Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-03-30
2003-09-23
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S096000
Reexamination Certificate
active
06623097
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a thin film formation method by an ink jet method, an ink jet apparatus, a production method of an organic EL (electro-luminescence) device, and an organic EL device.
2. Description of Related Art
An organic EL display including organic EL devices (light emitting device having a light emitting layer made of an organic material interposed between an anode and a cathode) so arranged as to correspond to pixels has been rapidly developed in recent years as a spontaneous light emitting display that will replace current liquid crystal displays. Materials of the light emitting layer of the organic EL device can include aluminum quinolynol complexes (Alq3) and poly(paraphenylene)vinylene (PPV) as an organic material having a high molecular weight.
As disclosed in “Appl. Phys. Lett.” 51(12), Sep. 21, 1987, 913, it is known to form a film of a light emitting layer made of an organic material having a low molecular weight by vacuum evaporation. Another reference, “Appl. Phys. Lett.” 71(1), Jul. 7, 1997, p.34 et seq. describes the film formation of a light emitting layer made of an organic material having a high molecular weight.
In organic EL devices for display, it is necessary to form an anode at each pixel position on a substrate and to dispose a light emitting layer on each anode. If the arrangement of the light emitting layer can be performed by an ink jet method, precise patterning can be made within a short time because application and patterning can be conducted simultaneously. Moreover, since the amount of materials to be used is that which is minimum necessary, the materials can be used without waste and the production cost can be lowered.
To arrange the light emitting layer by an ink jet method, it is necessary to use a material in the liquid form. When a polymer material such as PPV is used as the material of the light emitting layer, the arrangement can be made by the ink jet method if a precursor solution of the polymer material is used. Japanese Patent Laid-Open Publication Nos. 11-40358, 11-54270 and 11-339957 teach to arrange a light emitting layer made of a PPV type polymer material in accordance with the ink jet method.
As shown in
FIG. 1A
, in the liquid arrangement by the conventional ink jet method, an ink jet head
2
smaller than a substrate
1
, for example, is employed. The inside of the surface of the substrate
1
is so divided into a plurality of regions
11
to
15
as to correspond to the length of rows of nozzles
3
of the head
2
. The liquid is serially discharged from the nozzles
3
of the head
2
while the substrate
1
or the head
2
is being moved.
According to this method, however, when a solvent of the liquid to be discharged is a solvent having a large density, a solvent vapor evaporating from droplets is likely to stay inside the substrate surface. When a droplet A having an early arrangement order on the substrate is compared with a droplet B having a late arrangement order, for example, as shown in
FIG. 1B
, the droplet B having a late arrangement order is discharged in an atmosphere in which the partial pressure of the solvent vapor is high. As a result, a drying rate of the droplet B is lower than that of the droplet A. The droplet A arranged previously, too, is affected by the solvent vapor staying inside the substrate surface and in some cases, it is again dissolved after drying or its drying rate becomes lower.
Therefore, when a solution prepared by dissolving a plurality of polymer materials having mutually different molecular weight or polarity in a solvent having a large density is arranged on the substrate by the conventional ink jet method, the droplets having a low drying rate are likely to result in a thin film in which a plurality of polymer materials are in the phase separation state. When the drying rates of the droplets are different inside the substrate surface, the condition of the resultant thin film becomes different depending on the position inside the substrate surface.
As described above, when the conventional ink jet method is employed to arrange the light emitting layer in the organic EL display, luminance is likely to vary inside and among pixels.
SUMMARY OF THE INVENTION
In view of the problems with the conventional technologies, the present invention is directed to obtain a thin film having high uniformity inside a substrate surface even when a solvent of a liquid to be discharged has a large density in a formation method of a thin film by an ink jet method.
In a method of forming a thin film by an ink jet method including the step of discharging a liquid containing thin film-forming materials and a solvent from liquid discharge ports to each position on a substrate while the liquid discharge ports are being moved relatively to the substrate, the present invention provides a thin film formation method by an ink jet method characterized in that subsequent droplets are arranged while a solvent vapor evaporating from droplets arranged previously on the substrate is compulsively removed from inside the substrate surface.
In a method of forming a thin film by an ink jet method including the step of discharging a liquid containing thin film-forming materials and a solvent from liquid discharge ports to each position on a substrate while the liquid discharge ports are being moved relatively to the substrate, the present invention provides a thin film formation method by an ink jet method characterized in that a solvent vapor evaporating from droplets arranged previously on the substrate is compulsively removed from inside the substrate surface immediately after the arrangement of the droplets.
The present invention further provides an ink jet apparatus including gas blowing means for blowing a gas to a surface of a liquid discharged surface on which droplets have already been arranged.
The present invention provides a thin film formation method by an ink jet method including the steps of moving relatively liquid discharge ports with respect to a substrate, discharging a liquid containing thin film-forming materials and a solvent to each position of the substrate from the liquid discharge ports and arranging successively droplets at positions on the substrate. The present invention further has a feature in that a solvent vapor evaporating from the droplets arranged previously is compulsively removed from inside the substrate and subsequent droplets are arranged.
Accordingly, even when the solvent of the liquid to be discharged has a large density, the method described above prevents the solvent vapor evaporating from the droplets arranged previously on the substrate from staying inside the substrate surface. Consequently, the liquid at positions of a late arrangement order can be discharged at a low partial vapor pressure of the solvent. A solvent having a large density is, for example, cyclohexylbenzene, tetralin, tetramethylbenzene, dodecylbenzene or diethylbenzene.
In this way, it becomes possible to prevent a drying rate of the droplets at the positions of the late arrangement order from becoming lower than that of the droplets at positions of the early arrangement order. It also becomes possible to prevent the droplets at positions of the early arrangement order from being re-melt after drying, and to prevent the drying rate of such droplets from being retarded. Since the delay of the drying rate of the droplets can thus be prevented, formation of a thin film, in which a plurality of polymer materials having different molecular weight and different polarity exist in a phase separation state, can be prevented even when a solution in which such polymer materials are dissolved in a solvent having a great density is used as a discharging liquid.
In a thin film formation method by an ink jet method including the steps of discharging a solution containing the thin film-forming materials and the solvent from liquid discharge ports to each position of a substrate while the liquid discharge ports are being moved relatively to the substrate, and th
Morii Katsuyuki
Okada Nobuko
Seki Shun-ichi
Oliff & Berridg,e PLC
Seiko Epson Corporation
Vo Anh T. N.
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