Method for manufacturing separator for electrical storage device

A method for producing a separator for a lithium ion secondary battery having a thermoplastic polymer layer, wherein the separator comprises a substrate and the thermoplastic polymer layer disposed on a part of one or both sides of the substrate, and the thermoplastic polymer layer has a dotted, unit pattern, and an air permeability of the separator is 40 seconds/100 cm3 or greater and 500 seconds/100 cm3 or lower, the method comprising:

• inspecting a surface of the separator using an inspection device including two or more light sources that simultaneously irradiate light onto an inspection portion of the separator at an incident angle θ of 60° to 90°, a camera, an adsorption stage with a suction hole, and a suction unit below the adsorption stage;
• and
• determining a coverage ratio of the thermoplastic polymer layer based on an image photographed by the camera,
• wherein the two or more light sources are located at equally spaced positions in a circumferential direction around the inspection portion of the separator,
• wherein a first of the two or more light sources irradiates the inspection portion of the separator in a first direction, a second of the two or more light sources irradiates the inspection portion of the separator in a second direction, and the first direction is different from the second direction, and
• wherein the suction unit causes the separator to be adsorbed to the adsorption stage by air suction.

A method for producing a separator for a lithium ion secondary battery having a thermoplastic polymer layer, wherein:

• the separator comprises a substrate and the thermoplastic polymer layer disposed on a part of one or both sides of the substrate,
• the thermoplastic polymer layer has a dotted, unit pattern, and
• a thickness of the thermoplastic polymer layer is 0.01 μm or greater and 10.0 μm or smaller, the method, comprising:
• continuous coating of the thermoplastic polymer layer onto the substrate;
• inspecting a surface of the separator during the continuous coating using an inspection device including a light source that irradiates light onto an inspection portion of the separator at an incident angle θ of 60° to 90°, and a camera;
• and
• determining a coverage ratio of the thermoplastic polymer layer based on an image photographed by the camera,
• wherein the inspection portion of the separator is a section in contact with a roll, and the distance from the inspection portion of the separator to the camera is 10 mm to 1000 mm,
• wherein the camera is positioned at an angle in the range of −5° to +5° with respect to an angle of reflection of incident light to the inspection portion of the separator from the light source, and
• wherein the light source has a single-side length or a diameter of 200 mm to 3000 mm.