Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified... – Alignment layer of specified composition
Reexamination Certificate
1999-05-18
2002-12-17
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
Alignment layer of specified composition
C252S299400, C349S124000, C556S471000, C556S473000, C556S484000
Reexamination Certificate
active
06495221
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a chemical adsorbent which can form a monomolecular thin film wherein component molecules are aligned in a predetermined direction, a liquid crystal alignment layer utilizing the same and a liquid crystal display device utilizing the same, and additionally, a method of manufacturing the above-mentioned chemical adsorbent and the like.
BACKGROUND ART
In recent years, although a liquid crystal display device has been spread rapidly as a means of actualizing the downsizing and lightening of information apparatus, coating materials for manufacturing a liquid crystal alignment layer, which is an important constituent of the device, are limited. Consequently, a new material for the alignment layer having an unprecedented characteristic is desired according to the improvement of a liquid crystal display device in performance.
A color liquid crystal display device has a structure wherein a pair of substrates with a transparent electrode arrayed generally in a matrix and a liquid crystal alignment layer formed on the transparent electrode are opposed through the liquid crystal alignment layers with a certain gap and a liquid crystal is sealed between the gap. More specifically, a macromolecular film is formed on each surface of a first glass substrate with a pixel electrode and a thin-film transistor (TFT) array and a second glass substrate with a plurality of red, blue and green color filters and a common transparent electrode on the color filters, and an alignment of the liquid crystal is provided by rubbing the coated planes. Secondly, the first glass substrate and the second glass substrate are opposed through the coated planes (the liquid crystal alignment layers) with a spacer interposed, and an empty cell (a panel structure) is made by adhesion of a periphery of the substrates. A liquid crystal display device is constituted by sealing with an injection of such a liquid crystal as twisted nematic (TN) into the empty cell, and additionally, a liquid crystal display device as a optical display device is constituted by disposing polarizers on the front and back sides of the device as well as a backlight outside the first glass substrate.
A liquid crystal display device having such a structure applies a voltage between the electrodes to obtain an ON/OFF state with the TFT and controls a light transmission by changing an alignment state of the liquid crystal and displays an arbitrary image. Therefore, the liquid crystal alignment layers for controlling the alignment state of the liquid crystal on a path of the light transmission play an extremely important role of affecting a display performance.
A polyimide film has conventionally been used widely as coating materials for such a liquid crystal alignment layer in terms of superiority in affinity with the liquid crystal, heat-resistance and adhesion to the substrate. The following methods are used for manufacturing the polyimide film: a method wherein the polyimide film is made by changing the polyamic acid into imide while burning the substrate after rotational-coating on a substrate a solution wherein polyamic acid, which is a precursor polymer of polyimide, is dissolved in such an organic solvent as xylene; and a method wherein the polyimide film is made by evaporating the solvent after rotational-coating on a substrate a solution wherein polyimide is dissolved in such organic solvents as DMF (N,N-dimethylformamide), DMAc (dimethylacetamide), butylcellosolveacetate and N-methyl-2-pyrrolidone.
However, a polyimide film has the following problems and thereby is not enough satisfactory for a liquid crystal alignment layer. That is:
(1) In the method by using polyamic acid which is a precursor substance, it is necessary to burn at a high temperature of 250° C. and above in order to change into imide sufficiently. In the method by using polyimide, it is necessary to remove the solvent at a considerably higher temperature because of no low boiler suitable for dissolving the polyimide. Such organic solvents as the above-mentioned DMF, DMAc, butylcellosolveacetate and N-methyl-2-pyrrolidone can be used as a solvent for dissolving the polyimide. however, since every solvent has a high boiling point (153° C., 165° C., 192° C., 202° C. respectively) and is flammable, it is necessary to consider explosion-protection while manufacturing the polyimide film by evaporating and drying the solvent at a high temperature. Consequently, a particular device is necessary for heating in manufacturing a polyimide film, whereby its manufacturing costs are raised. Moreover, there is the possibility that such a circuit as TFT will be damaged by heating.
(2) Furthermore, since polyimide is not sufficiently made into a film, it is difficult to manufacture a thin film with a uniform coating thickness. Consequently, since display unevenness resulting from non-uniformity of coating thickness occurs and a thick film functions as an insulation film, another problem is that it is difficult to actualize a liquid crystal display device having a low driving voltage.
(3) In addition to the above, the following problems are caused in rubbing operation for providing an alignment.
1 If a film has irregularities on its surface, recessed portions fail to be rubbed, particularly, in the case of a panel with a large area, the panel fail to be rubbed uniformly. Accordingly, such problems are caused as the occurrence of alignment defect and display unevenness, and display sticking.
2 Furthermore, static electricity is generated on an alignment layer and the static electricity results in deteriorating the function of a TFT.
3 In addition, dust comes out of rubbing materials (cotton cloth or the like) and the dust results in display unevenness and a change of a substrate gap.
Consequently, various noncontact type aligning methods are proposed for the purpose of solving the above-mentioned problems in a rubbing method.
In Japanese Unexamined Patent Publication No. 5-53118, a technique is proposed wherein a layer of a photosensitive composition is formed on a substrate, grooves of a predetermined pattern are formed on the composition layer by exposing and heat-treating, and an alignment is provided by the grooves. However, the technique requires high photo energy for forming the grooves. Moreover, since it is difficult to form uniform grooves, such problems are caused as the occurrence of display unevenness and the like, and alignment control force is not sufficient.
In Japanese Unexamined Patent Publication No. 7-72483, a technique is proposed wherein an alignment is provided by polymerizing the polyimide or the like while irradiating linearly polarized light to a compound layer for forming an alignment layer comprising polyimide or polyimide precursor. However, since the technique uses polyimide which is an organic polymer, the technique can not solve a problem of a rise in a liquid crystal driving voltage caused by a thick coating. Another problem is that the fixing force of an alignment layer on a substrate is not sufficient.
In Japanese Unexamined Patent Publication No. 7-318942, a technique is proposed wherein a molecular structure having an alignment is made by causing another reaction of combination or decomposition in a molecular chain of the alignment layer while irradiating from a diagonal direction to an alignment layer having a macromolecular structure. However, since the technique also is intended for an alignment layer which is made of such organic polymers as polyimide, polyvinyl alcohol and polystyrene, the technique can not solve the above-mentioned problems of a thick coating and a low fixing force on a substrate. Moreover, the irradiation from a diagonal direction to an alignment layer is essential for providing a pretilt angle and the technique requires a irradiation device with high precision for irradiating accurately from a diagonal direction, whereby manufacturing costs are raised.
In addition to the above-mentioned problems, the problem of a liquid crystal display device in a twisted nematic mode or the like i
Nomura Takaiki
Ogawa Kazufumi
Ohtake Tadashi
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Wu Shean C.
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