Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Patent
1989-05-24
1991-04-30
Yusko, Donald J.
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
313502, 313504, 313506, H01J 6304
Patent
active
050121561
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a dispersion-type electroluminescence device excellent in electrical characteristics (hereinafter referred to as "dispersion-type EL device") and more particularly to a dispersion-type EL device which is low in current density, excellent in luminous efficiency and prevented from formation of uneven luminance.
BACKGROUND ART
FIG. 1 is a longitudinal-sectional view of a conventional dispersion-type EL device wherein 1 indicates a back electrode made of Al foil and the like, 2 indicates an insulator layer, 3 indicates a luminous layer, 4 indicates a transparent electrode, 5 indicates a moisture absorbing film and 6 indicates a moisture-proof film.
The luminous layer in a dispersion-type EL device is usually formed by dispersing phosphor powders of about 10-about 50 .mu.m in particle size in a dielectric cellulosic resin composition dissolved in an organic solvent and coating this dispersion on an insulator layer at a film thickness of about 20--about 70 .mu.m by doctor blade method, silk screening method, etc.
However, according to the above procedure, it is difficult to arrange uniformly the phosphor particles and coat the luminous layer with a smooth surface and there occur spaces between the phosphor particles, resulting in dented portions where the particles are not present, namely, uneven surface of the luminous layer.
In the device made by the conventional method according to which a transparent electrode is formed over the luminous layer of such surface state, it is difficult to apply uniform electrical field to the phosphor particles owing to difference in distance between electrodes and as a result not only scattering of luminance is brought about, but also current is concentrated to the dented portions to cause increase of current density of the EL device and deteriorate the luminous efficiency.
Under the circumstances, the inventors have conducted intensive research in an attempt to obtain a dispersion-type EL device which has a low current density, is excellent in luminous efficiency and is free from uneven luminance. As a result, it has been found that a dispersion-type EL device which satisfies the above requirements can be obtained by filling the dented portions on the surface of the luminous layer with a dielectric resin composition having lower dielectric constant than that of the dielectric resin composition which constitutes the luminous layer, thereby to nearly smoothen the surface of the luminous layer and thereafter producing a usual EL device therefrom. Thus, the present invention has been accomplished.
DISCLOSURE OF INVENTION
The present invention resides in providing a dispersion-type EL device comprising a back electrode layer and, laminated thereon, an insulator layer, a luminous layer and a transparent electrode layer wherein dented portions present in upper parts of the luminous layer are coated with a resin composition which is lower in dielectric constant than a dielectric resin composition used for formation of the luminous layer, but which has a dielectric constant of about 5 or higher.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 s a longitudinal section of a conventional dispersion-type EL device and FIG. 2 shows a longitudinal section of a dispersion-type EL device of the present invention wherein the reference numbers have the following meaning.
1-- back electrode; 2-- insulator layer; 3-- luminous layer; 4-- transparent electrode; 5-- moisture absorption film; 6-- moisture-proof film; 7-- low dielectric resin composition layer
The present invention will be explained in more detail referring to the drawings.
FIG. 2 is a longitudinal-sectional view of the dispersion-type EL device of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 2, 1 indicates a back electrode made of aluminum foil and the like and 2 indicates an insulator layer formed by coating on the back electrode a mixture prepared by dispersing highly insulating powders such as barium titanate in a highly dielectric resin composition by rol
REFERENCES:
patent: 4143297 (1979-03-01), Fischer
patent: 4482580 (1984-11-01), Emmett et al.
patent: 4767679 (1988-08-01), Kawachi
Database Derwent World Patent Index, An 80-33981C (19); JP-B-80 014 516 (Matsushita Elec. Ind. K.K.) 17-04-1980 *Abstract*.
Kadokura Hidekimi
Tanahashi Masayoshi
Yoshitake Hiroshi
Hamadi Diab
Sumitomo Chemical Company Limited
Yusko Donald J.
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