Liquid crystal display devices and processes for producing...

Details Liquid crystal display devices and processes for producing... Liquid crystal display devices and processes for producing...

1999-12-06

2001-10-09

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

With bonding or intermediate layer of specified composition

C252S299500, C349S155000, C349S156000

Reexamination Certificate

active

06299949

ABSTRACT:

TECHNICAL FIELD
The present invention relates to color liquid crystal display devices. More particularly, the present invention relates to liquid crystal display devices, with a liquid crystal being sandwiched and supported between substrates, which can maintain a predetermined substrate-substrate spacing, and processes for producing the same.
BACKGROUND OF THE INVENTION
Liquid crystal display devices have a structure comprising: two transparent substrates, of glass or the like, each having a transparent electrode provided while leaving a gap of about 1 to 10 &mgr;m between the two substrates; and a liquid crystal material filled into the gap. In this liquid crystal display devices, a voltage is applied across the electrodes to align the liquid crystal in a given direction to create transparent portions and opaque portions, thereby displaying images. In color liquid crystal display devices, a color filter composed of colored layers of three colors corresponding to the three primary colors of light, red (R), green (G), and blue (B), and a black matrix layer (Bk) suitably disposed among the three colored layers is provided on any transparent electrode substrate, and the three primary colors are added by shutter operation of the liquid crystal to display desired colors.
The color filter for color liquid crystal display devices comprises a transparent substrate, colored layers, a protective layer, and a transparent conductive layer stacked in that order on top of one another. In this case, the gap between the color filter and the transparent substrate having thereon electrodes or thin-film transistors provided so as to face the positions of R, G, B, and Bk is maintained at several &mgr;m, and a liquid crystal material is filled into the gap to form a liquid crystal display device.
Color liquid crystal display devices are classified into a simple matrix system and an active matrix system according to the drive method of the liquid crystal. In recent years, by virtue of excellent image quality, close control of the individual pixels, and high operating speed, the active matrix system has become adopted for display devices for personal computers and the like.
In the liquid crystal display device of the active matrix system, a thin-film transistor (TFT) device is provided on a glass substrate for each pixel, and the shutter operation of the liquid crystal in each pixel is controlled by the switching operation of each TFT device. A uniform transparent electrode film as a counter electrode is provided so as to face these TFT devices.
Tin oxide, indium oxide, or a composite oxide of these oxides called “ITO” is used in the transparent electrode film. The transparent electrode film may be formed by various methods, such as vapor deposition, ion plating, and sputtering. Since, however, the protective layer as a layer underlying the transparent electrode for color filters is formed of a synthetic resin, the transparent electrode should be formed at a relatively low temperature from the viewpoint of the heat resistance of the protective layer. For this reason, sputtering has been extensively used for the production of transparent electrodes for color filters.
FIG. 4
is a cross-sectional view of a liquid crystal display device using TFT. As shown in
FIG. 4
, the construction of a liquid crystal display device
41
is such that a color filter
42
disposed so as to face an opposed substrate
43
, with TFT formed thereon, while leaving a predetermined spacing between the color filter
42
and the TFT substrate
43
and the color filter is joined to the TFT substrate with the aid of a sealant
44
comprising reinforcing fibers incorporated into an epoxy resin or the like. The space defined by the color filter and the TFT substrate is filled with a liquid crystal
45
. When the spacing between the color filter and the TFT substrate is not accurately maintained, a variation in thickness of the liquid crystal layer occurs. This thickness difference causes a difference in optical rotatory power in the liquid crystal, leading to unfavorable phenomena, such as coloration of the liquid crystal, or unsatisfactory color display due to color shading. In order to avoid these unfavorable phenomena, an attempt to accurately maintain the spacing between the color filter and the TFT substrate has been made by incorporating a large number of synthetic resin, glass, alumina, or other material particles or rods having a size of 3 to 10 &mgr;m, called “spacer”
46
, into the liquid crystal, or by using a spacer formed of a patterned photocured resin layer or the like.
When the particles or rods are used as the spacer, they are incorporated, in a large amount of about 100 particles or rods/mm
2
, into the liquid crystal. Therefore, filling of a mixture of the spacer particles or rods with a highly viscous liquid crystal into the space between the color filter and the TFT substrate sometimes poses a problem that the spacer particles or rods are not homogeneously dispersed in the liquid crystal and are localized in part of the liquid crystal. This phenomenon deteriorates the display quality in a portion where the spacer is localized, and, in addition, poses an additional problem associated with accurately maintaining the spacing between the color filter and the TFT substrate. Previously spreading a spacer on the color filter by a wet or dry process requires a special device for attaining even spacer density distribution at the time of spreading and, at the same time, requires a device for preventing the spacer from moving at the time of filling of the liquid crystal.
The spacer formed of a patterned cured resin layer or the like should satisfy the following requirements. Specifically, in the preparation of liquid crystal cells, sealing is performed at a temperature of 120 to 180° C. Regarding this heat contact bonding, ensuring a desired cell gap is required. Further, after the preparation of the liquid crystal cells, in consideration of a fluctuation in optical properties or liquid crystal layer thickness due to a temperature change of the liquid crystal layer at the time of a reliability test or during the operation of the liquid crystal display device, the liquid crystal display device should cope with an increase in cell thickness at high temperatures and can inhibit a low-temperature foaming phenomenon in the liquid crystal layer at low temperatures.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the present invention to provide a liquid crystal display device which can assure a desired cell gap at the time of heat contact bonding involved in the assembling of cells in a liquid crystal display device and, after the preparation of liquid crystal cells, has excellent reliability, can cope with an increase in cell thickness at high temperatures, and can inhibit a foaming phenomenon in a liquid crystal layer at low temperatures.
According to one aspect of the present invention, there is provided a first liquid crystal display device comprising: two substrates; a liquid crystal sandwiched and supported between the two substrates; and spacers, for maintaining a predetermined substrate-substrate spacing, provided on at least one of the substrates in its portion where the liquid crystal is sandwiched and supported, the spacers being formed of a photocured resin layer, the photocured resin layer having such properties that, as determined by the measurement of dynamic viscoelasticity in the temperature range of −40° C. to 80° C., the storage modulus (E′) is not more than 5.0×10
9
Pa with the loss tangent {tan &dgr;=E″ (loss modulus)/E′} being not more than 0.1 and, as determined by the measurement of dynamic viscoelasticity in the temperature range of 120° C. to 180° C., the storage modulus (E′) is not less than 5.0×10
7
Pa with the loss tangent {tan &dgr;=E″ (loss modulus)/E′} being not more than 0.3.
According to another aspect of the present invention, there is provided a second liquid crystal display device compri

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