Polyimide-based film and flexible display panel including the same

1. A polyimide-based film having different surface energies from each other on both surfaces, wherein when a surface energy of a first surface having a relatively low surface energy is A, and a surface energy of a second surface having a relatively high surface energy is B, the following equation is satisfied:

B/A≥ 1.3.   [Equation 1]

wherein the polyimide-based film comprises a polyamideimide-based resin that is a copolymer, the copolymer comprising:

a unit consisting of an amine-terminal polyamide oligomer derived from a first fluorine-based diamine and an aromatic diacid dichloride;

a unit derived from a second fluorine-based aromatic diamine;

a unit derived from an aromatic dianhydride; and

a unit derived from a cycloaliphatic dianhydride,

wherein a content of the unit consisting of an amine-terminal polyamide oligomer is 50% or more, based on mass; and

wherein the polyimide-based film has a modulus in accordance with ASTM D882 of 3 GPa or more, an elongation at break of 8% or more, a light transmittance of 5% or more as measured at 388 nm in accordance with ASTM D1746, a total light transmittance of 87% or more as measured at 400 to 700nm, a haze of 2.0% or less, a yellow index of 5.0 or less, and a b* value of 2.0 or less.

2. The polyimide-based film of claim 1 , wherein in Equation 1 , B/A is 1.5 or more.

3. The polyimide-based film of claim 1 , wherein the surface energy A of the first surface is 20 to 30 mN/m and the surface energy B of the second surface is 30 to 50 mN/m.

4. The polyimide-based film of claim 1 , wherein the polyimide-based film is produced by a solution casting method, the first surface of both surfaces is a surface in contact with air during the solution casting, and the second surface is a surface in contact with a substrate.

5. The polyimide-based film of claim 4 , wherein a surface energy difference between the first surface and the second surface is adjusted by adjusting a surface roughness (Ra) of the substrate so that the surface energies of the first surface and the second surface are different.

6. The polyimide-based film of claim 5 , wherein the surface roughness of the substrate is adjusted to 0.02 μm or less to adjust the surface roughness of the second surface to 0.02 μm or less.

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 one surface or both surface of 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 antistatic layer, an anti-fingerprint layer, an antifouling layer, an anti-scratch layer, a low-refractive layer, an antireflective layer, and shock absorption layer.

10. A flexible display panel comprising the polyimide-based film of claim 1 .

11. The polyimide-based film of claim 1 , wherein the polyimide-based film consists of a polyamideimide resin and optionally one or more additives selected from the group consisting of a flame retardant, an adhesion improver, an antioxidant, a UV inhibitor, and a plasticizer.

12. The polyimide-based film of claim 1 , wherein the polyamideimide-based resin is a quaternary copolymer.