Retardation film and production method therefor, polarizing plate, and display device

A method of producing a retardation film which satisfies the following formulas (1) and (2):

• 0.7<Re1[450]/Re1[550]<0.97 (1);
• and
• 1.5×10−3<Δn<6.0×10−3 (2)
• (where:
• Re1[450] and Re1[550] represent, respectively, in-plane retardation values of the retardation film as measured with light of a wavelength of 450 nm and light of a wavelength of 550 nm, at 23° C.;
• and Δn represents an in-plane birefringence of the retardation film as measured with light of a wavelength of 550 nm), the method comprising:
• continuously conveying and supplying a long polymer film;
• stretching the polymer film in a direction transverse to a conveyance direction;
• shrinking the polymer film in the transverse direction at a first shrinkage temperature T1 (° C.);
• and
• shrinking the polymer film to shrink in the transverse direction at a second shrinkage temperature T2 (° C.),
• wherein the first shrinkage temperature T1 (° C.) and the second shrinkage temperature T2 (° C.) satisfy the following formula (3):
• 1<(T1−T2)≦10 (3).

A retardation film which satisfies the following formulas (1), (2) and (8):

• 0.7<Re1[450]/Re1[550]<0.97 (1)
• 1.5×10−3<Δn<6.0×10−3 (2)
• |Re1[450]/Re1[550]−Re2[450]/Re2[550]|<0.02 (8)
• (where Re1[450] and Re1[550] represent, respectively, in-plane retardation values of the retardation film as measured with light of a wavelength of 450 nm and light of a wavelength of 550 nm, at 23° C.;
• Δn represents an in-plane birefringence of the retardation film as measured with light of a wavelength of 550 nm;
• and Re2[450] and Re2[550] represent, respectively, in-plane retardation values of the retardation film as measured with light of a wavelength of 450 nm and light of a wavelength of 550 nm, at 23° C., and after subjecting the retardation film to a heat treatment at 90° C. for 100 hours.