Polymeric piezoelectric film and manufacturing method thereof

A polymeric piezoelectric film, comprising a helical chiral polymer (A) having a weight average molecular weight of from 50,000 to 1,000,000 and optical activity, wherein, in the film:

• a crystallinity given by a DSC method is from 20% to 80%;
• a standardized molecular orientation MORc is from 3.5 to 15.0 when a reference thickness measured by a microwave transmission-type molecular orientation meter is 50 μm;
• and
• when a direction parallel to a phase difference streak is a direction X, a direction perpendicular to the direction X and parallel to a main plane of a film is a direction Y, and the phase difference streak is evaluated by an evaluation method A, per a length of 1,000 mm in the direction Y, a number of phase difference streaks with an evaluation value of 60 or more is 0, and a sum of evaluation values of phase difference streaks with an evaluation value of 20 or more is 1000 or less,
• the evaluation method A comprising:
• (a) with respect to the direction Y, acquiring in-plane phase difference data of a film at intervals of 0.143 mm to obtain an in-plane phase difference profile;
• (b) performing fast Fourier transformation on the obtained in-plane phase difference profile, removing low frequency components using 0.273/mm as a cutoff frequency, and then performing inverse Fourier transformation;
• (c) calculating slopes of two adjacent points with respect to the in-plane phase difference profile after inverse Fourier transformation and converting the slopes into a slope profile;
• and
• (d) taking a height from a bottom point of a valley of the obtained slope profile to an apex of a mountain adjacent to the valley as an evaluation value of a phase difference streak.