Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified... – Alignment layer of specified composition
Reexamination Certificate
2000-07-05
2002-09-17
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
Alignment layer of specified composition
C252S299400, C427S387000, C427S510000, C427S515000
Reexamination Certificate
active
06451392
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a novel chemical adsorbate compound chemically adsorbed onto a surface of a substrate material. This chemical adsorbate compound is usable as a functional film for modifying properties of the surface of the substrate material, and as a liquid crystal alignment film for controlling the alignment of liquid crystal molecules. The present invention also relates to a liquid crystal alignment film employing this novel chemical adsorbate compound. The present invention further relates to a liquid crystal display device comprising this liquid crystal alignment film as a component thereof.
(2) Description of the Prior Art
In recent years, as the size and weight reduction of information processing equipment advances, liquid crystal displays have increasingly found widespread use. The liquid crystal display devices generally require liquid crystal alignment films for aligning liquid crystal molecules, but not many materials are suitable for candidate materials for the liquid crystal alignment films. As the performance of the liquid crystal devices becomes increasingly higher, there is an increasing demand for novel materials for liquid crystal alignment films which exhibit improved characteristics.
Conventionally, polymers such as polyimides and polyvinyl alcohols have been utilized for the materials for liquid crystal alignment films. However, such films made of polymers are generally large in thickness and electrically insulative, and therefore tend to cause image sticking, degradation of effective electric field, and similar undesirable effects. Moreover, such films are fixed to substrates by so-called anchoring effect, thus showing weak bonding or adhesive characteristics.
In addition, such films made of polyimides or the like have a structure such that polymer molecules are bonded each other in an intricately intertwined manner, and liquid crystal molecules cannot enter inside the films. Therefore, in such films, only the surface layer where the foremost ends of the polymer molecules protrude serves to control the alignment of liquid crystal molecules, and the rest of the portion of the film does not influence the alignment of liquid crystal molecules. Hence, the films made of polymers cannot exhibit sufficient alignment control performance over liquid crystal molecules.
Furthermore, while the films made of polymers are generally given alignment control characteristic by rubbing, alignment system made by rubbing is susceptible to external degrading factors such as heat or friction. Thus, the liquid crystal alignment films made by rubbing have a drawback that the films cannot exhibit sufficient alignment control characteristic or alignment stability. Further, rubbing causes the following drawbacks.
i) When a film surface has roughness, depressed portions of the film surface cannot be rubbed. The unrubbed portions cause alignment defects, which in turn cause image sticking and unevenness in displayed images.
ii) Rubbing treatment causes static charge, which damages the TFTs formed underneath the alignment film.
iii) By rubbing, dust is produced from a rubbing cloth (cotton cloth or the like) and film surface. The dust can cause uneveness in displayed images and undesirable variation in the cell gap.
In order to provide a solution to such problems of rubbing as described above, some non-contact alignment techniques have been suggested. However, none of the techniques has yet achieved completely satisfactory results. For example, Japanese Unexamined Patent Publication No. 5-53118 discloses the following technique; a layer of a photosensitive compound is formed on a substrate, and grooves having a prescribed pattern are formed in the photosensitive compound layer by light exposure and heat treatment, thus realizing an alignment control characteristic by the grooves. This technique, however, requires a large light energy for producing the grooves. Moreover, uniform grooves are difficult to form, and uneveness in displayed images tends to occur. The alignment control performance is also insufficient.
Japanese Unexamined Patent Publication No. 7-72483 discloses the following technique; alignment control characteristic in an alignment film is realized by applying a linear polarized light to a layer of a compound for forming the alignment film containing polyimide or polyimide precursor to polymerize the polyimide or polyimide precursor. However, this technique employs polyimide, which is an organic polymer, and therefore cannot solve the problem of the large film thickness, which induces an increase in liquid crystal driving voltage. Another problem is that the adhesiveness of the resultant alignment film to the substrate is not sufficient.
Japanese Unexamined Patent Publication No. 7-318942 disclose the following technique; in an alignment film, a molecular structure having an alignment control characteristic is realized by applying a light from an oblique direction to the alignment film having a polymer structure to create different bonds or decomposition in the molecular chains in the film. However, this technique also employs alignment films made of organic polymers such as polyimide, polyvinyl alcohol, polystyrene, and the like. Therefore, this technique as well cannot solve the above-described problems of large film thickness and small adhesiveness to the substrate. In addition, this technique requires that a light be applied from an oblique direction to the alignment film in order to produce a pretilt angle, and this leads to increase in manufacturing cost since an accurate light irradiation from an oblique direction calls for a high accuracy apparatus for light irradiation.
Further, twisted-nematic mode or the like liquid crystal display devices employing prior art liquid crystal alignment film have another problem of narrow viewing angles. In view of this problem, for example, Japanese Unexamined Patent Publication No. 6-173135 discloses the following technique; an alignment film comprising a plurality of micro-regions having different liquid crystal alignment directions are realized by repeating the consecutive steps in which an alignment film is rubbed in a certain direction, thereafter prescribed regions of the rubbed film are coated with a resist, and the film is rubbed in the reverse direction. However, in order to form a plurality of domains having different alignment directions by a rubbing method (contact method), it is necessary to repeat complicated steps of masking and rubbing each time corresponding to the divided domains. Accordingly, by this technique, production efficiency is degraded, and the problems of the static charge and dust produced by rubbing are further worsened.
In order to improve viewing angles, it is. possible to employ the non-contact methods as described above. However, those prior art non-contact techniques (Japanese Unexamined Patent Publication Nos. 5-53118, 7-72483, and 7-318942) have the problems of large film thickness and insufficient adhesiveness to the substrate, and therefore cannot provide satisfactory liquid crystal alignment films.
In view of these problems, the present inventors have proposed a technique for producing a novel nanosized liquid crystal alignment film in Japanese Unexamined Patent Publication No. 3-7913. In this technique, an alignment film is composed of a monomolecular layer in which a silane-based chemical adsorbate compound (also referred to as a “surfactant”) is chemically adsorbed onto a substrate surface. According to this technique, an ultra thin transparent film firmly bonded to the substrate surface can be easily formed in an efficient manner. Furthermore, this technique can provide, without rubbing, a liquid crystal alignment film having a certain alignment control performance. However, in this technique, there still is room for improvement in the thermal stability and alignment control performance of the alignment film.
SUMMARY OF THE INVENTION
The present invention comprises a series of groups, namely, a first group, a secon
Nomura Takaiki
Ogawa Kazufumi
Ootake Tadashi
Takebe Takako
Parkhurst & Wendel L.L.P
Wu Shean C.
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