Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-09-16
2004-11-16
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06819390
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a liquid crystal device, a method for manufacturing the same, and an electronic device equipped with the liquid crystal device. More particularly, the invention relates to a technique of placing spacers between a pair of substances.
2. Description of Related Art
Related art liquid crystal devices can be constructed such that a lower substrate and an upper substrate are bonded together with a seal member in the respective peripheries of the substrates, and a liquid crystal layer is sealed between the pair of substrates. The related art also places spacers, such as resin balls, glass balls, or columnar resin members, between the pair of substrates in order to keep the substrate spacing evenly in the substrate surfaces.
In general, such liquid crystal devices are manufactured by the following process steps of: depositing electrodes and alignment layers on each of the lower substrate and the upper substrate; printing an uncured seal member on the periphery of, for example, the lower substrate with an opening serving as a liquid crystal inlet formed therein; spraying spacers on the surface of the substrate or the other substrate; and bonding the lower substrate and the upper substrate together through a seal member, thereby forming a hollow liquid crystal cell. Then, curing the uncured seal member; injecting a liquid crystal into the liquid crystal cell through the liquid crystal inlet that is formed in the seal member in advance, by vacuum injection; sealing the inlet with a seal member; and finally, bonding an optical film, such as a retardation film or a polarizer, on the outer surfaces of the lower substrate and the upper substrate, thereby forming a liquid crystal device.
For the spacer spraying step for example, a method can be used in which spacers are evenly sprayed on the substrate by spraying a spacer dispersion liquid in which spacers are dispersed in a prescribed solvent. On the other hand, for example, a technique of arranging spacers in a specific region in a liquid crystal cell by ink jetting (droplet discharge method) is disclosed in Japanese Unexamined Patent Application Publication No. 2001-188235. The spacers act to keep the substrate spacing evenly, whereas they exert a negative influence on display, for example, they cause light leakage and misalignment of a liquid crystal when arranged in a pixel region. Therefore, liquid crystal devices in which spacers are selectively arranged only in a non-pixel region in a liquid crystal cell, and a method for manufacturing the same is disclosed in Japanese Unexamined Patent Application Publication Nos. 54-107754 and 2-308224. For example, Japanese Unexamined Patent Application Publication No. 9-105946 discloses a method of placing spacers in a non-pixel region by ink jetting. Another example is a specific spacer fixed-point placement device by ink jetting, as disclosed in Japanese Unexamined Patent Application Publication No. 2002-72218.
As described above, the related art includes methods of arranging spacers in a non-pixel region which is not involved directly in display. Although it is necessary to arrange a predetermined number of spacers or more in the liquid crystal cell in view of keeping the substrate spacing evenly, it is preferable to place a reduced or minimum number of spacers needed in consideration of a bad influence on display. From the above viewpoint, the related art techniques give no consideration to a beneficial or the optimum number (density) of spacers at all. Accordingly, a standard of a beneficial or the optimum number (density) of spacers has been required to reduce uneven display due to uneven cell thickness (substrate spacing) in the substrate surface and a decrease in contrast due to light leakage owing to the presence of spacers and misalignment and so on, thereby enhancing display quality.
It has also been required to provide a method of stably controlling the number of spacers by ink jetting. Specifically, the ink jetting only emits ink (liquid). However, in order to emit a dispersion liquid that contains a solid matter, such as a spacer, only in a fixed region, the diameter of the nozzle of the ink jet unit must be optimized. However, there has been no indicator for the most suitable nozzle diameter for the spacer dispersion liquid.
SUMMARY OF THE INVENTION
The present invention addresses the above and/or other circumstances, and provides a liquid crystal device that is superior in display quality by providing a beneficial or optimized number (density) of spacers in arranging the spacers in fixed points in a substrate surface with a droplet discharge unit, such as an ink jet unit, a method for manufacturing the liquid crystal device, and an electronic device including the liquid crystal device.
According to a first exemplary embodiment of the present invention, a liquid crystal device is provided in which a pair of substrates is opposed to each other through a seal member and a liquid crystal and spacers are contained in a sealed space enclosed with the pair of substrates and the seal member. The spacers are placed on all or part of intersection points of a plurality of first parallel phantom lines extending in a first direction and a plurality of second parallel phantom lines extending in a second direction different from the first direction with the spacers arranged separately, in aggregation, or in a mixture thereof. The density of spacers is from 50 to 300/mm
2
and the average number of spacers on all the intersection points is from 0.2 to 3.
According to the invention, the density of spacers is from 50 to 300/mm
2
and the average number of spacers on all the intersection points of the first phantom lines and the second phantom lines is from 0.2 to 3. Accordingly, deterioration in display quality due to the spacers can be sufficiently reduced so that display quality can be enhanced.
The liquid crystal device of the invention is manufactured by the below-described method such that the spacers are placed on all or part of intersection points of a plurality of first parallel phantom lines extending in a first direction and a plurality of second parallel phantom lines extending in a second direction different from the first direction with the spacers arranged separately, in aggregation, or a mixture thereof. Specifically, according to the method for manufacturing the liquid crystal device of the present invention, a spacer dispersion liquid having the spacers dispersed in a predetermined solvent is dropped on the substrate with a droplet discharge unit, and each droplet contains a random number of spacers. The solvent is evaporated after dropping, so that the spacers are left on the substrate. Since the droplet discharge unit is used, the spacers are not irregularly arranged on the substrate but are separately arranged on the intersection points of the plurality of first parallel phantom lines extending in a first direction corresponding to an arrangement direction of nozzles of the droplet discharge unit and the plurality of second parallel phantom lines extending in the second direction corresponding to a scanning direction of the nozzles of the droplet discharge unit. In the invention, the reason why the spacers are placed on all or part of the intersection points is because the number of spacers contained in the droplet is random and relatively small, so that even when droplet was dropped, it may contain no spacer, finally some points may contain no spacer.
The base for the above numerical range is described below via Examples. When the density of spacers becomes smaller than 50/mm
2
, the substrate spacing cannot be sufficiently kept by the spacers, so that unevenness in cell thickness is increased to significantly decrease display quality. On the other hand, when the density of spacers becomes larger than 300/mm
2
, bubbles generate in a liquid crystal at low temperature, causing a failure called vacuum bubbles. This is because, since a liquid crystal has a higher thermal expansion coefficient than t
Hirata Yoshitomo
Kosuge Masahiro
Momose Yoichi
Onizuka Emiko
Washizawa Takehito
Seiko Epson Corporation
Ton Toan
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