JPH04328523A - Polymer dispersion type liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent the leak out of the scattered light between adjacent pixels and to improve the contrast of a display screen by providing partition walls of a shape enclosing the pixel electrodes. CONSTITUTION:This display element has the pixel transparent electrodes 1 disposed in a matrix form and TFTs 2, the sources of which are connected to the pixel transparent electrodes 1, the drains of which to data lines 3, and the gates of which to address lines 4. An acrylic photosensitive resin contg. black pigments is screen printed on this TFT side substrate and is cured by irradiation with UV rays to form the partition walls 5. A mixture composed of a photosetting acrylic resin compsn. and a nematic liquid crystal is applied on the TFT substrate and is cured by irradiation with UV rays, by which the resin is cured and the polymer dispersed liquid crystal layer is formed. The polymer dispersed liquid crystal layer formed in such a manner is completely separated by each of the respective pixels. Then, the scattered light is shielded and is limited only into the pixels, by which the difference in the lightness of the pixels between the pixels of the on state and the pixels of the off state is expanded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer dispersed liquid crystal display element.

0002

[Prior Art] Conventional liquid crystal display devices control the transmission and blocking of incident light using two polarizing plates.
The light utilization efficiency is extremely low; for example, in active matrix liquid crystal display elements for color display, the value is 2.
Only ~3%. For this reason, a relatively large backlight is required, and if the polarizing plate generates a large amount of heat, a cooling device is also required, which greatly impairs the advantages of liquid crystal display elements such as small size, light weight, and low power consumption.

Polymer-dispersed liquid crystal display elements have recently attracted attention in order to overcome the problems of conventional liquid crystal display elements. This device uses a composite material in which liquid crystal is dispersed in a polymer, and displays information based on the presence or absence of light scattering due to differences in the arrangement of the liquid crystal.

In a polymer-dispersed liquid crystal display element, a composite in which liquid crystal is dispersed in a polymer is sandwiched between two transparent electrodes placed in parallel. When no voltage is applied, the liquid crystals are arranged randomly, so that light incident on the liquid crystals is scattered in all directions. When reflected light is used, the display state at this time is a bright state. On the other hand, when a voltage is applied, the electric field aligns the liquid crystals in the direction of the electric field, and the composite becomes transparent. When using reflected light, the display state at this time is a dark state.

[0005] In polymer dispersion type display elements, light is not cut by the polarizing plate, so sufficient brightness is ensured with ambient light in the case of reflective type and a relatively small amount of backlight in case of transmissive type. It has great potential to be smaller, lighter, and consume less power than conventional liquid crystal display elements, and is expected to be used as a future liquid crystal display element.

[0006]

[Problems to be Solved by the Invention] Polymer-dispersed liquid crystal display elements have greatly improved light utilization efficiency, but on the other hand,
The problem is that the contrast decreases due to the scattered light. In the polymer-dispersed type, when pixel A is in a voltage-off state, incident light is scattered in random directions at pixel A, and therefore scattered light also enters adjacent pixel B. When this adjacent pixel B is in the on state, it should be completely transparent, but since the scattered light that has entered from the adjacent pixel A in the off state behaves like birefringence and Rayleigh scattering, Part of the scattered light leaks out from pixel B, resulting in a state different from the completely transparent state. For this reason, the difference in brightness between pixels in the on-state and off-state becomes small, and the contrast of the display screen decreases.

[0007]

In the polymer-dispersed liquid crystal display element of the present invention, light-shielding partition walls are provided in the polymer-liquid crystal composite at positions corresponding to between adjacent pixels.

[0008]

[Operation] Since the scattered light leaking between adjacent pixels is blocked by the partition wall provided between each pixel and is limited to only within the pixel, the difference in brightness between the pixels in the on state and the pixels in the off state increases. Therefore, display contrast is improved compared to the polymer-dispersed liquid crystal display element before improvement.

[0009]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

0010

[First Embodiment] A first embodiment of the present invention relates to a thin film transistor (TFT) type active matrix liquid crystal display element. FIG. 1 is a partial plan view of the TFT side substrate. In the figure, 1 is a pixel transparent electrode arranged in a matrix, 2 is a TFT whose source is connected to the pixel transparent electrode 1, whose drain is connected to a data line 3, and whose gate is connected to an address line 4.

[0011] On this TFT side substrate, an acrylic photosensitive resin containing a black pigment was screen printed, and then cured by ultraviolet irradiation to form partition walls 5 as shown in FIG. At this time, the thickness of the partition wall was 5 μm. Next, a mixture of a photocurable acrylic resin composition and a nematic liquid crystal was applied onto this TFT substrate, and the resin was further cured by ultraviolet irradiation to form a polymer-dispersed liquid crystal layer. The polymer-dispersed liquid crystal layer formed at this time was almost completely separated for each pixel. A polymer-dispersed liquid crystal display element was fabricated by overlapping an opposing transparent electrode substrate. When voltage was applied to this liquid crystal element and alternating black and white patterns were displayed on the screen, there was a clear difference in brightness between black and white at the boundary between the black and white patterns.

0012

[Second Embodiment] FIG. 3 is a partial plan view of a TFT substrate used in a second embodiment of the present invention. In contrast to the previous embodiment in which the pixels were arranged in a mosaic pattern, in this embodiment the pixels are arranged in a triangular arrangement. In FIG. 3, reference numeral 1a indicates a transparent pixel electrode, and one pixel is constituted by a pair of transparent pixel electrodes. 2a is T
In the FT pair, 3 is a data line and 4 is an address line. This T
A chromium film with a thickness of 3 μm was formed on the FT substrate by sputtering and patterned by photoetching to form partition walls 5 shown in FIG.

Next, a solution of a mixture of polymethyl methacrylate (PMMA) and nematic liquid crystal dissolved in acetone was applied onto this TFT substrate, and this was further dried and hardened to form a polymer-dispersed liquid crystal layer. In this example, the thickness of the polymer-dispersed liquid crystal layer was made thicker than that of the partition walls so that the liquid crystal layer was not completely separated. A color filter substrate having a color filter 6 and a black matrix 7 shown in FIG. 5 was superimposed on this TFT substrate to produce a polymer dispersed liquid crystal display element. FIG. 6 is a plan view showing the overlapping state of patterns in pixels of this device.

[0014] A voltage is applied to this liquid crystal element to alternately make it bright and bright.
When a dark pattern was displayed on the screen, there was a clear difference in brightness at the boundary between the bright and dark patterns.

[0015]

[Modifications of the Embodiments] Although the preferred embodiments have been described above, the present invention is not limited thereto. The partition wall may be, for example, a dyed gelatin film or an inorganic insulating film. In the polymer-liquid crystal composite, the liquid crystal may be continuous or separated into droplets. Any of the materials reported for the composite material can be used. Further, as for the manufacturing method thereof, instead of the coating method or the casting method, a method such as a method in which a composite sheet is prepared and then sandwiched between two substrates can be adopted. Furthermore, the present invention is applicable not only to active matrix type liquid crystal display elements but also to other types of liquid crystal display elements.

[0016]

[Comparative example] A mixture of a photocurable acrylic resin composition and a nematic liquid crystal was applied on the TFT side substrate shown in Figure 1 without forming a light-shielding layer, and the resin was further cured by ultraviolet irradiation to disperse the polymer. A liquid crystal layer was formed. The thickness of this polymer-dispersed liquid crystal layer was 5 μm. A polymer-dispersed liquid crystal display element was fabricated by overlapping an opposing transparent electrode substrate.

When a voltage was applied to this liquid crystal element and an alternating black and white pattern was displayed on the screen, the difference in brightness between black and white at the boundary between the black and white patterns was due to scattered light leaking into adjacent pixels. It was not clear.

[0018]

As explained above, the present invention separates a polymer-liquid crystal composite by a partition wall having a shape surrounding a pixel electrode in a polymer-dispersed liquid crystal display element. Leakage of scattered light between adjacent pixels is prevented, and the difference in brightness between the white display area and the black display area is made clear. Therefore, the present invention solves the problems of polymer-dispersed liquid crystal display elements, which have high light utilization efficiency, small size, light weight, and low power consumption, but have poor contrast. The above effect is extremely large.

[Brief explanation of drawings]

FIG. 1: TFT for explaining the first embodiment of the present invention
A plan view of the substrate.

FIG. 2 is a plan view of a TFT substrate according to the first embodiment of the present invention.

FIG. 3: TFT for explaining the second embodiment of the present invention
A plan view of the substrate.

FIG. 4 is a plan view of a TFT substrate according to a second embodiment of the present invention.

FIG. 5 is a pattern diagram of a color filter substrate according to a second embodiment of the present invention.

FIG. 6 is a pattern diagram showing a state in which a TFT substrate and a color filter substrate according to a second embodiment of the present invention are overlapped.

[Explanation of symbols]

1... Pixel transparent electrode, 1a... Transparent pixel electrode,
2...TFT, 2a...TFT pair,
3...Data line, 4...Address line, 5
...bulkhead.

Claims (2)

[Claims] [Claim 1] A polymer in which liquid crystals are dispersed in the polymer.
1. A polymer-dispersed liquid crystal display element using a liquid crystal composite, characterized in that a partition wall is provided between each pixel to block light leaking from an adjacent pixel. 2. The polymer-dispersed liquid crystal display element according to claim 1, wherein the height of the partition wall is approximately equal to the thickness of the polymer-liquid crystal composite.