Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
1998-04-29
2001-11-06
Kelly, C. H. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299400, C349S191000
Reexamination Certificate
active
06312769
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a liquid crystal alignment layer, a production method for the same and a liquid crystal display device comprising the same. More specifically, it relates to a method of producing a liquid crystal alignment layer by aligning molecules in a surface portion of the layer through exposure to polarized pulsed laser beam, a liquid crystal alignment layer produced by the method and a liquid crystal display device comprising the same.
Currently, there is known an TN (Twisted Nematic) liquid crystal display device having so-called TN liquid crystal cells, which is produced by forming a liquid crystal alignment layer on the surface, having a transparent conductive film, of a substrate to prepare a substrate for a liquid crystal display device, arranging two of the substrate to face each other, forming a nematic liquid crystal layer having dielectric anisotropy between the two substrates to form a sandwich-structured cell and twisting the long axis of the liquid crystal molecules at 90° from one substrate toward the other substrate continuously.
The alignment of the liquid crystal molecules of a liquid crystal display device such as this TN liquid crystal display device is generally effected by a liquid crystal alignment layer provided with an ability to align liquid crystal molecules, by rubbing.
However, this rubbing involves the following problems:
(1) Since static electricity may cause the destruction of a TFT device, its production machine takes generally countermeasures against static electricity. However, the countermeasures are not perfect against static electricity generated by rubbing.
(2) Since rubbing produces dust, cleaning is required as a subsequent step, thereby increasing the number of steps.
(3) Since a stepped portion and a flat portion of an alignment layer having the stepped portion differ from each other in rubbing conditions, alignment anchoring force and tilt angle are liable to be uneven.
(4) Since rubbing is carried out in a single direction, the production process of an alignment layer comprising divided alignment pixels becomes complicated.
(5) To uniformly rub an alignment layer for a large-sized substrate, for example, measuring 550×650 mm or more, a special equipment is required.
To avoid the above problems, methods for providing a liquid crystal alignment layer with an ability to align liquid crystal molecules, without necessity of rubbing treatment (to be referred to as “non-rubbing treatment” hereafter) have also been developed. One of the methods is to expose a liquid crystal alignment layer to laser beam.
JP-A 2-196219 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a method of producing a liquid crystal alignment layer by exposing the surface of a polymer film on an electrode substrate in a liquid crystal display device to high-intensity beam from an ultraviolet laser such as an XeF, XeCl, KrF, ArF or F2 excimer laser to form a periodic surface structure.
JP-A 6-130390 discloses a method of irradiating an alignment layer, which aligns the liquid crystal molecules formed on the substrate in a predetermined direction, with beam from an excimer laser through a mask having a large number of slit holes parallel to one another, while the inside of the container is deaerated, in a vacuum container.
JP-A 5-232472 discloses a method of producing an electro-optic device comprising an alignment layer is formed on the surfaces, which are arranged to face each other, of a pair of transparent substrates with liquid crystals are filled into the space between the pair of transparent substrates, the method comprising the steps of forming the alignment layer having spacers for supporting a liquid crystal film on the opposing surfaces of the transparent substrates and exposing the alignment layer to laser beam to align the liquid crystal molecules.
In either one of the above methods, since polymer molecules in a surface portion of the alignment layer are cut in a certain cycle and the cut atoms or molecules are oxidized to gasify when the liquid crystal alignment layer is exposed to laser beam, a periodic surface structure is produced on the surface of the alignment layer. Therefore, these methods have defects in that the environment of a clean room is polluted by gasified decomposed products and that since a periodic surface structure is produced on the surface by the decomposition of the polymer molecules, the electric characteristics of the surface are not satisfactory.
It is therefore an object of the present invention to provide a novel method for aligning molecules in a surface portion of an alignment layer by a non-rubbing treatment.
It is another object of the present invention to provide a method capable of aligning molecules in a surface portion of an alignment layer effectively without generating dust or decomposed products.
It is still another object of the present invention to provide a method capable of forming a periodic surface structure, which provide an ability to align liquid crystal molecules, on the surface of an alignment layer non-destructively without decomposing the molecules in a surface portion of the alignment layer.
It is still another object of the present invention to provide a liquid crystal alignment layer composed of a polyimide film and having irregularities or swells formed on the surface non-destructively and periodically.
It is still another object of the present invention to provide a liquid crystal display device comprising the above liquid crystal alignment layer of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention can be attained by a method of producing a liquid crystal film comprising exposing an organic film to polarized pulsed laser beam having a pulse energy (about 1 mJ/cm
2
to 3 mJ/cm
2
) much lower than the lowest critical pulse energy (about 10 mJ/cm
2
) by which the decomposition by exposure of polymer molecules occurs, to align polymer molecules in a surface portion of the organic film.
According to the present invention, secondly, there is provided a liquid crystal alignment layer which is composed of a polyimide film and has molecules aligned through exposure to polarized pulsed laser beam, in a surface portion thereof.
According to the present invention, thirdly, there is provided a liquid crystal display device comprising the above liquid crystal alignment layer of the present invention.
FIG. 1
of the annexed drawing shows the relationship between the transmittance (%) of a liquid crystal display device and voltage (volt). A curve A is drawn for a liquid crystal display device comprising a liquid crystal alignment layer exposed to laser beam and a curve B is drawn for a liquid crystal display device comprising a rubbed liquid crystal alignment layer.
A description is first given of the method of the present invention.
In the method of the present invention, the organic film for forming a liquid crystal alignment layer is formed from an organic polymer. Illustrative examples of the organic polymer include polyimides, polysulfones, polyesters, polyamides, poly(meth)acrylates, polycarbonates, polyphenylene sulfides, polyphenylene oxides, norbornene resins and the like.
Any known organic polymers can be used. Of these, organic polymers having a secondary transition point (Tg) or melting point (Tm) of at least about 90° C. and an SP (solubility parameter) value of at least 8.5 are preferred.
Tg is more preferably at least 150° C., particularly preferably at least 180° C.
These organic polymers which do not swell with an ordinary solvent such as an alcohol or ketone are used advantageously.
A polyimide, one of the organic polymers, contains recurring units represented by the following formula (I):
wherein R
01
is a tetravalent organic group and R
02
is a divalent organic group.
R
01
is a tetravalent organi
Hiraoka Hiroyuki
Kimura Masayuki
Kimura Shin-ichi
Matsuki Yasuo
Ogawa Toshihiro
JSR Corporation
Kelly C. H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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