Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-04-25
2003-09-23
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06624861
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a color filter and a liquid crystal display device, and more particularly to a liquid crystal display device having excellent (improved) display quality and a color filter for use in the liquid crystal display device.
BACKGROUND ART
In recent years, color liquid crystal display devices have drawn attention as flat displays. One example of the color liquid crystal display devices is a transmission liquid crystal display device such that a color filter comprising a black matrix, a colored layer of a plurality of colors (in general, the three primary colors of red (R), green (G), and blue (B)), a common transparent electrode layer, and an aligning layer is provided so as to face a counter electrode substrate comprising a thin film transistor (a TFT device), an pixel electrode, and an aligning layer, while leaving a predetermined gap between the color filter and the counter electrode substrate, and a liquid crystal material is poured into the gap to form a liquid crystal layer. Another example of the color liquid crystal display devices is a reflection liquid crystal display device wherein, in the above color filter, a reflective layer is provided between the substrate and the colored layer.
In these color liquid crystal display devices, a change in the state of alignment of the liquid crystal caused, for example, by an alignment failure of the liquid crystal, a change in voltage applied to the liquid crystal, and a variation in voltage within the display surface, results in the occurrence of display failures (unacceptable display phenomena) which are classified into sticking and white stain (uneven whiteness).
Sticking is a phenomenon such that, when a voltage has been applied to an identical pixel for a given period of time followed by a lowering in voltage or the stop of the application of the voltage, the transmittance of this pixel becomes different from the transmittance of pixels, located around this pixel, to which the voltage has not been applied for the given period of time, and, as a result, an uneven display is visually perceived and is continued even after standing for a long period of time. In the sticking phenomenon of normally white panels, the pixel, to which a voltage has been applied for a given period of time, is seen more darkly than pixels located around this pixel. This sticking phenomenon is attributable to the fact that an ionic material is deposited on an electrode during the application of the voltage and, after the stop of the application of the voltage, remains adsorbed on the electrode and, as a result, the voltage derived from the ionic material continues to act on the liquid crystal.
On the other hand, uneven whiteness is a phenomenon such that an uneven display is visually perceived due to the fact that, when a voltage is applied to display a black screen, the transmittance does not become zero in a part of the display region. The cause of this phenomenon is considered as follows. Although the voltage applied across the electrodes should be kept constant, when an ionic material is present in the liquid crystal, this ionic material is moved, that is, a current flows, resulting in a drop of voltage across the electrodes.
It is considered that the above-described ionic material causative of display failure phenomena does not stay on the electrode and easily migrates within the liquid crystal layer. Various sources are considered for the ionic material, and the control of impurities contained, for example, in liquid chemicals, air, and pure water used in the production process of liquid crystal display devices, the control of dust generated, for example, from apparatuses and human body, and the optimization of process conditions are carried out in order to prevent the occurrence of display failures. Further, surface cleaning of color filters and counter electrode substrates and the removal of impurities, such as residues produced, for example, from ultraviolet irradiation and surface polishing in the production process of liquid crystal display devices, are also carried out.
These measures can reduce display failure phenomena. In display under severe conditions, such as display for a long period of time or display under high temperature and high humidity conditions, however, the probability of occurrence of display failures is still high.
Further, in recent years, efforts are being directed toward a lowering in drive voltage to realize low power consumption of color liquid crystal display devices. In order to realize the low voltage drive, it is necessary to set at a low value the threshold voltage of liquid crystals used. This has led to studies on liquid crystal display devices using liquid crystals having high permittivity anisotropy &Dgr;&egr; of liquid crystals. In general, however, the polarity of liquid crystals is likely to increase with increasing the permittivity anisotropy &Dgr;&egr;. Therefore, impurities are likely to be eluted from a color filter or a counter electrode substrate in contact with the liquid crystal into the liquid crystal. This is likely to cause the above-described display failures.
Under these circumstances, the present invention has been made, and it is an object of the present invention to provide a color filter, which can prevent, on a higher level, a liquid crystal layer from being contaminated with ionic materials, and a liquid crystal display device having improved display quality.
DISCLOSURE OF THE INVENTION
The present inventors have considered that members in contact with a liquid crystal layer in a liquid crystal display device are one of sources for the above-described ionic material and have directed attention, as properties having a correlation with display failures caused by ionic materials which have migrated from the member constituting a color filter or a liquid crystal display device into the liquid crystal layer, to the influence of a color filter or the like after impurity elution on the voltage holding ratio of the liquid crystal. This has led to the completion of the present invention.
Specifically, in order to attain the above object, according to one aspect of the present invention, there is provided a color filter comprising at least a substrate and a colored layer of a plurality of colors provided in a predetermined pattern on the substrate, wherein, after impurity elution, the color filter permits a liquid crystal to have a voltage holding ratio of not less than 90%.
Preferably, the color filter of the present invention further comprises a light shielding layer provided in a predetermined pattern.
Preferably, the color filter according to the present invention further comprises a transparent protective layer provided on the colored layer so as to cover at least the colored layer.
In this case, preferably, a transparent columnar convex is provided in a plurality of predetermined sites on the substrate so as to be protruded from the transparent protective layer.
Preferably, the color filter according to the present invention, a reflective layer is provided between the substrate and the colored layer.
According to another aspect of the invention, there are provided the following first to fifth liquid crystal display devices.
The first liquid crystal display device according to the present invention comprises: a color filter; a counter electrode substrate provided so as to face the color filter while leaving a gap between the color filter and the counter electrode substrate through a seal member; and a liquid crystal layer sealed into the gap, said color filter comprising a common transparent electrode layer provided in any one of the above color filters.
The second liquid crystal display device according to the present invention comprises: a color filter; a counter electrode substrate provided so as to face the color filter while leaving a gap between the color filter and the counter electrode substrate through a seal member; and a liquid crystal layer sealed into the gap, said color filter comprising a common transparent electrode layer provided in
Miyakawa Shunji
Tanaka Tomio
Dai Nippon Printing Co. Ltd.
Parkhurst & Wendel L.L.P.
Rude Timothy L
Ton Toan
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