JP2019145441A - Manufacturing method and manufacturing device for cell separator - Google Patents

Abstract

To provide a manufacturing method and manufacturing device for a cell separator with which conveyance break and conveyance streaks hardly occur, and which can be processed at high speed.SOLUTION: The manufacturing process sequentially includes a coating process, a solidification process having a solidification tank 2, a washing process having a washing tank 3, and a drying process, with a polyolefin resin porous film made into a laminated polyolefin microporous film 1 through the coating process. Conveyance support rolls 6 are installed between the tanks or above the tanks, and a liquid draining device 5 is installed in at least one of the solidification tank of the solidification process and the washing tank of the washing process between a liquid surface and the downstream-side conveyance support roll on a circumference which the laminated polyolefin microporous film and the conveyance support roll are in contact with, and a curvature correction device 4 in contact with an end of the polyolefin microporous film between the liquid surface and the conveyance support rolls is installed on at least one end of the polyolefin microporous film. The width of the polyolefin microporous film is 600-2,000 mm, and the thickness is 3-8 μm, and the conveyance speed is 50 m/minute or faster.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a battery separator manufacturing method and manufacturing apparatus. In particular, it is useful as a production method and production apparatus for a battery separator having a 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 polyethylene microporous membrane having a pore closing effect that blocks ion permeation and suppresses excessive temperature rise is preferably used. 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 microporous 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. For this reason, a separator in which various porous layers are laminated on a microporous film has been studied so far.

  For the porous layer, polyamideimide resin, polyimide resin, aromatic polyamide resin, fluorine resin having excellent electrode adhesion, etc. having both heat resistance and electrolyte permeability are preferably used. In addition, the porous layer as used in the field of this invention means the layer containing resin which provides or improves at least 1 function, such as heat resistance, adhesiveness with an electrode material, electrolyte solution permeability.

  In order to reduce the cost of battery separators, it is expected that the processing speed (conveying speed) and the width will be further increased in the microporous film forming process and the 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.

  Typical examples of the resin that imparts or improves at least one function such as heat resistance, adhesion to electrode materials, electrolyte solution permeability, and the like include, for example, polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene. Nitrogen-containing resins such as fluorine-based resins, polyamide imides, and aromatic polyamides are listed. In order to laminate these resins as a porous layer on a polyolefin microporous membrane, a coating solution containing these resins is applied to the polyolefin microporous membrane and then immersed in a coagulation tank to convert the resin into a three-dimensional network membrane. Generally, there is a method of obtaining a battery separator by drying through a water washing step having a plurality of water washing tanks (hereinafter sometimes referred to as a coagulation step). In order to enter from the coagulation tank to the water washing tank, from the upstream water washing tank to the downstream water washing tank via the conveyance support roll, it is usually necessary to convey the film obliquely or horizontally as shown in FIG. At this time, when the polyolefin microporous membrane after coating (hereinafter sometimes abbreviated as a laminated polyolefin microporous membrane) is pulled up from the upstream rinsing tank and enters the downstream rinsing tank, a part of the rinsing water is It is brought into the downstream washing tank by the accompanying flow. Carrying in by the accompanying flow is particularly remarkable on the upper surface side without the conveyance support roll. For this reason, the water washing efficiency tends to be lowered, and this is particularly noticeable in high-speed conveyance at 50 m / min or more.

  By installing a liquid draining device such as a draining roll or a blade on the upper surface side in order to suppress the carry-in of the flush water downstream, it is possible to suppress the carry-in of the flush water downstream.

  However, the washing water scraped off by the liquid draining device on the upper surface flows to both ends of the laminated polyolefin microporous membrane, and the laminated polyolefin microporous membrane is affected by the weight of the washing water and the flow rate difference of the washing water scraped off from the front and back. The end tends to bend.

Since the polyolefin microporous membrane is softer than a general non-porous film, this tendency is remarkable. In the case of relatively low speed conveyance at a conveyance speed of less than 50 m / min, the curvature may be corrected immediately before the conveyance support roll or the liquid draining device. Often leads to breakage in conveyance. In particular, it is remarkable when the thickness of the polyolefin microporous membrane is less than 8 μm and the width exceeds 600 mm.
It is possible to increase the number of washing tanks if it is only to improve the cleanliness by washing with water, and it is possible to wash with a large amount of water, but it is not only a cost increase factor, but it is inevitable if the number of water tanks is increased Since the number of rolls in contact with the laminated polyolefin microporous membrane increases, the tension applied to the laminated polyolefin microporous membrane increases due to resistance caused by washing water, and the membrane becomes easily deformed.

  Various studies have been made to solve the above problems.

  In Example 1 of Patent Document 1, a polypropylene microporous film having a thickness of 25.6 μm is moved at a speed of 3 m / min, a polyvinylidene fluoride (PVdF) copolymer is applied, and solidified in a coagulation bath. The composite porous membrane is obtained by washing with water and drying.

  In Example 1 of Patent Document 2, an equal amount of a coating solution containing polymetaphenylene isophthalamide and magnesium hydroxide is applied to both sides of a long 1 m wide polyethylene microporous membrane, and both sides of the porous substrate are coated. The coating layer is formed on the substrate, the porous substrate after the coating layer is formed is conveyed to a coagulation tank and immersed in a coagulating liquid to solidify the resin contained in the coating layer, and conveyed at a conveyance speed of 70 m / min. Then, after washing out from the washing tank and passing through a drying apparatus equipped with a heating roll, a composite membrane is obtained.

  In Patent Document 3, when the separator after application is pulled up from the water with the cleaning tank, the cleaning water is scraped off by a rod-shaped member arranged in parallel with the separator, and the cleaning water is brought into the downstream cleaning tank. Suppressed.

  In patent document 4, in the manufacturing method of the film which wash | cleans a film in the washing | cleaning process which has several washing tanks, wash water is installed by installing three rolls so that both surfaces of a film may contact | connect between two washing tanks. It is scraped off to prevent the washing water from being brought into the downstream washing tank.

  In the future, the transport speed during coating will tend to be further increased. In particular, soft materials such as polyolefin microporous membranes used in battery separators will be bent during transport as the transport speed increases. It tends to occur. This tendency becomes more prominent as the thickness of the polyolefin microporous film serving as the base material is thinner and wider.

JP 2011-012266 A Japanese Patent No. 6028129 JP 2017-004931 A JP 2017-087173 A

  The present inventors have envisioned that lithium ion secondary batteries will become more cost-effective in the future, and a battery separator manufacturing method and manufacturing apparatus in which a porous layer is laminated on at least one surface of a microporous film made of polyolefin resin. Therefore, the present invention provides a manufacturing method and a manufacturing apparatus capable of high-speed processing that are unlikely to be broken during conveyance even if the battery separator is widened and thinned. The above-mentioned problem is not observed in a general thermoplastic resin film coating process with relatively high rigidity, and is a problem specific to battery separators.

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 battery separator manufacturing method in which a porous layer is laminated on at least one surface of a polyolefin resin porous membrane, wherein the battery separator manufacturing process includes an application process, a coagulation process having a coagulation tank, and a washing tank. A transporting support roll is installed between or above each tank, and at least one of the coagulation tank in the coagulation process and the water washing tank in the water washing process has a liquid level. A liquid draining device is provided on the opposite side to the side where the laminated polyolefin microporous membrane and the conveyance support roll are in contact between the downstream conveyance support roll and on the circumference where the laminated polyolefin microporous membrane and the conveyance support roll are in contact. And a curvature correcting device in contact with an end of the laminated polyolefin microporous membrane between the liquid level and the transport support roll is at least the laminated polyolefin microporous membrane. A separator for a battery, characterized in that the polyolefin microporous membrane is installed at the other end, the width of the polyolefin microporous membrane is 600 mm to 2000 mm, the thickness is 3 μm to 8 μm, and the transport speed is 50 m / min It is a manufacturing method.
(2) The liquid draining device is preferably a roll or a bar.
(3) The contact pressure of the liquid draining device through the transport support roll and the laminated polyolefin microporous membrane is preferably 0.01 MPa or more and 1.0 MPa or less.
(4) It is preferable that the said curvature correction apparatus is an edge part support roll.
(5) It is preferable that the angle formed by the center axis of the end line of the end support roll and the extension line of the end support roll tip is 45 ° or less.
(6) It is preferable that the end surface of the said end part support roll is a spherical surface.
(7) It is preferable that the distance of the conveyance direction of the upstream edge part of the contact surface of a lamination | stacking polyolefin microporous film and a conveyance support roll and the downstream edge part of the contact surface of the said curvature correction apparatus is 500 mm or less.
(8) The porous layer preferably contains at least one resin selected from polyvinylidene fluoride, polyvinylidene fluoride copolymer, wholly aromatic polyamide, and polyamideimide.
(9) A battery separator manufacturing apparatus in which a porous layer is laminated on at least one surface of a polyolefin resin porous membrane, wherein the battery separator manufacturing apparatus sequentially includes a coating apparatus, a coagulation tank, a washing tank, and a drying apparatus. In addition, a transport support roll is installed between each tank or above each tank, and at least one of the coagulation tank and the water washing tank is between the liquid level setting range of the tank and the downstream transport support roll. A liquid draining device is installed on the side opposite to the side where the laminated polyolefin microporous membrane and the conveyance support roll are in contact with each other and on the circumference where the laminated polyolefin microporous membrane and the conveyance support roll are in contact. Further, the width through which the laminating polyolefin microporous membrane passes between the liquid level setting range of the tank and the end of the laminating polyolefin microporous membrane between the conveying support rolls Apparatus for manufacturing a battery separator, characterized by being installed in at least one end of the direction.

  According to the production method and production apparatus of the present invention, a battery separator in which a porous layer is laminated on a thin and wide polyolefin microporous membrane can be produced with high yield.

It is the schematic which shows an example of a coagulation tank and a washing tank. It is a schematic diagram (sectional view) showing an example of a curvature correcting device. It is sectional drawing which shows an example of the contact method of a lamination | stacking polyolefin microporous film and a curvature correction apparatus. It is the schematic which shows the holding angle in case a curvature correction apparatus is located in the upper surface of a lamination polyolefin microporous membrane.

  In the drawings, in order to make each configuration easy to understand, some parts are emphasized or some parts are simplified, and actual structures, shapes, scales, and the like may be different.

  A method for producing a battery separator having a porous layer on the surface of the polyolefin microporous membrane of the present invention will be described below.

  First, the polyolefin microporous membrane of the present invention will be described. The polyolefin microporous membrane is a microporous membrane containing a polyolefin resin. The polyolefin microporous membrane is not particularly limited, and a polyolefin microporous membrane used for a known battery separator can be used. In the present specification, the microporous membrane means a membrane having voids connected to the inside. Hereinafter, although an example of a polyolefin microporous film is demonstrated, the polyolefin microporous film used for this invention is not limited to this.

  The upper limit of the thickness of the polyolefin microporous membrane used in the present invention is preferably 8 μm, more preferably 7 μm, and even more preferably 6 μm. The lower limit is preferably 3 μm, more preferably 4 μm. If the thickness of the polyolefin microporous 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 will not be restricted, and will proceed in the future. Suitable for increasing battery capacity.

  The lower limit of the width of the polyolefin microporous membrane of the present invention is preferably 600 mm, more preferably 610 mm. The upper limit is preferably 2000 mm, more preferably 1500 mm, and still more preferably 1200 mm. If the width of the polyolefin microporous membrane exceeds 2000 mm, it may be difficult to obtain a wound body while maintaining flatness.

  The present invention has a remarkable effect when the thickness and width of the polyolefin microporous membrane are within the above ranges.

  The upper limit of the air permeability resistance of the polyolefin microporous membrane is preferably 300 sec / 100 mL Air, more preferably 200 sec / 100 mL Air, more preferably 150 sec / 100 mL Air, and the lower limit is preferably 50 sec / 100 mL Air, more preferably 70 sec / 100 mL Air. More preferably, it is 100 sec / 100 mL Air. The air resistance can be determined by a method based on JIS P 8117.

The upper limit of the porosity of the polyolefin microporous 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%. The porosity of the polyolefin microporous membrane can be obtained from the following formula.
Porosity of polyolefin microporous membrane (%) = [1− (film thickness of polyolefin microporous membrane / weight of polyolefin microporous membrane) / true density of polyolefin microporous membrane] × 100
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 size of the polyolefin microporous 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. In addition, an average hole diameter can be calculated | required by the method based on JISK3832.

  When the average pore diameter of the polyolefin microporous membrane is within the above preferred range, an appropriate peel strength of the porous layer can be obtained due to the anchor effect of the functional resin. In addition, when the porous layer is stacked, the air resistance is prevented from deteriorating significantly, and the response to the temperature of the pore clogging phenomenon is not slowed down. I don't have to.

  The polyolefin resin constituting the polyolefin microporous membrane is preferably polyethylene or polypropylene. 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 present 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.

The polyethylene mixture, the mixture Mw of 5 × 10 ⁵ or more ultra-high molecular weight polyethylene and Mw consists at least 1 × 10 ⁴ 5 × 10 ⁵ or less of polyethylene. Mw can be determined by gel permeation chromatography (GPC method). 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 Mw of 1 × 10 ⁴ or more and 5 × 10 ⁵ or less, 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. Within the above range, it is easy to transport even a laminated polyolefin microporous membrane that is thin and has a width of 600 mm or more while maintaining good shutdown performance.

  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 ultrahigh molecular weight polyethylene content is within the above preferred range, sufficient tensile strength can be obtained even when the thickness of the polyethylene microporous membrane is reduced. The tensile strength is preferably 100 MPa or more, and the upper limit is not particularly defined. The tensile strength can be determined by a method based on ASTM D822. Within the above range, it is easy to transport even a laminated polyolefin microporous membrane that is thin and has a width of 600 mm or more while maintaining good shutdown performance.

  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. Mn can be determined by gel permeation chromatography (GPC method). When the range of Mw / Mn is within the above preferred range, it is easy to extrude the polyethylene resin, and when the thickness of the polyethylene microporous film is reduced, sufficient mechanical strength can be obtained. 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. When the Mw / Mn is in the above range, it is easy to transport even a thin laminated polyolefin microporous film having a width exceeding 600 mm while maintaining good shutdown performance.

  The polyethylene microporous 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.

  Next, the lamination method of the porous layer used for this invention is demonstrated.

  The method for producing a battery separator of the present invention comprises a step of applying a coating liquid in which a resin such as a fluorine-based resin or a polyamide-imide resin is soluble and dissolved in a solvent miscible with water to at least one surface of the polyolefin microporous membrane In addition, a coagulation process having a coagulation tank, a water washing process having a water washing tank, and a drying process are sequentially included, and a conveyance support roll for conveying and supporting the laminated polyolefin microporous film is installed between the respective tanks. A curvature correcting device is provided between the liquid level of the liquid or the washing water and the conveyance support roll. The liquid draining device is provided on the surface opposite to the side where the laminated polyolefin microporous membrane and the conveyance support roll are in contact, and on the circumference of the conveyance support roll where the laminated polyolefin microporous membrane and the conveyance support roll are in contact. Yes. These curving straightening devices, conveyance support rolls, and liquid draining devices may be at least one of a coagulation tank in the coagulation process and a water washing tank in the water washing process, that is, only the coagulation tank, only the water washing tank, or the coagulation tank. It can be provided in both the washing tank.

  FIG. 1 is a process diagram showing an example of a coagulation tank 2 in a coagulation process and a water washing tank 3 in a water washing process used in the present invention. FIG. 1 shows an example in which two water washing tanks are provided in series.

  In FIG. 1, the conveyance support roll 6 is provided on the liquid level of the coagulating liquid or washing water and on the downstream side of the coagulating liquid or washing water. The liquid draining device 5 is installed on the surface opposite to the side where the laminated polyolefin microporous membrane and the conveyance support roll are in contact, and on the circumference where the laminated polyolefin microporous membrane and the conveyance support roll are in contact with each other. Between the liquid draining device 5 and the liquid draining device 5, the curvature correcting devices 4 at both ends of the laminated polyolefin microporous membrane are installed.

  The transport support roll 6, the liquid draining device 5, and the curving straightening device 4 are preferably disposed between all the tanks as a set.

  The conveyance support roll is preferably a metal roll that has been subjected to hard chrome plating with a surface roughness of 0.3S to 5.0S (JIS B 0601). When the surface roughness is in the above range, the surface of the porous layer or the surface of the polyolefin microporous membrane can be suppressed from being damaged by the contact pressure. The conveyance support roll may be a drive roll or a free roll.

  The liquid draining device is preferably a roll, a bar, or a doctor blade disposed in a direction perpendicular to the traveling direction of the laminated polyolefin microporous membrane. Further, by arranging the liquid draining device on the circumference of the transport support roll, a nip effect can be obtained and liquid draining can be performed more efficiently. The contact pressure of the liquid draining device via the transport support roll and the laminated polyolefin microporous membrane is preferably 0.01 MPa or more and 1.0 MPa or less, more preferably 0.02 MPa or more and 0.8 MPa or less, and further preferably It is 0.03 MPa or more and 0.5 MPa or less. Within this range, the liquid can be drained efficiently, and the pores of the polyolefin microporous membrane are not crushed.

  When the liquid draining device is a roll or a bar, it may be rotated according to the conveyance speed of the laminated polyolefin microporous film, or may not be rotated. In order to obtain a more efficient liquid draining effect, it is preferable not to rotate. The material of the roll, bar, or doctor blade may be made of metal, resin, or rubber.

  In this invention, the curvature correction apparatus for correcting the curvature of the both ends of a laminated polyolefin microporous film is installed between the liquid level of a coagulation tank or a washing tank, and a conveyance support roll. An end support roll is preferable for the curvature correcting device installed at both ends of the laminated polyolefin microporous membrane.

  The curvature correcting device is preferably in contact with the laminated polyolefin microporous membrane in the range of 3 mm to 100 mm, more preferably 5 mm to 70 mm, and even more preferably 10 mm to 50 mm. Within this range, it is possible to secure a region in which the coagulated water or flush water flows to the liquid surface at the center in the width direction without the laminated polyolefin microporous membrane being detached from the curvature correction device during conveyance. If it is less than 3 mm, a sufficient curvature correction effect may not be obtained. If it exceeds 100 mm, it is not preferable because the coagulating liquid or washing water may be prevented from flowing down from the transport support roll or the liquid draining device, or the curvature correcting device may damage the laminated polyolefin microporous membrane.

  FIG. 3 is a cross-sectional view showing an example of a method of contacting the laminated polyolefin microporous membrane and the curvature correcting device, and the laminated polyolefin microporous membrane 7 and the curvature correcting device 4 are in contact with each other on the surface 8.

  The distance in the transport direction between the upstream end of the contact surface of the laminated polyolefin microporous membrane and the transport support roll and the downstream end of the contact surface of the curvature correcting device is preferably 500 mm or less. If it exceeds 500 mm, a sufficient curvature correction effect may not be obtained. The lower limit is not particularly defined, but is preferably 1 mm or more. If the distance is less than 1 mm, the curvature correcting device and the transport support roll may come into contact with each other, which is not preferable.

  When the curving straightening device is an end support roll, the end support roll has a contact area in contact with the laminated polyolefin microporous membrane and a laminated polyolefin microscopic taper whose diameter is gradually tapered toward the center of the laminated polyolefin microporous membrane. It has a shape having a non-contact region that does not contact the porous membrane. The angle formed by the extension line of the end support roll tip and the center axis of the end support roll is preferably 45 ° or less, and may be a spherical surface (see FIG. 2). If it is the said aspect, curvature can be corrected without making a stripe | line-like wound (conveyance streak) at the edge part of an end part support roll in a laminated polyolefin microporous film.

  FIG. 2 is a cross-sectional view showing an example of a curvature correcting device, (A) is an example of a curvature correcting device a in which the angle formed by the extension line of the end support roll tip and the center axis of the end support roll is 15 °. (B) is an example of a curvature correction device b, 30 °, (C) is an example of a curvature correction device c, a spherical surface, and (D) is an example of a curvature correction device d, showing an example of 90 °.

  It is preferable to install the curvature correcting devices on both ends of the laminated polyolefin microporous membrane and on the front and back thereof.

  The holding angle 9 of the laminated polyolefin microporous membrane in the curvature correcting device is preferably 150 ° or more and 180 ° or less both when the curvature correcting device is on the upper surface and on the lower surface of the laminated polyolefin microporous membrane (see FIG. 4). The holding angle means an angle formed by a tangent to the laminated polyolefin microporous membrane on the upstream side of the curvature correcting device and a tangent to the laminated polyolefin microporous membrane on the downstream side of the curvature correcting device. When the hugging angle is less than 150 °, a conveyance streak may occur in the laminated polyolefin microporous film.

  By immersing the microporous film coated with the coating 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 coagulating liquid 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 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 number of washing tanks in the washing step is preferably 2 to 5 tanks. In one tank, sufficient cleaning may not be performed. If the tank is 6 tanks or more, the laminated polyolefin microporous film is easily deformed by high tension due to water resistance, which is not preferable. According to the present invention, a sufficient cleaning effect can be obtained in 2 to 5 tanks. The flush water may be fed forward from the downstream flush tank to the upstream flush tank using, for example, a liquid level drop.

  The capacity of the water in the washing tank is preferably large from the viewpoint of contamination from the previous process, but is preferably small from the viewpoint of cost. 500 L to 2000 L is an appropriate range.

  The conveying speed in the production method of the present invention is preferably 50 m / min or more. According to the present invention, even if the conveyance speed is 50 m / min or more, the occurrence of conveyance breakage during conveyance can be greatly suppressed. From the viewpoint of productivity, the conveyance speed is more preferably 55 m / min or more, and still more preferably 60 m / min or more. The upper limit is not particularly defined, but is preferably 120 m / min or less. If it exceeds 120 m / min, the laminated polyolefin microporous membrane may be insufficiently washed with water. The present invention has a remarkable effect when the conveyance speed is 50 m / min or more.

  Next, the porous layer used in the present invention will be described.

  The resin constituting the porous layer is not particularly limited as long as it is a resin that can provide adhesion to an electrode material and a function of suppressing heat shrinkage (heat resistance), but a fluorine resin having excellent electrode adhesion is preferable. These resins may be used alone or in combination with other materials.

  Hereinafter, the fluororesin will be described in detail as an example.

  The fluororesin comprises at least one 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 it. 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, appropriate 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.

  In the porous layer of the present invention, a coating solution in which the resin is soluble and dissolved in a solvent miscible with water is applied to a predetermined microporous polyolefin membrane, the resin and the solvent are phase-separated, and then charged into a coagulation tank. And 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.

  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 porous layer may not be acquired by making an upper limit into the said preferable range.

  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 porous layer is preferably 12 μm, more preferably 10 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.

  About the film thickness of a porous layer, Preferably it is 1-5 micrometers, More preferably, it is 1-4 micrometers, More preferably, it is 1-3 micrometers. The film thickness of the porous layer can be determined by subtracting the film thickness of the polyolefin microporous film before coating from the film thickness of the laminated polyolefin microporous film. Each film thickness can be determined using a contact-type film thickness meter.

  When the film thickness is 1 μm or more, adhesion to the electrode is ensured, and the polyolefin microporous film is prevented from being melted and shrunk at a 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.

The porosity of the porous layer is preferably 30 to 90%, more preferably 40 to 70%. When the porosity of the porous layer is 30% or more, an increase in the 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 porosity of the porous layer can be obtained by the following equation.
Porosity of porous layer (%) = [1− (film thickness of porous layer / weight per unit area of porous layer) / true density of porous layer] × 100

  Hereinafter, although an example is shown and explained concretely, the present invention is not restrict | limited at all by these examples.

(1) Conveying folds For each level of Examples and Comparative Examples, a battery separator having a length of 2000 m was produced, and during the period from the coagulation tank to the final rinsing tank outlet, visual conveyance was observed, and conveyance breakage occurred. The case where it did not occur was considered good. In addition, the conveyance speed was increased stepwise from the start of coating, and 2000 m was evaluated from the time when the specified conveyance speed was reached.

(2) Conveying streaks For each level of the examples and comparative examples, a battery separator was produced with a length of 2000 m, and during that time, the streak tank was visually observed from the final rinsing tank outlet, and the streaks generated by the straightening device. The case where it did was bad and the case where it did not generate | occur | produced was made favorable. In addition, the conveyance speed was increased stepwise from the start of coating, and 2000 m was evaluated from the time when the specified conveyance speed was reached.

(3) Contamination prevention effect by bringing coagulation liquid and washing water for each level of Examples and Comparative Examples N-methyl-2-pyrrolidone (NMP) of final washing tank after producing separator for battery with total length of 20000 m ) The concentration was determined. The smaller the NMP concentration in the final rinsing tank, the better the anti-contamination effect due to carry-in.
The NMP concentration in the initial coagulation tank was 15% by weight, and the NMP concentration was measured by calculating the Brix value using a pocket saccharimeter PAL-1 (manufactured by Atago Co., Ltd.) and measuring the NMP concentration with a calibration curve. The detection limit of the pocket sugar content meter PAL-1 (manufactured by Atago Co., Ltd.) is 0.1 Brix%.

(4) Thickness measurement Using a contact-type film thickness meter ("Lightmatic" (registered trademark) VL-50-B manufactured by Mitutoyo Corporation), the film thicknesses of the microporous film and the separator were measured. In the measurement, 20 points were measured under the condition of a weight of 0.01 N using a carbide spherical measuring element φ9.5 mm, and the average value of the obtained measured values was taken as the film thickness.

[Example 1]
(Adjustment of coating solution)
A polyvinylidene fluoride-hexafluoropropylene copolymer (weight average molecular weight 1 million) was used as the fluorine resin. Fluorine resin, alumina particles (average particle size 1.0 μm), and NMP were blended at a weight ratio of 4: 9: 87, respectively, and sufficiently stirred to prepare a coating solution.

(Lamination of porous layer)
An apparatus having a coagulation tank and a washing tank shown in FIG. 1 by applying the coating liquid on both surfaces of a polyethylene microporous film (width: 610 mm, thickness: 5 μm, porosity: 35%) as a polyolefin microporous film. And dried by passing through a hot air drying oven at 45 ° C. to obtain a battery separator having a final thickness of 8 μm. At this time, the conveyance speed was increased stepwise over 5 minutes, and the battery separator was wound up 2000 m from the point when it reached 50 m / min. At this time, the coagulating liquid temperature and the washing water temperature were both 25 ° C.

In addition, the conditions of the apparatus which has a coagulation tank and a washing tank shown in FIG. 1 were as follows.
・ NMP concentration in coagulation tank: 15% by weight
・ Supporting roll: Hard chromium plated φ80 metal roll with surface roughness 0.3S ・ Liquid draining device: φ24 surface layer is ethylene propylene diene (EPDM) rubber roll ・ Transporting support roll and laminated polyolefin microporous membrane Contact pressure of liquid draining device: 0.02 MPa
Curvature straightening device: Teflon resin end support roll with an angle of 15 ° between the tip extension line and the central axis (diameter straightening device a)
-Contact length from the end of the laminated polyolefin microporous membrane of the curvature correction device: 20 mm at both ends
-Distance in the transport direction between the upstream end of the contact surface of the laminated polyolefin microporous membrane and the transport support roll and the downstream end of the contact surface of the curvature correcting device: 250 mm
・ Capacity of coagulation tank and washing tank: 700L each
[Example 2]
A battery separator was produced in the same manner as in Example 1 except that a polyethylene microporous membrane (width 610 mm, thickness 7 μm, porosity 40%) was used as the polyolefin microporous membrane.

[Example 3]
A battery separator was produced in the same manner as in Example 1 except that a polyethylene microporous membrane (width 1050 mm, thickness 5 μm, porosity 35%) was used as the polyolefin microporous membrane.

[Example 4]
A battery separator was produced in the same manner as in Example 1 except that the conveyance speed was increased stepwise over 7 minutes and the battery separator was wound up 2000 m from the point when it reached 70 m / min.

[Example 5]
A battery separator was produced in the same manner as in Example 1 except that the conveyance speed was increased stepwise over 9 minutes and 2000 m of the battery separator was taken up from the point when it reached 90 m / min.

[Example 6]
A battery separator was manufactured in the same manner as in Example 1 except that a Teflon resin end support roll (curve straightening device b) having a diameter of 20 mm and an angle between the extension line of the tip and the central axis of 30 ° was used as the straightening device. did.

[Example 7]
A battery separator was produced in the same manner as in Example 1 except that a Teflon resin end support roll (curve straightening device c) having a diameter of 20 mm and a spherical tip was used as the straightening device.

[Example 8]
A battery separator was produced in the same manner as in Example 1 except that a Teflon resin end support roll (curve straightening device d) having a diameter of 20 mm and an angle between the tip surface and the central axis of 90 ° was used as the straightening device.

[Example 9]
Battery as in Example 1 except that the distance in the transport direction between the upstream end of the contact surface of the laminated polyolefin microporous membrane and the transport support roll and the downstream end of the contact surface of the curving straightening device was 450 mm. A separator was manufactured.

[Example 10]
A battery separator was produced in the same manner as in Example 1 except that the contact pressure of the liquid draining device via the transport support roll and the laminated polyolefin microporous membrane was 1.0 MPa.

[Comparative Example 1]
A battery separator was prepared in the same manner as in Example 1 except that a polyethylene microporous membrane (width 400 mm, thickness 5 μm, porosity 35%) was used as the polyolefin microporous membrane, and the liquid draining device and the curvature correcting device were not used. Manufactured.

[Comparative Example 2]
A battery separator was produced in the same manner as in Example 1 except that the conveyance speed was increased stepwise over 1 minute, and 2000 m of the battery separator was taken up from the time when it reached 3 m / min.

[Comparative Example 3]
A battery separator was produced in the same manner as in Example 4 except that the liquid draining device and the curvature correcting device were not used.

[Comparative Example 4]
A battery separator was produced in the same manner as in Comparative Example 1, except that a polyethylene microporous membrane (width 610 mm, thickness 16 μm, porosity 45%) was used as the polyolefin microporous membrane.

[Comparative Example 5]
A battery separator was produced in the same manner as in Example 1 except that the curvature correcting device was not used.

[Comparative Example 6]
A battery separator was produced in the same manner as in Example 1 except that the position of the liquid draining device was set at the midpoint between the conveyance support roll and the curvature correcting device.

  The production conditions and evaluation results of Examples 1 to 10 and Comparative Examples 1 to 6 are shown in Table 1.

1: Laminated polyolefin microporous membrane 2: Coagulation tank 3: Washing tank 4: Curvature straightening device 5: Liquid draining device 6: Conveyance support roll

Claims (9)

A method for producing a battery separator comprising a porous layer laminated on at least one surface of a polyolefin resin porous membrane, wherein the battery separator production process comprises a coating process, a coagulation process having a coagulation tank, and a water washing process having a water washing tank. And a drying step, and the polyolefin resin porous membrane is formed into a laminated polyolefin microporous membrane through the coating step, and a transport support roll is installed between or above the tanks, and the coagulation tank in the coagulation process and the water washing process in the water washing process At least one of the tanks is on the side opposite to the side where the laminated polyolefin microporous membrane and the conveying support roll are in contact between the liquid level and the conveying support roll on the downstream side, and the laminated polyolefin microporous membrane and the conveying support roll A liquid draining device is installed on the circumference where the liquid is in contact, and the laminated polyolefin microporous membrane between the liquid surface and the transport support roll A curvature correcting device in contact with the portion is installed at at least one end of the laminated polyolefin microporous membrane, the polyolefin microporous membrane has a width of 600 mm to 2000 mm, a thickness of 3 μm to 8 μm, and a conveying speed Is 50 m / min or more, The manufacturing method of the separator for batteries characterized by the above-mentioned. The method for producing a battery separator according to claim 1, wherein the liquid draining device is a roll or a bar. The method for producing a battery separator according to claim 1 or 2, wherein the contact pressure of the liquid draining device via the transport support roll and the laminated polyolefin microporous membrane is 0.01 MPa or more and 1.0 MPa or less. The method for producing a battery separator according to any one of claims 1 to 3, wherein the curvature correcting device is an end support roll. 5. The method for producing a battery separator according to claim 4, wherein an angle formed between an end surface of the end support roll and a central axis of an extension line of the end support roll tip is 45 ° or less. The battery separator manufacturing method according to claim 4, wherein an end surface of the end support roll is a spherical surface. The distance in the transport direction between the upstream end of the contact surface of the laminated polyolefin microporous membrane and the transport support roll and the downstream end of the contact surface of the curving straightening device is 500 mm or less. A method for producing a battery separator according to any one of claims 6 to 10. The method for producing a battery separator according to any one of claims 1 to 7, wherein the porous layer contains at least one resin selected from polyvinylidene fluoride, polyvinylidene fluoride copolymer, wholly aromatic polyamide, and polyamideimide. An apparatus for manufacturing a battery separator in which a porous layer is laminated on at least one surface of a polyolefin resin porous film, wherein the battery separator manufacturing apparatus includes a coating apparatus, a coagulation tank, a washing tank, and a drying apparatus in order, A conveyance support roll is installed between or above each tank, and at least one of the coagulation tank and the washing tank passes through the coating device between the liquid level setting range of the tank and the conveyance support roll on the downstream side. A liquid draining device is installed on the opposite side to the side where the laminated polyolefin microporous membrane and the conveyance support roll are in contact with each other, and on the circumference where the laminated polyolefin microporous membrane and the conveyance support roll are in contact, Between the liquid level setting range of the tank and the conveyance support roll, the curvature correcting device in contact with the end of the laminated polyolefin microporous membrane is in the width direction through which the laminated polyolefin microporous membrane passes. Apparatus for manufacturing a battery separator, characterized by being installed at one end even without.