Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-03-05
2002-11-05
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S096000
Reexamination Certificate
active
06476892
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical compensatory sheet consisting of one cellulose acetate film. The invention also relates to a polarizing plate and a liquid crystal display equipped with the optical compensatory sheet.
BACKGROUND OF THE INVENTION
A cellulose acetate film has been used for various photographic or optical materials because it is sturdy and hardly flamed. The cellulose acetate film is a typical photographic support. The cellulose acetate film is also used in a liquid crystal display. Since the cellulose acetate film has a high optical isotropy (i.e., a low retardation value) compared with other polymer films, the cellulose acetate film is usually used as an optical isotropic element (e.g., a transparent protective film of a polarizing plate) of a liquid crystal display.
In contrast, an optical compensatory sheet (a retardation film) used in a liquid crystal display must have a high optical anisotropy (i.e., a high retardation value). Accordingly, a synthetic polymer film giving a high retardation value, such as a polycarbonate film or a polysulfone film, is usually used as an optical compensatory sheet.
Generally in the field of optical materials, the synthetic polymer film is used as an optically anisotropic film (having a high retardation value), while a cellulose acetate film is used was an optical isotropic film (having a low retardation value).
European Patent No. 0911656 A2, however, discloses a cellulose acetate film having a high retardation value. The film is used as a support of an optical compensatory sheet, which comprises the support and an optically anisotropic layer containing a discotic liquid crystal molecule.
SUMMERY OF THE INVENTION
An object of the present invention to optically compensate a liquid crystal cell by using only one cellulose acetate film.
Another object of the invention is to provide an optical compensatory sheet consisting of one cellulose acetate film.
A further object of the invention is to add an optical compensatory function to a polarizing plate without increasing members of the plate.
A furthermore object of the invention to provide a liquid crystal display optically compensated by a cellulose acetate film.
The present invention provides an optical compensatory sheet consisting of one cellulose acetate film which comprises cellulose acetate having an acetic acid content in the range of 59.0 to 61.5% and an aromatic compound having at least two aromatic rings, said aromatic compound being contained in the film in an amount of 0.01 to 20 weight parts based on 100 weight parts of the cellulose acetate, and said cellulose acetate film giving an Re retardation value of 20 to 70 nm and an Rth retardation value of 70 to 400 nm.
The invention also provides a polarizing plate comprising a polarizing membrane and two transparent protective films provided on both sides of the membrane, wherein one of the transparent protective films consists of one cellulose acetate film which comprises cellulose acetate having an acetic acid content in the range of 59.0 to 61.5% and an aromatic compound having at least two aromatic rings, said aromatic compound being contained in the film in an amount of 0.01 to 20 weight parts based on 100 weight parts of the cellulose acetate, said cellulose acetate film giving an Re retardation value of 20 to 70 nm and an Rth retardation value of 70 to 400 nm, and said polarizing membrane being so placed that a slow axis of the cellulose acetate film is essentially parallel to a transparent axis of the polarizing membrane.
The invention further provides a liquid crystal display comprising a liquid crystal cell and two polarizing plates provided on both sides of the cell, said polarizing plate comprising a polarizing membrane and two transparent protective films provided on both sides of the membrane, wherein an optical compensatory sheet is provided between the liquid crystal cell and one of the polarizing plates, said optical compensatory sheet consisting of one cellulose acetate film which comprises cellulose acetate having an acetic acid content in the range of 59.0 to 61.5% and an aromatic compound having at least two aromatic rings, said aromatic compound being contained in the film in an amount of 0.01 to 20 weight parts based on 100 weight parts of the cellulose acetate, said cellulose acetate film giving an Re retardation value of 20 to 70 nm and an Rth retardation value of 150 to 400 nm, and said cellulose acetate film and the polarizing membrane neighboring the film being so placed that a slow axis of the cellulose acetate film is essentially parallel to a transparent axis of the polarizing membrane.
The invention furthermore provides a liquid crystal display comprising a liquid crystal cell and two polarizing plates provided on both sides of the cell, said polarizing plate comprising a polarizing membrane and two transparent protective films provided on both sides of the membrane, wherein one of the two transparent protective films placed between the cell and the membranes consists of one cellulose acetate film which comprises cellulose acetate having an acetic acid content in the range of 59.0 to 61.5% and an aromatic compound having at least two aromatic rings, said aromatic compound being contained in the film in an amount of 0.01 to 20 weight parts based on 100 weight parts of the cellulose acetate, said cellulose acetate film giving an Re retardation value of 20 to 70 nm and an Rth retardation value of 150 to 400 nm, and said cellulose acetate film and the polarizing membrane neighboring the film being so placed that a slow axis of the cellulose acetate film is essentially parallel to a transparent axis of the polarizing membrane.
The invention still further provides a liquid crystal display comprising a liquid crystal cell and two polarizing plates provided on both sides of the cell, said polarizing plate comprising a polarizing membrane and two transparent protective films provided on both sides of the membrane, wherein an optical compensatory sheet is provided between the liquid crystal cell and each polarizing plate, said optical compensatory sheet consisting of one cellulose acetate film which comprises cellulose acetate having an acetic acid content in the range of 59.0 to 61.5% and an aromatic compound having at least two aromatic rings, said aromatic compound being contained in the film in an amount of 0.01 to 20 weight parts based on 100 weight parts of the cellulose acetate, said cellulose acetate film giving an Re retardation value of 20 to 70 nm and an Rth retardation value of 70 to 200 nm, and said cellulose acetate film and the polarizing membrane neighboring the film being so placed that a slow axis of the cellulose acetate film is essentially parallel to a transparent axis of the polarizing membrane.
The invention still furthermore provides a liquid crystal display comprising a liquid crystal cell and two polarizing plates placed on both sides of the cell, said polarizing plate comprising a polarizing membrane and two transparent protective films provided on both sides of the membrane, wherein each of the two transparent protective films placed between the cell and the membranes consists of one cellulose acetate film which comprises cellulose acetate having an acetic acid content in the range of 59.0 to 61.5% and an aromatic compound having at least two aromatic rings, said aromatic compound being contained in the film in an amount of 0.01 to 20 weight parts based on 100 weight parts of the cellulose acetate, said cellulose acetate film giving an Re retardation value of 20 to 70 nm and an Rth retardation value of 70 to 200 nm, and said cellulose acetate film and the polarizing membrane neighboring the film being so placed that a slow axis of the cellulose acetate film is essentially parallel to a transparent axis of the polarizing membrane.
The present inventor has improved the cellulose acetate film disclosed in European Patent No. 0911656 A2, and succeeded in optically compensating a liquid crystal cell by using the improved film only.
The cellul
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Ton Toan
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