Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-09-24
2003-09-02
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S502000, C313S506000, C313S509000, C252S301360
Reexamination Certificate
active
06613455
ABSTRACT:
FIELD
The present invention relates to an electroluminescent device (hereinafter referred to as “EL device”) having a luminescent layer which comprises luminescent particles and a binder resin. In particular, the present invention relates to an EL device which can achieve a high luminescent efficiency.
BACKGROUND
EL devices having a so-called “dispersion type luminescent layer” which is formed by dispersing luminescent particles such as phosphor particles in binder resins such as polymers having a high dielectric constant are known from the following publications.
For example, JP-B-59-14878 discloses an EL device comprising a transparent substrate, a transparent electrode layer, an insulating layer consisting of a vinylidene fluoride binder resin, a luminescent layer comprising a vinylidene fluoride binder resin and phosphor particles, the same insulating layer as above, and a rear electrode, which are laminated in this order. JP-B-62-59879 discloses an EL device comprising a polyester film, an ITO electrode, a luminescent layer which comprises phosphor particles and a cyanoethylated ethylene-vinyl alcohol copolymer (a binder resin), and an aluminum foil (a rear electrode), which are laminated in this order.
Unfortunately, however, it is difficult to increase the luminance in the case of such “dispersion type luminescent layers”. The reason for this is that luminescent particles, which have a larger specific gravity than binder resins, tend to sink in a coating for forming luminescent layers comprising luminescent particles dispersed in the solution of binder resins, and thus it is difficult to uniformly disperse the luminescent particles in the luminescent layers formed from such a coating. Furthermore, the dispersibility deteriorates when the amount of luminescent particles in the coating is increased to increase the filling rate of luminescent particles in the luminescent layer. The filling rate of the luminescent particles is at most 20 volume % of the coating weight. In addition, it is relatively difficult to increase the coating thickness of the luminescent layer while maintaining the uniformity of a thickness using such a dispersion type coating. Therefore; when the number of applications of the coating is increased to increase the thickness of the luminescent layer, the productivity decreases, and it is difficult to produce a roll-form EL device having a large area.
EL devices having a “lamination type luminescent layer” are known as one measure to solve the drawbacks of the “dispersion type luminescent layers”. For example, U.S. Pat. Nos. 5,019,748 and 5,045,755 disclose an EL device having a lamination type luminescent layer, which consists of a three-layer laminate comprising: (1) a first dielectric adhesive layer with a high dielectric constant applied on the transparent conductive layer of a transparent substrate; (2) a phosphor particle layer in the form of a substantially single layer (having a thickness not exceeding the largest size of particles), which is formed by electrostatically applying dry phosphor particles (luminescent particles) on the first dielectric adhesive layer; and (3) a second dielectric layer placed on the phosphor particle layer and containing a dielectric material with a high dielectric constant, which layer fills the spaces between adjacent phosphor particles. A rear electrode is applied on the surface of the second dielectric layer, and thus the second dielectric layer functions as an insulating layer.
In contrast with the above “dispersion type luminescent layer”, it is possible to continuously carry out the coating processes, and it is possible to produce a roll-form EL device by the disclosed method. However, the above publications and patent specifications do not disclose any specific manner to form a continuous terminal (buss), through which electricity (voltage) may be applied from outside to the transparent conductive layer, e.g., along the lengthwise direction of the transparent substrate in the production process of a roll-form EL device.
To increase the area of EL devices, it is a key factor how a terminal (buss), which supplies electricity (voltage) to a transparent conductive layer from the outside, is provided. For example, in the case of EL devices for displays with a small area, busses which are not electrically in contact with a rear electrode, can be formed on a transparent conductive layer by effectively repeating screen printing. However, none of the above cited publications or patents disclose the formation of busses continuously in the lengthwise direction of the device, or any methods for such formation.
U.S. Pat. No. 4,143,297 refers to electroluminescent information display panels which are said to be suitable for uses extending from simple numeric displays to color TV panels. The display panel comprises a body of insulating resin having a layer of electroluminescent particles embedded therein. This layer is a monoparticle layer. The resin has a dielectric constant higher than that of the particles and includes fluorescent material on at least one side of the layer of electroluminescent particles. Furthermore, insulating coatings on both front and back surfaces of the resin body, a transparent front electrode extending over the insulating coating of the front surface, a back electrode disposed on the insulating coating on the back surface and means for electrically energizing the electrons are provided. At least one element of the display panel adjacent the back thereof is black and sufficiently opaque to absorb substantially all the light reaching it.
WO 98/53645 refers to an electroluminescent device and a method for producing the same. Among others the electroluminescent device comprises a luminescent layer comprising a transparent support layer comprising a matrix resin, an insulating layer comprising an insulating material and a luminescent particle layer consisting essentially of particles which comprise luminescent particles and which are embodied in both the support layer and the insulating layer.
Conventional “lamination type luminescent layers” have several drawbacks. For example, EL devices having “lamination type luminescent layers” can emit light at a luminance equal to or higher than that of EL devices having “dispersion type luminescent layers” when they are connected with a power source having the same frequency and the same voltage. However, the luminescent efficiency is not improved so greatly, or sometimes it may deteriorate.
Luminescent efficiency (“&eegr;”) is a value defined by the following formula:
&eegr;=
L×&pgr;×S/P
where:
P is a used electricity (effective electric power) (unit: W),
L is a luminance measured with a luminance meter (unit: cd/m
2
),
S is the area of a luminescent surface, and
&pgr; is the ratio of the circumference of a circle to its diameter.
In other words, a low luminescent efficiency means a low luminance per unit effective electric power, and thus a low power efficiency. Accordingly, it is a goal to improve the luminescent efficiency from the viewpoint of energy-saving.
SUMMARY
In one embodiment, the present invention provides an EL device having an effectively improved luminescent efficiency. Preferred such electroluminescent devices comprise:
a transparent conductive layer,
a binder layer placed on the back surface of the transparent conductive layer, a luminescent-particle layer comprising a substantially single layer of particles containing luminescent particles, which layer is applied on the back surface of the transparent conductive layer through the binder layer,
an insulating layer comprising insulating particles, which is placed on the back surface of the luminescent-particle layer, and
a rear electrode placed on the back surface of the insulating layer, wherein the luminescent particles are embedded in the binder layer, or the luminescent particles are substantially not embedded in the insulating layer.
In another embodiment, the present invention provides a method for the production of an EL device, which method can produce a sheet-form
Abe Hidetoshi
Araki Yoshinori
Kobayashi Mitsuaki
Matsumoto Kazumi
3M Innovative Properties Company
Fischer Carolyn A.
Garrett Dawn
Kelly Cynthia H.
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