Reflective liquid crystal display device and reflective liquid crystal display device incorporating touch panel arranged therefrom

• US 7,023,510 B2
• Filed: 10/19/2004
• Issued: 04/04/2006
• Est. Priority Date: 04/23/1997
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Okamoto, Masayuki, Mitsui, Seiichi, Satoh, Takashi
• Primary Examiner(s): Parker, Kenneth
• Assistant Examiner(s): Chung, David Y.
• Application Number:
  US10/967,216
• Publication Number:
  US 20050078238A1
• Time in Patent Office: 532 Days
• Field of Search: 349/113, 349/119, 349/98
• US Class Current: 349/113
• CPC Class Codes: G02F 1/133528 Polarisers
• CPC Class Codes: G02F 1/133531 characterised by the arrangement of polariser or analyser axes
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605
• CPC Class Codes: G02F 1/133602 Direct backlight
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• 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 1/1396 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell G02F1/141 takes precedence
• CPC Class Codes: G02F 1/1398 the twist being below 90°
• CPC Class Codes: G02F 2202/40 Materials having a particular birefringence, retardation
• CPC Class Codes: G02F 2413/03 Number of plates being 3
• CPC Class Codes: G02F 2413/07 All plates on one side of the LC cell
• CPC Class Codes: G02F 2413/08 with a particular optical axis orientation
• CPC Class Codes: G02F 2413/10 with refractive index ellipsoid inclined, or tilted, relative to the LC-layer surface O plate

Abstract

A reflective color liquid crystal display device with a liquid crystal layer sandwiched between a first substrate having a light reflectibility and a second substrate having a light transmissibility. The liquid crystal layer being composed of twist-aligned nematic liquid crystal having a positive dielectric anisotropy. A circularly polarizing unit, including a single linear polarizer plate, selectively passes either right handed or left handed circularly polarized light out of natural light. The circularly polarizing unit is disposed so that a major surface of the circularly polarizing unit is on a liquid crystal layer side, the circularly polarized light exiting the circularly polarizing unit through the major surface when natural light enters the circularly polarizing unit. Various parameters of the liquid crystal layer are optimized for a liquid crystal layer having a twist angle in the range of 0° to 100°.

Claims

1. A reflective liquid crystal display device, comprising:

a first substrate having a light reflectibility;

a second substrate having a light transmissibility;

a liquid crystal layer sandwiched between the first substrate and the second substrate, the liquid crystal layer being composed of twist-aligned nematic liquid crystal having a positive dielectric anisotropy; and

a circular polarizing unit comprising a linear polarizer and at least one optical retardation compensator unit, said circular polarizer unit selectively passes either right handed or left handed substantially circularly polarized light out of natural light in the visible spectrum; and

said at least one optical retardation compensator unit being provided between the linear polarizer and the liquid crystal layer to minimize influence from a residual phase difference of the liquid crystal layer,

wherein,

the circular polarizing unit is disposed such that a major surface of the circular polarizing unit is on a liquid crystal layer side, the substantially circularly polarized light exiting the circular polarizing unit through the major surface when natural light enters the circular polarizing unit.

2. The reflective liquid crystal display device as set forth in claim 1, wherein

the circular polarizing unit includes:

a first optical retardation compensator plate having a retardation in a substrate normal direction set to not less than 100 nm and not more than 180 nm;

a second optical retardation compensator plate having a retardation in a substrate normal direction set to not less than 200 nm and not more than 360 nm; and

a linear polarizer plate, the first optical retardation compensator plate, the second optical retardation compensator plate, and the linear polarizer plate being stacked in this order when viewed from the liquid crystal layer, and

|2×

θ

2−

θ

1| has a value not less than 35° and

not more than 55°

, where θ

1 represents an angle formed by a slow axis of the first optical retardation compensator plate and either a transmission axis or an absorption axis of the linear polarizer plate, and θ

2 represents an angle formed by a slow axis of the second optical retardation compensator plate and either the transmission axis or the absorption axis of the linear polarizer plate.

3. The reflective liquid crystal display device as set forth in claim 2, wherein the twist angle of the liquid crystal layer is in a range from 60°

to 100°

,

the product of the birefringence difference of the liquid crystal in the liquid crystal layer and the thickness of the liquid crystal layer is not less than 250 nm and not more than 330 nm, and

either the transmission axis or the absorption axis of the linear polarizer plate forms an angle, θ

3, of not less than 20° and

not more than 70°

, or not less than 110° and

not more than 150°

with an alignment direction of the liquid crystal molecules in a close proximity of the second substrate.

4. The reflective liquid crystal display device as set forth in claim 1, wherein

the first substrate having a light reflexibility includes a light reflective film, and

the light reflective film has smooth and continuously changing concavities and convexities, and is made of a conductive material.

5. The reflective liquid crystal display device as set forth in claim 1, wherein

said one of said optical retardation compensator unit and said plurality of optical retardation compensator units has an inclined optical axis, or a three-dimensionally aligned optical axis having therein a continuously varying inclined direction.

6. The reflective liquid crystal display device as set forth in claim 1, wherein the liquid crystal layer has a birefringence difference, which, if multiplied by a thickness of the liquid crystal layer, produces a product of not less than 150 nm and not more than 350 nm.

7. The reflective liquid crystal display device as set forth in claim 6, wherein the liquid crystal layer has a twist angle in a range of 45°

to 100°

.

8. The reflective liquid crystal display device as set forth in any one of claims 1 through 3, wherein the substantially circularly polarized light includes elliptically polarized light.

9. The reflective liquid crystal display device as set forth in claim 1, wherein the circular polarizing unit has a compensated retardation value to minimize influence from a residual phase difference of the liquid crystal layer.

10. The reflective liquid crystal display device as set forth in claim 9, wherein the retardation value of the circular polarizing unit is compensated by a value within a range of 10 nm to 50 nm.

11. The reflective liquid crystal display device as set forth in any one of claims 1 through 3, wherein

the circular polarizing unit performs as an optical retardation compensator that minimizes influence from a residual phase difference of the liquid crystal layer during application of a voltage to the liquid crystal layer.

12. The reflective liquid crystal display device as set forth in claim 1, wherein

the circular polarizing unit includes,

a first optical retardation compensator plate,

a second optical retardation compensator plate having a retardation in a substrate normal direction set to not less than 200 nm and not more than 360 nm, and

a linear polarizer plate, and

wherein, |2×

θ

2−

θ

1| has a value not less than 35° and

not more than 55°

, where θ

1 represents an angle formed by a slow axis of the first optical retardation compensator plate and either a transmission axis or an absorption axis of the linear polarizer plate, and θ

2 represents an angle formed by a slow axis of the second optical retardation compensator plate and either the transmission axis or the absorption axis of the linear polarizer plate,

a direction of the slow axis of the first optical retardation compensator plate is parallel to an alignment direction of a liquid crystal in a middle of the liquid crystal later in a thickness direction, and

a retardation in the substrate normal direction of the first optical retardation compensator plate is set to a retardation that is smaller, by 10 nm to 50 nm, than a retardation for not less than 100 nm and not more than 180 nm that provides, across an entire visible range, a phase difference equivalent to a quarter wavelength.

13. The reflective liquid crystal display device as set forth in claim 1, wherein

the circular polarizing unit includes,

a first optical retardation compensator plate,

a second optical retardation compensator plate having a retardation in a substrate normal direction set to not less than 200 nm and not more than 360 nm, and

a linear polarizer plate, and

wherein, |2×

θ

2−

θ

1| has a value not less than 35° and

not more than 55°

, where θ

1 represents an angle formed by a slow axis of the first optical retardation compensator plate and either a transmission axis or an absorption axis of the linear polarizer plate, and θ

2 represents an angle formed by a slow axis of the second optical retardation compensator plate and either the transmission axis or the absorption axis of the linear polarizer plate,

the slow axis of the first optical retardation compensator plate is orthogonal to an alignment direction of a liquid crystal in a middle of the liquid crystal later in a thickness direction, and

a retardation in the substrate normal direction of the first optical retardation compensator plate is set to

a retardation that is greater, by 10 nm to 50 nm, than a retardation for not less than 100 nm and not more than 180 nm that provides, across an entire visible range, a phase difference equivalent to a quarter wavelength.