Abstract: A nonaqueous electrolyte secondary battery separator which has a low shutdown temperature, a high mechanical strength, and a high ion permeability is provided. The nonaqueous electrolyte secondary battery separator contains a polyolefin-based resin as a main component. The nonaqueous electrolyte secondary battery separator has a maximum heating value of not less than 30 mW/g observed during isothermal crystallization of the nonaqueous electrolyte secondary battery separator at 128° C.

Abstract: A nonaqueous electrolyte secondary battery separator having excellent impact absorbency includes a polyolefin porous film having a full width W at half maximum of a peak of an MD component of not less than 30 degrees. The full width W at half maximum of the peak of the MD component is calculated from an azimuthal profile of a scattering peak on a plane obtained by wide-angle X-ray scattering measurement that is carried out by irradiating a surface of the polyolefin porous film with an X-ray from a direction vertical to the surface of the polyolefin porous film, and/or having a maximum-to-minimum intensity ratio r of not more than 3.6. The maximum-to-minimum intensity ratio r is calculated from a Fourier transformed azimuthal profile obtained by observing the surface of the polyolefin porous film by SEM.

Abstract: A nonaqueous electrolyte secondary battery separator having excellent impact resistance contains a polyolefin porous film. The nonaqueous electrolyte secondary battery separator has a (200) plane peak area ratio R of not less than 0.15; the (200) plane peak area ratio R is a ratio of a peak area I(200) of a diffraction peak on a (200) plane to a peak area I(110) of a diffraction peak on a (110) plane and is calculated from a diffraction intensity profile obtained by wide-angle X-ray diffraction that is carried out by irradiating a surface of the nonaqueous electrolyte secondary battery separator with an X-ray from a direction vertical to the surface of the nonaqueous electrolyte secondary battery separator.

Abstract: An inspection method with which a separator having improved quality can be efficiently obtained is provided. The inspection method is a method for inspecting a nonaqueous electrolyte secondary battery separator that includes a polyolefin porous film. The inspection method includes a step of detecting a defect in the polyolefin porous film with the use of a color camera.

Abstract: A nonaqueous electrolyte secondary battery separator which has a low shutdown temperature, a high mechanical strength, and a high ion permeability is provided. The nonaqueous electrolyte secondary battery separator contains a polyolefin-based resin as a main component. The nonaqueous electrolyte secondary battery separator has a maximum heating value of not less than 30 mW/g observed during isothermal crystallization of the nonaqueous electrolyte secondary battery separator at 128° C.