Liquid crystal display with neutral dark state

• US 20050140895A1
• Filed: 12/24/2003
• Published: 06/30/2005
• Est. Priority Date: 12/24/2003
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Watson, Philip E., Ralli, Philip J., Cael, John J.
• Granted Patent: US 7,057,682 B2
• Time in Patent Office: Days
• US Class Current: 349/141
• CPC Class Codes: G02F 1/133528 Polarisers
• CPC Class Codes: G02F 1/134363 for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]

Abstract

A polarizer is used with a liquid crystal display (LCD) cell whose liquid crystal molecules are switched in the plane of the cell. The LCD has birefringent properties that are different from other types of LCD cell and, unlike other types of LCD, the image contrast is maintained and there is little color shift in the dark state when a low birefringence polarizer is used with the SIP LCD cell. In one embodiment, the x-z retardation of the layers between the polarization-sensitive absorbing layer and the LCD is less than 20 nm. In another embodiment, the x-z birefringence is less than 0.0005. The low levels of retardation and birefringence may be achieved by omitting the commonly used cellulose triacetate layer between the polarization-sensitive absorbing layer and the LCD.

Claims

1. A liquid crystal display, comprising:

a switched-in-plane (SIP) liquid crystal display (LCD) cell; and

a first absorbing polarizer disposed on a first side of the LCD cell, the first absorbing polarizer including a layer of polarization-sensitive absorbing material, material layers between the layer of polarization-sensitive absorbing material and the LCD cell being free of cellulose triacetate (TAC).

2. A display as recited in claim 1, wherein the first absorbing polarizer is an intrinsic absorbing polarizer.

3. A display as recited in claim 2, wherein the intrinsic absorbing polarizer is a K-type polarizer.

4. A display as recited in claim 2, wherein the intrinsic absorbing polarizer is a KE-type polarizer.

5. A display as recited in claim 1, wherein the first absorbing polarizer is disposed on a viewing side of the LCD cell.

6. A display as recited in claim 1, wherein the LCD cell is an in-plane switched (IPS) LCD cell.

7. A display as recited in claim 1, further comprising a second absorbing polarizer disposed on a second side of the LCD cell opposite the first side.

8. A display as recited in claim 1, further comprising a light source disposed on an illumination side of the LCD cell.

9. A display as recited in claim 8, further comprising a light guide disposed to direct the light from the light source towards the LCD cell.

10. A display as recited in claim 8, further comprising a transflector disposed between the LCD cell and the light source.

11. A display as recited in claim 8, further comprising at least one light management layer disposed between the LCD cell and the light source.

12. A display as recited in claim 1, further comprising a controller coupled to the LCD cell to control an image imposed by the LCD cell on light passing through the LCD cell.

13. A display as recited in claim 1, wherein the first absorbing polarizer provides a moisture vapor transmission rate of less than about 4.6 gm/m²/day and an oxygen transmission rate of less than about 0.005 ml/m²/day to the LCD cell.

14. A liquid crystal display, comprising:

a switched-in-plane (SIP) liquid crystal display (LCD) cell; and

a first absorbing polarizer, comprising one or more layers including at least an absorbing polarizing layer, disposed on a first side of the LCD cell, the first absorbing polarizer and the LCD cell each lying parallel to an x-y plane defined by orthogonal x- and y-axes, a z-axis being orthogonal to both the x-axis and the y-axis, the first absorbing polarizer defining a transmission polarization direction for light transmitted through the first absorbing polarizer, the transmission polarization direction being parallel to the x-axis, wherein an x-z retardation coefficient, b_{xz total}, is defined for the first absorbing polarizer as

b_{xz total}=Σ

(n_xi−

n_z)1_i,

where n_xi is the refractive index for light polarized parallel to the x-axis in the ith layer of the first absorbing polarizer, n_zi is the refractive index for light polarized parallel to the z-axis in the ith layer of the first absorbing polarizer and lI is the thickness of the ith layer of the first absorbing polarizer in the z-direction, where i is an integer identifying different layers of the first absorbing polarizer, and b_{xz total}=Σ

(n_xi−

n_zi)1_i is less than 20 nm.

15. A display as recited in claim 14, wherein b_{xz total} is less than 10 nm.

16. A display as recited in claim 14, wherein b_{xz total} is less than 5 nm.

17. A display as recited in claim 14, wherein the SIP LCD cell is an in-plane switched (IPS) cell.

18. A display as recited in claim 14, wherein an absolute value of the difference between n_x of the first absorbing polarizing layer and n_z of the first absorbing polarizing layer is less than 0.0005.

19. A display as recited in claim 14, wherein the absorbing polarizer layer comprises an intrinsic absorbing polarizer layer.

20. A display as recited in claim 18, wherein the intrinsic absorbing polarizer layer is a K-type polarizer layer.

21. A display as recited in claim 18, wherein the intrinsic absorbing polarizer layer is a KE-type polarizer layer.

22. A display as recited in claim 14, wherein the first absorbing polarizer further comprises one or more vapor barrier layers to prevent water vapor from reaching the absorbing polarizing layer.

23. A display as recited in claim 14, wherein the first absorbing polarizer is disposed on a viewing side of the LCD cell.

24. A display as recited in claim 14, further comprising a second absorbing polarizer disposed on a second side of the LCD cell opposite the first side.

25. A display as recited in claim 14, further comprising a light source disposed on an illumination side of the LCD cell.

26. A display as recited in claim 25, further comprising a light guide disposed to direct the light from the light source towards the LCD cell.

27. A display as recited in claim 25, further comprising a transflector disposed between the LCD cell and the light source.

28. A display as recited in claim 25, further comprising at least one light management layer disposed between the LCD cell and the light source.

29. A display as recited in claim 14, further comprising a controller coupled to the LCD cell to control an image imposed by the LCD cell on light passing through the LCD cell.

30. A display as recited in claim 14, wherein the first absorbing polarizer provides a moisture vapor transmission rate of less than about 4.6 gm m²/day and an oxygen transmission rate of less than about 0.005 ml/m²/day to the LCD cell.

31. A liquid crystal display, comprising:

a switched-in-plane (SIP) liquid crystal display (LCD) cell; and

a first absorbing polarizer, having an absorbing polarizing layer, disposed on a first side of the LCD cell, the first absorbing polarizer and the LCD cell each lying parallel to an x-y plane defined by orthogonal x- and y-axes, a z-axis being orthogonal to both the x-axis and the y-axis, the first absorbing polarizer defining a transmission polarization direction for light transmitted through the first absorbing polarizer, the transmission polarization direction being parallel to the x-axis, where n_x is the refractive index for light polarized parallel to the x-axis in the absorbing polarizing layer and n_z is the refractive index for light polarized parallel to the z-axis in the absorbing polarizing layer, an absolute value of Δ

n_xz=n_x−

n_z being less than 0.0005.

32. A display as recited in claim 31, wherein the absorbing polarizing layer has a thickness in the z-direction of 1, an absolute value of b=Δ

n_xz times 1 being less than 20 nm.

33. A display as recited in claim 32, wherein an absolute value of b is less than 10 nm.

34. A display as recited in claim 32, wherein an absolute value of b is less than 5 nm.