Compositions – Organic luminescent material containing compositions – Synthetic resin containing
Reexamination Certificate
2002-07-29
2003-11-04
Koslow, C. Melissa (Department: 1755)
Compositions
Organic luminescent material containing compositions
Synthetic resin containing
C313S501000, C428S690000
Reexamination Certificate
active
06641755
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fluorescence conversion medium, and a display device comprising it. More precisely, the invention relates to a fluorescence conversion medium having the advantages of stable fluorescence conversion capability, good heat resistance and good light resistance and favorable to high-resolution multi-color image display, and relates to a display device comprising the fluorescence conversion medium. The “fluorescence conversion medium” referred to herein is meant to indicate a concept including thin-film fluorescence conversion media to relatively thick fluorescence conversion media.
BACKGROUND ART
Electronic display devices are referred to as “man-machine-interface” display devices, having an important role of “interface” to transmit various visual informations to “man” from “machine” while connecting “man” and “machine” via “interface”.
Known are two types of such electronic display devices, light-emitting one and light-receiving one. Light-emitting display devices include, for example, CRT (cathode ray tube), PDP (plasma display panel), ELD (electroluminescent display), VFD (visual fluorescence display), LED (light emitting diode), etc. Light-receiving display devices include, for example, LCD (liquid crystal display), ECD (electrochemical display), EPID (electrophoretic image display), SPD (scattered particle orientation display), TBD (tinted board rotation display), PLZT (transparent ferroelectric PLZT [(Pb, La)(Zr, Ti)O
3
] ceramic display), etc.
For full-color imaging in light-emitting electronic displays such as those mentioned above, known are (1) a method of disposing multicolor emitting zones (for example, for three primary colors of red, blue and green) in such a manner that they are planarly spaced from each other to separately emit the individual colors, (2) a system including LCD, in which, however, the white light from the backlight is separated into different colors through a color filter, and (3) a method of disposing a plurality of fluorescence conversion layers in such a manner that they are planarly spaced from each other so as to receive one color (for example, blue) emitted by a color emitter and change it into different colors (for example, red, green) to emit them.
However, as requiring different light emitters (light-emitting elements) to be separately prepared for red, blue and green, the method (1) is problematic in that the process of selecting the materials for the light emitters and disposing the light emitters in a fine pattern where they are planarly spaced from each other often involves many difficulties. The system (2) in which white light is separated into different colors is also problematic in that the reduction in the brightness of the separated colors is inevitable (in case where white light is separated into three primary colors, the brightness of the separated three colors is reduced to less than ⅓).
As opposed to these, in the method (3) in which are used fluorescence conversion layers that receive one color from a light emitter, the fluorescence conversion layers are disposed in a fine pattern so as to be planarly spaced from each other separately from the site that absorbs light. Therefore, it is believed that the process of forming the pattern of the fluorescence conversion layers for the method is simple and easy. In principle, in addition, the color brightness is not reduced by fluorescence conversion in the method.
In the method where one color from a light emitter is converted into plural colors through such fluorescence conversion layers, it is desirable that the color from the light emitter has high energy. For example, in the method, blue of visible light, if emitted by the light emitter, can be converted into green or red having lower energy, and it enables multi-color imaging of three primary colors. Also in the method, UV from the light emitter enables multi-color imaging of three primary colors.
In particular, organic electroluminescent (“electroluminescent or electroluminescence” is hereinafter referred to as EL) devices realize high-efficiency and high-luminance blue emission. In addition, as they are made of organic substances, it is much expected that organic EL devices will enable all types of color emission by suitably planning the organic compounds for them.
Heretofore, inorganic fluorescent pigments are used in fluorescence conversion layers, typically as in CRT. For example, used are inorganic crystals of high-purity phosphors of zinc sulfide or alkaline earth metal sulfides, to which is added a minor metal (copper, silver, manganese, bismuth, lead) serving as an activator for enhancing the fluorescence from the phosphor crystals. For example, in combinations of zinc sulfide and an activator of copper, manganese, silver or bismuth, copper assists green emission, manganese assists yellow emission, silver assists violet emission, and bismuth assists red emission. Such a fluorescent pigment is mixed and dispersed in a binder resin to give a slurry or paste, which is applied to a substrate to form a fluorescence conversion layer. However, the fluorescence conversion layer containing such an inorganic fluorescent pigment is defective in that the light emitter applicable to it for fluorescence emission is limited only to that capable of emitting high-energy light of electron beams and up to UV rays, and only some types of the light emitter applicable to it are-available.
On the other hand, daylight fluorescent pigments are known except for in organic fluorescent pigments. They include pigment-type ones and synthetic resin solid solution-type ones, and visible light emitters are applicable to them.
Pigment-type, daylight fluorescent pigments have the capability of fluorescence emission by themselves and are insoluble in water. Lumogen Colors of those pigments for yellow, green, orange, red and blue emission are known, but, except Lumogen Yellow, they are not so good in point of their fluorescence intensity and color sharpness and are therefore relatively impracticable. Only a few types of the pigments are available for practical use. Synthetic resin solid solution-type, daylight fluorescent pigments are produced by dissolving fluorescent dyes in synthetic resins such as melamine resins, urea resins, sulfonamide resin or the like, followed by curing them and physically grinding them into pigments. These pigments give relatively intense fluorescence. However, as being physically ground, their particles are relatively large in size. Therefore, when such large pigment particles are mixed and dispersed in binder resins to form slurries or pastes and when the resulting slurries or pastes are applied to substrates to form fluorescence conversion layers, then the layers could not be transparent since the pigment particles existing in them will scatter the light from light emitters. In addition, the layers could not be well planarized owing to the large pigment particles. The problem with the pigment layers is that their fluorescence conversion efficiency is low.
In Japanese Patent Laid-Open No. 176366/1997, disclosed is a light-transmitting and light-scattering resin composition that comprises fluorescent particles dispersed in a transparent resin. In the resin composition, the fine particles scatter the incident light applied thereto, and therefore the composition has the light-scattering ability. However, in order that the resin composition could sufficiently scatter the incident light applied thereto, the diameter of the pigment particles in the composition must be larger than the wavelength of visible light (at least about 700 nm). Therefore, the fluorescence conversion layers of the resin composition could not be transparent but are cloudy like frosted glass, and the problem with them is that their fluorescence conversion efficiency is low.
One recent approach to solving the problem is a fluorescence conversion film that contains a coloring matter (fluorescent coloring matter), as in Japanese Patent Laid-Open No. 152897/1991.
The fluorescence conversion film is
Eida Mitsuru
Ishikawa Motoharu
Tomoike Kazuhiro
Idemitsu Kosan Co. Ltd.
Koslow C. Melissa
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