Optical compensation film
A copolymer for optical compensation film showing a negative orientation birefringence, having excellent transparency, heat resistance, film strength, and optical properties, and is capable of obtaining a beautiful film suitable for an optical compensation film is provided. A copolymer for optical compensation film, containing: 45 to 80 mass % of an aromatic vinyl monomer unit; 5 to 45 mass % of a (meth)acrylic acid ester monomer unit; and 5 to 20 mass % of an unsaturated dicarboxylic acid anhydride monomer unit; wherein the copolymer has an average number molecular weight (Mn) of 5.5×10 4 to 9×10 4 and a weight average molecular weight (Mw) of 14×10 4 to 20×10 4 ; and the copolymer has a haze of 1% or less, the haze being measured with a 2 mm thick sample in accordance with ASTM D1003, is provided.
1. An optical compensation film, wherein
the optical compensation film has a refractive index profile of nx>nz>ny and is obtained by laminating Film A and Film B, Film A being obtained by stretching a thermoplastic resin film showing a negative orientation birefringence, Film B being obtained by stretching a thermoplastic resin showing a positive orientation birefringence; and
the thermoplastic resin film for Film A
comprises a copolymer, wherein
the copolymer comprises:
45 to 80 mass % of an aromatic vinyl monomer unit;
5 to 45 mass % of a (meth)acrylic acid ester monomer unit; and
5 to 20 mass % of an unsaturated dicarboxylic acid anhydride monomer unit; wherein
the copolymer has an average number molecular weight (Mn) of 5.5×10 4 to 9×10 4 and a weight average molecular weight (Mw) of 14×10 4 to 20×10 4 ; and
the copolymer has a haze of 1% or less, the haze being measured with a 2 mm thick sample in accordance with ASTM D1003, wherein
Film A and Film B are laminated so that slow axes thereof cross at right angles, allowing in-plane phase difference to satisfy the relationship of Re(450)<Re(590)<Re(750), Re(450), Re(590), and Re(750) being in-plane phase difference for the wavelengths of 450 nm, 590 nm, and 750 nm, respectively.
2. The optical compensation film of claim 1 , wherein Film A is obtained by stretching a film manufactured by melt extrusion.
3. The optical compensation film of claim 1 , wherein Nz coefficient is 0.4 to 0.6.
4. The optical compensation film of claim 1 , wherein
the copolymer comprises:
55 to 75 mass % of the aromatic vinyl monomer unit;
15 to 35 mass % of the (meth)acrylic acid ester monomer unit; and
10 to 15 mass % of the unsaturated dicarboxylic acid anhydride monomer unit.
5. The optical compensation film of claim 1 , wherein the aromatic vinyl monomer unit is a styrene unit.
6. The optical compensation film of claim 1 , wherein the (meth)acrylic acid ester monomer unit is a methyl methacrylate unit.
7. The optical compensation film of claim 1 , wherein the unsaturated dicarboxylic acid anhydride monomer unit is a maleic acid anhydride unit.