Retardation film, laminated polarizing film, and liquid crystal display device

• US 8,203,676 B2
• Filed: 05/30/2008
• Issued: 06/19/2012
• Est. Priority Date: 06/01/2007
• Status: Expired due to Fees

• Current Assignee: Teijin Limited
• Original Assignee: Teijin Limited
• Inventors: Uchiyama, Akihiko, Ono, Yuhei, Matsuo, Jyuhou, Kitazawa, Satoshi
• Primary Examiner(s): Wong, Tina
• Application Number:
  US12/602,595
• Publication Number:
  US 20100283949A1
• Time in Patent Office: 1,481 Days
• Field of Search: None
• US Class Current: 349/117
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02F 1/133634 the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis
• CPC Class Codes: G02F 1/133637 characterised by the wavelength dispersion
• CPC Class Codes: G02F 2201/16 series; tandem
• CPC Class Codes: G02F 2202/40 Materials having a particular birefringence, retardation

Abstract

The present invention provides a retardation film which can remarkably improve the controllability of retardation, and can also sufficiently control the wavelength dependency of retardation. The retardation film of the present invention can achieve a widening of the viewing angle at a high degree, when it is applied to a liquid crystal display device. Further, the present invention provides a laminated polarizing which comprises the retardation film and enables widening the viewing angle. Furthermore, the present invention provides a liquid crystal display device having high performance, especially a widened viewing angle. The retardation film of the present invention comprises a structural body which simultaneously has form birefringence and molecular-orientation birefringence. Specifically, the retardation film comprises a periodic structure (13) having a unit of at least two layers (11, 12) having different average refractive indices from each other, and at least one of the at least two layers is a layer having optical anisotropy due to molecular-orientation birefringence.

Claims

1. A retardation film,

wherein the film comprises a periodic structure which has a unit of at least two layers having different average refractive indices from each other,

wherein the periodic structure exhibits form birefringence, and

wherein at least one layer of the at least two layers is a layer (A) having optical anisotropy due to molecular-orientation birefringence.

2. The retardation film according to claim 1, wherein the layer (A) having optical anisotropy due to molecular-orientation birefringence has optical anisotropy within a plane due to molecular-orientation birefringence.

3. The retardation film according to claim 1, wherein the layer (A) having optical anisotropy due to molecular-orientation birefringence is a layer (a) having negative optical anisotropy due to molecular-orientation birefringence.

4. The retardation film according to claim 1, wherein at least one other layer of the at least two layers is a layer (i) having approximate optical isotropy or a layer (b) having negative optical anisotropy due to molecular-orientation birefringence.

5. The retardation film according to claim 1, wherein the optical thickness (nd (nm)) of each layer of the unit in the periodic structure is λ

/5 or less.

6. The retardation film according to claim 1, wherein the number of layers constituting the periodic structure is from 100 to 30000.

7. The retardation film according to claim 4, wherein the periodic structure satisfies the following formula (2):

0.001<

|δ

n|<

0.5 

 

(2)

(wherein, δ

n represents a difference between an average refractive index of the layer (a) having negative optical anisotropy and an average refractive index of the layer (i) having approximate optical isotropy or the layer (b) having negative optical anisotropy).

8. The retardation film according to claim 4, wherein the layer (a) having negative optical anisotropy and/or the layer (b) having negative optical anisotropy satisfies the following formula (1):

0.0001<

|n_nx−

n_ny|<

0.1 

 

(1)

(wherein,

n_nx;

the three-dimensional refractive index in the x-axis direction of the layer (a) having negative optical anisotropy or the layer (b) having negative optical anisotropy;

n_y;

the three-dimensional refractive index in the y-axis direction of the layer (a) having negative optical anisotropy or the layer (b) having negative optical anisotropy;

x axis;

the slow axis of the periodic structure within a plane of the periodic structure;

y axis;

the axis perpendicular to the x axis within a plane of the periodic structure).

9. The retardation film according to claim 1, wherein an orientation index in a thickness direction (N_Z (λ

)) of the periodic structure satisfies the following formula (5);

10. The retardation film according to claim 1, wherein molecular-orientation birefringence is exhibited by a molecular orientation of a polymer constituting the layer (A) having optical anisotropy.

11. The retardation film according to claim 3, wherein the layer (a) having negative optical anisotropy comprises a polymer having negative molecular polarizability anisotropy.

12. The retardation film according to claim 4, wherein the layer (i) having approximate optical isotropy is made of a polymer.

13. The retardation film according to claim 1, wherein an in-plane retardation value (R (nm)) of the periodic structure satisfies the following formula (6):

10 nm<

R<

1000 nm 

 

(6).

14. The retardation film according to claim 1, wherein molecular-orientation birefringence is exhibited by stretching.

15. The retardation film according to claim 1, wherein the retardation film is obtained by forming a multilayer film by multilayer melt extrusion of polymers and then stretching the multilayer film.

16. The retardation film according to claim 1, wherein an absolute value of a photoelastic coefficient is 15×

10<sup>−

12</sup> Pa<sup>−

1</sup> or less.

17. The retardation film according to claim 1, wherein the retardation film has a protective film (X) laminated on the both sides thereof, and wherein the protective film (X) is made of a thermoplastic resin composition (P) having a rupture strength of 10 to 50 MPa, a rupture elongation of 300 to 1500%, a surface impact fracture energy of 5×

10<sup>−

4</sup>J/μ

m or more, and a dynamic storage elastic modulus and a dynamic loss elastic modulus of 1×

10⁵ to 2×

10⁸ Pa at −

40°

C. and a frequency of 1 Hz, and is approximately optically isotropic.

18. The retardation film according to claim 1, wherein the layer (A) having negative optical anisotropy due to molecular-orientation birefringence is made of a styrene resin comprising a copolymer of styrene and maleic anhydride at a styrene/maleic anhydride copolymerization molar ratio of 70/30 to 86/14, and has a photoelastic coefficient of 8×

10<sup>−

12</sup> Pa<sup>−

1</sup> or less.

19. The retardation film according to claim 1, wherein the retardation film has observation wavelengths λ

(nm) and λ

′

(nm) (400 nm≦

λ

<

λ

′

≦

700 nm) satisfying the following relationship;

|{Rth(λ

)/Rth(λ

′

)}−

{R(λ

)/R(λ

′

)}|≧

0.1.

20. The retardation film according to claim 1, wherein the retardation film has observation wavelengths λ

(nm) and λ

′

(nm) (400 nm≦

λ

<

λ

′

≦

700 nm) satisfying the following relationship;

one of {R(λ

)/R(λ

′

)} and {Rth(λ

)/Rth(λ

′

)} is less than one, and the other is more than one.

21. The retardation film according to claim 1,

wherein the layer (A) having optical anisotropy due to molecular-orientation birefringence is a layer (a) having negative optical anisotropy due to molecular-orientation birefringence, and at least one other layer of the at least two layers is a layer (i) having approximate optical isotropy,

wherein the layer (a) having negative optical anisotropy and the layer (i) having approximate optical isotropy have optical anisotropies within planes due to molecular-orientation birefringence, and

wherein the slow axis of the layer (a) having negative optical anisotropy and the slow axis of the layer (i) having approximate optical isotropy are arranged in approximately perpendicular or approximately parallel to each other.

22. The retardation film according to claim 1,

wherein the layer (A) having optical anisotropy due to molecular-orientation birefringence is a layer (a) having negative optical anisotropy due to molecular-orientation birefringence, and at least one other layer of the at least two layers is a layer (b) having negative optical anisotropy due to molecular-orientation birefringence, and the layer (a) having negative optical anisotropy and the layer (b) having negative optical anisotropy have optical anisotropies within planes due to molecular-orientation birefringence, and

wherein the slow axis of the layer (a) having negative optical anisotropy and the slow axis of the layer (b) having negative optical anisotropy are arranged in approximately parallel to each other.

23. The retardation film according to claim 1, wherein the periodic structure comprises a unit of a layer (a) having negative optical anisotropy, and a layer (i) having approximate optical isotropy or a layer (b) having negative optical anisotropy, and

wherein when the periodic structure comprises a unit of the layer (a) having negative optical anisotropy and the layer (i) having approximate optical isotropy, the following formulae (3) and (4) are satisfied, and when the periodic structure comprises a unit of the layer (a) having negative optical anisotropy and the layer (b) having negative optical anisotropy, the following formulae (3), (4) and (4′

) are satisfied;

24. The retardation film according to claim 1, wherein the periodic structure comprises a unit of a layer (a) having negative optical anisotropy, and a layer (i) having approximate optical isotropy or a layer (b) having negative optical anisotropy, and has observation wavelengths λ

(nm) and λ

′

(nm) (400 nm ≦

λ

<

λ

′

≦

700 nm) satisfying the following formula (200);

25. The retardation film according to claim 1, wherein the periodic structure comprises a unit of a layer (a) having negative optical anisotropy, and a layer (i) having approximate optical isotropy or a layer (b) having negative optical anisotropy, and has observation wavelengths λ

(nm) and λ

′

(nm) (400 nm ≦

λ

<

λ

′

≦

700 nm) satisfying that one of the following formulae (100) and (100′

) is less than one, and the other is more than one;

26. A laminated polarizing film, wherein the laminated polarizing film is a laminate of the retardation film of claim 1 and a polarizing film.

27. A liquid crystal display device, provided with the retardation film of claim 1.