Polyimide-based film and window cover film using same
The present invention relates to a polyimide-based film exhibiting excellent visibility, a method for preparing same, and a display device including the prepared film. Particularly, the present invention relates to a polyimide-based film, a window cover film, and a display panel including same. The polyimide-based film maintains linear polarization with respect to incident polarization in the direction of an inclination as well as incident polarization in the direction of a normal line of the film.
1. A polyimide-based film of which a circular retardance value with respect to an omnidirectional angle of 0° to 360° is−30° to 30° when incident light passes through the polyimide-based film in a state in which a tilt angle of linear polarization of the incident light with respect to a thickness direction of the polyimide-based film is 0 to 60°,
wherein the polyimide-based film has a polyamide-imide structure, and
wherein the polyimide-based film includes a unit derived from a fluorine-based aromatic diamine, a unit derived from an aromatic dianhydride, a unit derived from an aromatic diacid dichloride, and a unit derived from a cycloaliphatic dianhydride.
2. The polyimide-based film of claim 1 , wherein the circular retardance value is −10° to 10°.
3. The polyimide-based film of claim 2 , wherein the circular retardance value is −1° to 1°.
4. The polyimide-based film of claim 1 , wherein the polyimide-based film has in-plane retardation (Rin) of 500 nm or less as measured at 400 nm to 800 nm using an Axoscan equipment, and uniformity of the in-plane retardation within ±20%.
5. The polyimide-based film of claim 4 , wherein the polyimide-based film has uniformity within ±10%.
6. The polyimide-based film of claim 1 , wherein
the polyimide-based film has a modulus of 3 GPa or more and an elongation at break of 8% or more as measured according to ASTM D822, and a light transmittance of 5% or more measured at 388 nm, a total light transmittance of 87% or more measured at 400 to 700 nm, a haze of 2.0% or less, a yellowness of 5.0 or less, and a b* value of 2.0 or less as measured according to ASTM D1746.
7. The polyimide-based film of claim 1 , wherein the polyimide-based film has a thickness of 30 to 110 μm.
8. A window cover film, comprising: the polyimide-based film of claim 1 ; and
a coating layer formed on the polyimide-based film.
9. The window cover film of claim 8 , wherein
the coating layer is any one or more selected from a hard coating layer, an anti-static layer, an anti-fingerprint layer, an anti-fouling layer, an anti-scratch layer, a low refractive layer, an anti- reflection layer, and an impact absorbing layer.
10. A flexible display panel comprising the polyimide-based film of claim 1 .