| CPC C08J 5/18 (2013.01) [C08G 73/14 (2013.01); C08J 2379/08 (2013.01)] | 12 Claims |
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1. A polyamideimide film having a photoelastic coefficient in a transverse direction of less than 2.0×10−8 m2/N and a wavelength dispersibility in which an in-plane birefringence value (Δnin) satisfies the following Relations 1 and 2:
1.0<Δnin (450 nm)/Δnin (550 nm)<1.3 [Relation 1]
0.7<Δnin (650 nm)/Δnin (550 nm)<1.0 [Relation 2]
wherein
Δnin (450 nm), Δnin (550 nm), and Δnin (650 nm) are in-plane birefringence values measured at wavelengths of 450 nm, 550 nm, and 650 nm, respectively, and
in which a birefringence value in a thickness direction (Ani) satisfies the following Relations 3 and 4:
0.9<Δnth (450 nm)/Δnth (550 nm)<1.3 [Relation 3]
0.7<Δnth (650 nm)/Δnth (550 nm)<0.9 [Relation 4]
wherein
Δnth (450 nm), Δnth (550 nm), and Δnth (650 nm) are birefringence values in the thickness direction of the film measured at wavelengths of 450 nm, 550 nm, and 650 nm, respectively,
the polyamideimide is derived from a monomer mixture consisting of dianhydride, diamine, and aromatic diacid dichloride, wherein the diamine consists of 2,2′-bis(trifluoromethyl)-benzidine, the dianhydride consists of 4,4′-hexafluoroisopropylidene diphthalic anhydride or 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and the diacid dichloride consists of terephthaloyl dichloride or isophthaloyl dichloride, and
the polyamideimide is dried in a first drying process and is simultaneously stretched and dried over three or more stretching areas in a second drying process, the second drying process performed for a total of 1 to 20 minutes and satisfies the following Equation 1 and Equation 2:
5≤T2−T1≤50 (Equation 1)
5≤T3−T2≤100 (Equation 2)
wherein T1 is a drying temperature (° C.) in a first area during a stretching process of the polyamideimide film, T2 is a drying temperature (° C.) in a second area during a stretching process of the polyamideimide film, and T3 is a drying temperature (° C.) in a third area during a stretching process of the polyamideimide film.
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