Polymer film and preparation method thereof
The polymer film according to an embodiment comprises at least one polymer resin selected from the group consisting of a polyamide-based resin, a polyimide-based resin, and a polyamide-imide-based resin, and has a haze of 0.6% or less and an in-plane retardation within a specific range for each wavelength band in the visible light region. The polymer film, which has an in-plane retardation within a specific range for each wavelength band in the visible light region, is excellent in transparency and optical properties, and it can remarkably reduce the rainbow phenomenon and improve the reflection appearance.
1. A polymer film, which comprises at least one polymer resin selected from the group consisting of a polyamide-based resin, a polyimide-based resin, and a polyamide-imide-based resin, which has a glossiness of 90 GU to 120 GU,
wherein the polymer film has a haze of 0.6% or less and an in-plane retardation deviation ratio (A) represented by the following Equation 1 of −0.5 or more, and
R1 in the following Equation 1 is 1,000 nm or less:
A =( R 2− R 1)/(λ2−λ1) [Equation 1]
in the above, λ1 is 400 nm, λ2 is 800 nm, R1 is the in-plane retardation of the polymer film measured with light having a wavelength of λ 1 , and R2 is the in-plane retardation of the polymer film measured with light having a wavelength of λ 2 .
2. The polymer film of claim 1 , wherein A is −0.4 or more, R1 is 400 nm or less, and R2 is 300 nm or less.
3. The polymer film of claim 1 , wherein R1 is larger than R2.
4. The polymer film of claim 1 , which has an in-plane retardation deviation gap (G) represented by the following Equation 2 of 100 nm or less:
G=|R 3−{ R 1+ A (λ3−λ1)}| [Equation 2]
in the above, λ3 is 550 nm, and R3 is the in-plane retardation of the polymer film measured with light having a wavelength of λ3.
5. The polymer film of claim 1 , which comprises the at least one polymer resin selected from the group consisting of a polyamide-based resin, a polyimide-based resin, and a polyamide-imide-based resin in an amount of 90% by weight or more based on the total weight of the polymer film.
6. The polymer film of claim 1 , which has a light transmittance at a wavelength of 550 nm of 80% or more, a yellow index of 3 or less, and a thickness of 30 μm to 100 μm.
7. The polymer film of claim 1 , which has a refractive index of 1.6 to 1.7.
8. The polymer film of claim 1 , which has an Ra represented by the following Equation 5 of 1.0 to 1.4 and an Rb represented by the following Equation 6 of 0.7 to 1.0:
Ra=R 450 /R 550 [Equation 5]
Rb=R 650 /R 550 [Equation 6]
in the above, R 450 , R 550 , and R 650 are the in-plane retardations of the polymer film measured with light having a wavelength of 450 nm, 550 nm, and 650 nm, respectively.
9. A process for preparing the polymer film of claim 1 , which comprises:
forming an unstretched sheet from at least one polymer resin selected from the group consisting of a polyamide-based resin, a polyimide-based resin, and a polyamide-imide-based resin;
stretching the unstretched sheet at a stretching ratio of 1.01 to 1.5 in the MD direction or the TD direction; and
heat setting the stretched sheet.
10. The process of claim 9 for preparing the polymer film, wherein the stretching is carried out at a stretching temperature higher or lower than the glass transition temperature (Tg) of the polymer resin by 5° C. to 20° C.