Multilayer optical film having high heat resistance and method for manufacturing the same

A method for manufacturing a multilayer optical film comprising the step of:

• (a) melting extrusion a first resin comprising a crystalline naphthalene dicarboxylic-acid polyester and a second resin comprising PETG respectively and then alternately laminating the first resin and the second resin;
• and
• (b) elongating the laminated sheet in the step (a) and then thermosetting the laminated sheet,
• wherein the crystalline naphthalene dicarboxylic-acid polyester of the first resin is polyethylenenaphthalate (PEN) manufactured by polycondensation of naphthalatedicarboxylic-acid and ethyleneglycol,
• wherein a glass transfer temperature of the second resin is 100 to 140° C.,
• wherein the PETG of the second resin comprises an amount of cyclohexanedimethanol (CHDM) of 60% to 70%
• wherein laminated sheet in the step (b) is elongated in at least one direction among a longitudinal direction or a vertical direction, and
• wherein a temperature of the melted extrusion is 280 to 300° C.