US 11,745,470 B2
Polyester film and flexible display device comprising the same
Gun Uk Kim, Gyeonggi-do (KR); Young Min Heo, Gyeonggi-do (KR); Sechul Lee, Gyeonggi-do (KR); and Sang Min Choi, Gyeonggi-do (KR)
Assigned to SK microworks Co., Ltd., Gyeonggi-do (KR)
Filed by SK microworks Co., Ltd., Gyeonggi-do (KR)
Filed on Apr. 30, 2020, as Appl. No. 16/863,602.
Claims priority of application No. 10-2019-0053677 (KR), filed on May 8, 2019.
Prior Publication US 2020/0353734 A1, Nov. 12, 2020
Int. Cl. B32B 17/10 (2006.01); B32B 27/36 (2006.01); H05K 5/00 (2006.01); H05K 5/03 (2006.01); B32B 27/08 (2006.01); B32B 27/28 (2006.01); C08J 5/18 (2006.01); C08G 63/06 (2006.01)
CPC B32B 17/10 (2013.01) [B32B 27/08 (2013.01); B32B 27/281 (2013.01); B32B 27/36 (2013.01); C08G 63/065 (2013.01); C08J 5/18 (2013.01); H05K 5/0017 (2013.01); H05K 5/03 (2013.01); B32B 2307/412 (2013.01); B32B 2457/20 (2013.01); C08J 2367/03 (2013.01)] 7 Claims
OG exemplary drawing
 
1. A polyester film,
which withstands 200,000 times or more of repeated folding at an angle of 135° until it is broken and satisfies the following relationship (1):
V2/V1≤1.2  (1)
wherein V1 and V2 are the deformed dimensions (mm) as compared with the initial dimensions upon 10 times of repetition of a procedure in which a film is strained by 2 mm as compared with the initial dimension in an in-plane first direction and in an in-plane second direction perpendicular to the first direction, respectively, and maintained for 10 seconds, and the film is then relaxed and maintained for 10 seconds,
wherein the ratio of V2/V1 is 1.12 or more,
wherein the polyester film is biaxially stretched in the in-plane first direction and in the in-plane second direction,
wherein the stretching ratio in the in-plane direction is 3.3 to 3.5 and the stretching ratio in the in-plane second direction is 3.5 to 3.8,
wherein the ratio (d2/d1) of the stretching ratio in the in-plane second direction (d2) to the stretching ratio in the in-plane first direction (d1) is 1.05 to 1.1,
wherein the polyester film has a thickness direction retardation (Rth) of 5,000 nm to 16,000 nm,
wherein the polyester film has an in-plane retardation (Ro) of 1,200 nm or less, and
wherein the polyester film comprises a polyester resin, and the polyester resin is a polyethylene terephthalate (PET) resin, wherein V2 is 0.7 mm or less, and wherein the polyester film is applied to a cover of a flexible display device.