Polarizing plate protective film, dope composition, method for manufacturing polarizing plate protective film, polarizing plate, and liquid crystal display device

A dope composition, containing:

• an acrylic resin,
• wherein the acrylic resin includes a methyl methacrylate unit a,
• a mass fraction of an alkyl (meth)acrylate unit b other than methyl methacrylate is less than 5 mass %,
• a weight average molecular weight is 250,000 to 4,000,000, and
• a weight decreasing amount at the time of being heated at 140° C. for 1 hour is less than or equal to 0.5%.

A method for manufacturing a polarizing plate protective film, comprising:

• a film forming step of forming a film by casting a solution in which an acrylic resin is dissolved in a solvent onto a support and by drying the solution, and of peeling off the film;
• a first stretching step of stretching the film in a longitudinal direction;
• and
• a second stretching step of stretching the film in a width direction,
• wherein the acrylic resin includes a methyl methacrylate unit a,
• a mass fraction of an alkyl (meth)acrylate unit b other than methyl methacrylate is less than 5 mass %,
• a weight average molecular weight is 250,000 to 4,000,000,
• a weight decreasing amount at the time of being heated at 140° C. for 1 hour is less than or equal to 0.5%002C
• when a residual volatile content of the film is set to A1 and a surface temperature of the film is set to T1 in the first stretching step, and a residual volatile content of the film is set to A2 and a surface temperature of the film is set to T2 in the second stretching step, conditions of Expressions (1) and (2) described below are satisfied, and
• unit of A1 and A2 is %, and unit of T1 and T2 is ° C.
• T1≦170−2.8A1 Expression (1)
• T2≦170−2.8A2 Expression (2)