Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-03-26
2003-09-30
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06628360
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-087245, filed Mar. 27, 2000; and No. 2000-087248, filed Mar. 27, 2000, the entire contents of both of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device including a liquid crystal layer having liquid crystal molecules homogeneously aligned between opposed substrates.
A TN (Twisted Nematic) type liquid crystal display device, in which a liquid crystal layer having its molecule alignment twisted at a predetermined angle is sealed between a pair of substrates, and a pair of polarizing plates are arranged on the substrates interposed therebetween, is widely applicable as various types of display elements, because of a high contrast and excellent electro-optic properties.
The TN type liquid crystal display device has a high contrast at front view. It unpreferably shows great changes in contrast when observed in a direction inclined from its normal line, and therefore has a narrow viewing angle. To widen the viewing angle, an optical compensation element, such as a retardation plate, is used.
Since, however, the liquid crystal layer of the TN type liquid crystal display device has a twisted molecule alignment, it is difficult to perform a sufficient optical compensation.
In the case of a liquid crystal device of a homogeneous-alignment type, in which liquid crystal molecules sealed between a pair of substrates are aligned in one direction in their initial state, i.e. the molecule alignment is not twisted, it is easier to compensate for its optical properties and to widen its viewing angle than in the TN type liquid crystal display device.
The homogeneous-alignment type liquid crystal display device comprises a liquid crystal element, in which nematic liquid crystal molecules having a positive dielectric anisotropy and a homogeneous alignment are sealed as a liquid crystal layer between a pair of transparent substrates having transparent electrodes mounted on their opposed inner surfaces and alignment films mounted on the electrodes. The device further includes a pair of polarizing plates provided with the liquid crystal element interposed therebetween.
In a conventional homogeneous-alignment type liquid crystal display device, the stability of the homogenous molecule alignment of the liquid crystal layer depends upon the anchoring of the alignment film and the natural cohesive power of the nematic liquid crystal (the intermolecular force of liquid crystal molecules, which urges the molecules to be arranged in one direction). This means that the liquid crystal molecules may be irregularly aligned.
In other words, in the initial state of alignment, an irregular alignment may easily occur, in which the major axes of liquid crystal molecules are not uniformly aligned in one direction.
Further, in the homogenous-alignment type liquid crystal display device, the axes of molecules will be changed to accord with a direction perpendicular to the surface of the substrate in accordance with an electric field applied between the electrodes on the substrates. If the electric field is turned off after the molecules thus move to a large extent, the molecules do not return to the original state of homogeneous alignment in which the directors of the molecules are arranged in one direction, thereby raising an irregular alignment.
Moreover, in such a type liquid crystal display device, disclination may be created by an irregular alignment around each pixel electrode formed on the inner surface of one of the substrates. This irregular alignment occurs due to the influence of, for example, the height difference between the pixel electrodes and their peripheral wiring, and an electric field that occurs between each pixel electrode and the wiring.
In addition, if the substrate of the liquid crystal element is deformed by an external force and the alignment state of liquid crystal molecules at and around the deformed portion is greatly changed, the molecules do not return, even after the deformed substrate is restored, to the original state of homogeneous alignment in which the directors of the molecules are arranged in one direction, thereby raising an irregular alignment.
As described above, the conventional homogenous-alignment type liquid crystal display device is disadvantageous in that the homogenous alignment state of liquid crystal molecules will easily become irregular, thereby raising a defective state, i.e. a degraded contrast in the irregularly aligned region of the display.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to provide a liquid crystal display device having a liquid crystal layer in which molecules are uniformly aligned in a less defective state, thereby maintaining a high quality display.
It is another object of the invention to provide a homogenous-alignment type liquid crystal display device, in which the occurrence of disclination around each pixel electrode is suppressed, and hence which can display high quality images.
To attain the objects, the invention provides a liquid crystal display device comprising: a first substrate having at least one first electrode formed thereon; a second substrate having a plurality of second electrodes formed thereon and opposed to the first electrode, the second substrate being opposed to the first substrate with a predetermined gap therebetween, the second electrodes being arranged to form a matrix display section having a plurality of pixels arranged in a matrix of rows and columns, each of the pixels being defined by an area in which the first electrode is opposed to each of the second electrodes; a first alignment film formed on the second substrate with the second electrodes, an aligning treatment being executed on the first alignment film in a first direction that intersects, at an angle of 5° to 10°, one of a row direction and a column direction of the matrix display section; a second alignment film formed on the first substrate having the first electrode formed thereon, an aligning treatment being executed on the second alignment film in a second direction substantially parallel to the first direction of the first alignment film; and a liquid crystal sealed between the first and second substrates and constituting a liquid crystal layer that ranges from liquid crystal molecules adjacent to the first alignment film to liquid crystal molecules adjacent to the second alignment film, all liquid crystal molecules in the liquid crystal layer being arranged in one direction.
Since, in this liquid crystal display device, the alignment directions of the inner surfaces of a pair of substrates obliquely intersect, at an angle of 5° to 10°, one of a row direction and a column direction of the matrix in one direction, the occurrence of disclination is suppressed, which is due to a lateral electric field created between each pixel electrode and a line adjacent thereto, and/or due to the influence of a height difference between each pixel and a line adjacent thereto, or due to the influence of the aligning treatment. As a result, a high-quality image can be displayed.
In the above structure, it is preferable that the first direction, in which the aligning treatment is executed on the first alignment film, intersects, at an angle of 7° to 8°, one of the row direction and the column direction of the matrix display section. Most preferably, the angle is 7.5°.
Preferably, the liquid crystal display device further comprises a pair of polarizing plates each provided at an outer side of a corresponding one of the first and second substrates, the polarizing plates having their respective optical axes arranged perpendicular to each other. More preferably, the optical axis of one of the polarizing plates intersects, substantially at an angle of 45°, the second and first directions of the respective second and first alignment films respectively provided on the first and second substrates.
Further prefera
Kizaki Seiichi
Yamada Hiroko
Casio Computer Co. Ltd.
Frishauf Holtz Goodman & Chick P.C.
Parker Kenneth
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