Patent ID: 8277950

Claim:
A laminated optical film comprising: a first retardation film including a stretched homo polypropylene resin having an isotactic index more than 85 percent, wherein the homo polypropylene resin has a melt flow rate in the range of 1 to 15 g/10 min and where at least the first retardation film is made by stretching an unstretched film, the unstretched film is made by melting, mixing, and extruding the homo polypropylene resin, and quickly casting the homo polypropylene resin by a cast drum where the cast drum has a surface temperature in the range of 5 to 35 degrees Celsius, and wherein a value subtracting an average in-plane retardation value of the retardation film from the in-plane retardation value at the retardation film is in a range of ±5 nm, wherein the in-plane retardation value is defined by the following: Re =( Nx−Ny )* D [Formula 1] where Nx is a refractive index in a direction of an axis representing a maximum refractive index, Ny is a refractive index of a direction perpendicular to the axis, and D is a thickness (nm) of the retardation film, and wherein the retardation film has a zero wavelength dispersibility where a retardation value increases or decreases as a wavelength of a transmitted light is longer, the zero wavelength dispersibility having a maximum or minimum wavelength dispersibility ratio in a range of 1±0.1, wherein the wavelength dispersibility ratio is defined by the following formula: Wavelength Dispersibility Ratio= Re/Re (550) [Formula 2] where Re is an in-plane retardation value in the wavelength of a visible region (400 nm to 800 nm) and Re(550) is an in-plane retardation value at the wavelength of 550 nm; and a second retardation film laminated on the first retardation film, wherein the second retardation film has a negative wavelength dispersibility where a retardation value decreases as a wavelength of a transmitted light is longer, the negative wavelength dispersibility having a maximum or minimum wavelength dispersibility ratio beyond a range of 1±0.1, and wherein the laminated retardation film has a positive wavelength dispersibility where a retardation value increases as the wavelength of a transmitted light is longer, the positive wavelength dispersibility having a maximum or minimum wavelength dispersibility ratio beyond a range of 1±0.1, wherein the wavelength dispersibility ratio is defined by Formula 2.