The present invention relates to a liquid crystal device for use in, e.g., a display apparatus for displaying images including characters and/or figures, particularly a liquid crystal device using a chiral smectic liquid crystal suitable for full-color display and a liquid crystal device having a stripe electrode structure suitable for a simple matrix driving. The present invention also relates to a process for producing the liquid crystal device and a color liquid crystal display apparatus using the liquid crystal device.
A display device of the type which controls transmission of light in combination with a polarizing device by utilizing the refractive index anisotropy of ferroelectric (or chiral smectic) liquid crystal molecules has been proposed by Clark and Lagerwall (U.S. Pat. No. 4,367,924, etc.). The ferroelectric liquid crystal has generally chiral smectic C phase (SmC*) or H phase (SmH*) of a non-helical structure in a certain temperature region and, in the SmC* or SmH* phase, shows a property of assuming either one of a first optically stable state and a second optically stable state (bright and dark states) responding to an electrical field applied thereto and maintaining such a state in the absence of an electrical field, namely bistability, and also has a quick responsiveness to the change in electrical field. Thus, it is expected to be utilized in a high speed and memory type display device and particularly to provide a large-area, high-resolution display based on its excellent function.
FIG. 1 shows a sectional view of a liquid crystal device using a ferroelectric liquid crystal based on two-valued (white and black) display.
Referring to FIG. 1, the liquid crystal device (panel) includes insulating substrates 1a and 1b, transparent electrodes 6a and 6b, auxiliary electrodes 7a and 7b, short-circuit prevention layers 8a and 8b, roughened surface-forming layers 9a and 9b, alignment layers 10a and 10b, an adhesive bead 11 (after adhesion), a spacer bead 12, and a liquid crystal layer 13. Each of the transparent electrodes 6a and 6b constitutes drive electrodes in combination with the auxiliary electrodes 7a and 7b, respectively. The drive electrodes (including the electrodes 6a and 7a and the electrodes 6b an 7b, respectively) intersect with each other at right angles to form a matrix electrode structure. At each intersection, one pixel is constituted and corresponds to a region between two broken lines in FIG. 1.
In order to ensure a good impact (shock) resistance and keep a uniform thickness of a liquid crystal layer, an ordinary liquid crystal panel needs to use spacer beads 12 composed of an adhesive and softer material (than the spacer beads), i.e., for effecting adhesion between the upper and lower substrate members (structures) as described above.
Such spacer beads and adhesive beads have been dispersed together on one of the pair of substrate in an ordinary (liquid crystal) panel production process (substrate production process). However, in the subsequent steps, particularly in the step of applying the pair of substrates to each other, the adhesive beads are liable to be moved due to flowability and poor adhesiveness thereof at that time, thus adversely affecting performances of a resultant liquid crystal panel.
Further, the above-mentioned liquid crystal device using a ferroelectric liquid crystal has a very small cell gap (i.e., a thickness of a ferroelectric liquid crystal layer), so that the injection of the liquid crystal into the cell gap of a blank cell is not readily performed, thus resulting in a defective liquid crystal panel in a relatively high proportion. For this reason, the ferroelectric liquid crystal device is required to improve a production yield.
There has been known a liquid crystal device including the above ferroelectric liquid crystal device having a matrix electrodes structure such that a pair of substrates (electrode plates) each provided with a group of electrodes in the form of stripes are oppositely disposed so as to form a pixel at each intersection at right angles and a gap between the substrate is filled with a liquid crystal. In case where such a liquid crystal device causes a short-circuit between the electrodes and has an electrode resistance out of its specifications, it is almost difficult to repair or replace such defective electrodes. For this reason, in an actual production line, after the formation of upper and lower electrode groups, all of the electrodes are subjected to inspection (check) with respect to short-circuit and electrode (wire) resistance by placing an inspection terminal on each lead-out portion of the electrodes, thus removing defective products from the production line.
As the number of pixels per unit display area is increased for providing a higher definition display image, an electrode width for each stripe electrode becomes narrower (smaller). Accordingly, in this case, an inspection terminal is not readily placed on a lead-out portion of an objective electrode in the above-described inspection stage, thus being liable to fail to perform a correct inspection operation.
Further, in order to reduce the electrode (wire) resistance, a metal wire (metal layer) as an auxiliary electrode is generally formed on a transparent electrode within an extent not impairing a display quality. The metal wire is liable to be damaged (e.g., burned out) by an inspection terminal having a narrowed top portion corresponding to a small electrode width or is liable to cause short-circuiting with a metal piece (fragment) scraped off or removed by the terminal.
In case where the liquid crystal device as described above is incorporated into a color liquid crystal display apparatus, a color filter comprising color filter segments of at least three colors including red (R), green (G), blue (B), and optional transparent color (W: white) in the form of stripes or a mosaic color filter wherein any adjacent (parallel) two color filter elements (comprising R, G, B and optional W segments) in one direction are shifted from each other by xc2xd pitch of one color filter segment in the direction may generally be used. Such a color filter is generally disposed at an inner surface of one of upper and lower (a pair of) glass substrates (i.e., on a side closer to a liquid crystal layer), whereby a resultant liquid crystal device has different layer structures with respect to the upper and lower substrates different from the case of a monochromatic (white and block) liquid crystal display apparatus.
In another aspect, a chiral smectic liquid crystal (e.g., a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal) shows one orientation (alignment) state under application of an electric field of one polarity based on a certain reference potential level and shows the other orientation state under application of an electric field of the opposite polarity. Such a property is quite different from that of a twisted nematic (TN)-type liquid crystal. There has been developed a color liquid crystal display apparatus utilizing the above property of the chiral smectic liquid crystal.
The above-mentioned two orientation states of the chiral smectic liquid crystal are required to have potential energies having symmetry. However, if a pair of (upper and lower) substrates have different layer structures thereon from each other as described above, the potential energies of the two orientation states are liable to become asymmetrical. The asymmetry of the potential energies is liable to cause that of switching threshold values between orientation state and the other orientation state.
The above problem is peculiar to the chiral smectic liquid crystal and does not substantially arise in the case of the TN liquid crystal. Particularly, the asymmetry of switching threshold values is liable to narrow (decrease) a drive margin (a margin allowing a good display state) determining a latitude in selecting drive signal waveform conditions, such as a voltage level, a pulse width and a frequency.
Accordingly, in the color liquid crystal display apparatus, it is important to find out a parameter (or factor) largely affecting the drive margin and to appropriately select and control such a parameter for providing a wider drive margin.
A first object of the present invention is to provide a liquid crystal (particularly a chiral smectic liquid crystal) device allowing a uniform liquid crystal layer thickness and a good shock (impact) resistance to retain good panel performance and improved in production yield and capable of realizing a full color display apparatus having high qualities comparable to those of a display apparatus using a cathode ray tube (CRT).
A second object of the present invention is to provide a liquid crystal device having a electrode structure capable of readily ensuring inspection (check) regarding an occurrence of short-circuit and an electrode (or wire) resistance without damaging electrodes used.
A third object of the present invention is to provide a color liquid crystal display apparatus capable of effecting good display in any operation conditions while retaining a wider drive margin.
According to the present invention, the above first object is principally accomplished by a liquid crystal device, comprising: a pair of substrates each provided with an electrode including one substrate having thereon a color filter and a coating layer, and a liquid crystal layer comprising a chiral smectic liquid crystal disposed together with spacer beads between the pair of substrates, wherein
the liquid crystal layer has a thickness smaller than a diameter of the spacer beads and a maximum thickness of the coating layer, the coating layer having a pencil hardness of at most 7 H.
The above objects of the present invention are accomplished by a process for producing a liquid crystal device, comprising the steps of:
forming on a first insulating substrate a light-interrupting layer, a color filter comprising plural color filter segments, a coating layer, a barrier layer, a transparent electrode, an auxiliary electrode, a short-circuit prevention layer, a roughened surface-forming layer, and an insulating layer in succession in this order,
forming on a second insulating substrate a transparent electrode, an auxiliary electrode, a short-circuit prevention layer, a roughened surface-forming layer, and an insulating layer in succession in this order,
rubbing the surface of each of the insulating layers on the first and second substrates, dispersing adhesive beads over the alignment layer surface formed on the first substrate or the second substrate,
disposing a sealing agent having a prescribed pattern on the insulating layer surface formed on the second substrate or the first substrate,
dispersing spacer beads over the alignment layer surface provided with the sealing agent,
adhesively bonding the first and second substrate to each other while fixing the first or second substrate over which the adhesive beads are dispersed,
scribing the first and second substrates to remove an unnecessary portion,
injecting a chiral smectic liquid crystal from an injection port into a gap between the first and second substrates, and
sealing up the injection port.
According to the present invention, the above second object is principally attained by a liquid crystal device, comprising: a pair of oppositely disposed substrates each provided with a group of transparent electrodes in the form of stripes, and a liquid crystal disposed between the substrates, wherein
each of the transparent electrodes partially has an auxiliary electrode in its length direction and has both lead-out end portions in a region other than a display region, each of the lead-out end portions including an exposed check portion where the auxiliary electrode is patternized so as to expose the transparent electrode.
In this case, the exposed check portions may preferably have a width larger than that of the remaining portion and are disposed alternately at every transparent electrode in their width direction.
Further, each of the exposed check portion may preferably have both end portions where the auxiliary electrode is connected so as to enclose the exposed check portion.
The device may preferably include a dummy electrode in a region other than a display region so as to form a pattern similar to those of groups of data electrodes and scanning (common) electrodes, whereby measurement of an electrode resistance is performed without adversely affecting the data and scanning electrodes.
According to the present invention, the above third object is principally achieved by a color liquid crystal display apparatus, including:
a liquid crystal device, comprising: a pair of oppositely disposed first and second substrates each provided with a group of transparent electrodes in the form of stripes, and a liquid crystal layer comprising a chiral smectic liquid crystal disposed together with spacer beads between the pair of substrates, the first substrate having thereon a color filter comprising plural color filter segments and a coating layer, wherein the transparent electrodes on the second substrate have a width smaller than that of the transparent electrodes on the first substrate,
scanning signal supply means for supplying scanning signals to the transparent electrodes on the first substrate, and
data signal supply means for supplying data signals including an interval at a prescribed temperature or below to the transparent electrodes on the second substrate, each of the data signals corresponding to each of color filter segments of the color filter.
The above color liquid crystal apparatus is effective in ensuring a wide drive margin and providing a good display state in any environmental conditions by appropriately setting and fixing driving conditions allowing the wide drive margin based on its structural characteristic features.
The present invention further provides a liquid crystal device, comprising: a pair of oppositely disposed substrates each provided with a group of transparent electrodes, and a liquid crystal disposed between the substrates, the groups of transparent electrodes of the pair of substrates intersect with each other to form a pixel at each intersection, wherein
one of the substrates includes a light-interrupting layer for covering a part of the pixel located in a position corresponding to at least one end portion of the pixel.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.