| abstract |
A polyalkylene naphthalate for film comprising dicarboxylic acid units derived mainly from naphthalenedicarboxylic acid and glycol units derived mainly from an aliphatic glycol, characterized by containing (a) an antimony compound and (b) units of a quaternary phosphonium salt of a sulfonic acid having an ester-forming functional group in respective amounts satisfying the following relationships (1): 0∫Sb≤80, and (2): 0∫S/Sb≤0.4, wherein Sb and S represent the molar proportions (unit: mmol%) of the antimony compound (a) and the units (b), respectively, based on all dicarboxylic acid units contained in the polyalkylene naphthalate. The film has excellent surface smoothness and is suitable for use as a base film for magnetic recording media. It further has excellent suitability for high-speed winding and can be stably formed. The film can hence be produced industrially advantageously. |