Polyamide-based film, preparation method thereof, and cover window comprising same
Embodiments relate to a polyamide-based film that is colorless and transparent, is excellent in mechanical properties and optical properties, has a wide angle of view by securing at least a certain level of luminance at various angles, and, in particular, has gloss characteristics similar to those of glass, a process for preparing the same, and a cover window comprising the same. The polyamide-based film comprises a polyamide-based polymer, wherein when the polyamide-based film is placed on a surface light source, light is irradiated from the surface light source, and the luminance value (L 0 ) measured in the normal direction of the surface light source is 100%, the luminance value (L 50 ) measured in the direction of 50° from the normal direction of the surface light source is 25% or more.
1. A polyamide-based film, which comprises a polyamide-based polymer, wherein when the polyamide-based film is placed on a surface light source, light is irradiated from the surface light source, and the luminance value (L 0 ) measured in the normal direction of the surface light source is 100%, the luminance value (L 50 ) measured in the direction of 50° from the normal direction of the surface light source is 25% or more,
wherein the polyamide-based film further comprises a filler,
wherein the filler comprises barium sulfate,
wherein the content of the filler is 100 to 3,000 ppm based on the total weight of the solids content of the polyamide-based polymer, and
wherein the content of the residual solvent in the polyamide-based film is 1,500 ppm or less,
wherein the molar ratio of an imide-based repeat unit and an amide-based repeat unit in the polyamide-based polymer is 0:100 to 25:75, and wherein the polyamide-based film has an in-plane retardation of 800 nm or less and a thickness direction retardation of 5,000 nm or less.
2. The polyamide-based film of claim 1 , wherein the luminance value (L 20 ) measured in the direction of 20° from the normal direction of the surface light source is 70% or more, and the luminance value (L 60 ) measured in the direction of 60° from the normal direction of the surface light source is 19% or more.
3. The polyamide-based film of claim 1 , wherein the surface of the polyamide-based film has a glossiness at 20° (GL 20 ) of 90 to 130, a glossiness at 60° (GL 60 ) of 90 to 120, and a glossiness at 85° (GL 85 ) of 90 to 110.
4. The polyamide-based film of claim 1 , wherein the filler has an average particle diameter of 60 to 180 nm.
5. The polyamide-based film of claim 1 , which has a transmittance of 80% or more, a haze of 1% or less, and a yellow index or 5 or less measured at 550 nm.
6. A process for preparing the polyamide-based film of claim 1 , which comprises:
preparing a solution comprising a polyamide-based polymer in an organic solvent;
adding a filler dispersion in which a filler comprising barium sulfate is dispersed to the solution;
charging the solution comprising the filler dispersion into a tank;
extruding and casting the solution in the tank and then drying it to prepare a gel sheet; and
thermally treating the gel sheet.
7. The process of claim 6 for preparing the polyamide-based film, which comprises stretching the gel sheet after the step of preparing the gel sheet.
8. The process of claim 7 for preparing the polyamide-based film, wherein in the step of stretching the gel sheet, the stretching ratio in the transverse direction (TD) is 1.005 to 1.05, the stretching ratio in the longitudinal direction (MD) is 1.005 to 1.05, and the ratio of stretching in the transverse direction (TD) to that in the longitudinal direction (MD) is 0.96 to 1.04.
9. A cover window for a display device, which comprises a polyamide-based film and a functional layer,
wherein the polyamide-based film comprises a polyamide-based polymer, and
when the polyamide-based film is placed on a surface light source, light is irradiated from the surface light source, and the luminance value (L 0 ) measured in the normal direction of the surface light source is 100%, the luminance value (L 50 ) measured in the direction of 50° from the normal direction of the surface light source is 25% or more,
wherein the polyamide-based film further comprises a filler,
wherein the filler comprises barium sulfate,
wherein the content of the filler is 100 to 3,000 ppm based on the total weight of the solids content of the polyamide-based polymer, and
wherein the content of the residual solvent in the polyamide-based film is 1,500 ppm or less,
wherein the molar ratio of an imide-based repeat unit and an amide-based repeat unit in the polyamide-based polymer is 0:100 to 25:75, and wherein the polyamide-based film has an in-plane retardation of 800 nm or less and a thickness direction retardation of 5,000 nm or less.