Retardation film, polarizing plate and liquid crystal display device

1. A stretched retardation film, containing:

a cellulose ester having a total acyl substitution degree of 2.1 to 2.55, and an acetyl substitution degree of 1.0 to 2.1; and

an esterified compound in which all or a part of OH groups in a compound (B) are esterified, wherein the compound (B) consists of two to three of at least one type of a furanose structure and a pyranose structure which are bonded in the compound (B),

wherein the stretched retardation film has a thickness of 30 to 80 μm and is stretched 1.0 to 2.0 times in a width direction so as to exhibit the following retardation values for light having a wavelength of 590 nm under a condition of a temperature of 23° C. and a humidity of 55% RH:

an in-plane retardation value Ro represented by a Formula (i) is 20 to 80 nm,

a thickness-direction retardation value Rt represented by a Formula (ii) is 100 to 250 nm and

a ratio of Rt/Ro is 2.0 to 5.0,

Ro =( nx−ny )× d,   Formula (i):

Rt =(( nx+ny )/2− nz )× d,   Formula (ii):

wherein nx represents a refractive index in a film in-plane slow axis direction, ny represents a refractive index in a direction perpendicular to the slow axis, nz represents a refractive index in a film thickness direction, and d represents a film thickness in nm,

wherein the retardation film has a variation of 3 to 20 nm in a thickness direction retardation value due to a humidity change between 20% RH and 80% RH at a temperature of 23° C. when the film has a thickness of 30 to 80 μm.

2. The stretched retardation film of claim 1 , wherein the total acyl group substitution degree is 2.2 to 2.55.

3. The stretched retardation film of claim 1 , wherein the retardation film contains 5 to 30% by weight of the esterified compound.

4. The stretched retardation film of claim 1 , wherein the compound (B) is a compound having the furanose structure and the pyranose structure.

5. The stretched retardation film of claim 1 , wherein the compound (B) is lactose, sucrose, nystose, 1F-fructosylnystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose.

6. The stretched retardation film of claim 5 , wherein the compound (B) is sucrose.

7. A polarizing plate, comprising:

a polarizer; and

the stretched retardation film of claim 1 pasted on at least one surface of the polarizer.

8. A liquid crystal display device comprising:

a liquid crystal cell and

the polarizing plate of claim 7 .

9. A liquid crystal display device, comprising:

a liquid crystal cell and

the stretched retardation film of claim 1 .

10. The liquid crystal display device of claim 9 , wherein the liquid crystal cell is a VA type liquid crystal cell.