The present invention relates to a vertically aligned liquid crystal display device which performs simple-matrix driving (duty driving).
In order to increase the capacity and definition of a vertically aligned liquid crystal display device by simple-matrix driving, high duty driving must be performed. As a prior art example of such a vertically aligned liquid crystal display device, Patent Literature 1 discloses a vertical alignment liquid crystal display element which performs a displaying operation by the time-division driving at a large duty ratio.
When a vertically aligned liquid crystal display device is driven at a high duty ratio, however, the ON transmittance is lowered. Therefore, the display becomes dark, and the contrast is lowered.
By contrast, when the phase difference value in the thickness direction of a liquid crystal layer is increased, the ON transmittance is raised, but the viewing angle is narrowed because, in the vertical alignment type, the bi-refringence change of the liquid crystal layer due to inclination is large.
Therefore, it is an object of the invention to provide a vertically aligned liquid crystal display device in which the phase difference value in the thickness direction of a liquid crystal layer is increased beyond a usual range, whereby the ON transmittance in high duty driving is increased to improve the contrast and the viewing angle.
Characteristics requested in a vertically aligned liquid crystal display device include a high contrast, a high-speed responsibility, and a wide viewing angle. It is the that the phase difference value in the thickness direction of a liquid crystal layer (liquid crystal cell) is preferably in a range of from 80 nm to 400 nm. It is generally known that, when a high contrast and a high-speed responsibility are further considered, the adequate region is more narrowed, and the target value is 240 to 280 nm.
In the invention, as set forth in claim 1, the above-discussed problems are solved by a vertically aligned liquid crystal display device in which a liquid crystal layer is interposed between a first glass substrate which is transparent, and in which, among first and second transparent electrodes that are opposed to each other across a gap, the first transparent electrodes are disposed, and a second glass substrate which is transparent, and in which the second transparent electrodes are disposed, the liquid crystal layer being configured by liquid crystal which has a negative dielectric constant anisotropy, and in which alignment of liquid crystal molecules is substantially perpendicular to the first and second glass substrates, the alignment of the liquid crystal molecules being made substantially parallel to the first and second glass substrates when a voltage is applied between the first and second transparent electrodes, a first polarizing plate which has an absorption axis extending in a predetermined direction is placed on a side of the first glass substrate opposite to a side that is contacted with the liquid crystal layer, and a second polarizing plate which has an absorption axis extending in a direction perpendicular to the absorption axis of the first polarizing plate is placed on a side of the second glass substrate opposite to a side that is contacted with the liquid crystal layer, wherein, when a refractive index in a long axis direction of the liquid crystal molecules is indicated as ne, a refractive index in a short axis direction is indicated as no, ne−no=Δn, and a thickness of the liquid crystal layer is indicated as d, a phase difference value which is given by Δn·d, and which is in a thickness direction of the liquid crystal layer is set in a range of from 500 nm to 1,600 nm, a first phase difference plate is inserted between the first and second polarizing plates, and the first phase difference plate is a uniaxial phase difference plate which has a negative refractive index anisotropy that, when a refractive index in a slow axis direction showing a maximum refractive index in a plane is indicated as nx, a refractive index in a fast axis direction perpendicular to the slow axis direction in a plane is indicated as ny, and a refractive index in a thickness direction is indicated as nx, shows nx=ny>nz, a phase difference value in the thickness direction that, when a thickness is indicated as d1, is given by |(nx+ny)/2−nz|·d1 being set in a range of from 220 nm to 1,320 nm, the first phase difference plate having an optical axis perpendicular to the first and second glass substrates.
As set forth in claim 2, the problems are solved by a vertically aligned liquid crystal display device according to claim 1, wherein a second phase difference plate is additionally inserted between the first and second polarizing plates, and the second phase difference plate is a uniaxial phase difference plate which has a positive refractive index anisotropy that shows nx>ny=nz, a phase difference value in a plane that, when a thickness is indicated as d2, is given by |(nx−ny)|·d2 being set in a range of from 1 nm to 100 nm, the second phase difference plate having an optical axis parallel to the first and second glass substrates.
As set forth in claim 3, the problems are solved by a vertically aligned liquid crystal display device according to claim 2, wherein, in place of the first and second phase difference plates, a third phase difference plate is inserted between the first and second polarizing plates, and the third phase difference plate is a biaxial phase difference plate which has a refractive index anisotropy that shows nx>ny>nz, a phase difference value in a plane that, when a thickness is indicated as d3, is given by |(nx−ny)|·d3 being set in a range of from 1 nm to 100 nm, a phase difference value in the thickness direction that is given by |(nx+ny)/2−nz|·d3 being set in a range of from 220 nm to 1,320 nm, the third phase difference plate having an in-plane slow axis parallel to the first and second glass substrates.
According to the vertically aligned liquid crystal display devices set forth in claims 1, 2, and 3 of the invention, the birefringence of the liquid crystal layer in which the phase difference value in the thickness direction is increased beyond a usual range (from 80 nm to 400 nm) can be compensated by the phase difference plate, and hence the ON transmittance in high duty driving can be increased, so that the contrast and the viewing angle can be improved.
a) is a diagram showing liquid crystal alignment in an undriven state of the embodiments of the VA liquid crystal display devices set forth in claims 1 to 3 of the invention, and
1, 2, 3 VA liquid crystal display device
4 liquid crystal panel
4
a panel body
5 first glass substrate
5
a first transparent electrode
6 second glass substrate
6
a second transparent electrode
8 liquid crystal layer
8
a liquid crystal molecule
9 first polarizing plate
9
a absorption axis
10 second polarizing plate
10
a absorption axis
13 first phase difference plate
14 second phase difference plate
15 third phase difference plate
Hereinafter, embodiments of the vertically aligned liquid crystal display devices (hereinafter, referred to as “VA liquid crystal display devices”) set forth in claims 1 to 3 of the invention will be described with reference to the drawings.
The VA liquid crystal display devices 1, 2, 3 (1: the VA liquid crystal display device of the embodiment of the VA liquid crystal display device set forth in claim 1 of the invention, 2: the VA liquid crystal display device of the embodiment of the VA liquid crystal display device set forth in claim 2 of the invention, and 3: the VA liquid crystal display device of the embodiment of the VA liquid crystal display device set forth in claim 3 of the invention) include a liquid crystal panel 4, and display an image by using the liquid crystal panel 4.
As shown in
In the panel body 4a, the gap (cell gap) between the first and second glass substrate 5 and 6 is filled with liquid crystal (nematic liquid crystal) having a negative dielectric constant anisotropy, by the vacuum filling method, the dripping method, or the like, thereby forming a liquid crystal layer 8. In the thus formed liquid crystal layer 8, the thickness d of the liquid crystal layer 8 is set by the diameter of the polymer balls 7 which are used as spacer members.
In the outside of the panel body 4a, a first polarizing plate 9 is bonded to the substrate surface (panel back face) opposite to the side of the first glass substrate 5 which is contacted with the liquid crystal layer 8, and a second polarizing plate 10 is bonded to the substrate surface (panel front face) opposite to the side of the second glass substrate 6 which is contacted with the liquid crystal layer 8, thereby completing the liquid crystal panel 4.
As shown in
As shown in
In the thus configured liquid crystal panel 4, in an undriven state where no voltage is applied between the first and second transparent electrodes 5a and 6a, as shown in
By contrast, in a driven state where the voltage is applied between the first and second transparent electrodes 5a and 6a, as shown in
As apparent from the above, each of the VA liquid crystal display devices 1, 2, 3 is a vertically aligned liquid crystal display device in which the liquid crystal layer 8 configured by the liquid crystal which has a negative dielectric constant anisotropy, and in which the alignment of the liquid crystal molecules 8a is substantially perpendicular to the first and second glass substrates 5 and 6, and, when a voltage is applied between the first and second transparent electrodes 5a and 6a, the alignment of the liquid crystal molecules 8a is substantially parallel to the first and second glass substrates 5 and 6 is interposed between the first glass substrate 5 which is transparent, and in which, among the first and second transparent electrodes 5a and 6a that are opposed to each other across the gap, the first transparent electrode 5a is disposed, and the second glass substrate 6 which is transparent, and in which the second transparent electrode 6a is disposed, the first polarizing plate 9 which has the absorption axis 9a extending in a predetermined direction is placed on the side of the first glass substrate 5 opposite to the side that is contacted with the liquid crystal layer 8, and the second polarizing plate 10 which has the absorption axis 10a extending in a direction perpendicular to the absorption axis 9a of the first polarizing plate 9 is placed on the side of the second glass substrate 6 opposite to the side that is contacted with the liquid crystal layer 8. The device performs simple-matrix driving (duty driving), and, in response to the requests of a large capacity and high definition, performs high duty driving.
In the VA liquid crystal display device 1 shown in
Here, the phase difference value in the thickness direction of the liquid crystal layer 8 is given by Δn·d where Δn=ne−no, ne is the refractive index (refractive index of extraordinary light) in the long axis direction of the liquid crystal molecules 8a, no is the refractive index (refractive index of ordinary light) in the short axis direction of the liquid crystal molecules 8a, and d is the thickness of the liquid crystal layer 8.
In the VA liquid crystal display device 1 shown in
The first phase difference plate 13 is a uniaxial phase difference plate (negative C plate) which has a negative refractive index anisotropy that, when the refractive index in the slow axis direction showing the maximum refractive index in a plane is indicated as nx, the refractive index in the fast axis direction perpendicular to the slow axis direction in a plane is indicated as ny, and the refractive index in the thickness direction is indicated as nz, shows nx=ny>nz, in which the phase difference value in the thickness direction that, when the thickness is indicated as d1, is given by |(nx+ny)/2−nz|·d1 is set in a range of from 220 nm to 1,320 nm, and which has the optical axis perpendicular to the first and second glass substrates, and compensates the birefringence of the liquid crystal layer 8.
In
(A): between the first glass substrate 5 and the first polarizing plate 9;
(B): between the first glass substrate 5 and the first transparent electrode 5a;
(C): between the first transparent electrode 5a and the first alignment film 5b;
(D): between the second transparent electrodes 6a and the second alignment film 6b;
(E): between the second glass substrate 6 and the second transparent electrodes 6a; and
(F): between the second glass substrate 6 and the second polarizing plate 10.
Namely, (A) to (C) are phase difference plate insertion places on the light incidence side of the liquid crystal layer 8, and (D) to (F) are phase difference plate insertion places on the light emission side of the liquid crystal layer 8. Furthermore, (A) and (F) are phase difference plate insertion places outside the panel body 4a, and (B) to (E) are phase difference plate insertion places inside the panel body 4a.
The VA liquid crystal display device 1 shown in
Next,
In the VA liquid crystal display device 2 shown in
The second phase difference plate 14 is a uniaxial phase difference plate (positive a plate) which has a positive refractive index anisotropy that shows nx>ny=in which the phase difference value in a plane that, when the thickness is indicated as d2, is given by |(nx−ny)|·d2 is set in a range of from 1 nm to 100 nm, and which has the optical axis parallel to the first and second glass substrates 5 and 6.
The VA liquid crystal display device 2 shown in
In the VA liquid crystal display device 3 shown in
The third phase difference plate 15 is a biaxial phase difference plate which has a refractive index anisotropy that shows nx>ny>nz, in which a phase difference value in a plane that, when the thickness is indicated as d3, is given by |(nx−ny)|·d3 is set in a range of from 1 nm to 100 nm, and which has a phase difference value in the thickness direction that is given by |(nx+ny)/2−nz|·d3 is set in a range of from 220 nm to 1,320 nm, and which has an in-plane slow axis parallel to the first and second glass substrates 5 and 6.
The VA liquid crystal display device 3 shown in
In
When the VA liquid crystal display devices 1, 2, 3 were driven at a high duty ratio of 1/60, a viewing angle of 50° or more in each of right and left at a contrast ratio of 10:1 in the right and left direction, and 50° or more at a contrast ratio of 20:1 in the upper direction was realized. The results were confirmed by using a conoscope manufactured by AUTRONIC-MELCHERS GmbH.
In the VA liquid crystal display devices 1, 2, 3, as compared with the optical compensation of the liquid crystal panel 4 due to the use of the one or more first phase difference plates 13 in the VA liquid crystal display device 1, the combination of the two third phase difference plates 15 in the VA liquid crystal display device 3 exerts a higher compensation effect, and followed by that of the first phase difference plate 13 and the second phase difference plate 14 in the VA liquid crystal display device 2.
Alternatively, the first phase difference plate 13 and the third phase difference plate 15 may be combined with each other, and the combination can exert a compensation effect subsequent to the VA liquid crystal display device 3.
In the VA liquid crystal display device 40 shown in
The VA liquid crystal display device 40 shown in
Number | Date | Country | Kind |
---|---|---|---|
2008-203129 | Aug 2008 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/052152 | 2/9/2009 | WO | 00 | 2/4/2011 |