Optical film and liquid crystal display using the same

A polarizing plate comprising a first protective film for the polarizing plate, a polarizing element, and a second protective film for the polarizing plate,

• wherein at least one of the first protective film and the second protective film comprises a fatty acid cellulose ester film having an acetyl group and a propionyl group,
• a sum of degree of acetyl substitution (DSac) and degree of propionyl substitution (DSpr) of the fatty acid cellulose ester of the fatty acid cellulose ester film being 2.8 or less, a retardation value (Rt value) in the thickness direction defined by Formula 1 being 60 to 300 nm,
• Rt value={(nx+ny)/2 −nz}×d Formula 1
• wherein nx represents the refractive index of the fatty acid cellulose ester film in the direction giving maximum refractive index in the plane of the fatty acid cellulose ester film, ny represents the refractive index of the fatty acid cellulose ester film in the direction perpendicular to the direction giving maximum refractive index in the plane of the fatty acid cellulose ester film, nz represents the refractive index of the fatty acid cellulose ester film in the thickness direction, and d (nm) represents the thickness of the fatty acid cellulose ester film.

A liquid crystal display comprising a first polarizing plate, a liquid crystal cell, and a second polarizing plate provided at an inner portion with respect to the first polarizing plate and the liquid crystal cell, wherein

• the first polarizing plate has a first polarizing element, a first protective film provided on a surface of the first polarizing element which surface is not faced to the liquid crystal cell, and a second protective film provided on a surface of the first polarizing element which surface is faced to the liquid crystal cell,
• the second polarizing plate has a second polarizing element, a third protective film provided on a surface of the second polarizing element which surface is faced to the liquid crystal cell, and a fourth protective film provided on a surface of the second polarizing element which surface is not faced to the liquid crystal cell,
• wherein at least one of the first protective film, the second protective film, the third protective film and the fourth protective film comprises a fatty acid cellulose ester film having an acetyl group and a propionyl group,
• a sum of degree of acetyl substitution (DSac) and degree of propionyl substitution (DSpr) of the fatty acid cellulose ester of the fatty acid cellulose ester film being 2.8 or less, a retardation value (Rt value) in the thickness direction defined by Formula 1 being 60 to 300 nm,
• Rt value={(nx+ny)/2 −nz}×d Formula 1
• wherein nx represents the refractive index of the fatty acid cellulose ester film in the direction giving maximum refractive index in the plane of the fatty acid cellulose ester film, ny represents the refractive index of the fatty acid cellulose ester film in the direction perpendicular to the direction giving maximum refractive index in the plane of the fatty acid cellulose ester film, nz represents the refractive index of the film in the thickness direction, and d (nm) represents the thickness of the fatty acid cellulose ester film.