1. Field of the Invention
The present invention relates to a method of manufacturing a light emitting display panel having an electroluminescent element (the term “electroluminescent” is hereinafter sometimes abbreviated as “EL”). In addition, the present invention relates to a light emitting display panel having an EL element.
2. Description of the Related Art
An EL element is excited to emit a light when an electric field is applied to a fluorescent compound therein. The EL element has a high visibility because of its self-emitting property. In addition, the EL element is excellent in shock resistance because it is a complete solid body. Especially, an organic EL element that includes an organic component as a fluorescent material has the following advantageous features. At first, the organic EL element has a high luminous efficiency, that is, a highly bright light is realized by an applied voltage as low as less than 10V. Then, the organic EL element can emit a light with a simple element structure. Further, the organic EL element has a long life duration. In addition, the organic EL element has a layered structure in which a hole-transporting layer, a luminescent layer and an electron-injecting layer are mainly formed between an anode and a cathode. Each layer can be formed to have a nanoscale thickness, which is advantageous in that a reduction of thickness and weight of the element can be facilitated. In addition, each layer can be manufactured by applying a coating liquid in which a polymer material is dissolved. Thus, when manufacturing the respective layers, a printing method to a paper and an ink jet method can be applied to the manufacturing step.
A light emitting display panel, in which an organic EL element having the various advantages described above is formed on or above a flexible substrate, has a flexibility as a whole. Therefore, such a light emitting display panel has been recently expected to be employed in an advertisement display (an electric spectaculars panel, for example) which emits a light to display a certain pattern, and a relatively inexpensive display which emits a light to display a simple sign. It has also been under review to apply such a light emitting display panel to various kinds of display panels such as a thin-film panel, a band-shaped panel, a circular panel, and so on (for example, please see Japanese Patent Laid-Open Publication No. 15859/2002 (claims and FIG. 1)).
In a conventional method of manufacturing a light emitting display panel, a glass substrate is generally used. Basically, such a manufacturing method includes the steps of: supplying a glass substrate; forming a transparent electrode, an EL layer, and so on; and discharging a manufactured light emitting display panel. Each handling between the steps is carried out by receiving the glass substrate in a cassette.
An invention of improvement for manufacturing a light emitting display panel is disclosed in Japanese Patent Laid-Open Publication No. 208878/1998 (claims and FIG. 1) in which a layered body, which has an EL layer therein and is separately formed, is laminated by a pair of carrier films so as to manufacture a light emitting display panel.
However, in a method of manufacturing a flexible light emitting display panel employing the above flexible substrate, when each layer is directly formed on the flexible substrate, there is a possibility that thicknesses of the respective layers (especially a thickness of the EL layer which influences ununiformity of a light emitting strength) become uneven because of a flexibility of the flexible substrate itself. In order to restrain the unevenness, a different step from that for the glass substrate is additionally needed, which may impair the productivity.
Regarding a light emitting display panel itself, in the market, a light emitting display panel is requested to be superior in a soliciting effect, i.e., a publicizing and advertising effect on soliciting purchasers to purchase things. For example, at first, a light emitting display panel is requested to be noticed by purchasers.
A light emitting display panel is also requested to be flexible enough to be freely attached on or incorporated in variously shaped objects. In addition, in order to be arranged in various environments, a light emitting display panel is requested to be hardly affected by factors of environment such as moisture (steam), oxygen, or the like. Furthermore, suppliers have been studying a structure design of a light emitting display panel that can be manufactured at a low cost.