Polarizing plate protective film, polarizing plate, and liquid crystal display

1. A polarizing plate protective film comprising:

a cellulose ester film containing Polymer X and Polymer Y which have no aromatic ring in their molecule and exhibits negative birefringence; and

a hard coat layer on the cellulose ester film;

the cellulose ester film exhibits a retardation value Ro, defined by Expression (I) of 0 to 10 nm and a retardation value Rt, defined by Expression (II), of −20 to 20 nm:

Ro =( nx−ny )× d   Expression (I):

Rt ={( nx+ny )/2 −nz}×d   Expression (II):

wherein nx is a refractive index in a slow axis direction in a plane of the polarizing plate protective film, ny is a refractive index in a direction orthogonal to the slow axis in the plane, nz is a refractive index in a film thickness direction, and d is a film thickness (nm), and

wherein a difference value ΔRt, defined by Expression (III), is less than 15 nm n,

Δ Rt (nm)=Rt(23° C.,80% RH )− Rt (23° C.,20% RH )  Expression (III)

where Rt (23° C., 80% RH) represents a retardation value Rt measured after the cellulose ester film was placed under an environment of 23° C. and 80% RH for 10 hours, and Rt (23° C., 20% RH) represents a retardation value Rt measured after the cellulose ester film was placed under an environment of 23° C. and 20% RH for 10 hours, wherein

Polymer X has a weight average molecular weight of 5000-30000 and is obtained via copolymerization of ethylenically unsaturated monomer Xa having neither an aromatic ring nor a hydrophilic group in the molecule, and ethylenically unsaturated monomer Xb having no aromatic ring but having a hydrophilic group in the molecule; and wherein the Polymer X is represented by Formula (1), and

Polymer Y is represented by Formula (2):

—([CH 2 —C(—R 1 )(—CO 2 R 2 )] m [CH 2 —C(—R 3 )(—CO 2 R 4 —OH)-] n -[Xc] p -  Formula (1):

Ry-[CH 2 —C(—R 5 )(—CO 2 R 6 —OH)-] k -[Yb] q -  Formula (2)

wherein

R 1 , R 3 , and R 5 are H or CH 3 ,

R 2 is an alkyl group of a carbon number of 1-12 or a cycloalkyl group,

R 4 and R 6 are —CH 2 —, —C 2 H 4 —, or —C 3 H 6 —,

Ry is OH, H, or an alkyl group of a carbon number of at most 3,

Xc is a monomer unit polymerizable with Xa or Xb,

Yb is a monomer unit copolymerizable with Ya; and

m, n, k, p, and q are molar composition ratios wherein m≠0, n≠0, k≠0, m+n+p=100, and k+q=100.

2. The polarizing plate protective film described in claim 1 ,

wherein Polymer Y has a weight average molecular weight of 500-3000 and is obtained via polymerization of ethylenically unsaturated monomer Ya having no aromatic ring.

3. The polarizing plate protective film described in claim 1 ,

wherein the cellulose ester film further comprises a polyester which has no aromatic ring in its molecule and exhibits negative birefringence, the polyester is represented by Formula (3) or (4):

B 1 -(G-A-) w G-B 1   Formula (3):

wherein B 1 is a monocarboxylic acid, G is a dihydric alcohol, A is a dibasic acid; B 1 , G and A each contain no aromatic ring, w is a repetition number, and a plurality of B 1 and G may be the same or different:

B 2 -(A-G-) z A-B 2   Formula (4):

wherein B 2 is a monohydric alcohol, G is a dihydric alcohol, A is a dibasic acid; B 2 , G, and A each contain no aromatic ring, z is a repetition number, and a plurality of B 2 and G may be the same or different.

4. The polarizing plate protective film described in claim 1 , wherein the thickness of the hard coat layer is 1-30 μm.

5. A polarizing plate, comprising

a polarizer; and

the polarizing plate protective film described in claim 1 ,

wherein a surface of the polarizing plate protective film opposite to a surface provided with the hard coat layer is pasted on one surface of the polarizer.

6. A liquid crystal display, comprising:

a liquid crystal cell; and

the polarizing plate described in claim 5 .

7. The polarizing plate protective film described in claim 1 , wherein the cellulose ester film has a thickness of 15 to 60 μm.

8. The polarizing plate protective film described in claim 1 , wherein ΔRt is less than 10 nm.

9. The polarizing plate protective film described in claim 1 , wherein the hard coat layer is a cured layer formed by irradiating a curable resin layer with light.