Polyester film and use thereof
In order to provide a foldable display that is suitable for mass production and that has no risk of image distortion at its folding portion after the display is repeatedly folded, the invention provides a polyester film for foldable displays in which no cracks occurs in the folding portion. In particular, the invention provides a polyester film for a foldable display, the film having a thickness of 10-125 μm and a high-temperature hold angle in a bending direction of 70° or more, wherein the high-temperature hold angle refers to an angle of a crease formed after fixing the film at a heating temperature of 85° C. for 18 hours in such a manner that a strain of 1.7% is applied to both surfaces of a bent portion of the film, and the bending direction refers to a direction that is orthogonal to a folding portion.
1 . A polyester film for a foldable display, wherein the polyester film is a single-layer film comprising 95 weight % or more of a polyethylene-2,6-naphthalene dicarboxylate homopolymer satisfying the following conditions:
(1) having a refractive index in a bending direction of 1.644 to 1.730, and
(2) having a refractive index in a folding direction of 1.770 to 1.854, and
(3) having a thickness of 10 μm or more and 125 μm or less and a high-temperature hold angle in a bending direction of 70° or more, wherein the high-temperature hold angle refers to an angle of a crease formed after fixing the polyester film at a heating temperature of 85° C. for 18 hours in such a manner that a strain of 1.7% is applied to both surfaces of the polyester film at a bent portion, and the bending direction refers to a direction that is orthogonal to a folding portion.
2 . The polyester film for a foldable display according to claim 1 , having a density of 1.349 g/cm 3 or more.
3 . The polyester film for a foldable display according to claim 2 , comprising an easy-to-adhere layer on at least one surface of the polyester film.
4 . A foldable display comprising the polyester film for a foldable display of claim 3 , the polyester film being disposed as a back protection film, wherein the polyester film is a single continuous polyester film placed through the folding portion of the foldable display.
5 . A mobile device comprising the foldable display of claim 4 .
6 . A foldable display comprising the polyester film for a foldable display of claim 2 , the polyester film being disposed as a back protection film, wherein the polyester film is a single continuous polyester film placed through the folding portion of the foldable display.
7 . A mobile device comprising the foldable display of claim 6 .
8 . The polyester film for a foldable display according to claim 1 , comprising an easy-to-adhere layer on at least one surface of the polyester film.
9 . A foldable display comprising the polyester film for a foldable display of claim 8 , the polyester film being disposed as a back protection film, wherein the polyester film is a single continuous polyester film placed through the folding portion of the foldable display.
10 . A mobile device comprising the foldable display of claim 9 .
11 . A foldable display comprising the polyester film for a foldable display of claim 1 , the polyester film being disposed as a back protection film, wherein the polyester film is a single continuous polyester film placed through the folding portion of the foldable display.
12 . A mobile device comprising the foldable display of claim 11 .