Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1999-07-08
2002-11-12
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S506000
Reexamination Certificate
active
06479930
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a dispersion-type electroluminescence element (dispersion-type EL element) for use in various electronic appliances as back lighting for the display section or the operating section.
BACKGROUND OF THE INVENTION
An increasing number of electronic appliances, which have been diversifying into quite a number of different configurations, incorporate a back lighting tool behind their liquid crystal display panels or operating sections in order to facilitate an easier handling or an easier recognition by the eyes in the darkness. Dispersion-type EL elements have been widely used as the back lighting tool.
A conventional dispersion-type EL element is described in the following with reference to the drawings.
In the drawings, the illustrations have been shown magnified in the direction of thickness for the sake of easier description of the structure.
FIG. 16
is a cross sectional view of a conventional dispersion-type EL element. On one of the surfaces of a flexible light-transmitting insulation film
1
made of polyethylene terephthalate or the like material, a light-transmitting electrode layer
2
of indium tin oxide (hereinafter referred to as ITO) is formed through a sputtering process or an electron beam method. On top of the electrode layer
2
, a luminescence layer
3
comprising a fluorocarbon rubber, cyano- group resin, or the like dielectric resin having a high permittivity dispersed with zinc sulfide or the like fluorescent powder as the luminous body, a dielectric layer
4
of dielectric resin having a high permittivity dispersed with barium titanate or the like dielectric powder, a back electrode layer
5
composed of silver, carbon-resin group or the like conductive material connected with the dielectric layer
4
, and an insulation layer
6
composed of epoxy resin, polyester resin or the like material are formed one layer after the other in the order by a printing process.
Wiring patterns
7
A,
7
B composed of silver or a conductive material of carbon-resin group are connected at the end portion to the light-transmitting electrode layer
2
and the back electrode layer
5
, respectively.
When a dispersion-type EL element of the above-described structure is incorporated in an electronic appliance and an AC voltage is provided from a circuit (not shown) of the appliance on the wiring patterns
7
A and
7
B, which being connected respectively with the light-transmitting electrode layer
2
and the back electrode layer
5
, the luminescence layer
3
of the dispersion-type EL element is driven to generate light. The light illuminates a display window, a liquid crystal display panel, etc. from behind. Thus, the display or an operating section can be easily recognized or identified even in a dark operational environment.
Color of a light to be emitted from a dispersion-type EL element is determined by a kind of fluorescent powder dispersed in the luminescence layer
3
made of a dielectric resin having a high permittivity. The luminescence color can be converted into a color other than the intrinsic color of the fluorescent powder, by dispersing a fluorescent dye or a fluorescent pigment in the dielectric resin having a high permittivity, or by tinting the insulation film
1
.
In a dispersion-type EL element having the above-described conventional structure, however, only a single color is available although a luminescence color can be converted into other color by dispersing a fluorescent dye or a fluorescent pigment in the dielectric resin having a high permittivity forming the luminescence layer
3
, or by tinting the insulation film
1
. When a plurality of luminescence colors are needed, a plurality of dispersion-type EL elements have to be installed in an electronic appliance. This incurs an increased number of parts in an appliance, which leads to an additional cost and time for the fabricating operation. Thus the total cost goes higher.
Another conventional dispersion-type EL element is shown in FIG.
17
. On the upper surface of a light-transmitting insulation film
101
, a light-transmitting electrode layer
102
of ITO or the like material is provided in the form of thin film by a vacuum sputtering process or the like method. On top of the electrode layer
102
, a luminescence layer
103
comprising a cyano-group resin or a fluorocarbon rubber group resin having a high permittivity dispersed with granular fluorescent powder such as a copper-doped zinc sulfide, etc., and a dielectric layer
104
comprising a synthetic resin of the same group as the material of luminescence layer
103
dispersed with barium titanate or the like powder of high permittivity are formed respectively in the order by a coating process. Further on top, a back electrode layer
105
composed of a paste of silver-resin group or a carbon-resin group material and an insulation layer
106
for protecting the back electrode layer
105
from contacting with outside element are formed respectively. And then, an outlet electrode
107
of the light-transmitting electrode layer
102
and an outlet electrode
108
of the back electrode layer
105
are formed respectively. When an AC voltage is applied between the outlet electrode
107
and the outlet electrode
108
, the fluorescent powder being dispersed in the luminescence layer
103
is driven to produce a plane luminescence at the light-transmitting insulation layer
101
side.
With the above-described structure as the basis, a conventional dispersion-type EL element (Japanese Patent Publication No.60-130097) comprises a light-transmitting electrode layer
109
disposed in the form of a number of stripes, as shown in FIG.
18
(
a
). The electrode stripes in the odd number rows are connected together at one end, while those in the even number rows are connected together at the other end; thus, the light-transmitting electrode layer
109
is formed of two comb-shape electrodes
110
and
111
integrated into one entity without making mutual contact to each other. A luminescence layer
112
comprising two different luminescence colors is provided on the comb-shape electrodes
110
,
111
in an arrangement where the luminescence color
112
A is located on the odd number rows, while the luminescence color
112
B is on the even number rows, as illustrated in FIG.
18
(
b
). A multi-color luminescence is made available by applying independent voltages on two respective comb-shape electrodes
110
,
111
.
However, in a conventional dispersion-type EL element of the above-described structure, where two kinds of luminous bodies
112
A,
112
B composed of synthetic resin dispersed respectively with different fluorescent powders for producing different luminescence colors are provided by a screen printing process, or the like process, in the form of stripes one after the other on a location corresponding to respective comb-shape light-transmitting electrodes
110
,
111
, it is difficult to provide the stripes of a small line-width precisely into a fine-pitch pattern because fluorescent powders generally have a relatively large grain diameter of approximately 30 &mgr;m in average. If the stripe lines are formed in a rough-pitch pattern, the luminescence would appear to the eyes in a striped pattern rather than a plane luminescence when a voltage is applied on either one of the light-transmitting electrodes
110
,
111
for producing a single-color luminescence. Thus the luminescence can hardly be recognized as a plane luminescence.
Furthermore, because of the large grain diameter of the fluorescent powder, thickness of the luminescence layer
112
is great and the surface condition is bumpy. When providing the luminous bodies
112
A,
112
B of two different colors alternately in a stripe form through a printing process, if there is a small deviation in the dimensions edges of the adjacent layers of different colors would readily be overlapped and the layer thickness of the overlapped portion increases, which makes the surface condition even bumpier. Then the printing of dielectric layer and back electr
Chikahisa Yosuke
Ikoma Heiji
Nishioka Naohiro
Tanabe Koji
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Williams Joseph
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