Method for manufacturing separator for power storage device

Abstract

Provided is an inspection device or manufacturing method for a separator having a thermoplastic polymer layer, characterized in that the separator S includes a substrate and a thermoplastic polymer layer present locally on one or both faces of the substrate, and the inspection device or manufacturing method includes a process of inspecting the surface of the separator S, and the inspection of the separator is performed using an inspection device having a light source 1 and a camera 2, the light source 1 irradiating light at an angle of 60° or more and 90° or less with respect to the incident angle of the inspection portion of the separator.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a separator for energy storage devices. Background Technology

[0002] Currently, the development of energy storage devices, represented by lithium-ion secondary batteries, is actively underway. Typically, in energy storage devices, a microporous membrane (separator) is placed between the positive and negative electrodes. The separator prevents direct contact between the positive and negative electrodes while allowing the electrolyte held within the micropores to pass through, thus enabling ion permeation.

[0003] For separators, safety-related properties are required, such as the ability to rapidly terminate the battery reaction under abnormal heating (fusible characteristic) and the ability to maintain shape even at high temperatures to prevent dangerous situations where the positive and negative electrodes react directly (short-circuit withstand characteristic). Furthermore, to increase the capacity of energy storage devices, techniques are commonly used to reduce the volume of the wound body formed by hot-pressing the laminate of electrodes and separators. To fix the electrodes and separators after pressurization and maintain the volume under pressurization, techniques are also used to improve the adhesion of the separator to the electrodes by depositing a thermoplastic polymer layer on the separator that provides adhesion under specified conditions.

[0004] For example, Patent Document 1 discloses a separator that aims to provide excellent adhesion to electrodes and excellent operability. The separator comprises a thermoplastic polymer layer on a polyolefin microporous membrane as a substrate, having portions containing a thermoplastic polymer and portions not containing a thermoplastic polymer. The thermoplastic polymer has at least two glass transition temperatures, at least one of which is in a region below 20°C and at least one of which is in a region above 20°C.

[0005] On the other hand, a method for inspecting metal sheets that is not used for separators is disclosed, which uses coaxial incident illumination or oblique illumination to irradiate a metal sheet with multiple micron-sized protrusions formed on its surface at micron-sized intervals with light of a width in a direction perpendicular to the optical axis, and detects defective locations where no protrusions are formed (Patent Document 2).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2014 / 017651

[0009] Patent Document 2: Japanese Patent Application Publication No. 2010-008266 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] Due to increased environmental awareness in recent years, energy storage devices such as electric vehicles (EVs) have received much attention. In the lithium-ion secondary batteries used in these energy storage devices, separators that are adhesive to the electrodes are used to improve the productivity of the electrode and separator stacking process.

[0012] As an adhesive separator that adheres to the electrodes, an adhesive layer is sometimes applied to the surface of the separator, and the coverage area of ​​the adhesive layer is at a constant ratio. If the coverage area of ​​the adhesive layer is too small compared to the specified ratio, sufficient adhesion cannot be obtained between the separator and the electrodes; if the coverage area of ​​the adhesive layer is too large compared to the specified ratio, the battery resistance increases, resulting in poor output or lifespan.

[0013] Therefore, in order to ensure that the coverage area of ​​the adhesive layer on the surface of the adhesive spacer is constant, an inspection device for measuring the coverage area of ​​the adhesive layer is desired. However, existing inspection devices have not explored techniques for measuring the coverage area of ​​the adhesive layer on the spacer with high precision. In particular, the adhesive layer is usually an organic component, and the boundary between the adhesive layer and the surface of the substrate, which is also an organic component, is difficult to distinguish. Furthermore, the thickness of the adhesive layer on the spacer is 0.1 μm to several μm, with almost no height difference, making it very difficult to inspect only the adhesive layer portion. Therefore, as an area management method, it is necessary to use a scanning electron microscope to extract and evaluate each sample individually, which results in a significant consumption of labor and time in management.

[0014] The present invention was made in view of the above circumstances, and its object is to provide an inspection apparatus and a manufacturing method for separators, which can measure with high precision and efficiency the coverage area of ​​the thermoplastic polymer layer on the surface of the separator having a thermoplastic polymer layer as an adhesive layer.

[0015] Solution for solving the problem

[0016] In order to solve the above-mentioned problems, the inventors conducted research and discovered that the above-mentioned problems could be solved by using an inspection device for adhesive separators having the following configuration, thereby completing the present invention. That is, the present invention is as follows.

[0017] [1] An inspection device for a separator, characterized in that it is an inspection device for a separator having a thermoplastic polymer layer.

[0018] The aforementioned separator comprises a substrate and a thermoplastic polymer layer partially present on one or both sides of the substrate.

[0019] The inspection device described above has a light source and a camera, wherein the light source illuminates the inspected portion of the separator at an angle of incidence θ of 60 degrees or more and 90 degrees or less.

[0020] [2] The inspection device for the separator according to item 1, wherein the distance from the surface of the separator to the camera is 10 mm or more and 1000 mm or less.

[0021] [3] The inspection device for the separator according to item 1 or 2, wherein the camera is set in an angle range of more than -5 degrees and less than +5 degrees relative to the reflection angle of light incident from the light source.

[0022] [4] The inspection device for the separator according to any one of items 1 to 3 has a stand for fixing the camera, and the stand has a platform that can move the camera along any one or more of the following directions: front and back, left and right, up and down.

[0023] [5] An inspection device for a separator according to any one of items 1 to 4, wherein the size of the light source is 1 mm or more and 3000 mm or less.

[0024] [6] An inspection device for a partition according to any one of items 1 to 5, wherein two or more of the above-mentioned light sources are used to irradiate the inspection portion of the partition.

[0025] [7] The inspection device for the separator according to item 6, wherein the two or more light sources are arranged at equal intervals in such a way as to surround the inspection portion of the separator.

[0026] [8] A method for manufacturing a separator, characterized in that it is a method for manufacturing a separator having a thermoplastic polymer layer.

[0027] The aforementioned separator comprises a substrate and a thermoplastic polymer layer partially present on one or both sides of the substrate.

[0028] The method for manufacturing the separator includes a step of inspecting the surface of the separator, and inspecting the separator using an inspection device having a light source and a camera, wherein the light source illuminates the separator at an angle of incidence θ relative to the inspected portion of the separator at an angle of 60 degrees or more and 90 degrees or less.

[0029] [9] The method for manufacturing the separator according to item 8, wherein the thermoplastic polymer layer comprises a particulate polymer compound.

[0030]

[10] In the method for manufacturing the separator according to item 9, the average particle size of the above-mentioned particulate polymer is 50 nm or more and 10,000 nm or less.

[0031]

[11] The method for manufacturing a separator according to any one of items 8 to 10, wherein the thermoplastic polymer exists in a form having a unit pattern, the unit pattern being a repeat of a certain pattern.

[0032]

[12] The method for manufacturing a separator according to any one of items 8 to 11, wherein an inorganic filler layer is present on one or both sides of the substrate, and the thermoplastic polymer layer is present at least partially on the inorganic filler layer.

[0033]

[13] In the method for manufacturing the separator according to item 12, the volume average particle size of the inorganic filler contained in the inorganic filler layer is 50 nm or more and 2000 nm or less.

[0034]

[14] In the method for manufacturing the separator according to item 12 or 13, the volume average particle size D1 of the thermoplastic polymer and the volume average particle size D2 of the inorganic filler satisfy the following formula:

[0035] D1 / D2≤0.8 or D1 / D2≥1.2.

[0036]

[15] A method for manufacturing a separator, characterized in that it is a method for manufacturing a separator having a thermoplastic polymer layer.

[0037] The aforementioned separator comprises a substrate and a thermoplastic polymer layer partially present on one or both sides of the substrate.

[0038] The manufacturing method of the separator includes an inspection step of inspecting the surface of the separator using an inspection device equipped with a light source and a camera, wherein the light source illuminates the surface of the separator at an angle θ of 60 degrees or more and 90 degrees or less relative to the surface of the separator.

[0039] The above inspection process includes an inspection step that detects the shape and / or coverage of the thermoplastic polymer layer based on an image obtained by taking a picture using the camera.

[0040]

[16] In the method for manufacturing the separator according to item 15, in the above inspection process, the condition of the separator is further determined based on the shape and / or coverage obtained in the above inspection process.

[0041] Additionally, the following examples illustrate a portion of preferred embodiments of the invention.

[0042]

[17] An inspection device for a separator according to any one of items 1 to 7, wherein the incident angle θ is 75 degrees or more and less than 90 degrees.

[0043]

[18] The method for manufacturing the separator according to item 11, wherein the size of the unit pattern is 10 μm × 10 μm or more and 10 mm × 10 mm or less.

[0044]

[19] The method for manufacturing a separator according to any one of items 12 to 14, wherein the amount of binder contained in the inorganic filler layer is 0.5 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the inorganic filler.

[0045] Furthermore, the elements described in any one of the above items 9 to 14, 18 and 19 can be the description of the separator in the invention of the inspection device, and the elements described in any one of the above items 2 to 7 and 17 can be the description of the inspection device in the invention of the method for manufacturing the separator.

[0046] The effects of the invention

[0047] According to the present invention, the coverage area of ​​the thermoplastic polymer layer on the surface of a separator having a thermoplastic polymer layer can be measured with high precision and efficiency. In particular, the method of evaluating the coverage area of ​​the thermoplastic polymer layer by evaluating the image of the coating surface of the thermoplastic polymer layer after the thermoplastic polymer layer has dried is simple and can be performed without damaging the separator. Therefore, it can be said to be helpful for the development of excellent separators, the management of manufacturing processes, etc. Attached Figure Description

[0048] Figure 1 A side view showing an example of an inspection device.

[0049] Figure 2 A top view showing an example of an inspection device.

[0050] Figure 3 A side view showing an example of an inspection device.

[0051] Figure 4 This diagram illustrates an example of a configuration pattern for a thermoplastic polymer. Detailed Implementation

[0052] Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as "this embodiment") will be described in detail with reference to the accompanying drawings, but the present invention is not limited to the following embodiments. Various modifications can be made to the present invention without departing from its spirit.

[0053] The terms "on" and "formed on the surface" in this specification do not limit the positional relationship of the components to "directly above". For example, the expressions "a thermoplastic polymer layer containing a thermoplastic polymer formed at least partially on at least one side of a substrate", "a thermoplastic polymer layer formed on a substrate", and "a thermoplastic polymer layer formed on the surface of a substrate" do not preclude the inclusion of any layer (a heat-resistant layer, such as an inorganic filler porous layer) between the substrate and the thermoplastic polymer layer.

[0054] In this specification, "adhesion" refers to adhesion under high temperature and pressure (assuming adhesion to the electrodes), and "adhesion" refers to the adhesion between the separators when they are in a wound state at room temperature (the separators are pressed together, which is the same as "stickiness"). Additionally, "bonding" refers to the adhesive force between the substrate and the adhesive.

[0055] In this specification, "(meth)acrylic acid" refers to "acrylic acid" and its corresponding "methacrylic acid", "(meth)acrylate" refers to "acrylate" and its corresponding "methacrylate", and "(meth)acryloyl" refers to "acryloyl" and its corresponding "methacryloyl".

[0056] It should be noted that the MD direction refers to the mechanical direction when continuously molding polyolefin microporous membranes, for example, while the TD direction refers to the direction that crosses the MD direction at a 90° angle.

[0057] Furthermore, unless otherwise stated, the “~” in the numerical range in this specification means that the values ​​recorded before and after it are included as the upper and lower limits.

[0058] <Manufacturing Method of Separator>

[0059] One aspect of the present invention provides a method for manufacturing a separator.

[0060] The method for manufacturing a separator according to the first embodiment is characterized in that it is a method for manufacturing a separator having a thermoplastic polymer layer (containing a thermoplastic polymer layer), the separator comprising a substrate and a thermoplastic polymer layer partially present on one or both sides of the substrate, the method for manufacturing the separator comprising a step of inspecting the surface of the separator, the inspection of the separator being performed using an inspection device having a light source and a camera, wherein the light source irradiates light at an angle of incidence θ relative to the inspected portion of the separator at an angle of 60 degrees (°) or more and 90 degrees or less.

[0061] The manufacturing method of the separator according to the second embodiment is characterized in that, like the first embodiment, it includes an inspection step of inspecting the surface of the separator having a thermoplastic polymer layer (containing a thermoplastic polymer layer) using an inspection device, and the shape and / or coverage of the thermoplastic polymer layer are detected based on the image captured by the camera of the inspection device in the inspection step.

[0062] The inspection method involved in the manufacturing method of the separator is an inspection method using oblique lighting during the process of inspecting the surface of the separator (the inspection part of the separator). This method measures the area and / or shape of the pattern of the thermoplastic polymer layer (containing the thermoplastic polymer layer) of the separator after coating and drying, and determines whether it is good or bad. Specifically, by irradiating the thermoplastic polymer layer of the object under inspection with an incident angle θ of 60 degrees or more and 90 degrees or less, the contrast of the thermoplastic polymer layer is highlighted, and the patterned coating area is identified. This allows for high-precision and efficient measurement of the area (e.g., coverage) and / or shape of the pattern of the thermoplastic polymer layer formed on the separator.

[0063] Furthermore, as described later, by appropriately selecting the parameters of the separator, the contrast of the thermoplastic polymer layer can be further enhanced under light irradiation, thereby more reliably identifying the patterned coating. This allows for more precise and efficient measurement of the area or shape of the pattern formed on the separator containing the thermoplastic polymer layer. Thus, the present invention enables the efficient manufacture of highly reliable separators.

[0064] [Inspection device]

[0065] Another aspect of the present invention provides an inspection device.

[0066] The inspection device according to the third embodiment is characterized in that it is an inspection device having a separator having a thermoplastic polymer layer, the separator comprising a substrate and a thermoplastic polymer layer partially present on one or both sides of the substrate, and the inspection device having a light source and a camera that irradiates light at an angle of 60 degrees (°) or more and 90 degrees or less with respect to the inspection portion of the separator.

[0067] Figures 1-3 This figure illustrates an example configuration of an inspection apparatus for inspecting separators in the manufacturing method of the present invention. The inspection apparatus includes a light source 1 and a camera 2. The surface of the separator S can be photographed and inspected (online) on the production line or off-line.

[0068] Light source 1 illuminates the surface of the separator S. There are no particular restrictions on the type of light source 1; fluorescent lamps, mercury lamps, LEDs, etc., can be used. However, LEDs are preferred from the viewpoint of light source stability. When using an LED as light source 1, any wavelength can be selected; however, from the viewpoint of highlighting the contrast of the pattern on the thermoplastic polymer layer, a wavelength of 630 nm is preferred.

[0069] When the direction perpendicular to the plane of the separator S is set to 0 degrees, the incident angle θ of the light from the light source 1 relative to the inspection portion S1 of the separator S is 60 degrees or more and 90 degrees or less, preferably 75 degrees or more and less than 90 degrees, and more preferably 80 degrees or more and less than 90 degrees. By setting the incident angle θ of the light from the light source 1 to the above range, the unevenness of the pattern of the thermoplastic polymer layer can be highlighted, the contrast of the pattern of the thermoplastic polymer layer can be reflected more clearly, and a more reliable inspection can be performed. For the separator disposed on the roller, the direction perpendicular to the tangent of the inspection portion S1 is set to 0 degrees.

[0070] Conversely, if the incident angle θ of the light from light source 1 relative to the plane of separator S is less than 60 degrees, the unevenness of the pattern in the thermoplastic polymer layer becomes unclear, and the contrast of the pattern in the thermoplastic polymer layer cannot be clearly reflected, resulting in insufficient inspection accuracy. Furthermore, if the incident angle θ is greater than 90 degrees, sufficient light cannot be irradiated onto the inspection area S1, resulting in an unclear image.

[0071] The distance from the light source 1 to the surface of the separator S is preferably 500 mm or less, more preferably 300 mm or less, and even more preferably 100 mm or less. By bringing the distance between the light source 1 and the separator S closer, the pattern of the thermoplastic polymer layer can be captured at high resolution.

[0072] The number of light sources 1 is not particularly limited, but it is preferable to use two or more light sources 1 to illuminate the inspection portion S1 of the separator S from different directions. Specifically, as follows: Figure 2 As shown in the top view, it is preferable to arrange two or more light sources 1 at equal intervals in a manner that surrounds the inspection portion S1 of the separator S (shown by the diagonal line in the figure). Figure 2 An example using eight light sources 1 is shown. By uniformly illuminating the thermoplastic polymer layer with light from multiple light sources 1, the shadows of the patterned portions of the thermoplastic polymer layer can be spread more evenly, the contrast of the pattern of the thermoplastic polymer layer can be reflected more clearly, and more reliable inspection can be performed. From a spatial point of view, the number of light sources 1 is preferably 50 or less.

[0073] The shape of the light source 1 is not particularly limited, and it can take a flexible shape, such as a sphere, rod, or arc. The size of the light source 1 is not particularly limited, but the length or diameter of one side is preferably 1 mm or more and 3000 mm or less. Furthermore, when not configuring two or more light sources 1, it is preferable to use a light source with a length or diameter of one side of 100 mm or more and 3000 mm or less, and more preferably a light source with a length or diameter of one side of 200 mm or more and 1500 mm or less. By adjusting the length or diameter of one side of the light source to 100 mm or more, the influence of the patterned portion of the thermoplastic polymer layer can be reduced; by adjusting it to 3000 mm or less, the space required to install the inspection equipment can be reduced.

[0074] There are no particular restrictions on camera 2; any commercially available camera can be used, preferably a CCD image sensor or a CMOS image sensor. From a resolution perspective, a CMOS image sensor is more preferred. There are no particular restrictions on the resolution of camera 2, but for observing fine patterns, a camera with 1 million pixels or more is preferred.

[0075] The distance from camera 2 to the surface of separator S (the inspection part of separator) can be any value as long as the surface image can be detected. This distance is preferably 10 mm or more and 3000 mm or less. Especially when the inspection equipment is set up online, it is preferable to set this distance to 250 mm or more and 2000 mm or less, and more preferably to 500 mm or more and 1000 mm or less. By setting the distance from the camera to the surface of separator S to 250 mm or more, it is less likely to come into contact with the separator if the separator's position deviates during travel. Furthermore, by setting the above distance to 3000 mm or less, a focal distance suitable for the camera resolution can be set.

[0076] There are no particular restrictions on the position of camera 2. When the direction perpendicular to the plane of the separator S is set to 0 degrees, it is preferable to be above 0 degrees. Figure 3 (A) and / or below 90 degrees ( Figure 3 The camera is taken at an angle of (B). A more preferred upper limit is 75 degrees or less, and even more preferably 60 degrees or less. By setting the camera 2 within the above-mentioned range, errors caused by the shadow portion of the pattern can be reduced, enabling more reliable inspection. Furthermore, when setting up the inspection equipment online, when irradiating light from a light source relative to the surface of the separator to be inspected at an incident angle θ and a reflection angle θ, it is preferable to set the camera within an angle range of -5 degrees (°) or more and +5 degrees relative to the aforementioned reflection angle. By setting it in this position, the sensitivity of the camera 2 can be improved, enabling inspection of separators transported at high speeds.

[0077] Camera 2 is preferably fixed to a dedicated stand. The stand is preferably a platform that can move along one or more of the following directions: front-back, left-right, up-down, so as to be adjusted to a suitable position for each inspection.

[0078] When conducting an online inspection, such as Figure 3 (A) or Figure 3 As shown in (B), the portion of the conveyed separator S in contact with the roller 11 can be photographed, as can the portion not in contact with the roller 11. To avoid blurry camera focus, observation is preferably performed above the roller 11. When observing above the roller 11, the diameter of the roller 11 is preferably 10 mm or more, more preferably 30 mm or more, and even more preferably 50 mm or more. By increasing the diameter of the roller 11, the curvature of the inspection portion S1 on the surface of the separator S decreases, making the captured image less prone to blurring.

[0079] When shooting offline, the separator S can be placed on the platform 10 or the like for shooting, or it can be shot while it is floating above the platform 10. From the viewpoint of keeping the separator S stationary, the method of shooting while it is placed on the platform 10 is preferred. In addition, when inspecting the separator S on the platform 10, from the viewpoint of keeping the separator S stationary without wrinkles, it is preferred to inspect it by placing a glass plate on the separator S.

[0080] Furthermore, from the viewpoint of keeping the surface state of the inspection section S1 constant, it is ideal to use an adsorption platform that has a suction hole in the platform 10 and a suction section on the lower side of the platform 10, and adsorbs the separator S by suctioning air.

[0081] The image captured by the camera 2 can be processed using image processing software to binarize the captured pattern to level 256. As a result, the surface of the separator S is divided into a portion covered by the thermoplastic polymer layer and a portion not covered by the thermoplastic polymer layer. Furthermore, the area, length (shape), etc., of the divided portion are measured using the image processing software.

[0082] Image processing software can be commercially available, such as ImageJ.

[0083] As described above, the area and / or shape of the pattern of the thermoplastic polymer layer on the separator are measured, and its quality is judged according to the specified criteria. When a separator is judged to be defective, it is preferable to reset the manufacturing conditions such as the coating conditions, drying time, and temperature of the thermoplastic polymer layer to a suitable range. It should be noted that separators judged to be defective can be marked to separate them from separators judged to be good and removed from the production line.

[0084] In the first or second embodiment, when a thermoplastic polymer layer is continuously coated onto an isotropic strip separator using a coating machine, the area and / or shape of the dried thermoplastic polymer layer can be continuously measured at predetermined time intervals according to the above conditions, and it can be determined whether it is good.

[0085] For example, when the incident angle θ relative to the plane of the separator is in the range of 60 degrees or more and 90 degrees or less (preferably 75 degrees or more and less than 90 degrees), the area and / or shape of the pattern of the thermoplastic polymer layer of the separator are continuously measured at predetermined time intervals. A separator that satisfies all the criteria for the area and / or shape of the continuously measured pattern is judged to be good. Thus, in the first or second embodiment, online inspection can be performed while continuous coating is being applied.

[0086] The method of the first or second embodiment, which measures the area and / or shape of the thermoplastic polymer layer and evaluates whether the thermoplastic polymer layer is suitably formed on the surface of the separator according to a pattern, has the following advantages: (1) It is a simple method that does not require the use of special equipment; (2) It can evaluate whether the thermoplastic polymer layer is suitably formed in a short time without damaging the separator; (3) It can perform the evaluation non-destructively in a short time using a simple method, so that the quality can be confirmed online in the separator manufacturing process; (4) Since the quality can be confirmed online, feedback can be given on manufacturing conditions such as coating conditions, drying temperature, and drying time.

[0087] In the inspection or manufacturing of separators, it is preferable to have a process that determines whether the separator is qualified or not based on the inspected area (e.g., coverage) and / or shape, and provides feedback on the qualification or non-qualification result. In determining qualification or non-qualification, a "no" is determined if the specified criteria are not met. By including the above feedback process, efficient automatic judgment based on AI is possible.

[0088] The separators after the above inspection process can be processed into specified dimensions as needed, thereby manufacturing the separators.

[0089] As described above, the method of measuring the area and / or shape of the pattern of the thermoplastic polymer layer on the surface of the separator after coating and drying the thermoplastic polymer layer to evaluate whether the thermoplastic polymer layer is good is relatively simple and can be evaluated without damaging the separator. Therefore, it can be said to help in the development of excellent separators and the management of manufacturing processes.

[0090] Therefore, the present invention can efficiently manufacture highly reliable separators.

[0091] <Separator>

[0092] The separator inspected using the above inspection method is a separator for an energy storage device, comprising a substrate and a thermoplastic polymer layer (containing a thermoplastic polymer layer) formed on at least one side of the substrate. The method of forming the thermoplastic polymer layer on only one side of the separator and the method of forming the thermoplastic polymer layer on both sides of the separator are both included within the scope of this invention. Furthermore, in the separator of the first or second embodiment, an inorganic filler layer (inorganic filler porous layer) may be present on one or both sides of the substrate; in this case, a portion of the surface of the inorganic filler layer is covered by a thermoplastic polymer.

[0093] In particular, in the first or second embodiment, by appropriately selecting the parameters of the separator, it is possible to highlight the contrast of the patterned coating in the inspection method described above, thereby enabling the identification of the pattern and allowing for the high-precision and efficient measurement of the area and / or shape of the pattern containing the thermoplastic polymer layer formed on the separator.

[0094] The preferred embodiments of each component that can constitute the separator are described in detail below.

[0095] [Substrate]

[0096] The substrate itself can be any substrate conventionally used as a separator. As a substrate, a porous membrane is preferred, and even more preferred are fine-pore porous membranes with high resistance to organic solvents and low electronic conductivity, high ionic conductivity, and high tolerance to organic solvents. Examples of such porous membranes include, for instance, microporous membranes containing resins as the main component, such as polyolefins (e.g., polyethylene, polypropylene, polybutene, and polyvinyl chloride), mixtures thereof, or copolymers of their monomers; microporous membranes containing resins as the main component, such as polyethylene terephthalate, polycyclic olefins, polyethersulfone, polyamide, polyimide, polyimide amide, polyaromatic polyamide, polycyclic olefins, nylon, and polytetrafluoroethylene; porous membranes (woven fabrics) made of polyolefin fibers; nonwoven fabrics made of polyolefin fibers; paper; and aggregates of insulating material particles. They can be used individually or in combination of two or more.

[0097] From the viewpoint of increasing the ratio of active materials in the energy storage device by making the separator thinner, thereby increasing the capacity per unit volume, polyolefin microporous membranes containing polyolefin-based resins as the main component are preferred. For polyolefin microporous membranes, the excellent coatability of the coating liquid, after coating the membrane with a coating solution, facilitates a thinner separator thickness.

[0098] It should be noted that "containing a polyolefin-based resin as a main component" means that it contains more than 50% by mass relative to the total mass of the substrate. When using a polyolefin microporous membrane as the substrate, the content of polyolefin resin in the polyolefin microporous membrane is not particularly limited. However, from the viewpoint of closing performance when used as a separator, it is preferable that 50% by mass and 100% by mass of the total components constituting the polyolefin microporous membrane are polyolefin resin. The content of polyolefin resin is preferably 75% by mass or more, more preferably 85% by mass or more, further preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and can be 100% by mass.

[0099] There are no particular limitations on the polyolefin resin used; it can be any polyolefin resin that can be used in common extrusion molding, injection molding, blow molding, and blow molding. Examples of polyolefin resins include homopolymers with monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, as well as copolymers and multi-stage polymers of two or more of these monomers. These homopolymers, copolymers, and multi-stage polymers can be used alone or in combination of two or more.

[0100] Representative examples of polyolefin resins are not particularly limited, and can include, for example, polyethylene, polypropylene, and polybutene. More specifically, examples include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene atactic copolymer, polybutene, and ethylene-propylene rubber. They can be used alone or in combination of two or more. From the viewpoint of pore-closing properties due to heat melting, polyethylene such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene is preferred as a polyolefin resin. High-density polyethylene is particularly preferred from the viewpoint of low melting point and high strength, and more preferably has a density of 0.93 g / cm³ as measured according to JIS K 7112. 3 The above refers to polyethylene. There are no particular limitations on the polymerization catalyst used in manufacturing these polyethylenes; examples include Ziegler-Natta catalysts, Philips catalysts, and metallocene catalysts. However, from the viewpoint of controlling the balance between low melting point, high strength, permeability, and thermal properties, it is preferable to use polyethylene as the main component.

[0101] To improve the heat resistance of the substrate, a more preferred polyolefin microporous membrane comprises polypropylene and polyolefin resins other than polypropylene. Here, the stereostructure of polypropylene is not limited and can be any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Furthermore, examples of polyolefin resins other than polypropylene include homopolymers with monomers such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, as well as copolymers and multi-stage polymers of two or more of these monomers; specific examples are those already described above. The polymerization catalyst used in the manufacture of polypropylene is not particularly limited, and examples include Ziegler-Natta catalysts and metallocene catalysts.

[0102] The proportion of polypropylene in the total amount of polyolefin in polyolefin microporous membranes

[0103] There are no particular limitations on the (polypropylene / polyolefin) content, but from the viewpoint of balancing heat resistance and good sealing function, it is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, and even more preferably 4 to 10% by mass. From the same viewpoint, the content ratio of olefin resins other than polypropylene, such as polyethylene, in the polyolefin microporous membrane relative to the total polyolefin content (olefin resins other than polypropylene / polyolefin) is preferably 65 to 99% by mass, more preferably 80 to 97% by mass, and even more preferably 90 to 96% by mass.

[0104] Examples of polyolefin resins other than polyethylene and polypropylene include polybutene and ethylene-propylene random copolymers.

[0105] The viscosity-average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane is not particularly limited, but is preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, and even more preferably 100,000 or more and less than 1 million. When the viscosity-average molecular weight is 30,000 or more, there is an increase in melt tension during melt molding, resulting in better formability, and a tendency to achieve high strength due to the entanglement of polymers, which is therefore preferred. On the other hand, when the viscosity-average molecular weight is 12 million or less, there is a tendency to easily and uniformly melt-mix, resulting in excellent sheet formability, especially thickness stability, which is therefore preferred. Furthermore, if the viscosity-average molecular weight is less than 1 million, there is a tendency for the pores to become clogged easily when the temperature rises, resulting in better closure function, which is therefore preferred. It should be noted that the viscosity-average molecular weight (Mv) can be calculated based on ASTM-D4020, from the intrinsic viscosity [η] measured using decahydronaphthalene as a solvent at a measurement temperature of 135°C, using the following formula.

[0106] Polyethylene: [η] = 6.77 × 10 -4 Mv 0.67 (Chiang Formula)

[0107] Polypropylene: [η] = 1.10 × 10 -4 Mv 0.80

[0108] It should be noted that, for example, a mixture of a polyolefin with a viscosity-average molecular weight of 2 million and a polyolefin with a viscosity-average molecular weight of 270,000, or a mixture with a viscosity-average molecular weight of less than 1 million, can be used instead of using a polyolefin with a viscosity-average molecular weight of less than 1 million alone.

[0109] Furthermore, the substrate may contain any additives. Such additives are not particularly limited, and examples include polymers other than polyolefins; inorganic particles; antioxidants such as phenolic, phosphorus-based, and sulfur-based agents; metallic soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. The total content of these additives relative to 100 parts by weight of the polyolefin resin in the polyolefin microporous membrane is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less.

[0110] The porosity of the substrate is not particularly limited, but is preferably 20% or more, more preferably 30% or more, and even more preferably greater than 35%. On the other hand, this porosity is preferably 80% or less, more preferably 70% or less. From the viewpoint of more effectively and reliably ensuring the permeability of the separator, a porosity of 20% or more is preferred. On the other hand, from the viewpoint of more effectively and reliably ensuring puncture strength, a porosity of 80% or less is preferred. Porosity can be, for example, determined by the volume (cm³) of the substrate sample. 3 ), mass (g), membrane density (g / cm³) 3 The value can be obtained using the following formula.

[0111] Porosity = (Volume - Mass / Film Density) / Volume × 100

[0112] Here, for example in the case of a polyolefin porous membrane made of polyethylene, the membrane density can be assumed to be 0.95 g / cm³. 3 The porosity can be adjusted by changing the stretching ratio of the polyolefin microporous membrane. In particular, by keeping the porosity of the substrate within the above-mentioned range, the contrast between the patterned portion of the substrate and the thermoplastic polymer layer becomes better when inspecting the surface of the separator using the above-mentioned inspection method, enabling more reliable inspection.

[0113] There are no particular limitations on the air permeability of the substrate, but it is preferably 10 seconds / 100cm. 3 The above is preferred to be 50 seconds per 100cm. 3 The preferred value is 1000 seconds per 100cm. 3 The following is more preferably 500 seconds / 100cm 3From the perspective of suppressing the self-discharge of energy storage devices, it is preferable to set the air permeability to 10 seconds / 100cm. 3 That's all. On the other hand, from the viewpoint of obtaining good charge and discharge characteristics, it is preferable to set the air permeability to 1000 seconds / 100cm. 3 The following air permeability is based on the air resistance measured according to JIS P-8117. Air permeability can be adjusted by changing the stretching temperature and / or stretch ratio of the substrate.

[0114] The average pore size of the substrate is preferably 0.15 μm or less, more preferably 0.1 μm or less, and most preferably 0.01 μm or more. Setting the average pore size to 0.15 μm or less is suitable from the viewpoint of suppressing self-discharge and capacity reduction in energy storage devices. The average pore size can be adjusted by changing the stretching ratio during substrate manufacturing, etc.

[0115] The puncture strength of the substrate is not particularly limited, but is preferably 200 gf / 20 μm or more, more preferably 300 gf / 20 μm or more, even more preferably 400 gf / 20 μm or more, preferably 2000 gf / 20 μm or less, and more preferably 1000 gf / 20 μm or less. From the viewpoint of suppressing film rupture caused by active material or the like falling off when the separator is wound together with the electrode, and from the viewpoint of suppressing short circuits caused by electrode expansion and contraction associated with charging and discharging, a puncture strength of 200 gf / 20 μm or more is preferred. On the other hand, from the viewpoint of reducing width shrinkage caused by orientation relaxation during heating, a puncture strength of 2000 gf / 20 μm or less is preferred. The puncture strength can be measured based on the method described in the examples. The puncture strength can be adjusted by adjusting the stretching ratio of the substrate and / or the stretching temperature, etc.

[0116] The thickness of the substrate is not particularly limited, but is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. From the viewpoint of improving mechanical strength, it is preferable to set the film thickness to 2 μm or more. On the other hand, setting the film thickness to 100 μm or less can reduce the volume occupied by the separator in the energy storage device, which tends to be more advantageous in terms of increasing the capacity of the energy storage device, and is therefore preferred.

[0117] [Contains thermoplastic polymer layer]

[0118] The thermoplastic polymer layer contains a thermoplastic polymer. The thermoplastic polymer layer can be disposed on the entire surface of the substrate or locally. To ensure high ion permeability of the resulting energy storage device, it is more preferable to dispose of the thermoplastic polymer layer only locally on the surface of the substrate.

[0119] The thermoplastic polymer layer is configured to be directly bonded to the electrode. The at least one thermoplastic polymer layer of the separator is preferably configured to be directly bonded to the electrode, for example, by bonding at least a portion of the substrate to the electrode via the thermoplastic polymer layer.

[0120] The amount of thermoplastic polymer layer coated on the substrate, i.e., the amount of thermoplastic polymer layer formed per unit area on one side of the substrate (the amount of layer prepared), is preferably 0.01 g / m² based on solid content. 2 The above, more preferably 0.03 g / m 2 That's all. Furthermore, the preferred coating amount is 2.0 g / m³. 2 The following is a further preferred value of 1.5 g / m 2 The coating amount is set to 0.01 g / m. 2 When the above is achieved, the resulting separator can improve the adhesion between the thermoplastic polymer layer and the electrode, resulting in more uniform charging and discharging, and improving device characteristics (e.g., battery cycle characteristics), therefore it is preferred. On the other hand, from the viewpoint of further suppressing the decrease in ion permeability, it is preferable to set the coating amount to 2.0 g / m 2 the following.

[0121] The proportion of the area of ​​the thermoplastic polymer layer on the total area of ​​the substrate, i.e., the coverage area of ​​the thermoplastic polymer layer on the substrate, is preferably 95% or less, preferably 80% or less, more preferably 50% or less, and particularly preferably 35% or less. Furthermore, this surface coverage is preferably 5% or more, more preferably 10% or more, and particularly preferably 15% or more. From the viewpoint of improving ion permeability and rate performance, it is preferable to set this coverage area proportion to 95% or less. This ensures output. From the viewpoint of increasing the contact area between the exposed portion of the substrate surface (the portion without the thermoplastic polymer layer) and other substrates or other thermoplastic polymer layers when only the separator is wound, thereby ensuring anti-adhesion, it is preferable to set the coverage area proportion to 50% or less. Furthermore, it is also preferable from the viewpoint of further suppressing thermoplastic polymer clogging of the substrate pores and further improving the permeability of the separator. On the other hand, from the viewpoint of further improving adhesion to the electrodes, it is preferable to set the coverage area proportion to 5% or more.

[0122] The coverage area ratio can be adjusted, for example, by changing the type or concentration of the thermoplastic polymer in the coating liquid applied to the substrate surface, the amount of coating liquid applied, the coating method, and the coating conditions in the manufacturing method of the separator described later. However, the methods for adjusting the coating area are not limited to these.

[0123] When a thermoplastic polymer layer is disposed only locally on the surface of a substrate, the form (pattern) of the thermoplastic polymer is not particularly limited, but a state in which a certain pattern (unit pattern) exists periodically (repeatedly) at a certain frequency is preferred. Examples of such a configuration pattern include... Figure 4 The following are examples: (A) dotted, (B) grid-like, (C) striped, (D) bar-like, (E) tortoise-shell-like, and combinations thereof. From the viewpoints of electrolyte dispensing efficiency and productivity, the dotted pattern is preferred.

[0124] The size of the unit pattern constituting the thermoplastic polymer pattern is preferably 10 μm × 10 μm or more and 10 mm × 10 mm or less. By making the unit pattern size 10 μm or more, observation at low magnification is possible when inspecting the surface of the separator using the above inspection method, ensuring sufficient operational efficiency. Furthermore, by making the unit pattern size 10 mm or less, representative values ​​can be obtained through photography with minimal error.

[0125] For example, when the unit pattern is dot-shaped, the dot diameter is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more. Furthermore, the dot diameter is preferably 1 mm or less, and even more preferably 500 μm or less. By making the dot diameter 50 μm or more, the ion flow in the electrolyte becomes better, and the permeability is more excellent. By making the dot diameter 1 mm or less, the spacer and electrode can be bonded more uniformly, and the in-plane current density can be more uniform. Furthermore, by providing portions of uncoated thermoplastic polymer in the dot-shaped configuration pattern, the in-plane current density can be made more uniform.

[0126] When a thermoplastic polymer layer is locally configured, it is desirable that the coverage area ratio is uniform within a certain area range. Specifically, when observing the surface of the separator using SEM, it is preferable that the rate of change of the coverage area ratio shown in the following formula is within ±50% within an observation field of view of 2 mm × 2 mm or more.

[0127] (Change rate of coverage area ratio (%)) = (C1-C2) / C1×100

[0128] Here, C1 represents the coverage area ratio within any observation field of 2mm × 2mm or larger, and C2 represents the coverage area ratio within other observation field of 2mm × 2mm or larger. For example, for a separator with a thermoplastic polymer layer locally disposed, it is preferable that when the measured coverage area ratio within a certain 2mm × 2mm observation field of view is 50%, the coverage area ratio within a 10mm × 10mm observation field of view is 25% or more and 75% or less when observing any other part of the separator.

[0129] Regarding the thickness of the thermoplastic polymer layer, it is preferably 0.01 μm or more, more preferably 0.1 μm or more, measured from one side of the substrate. Furthermore, its thickness is preferably 10.0 μm or less, more preferably 5.0 μm or less, measured from one side of the substrate. From the viewpoint of uniformly exhibiting the adhesion between the electrode and the substrate, it is preferable to set this thickness to 0.01 μm or more, which results in improved device characteristics. Additionally, from the viewpoint of suppressing a decrease in ion permeability, it is preferable to set this thickness to 10.0 μm or less. The thickness of the thermoplastic polymer layer can be adjusted, for example, by changing the type or concentration of the thermoplastic polymer in the coating liquid applied to the substrate, the amount of coating liquid applied, the coating method, and the coating conditions. However, the method for adjusting the thickness is not limited to these. The thickness of the thermoplastic polymer layer is measured based on the method described in the examples.

[0130] (Particulate polymer)

[0131] The thermoplastic polymer contained in the thermoplastic polymer layer preferably contains a particulate polymer compound (particulate polymer). In the following description, "olefin unsaturated monomer" refers to a monomer having one or more olefin unsaturated bonds within its molecule. By including the particulate polymer in the thermoplastic polymer, both excellent adhesion to the electrode and excellent ion permeability can be achieved.

[0132] In particular, by including particulate polymer in the thermoplastic polymer, when inspecting the surface of the separator using the above-described inspection method, the scattering of light irradiated onto the thermoplastic polymer layer can be promoted, resulting in better contrast between the patterned areas of the substrate or inorganic filler layer and the thermoplastic polymer layer, thus enabling more reliable inspection.

[0133] Specific examples of particulate polymers include acrylic polymers, conjugated diene polymers, acrylic polymers, polyvinyl alcohol resins, and fluorinated resins. Among these, acrylic polymers are preferred from the viewpoint of latex adhesion and permeability. Furthermore, acrylic polymers and fluorinated resins are preferred from the viewpoint of voltage resistance, and conjugated diene polymers are preferred from the viewpoint of easy integration with electrodes. Moreover, from the viewpoint of more effectively and reliably exerting the effects of the present invention, particulate polymers comprising particulate copolymers are preferred. Particulate polymers can be used alone or in combination of two or more.

[0134] Furthermore, the thermoplastic polymer contained in the thermoplastic polymer layer preferably comprises 60% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 98% by mass or more of particulate polymer relative to its total amount. It should be noted that the thermoplastic polymer layer may include thermoplastic polymers other than particulate polymers to a degree that does not impair the effects of the present invention.

[0135] Conjugated diene polymers are polymers having a conjugated diene compound as a monomer unit. Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, and substituted and side-chain conjugated hexadienes; one or more of these can be used alone or in combination. 1,3-butadiene is particularly preferred. Furthermore, conjugated diene polymers may contain (meth)acrylic acid compounds or other monomers as monomer units. Examples of such monomers include styrene-butadiene copolymers and their hydrogenates, acrylonitrile-butadiene copolymers and their hydrogenates, and acrylonitrile-butadiene-styrene copolymers and their hydrogenates.

[0136] Examples of polyvinyl alcohol-based resins include polyvinyl alcohol and polyvinyl acetate. Examples of fluorinated resins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-hexafluoropropylene copolymer, PVDF-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer.

[0137] Acrylic polymers are polymers having (meth)acrylic compounds as monomer units, i.e., polymerization units. (Meth)acrylic compounds refer to at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylates. Examples of such compounds include those shown in the following formulas.

[0138] CH2=CR Y1 -COO-R Y2

[0139] In the formula, R Y1 R represents a hydrogen atom or a methyl group. Y2 Represents a hydrogen atom or a hydrocarbon group with a monovalent charge. R Y2When the hydrocarbon group is monovalent, it may have substituents and heteroatoms within the chain. Examples of monovalent hydrocarbon groups include linear or branched chain alkyl, cycloalkyl, and aryl groups. Examples of substituents include hydroxyl and phenyl groups, and examples of heteroatoms include halogen atoms and oxygen atoms. (Meth)acrylate compounds may be used alone or in combination of two or more. Examples of such (meth)acrylate compounds include (meth)acrylate, chain alkyl esters of (meth)acrylate, cycloalkyl esters of (meth)acrylate, (meth)acrylates containing hydroxyl groups, and (meth)acrylates containing phenyl groups.

[0140] As for R Y2 One type of chain alkyl group, more specifically, includes chain alkyl groups with 1 to 3 carbon atoms such as methyl, ethyl, n-propyl, and isopropyl; n-butyl, isobutyl, tert-butyl, n-hexyl, and 2-ethylhexyl; and chain alkyl groups with 4 or more carbon atoms such as lauryl. Additionally, as R... Y2 One of the aryl groups, for example, is the phenyl group. As a group having such an R... Y2 Specific examples of (meth)acrylate monomers include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate, which are (meth)acrylates having chain-like alkyl groups; and (meth)acrylates having aromatic rings, such as phenyl methacrylate and benzyl methacrylate.

[0141] From the viewpoint of improving the adhesion of the separator to the electrode (electrode active material), monomers having a chain alkyl group having 4 or more carbon atoms are preferred, and more specifically, R is preferred. Y2 The monomer is a (meth)acrylate monomer that is a chain alkyl group having 4 or more carbon atoms. More specifically, it is preferably selected from at least one of the group consisting of butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate. It should be noted that there is no particular limit to the upper limit of the number of carbon atoms in the chain alkyl group having 4 or more carbon atoms; for example, it can be 14, preferably 7. These (meth)acrylate monomers can be used alone or in combination of two or more.

[0142] (Meth)acrylate monomers are also preferably used in place of monomers having a chain alkyl group having 4 or more carbon atoms, or to include cycloalkyl groups as R in the monomer. Y2The monomers. This further improves the adhesion of the separator to the electrode. More specifically, examples of such cycloalkyl monomers include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and adamantyl (meth)acrylate. The alicyclic ring constituting the cycloalkyl group preferably has 4 to 8 carbon atoms, more preferably 6 to 7, and particularly preferably 6. Furthermore, the cycloalkyl group may or may not have substituents. Examples of substituents include methyl and tert-butyl. From the perspective of good polymerization stability during the preparation of acrylic polymers, at least one of these is preferably selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate. They can be used alone or in combination of two or more.

[0143] Acrylic polymers preferably replace the aforementioned monomers or, more preferably, incorporate crosslinking monomers as (meth)acrylate monomers. There are no particular limitations on the crosslinking monomers; examples include monomers having two or more free radical polymerizable double bonds, and monomers having functional groups that provide a self-crosslinking structure during or after polymerization. They can be used alone or in combination of two or more.

[0144] Monomers having two or more free radical polymerizable double bonds include, for example, divinylbenzene and polyfunctional (meth)acrylates. Polyfunctional (meth)acrylates can be at least one selected from the group consisting of difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional (meth)acrylates. Specifically, examples include, for instance, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. They can be used alone or in combination of two or more. From the same viewpoint as described above, at least one of trimethylolpropane triacrylate or trimethylolpropane trimethacrylate is preferred.

[0145] Examples of monomers having functional groups that provide a self-crosslinking structure during or after polymerization include monomers having an epoxy group, monomers having a hydroxymethyl group, monomers having an alkoxymethyl group, and monomers having a hydrolyzable silyl group. Among monomers having an epoxy group, alkoxymethyl-containing olefinic unsaturated monomers are preferred, specifically examples include glycidyl (meth)acrylate, 2,3-epoxycyclohexyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate, and allyl glycidyl ether.

[0146] Examples of monomers containing a hydroxymethyl group include N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, dihydroxymethylacrylamide, and dihydroxymethylmethacrylamide. As monomers containing an alkoxymethyl group, alkene-unsaturated monomers containing an alkoxymethyl group are preferred, specifically examples include N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-butoxymethylmethacrylamide. Examples of monomers containing a hydrolyzable silyl group include vinylsilane, γ-acryloyloxypropyltrimethoxysilane, γ-acryloyloxypropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropyltriethoxysilane. These can be used alone or in combination of two or more.

[0147] Furthermore, the aforementioned acrylic polymers can be further equipped with monomers other than those described above as monomer units to improve various qualities and physical properties. Examples of such monomers include, for instance, monomers with carboxyl groups (except for (meth)acrylic acid), monomers with amide groups, monomers with cyano groups, monomers with hydroxyl groups, and aromatic vinyl monomers (except for divinylbenzene). Moreover, various vinyl monomers with functional groups such as sulfonic acid groups or phosphate groups, and vinyl acetate, vinyl propionate, vinyl tert-carbonate, vinylpyrrolidone, methyl vinyl ketone, butadiene, ethylene, propylene, vinyl chloride, and vinylidene chloride can also be used as needed. They can be used alone or in combination of two or more. Additionally, such other monomers can simultaneously belong to two or more of the monomers described above.

[0148] Examples of monomers having an amide group include (meth)acrylamide. As monomers having a cyano group, olefinically unsaturated monomers having a cyano group are preferred; specifically, examples include (meth)acrylonitrile. As monomers having a hydroxyl group, examples include 2-hydroxyethyl (meth)acrylate.

[0149] Examples of aromatic vinyl monomers include styrene, vinyltoluene, divinylbenzene, and α-methylstyrene. Styrene is preferred.

[0150] Regarding the proportion of (meth)acrylic compounds as monomer units, i.e., polymer units, in the acrylic polymer, it is preferably 5% by mass or more and 95% by mass or less relative to 100% by mass of the acrylic polymer. The lower limit is more preferably 15% by mass, further preferably 20% by mass, and particularly preferably 30% by mass. A monomer unit content of 5% by mass or more is preferred from the viewpoint of adhesion to the substrate and oxidation resistance. On the other hand, a more preferred upper limit is 92% by mass, a further preferred upper limit is 80% by mass, and a particularly preferred upper limit is 60% by mass. A monomer content of 95% by mass or less improves adhesion to the substrate, and is therefore preferred.

[0151] When the acrylic polymer has (meth)acrylate alkyl esters or (meth)acrylate cycloalkyl esters as monomer units, the total content of these monomers relative to 100% by mass of the acrylic polymer is preferably 3% by mass or more and 92% by mass or less, more preferably 10% by mass or more and 90% by mass or less, even more preferably 15% by mass or more and 75% by mass or less, and particularly preferably 25% by mass or more and 55% by mass or less. A content of 3% by mass or more of these monomers is preferred from the viewpoint of improving oxidation resistance, and a content of 92% by mass or less is preferred because it improves adhesion to the substrate.

[0152] When an acrylic polymer contains (meth)acrylic acid as a monomer unit, its content ratio relative to 100% by mass of the acrylic polymer is preferably 0.1% by mass or more and 5% by mass or less. When the content ratio of the above monomer is 0.1% by mass or more, there is a tendency to improve the buffering capacity of the separator in the swollen state, and when it is 5% by mass or less, there is a tendency to have good polymerization stability.

[0153] When the acrylic polymer has a crosslinking monomer as a monomer unit, the content of the crosslinking monomer in the acrylic polymer is preferably 0.01% by mass or more and 10% by mass or less relative to 100% by mass of the acrylic polymer, more preferably 0.1% by mass or more and 5% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less. When the content of the above monomer is 0.01% by mass or more, the electrolyte resistance is further improved, and when it is 10% by mass or less, the decrease in buffering capacity under the swelling state can be further suppressed.

[0154] As an acrylic polymer, any of the following methods are preferred. All copolymer percentages below are based on 100% by mass of the copolymer.

[0155] (1) A copolymer having (meth)acrylate as a monomer unit (except for the copolymers of (2) and (3) described below). Preferably, it is a copolymer having 5% or less (more preferably 0.1% or more and 5% or less) of (meth)acrylate, 3% or more and 92% or less (more preferably 10% or more and 90% or less, further preferably 15% or more and 75% or less, particularly preferably 25% or more and 55% or less) of (meth)acrylate monomer, at least 15% or less (more preferably 10% or less) of at least one monomer selected from the group consisting of monomers having amide groups, monomers having cyano groups, and monomers having hydroxyl groups, and 10% or less (more preferably 0.01% or more and 5% or less, further preferably 0.1% or more and 3% or less) of crosslinking monomer;

[0156] (2) A copolymer having aromatic vinyl monomers and (meth)acrylate monomers as monomer units. Preferably, it is a copolymer having 5% or more and 95% or less of aromatic vinyl monomers (more preferably 10% or more and 92% or less, further preferably 25% or more and 80% or less, particularly preferably 40% or more and 60% or less), 5% or less of (meth)acrylate (more preferably 0.1% or more and 5% or less), 5% or more and 95% or less of (meth)acrylate monomers (more preferably 15% or more and 85% or less, further preferably 20% or more and 80% or less, particularly preferably 30% or more and 75% or less), at least 10% or less of at least one monomer selected from the group consisting of monomers having amide groups, monomers having cyano groups, and monomers having hydroxyl groups, and 10% or less of a crosslinking monomer (more preferably 0.01% or more and 5% or less, further preferably 0.1% or more and 3% or less); and

[0157] (3) A copolymer containing a cyano-based monomer and a (meth)acrylate monomer as monomer units. Preferably, it is a copolymer containing 1% or more and 95% or less (more preferably 5% or more and 90% or less, and even more preferably 50% or more and 85% or less) of cyano-based monomer, 5% or less (preferably 0.1% or more and 5% or less) of (meth)acrylate monomer, 1% or more and 95% or less (more preferably 5% or more and 85% or less, and even more preferably 10% or more and 50% or less) of (meth)acrylate monomer, at least 10% or less (more preferably 5% or less) of at least one monomer selected from the group consisting of amide-based monomer, cyano-based monomer, and hydroxyl-based monomer, and 10% or less (more preferably 0.01% or more and 5% or less, and even more preferably 0.1% or more and 3% or less) of crosslinking monomer.

[0158] In the copolymer described above (2), a hydrocarbon ester of (meth)acrylic acid is preferably used as the (meth)acrylic acid ester monomer. In this case, the copolymerization ratio of the hydrocarbon ester of (meth)acrylic acid is preferably 0.1% by mass or more and 5% by mass or less. Furthermore, when the copolymer described above (2) contains a monomer having an amide group, its copolymerization ratio is preferably 0.1% by mass or more and 5% by mass or less. Moreover, when the copolymer described above (2) contains a monomer having a hydroxyl group, its copolymerization ratio is preferably 0.1% by mass or more and 5% by mass or less.

[0159] In the copolymer of (3) above, the (meth)acrylate monomer preferably includes at least one selected from the group consisting of (meth)acrylate alkyl esters and (meth)cycloalkyl esters. The (meth)acrylate alkyl ester is preferably a alkyl ester having 6 or more carbon atoms. The copolymerization ratio of the (meth)acrylate alkyl ester in the copolymer of (3) is preferably 1% by mass or more and 95% by mass or less, more preferably 3% by mass or more and 90% by mass or less, and even more preferably 5% by mass or more and 85% by mass or less. The upper limit of this copolymerization ratio can be 60% by mass, particularly 40% by mass or 30% by mass, and especially preferably 20% by mass. The copolymerization ratio of the (meth)acrylate cyclohexylalkyl ester in the copolymer of (3) is preferably 1% by mass or more and 95% by mass or less, more preferably 3% by mass or more and 90% by mass or less, and even more preferably 5% by mass or more and 85% by mass or less. The upper limit of this copolymerization ratio can be 60% by mass, particularly 50% by mass, and especially preferably 40% by mass. Furthermore, when the copolymer of (3) above contains a monomer having an amide group, its copolymerization ratio is preferably 0.1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 10% by mass or less. Moreover, when the copolymer of (3) above contains a monomer having a hydroxyl group, its copolymerization ratio is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 10% by mass or less.

[0160] For example, in an aqueous medium, in a dispersion system consisting of the aforementioned monomers, surfactants, free radical polymerization initiators, and other additives used as needed, a monomer composition containing the aforementioned monomers is polymerized to obtain an acrylic polymer. During polymerization, various methods can be used as needed, such as methods that keep the composition of the supplied monomer composition constant throughout the polymerization process, or methods that impart morphological compositional changes to the resulting resin dispersion particles by causing the composition of the supplied monomer composition to change sequentially or continuously during polymerization. When obtaining an acrylic polymer by emulsion polymerization, for example, it can be in the form of an aqueous dispersion (latex) containing water and particulate acrylic polymer dispersed in the water.

[0161] A surfactant is a compound having at least one hydrophilic group and at least one lipophilic group in one molecule. Surfactants will be discussed later, so this will not be elaborated upon here.

[0162] Furthermore, a free radical polymerization initiator is a substance that decomposes into free radicals due to heat or reducing agents, and initiates the addition polymerization of monomers. Free radical polymerization initiators will be explained later, so this will be omitted here.

[0163] From the viewpoint of improving the adhesion between the separator and the electrode, improving the high-temperature storage and cycling characteristics of the energy storage device, and realizing the thin film of the electrode-separator adhesive, acrylic copolymer latex formed from an emulsion containing monomers, emulsifiers, initiators and water is preferred in the form of thermoplastic polymers.

[0164] From the viewpoint of electrode adhesion and ion permeability, the glass transition temperature (Tg) of the particulate polymer is preferably -50°C or higher, more preferably -30°C or higher, and even more preferably 20°C or higher. Furthermore, from the viewpoint of suppressing adhesion, it is even more preferably 40°C or higher. Moreover, from the viewpoint of maintaining the particulate state at room temperature, it is preferably 25°C or higher. Additionally, the glass transition temperature of the particulate polymer is preferably 200°C or lower. The glass transition temperature refers to the intermediate point glass transition temperature described in JISK 7121, and can be determined by a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the glass transition temperature can be taken as the temperature at the intersection of the curve showing the phased changes of the glass transition and a straight line equidistant from the baseline of the DSC curve extending from the low-temperature side to the high-temperature side, and another straight line extending the baseline of the DSC curve from the high-temperature side to the low-temperature side. More specifically, it can be determined based on the method described in the examples. Additionally, "glass transition" refers to the change in heat flux accompanying the change in the state of the polymer used as a test piece during DSC, occurring on the endothermic side. This change in heat flux is observed in the DSC curve as a step-like change. A "step-like change" indicates the portion of the DSC curve where the curve deviates from the previous low-temperature baseline and moves to a new high-temperature baseline. It should be noted that the shape formed by the combination of step-like changes and peaks is also included in the step-like change. Furthermore, in the step-like change portion, if the upper side is set as the exothermic side, it can also be represented as the point where an upward-convex curve changes to a downward-convex curve. A "peak" represents the portion of the DSC curve where the curve deviates from the low-temperature baseline and then returns to that baseline. The "baseline" represents the DSC curve in the temperature region where no transition or reaction occurs in the test piece.

[0165] The glass transition temperature (Tg) of a particulate polymer can be appropriately adjusted, for example, by changing the types of monomers used in the manufacture of the particulate polymer and the proportions of the monomers when the particulate polymer is a copolymer. That is, for each monomer used in the manufacture of the particulate polymer, the approximate glass transition temperature can be estimated from the Tg of the homopolymer (as typically shown in the "Polymer Handbook") and the proportions of the monomers. For example, copolymers of monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid, which copolymerize homopolymers providing a Tg of approximately 100°C at high ratios, have high Tg; copolymers of monomers such as n-butyl acrylate and 2-ethylhexyl acrylate, which copolymerize homopolymers providing a Tg of approximately -50°C at high ratios, have low Tg.

[0166] In addition, the Tg of the copolymer can be roughly calculated using the FOX formula shown in the following equation (1).

[0167] 1 / Tg=W1 / Tg1+W2 / Tg2+···+Wi / Tgi+···Wn / Tgn(1)

[0168] In this formula, Tg(K) is the Tg of the copolymer, Tgi(K) is the Tg of the homopolymer of monomer i, and Wi is the mass percentage of each monomer.

[0169] In the preferred embodiment, the glass transition temperature Tg of the particulate polymer is the value measured by the DSC method described above.

[0170] From the viewpoint of wettability to the substrate, adhesion between the substrate and the thermoplastic polymer layer, and adhesion to the electrode, it is preferable that the thermoplastic polymer layer contains a polymer with a glass transition temperature below 20°C. From the viewpoint of ion permeability, the glass transition temperature of the polymer with a glass transition temperature below 20°C is preferably -100°C or higher, more preferably -50°C or higher, and even more preferably -40°C or higher. From the viewpoint of adhesion between the polyolefin microporous membrane and the thermoplastic polymer layer, it is preferably below 20°C, more preferably below 15°C, and even more preferably below 10°C.

[0171] From the viewpoint of improving manufacturability during manufacturing, the particulate polymer preferably has at least two glass transition temperatures. That is, it is preferable that the thermoplastic polymer layer comprises two or more thermoplastic polymers with different glass transition temperatures. There is no limitation on the method for giving the particulate polymer at least two glass transition temperatures; methods such as mixing two or more particulate polymers and using particulate polymers with a core-shell structure are examples. The core-shell structure is a structure having a central portion and an outer shell portion covering the central portion; it is a two-layered polymer composed of polymers of different types or compositions. In particular, by combining polymers with high and low glass transition temperatures in the polymer mixing and core-shell structure, the overall glass transition temperature of the particulate polymer can be controlled. Furthermore, various functions can be imparted to the particulate polymer as a whole.

[0172] For example, when two or more particulate polymers are mixed, especially when one or more polymers with a glass transition temperature above 20°C are mixed with one or more polymers with a glass transition temperature below 20°C, it is possible to better balance tackiness resistance and coating properties on the substrate. Regarding the mixing ratio of each polymer, the ratio of the polymer with a glass transition temperature above 20°C to the polymer with a glass transition temperature below 20°C is preferably in the range of 0.1:99.9 to 99.9:0.1, more preferably 5:95 to 95:5, even more preferably 50:50 to 95:5, and particularly preferably 60:40 to 90:10.

[0173] When using granular polymers with a core-shell structure, the adhesion and compatibility of the thermoplastic polymer layer to other components (such as substrates) can be adjusted by selecting the type of polymer in the outer shell portion. Furthermore, by selecting the type of polymer in the central portion, adhesion to electrodes after hot pressing can be improved, for example. Alternatively, the viscoelasticity of the thermoplastic polymer layer can be controlled by combining a highly viscous polymer with a highly elastic polymer.

[0174] It should be noted that the glass transition temperature of the shell portion of the thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably 20°C or higher, more preferably 80°C or higher, more preferably 200°C or lower, and even more preferably 130°C or lower. Furthermore, the glass transition temperature of the core portion of the thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably 20°C or higher, more preferably 20°C or higher and 200°C or lower, and even more preferably 40°C or higher and 200°C or lower.

[0175] The arithmetic mean particle size of the particulate polymer is preferably 50 nm or more, more preferably 150 nm or more, and even more preferably 200 nm or more. Furthermore, the arithmetic mean particle size of the particulate polymer is 10,000 nm or less, preferably 1,200 nm or less, more preferably 1,000 nm or less, and even more preferably 700 nm or less. By making the arithmetic mean particle size 10 nm or more, the ion permeability of the separator can be maintained at a higher level. Therefore, in this case, it is preferable from the viewpoint of improving the adhesion between the electrode and the separator, the cycle characteristics of the energy storage device, and the rate capability. Additionally, when forming a thermoplastic polymer layer containing particulate polymer from an aqueous dispersion, it is preferable to make the arithmetic mean particle size 10,000 nm or less from the viewpoint of ensuring its dispersion stability. It is also preferable from the viewpoint of being able to freely control the thickness of the thermoplastic polymer layer and preventing the thermoplastic polymer from detaching from the separator after drying.

[0176] Based on these considerations, the arithmetic mean particle size of the particulate polymer is particularly preferably 50 nm or more and 10,000 nm or less. By adhering to this range, when inspecting the surface of the separator using the aforementioned inspection method, the contrast between the substrate or inorganic filler layer and the patterned portion of the thermoplastic polymer is better, enabling more reliable inspection.

[0177] The arithmetic mean particle size of particulate polymers can be determined based on the methods described in the following examples.

[0178] The thermoplastic polymer layer may contain two or more particulate polymers with different arithmetic mean particle sizes. For example, a combination of particulate polymers with an arithmetic mean particle size of 10 nm or more and 400 nm or less (hereinafter referred to as "small-diameter particles") and particulate polymers with an arithmetic mean particle size of more than 100 nm and 2000 nm or less (hereinafter referred to as "large-diameter particles") is preferred.

[0179] The surfactants used in the polymerization of particulate polymers are compounds having at least one hydrophilic group and at least one lipophilic group in one molecule. Examples of surfactants include polyether surfactants; non-reactive anionic surfactants such as alkyl sulfates, polyoxyethylene alkyl ether sulfates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether disulfonates, naphthalene sulfonic acid formalin condensates, polyoxyethylene polycyclic phenyl ether sulfates, polyoxyethylene styrene phenyl ether sulfates, fatty acid salts, alkyl phosphates, and polyoxyethylene alkylphenyl ether sulfates; and non-reactive nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene styrene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, glycerol fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, alkylalkanolamides, and polyoxyethylene alkylphenyl ethers. In addition to these, so-called reactive surfactants can be used, which incorporate olefinic double bonds into the chemical structure of surfactants having both hydrophilic and lipophilic groups.

[0180] Anionic surfactants among reactive surfactants include, for example, olefinic unsaturated monomers having sulfonic acid groups, sulfonate groups, or sulfate groups and their salts, preferably compounds having sulfonic acid groups or groups having their ammonium salts or alkali metal salts (ammonium sulfonate groups or alkali metal sulfonate groups). Specifically, examples include: alkylallyl sulfonated succinates (e.g., Eleminol JS-20 manufactured by Sanyo Chemical Co., Ltd., and Latemul S-120, S-180A, and S-180 manufactured by Kao Corporation), polyoxyethylene alkylpropylene phenyl ether sulfates (e.g., Aquaron HS-10 manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), and α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfates (e.g., Adeka manufactured by ADEKA Co., Ltd.). Reasoap (trademark, same below) SE-10N), ammonium = α-sulfonated-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (e.g., Aquaron KH-10 manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), styrene sulfonate (e.g., Spinomar (trademark) NaSS manufactured by Tosoh Organic Chemicals Co., Ltd.), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-polyoxyethylene sulfate (e.g., AdekaReasoap SR-10 manufactured by ADEKA Co., Ltd.), and sulfate salts of polyoxyethylene polyoxybutene (3-methyl-3-butenyl) ether (e.g., Latemul PD-104 manufactured by Kao Corporation).

[0181] In addition, examples of nonionic surfactants among reactive surfactants include α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxy polyoxyethylene (examples include Adeka Reasoap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropylene phenyl ether (examples include Aquaron RN-10, RN-20, RN-30, RN-50 manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-hydroxy polyoxyethylene (examples include AdekaReasoap ER-10 manufactured by ADEKA Co., Ltd.), and polyoxyethylene polyoxybutene (3-methyl-3-butenyl) ether (examples include Latemul PD-420 manufactured by Kao Corporation). Relative to 100 parts by weight of the monomer composition, it is preferable to use 0.1 parts by weight or more and 5 parts by weight of surfactant. Surfactant may be used alone or in combination of two or more.

[0182] As a free radical polymerization initiator used in the polymerization of particulate polymers, it is a substance that initiates the addition polymerization of monomers by free radical decomposition due to heat or reducing agents. Either inorganic or organic initiators can be used. Water-soluble or oil-soluble polymerization initiators can be used. Examples of water-soluble polymerization initiators include persulfates, peroxides, water-soluble azo compounds, and peroxide-reducing redox systems. Examples of persulfates include potassium persulfate (KPS), sodium persulfate (NPS), and ammonium persulfate (APS); examples of peroxides include hydrogen peroxide, tert-butyl hydroperoxide, tert-butyl maleate peroxide, succinic acid peroxide, and benzoyl peroxide; examples of water-soluble azo compounds include 2,2-azobis(N-hydroxyethyl isobutylamide), 2,2-azobis(2-amidinylpropane)dichloride, and 4,4-azobis(4-cyanopentanoic acid); and examples of peroxide-reducing agent redox systems include initiators formed by combining one or more of the following reducing agents among the above peroxides: sodium formaldehyde sulfoxylate, sodium bisulfite, sodium thiosulfate, sodium hydroxymethanesulfinate, L-ascorbic acid, and their salts, cuprous salts, and ferrous salts.

[0183] The free radical polymerization initiator can preferably be used at a concentration of 0.05 parts by weight or more and 2 parts by weight or less relative to 100 parts by weight of the monomer composition. The free radical polymerization initiator can be used alone or in combination of two or more.

[0184] It should be noted that when a monomer composition comprising an olefinically unsaturated monomer (P) having a polyalkylene glycol group, an olefinically unsaturated monomer (A) having a cycloalkyl group, and other monomers (B) is emulsion polymerized to form a dispersion in which polymer particles are dispersed in a solvent (water), the solid content of the resulting dispersion is preferably 30% by mass or more and 70% by mass or less. To ensure long-term dispersion stability, it is preferable to adjust the pH of the dispersion to a range of 5 to 12. The pH is preferably adjusted using amines such as ammonia, sodium hydroxide, potassium hydroxide, and dimethylaminoethanol, and more preferably using ammonia (water) or sodium hydroxide.

[0185] The aqueous dispersion comprises a polymer obtained by polymerizing a monomer composition containing the aforementioned specific monomers in the form of particles (polymer particles) dispersed in water. In addition to water and the polymer, the aqueous dispersion may also contain solvents such as methanol, ethanol, and isopropanol, or dispersants, lubricants, thickeners, bactericides, etc. A layer containing a thermoplastic polymer can be easily formed by coating; therefore, it is preferable to form a particulate polymer through emulsion polymerization, and the resulting particulate polymer emulsion is used as an aqueous latex.

[0186] [Optional layer]

[0187] The inclusion of an optional layer, such as an inorganic filler layer (inorganic filler porous layer), between the substrate and the thermoplastic polymer layer is also within the scope of this invention. The inorganic filler porous layer contains inorganic filler and has multiple pores.

[0188] In this section, the inorganic filler porous layer is described in a manner in which at least a thermoplastic polymer layer is partially present on the inorganic filler layer, or in other words, an inorganic filler porous layer is included between the substrate and the thermoplastic polymer layer. However, optional layers such as inorganic filler porous layers may be omitted in this invention.

[0189] (Inorganic packing)

[0190] As an inorganic filler, there are no particular restrictions; fillers with a melting point above 200°C, high electrical insulation, and electrochemical stability within the operating range of energy storage devices such as lithium-ion secondary batteries can be used.

[0191] As inorganic fillers, there are no particular limitations, and examples include inorganic oxides (oxide-based ceramics) such as alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, and iron oxide; inorganic nitrides (nitride-based ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum hydroxide, potassium titanate, talc, kaolinite, dickite, perlite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. They can be used alone or in combination of two or more.

[0192] The volume average particle size (D50) of the inorganic filler is, for example, 50 nm or more, preferably 250 nm or more, and more preferably 500 nm or more. Furthermore, the average particle size is, for example, 2000 nm or less, preferably 950 nm or less, and more preferably less than 600 nm.

[0193] By ensuring the average particle size of the inorganic filler is 50 nm or more, good permeability can be ensured. On the other hand, by ensuring the average particle size is 2000 nm or less, good heat resistance can be ensured. In particular, by ensuring the average particle size is within the above range, the contrast between the patterned areas of the inorganic filler layer and the thermoplastic polymer layer becomes better when inspecting the surface of the separator using the above inspection method, enabling more reliable inspection.

[0194] As a method for adjusting the particle size and distribution of inorganic fillers, one example is the method of reducing the particle size by crushing the inorganic fillers using appropriate crushing devices such as ball mills, bead mills, or jet mills.

[0195] Regarding the particle size distribution of inorganic fillers, the peak in the frequency-to-particle-size graph can be a single peak. However, it can also be a trapezoidal graph with two peaks or no peaks at all.

[0196] Examples of inorganic packing shapes include plate-like, scaly, needle-like, columnar, spherical, polyhedral, and block-like. Multiple inorganic packing materials with these shapes can also be used in combination.

[0197] The proportion of inorganic filler in the porous layer of inorganic filler relative to the total amount of the porous layer of inorganic filler is, for example, 20% or more by mass and less than 100% by mass, 30% or more by mass and less than 80% by mass, 35% or more by mass and less than 70% by mass, and further 40% or more by mass and less than 60% by mass.

[0198] When the volume average particle size of the thermoplastic polymer is set as D1 and the volume average particle size of the inorganic filler is set as D2, it is preferable that D1 and D2 satisfy the following formula:

[0199] D1 / D2≤0.8 or D1 / D2≥1.2.

[0200] Furthermore, it is preferable that D1 and D2 satisfy the following formula:

[0201] 0.025≤D1 / D2≤0.8 or 200≥D1 / D2≥1.2

[0202] Further optimization satisfies the following formula:

[0203] D1 / D2≤0.5 or D1 / D2≥2.0, with particular preference given to satisfying the following formula:

[0204] D1 / D2≤0.3 or D1 / D2≥3.0.

[0205] By setting the volume average particle size ratio D1 / D2 of the thermoplastic polymer to the inorganic filler to be within the above range, the contrast between the patterned areas of the inorganic filler layer and the thermoplastic polymer layer becomes better when the surface of the separator is inspected using the above inspection method, enabling more reliable inspection.

[0206] (Resin adhesive)

[0207] There are no particular restrictions on the type of resin used as a resin binder in the inorganic filler porous layer. Resins that are insoluble in the electrolyte of energy storage devices such as lithium-ion secondary batteries and are electrochemically stable within the operating range of such devices can be used. In addition to the resin binder (A) contained in the inorganic filler porous layer and the particulate polymer (B) contained in the thermoplastic polymer layer, a bonding agent (C) contained in the thermoplastic polymer layer for bonding the particulate polymer (B) to the substrate or the inorganic filler porous layer can also be used. The resin binder (A) and bonding agent (C) are generally not particulate in the separator. On the other hand, the particulate polymer (B) is particulate in the separator, and the particulate polymer (B) may contain a different type of resin than the resin binder (A) and bonding agent (C).

[0208] Specific examples of such resins include, for instance, polyolefins such as polyethylene and polypropylene; fluorinated resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorinated rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers and ethylene-tetrafluoroethylene copolymers; rubbers such as styrene-butadiene copolymers and their hydrogenates, acrylonitrile-butadiene copolymers and their hydrogenates, acrylonitrile-butadiene-styrene copolymers and their hydrogenates, methacrylate-acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and resins with melting points and / or glass transition temperatures of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene ether, polyetherimide, polyamide-imide, polyamide, and polyester. These can be used alone or in combination of two or more.

[0209] Resin binders may include, for example, resin latex binders. As resin latex binders, copolymers of unsaturated carboxylic acid monomers with other monomers capable of copolymerizing with these monomers can be used. Examples of aliphatic conjugated diene monomers include butadiene and isoprene; examples of unsaturated carboxylic acid monomers include (meth)acrylic acid; and examples of other monomers include styrene. The polymerization method for such copolymers is not particularly limited, but emulsion polymerization is preferred. The method of emulsion polymerization is not particularly limited, and known methods can be used. The method of adding monomers and other components is not particularly limited; any method of one-time addition, batch addition, or continuous addition can be used. The polymerization method can also be any of one-stage polymerization, two-stage polymerization, or multi-stage polymerization with three or more stages.

[0210] Specific examples of resin adhesives include the following 1) to 7).

[0211] 1) Polyolefins: such as polyethylene, polypropylene, ethylene propylene rubber and their modifiers;

[0212] 2) Conjugated diene polymers: such as styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides;

[0213] 3) Acrylic polymers: such as methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers;

[0214] 4) Polyvinyl alcohol-based resins: such as polyvinyl alcohol and polyvinyl acetate;

[0215] 5) Fluorinated resins: such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer;

[0216] 6) Cellulose derivatives: such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and

[0217] 7) Resins with a melting point and / or glass transition temperature of 180°C or above, or polymers that do not have a melting point and have a decomposition temperature of 200°C or above: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide and polyester.

[0218] When the resin binder is a resin latex binder, its average particle size (D50) is, for example, 50–500 nm, 60–460 nm, and further 80–250 nm. The average particle size of the resin binder can be controlled, for example, by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material input sequence, and pH.

[0219] The proportion of resin binder in the inorganic filler layer is, for example, 0.5 parts by mass or more and 20 parts by mass or less, 1 part by mass or more and 15 parts by mass or less, 2 parts by mass or more and 10 parts by mass or less, and further 3 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of inorganic filler.

[0220] By ensuring that the proportion of resin binder in the inorganic filler layer is 0.5 parts by mass or more, good adhesion can be ensured; by ensuring that it is 20 parts by mass or less, good permeability can be ensured. In particular, by ensuring that the proportion of resin binder in the inorganic filler layer is within the above-mentioned range, the contrast between the patterned areas of the inorganic filler layer and the thermoplastic polymer layer becomes better when inspecting the surface of the separator using the above-described inspection method, enabling more reliable inspection.

[0221] The content of particulate polymer contained in the porous layer of inorganic filler can be set to less than 5% by volume, less than 3% by volume, and further less than 2% by volume of the particulate polymer contained in the separator.

[0222] The thickness of the inorganic filler porous layer can be set to, for example, 10.0 μm or less, and further to 6.0 μm or less. Alternatively, the thickness of the inorganic filler porous layer can be set to, for example, 0.5 μm or more. The layer density of the inorganic filler porous layer can be set to, for example, 0.5 g / (m³). 2 ·μm) or higher and 3.0g / (m 2 Below μm, it can be set to 0.7–2.0 cm. 3 .

[0223] (Optional ingredients)

[0224] The thermoplastic polymer layer may contain only a thermoplastic polymer, or it may contain optional components other than a thermoplastic polymer. Examples of optional components include, for instance, the inorganic fillers described above used to form the inorganic filler porous layer. The content of the thermoplastic polymer in the thermoplastic polymer layer is preferably 60% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 98% by mass or more, relative to the total amount of the thermoplastic polymer layer.

[0225] (Regarding the various characteristics of the separator)

[0226] The air permeability of the separator is preferably 40 seconds / 100cm. 3 Above and 500 seconds / 100cm 3 The following is more preferably 70 seconds per 100cm. 3 Above 300 seconds / 100cm 3 Hereinafter, 100 seconds / 100cm is further preferred. 3 Above 200 seconds / 100cm 3 Therefore, when this separator is used in energy storage devices, it exhibits higher ion permeability. This permeability is similar to that of the polyolefin porous substrate, and is a permeability resistance measured based on JIS P-8117.

[0227] By setting the air permeability of the separator to 40 seconds / 100cm 3 The above measures prevent self-discharge. Additionally, by setting it to 500 seconds per 100cm... 3 The following ensures good permeability. In particular, by keeping the air permeability of the separator within the above-mentioned range, when inspecting the surface of the separator using the above-mentioned inspection method, the air permeability will not be too high when the separator is adsorbed onto the platform of the inspection device. Therefore, it can be reliably adsorbed onto the platform, enabling more reliable inspection.

[0228] The thickness deviation of the separator relative to the layer thickness is preferably ±10 μm or less, more preferably ±5 μm or less, and even more preferably ±2 μm or less. This suppresses deviations in the transmittance and strength of the substrate. In particular, by keeping the thickness deviation of the separator within the above range, when inspecting the separator surface using the above inspection method, focus shift can be suppressed, image clarity ensured, and more reliable inspection can be performed.

[0229] <Specific methods in the manufacture of separators>

[0230] [Substrate Manufacturing Method]

[0231] There are no particular limitations on the method of manufacturing the substrate; any known manufacturing method can be used, such as either wet or dry porousing. Examples based on wet porousing, for instance, when the substrate is a polyolefin microporous membrane, include: a method of melt-blending a polyolefin resin composition with a plasticizer, molding it into a sheet, stretching it as needed, and then extracting the plasticizer to achieve porousing; a method of melt-blending a polyolefin resin composition containing a polyolefin-based resin as the main component, extruding it at a high draw ratio, and then achieving porousing by heat treatment and stretching to peel off the polyolefin crystal interface; a method of melt-blending a polyolefin resin composition with an inorganic filler, molding it into a sheet, and then achieving porousing by stretching to peel off the interface between the polyolefin and the inorganic filler; and a method of dissolving a polyolefin resin composition, immersing it in a poor solvent containing polyolefin to solidify the polyolefin, and then removing the solvent to achieve porousing.

[0232] Furthermore, methods for producing nonwoven fabrics or paper as substrates are known. Examples of such methods include: chemical bonding, which involves impregnating a mesh in an adhesive and drying it to bond the fibers; thermal bonding, which involves mixing a thermoplastic fiber into the mesh to partially melt the fiber and bond the fibers; needle punching, which involves repeatedly piercing the mesh with a barbed needle to mechanically entangle the fibers; and water jet weaving, which involves spraying a high-pressure water jet through a mesh (sieve) from a nozzle to intertwine the fibers.

[0233] The following describes a method for manufacturing polyolefin microporous membranes, specifically a method of melt-blending a polyolefin resin composition with a plasticizer, molding it into sheets, and then extracting the plasticizer. First, the polyolefin resin composition and plasticizer are melt-blended. Examples of melt-blending methods include: feeding the polyolefin resin and other additives as needed into a resin mixing apparatus such as an extruder, kneader, laboplaster, mixing roller, and Banbury mixer; heating and melting the resin components while introducing the plasticizer in any proportion and mixing. In this case, it is preferable to pre-mix the polyolefin resin, other additives, and plasticizer in a predetermined proportion using a Henschel mixer or similar equipment before feeding them into the resin mixing apparatus. More preferably, only a portion of the plasticizer is added during pre-mixing, and the remaining plasticizer is fed from the resin mixing apparatus side and mixed simultaneously.

[0234] As a plasticizer, a non-volatile solvent that can form a homogeneous solution above the melting point of polyolefins can be used. Specific examples of such non-volatile solvents include hydrocarbons such as liquid paraffin and solid paraffin; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin is preferred.

[0235] Regarding the ratio of the polyolefin resin composition to the plasticizer, there is no particular limitation as long as it allows for uniform melt mixing and molding into sheets. For example, the mass percentage of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less. Setting the mass percentage of the plasticizer within this range is preferable from the viewpoint of balancing melt tension during melt molding and the formation of a uniform and fine pore structure.

[0236] Then, the molten compound obtained by heating, melting, and mixing as described above is formed into a sheet. As a method for manufacturing the sheet, examples include: extruding the molten compound into a sheet using a T-die, contacting it with a heat conductor, and cooling it to a temperature sufficiently below the crystallization temperature of the resin component for curing. Examples of heat conductors used in cooling and curing include metal, water, air, and the plasticizer itself; metal rollers are preferred due to their high thermal conductivity. In this case, if the molten compound is sandwiched between the rollers during contact with the metal roller, the thermal conductivity is further increased, and the sheet becomes oriented, the film strength increases, and the surface smoothness of the sheet is improved, thus making it more preferable. The die lip spacing when extruding the sheet using a T-die is preferably 400 μm or more and 3000 μm or less, more preferably 500 μm or more and 2500 μm or less.

[0237] The resulting sheet-like molded body is then stretched. Uniaxial or biaxial stretching can be used as the stretching process. Biaxial stretching is preferred from the perspective of the strength of the resulting microporous membrane. When the sheet-like molded body is stretched at a high ratio along the biaxial direction, the molecules orient along the planar direction, resulting in a porous substrate that is less prone to cracking and has high puncture strength. Examples of stretching methods include simultaneous biaxial stretching, successive biaxial stretching, multi-segment stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the perspectives of improved puncture strength, uniform stretching, and closure properties.

[0238] The stretching ratio, measured in terms of area ratio, is preferably in the range of 20 to 100 times, and more preferably in the range of 25 to 50 times. Regarding the stretching ratio in each axial direction, it is preferably in the range of 4 to 10 times in the MD direction and 4 to 10 times in the TD direction, and more preferably in the range of 5 to 8 times in the MD direction and 5 to 8 times in the TD direction. Setting the stretching ratio within this range is preferable from the viewpoint of imparting sufficient strength, preventing film cracking during the stretching process, and achieving high productivity.

[0239] The sheet-shaped molded body obtained above can be further calendered. Calendering can be carried out, for example, by using a pressure method employing a dual-belt press. Calendering, in particular, can increase the orientation of the surface portion of the sheet-shaped molded body. The calendering ratio is preferably greater than 1 and less than 3, more preferably greater than 1 and less than 2. With a calendering ratio within this range, the film strength of the finally obtained porous substrate increases, and a more uniform porous structure can be formed along the thickness direction of the film, which is therefore preferred.

[0240] Next, the plasticizer is removed from the sheet-shaped molded body to obtain a porous substrate. Methods for removing the plasticizer include, for example, immersing the sheet-shaped molded body in an extraction solvent to extract the plasticizer, followed by thorough drying. The method for extracting the plasticizer can be either batch or continuous. To suppress shrinkage of the porous substrate, it is preferable to constrain the ends of the sheet-shaped molded body during the immersion and drying process. Furthermore, the residual amount of plasticizer in the porous substrate is preferably less than 1% by mass.

[0241] As the extraction solvent, it is preferable to use a solvent that is a poor solvent for polyolefin resins but a good solvent for plasticizers, and whose boiling point is lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as dichloromethane and 1,1,1-trichloroethane; non-chlorinated halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. It should be noted that these extraction solvents can be recovered and reused through operations such as distillation.

[0242] To suppress shrinkage of porous substrates, heat treatments such as heat setting and heat relaxation can be performed after the stretching process or after the formation of the porous substrate. Post-treatments such as hydrophilization treatment with surfactants or cross-linking treatment with ionizing radiation can also be applied to the porous substrate.

[0243] Examples of dry porousing methods, different from the wet porousing methods described above, are given below. First, a film is prepared by directly stretching and oriented the molten resin in an extruder without using solvents. Then, a microporous membrane is prepared by sequentially performing annealing, cold stretching, and hot stretching processes. In the dry porousing method, methods such as stretching and oriented molten resin through a T-die from an extruder, or blow molding, can be used; the method is not particularly limited.

[0244] [Preparation method for containing thermoplastic polymer layer]

[0245] A thermoplastic polymer layer is disposed on at least one side of the substrate thus manufactured. When an inorganic filler porous layer is disposed on the surface of the substrate, the thermoplastic polymer layer is disposed on the entire surface or a portion of the surface of the inorganic filler porous layer, and / or on the substrate surface where no inorganic filler porous layer is formed. There are no particular limitations on the method of disposing of the thermoplastic polymer layer; examples include, for instance, applying a coating liquid containing particulate polymer to the inorganic filler porous layer or the substrate.

[0246] As a coating liquid, a dispersion of the particulate polymer in a solvent that does not dissolve the polymer is preferred. Particularly preferred is that the particulate polymer can be synthesized by emulsion polymerization and the emulsion obtained by emulsion polymerization can be used directly as a coating liquid.

[0247] Regarding methods for coating a substrate with a coating liquid containing particulate polymers, there are no particular limitations as long as the desired coating pattern, coating thickness, and coating area can be achieved. Examples include gravure coating, small-diameter gravure coating, reverse roller coating, transfer roller coating, mating coating, dip coating, doctor blade coating, air knife coating, scraper coating, rod coating, extrusion coating, casting coating, mold coating, screen printing, spray coating, and inkjet coating. Among these, gravure coating or spray coating is preferred from the viewpoint that the coating shape of the particulate polymer has a high degree of freedom and that it is easy to obtain the preferred area ratio.

[0248] Water or a mixture of water and a water-soluble organic medium is preferred as the medium for the coating liquid. There are no particular limitations on the water-soluble organic medium; examples include ethanol and methanol. Water is more preferred among these. When the coating liquid is applied to a substrate, if it penetrates into the substrate, the particulate polymer containing the polymer can clog the surface and interior of the substrate's pores, easily leading to decreased permeability. In this regard, when water is used as the solvent or dispersion medium for the coating liquid, the coating liquid is less likely to penetrate into the substrate, and the particulate polymer containing the polymer tends to exist mainly on the outer surface of the substrate, thus more effectively suppressing the decrease in permeability, and is therefore preferred. Furthermore, ethanol and methanol are examples of solvents or dispersion media that can be used in combination with water.

[0249] Regarding methods for removing solvent from the coated film after coating, there are no particular limitations as long as the method does not adversely affect the substrate and the thermoplastic polymer layer. Examples include: drying at a temperature below the melting point of the substrate while it is fixed; drying under reduced pressure at low temperature; and immersing the particulate polymer in a poor solvent, causing the particulate polymer to solidify into particles while simultaneously extracting the solvent.

[0250] Methods for forming porous layers in inorganic packing

[0251] When an inorganic filler porous layer is disposed on at least one side of a substrate, there are no particular limitations on the method for forming the inorganic filler porous layer, and known methods can be used. Examples include: applying a coating liquid containing inorganic filler and a resin binder, if desired, to the substrate. When the substrate contains resin, such as a polyolefin microporous membrane, the raw material containing the inorganic filler and resin binder can be laminated with the resin-containing substrate raw material by co-extrusion, or the substrate and inorganic filler porous layer (membrane) can be prepared separately and then bonded together.

[0252] As a solvent for the coating liquid, it is preferred to use a solvent that can uniformly and stably disperse or dissolve inorganic fillers and resin binders used as needed. Examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, dichloromethane, and hexane.

[0253] Various additives can be added to the coating solution, such as dispersants like surfactants; thickeners; wetting agents; defoamers; pH adjusters including acids and alkalis, and other additives.

[0254] Methods for dispersing or dissolving inorganic fillers and resin binders as needed in a coating liquid include, for example, mechanical stirring using ball mills, bead mills, planetary ball mills, vibratory ball mills, sand mills, colloid mills, vertical ball mills, roller mills, high-speed impeller dispersers, distributors, homogenizers, high-speed impact mills, ultrasonic dispersers, and stirring blades.

[0255] Methods for applying coating liquid to a substrate include, for example, gravure coating, small-diameter gravure coating, reverse roller coating, transfer roller coating, mating coating, immersion coating, doctor blade coating, air knife coating, scraper coating, bar coating, extrusion coating, casting coating, mold coating, screen printing, and spray coating.

[0256] Regarding methods for removing solvent from the coated film after coating, there are no particular limitations as long as the method does not adversely affect the substrate. Examples include: drying at a temperature below the melting point of the substrate material while fixing the substrate; drying under reduced pressure at low temperature; and impregnating the resin binder with a poor solvent to allow the resin binder to solidify and simultaneously extract the solvent. Alternatively, it is permissible to leave a small amount of solvent within a range that does not significantly affect the equipment characteristics.

[0257] Then, the area (e.g., coverage) and / or shape of the pattern of the thermoplastic polymer layer on the surface of the separator are measured using the aforementioned inspection device. The quality of the thermoplastic polymer layer or the quality of the separator containing the thermoplastic polymer layer is evaluated based on predetermined criteria. Specifically, if the predetermined criteria are met, it can be determined as "good," and if the predetermined criteria are not met, it can be determined as "no." Therefore, the present invention enables the efficient manufacture of highly reliable separators.

[0258] As described above, the present invention provides, as one aspect, a method for manufacturing a separator, and as another aspect, an inspection device. The description of the separator in this specification can be considered a feature of the separator in the inspection device invention, and the description of the inspection device in this specification can be considered a feature of the inspection device in the method for manufacturing the separator. Specifically, for example, any one of items 9-14, 18, and 19 in the above-described [Solutions to the Problem] can be described as a separator in the inspection device invention, and any one of items 2-7 and 17 can be described as an inspection device in the method for manufacturing the separator. More specifically, preferred elements selected from the thermoplastic polymer layer and the inorganic filler layer described above can be described as a separator in the inspection device invention, and preferred elements selected from at least one of the group consisting of the separator, camera, and light source described above can be described as an inspection device in the method for manufacturing the separator.

[0259] Example

[0260] The physical property evaluation described in this embodiment section is performed according to the following method.

[0261] (1) Substrate thickness (μm)

[0262] A 10cm x 10cm square sample was cut from the substrate. Nine locations (3 points x 3 points) were selected in a grid pattern, and the thickness was measured using a miniature thickness gauge (Toyo Seiki Co., Ltd., model KBM) at room temperature (23 ± 2°C). The average value of the measurements from the nine locations was calculated as the thickness of the substrate. Furthermore, the differences between the maximum and minimum thickness values ​​and the average value were calculated as the thickness deviation.

[0263] (2) Porosity (%)

[0264] Cut a 10cm x 10cm square sample from the substrate and calculate its volume (cm²). 3 The density of the substrate was set to 0.95 (g / cm³) and mass (g). 3 Using these values, the porosity can be calculated using the following formula.

[0265] Porosity (%) = (1 - mass / volume / 0.95) × 100

[0266] (3) Breathability (seconds / 100cm) 3 )

[0267] For the separator, the air permeability resistance is measured using a Glaley air permeability meter G-B2 (model name) manufactured by Toyo Seiki Co., Ltd., based on JIS P-8117, and is taken as the air permeability. When the thermoplastic polymer layer exists only on one side of the substrate, a needle can be inserted from the side containing the thermoplastic polymer layer.

[0268] (4) Average particle size (D50) of particulate polymers and inorganic fillers.

[0269] The average particle size (D50) of particulate polymers and inorganic fillers was determined using a particle size analyzer (manufactured by Nikkiso Co., Ltd., product name "Microtrac UPA150"). The measurement conditions were set as follows: loading index = 0.20, measurement time 300 seconds, and the value of 50% of the obtained particle size (D50) was recorded as the average particle size.

[0270] (5) Coverage ratio of thermoplastic polymer layer based on SEM

[0271] The coverage area of ​​the thermoplastic polymer layer was determined using a scanning electron microscope (SEM) (model: S-4800, manufactured by HITACHI). Osmium was deposited on the spacers used as samples, and observation was performed at an accelerating voltage of 1.0 kV and 50x. The surface coverage was calculated using the following formula. The field of view was 2.54 mm × 1.58 mm. It should be noted that in the SEM images, areas where the porous structure of the substrate surface is not visible, or areas where the surface of any optional layer is not visible—specifically, areas where the porous structure of the inorganic filler porous layer is not visible—are considered as areas containing the thermoplastic polymer layer.

[0272] The percentage of the area covered by the thermoplastic polymer layer (%) = (Area of ​​the thermoplastic polymer layer ÷ (Area of ​​the substrate including the porous portion or the surface area of ​​the optional layer) + (Area of ​​the thermoplastic polymer layer) × 100

[0273] For the coverage area ratio in each sample, the above determination was performed three times, and the average value was taken.

[0274] [Manufacturing Example 1-1]

[0275] (Manufacturing of polyolefin microporous membrane B1)

[0276] 45 parts by mass of high-density polyethylene (HDPE) with a molecular weight (Mv) of 700,000 and homopolymer, 45 parts by mass of HDPE with a Mv of 300,000 and homopolymer, and 10 parts by mass of a mixture of polypropylene with a Mv of 400,000 and homopolymer and polypropylene with a Mv of 150,000 (mass ratio = 4:3) were dry-mixed using a drum mixer. One part by mass of tetra-[methylene-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant was added to 99 parts by mass of the resulting polyolefin mixture, and the mixture was dry-mixed again using a drum mixer to obtain a final mixture. The resulting mixture was fed into a twin-screw extruder under a nitrogen atmosphere via a feeder. Separately, liquid paraffin (kinematic viscosity at 37.78°C 7.59 × 10⁻⁶) was... -5 m 2 The liquid paraffin is injected into the extruder barrel via a plunger pump. The operating conditions of the feeder and pump are adjusted so that the proportion of liquid paraffin in the total 100 parts by mass of the extruded mixture is 65 parts by mass, i.e., the proportion of the resin composition is 35 parts by mass.

[0277] Next, the materials were melt-blended in a twin-screw extruder while being heated to 230°C. The resulting melt-blended material was extruded through a T-die onto a cooling roller with a surface temperature controlled at 80°C, allowing the extrudate to contact the cooling roller for casting. The material was then cooled and solidified to obtain a sheet. This sheet was stretched using a biaxial stretching machine at a ratio of 7 × 6.4 times and a temperature of 112°C. After impregnation with dichloromethane to remove liquid paraffin, it was dried and stretched twice in the transverse direction using a tenter frame at a temperature of 130°C. The stretched sheet was then relaxed by approximately 10% in the width direction and subjected to heat treatment to obtain the polyolefin microporous membrane B1 as the substrate.

[0278] The physical properties of the obtained polyolefin microporous membrane B1 were determined using the method described above. Furthermore, the obtained polyolefin microporous membrane was directly used as a separator and evaluated using the same method. The results are shown in Table 1.

[0279] [Manufacturing Examples 1-2 to 1-4] (Manufacturing of polyolefin microporous membranes B2 to B4)

[0280] By varying the temperature and relaxation rate during stretching, polyolefin microporous membranes B2, B3, and B4 were obtained as substrates in the same manner as in Manufacturing Example 1-1. The obtained polyolefin microporous membranes B2, B3, and B4 were evaluated in the same manner as in Manufacturing Example 1-1. The results are shown in Table 1.

[0281] [Table 1]

[0282]

[0283] <Synthesis of Particulate Polymer A1>

[0284] Add 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aquaron KH1025" (registered trademark, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., 25% aqueous solution, referred to as "KH1025" in the table; the same applies hereinafter) and 0.5 parts by mass of "Adeka Reasoap SR1025" (registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution, referred to as "SR1025" in the table; the same applies hereinafter) to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, and raise the internal temperature of the reaction vessel to 80°C. Then, while maintaining the internal temperature of the vessel at 80°C, add 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (referred to as "APS(aq)" in the table; the same applies hereinafter).

[0285] On the other hand, an emulsion was prepared by mixing a mixture of 38.5 parts by weight of methyl methacrylate, 19.6 parts by weight of n-butyl acrylate, 31.9 parts by weight of 2-ethylhexyl acrylate, 0.1 parts by weight of methacrylic acid, 0.1 parts by weight of acrylic acid, 2 parts by weight of 2-hydroxyethyl methacrylate, 5 parts by weight of acrylamide, 2.8 parts by weight of glycidyl methacrylate, 0.7 parts by weight of trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.), 0.3 parts by weight of γ-methacryloyloxypropyltrimethoxysilane, 7.5 parts by weight of ammonium persulfate (2% aqueous solution) and 52 parts by weight of deionized water using a homogenizer for 5 minutes.

[0286] The resulting emulsion was transferred from the dropping tank to the aforementioned reaction vessel. Dropping began 5 minutes after the addition of ammonium persulfate aqueous solution to the reaction vessel, and the entire emulsion was added over 150 minutes. During the dropping of the emulsion, the internal temperature of the vessel was maintained at 80°C.

[0287] After the emulsion was added dropwise, the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature to obtain the emulsion. The resulting emulsion was adjusted to pH 9.0 with an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex with a concentration of 40% by mass (raw material polymer A1). The obtained raw material polymer (aqueous dispersion) A1 was evaluated using the method described above. The results are shown in Table 2.

[0288] <Synthesis of Particulate Polymer A2>

[0289] The monomers, other raw materials, and polymerization conditions were modified according to those described in Table 2, and the copolymer latex (raw material polymer A2) was obtained in the same manner as the raw material polymer (aqueous dispersion) A1. The obtained raw material polymer (aqueous dispersion) A2 was evaluated using the methods described above. The results are shown in Table 2.

[0290] [Table 2]

[0291]

[0292] The abbreviations of the raw material names in Table 2 and Table 3 below have the following meanings.

[0293] <Emulsifier>

[0294] KH1025: A registered trademark of "Aquaron KH1025", manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., 25% aqueous solution.

[0295] SR1025: "Adeka Reasoap SR1025" registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution.

[0296] NaSS: Sodium p-styrenesulfonate

[0297] <Initiator>

[0298] APS: Ammonium persulfate (2% aqueous solution)

[0299] <Single>

[0300] ((meth)acrylic acid monomer)

[0301] MAA: Methacrylic acid

[0302] AA: Acrylic acid

[0303] ((meth)acrylate)

[0304] MMA: Methyl methacrylate

[0305] BA: n-Butyl acrylate

[0306] BMA: n-Butyl methacrylate

[0307] EHA: 2-Ethylhexyl acrylate

[0308] CHMA: Cyclohexyl methacrylate

[0309] (Aromatic vinyl monomers)

[0310] St: Styrene

[0311] (Contains cyano monomers)

[0312] AN: Acrylonitrile

[0313] (Monomers including other functional groups)

[0314] HEMA: 2-Hydroxyethyl methacrylate

[0315] AM: Acrylamide

[0316] (Cross-linked monomers)

[0317] GMA: Glycidyl methacrylate

[0318] A-TMPT: Trimethylolpropane triacrylate

[0319] AcSi: γ-methacryloyloxypropyltrimethoxysilane

[0320] (Manufacturing Example A3)

[0321] A portion of the aqueous dispersion A1 obtained in Manufacturing Example A1 was subjected to multi-stage polymerization using it as a seed polymer, thereby synthesizing aqueous dispersion A3. Specifically, a mixture of 20 parts by mass of aqueous dispersion A1 (converted to solids) and 70.4 parts by mass of deionized water was first added to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, and the internal temperature of the reaction vessel was raised to 80°C. Then, while maintaining the internal temperature of the vessel at 80°C, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) were added. This constitutes the initial feed.

[0322] On the other hand, an emulsion was prepared by mixing a mixture of 38.5 parts by weight of methyl methacrylate, 19.6 parts by weight of n-butyl acrylate, 31.9 parts by weight of 2-ethylhexyl acrylate, 0.1 parts by weight of methacrylic acid, 0.1 parts by weight of acrylic acid, 2 parts by weight of 2-hydroxyethyl methacrylate, 5 parts by weight of acrylamide, 2.8 parts by weight of glycidyl methacrylate, 0.7 parts by weight of trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.), 0.3 parts by weight of γ-methacryloyloxypropyltrimethoxysilane, 7.5 parts by weight of ammonium persulfate (2% aqueous solution), and 52 parts by weight of deionized water using a homogenizer for 5 minutes. The obtained emulsion was then added dropwise from a dropping tank to the above-mentioned reaction vessel. Dropping began 5 minutes after the addition of the ammonium persulfate aqueous solution to the reaction vessel, and all the emulsion was added dropwise over 150 minutes. During the dropwise addition of the emulsion, the internal temperature of the vessel was maintained at 80°C.

[0323] After the emulsion was added dropwise, the reaction vessel was kept at 80°C with stirring for 90 minutes, and then cooled to room temperature to obtain the emulsion. The resulting emulsion was adjusted to pH 9.0 with an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex with a concentration of 40% by mass (raw material polymer A3). The obtained raw material polymer A3 was evaluated using the method described above. The results are shown in Table 3.

[0324] (Manufacturing Example A4)

[0325] The composition and polymerization conditions of the seed polymer and other raw materials were changed according to those described in Table 3, and copolymer latex (raw material polymer A4) was obtained in the same manner as raw material polymer A3. The obtained raw material polymer A4 was evaluated using the methods described above. The results are shown in Table 3.

[0326] [Table 3]

[0327]

[0328] [Example I-1]

[0329] 20 parts by mass of raw material polymer A1 and 80 parts by mass of raw material polymer A4 were mixed and uniformly dispersed to prepare a coating liquid (30% by mass of solids) containing a thermoplastic polymer. At this time, carboxymethyl cellulose was added as a thickener at a rate of 1% by mass relative to the coating liquid, and the viscosity of the coating liquid was adjusted to 30 mPa·s. The coating liquid was then applied to one side (side (A)) of the polyolefin microporous membrane B1 with a thickness of 1 μm using a gravure coating machine. The thermoplastic polymer coating liquid was then coated... Figure 4 The dotted pattern shown in (A) is used. The size of each dot is set to 200 μm, and the distance between the centers of adjacent dots is 600 μm. The size of the unit pattern is 600 μm × 600 μm. The thermoplastic polymer covers 20% of the polyolefin microporous membrane. The coating solution is then dried at 40°C to remove water.

[0330] Furthermore, the coating liquid is also applied to the side (side (B)) of the polyolefin microporous membrane B1 opposite to side (A), and then dried in the same manner as described above. This process yields a separator with thermoplastic polymer layers formed on both sides of the polyolefin microporous membrane B1.

[0331] This process results in a separator with thermoplastic polymer layers formed on both sides of the polyolefin microporous membrane B1.

[0332] For the obtained separator, the area of ​​the thermoplastic polymer layer is determined by the following method.

[0333] use Figure 1 The inspection device shown determines the area covered by the pattern containing the thermoplastic polymer layer.

[0334] Eight 630nm wavelength LED light sources (spherical, 3mm diameter) are used as the light source, surrounding the partition and arranged at equal intervals. The distance from the light source to the surface of the partition is 35mm, the incident angle θ of the light relative to the plane of the partition is 85 degrees, the distance from the surface of the partition being inspected to the camera is 200mm, and the camera is positioned perpendicular to the plane of the partition being inspected.

[0335] The camera used was a VHX-7020 (Keyence Corporation, using a CMOS image sensor, 3.19 megapixels). Images were captured with the inspection area focused at 20x magnification. The resulting images were binarized using ImageJ image processing software to determine the pattern coverage area containing the thermoplastic polymer layer. Specifically, for the field of view obtained from the acquired images, the coverage area of ​​the thermoplastic polymer within the field of view was determined using ImageJ (version 1.46). Specifically, the captured image file was opened, and the entire field of view was selected using "Rectangular selections" to select the evaluation area. Then, binarization was performed to separate the thermoplastic polymer from the non-thermoplastic polymer area. Specifically, "Threshold" was selected, and the inversion range in the 256-order scale was set to "0-100" for processing.

[0336] With the separator stationary relative to the camera, perform the above-mentioned checks to determine the pattern coverage area containing the thermoplastic polymer layer.

[0337] In addition, for the same separator, the pattern coverage area containing the thermoplastic polymer layer is determined by SEM observation, and the deviation between the two is calculated.

[0338] The results are shown in Table 4.

[0339] [Examples I-2 to I-9, I-12 to I-14]

[0340] The composition of the inspection equipment, the type of substrate, the type of particulate polymer, the shape of the thermoplastic polymer, and the particle size of the thermoplastic polymer were changed according to the descriptions in Tables 4 and 5, respectively. Otherwise, the inspection was performed in the same manner as in Example 1, and the deviation from the SEM observation results was determined. It should be noted that the PVdF-HFP used in Examples I-5 was XPH-883 (Solvay). Furthermore, the "non-equal spacing" light source configuration in Examples I-4 refers to an arrangement where the surface of the separator being inspected is at a 45-degree angle (°) to the two light sources, and the inspection was performed with this configuration.

[0341] [Example I-10]

[0342] A coating solution was prepared by uniformly dispersing 92.0 parts by weight of aluminum hydroxide (average particle size 1000 nm) as an inorganic filler, 8.0 parts by weight of an acrylic latex suspension (solid content concentration 40%, average particle size 150 nm), and 1.0 part by weight of an aqueous solution of ammonium polycarboxylate (SAN NOPCO SNDispersant 5468) in 100 parts by weight of water. This solution was then coated onto the surface of the aforementioned polyolefin microporous membrane B1, which served as a porous substrate, using a microgravure coating machine. After drying at 60°C to remove water, an inorganic filler layer with a thickness of 4.0 μm was formed on the polyolefin resin porous membrane.

[0343] A thermoplastic polymer layer was formed on the inorganic filler layer in the same manner as in Example I-1 to obtain a separator. Except for the separator used, the same checks were performed as in Example I-1 to determine the deviation from the SEM observation results.

[0344] [Example I-11]

[0345] The inorganic filler particle size (nm) was changed as described in Table 5, and the separators were otherwise obtained in the same manner as in Examples I-8. Except for the separators used, the same checks were performed as in Example I-1 to determine the deviation from the SEM observations.

[0346] [Comparative Example I-1]

[0347] The configuration of the inspection equipment was changed as described in Table 5, and the deviation from the SEM observation results was calculated in the same manner as in Example I-1.

[0348] For Examples I-1 to I-14 and Comparative Example I-1, the configuration of the inspection equipment, the conditions of the separators, the observation results and the deviation are shown in Table 4 or Table 5.

[0349] [Table 4]

[0350]

[0351] [Table 5]

[0352]

[0353] [Example II-1]

[0354] Similar to Example I-1, a separator containing a thermoplastic polymer layer was formed on both sides of the polyolefin microporous membrane B1.

[0355] For the obtained separator, the area of ​​the thermoplastic polymer layer is determined by the following method.

[0356] For a device consisting of multiple rollers conveying separators, a light source and a camera are provided on one roller. Light sources (rod-shaped, 1000mm, LED) with a wavelength of 630nm are evenly spaced on both sides of the separator to be conveyed. The distance from the light source to the separator surface is 600mm, the incident angle θ of the light relative to the separator plane is 85 degrees, the distance from the inspected separator surface to the camera is 600mm, and the camera is positioned such that the reflection angle relative to the inspected separator surface is 0 degrees.

[0357] Surface images were captured using a 3.19-megapixel camera with a CMOS image sensor while conveying the separator at speeds of 200 m / min and 20 m / min. The acquired images were binarized using image processing software (ImageJ) to determine the pattern coverage area containing the thermoplastic polymer layer. Specifically, for the field of view obtained from the acquired images, the coverage area of ​​the thermoplastic polymer within the field of view was determined using the image analysis and processing software ImageJ (version 1.46). Specifically, the captured image file was opened, and the entire field of view was selected using "Rectangularselections" to select the evaluation area. Then, binarization was performed to separate the thermoplastic polymer from the non-thermoplastic polymer area. Specifically, "Threshold" was selected, and the inversion range in the 256-order set was set to "0-100" for processing.

[0358] The deviation is calculated by comparing the pattern coverage area of ​​the thermoplastic polymer layer obtained by the above method with the coverage area obtained by SEM observation in the same way as in Example I-1.

[0359] The results are shown in Table 6.

[0360] [Examples II-2 to II-5]

[0361] The configuration of the inspection equipment was changed as described in Table 6, and the inspection was performed in the same manner as in Example II-1 to determine the deviation from the SEM observation results.

[0362] [Comparative Example II-1]

[0363] The configuration of the inspection equipment was changed as described in Table 6, and the inspection was performed in the same manner as in Example II-1 to determine the deviation from the SEM observation results.

[0364] [Table 6]

[0365]

[0366] As can be clearly seen from Tables 4, 5, and 6, compared to the comparative example where the incident angle θ of light relative to the surface of the separator was set to 45 degrees, the deviation from the SEM-based measurement values ​​of the embodiments with an angle of 60 degrees or more and 90 degrees or less was smaller, confirming that the pattern coverage area containing the thermoplastic polymer layer could be measured with substantially high accuracy. In particular, it was confirmed that more accurate measurements could be performed by arranging multiple light sources at equal intervals.

[0367] Good results were also obtained when the thermoplastic polymer material was different or when a thermoplastic polymer layer was formed on an inorganic filler.

[0368] It was also confirmed that particularly good results could be obtained by optimizing the parameters of the separator.

[0369] Industrial availability

[0370] According to the present invention, the coverage area of ​​the thermoplastic polymer layer on the surface of a separator having a thermoplastic polymer layer can be measured with high precision and efficiency. In particular, the method of evaluating the coating surface of the thermoplastic polymer layer after it has dried, thereby evaluating the coverage area of ​​the thermoplastic polymer layer, is simpler. Furthermore, the evaluation can be performed without damaging the separator, thus contributing to the development of superior separators and the management of manufacturing processes.

[0371] Explanation of reference numerals in the attached figures

[0372] 1. Light source

[0373] 2. Camera

[0374] 10 platforms

[0375] 11 rollers

[0376] S-separator

[0377] S1 Inspection Section

Claims

1. An inspection device for a separator, characterized in that, It is an inspection device for separators with thermoplastic polymer layers. The separator comprises a substrate and a thermoplastic polymer layer partially present on one or both sides of the substrate. The inspection device has two or more light sources and a camera. The light sources illuminate the inspected portion of the separator at an angle of 60 degrees or more and 90 degrees or less with respect to the direction perpendicular to the plane direction of the separator being set to 0 degrees. The two or more light sources are arranged at equal intervals to surround the inspected portion of the separator.

2. The inspection device for the separator according to claim 1, wherein, The incident angle θ is greater than 75 degrees and less than 90 degrees.

3. The inspection device for the separator according to claim 1, wherein, The incident angle θ is above 80 degrees and below 90 degrees.

4. The inspection device for the separator according to any one of claims 1 to 3, wherein, The light source uses a wavelength of 630nm.

5. The inspection device for the separator according to any one of claims 1 to 4, wherein, The distance from the surface of the separator to the camera is more than 10 mm and less than 1000 mm.

6. The inspection device for the separator according to claim 5, wherein, The distance from the surface of the separator to the camera is more than 250 mm and less than 1000 mm.

7. The inspection device for the separator according to any one of claims 1 to 6, wherein, The camera is positioned within an angle range of more than -5 degrees and less than +5 degrees relative to the reflection angle of light incident from the light source.

8. The inspection device for the separator according to any one of claims 1 to 7, comprising a stand for fixing the camera, and the stand having a platform capable of moving the camera along any one or more of the following directions: front-back, left-right, up-down.

9. The inspection device for the separator according to any one of claims 1 to 8, wherein, The size of the light source is greater than 1 mm and less than 3000 mm.

10. A method for manufacturing a separator, characterized in that, It is a method for manufacturing a separator with a thermoplastic polymer layer. The separator comprises a substrate and a thermoplastic polymer layer partially present on one or both sides of the substrate. The method for manufacturing the separator includes a step of inspecting the surface of the separator, and using an inspection device having two or more light sources and a camera to inspect the separator. The light sources illuminate the separator at an angle of 60 degrees or more and 90 degrees or less relative to the inspected portion of the separator when the direction perpendicular to the plane direction of the separator is set to 0 degrees. The two or more light sources are arranged at equal intervals to surround the inspected portion of the separator.

11. The method for manufacturing a separator according to claim 10, wherein, The air permeability of the separator is 40 seconds / 100cm. 3 Above and 500 seconds / 100cm 3 the following.

12. The method for manufacturing the separator according to claim 10 or 11, wherein, The thickness deviation of the separator is less than ±10μm relative to the layer thickness.

13. The method for manufacturing the separator according to any one of claims 10 to 12, wherein, The thermoplastic polymer layer comprises particulate polymeric compounds.

14. The method for manufacturing a separator according to claim 13, wherein, The granular polymer is an acrylic polymer.

15. The method for manufacturing the separator according to claim 13 or 14, wherein, The average particle size of the granular polymer is greater than 50 nm and less than 10,000 nm.

16. The method for manufacturing the separator according to any one of claims 13 to 15, wherein, The thermoplastic polymer layer contains two or more particulate polymeric compounds having different arithmetic mean particle sizes. The particulate polymeric compounds include particulate polymeric compounds having an arithmetic mean particle size of 10 nm or more and 400 nm or less, and particulate polymeric compounds having an arithmetic mean particle size of more than 100 nm and 2000 nm or less.

17. The method for manufacturing the separator according to any one of claims 13 to 16, wherein, The thermoplastic polymer layer comprises one or more polymers in a region with a glass transition temperature above 20°C and one or more polymers in a region with a glass transition temperature below 20°C.

18. The method for manufacturing the separator according to any one of claims 10 to 17, wherein, The thermoplastic polymer exists in a unit pattern, and the unit pattern is a repeating pattern.

19. The method for manufacturing a separator according to claim 18, wherein, The size of the unit pattern is greater than 10μm×10μm and less than 10mm×10mm.

20. The method for manufacturing the separator according to any one of claims 10 to 19, wherein, An inorganic filler layer is present on one or both sides of the substrate, and the thermoplastic polymer layer is present at least partially on the inorganic filler layer.

21. The method for manufacturing a separator according to claim 20, wherein, The layer density of the inorganic filler layer is 0.5 g / (m³). 2 ·μm) or higher and 3.0g / (m 2 Below μm.

22. The method for manufacturing a separator according to claim 20 or 21, wherein, The inorganic filler layer contains inorganic fillers with a volume average particle size of 50 nm or more and 2000 nm or less.

23. The method for manufacturing the separator according to any one of claims 20 to 22, wherein, The volume average particle size D1 of the thermoplastic polymer and the volume average particle size D2 of the inorganic filler satisfy the following formula: D1 / D2≤0.8 or D1 / D2≥1.

2.

24. The method for manufacturing a separator according to claim 23, wherein, 0.025≤D1 / D2≤0.8 or 200≥D1 / D2≥1.

2.

25. The method for manufacturing the separator according to any one of claims 20 to 24, wherein, The amount of binder contained in the inorganic filler layer is more than 0.5 parts by mass and less than 20 parts by mass relative to 100 parts by mass of the inorganic filler.

26. A method for manufacturing a separator, characterized in that, It is a method for manufacturing a separator with a thermoplastic polymer layer. The separator comprises a substrate and a thermoplastic polymer layer partially present on one or both sides of the substrate. The method for manufacturing the separator includes an inspection step of inspecting the surface of the separator using an inspection device having two or more light sources and a camera. The light sources illuminate the surface at an angle θ of 60 degrees or more and 90 degrees or less relative to the surface of the separator when the direction perpendicular to the plane of the separator is set to 0 degrees. The two or more light sources are arranged at equal intervals surrounding the inspection portion of the separator. The inspection process includes a detection step that detects the shape and / or coverage of the thermoplastic polymer layer based on an image captured by the camera.

27. The method for manufacturing a separator according to claim 26, wherein, In the inspection process, the condition of the separator is further determined based on the shape and / or coverage obtained in the detection process.

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