenediamine, propylenediamine, and hexamethylenediamine are used as components to replace a part thereof. Diamines and their diisocyanates, alicyclic diamines such as 1,4-cyclohexanediamine, 1,3-cyclohexanediamine and dicyclohexylmethanediamine, and their diisocyanates, m-phenylenediamine, p-phenylenediamine, 4,4'-diamino Aromatic diamines such as diphenylmethane, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfone, benzidine, xylylenediamine, naphthalenediamine, and their diisocyanates Sulfonate, and the like, reactivity among these, cost, and most preferably dicyclohexylmethane diamine and its diisocyanates terms of electrolyte solution resistance, 4,4'-diaminodiphenylmethane, naphthalene diamines and these diisocyanates are preferred. In particular, o-tolidine diisocyanate (TODI), 2,4-tolylene diisocyanate (TDI) and blends thereof are preferred. In particular, in order to improve the adhesiveness of the heat-resistant porous B, o-tolidine diisocyanate (TODI) having high rigidity is 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol%, based on the total isocyanate. That's it.

  Polyamideimide resin is easy to stir in a polar solvent such as N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone while heating to 60-200 ° C. Can be manufactured. In this case, amines such as triethylamine and diethylenetriamine, alkali metal salts such as sodium fluoride, potassium fluoride, cesium fluoride, sodium methoxide, and the like can be used as a catalyst as necessary.

  When the polyamideimide resin is used in the present invention, the logarithmic viscosity is preferably 0.5 dl / g or more. When the logarithmic viscosity is less than 0.5 dl / g, sufficient meltdown characteristics may not be obtained due to a decrease in melting temperature, and the porous film becomes brittle due to low molecular weight, and the anchor effect is reduced, resulting in reduced adhesion. It is to do. On the other hand, the upper limit is preferably less than 2.0 dl / g in consideration of workability and solvent solubility.

(2) Fluorine-based resin Fluorine-based resin is selected from the group consisting of vinylidene fluoride homopolymer, vinylidene fluoride / fluorinated olefin copolymer, vinyl fluoride homopolymer, and vinyl fluoride / fluorinated olefin copolymer. It is preferable to use one or more selected. Further, a resin obtained by graft polymerization of maleic acid or the like may be used. These polymers have excellent adhesion to electrodes, high affinity with non-aqueous electrolytes, suitable heat resistance, and high chemical and physical stability against non-aqueous electrolytes. Affinity with the electrolytic solution can be sufficiently maintained even when used in

  The melting point of the fluororesin is preferably 150 ° C. or higher, more preferably 180 ° C. or higher, further preferably 210 ° C. or higher, and the upper limit is not particularly limited. When the melting point is higher than the decomposition temperature, the decomposition temperature may be in the above range. When the melting point is lower than 150 ° C., a sufficient heat-resistant film breaking temperature cannot be obtained, and high safety may not be ensured.

  The modified porous layer of the present invention applies a coating solution in which the resin is soluble and dissolved in a solvent miscible with water to a predetermined polyolefin porous membrane, phase-separates the resin and the solvent, and further a coagulation tank And is obtained by solidifying the resin. A phase separation aid may be added if necessary.

  Solvents (good solvents) that can be used to dissolve the resin include N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), hexamethyltriamide phosphate (HMPA), N, N -Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone, chloroform, tetrachloroethane, dichloroethane, 3-chloronaphthalene, parachlorophenol, tetralin, acetone, acetonitrile, etc. You can choose freely.

  Examples of the phase separation aid used in the present invention include water, ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, alkylene glycol such as hexanediol, polyalkylene glycol such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, water-soluble At least one selected from water-soluble polyester, water-soluble polyurethane, polyvinyl alcohol, carboxymethyl cellulose and the like.

  The addition amount of the phase separation aid is preferably 1 to 9% by weight, more preferably 2 to 8% by weight, and still more preferably 3 to 7% by weight with respect to the solution weight of the coating solution. By mixing these phase separation aids in the coating solution, it is possible to mainly control the air permeability resistance, the surface porosity, and the layer structure formation rate. By making the addition amount of the phase separation aid within the above preferred range, a remarkable increase in the phase separation rate may be observed. Further, it may be possible to prevent the coating liquid from becoming cloudy at the stage of mixing and precipitating the resin component.

  In the present invention, it is preferable to add inorganic particles or crosslinked polymer particles to the coating solution. By adding inorganic particles or cross-linked polymer particles to the coating solution, the effect of preventing internal short circuit (dendrite prevention effect) due to the growth of dendritic crystals of the electrode inside the battery, the reduction of thermal shrinkage, and the provision of slipperiness The effects such as can be obtained. The upper limit of the amount of particles added is preferably 98% by weight, more preferably 95% by weight. The lower limit is preferably 50% by weight, more preferably 60% by weight. Dendrites can be prevented by setting the lower limit of the amount of particles to be within the above preferred range. Moreover, sufficient adhesiveness of a modified porous layer may not be obtained by making an upper limit into the said preferable range.

  The average particle diameter of the particles is preferably 1.5 to 50 times the average pore diameter of the polyolefin porous membrane. More preferably, it is 2.0 times or more and 20 times or less. In addition, although the shape of particle | grains includes a true spherical shape, a substantially spherical shape, a plate shape, and a needle shape, it is not particularly limited. If the average particle size of the particles is less than 1.5 times the average pore size of the polyolefin porous membrane, depending on the size distribution, the pores of the polyolefin porous membrane may be clogged with a mixture of resin and particles. It may lead to a significant increase in air resistance. If the average particle diameter of the particles exceeds 50 times the average pore diameter of the polyolefin porous membrane, the particles may fall off during the battery assembly process, leading to serious battery defects.

  Inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite , Molybdenum sulfide, mica and the like.

  Examples of the crosslinked polymer particles include heat-resistant crosslinked polymer particles such as crosslinked polystyrene particles, crosslinked acrylic resin particles, and crosslinked methyl methacrylate particles.

  The solid concentration of the coating solution is not particularly limited as long as it can be uniformly applied, but is preferably 10% by weight or more and 90% by weight or less, and more preferably 20% by weight or more and 80% by weight or less. When the solid content concentration is less than 10% by weight, the obtained heat-resistant layer may become brittle. On the other hand, if it exceeds 80% by weight, the coatability is lowered.

  The upper limit of the total film thickness of the battery separator obtained by laminating the modified porous layer is preferably 35 μm, more preferably 30 μm. The lower limit is preferably 5 μm, more preferably 7 μm. Sufficient mechanical strength and insulation can be ensured by setting the lower limit of the total film thickness of the battery separator within the preferred range. Moreover, the fall of a capacity | capacitance can be avoided by reducing the electrode area which can be filled in a container by making an upper limit into the said preferable range.

  The film thickness of the modified porous layer is preferably 1 to 5 μm, more preferably 1 to 4 μm, and still more preferably 1 to 3 μm. When the film thickness is 1 μm or more, adhesion to the electrode is ensured, and the polyolefin porous film is prevented from being melted and shrunk at the melting point or more, and the film breaking strength and insulation can be secured. Moreover, if it is 5 micrometers or less, winding volume can be suppressed and it is suitable for the high capacity | capacitance of the battery which will progress from now on. Furthermore, curling is prevented from increasing, leading to an improvement in productivity in the battery assembly process. Further, by optimizing the proportion of the polyolefin porous membrane, a sufficient pore blocking function can be obtained and abnormal reactions can be suppressed.

  The porosity of the modified porous layer is preferably 30 to 90%, more preferably 40 to 70%. When the porosity of the modified porous layer is 30% or more, an increase in electrical resistance of the film can be prevented and a large current can be passed, and when the porosity is 90% or less, the film strength can be maintained.

  The air resistance of the modified porous layer is preferably 1 to 600 sec / 100 cc Air measured by a method based on JIS-P8117. More preferably, it is 50-500 sec / 100ccAir, More preferably, it is 100-400sec / 100ccAir. When the air permeability resistance is less than 1 sec / 100 cc Aircc, the film strength is weak, and when it exceeds 600 sec / 100 cc Air, the cycle characteristics may be deteriorated.

Hereinafter, although an example is shown and explained concretely, the present invention is not restrict | limited at all by these examples.
Coating stripe evaluation method The battery separators obtained in the examples and comparative examples were slit to obtain a roll having a width of 300 mm and a length of 600 m. This roll is visually observed while being wound under a fluorescent lamp at a conveyance speed of 5 m / min. The roll extends in the conveyance direction, the length is approximately 5 to 100 cm, and a plurality or a whole coating width at intervals of 1 to 50 mm in the coating width direction. The generation | occurrence | production location per 500 m of the coating stripe over which it covered was counted.
In addition, the length was approximately 5 to 100 cm, and a coating streak group covering a plurality of coatings or the entire coating width at 1 to 50 mm intervals in the coating width direction was counted as one place.

Example 1
(Adjustment of coating solution)
A polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF / HFP = 92/8 (weight ratio), weight average molecular weight of 1,000,000) was used as the fluorine resin. Fluorine-based resin, alumina particles (average particle size: 1.0 μm) and N-methyl-2-pyrrolidone were blended in a weight ratio of 5:12:83, respectively, and the resin components were completely dissolved. Along with Toray Industries, trade name “Traceram” (registered trademark) beads, 0.5 mm in diameter), the mixture was placed in a polypropylene container and dispersed for 6 hours with a paint shaker (Toyo Seiki Seisakusho). Subsequently, it filtered with the filter of 5 micrometers of filtration limits, and prepared the coating liquid (a). The coating solution was stored tightly so as not to touch outside air as much as possible until coating.
(Lamination of modified porous layer)
The coating liquid (a) on both surfaces of a polyethylene porous film (thickness 5 μm, air resistance 170 sec / 100 cc Air) as a polyolefin porous film at a conveying speed of 30 m / min using the coating apparatus A by the blade coating method. Was applied to an aqueous solution (coagulation tank), washed with pure water, and then dried by passing through a hot air drying oven at 70 ° C. to obtain a battery separator having a final thickness of 13 μm. At this time, a Y-shaped jig (anti-blurring device) shown in FIG. 4 was installed at both ends of the porous film coated with the coating solution as shown in FIG. 5 50 mm below the blade tip of the coating device.

Example 2
A battery separator was obtained in the same manner as in Example 1 except that a polyethylene porous membrane (thickness 9 μm, air permeability resistance 115 sec / 100 cc Air) was used.

Example 3
A battery separator was obtained in the same manner as in Example 1 except that a polyethylene porous membrane (thickness 16 μm, air permeability resistance 120 sec / 100 cc Air) was used.

Example 4
A battery separator was obtained in the same manner as in Example 1 except that a polyethylene porous membrane (thickness 20 μm, air permeability resistance 150 sec / 100 cc Air) was used.

Example 5
(Synthesis of polyamide-imide resin)
In a four-necked flask equipped with a thermometer, a condenser tube, and a nitrogen gas inlet tube, 1 mole of trimellitic anhydride (TMA), 0.8 mole of o-tolidine diisocyanate (TODI), 2,4-tolylene diisocyanate (TDI) ) After adding 0.2 mol and 0.01 mol of potassium fluoride together with N-methyl-2-pyrrolidone so that the solid content concentration is 20% by weight and stirring at 100 ° C. for 5 hours, the solid content concentration is 14% by weight. % Was diluted with N-methyl-2-pyrrolidone to synthesize a polyamideimide resin solution.
(Adjustment of coating solution)
Polyamideimide resin solution, alumina particles (average particle size 0.5 μm), and N-methyl-2-pyrrolidone were blended in a weight ratio of 16:20:64, respectively, and zirconium oxide beads (Torayserum manufactured by Toray Industries, Inc.) (Registered Trademark) beads, 0.5 mm in diameter) were placed in a polypropylene container and dispersed with a paint shaker (manufactured by Toyo Seiki Seisakusho) for 6 hours. Subsequently, it filtered with the filter of the filtration limit 5 micrometers, and prepared the coating liquid (b).
(Lamination of modified porous layer)
A battery separator was obtained in the same manner as in Example 2 except that the coating liquid (b) was used.

Example 6
A coating liquid (c) was used in which the alumina particles were replaced with polymethyl methacrylate-based crosslinked particles (manufactured by Nippon Shokubai Co., Ltd., “Eposter” (registered trademark) MA, type 1002, average particle size 2.5 μm) A battery separator was obtained in the same manner as Example 2 except for the above.

Example 7
Example 2 except that the coating liquid (d) containing fluorine resin, alumina particles (average particle size 0.5 μm), and N-methyl-2-pyrrolidone in a weight ratio of 3:13:84 was used. Similarly, a battery separator was obtained.

Example 8
A battery separator was obtained in the same manner as in Example 2 except that the conveyance speed was 3 m / min.

Example 9
A battery separator was obtained in the same manner as in Example 2 except that the conveyance speed was 10 m / min.

Example 10
A battery separator was obtained in the same manner as in Example 2 except that the conveyance speed was 50 m / min.

Example 11
A battery separator was obtained in the same manner as in Example 2 except that the conveyance speed was 80 m / min.

Example 12
The coating apparatus B shown in FIG. 2 is used as the coating apparatus, and the Y-shaped jig (anti-blurring apparatus) shown in FIG. 4 is applied 100 mm below the die tip of the coating apparatus B as shown in FIG. A battery separator was obtained in the same manner as in Example 2 except that it was installed at both ends of the porous film coated with the liquid.

Example 13
The coating apparatus C shown in FIG. 3 is used as the coating apparatus, and the Y-shaped jig (anti-blurring apparatus shown in FIG. 4) is located 50 mm below the contact point between the straight rod of the coating apparatus C and the polyethylene porous film. As shown in FIG. 5, a battery separator was obtained in the same manner as in Example 2 except that it was installed at both ends of the porous membrane coated with the coating solution.

Comparative Example 1
A battery separator was obtained in the same manner as in Example 2 except that the anti-blurring device was not used.

Comparative Example 2
A battery separator was obtained in the same manner as in Comparative Example 1 except that the anti-blurring device was not used and the conveyance speed was 3 m / min.

Comparative Example 3
A battery separator was obtained in the same manner as in Comparative Example 1 except that the anti-blurring device was not used and the conveyance speed was 80 m / min.

Table 1 shows the production conditions of Examples 1 to 13 and Comparative Examples 1 to 3 and the number of coating lines generated.

1: Polyolefin porous film 2: Coating liquid 3: Blade 4: Porous film coated with coating liquid 5: Die 6: Backup roll 7: Tank 8: Straight bar 9: Y-shaped jig (anti-shake) apparatus)
10: Coating device 11: Coating end point

In order to solve the above-described problems, the battery separator manufacturing method of the present invention has the following configuration. That is,
1. A method for producing a battery separator in which a modified porous layer is formed on the surface of a polyolefin porous membrane,
(1) a step of simultaneously applying a coating solution obtained by dissolving a resin in a solvent on both surfaces of the polyolefin porous membrane;
(2) a step of solidifying the resin component in the applied coating liquid;
(3) a cleaning step;
(4) sequentially including a step of drying,
Between said step (1) and the step (2), at both ends of the polyolefin porous membrane is coated, comprising the step of contacting a device for preventing shaking of the polyolefin porous membrane during coating, wherein The manufacturing method of the separator for batteries whose conveyance speed of process (1)-(4) is 30-80 m / min.
2. 2. The method for producing a battery separator as described in 1 above, wherein the polyolefin porous membrane has a thickness of 9 μm or less.
3. 3. The method for producing a battery separator as described in 1 or 2 above, wherein the resin is a fluorine resin or a polyamideimide resin.
4). The manufacturing method of the battery separator as described in any one of the above 1-3, wherein the coating liquid contains inorganic particles or crosslinked organic particles.

Claims (4)

A method for producing a battery separator in which a modified porous layer is formed on the surface of a polyolefin porous membrane,
(1) a step of simultaneously applying a coating solution obtained by dissolving a resin in a solvent on both surfaces of the polyolefin porous membrane;
(2) a step of solidifying the resin component in the applied coating liquid;
(3) a cleaning step;
(4) including a step of drying,
Between the said process (1) and the said process (2), the process of making the coated polyolefin porous membrane contact an anti-blur apparatus, and the conveyance speed of (1)-(4) is 30 m / min or more A method for producing a battery separator. The method for producing a battery separator according to claim 1, wherein the polyolefin porous membrane has a thickness of 25 μm or less. The method for producing a battery separator according to claim 1 or 2, wherein the resin is a fluorine-based resin or a polyamide-imide resin. The manufacturing method of the battery separator as described in any one of Claims 1-3 in which a coating liquid contains an inorganic particle or a bridge | crosslinking organic particle.

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