Polymer film and preparation method thereof
Embodiments relate to a polymer film that is excellent in folding characteristics and transparency and maintains excellent mechanical properties even after repeated elongation and shrinkage in the elastic region, a process for preparing the same, and a front panel and a display device comprising the same. The polymer film comprises a polymer resin selected from the group consisting of a polyamide-based resin and a polyimide-based resin and has an MOR 0/9 of Equation A of 2% or less.
1. A polymer film for a display, which comprises a polymer resin selected from the group consisting of a polyamide-based resin and a polyimide-based resin, and which has an MOR 0/9 of the following Equation A of 2% or less, wherein a content of a residual solvent in the polymer film is 2,000 ppm or less:
MOR
0
/
9
(
%
)
=
❘
"\[LeftBracketingBar]"
MO
0
-
MO
9
❘
"\[RightBracketingBar]"
MO
9
×
100
[
Equation
A
]
in Equation A, MO0 refers to the initial modulus, and MO9 refers to the modulus measured after elongation and shrinkage are repeated 9 times wherein each elongation is 2%,
wherein the polymer resin comprises an imide-based repeat unit, an amide-based repeat unit or combinations thereof, with the proviso that a molar ratio of the imide-based repeat unit and the amide-based repeat unit ranges from 0:100 to 35:65,
wherein the polymer film for a display has a dMO 0/9 of the following Equation B of 0.18 GPa or less:
dMO 0/9 (GPa)=|MO0−MO9| [Equation B]
in Equation B, MO0 refers to the initial modulus, and MO9 refers to the modulus measured after elongation and shrinkage are repeated 9 times wherein each elongation is 2%, and
wherein the polymer film for a display has an IRS of the following Equation C of 100 or less:
IRS
=
IM
1
mol
+
RS
20
ppm
[
Equation
C
]
in Equation C, IM stands for the number of moles of the imide-based repeat unit when the total number of moles of the imide-based repeat unit and the amide-based repeat unit in the film is 100; and RS stands for the content (ppm) of the residual solvent in the film.
2. The polymer film for a display of claim 1 , wherein when the initial modulus is MO0, and the modulus measured after elongation and shrinkage are repeated n times wherein each elongation is 2% is MOn, the standard deviation in modulus calculated based on a total of 10 values, MO0 to MO9, is 0.06 GPa or less.
3. The polymer film for a display of claim 1 , which has an initial modulus (MO0) of 5.0 GPa or more, and a modulus (MO9) of 5 GPa or more when measured after elongation and shrinkage are repeated 9 times wherein each elongation is 2%.
4. The polymer film for a display of claim 1 , wherein the polymer resin comprises an imide-based repeat unit and an amide-based repeat unit, and the polymer film has an MPA of the following Equation D of 2% or less:
MPA (%)=MOR 0/9 /AM [Equation D]
in Equation D, AM stands for the number of moles of the amide-based repeat unit when the total number of moles of the imide-based repeat unit and the amide-based repeat unit in the film is 1.
5. The polymer film for a display of claim 1 , which has a transmittance of 80% or more, a haze of 1% or less, and a yellow index of 3 or less.
6. The polymer film for a display of claim 1 , which has an S 1 of the following Equation (1) of 40% or less, an S 2 of the following Equation (2) of 55% or less, and an S 3 of the following Equation (3) of 80% or less:
S 1 (%)=( L 1 %−1%)×100 [Equation (1)]
S 2 (%)={( L 2 %−2%)/2}×100 [Equation (2)]
S 3 (%)={( L 3 %−3%)/3}×100 [Equation (3)]
in Equations (1) to (3),
when the film is elongated, and when the load at the time the length is increased by 1% relative to the initial length is W 1 , the load at the time the length is increased by 2% is W 2 , and the load at the time the length is increased by 3% is W 3 ,
the ratio of the increased length to the initial length is Li % when the load Wi is applied for 1 hour in the longitudinal direction of the film,
the ratio of the increased length to the initial length is L 2 % when the load W 2 is applied for 1 hour in the longitudinal direction of the film, and
the ratio of the increased length to the initial length is L 3 % when the load W 3 is applied for 1 hour in the longitudinal direction of the film.
7. A process for preparing the polymer film of claim 1 , which comprises:
preparing a solution comprising a polymer resin selected from the group consisting of a polyamide-based resin and a polyimide-based resin in an organic solvent;
charging the solution comprising the polymer resin into a tank;
extruding and casting the polymer solution in the tank and then drying it to prepare a gel sheet; and
thermally treating the gel sheet,
wherein the highest temperature in the thermal treatment of the gel-sheet is 300° C. or higher.
8. The process of claim 7 for preparing the polymer film, wherein the thermal treatment is carried out until the content of the residual solvent contained in the film is 2,000 ppm or less.