Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-12-28
2003-04-22
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C428S076000, C313S512000, C313S506000, C427S066000, C257S100000, C156S067000, C156S230000
Reexamination Certificate
active
06551724
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic EL (Electro-luminescent) display device operating based on an electro-luminescent phenomenon and a method for manufacturing a same and more particularly to the organic EL display device in which a hygroscopic agent is enclosed_hermetically and a method for manufacturing a same.
The present application claims priority of Japanese Patent Application No. Hei 11-374834 filed on Dec. 28, 1999, which is hereby incorporated by reference.
2. Description of the Related Art
An EL display device using an electroluminescent phenomenon, since it has various advantages in that it can be configured so as to be of a spontaneous light-emitting type and of a thin flat-panel type, that it draws less power, that it can provide better viewability and fast responsivity and that it can display moving images, is considered to be promising for wider applications. Two types of EL display devices are known, one being an inorganic EL display device employing inorganic materials and another being an organic EL display device employing organic thin films. In recent years, since various organic luminescent compounds have been developed which enable light-emitting in multiple colors and allow a full color EL display device to be implemented, development of the organic EL display device is being promptly pursued. Such the organic EL display device is fabricated based on a phenomenon in which light is emitted when a hole injected from an anode and an electron injected from a cathode are recombined in a light-emitting layer composed of an organic luminescent substance having a fluorescent capability contained in an organic thin-film sandwiched between the anode and the cathode, that is, when they are changed from an excited state to a deactivated state. Moreover, recent prompt advancement of the EL display device is also attributable to greatly improved light-emitting efficiency and luminance achieved by employing a structure in which hole transporting layers and/or electron transporting layers are stacked as the light-emitting layer.
Though improvements have been made to increase its display life to a considerable extent, there are still left many factors of deterioration including occurrence of a dark spot being a region where no light is emitted, and sufficiently satisfactory display life has not yet been implemented. One of the factors of deterioration is an influence of moisture which is a problem specific to organic thin-film materials. That is, the organic EL device using such organic thin-film materials is easily affected by moisture existing in an area surrounding the organic EL display device; for example, there is a case where moisture permeating through an interface between a light-emitting layer and an electrode interferes with injection of an electron, causing occurrence of dark spots and corrosion of the electrode. To solve this problem, methods for preventing or removing the influence of moisture or a like by sealing the organic EL device hermetically are proposed. To prevent the influence of moisture, the organic EL device is put into a container being impermeable to moisture and is then enclosed together with nitrogen gas hermetically. Moreover, to remove the influence of moisture, a hygroscopic agent is enclosed into the moisture-impermeable container in which the organic EL device and the nitrogen gas are enclosed together.
FIG. 8
is a cross-sectional view of a conventional organic EL display panel in a sealing cap of which a hygroscopic agent is enclosed hermetically in order to remove an influence of moisture, which is disclosed in Japanese Patent Application Laid-open No. Hei 9-148066 (hereinafter referred to as a “first conventional example”). As shown in
FIG. 8
, the organic EL display device of the first conventional example is mainly constructed of a transparent glass substrate
51
, an organic EL layer-stacked body
55
composed of a transparent electrode
52
(as an anode) made from ITO (Indium Tin Oxide) or a like, an EL light-emitting layer
53
made from an organic EL material or a like and a counter electrode (as a cathode)
54
, each being stacked in this order, a glass sealing can
56
to seal the organic EL layer-stacked body
55
and a drying body
57
composed of a hygroscopic agent adhering to an inside surface of the glass sealing can
56
. To enclose the above drying body
57
in the glass sealing can
56
, two methods are available; one in which a hygroscopic compound is solidified to produce a formed body which is then fixed in the glass sealing can
56
and another in which the hygroscopic compound is put into an air-permeable bag which is then fixed in the glass sealing can
56
.
FIG. 9
is a cross-sectional view of another conventional organic EL display panel in a sealing cap of which a hygroscopic agent is enclosed hermetically, which is disclosed in Japanese Patent Application Laid-open No. Sho 61-96695 (hereinafter referred to as a “second conventional example”). As shown in
FIG. 9
, the organic EL display panel in the second conventional example is same as that in the first conventional example in that an organic EL device
62
formed on a glass substrate
61
is sealed hermetically by a sealing cap
63
. However, the organic EL display panel in the second conventional example differs from that in the first conventional example in that, instead of the drying body
57
employed in the first conventional example, a composite film
64
formed by making a composite substance composed of zeolite serving as the hygroscopitc agent, a carbon powder serving as a light-shielding substance, a light-absorbing substance and an organic resin serving as a binder, into a film-like material, is stuck to an inside surface of the sealing cap
63
. By configuring as above, an attempt has been made to implement the organic EL display panel having a tolerable life characteristic and contrast and being readily manufactured.
However, in the first conventional example, if the method in which the hygroscopic compound is solidified by using a binder to produce the formed body is employed when the drying body
57
is enclosed in the glass sealing can
56
, since an exposed surface area of the hygroscopic agent is made small, it causes a decrease in hygroscopic capability and, since mechanical strength of the formed body is required to some extent, the drying body
57
is not allowed to be thinner. Therefore, the organic EL display device of the first conventional example is not suitable for application for a thin-type organic EL display. Moreover, in the organic EL display device of the first conventional example, if the method in which the hygroscopic compound is put into the air-permeable bag which is then fixed in the glass sealing can
56
is employed, it is difficult to give a fixed shape to the drying body
57
because it is contained in a bag having no definite shape and, when the organic EL display panel is put in an inclined state, the drying body
57
containing the hygroscopic agent easily moves and leans, causing a touch with the organic EL layer-stacked body
55
which leads to deterioration of the organic EL layer-stacked body
55
by an external force.
Moreover, in the second conventional example, if the composite film
64
is peeled off from the sealing cap
63
, it comes in touch with the organic EL device
62
, causing damage to the EL device
62
. Since hygroscopic agent, carbon powder and binder are mixed to produce the composite film
64
, there is a risk that a function of the hygroscopic agent itself and/or a function of the light-shielding substance itself cannot be sufficiently implemented. Additionally, when components contained in the binder being an organic resin are partially left unreacted, the organic EL device is adversely affected by them.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide an organic EL display panel which is capable of reliably holding a hygroscopic agent in its sealing cap in a manner so as
Ishii Ikuko
Ooishi Mitsuma
Sakaguchi Yoshikazu
Suzuki Joji
Garrett Dawn
Katten Muchin Zavis & Rosenman
Kelly Cynthia H.
NEC Corporation
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