Polyester film for optical application
Disclosed is a polyester film for optical applications, and more specifically to a polyester film having refractive index of 1.6 to 1.7 and a film having refractive index of 1.4 to 1.6 on both surfaces of the polyester film, wherein a thickness of each coating layer is 0.03 to 0.1 μm and total light transmittance of the entire film is 93% or more. The polyester film according to the embodiment has total light transmittance higher than the polyester film without the coating layer and is more suitable to use the polyester film for optical applications due to the excellent adhesive strength between the polyester film and layer for the post-processing working.
1. A coated polyester film for optical applications comprising
a polyester film having refractive index of 1.6 to 1.7;
a first coating layer directly formed on one side of the polyester film and having refractive index 1.5 to 1.55; and
a second coating layer directly formed on the opposite side of the polyester film and having refractive index 1.4 to 1.48,
wherein a difference in refractive index between each coating layer and the polyester film is 0.05 or more,
a thickness of each coating layer is 0.03 to 0.1 μm, total light transmittance of the entire coated polyester film is 93% or more, and
the first coating layer is formed of a polyurethane resin and the second coating layer is formed of an acrylic resin.
2. The polyester film for optical applications according to claim 1 , wherein, any one of the coating layers further comprises components selected from an anti-static agent, ultraviolet stabilizer, waterproof agent, slip agent, and thermal stabilizer.
3. The polyester film for optical applications according to claim 1 , wherein any one of the coating layers further comprises a fluorescent whitening agent.
4. The polyester film for optical applications according to claim 1 , wherein the polyester film includes a filler.
5. The polyester film for optical applications according to claim 4 , wherein the filler is silica having an average particle size of 0.1 to 10 μm.
6. The polyester film for optical applications according to claim 1 , wherein the polyester film is a polyethyleneterephthalate film.
7. A method of manufacturing a coated polyester film, said method comprising:
extruding a polyester sheet;
stretching the polyester sheet to a machine direction (MD) wherein the refractive index of the polyester sheet is 1.6 to 1.7;
forming a first coating layer by directly applying a coating liquid containing a polyurethane resin on one side of the polyester sheet;
forming a second coating layer by directly applying a coating liquid containing an acrylic resin on the opposite side of the polyester sheet;
stretching thus both-side coated polyester sheet in a width direction (Transverse Direction; TD) vertical to the machine direction at a stretching temperature or more in the machine direction; and
heat setting the stretched coated polyester sheet,
wherein the first coating layer has refractive index of 1.5-1.55,
wherein the second coating layer has a refractive index of 1.4-1.48,
wherein a difference in refractive index between each coating layer and the polyester sheet is 0.05 or more,
a thickness of each coating layer is 0.03 to 0.1 μm, total light transmittance of the entire coated polyester film is 93% or more.
8. The method of manufacturing a polyester film for optical applications according to claim 7 , wherein said refractive index of the polyester film without the coating layer is 1.6 to 1.7.
9. The method of manufacturing a polyester film for optical applications according to claim 7 , wherein said coating solution further includes any one component selected from an anti-static agent, ultraviolet stabilizer, waterproof agent, slip agent, and thermal stabilizer.
10. The method of manufacturing a polyester film for optical applications according to claim 7 , wherein said coating solution further include a fluorescent whitening agent.
11. The method of manufacturing a polyester film for optical applications according to claim 7 , wherein said polyester sheet includes a filler.
12. The method of manufacturing a polyester film for optical applications according to claim 11 , wherein said filler is silica having an average particle size of 0.1 to 10 μm.