JP2014095838A - Liquid crystal display device - Google Patents

Abstract

An in-plane switching type liquid crystal display device suitable for time-division driving is provided.
A liquid crystal display device that is driven in a time-sharing manner with a duty ratio of 1 / N (N is an integer), and is provided on a first substrate and a second substrate that are arranged opposite to each other and on one surface side of the first substrate. First and second electrodes 14 and a liquid crystal layer provided between the first substrate and the second substrate, each of the first electrode and the second electrode extending in the first direction in plan view The electrode branches 31 are alternately arranged along a second direction orthogonal to the first direction, and the liquid crystal layer has an initial alignment direction 32 of liquid crystal molecules with respect to the first direction. The orientation is controlled so as to form an angle greater than 1 ° and less than 2 °.
[Selection] Figure 2

Description

  The present invention relates to a multiplex-driven liquid crystal display device.

  2. Description of the Related Art A segment display type liquid crystal display device having a display portion of an arbitrary shape such as a character or a pattern is widely known. In this segment display type liquid crystal display device, electrodes that have been patterned in advance are provided on each of the opposed substrates, a liquid crystal layer is provided between the substrates, and a polarizing plate is provided outside each substrate. A region where each electrode overlaps is defined as a display portion, and the brightness state of emitted light can be controlled by applying a voltage between the electrodes to change the alignment state of the liquid crystal molecules in the liquid crystal layer. However, in such a liquid crystal display device, the liquid crystal molecules in the liquid crystal layer change the tilt angle out of the plane with respect to the substrate surface. When it has a pretilt angle, the tilt direction of the liquid crystal molecules is biased to one position. As a result, viewing angle dependence occurs in the brightness and darkness of the emitted light in appearance observation.

  On the other hand, as an example of a liquid crystal display device excellent in viewing angle characteristics, for example, in Japanese Patent Laid-Open No. 56-91277, a display electrode and a common electrode formed in a comb shape are provided on one substrate, An in-plane switching type liquid crystal display device has been proposed in which a voltage is applied between both electrodes to change the alignment direction of liquid crystal molecules in the liquid crystal layer in the in-plane direction of the substrate. The liquid crystal display device disclosed in Patent Document 1 is an active matrix liquid crystal display device in which each pixel is switched using an active element such as a thin film transistor. Japanese Patent Application Laid-Open No. 7-72491 discloses a liquid crystal display device that switches pixels by simple matrix driving as another example of an in-plane switching type liquid crystal display device. According to these liquid crystal display devices, since the orientation direction of the liquid crystal molecules is controlled within the substrate surface, a wide viewing angle can be realized without using a viewing angle compensator.

  By the way, the above-described liquid crystal display devices of the preceding examples are of a type in which the pixels arranged in a matrix are individually switched. For example, a segment display type liquid crystal display device having a plurality of display portions of arbitrary shapes is used. There is no disclosure about the type of time-division driving. Here, in the active matrix type liquid crystal display device, since a voltage is selectively applied to each pixel, the steep characteristic (steepness) in the electro-optical characteristic is not particularly important. However, in a time-division-driven type liquid crystal display device, a non-selection voltage is also applied to the off-display portion, and so-called off-segment appearance (crosstalk) occurs if the steep characteristics are not good, Angular characteristics are significantly degraded and contrast characteristics are also degraded. Therefore, steep characteristics are very important in a liquid crystal display device of the type that is time-division driven. On the other hand, in the conventionally proposed in-plane switching type liquid crystal display device, when the display electrode and the common electrode are arranged so as to mesh with each other, the comb-like electrodes The response characteristics are improved by tilting the initial alignment direction of the liquid crystal molecules in the liquid crystal layer at a relatively large angle (for example, about 45 °) with respect to the extending direction (for example, JP-A-10-26767). However, in such a case, the steep characteristics deteriorate as the angle is set in the initial alignment direction of the liquid crystal molecules, so that it is not suitable for time-division driving.

JP 56-91277 A JP-A-7-72491 JP-A-10-26767

  A specific aspect of the present invention is to provide an in-plane switching type liquid crystal display device suitable for time-division driving.

  A liquid crystal display device according to one aspect of the present invention is a liquid crystal display device that is time-division driven at a duty ratio of 1 / N (N is an integer), and (a) a first substrate and a second substrate that are arranged to face each other. (B) a first electrode and a second electrode respectively provided on one surface side of the first substrate; (c) a liquid crystal layer provided between the first substrate and the second substrate; Each of the one electrode and the second electrode has a plurality of electrode branches extending in the first direction in plan view, and each of the electrode branches is alternately arranged along a second direction orthogonal to the first direction. (E) The liquid crystal layer is a liquid crystal display device in which the alignment is controlled so that the initial alignment direction of the liquid crystal molecules forms an angle of greater than 1 ° and less than 2 ° with respect to the first direction. Here, for example, the N can be set to 8 or less.

  According to the above configuration, an in-plane switching type liquid crystal display device suitable for time-division driving can be obtained.

  In the above liquid crystal display device, for example, it is preferable that the layer thickness of the liquid crystal layer is 4 to 7 μm, and the refractive index anisotropy of the liquid crystal material of the liquid crystal layer is 0.07. It is also preferable that the liquid crystal layer has a thickness of 4 to 6 μm, and the refractive index anisotropy of the liquid crystal material of the liquid crystal layer is 0.09. It is also preferable that the layer thickness of the liquid crystal layer is 4 μm and the refractive index anisotropy of the liquid crystal material of the liquid crystal layer is 0.1.

FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display device according to an embodiment. FIG. 2 is a plan view schematically showing the structure of the first electrode and the second electrode. FIG. 3 is a graph showing an example of electro-optical characteristics of the liquid crystal display device. FIG. 4 is a diagram showing an observation image of the alignment texture of the liquid crystal display device when θ = 1 °. FIG. 5 is a graph showing the retardation dependency of the voltage-transmittance characteristics of the liquid crystal display device. FIG. 6 is a graph showing the retardation dependence of the voltage-transmittance characteristics of the liquid crystal display device. FIG. 7 is a graph showing retardation dependency of voltage-transmittance characteristics of the liquid crystal display device. FIG. 8 is a graph showing the retardation dependency of the voltage-transmittance characteristics of the liquid crystal display device. FIG. 9 is a graph showing retardation dependency of voltage-transmittance characteristics of the liquid crystal display device. FIG. 10 is a graph showing the retardation dependence of the voltage-transmittance characteristics of the liquid crystal display device. FIG. 11 is a diagram illustrating voltage-transmittance characteristics of the liquid crystal display devices of the example and the comparative example.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display device according to an embodiment. The liquid crystal display device includes a first substrate 11 and a second substrate 12 that are disposed to face each other, and a liquid crystal layer 18 that is disposed between the first substrate 11 and the second substrate 12 as a basic configuration.

  The first substrate 11 and the second substrate 12 are transparent substrates such as a glass substrate and a plastic substrate, respectively. As shown in the figure, the first substrate 11 and the second substrate 12 are bonded together with a predetermined gap (for example, about 3 μm). The gap between the first substrate 11 and the second substrate 12 is held by a lot-like or spherical spacer contained in a frame-like sealing material (not shown) and spherical spacers that are uniformly distributed in the substrate surface.

  The first electrode 13 and the second electrode 14 are each provided on one surface side of the first substrate 11. The first electrode 13 and the second electrode 14 are each formed in a comb-teeth shape in which a plurality of electrode branches are connected, and are arranged so that the electrode branches are alternately meshed one by one (a figure to be described later). 2).

  The first alignment film 15 is provided on one surface side of the first substrate 11 so as to cover the first electrode 13 and the second electrode 14. The second alignment film 16 is provided on one surface side of the second substrate 12. As these first alignment film 15 and second alignment film 16, horizontal alignment films that restrict the alignment state of the liquid crystal layer 18 to horizontal alignment are used. Each alignment film is subjected to a uniaxial alignment process such as a rubbing process or a photo-alignment process. Note that the alignment treatment may be performed only on one of the alignment films.

  The liquid crystal layer 18 is provided between the first substrate 11 and the second substrate 12. The liquid crystal material constituting the liquid crystal layer 18 has a positive dielectric anisotropy Δε, for example. The liquid crystal layer 18 of the present embodiment is set to a horizontal alignment in which the alignment direction of liquid crystal molecules when no voltage is applied is substantially horizontal with respect to the substrate surfaces of the first substrate 11 and the second substrate 12.

  The first polarizing plate 21 is disposed outside the first substrate 11. Similarly, the second polarizing plate 22 is disposed outside the second substrate 12. For example, the absorption axis of the first polarizing plate 21 is arranged substantially parallel to the alignment direction when no voltage is applied to the liquid crystal molecules of the liquid crystal layer 18. Further, the second polarizing plate 22 is disposed, for example, substantially perpendicular to the absorption axis of the first polarizing plate 21.

  FIG. 2 is a plan view schematically showing the structure of the first electrode and the second electrode. As shown in the figure, the first electrode 13 is formed in a comb-like shape in which a plurality of electrode branches extending in the vertical direction in the drawing are connected. Similarly, the 2nd electrode 14 is formed in the comb-tooth shape which connected the several electrode branch extended in the up-down direction in the figure. The electrode branches of the first electrode 13 and the electrode branches of the second electrode 14 are alternately arranged one by one along the horizontal direction in the drawing so that the electrode branches mesh with each other in plan view as a whole. Has been placed. By applying a voltage between the first electrode 13 and the second electrode 14 as described above, an electric field is generated in a direction (indicated by a white arrow) that is substantially horizontal to the substrate surface and substantially orthogonal to each electrode branch. Can be made. When considering a segment display type liquid crystal display device by time-division driving, each electrode branch is preferably formed in a straight line shape (strip shape) as shown in the figure. In the previous example, it has been proposed to use a bent electrode branch in order to eliminate the coloring of the on-display part, but in this case, in the region where the switching direction of the liquid crystal molecules and the electric field direction are reversed. This is because the transmittance decreases.

  Here, the angle formed by the initial alignment direction 32 of the liquid crystal molecules of the liquid crystal layer 18 with respect to the extending direction 31 of each electrode branch is defined as θ. The initial alignment direction 32 of the liquid crystal molecules substantially coincides with the direction of the uniaxial alignment treatment performed on the alignment films 15 and 16, for example. At this time, the angle θ formed by the extending direction 31 of each electrode branch and the initial alignment direction 32 is set to be greater than 1 ° and 2 ° or less (1 ° <θ ≦ 2 °). The reason why the angle θ should be such a condition will be described below.

  FIG. 3 is a graph showing an example of electro-optical characteristics of the liquid crystal display device. As shown in the figure, voltage-transmittance characteristics are shown when the angle θ between the extending direction 31 of each electrode branch and the initial alignment direction 32 of the liquid crystal molecules is set between 0 ° and 3 °. As shown in the figure, when θ = 0 °, a characteristic in which the transmittance suddenly increases from a certain voltage (about 5.5 V in this example) is obtained, which is an ideal characteristic. However, when this condition is used in an actual liquid crystal display device, the directions in which the liquid crystal molecules rotate are equal in the two directions with respect to the electric field direction. This can result in display unevenness. Such a boundary line can occur even when θ = 1 °. FIG. 4 is a diagram showing an observation image of the alignment texture of the liquid crystal display device when θ = 1 °. A region represented as a bright state in the figure is a region where the alignment direction of the liquid crystal layer is changed by an electric field. If you look closely at this bright area, you can see that there are dark borders. As a result of further verification by the inventors of the present application, it has been found that the generation of the boundary line can be substantially suppressed by making the angle θ larger than 1 °. On the other hand, as shown in FIG. 3, as the angle θ is increased, the steep characteristic is degraded. Therefore, the angle θ needs to be 2 ° or less.

  5 to 10 are graphs showing the retardation dependency of the voltage-transmittance characteristics of the liquid crystal display device, respectively. Specifically, FIG. 5 shows a case where the cell thickness (liquid crystal layer thickness) is set to 3 μm, FIG. 6 shows a case where the cell thickness is set to 4 μm, FIG. 7 shows a case where the cell thickness is set to 5 μm, and FIG. 9 shows voltage-transmittance characteristics when the cell thickness is set to 7 μm, and the refractive index anisotropy Δn of the liquid crystal material is between 0.07 and 0.14, respectively. Is set. FIG. 10 shows voltage-transmittance characteristics when the cell thickness is set to 8 μm and Δn is set to 0.07. From the results shown in FIGS. 5 to 10, it can be seen that when the cell thickness is set to 4 to 5 μm when Δn is set to 0.09, a good steep characteristic can be obtained, and Δn is set to 0.1. When it is set, it can be seen that good steep characteristics can be obtained when the cell thickness is set to 4 μm.

  FIG. 11 is a diagram illustrating voltage-transmittance characteristics of the liquid crystal display devices of the example and the comparative example. In the liquid crystal display device of the example, the angle θ is set to 2 °, the rubbing process to each alignment film is anti-parallel (or parallel), and each alignment film is near the interface with the liquid crystal layer. The pretilt angle given to the liquid crystal molecules was prepared to be 1 ° or less. Further, the cell thickness is 4 μm, Δn is 0.09, the transmission axis direction of the front side polarizing plate is substantially coincident with the initial alignment direction of the liquid crystal molecules, and the transmission axis direction of the back side polarizing plate is the transmission axis direction of the front side polarizing plate. It arrange | positioned so that it might cross substantially orthogonally. On the other hand, the liquid crystal display device of the comparative example was manufactured under the same conditions as in the example except that the angle θ was set to 45 °. As shown in FIG. 11, the liquid crystal display device of the example has a steep characteristic (V90 / V10) obtained from the voltage-transmittance characteristic of 1.36, whereas the steep characteristic of the liquid crystal display device of the comparative example. Is 3.01. Usually, when the steep characteristic is 1.36 or less in the case of time-division driving, it can be driven sufficiently with 1/8 duty.

  In addition, this invention is not limited to the content of embodiment mentioned above, In the range of the summary of this invention, it can change and implement variously.

DESCRIPTION OF SYMBOLS 11: 1st board | substrate 12: 2nd board | substrate 13: 1st electrode 14: 2nd electrode 15, 16: Alignment film 18: Liquid crystal layer 21: 1st polarizing plate 22: 2nd polarizing plate 31: Extension of each electrode branch Direction 32: Initial alignment direction of liquid crystal molecules

Claims (5)

A liquid crystal display device driven in a time-sharing manner with a duty ratio of 1 / N (N is an integer),
A first substrate and a second substrate disposed opposite to each other;
A first electrode and a second electrode respectively provided on one side of the first substrate;
A liquid crystal layer provided between the first substrate and the second substrate;
Including
Each of the first electrode and the second electrode has a plurality of electrode branches extending in a first direction in a plan view, and the electrode branches alternate along a second direction orthogonal to the first direction. Are located in
The liquid crystal layer is controlled in alignment so that an initial alignment direction of liquid crystal molecules forms an angle of 1 ° to 2 ° with respect to the first direction.
Liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the liquid crystal layer has a thickness of 4 to 7 μm, and the liquid crystal material has a refractive index anisotropy of 0.07.   The liquid crystal display device according to claim 1, wherein the liquid crystal layer has a layer thickness of 4 to 6 μm, and the liquid crystal material has a refractive index anisotropy of 0.09.   The liquid crystal display device according to claim 1, wherein the liquid crystal layer has a layer thickness of 4 μm, and the liquid crystal material has a refractive index anisotropy of 0.1.   The liquid crystal display device according to claim 1, wherein the N is 8 or less.