Polymer film, polarizing plate protective film, polarizing plate and liquid crystal display device

A polymer film, comprising:

• a wavelength dispersion regulator represented by formula (I):
• wherein R1 and R2 each independently represents a hydrogen atom, an alkyl group or an aryl group, provided that both R1 and R2 are not hydrogen atoms at the same time;
• and
• R3 and R4 each independently represents an electron-withdrawing substituent, and R1 and R2, or R3 and R4 may be bonded together to form a ring, and
• wherein the polymer film has a retardation value that satisfies the following formulae (1) and (2):
• 70 nm≦Rth(548)≦300 nm Formula (1)
• Rth(628)<Rth(548)<Rth(446) Formula (2)
• wherein Rth(λ) represents a retardation value expressed in nm in a film thickness direction measured at a wavelength of λ nm, and
• wherein the polymer film further comprises a light-fastness improving agent represented by formula (II):
• wherein X1 represents —NR4—, —O— or —S—;
• X2 represents —NR5—, —O— or —S—;
• X3 represents —NR6—, —O— or —S—;
• R1, R2 and R3 each independently represents an alkyl group, an alkenyl group, an aryl group or a heterocyclic group;
• and
• R4, R5 and R6 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an aryl group or a heterocyclic group.