IPS LCD device having a wider viewing angle

1. An in-plane-switching-mode liquid crystal display (IPS LCD) device comprising:

a liquid crystal (LC) layer having a first optical axis;

first and second substrates sandwiching therebetween said LC layer, said first and second substrates being disposed on a light-emitting side and a light-incident side, respectively, of said LCD device;

first and second polarizing films sandwiching therebetween said first and second substrates and said LC layer, said first and second polarizing films having polarization axes extending normal to each other and being disposed on the light-emitting side and the light-incident side, respectively, of said LCD device, said second polarizing film including a first protective layer, a polarization layer and a second protective layer, which are disposed consecutively as viewed from said light-incident side, each of said first and second protective layers having a retardation depending on a thickness of said each of said first and second protective layer; and

an optical compensation layer disposed between said first polarizing film and said second polarizing film, wherein:

said optical compensation layer has a birefringence satisfying the relationship (ns−nz)/(ns−nf)≦0.5, where ns, of and nz are a refractive index along an in-plane slow axis, a refractive index along an in-plane fast axis, and a refractive index along a thickness direction, respectively, of said optical compensation layer;

an angle between said in-plane slow axis of said optical compensation layer and said first optical axis is within ±2 degrees; and

said optical compensation layer has an in-plane retardation N 1 (nm), and said second optical protective layer has a thickness D 1 (μm) satisfying the following relationship:

83.050−0.810× D 1 ≦N 1 ≦228.090−0.74× D 1 ,

in a range of 0<D 1 ≦80.

2. The IPS LCD device according to claim 1 , wherein 0<D 1 ≦40.

3. An in-plane-switching-mode liquid crystal display (IPS LCD) device comprising:

a liquid crystal (LC) layer having a first optical axis;

first and second substrates sandwiching therebetween said LC layer, said first and second substrates being disposed on a light-emitting side and a light-incident side, respectively, of said LCD device;

first and second polarizing films sandwiching therebetween said first and second substrates and said LC layer, said first and second polarizing films having polarization axes extending normal to each other and being disposed on the light-emitting side and the light-incident side, respectively, of said LCD device; and

first and second optical compensation layers disposed between said first polarizing film and said first substrate and between said second polarizing film and said second substrate, respectively, wherein:

each of said first and second optical compensation layers has a birefringence satisfying the relationship (ns−nz)/(ns−nf)≦0.5, where ns, of and nz are a refractive index along an in-plane slow axis, a refractive index along an in-plane fast axis, and a refractive index along a thickness direction, respectively, of said each of said first and second optical compensation layers;

an angle between said in-plane slow axis of said first optical compensation layer and said first optical axis is within ±2 degrees, and an angle between said in-plane slow axis of said second optical compensation layer and said first optical axis is within 90±2 degrees; and

said first and second optical compensation layers have in-plane retardations N 1 (nm) and N 2 (nm), respectively, satisfying the following relationship:

29.87+1.79 N 2 −0.048 N 2 2 +0.001 N 2 3 ≦N 1 ≦187.22−1.66 N 2 +0.0475 N 2 2 −0.0009 N 2 3

in a range of 0.6<N 2 ≦46.

4. The IPS LCD device according to claim 3 , wherein 150≦N 1 ≦185.

5. An in-plane-switching-mode liquid crystal display (IPS LCD) device comprising:

a liquid crystal (LC) layer having a first optical axis;

first and second substrates sandwiching therebetween said LC layer, said first and second substrates being disposed on a light-emitting side and a light-incident side, respectively, of said LCD device;

first and second polarizing films sandwiching therebetween said first and second substrates and said LC layer, said first and second polarizing films having polarization axes extending normal to each other and being disposed on the light-emitting side and the light-incident side, respectively, of the LCD device; and

first and second optical compensation layers disposed between said first polarizing film and said first substrate and between said second polarizing film and said second substrate, respectively, wherein:

each of said first and second optical compensation layers has a birefringence satisfying the relationship (ns−nz)/(ns−nf)≦0.5, where ns, of and nz are a refractive index along an in-plane slow axis, a refractive index along an in-plane fast axis, and a refractive index along a thickness direction, respectively, of said each of said first and second optical compensation layers;

an angle between said in-plane slow axis of each of said first and second optical compensation layers and said first optical axis is within ±2 degrees; and

said first and second optical compensation layers have in-plane retardations N 1 (nm) and N 2 (nm), respectively, satisfying the following relationship:

162.560−8.874 N 2 +2.258 N 2 2 −0.291 N 2 3 +0.0165 N 2 4 −0.000346 N 2 5 ≦N 1 ≦142.465+2.546 N 2 −0.017 N 2 2

in a range of 0.6≦N 2 ≦22;

73.04−0.977 N 2 +0.0220 N 2 2 ≦N 1 142.465+2.546 N 2 −0.017 N 2 2

in a range of 22<N 2 ≦62; and

73.04−0.977 N 2 +0.00220 N 2 2 ≦N 1 ≦1205.596−41.304 N 2 +0.586 N 2 2 −0.0028 N 2 3

in a range of 62<N 2 ≦92.

6. The IPS LCD device according to claim 5 , wherein 150≦N 1 ≦230.

7. An in-plane-switching-mode liquid crystal display (IPS LCD) device comprising:

a liquid crystal (LC) layer having a first optical axis;

first and second substrates sandwiching therebetween said LC layer, said first and second substrates being disposed on a light-emitting side and a light-incident side, respectively, of said LCD device;

first and second polarizing films sandwiching therebetween said first and second substrates and said LC layer, said first and second polarizing films having polarization axes extending normal to each other and being disposed on the light-emitting side and the light-incident side, respectively, of the LCD device; and

first and second optical compensation layers disposed between said first polarizing film and said first substrate and between said second polarizing film and said second substrate, respectively, wherein:

said first optical compensation layer has a birefringence satisfying the relationship (ns 1 −nz 1 )/(ns 1 −nf 1 ) 0.5, where ns 1 , nf 1 and nz 1 are a refractive index along an in-plane slow axis, a refractive index along an in-plane fast axis, and a refractive index along a thickness direction, respectively, of said first optical compensation layer;

said second optical compensation layer has a birefringence satisfying the relationship (ns 2 −nz 2 )/(ns 2 −nf 2 )≦−2, where ns 2 , nf 2 , nz 2 are a refractive index along an in-plane slow axis, a refractive index along an in-plane fast axis, and a refractive index along a thickness direction, respectively, of said second optical compensation layer;

an angle between said in-plane slow axis of said first optical compensation layer and said first optical axis is within ±2 degrees, and said second optical compensation layer has an optical axis substantially normal to a surface of second substrate; and

said first and second optical compensation layers have in-plane retardations N 1 (nm) and N 2 (nm), respectively, satisfying the following relationship:

36.859+7.617 N 2 ≦N 1 ≦168.193+9.783 N 2

in a range of 0<N 2 ≦6.0.