Liquid crystal device and liquid crystal injection method

Abstract: A liquid crystal injection method for a liquid crystal device including a region where image display pattern electrodes (112) are disposed within a cell surrounded by a seal (113) for enclosing a liquid crystal comprises injecting the liquid crystal while disposing a dummy pattern film (111) for promoting the liquid crystal injection at a part other than the region with the image display pattern electrodes (112) within the cell.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to a liquid crystal device and a liquid crystal injection method, more particularly to a liquid crystal device using a chiral smectic liquid crystal and a liquid crystal injection method for preparing the device. A liquid crystal display device is constituted by a pair of oppositely disposed substrates and a pair of stripe electrode groups respectively disposed on the substrates so as to intersect each other. In a lithographic step for forming such a group of stripe electrodes, particularly one for producing a liquid crystal display device having a display area of 25,4 cm (10 inch) or larger and a high definition requiring a resolution of 4 pel or more/mm, a high resolution and, in some cases, an alignment accuracy for superposing opaque electrodes for lowering the electric resistance of the stripe electrodes and for masking between pixels are required. For satisfying such performances, it has been practiced to divide each group of stripe electrodes into divisions, e.g., by a line intersecting the stripe electrodes, expose a division after a division, and join the divisions to form entire electrodes when exposure is performed by an exposure apparatus (e.g., "MAP-1500", mfd. by Canon K.K.). In this instance, the joints in the vertical direction have been conventionally disposed at positions superposed with an intersecting stripe electrode on the opposite substrate. In a conventional device, however, when such a pair of substrates are superposed with each other so that their stripe electrodes intersect each other and a liquid crystal is disposed therebetween to form a display device, and the device is driven by applying voltages to the stripe electrodes, an alignment deviation in the vertical direction of the stripes, if it is large, is liable to appear on a display screen and be noticed by human eyes, thus deteriorating the display quality. It is also practiced divide the stripe electrodes on one or both substrates by a line parallel to the stripe electrodes. In this instance, the joint in the parallel direction has been generally disposed on one stripe electrode on a single substrate. If the alignment deviation occurs in the parallel joint, the stripe electrode concerned is caused to have a different width from the other electrodes and provides pixels having different sizes (aperture areas), when intersected with the stripe electrodes on the opposite substrate, which are noticeable to human eyes. Further, in case of superposing opaque electrodes for lowering the electric resistance of the respective stripe electrodes on one or both substrates and for masking between the pixels, an alignment deviation thereof with the single electrode on which the parallel joint is formed is also noticeable on display. In a simple matrix cell, the electrode pattern is generally remarkably different between the display region and the peripheral part extended from the display region close to the seal, because..'the electrode pattern is modified at the latter part for loading or assemblage and the electrode for display is not provided near the seal. In the prior art, however, the heated and injected front of the ferroelectric liquid crystal tends to proceed between electrodes formed by etching due to its surface 'tension, thus resulting in difficulties as follows. At a part where the electrodes assume a different pattern from that of the display electrode, particularly at a part close to the seal, a much. longer time is required for liquid crystal injection than the display electrode region. As a result, the part where the liquid crystal has been injected at a different speed is liable to later result in a different alignment state, which can further affect the neighboring region to result in an inferior display quality as a whole. Further, on a conductor film or glass at a part where the liquid crystal has arrived at in a longer time, the liquid crystal is liable to move on later heating for re-alignment, etc., thus resulting in a vacuum void. SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a method of producing a liquid crystal display device, whereby the liquid crystal injection speed is made uniform, thereby uniformizing the alignment characteristic, over the entire cell area to provide an improved display quality; as well as a liquid crystal display device obtained thereby. According to the present invention, there is provided a liquid crystal device as defined in claim 1. According to another aspect of the present invention, there is provided a method for producing a liquid crystal display device as defined in claim 2. More specifically, when a ferroelectric liquid crystal is injected into a cell, the injected front thereof proceeds to be injected between the electrodes while being aided by surface 'tension or surface intersection with the electrodes. Accordingly, by disposing such a dummy pattern film, the liquid crystal injection can be appropriately controlled and uniformized, whereby the resultant alignment and therefore the image quality are improved, and the production yield at the time of mass production is stabilized. If the shape or design of the dummy pattern film is appropriately selected, the dummy pattern film can be used for prevention of the liquid crystal movement on heating after the injection or for ensuring a uniform cell gap and may also be used as an alignment mark required in the production process. 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. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partial plan view of an embodiment of the liquid crystal cell according to the invention. Figure 2 is a partial plan view of another embodiment of the liquid crystal cell according to the invention wherein the dummy pattern film is also used for another purpose. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinbelow, the present invention will be described with reference to the drawings. As to the description of possible constructions and production methods of liquid crystal display devices, especially the electrode parts thereof, reference is made to the embodiments illustrated by Figs. 1 to 10 and the related description, especially Examples 1 to 4 provided in EP-A-536 680 (representing the publication of the parent application). Specifically, a liquid crystal display device was formed by applying the above-treated two substrates so that the joint on one substrate was aligned with a metal electrode on the other substrate and vice versa. When the device was driven, the joints as a result of the four part division were not noticeable at all. Furthermore, by disposing a joint for forming a group of stripe electrodes in a direction perpendicular to the stripe electrodes at a non-display part on the counter substrate, it is possible to provide a liquid crystal display device free from lowering in display quality even if a larger tolerance is provided in joint deviation arising from an error in mechanical accuracy. In case where the liquid crystal display device has opaque metal electrodes for lowering the electric resistance of the stripe electrodes, the regions of the opaque metal electrodes may be included in the non-display region. The liquid crystal may preferably be a chiral smectic liquid crystal showing ferroelectricity. Figure 1 is a partial plan view of a liquid crystal cell according to an embodiment of the present invention. Referring to Figure 1, the liquid crystal cell includes pattern electrodes 112 for image display and dummy pattern films 111 for aiding the progress of a liquid crystal along them within a seal area 113. A liquid crystal injected through an injection port proceeds between a narrow path between image display pattern electrodes 112 left after etching. At this time, the liquid crystal proceeds at an identical speed also between the dummy pattern films up to a corner near the seal 113 under similar conditions as in the image display area. Figure 2 is a partial plan view of a liquid crystal cell according to another embodiment of the present invention. In this embodiment, a dummy pattern film for aiding the liquid crystal injection is also used for another purpose. More specifically, the cell includes image display pattern electrodes 112 and dummy pattern films 114 for aiding the liquid crystal injection within the seal area 113. The dummy pattern films 114 extends up to the seal area 113, whereby they also function to provide a uniform cell gap which is liable to be affected by the display pattern electrode thickness. The liquid crystal cell also includes dummy pattern films 115 which have a narrower width than the display pattern electrodes 112 and can be disposed in a higher density the in the display area. This is effective in preventing movement of a ferroelectric chiral smectic liquid crystal which is liable to move at the time of reheating after the injection and also in preventing the occurrence of a void caused by injection failure. Herein, the dummy pattern film may generally be of a similar material as a transparent image display pattern electrode or an opaque metal member but can be in a different shape as far as it shows the required effect of promoting the liquid crystal injection. As described above, by disposing a dummy pattern film for aiding liquid crystal injection, a liquid crystal can be satisfactorily injected up to a part where the liquid crystal is not readily filled, so that it is possible to shorten the time required for liquid crystal injection into a cell of an identical volume, thus enhancing the capacity of the production apparatus.

Claims: A liquid crystal display device comprising a pair of substrates; image display pattern electrodes (112) formed thereon; and a dummy pattern film (111; 114; 115) within a cell surrounded by a seal (113), wherein said dummy pattern film is formed on the substrates at areas not occupied by the image display pattern electrodes, the dummy pattern film being so designed that, when the liquid crystal is injected, it is promoted to these areas. A method of producing a liquid crystal display device including the steps of disposing a pair of substrates, forming image display pattern electrodes (112) thereon, forming with the substrates and a peripheral seal (113) a closed cell, and injecting a liquid crystal material within the cell, the method being characterized in that a dummy pattern film (111; 114; 115) is formed on the substrates at areas not occupied by the image display pattern electrodes, the dummy pattern film being so designed that, when the liquid crystal is injected, it is promoted to these areas. A method according to claim 2, wherein said dummy pattern film (114) is disposed to extend up to within said seal (113) for enclosing a liquid crystal. A method according to claim 2, wherein said dummy pattern film (115) has a width narrower than that of said image display pattern electrodes (112). A method according to claim 2, wherein said liquid crystal is a chiral smectic liquid crystal.

Inventors: MASAKI YUICHI, MITSUI MUTSUO, SUZUKI MASAAKI, YOSHIOKA TOSHIFUMI, MASAKI, YUICHI, MITSUI, MUTSUO, SUZUKI, MASAAKI, YOSHIOKA, TOSHIFUMI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G02F1
IPC codes: G02F1