Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Screen other than for cathode-ray tube
Reexamination Certificate
2000-04-26
2002-09-24
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Screen other than for cathode-ray tube
C349S106000, C359S891000
Reexamination Certificate
active
06455208
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a colored polymer thin film, a color filter, and a liquid crystal display.
1. Background Art
From the viewpoint of ease of thin film processing, and low cost, polymer thin films are used in a wide range of fields of optical part applications such as an optical waveguide, a matrix material for a color filter, and the like, electronics applications such as an interlayer insulator layer in LSI, a passivation layer, a buffer coat, and the like.
However, such polymer thin films generally have high birefringence, and thus cause a phase difference in transmitted light due to high retardation when used for a color filter, thereby increasing the viewing angle characteristic and deteriorating display performance of a liquid crystal display.
2. Disclosure of Invention
The present invention has been conceived in consideration of the above-described drawbacks of conventional techniques, and an object of the invention is to provide a liquid crystal display exhibiting excellent display performance.
The object of the present invention is achieved by a colored polymer thin film having an average refractive index of 1.60 to 1.90, and an absolute value of birefringence of 0.01 or less, and a color filer and a liquid crystal display using the polymer thin film.
BEST MODE FOR CARRYING OUT THE INVENTION
A colored polymer thin film of the present invention represents a thin film colored with a pigment, a dye, or the like, composed of a polymer such as an acrylic resin, an alkyd resin, polyester, polyimide, polyamidoimide, polyamide, or the like, and having a thickness of 0.1 to 500 &mgr;m. As a colorant, a pigment is,preferably used from the viewpoint of heat resistance.
In the present invention, optical characteristic values are defined as follows:
n
xy
: Refractive index when the vibration direction of light is parallel to the film plane of a thin film;
n
z
: Refractive index when the vibration direction of light is perpendicular to the film plane of a thin film;
d: Thickness of a thin film
Average refractive index (avg)=(2
n
xy
+n
z
)/3 Birefringence &Dgr;
n=n
xy
−n
z
Retardation: Product of birefringence and film thickness (&Dgr;n×d)
As these optical characteristic values, measurements of the colored polymer thin film at the peak wavelength of transmitted light were used. For example, light at a wavelength 610 nm is used for a red colored thin film, a wavelength 540 nm, a green colored thin film; a wavelength of 430 nm, a blue colored thin film.
As a result of various researches of the method of improving the display performance of a liquid crystal display, the inventors found that a color filter using a colored polymer thin film having an average refractive index in a specified range, and birefringence in a specified range is preferably used.
The viewing-angle characteristic of the liquid crystal. display is affected by the retardation of the color filter. Although a conventional liquid crystal display having a narrow viewing angle has substantially no problem, a liquid crystal display adapted for widening the viewing angle, for example, a viewing-angle widening film-system liquid crystal. display, or a transverse electric field driving-system (IPS system) liquid crystal display, requires a color filter having low retardation. In the liquid crystal display, in order to obtain excellent display performance that a transverse deviation in the viewing angle with contrast is 5° or less in terms of a simulation value, the retardation of the colored polymer thin film is preferably 25 nm or less. The retardation is more preferably, 15 nm or lees, more preferably 10 nm or less, more preferably 5 nm or less, most preferably 3 nm or less. Since the retardation is represented by the product of a birefringence and a film thickness, the retardation can be decreased by decreasing the thickness of the colored polymer thin film. However, the colored polymer thin film of a color filter for a liquid crystal display generally has a thickness of 1.0 to 2.0 &mgr;m, and it is difficult to further decreasing the thickness. Therefore, in order to decrease the retardation of the color filter, it is necessary to decrease the birefringence of the colored polymer thin film.
Namely, the colored polymer thin film of the present invention has an average refractive index of as high as 1.60 to 1.90, and an absolute value of birefringence of 0.01 or less, more preferably 0.005 or lees, more preferably 0.0025 or less, most preferably 0.001 or less. Particularly, a green colored thin film used for green pixels of the color filter has highest luminous transmittance and highest influence on the viewing-angle characteristic of the liquid crystal display, and thus the absolute value of birefringence is preferably as low as possible.
As a result of intensive research of the method of obtaining a colored polymer thin film having a high refractive index and low birefringence, it was found that the following two methods are effective. A first method is to contain a polymer having plane structural groups in side chains in the colored polymer thin film. This can suppress planar orientation of the colored polymer thin film, and attain a low birefringence without deteriorating other characteristics. A second method is to contain particles for reducing birefringence having a birefringence with a sign opposite to a polymer in the colored polymer thin film. This can compensate for the birefringence of the polymer, and decrease the birefringence without deteriorating other characteristics.
The first method is first described. The side chains of a polymer mean portions branching from the main chain direction of the polymer. The plane structural groups mean groups having at lest one aromatic ring. Examples of such plane structural groups include monocyclic groups such as a phenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a benzyl group, a phenethyl group, a styryl group, a cinnamyl group, and the like; polycyclic groups such as a naphthyl group, an anthryl group, a phenanthryl group, an indene group, an azurene group, a fluorene group,. and the like; heterocyclic groups such as a furyl group, a pyridyl group, and the like, all of which are described in “Nomenclature of Organic Compounds (New enlarged edition)” p61-63, p80-82 (by Ryo Shunei, Sankyo Shuppan). These groups may have a substituent such as a hydrocarbon group, a halogen, or the like. The molecular weight of the plane structural group is preferably in the range of 76 to 2000, more preferably in the range of 100 to 1000, because an excessively low molecular weight decreases the effect of suppressing orientation, while an excessively high molecular weight decreases the reactivity in polymer synthesis. As the plane structural group, fluorene groups are. particularly preferred from the viewpoint of a balance between the orientation suppressing effect and. polymer reactivity.
Fluorene groups are groups having a fluorene skeleton, and, of course, include groups having a hydrocarbon group, a halogen, or the like. Of monovalent fluorene groups to be bonded at any of the positions 1 to 9. and divalent fluorene groups to be bonded at the position 9, a monovalent or bivalent fluorene group, particularly a bivalent group, to be bonded at the position 9 is preferred from the viewpoint of the orientation suppressing effect.
Examples of polymer materials for forming the colored polymer thin film include acrylic resins, alkyd resins, polyester, polyimide, polyamidoimide, polyamide, and the like. However, from the viewpoint of heat resistance and refractive index, polyimide is preferred. Polyimide has high heat resistance and a high refractive index, and for example, in use as a color filter matrix material, a metal oxide film of ITO or the like can easily be formed on a polyimide thin film by sputtering and burning. In addition, since the refractive index of the polyimide thin film is close to that of ITO, an interface reflectance can be decreased.
Polyimide is generally obtained by heatin
Eguchi Masuichi
Tsukamoto Jun
Watanabe Takuo
Yamashiki Yuka
McPherson John A.
Toray Industries Inc.
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