Fluorescent layer forming apparatus

Details Fluorescent layer forming apparatus Fluorescent layer forming apparatus

2003-04-22

2004-07-06

Crispino, Richard (Department: 1734)

Coating apparatus

Projection or spray type

C239S390000, C239S594000

Reexamination Certificate

active

06758905

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application is related to Japanese Patent Application Nos. 2002-122963 filed on Apr. 24, 2002 and 2002-236057 filed on Aug. 13, 2002, whose priorities are claimed under 35 USC §119, the disclosure of which is incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for forming a fluorescent layer in a plasma display panel and, more particularly, to a fluorescent layer forming apparatus including an improved nozzle.
2. Description of the Related Art
A conventional fluorescent layer forming apparatus disclosed in Japanese Unexamined Patent Publication No. H11-204032 (1999) will be described with reference to
FIGS. 13
,
14
(A) and
14
(B). The conventional fluorescent layer forming apparatus includes a dispenser
201
which has a plurality of ejection ports generally linearly arranged at predetermined intervals. In a fluorescent layer forming process employing the conventional fluorescent layer forming apparatus, as shown in
FIG. 13
, a fluorescent material paste
207
prepared by dispersing fluorescent particles in a liquid medium is ejected from the dispenser
201
through a mask
226
into linear recesses defined between plural barrier ribs
224
arranged parallel to each other on a rear substrate
220
, and heat-treated for formation of fluorescent layers
225
. As shown in FIGS.
14
(A) and
14
(B), the dispenser
201
includes fine rod-shaped guides
221
which respectively project from the ejection ports generally centrally of the ejection ports. The fluorescent material paste
207
is ejected along the guides
221
, while the dispenser
201
is moved relative to the substrate
220
. Thus, the fluorescent layers
225
are formed in the linear recesses between the barrier ribs
224
.
In the conventional fluorescent layer forming apparatus, the fluorescent material paste which has a high viscosity and a low surface tension unlike water is attracted to the guides
221
and falls vertically downward. Where the guides
221
are each composed of a hair or a polyamide filament, the fluorescent material paste can be ejected with the guides
221
kept in contact with the bottoms of the recesses. Thus, the conventional fluorescent layer forming apparatus can assuredly apply the fluorescent material paste into the recesses.
In the conventional fluorescent layer forming apparatus having the aforesaid construction, the fluorescent material paste is simply ejected along the guides from the ejection ports. At this time, the fluorescent material paste is liable to clot around the guides to form relatively large clots, depending on the viscosity of the fluorescent material paste. As a result, the fluorescent material paste is likely to adhere onto top edges of the barrier ribs or to enter recesses adjacent to the intended recesses (thereby to be mixed in different color fluorescent material pastes applied in the adjacent recesses). Thus, the conventional fluorescent layer forming apparatus fails to accurately form the fluorescent layers.
SUMMARY OF THE INVENTION
To overcome the aforesaid drawback, the present invention is directed to a fluorescent layer forming apparatus which is capable of accurately forming a fluorescent layer without formation of a relatively large clot of a fluorescent material paste.
In accordance with one aspect of the present invention, there is provided a fluorescent layer forming apparatus for applying a fluorescent material paste into a recess defined between barrier ribs formed on a substrate for formation of a fluorescent layer in a plasma display panel production process, the apparatus comprising: a nozzle for ejecting the fluorescent material paste; and a plurality of fine attachments provided at one end of the nozzle with distal end portions thereof being arranged in convergent relation, whereby the fluorescent material paste is ejected along the plurality of fine attachments so as to be applied onto a predetermined position in the recess for the formation of the fluorescent layer. According to this inventive aspect, proximal ends of the fine attachments are fixed to the nozzle, and the distal ends of the fine attachments are arranged in convergent relation. When the fluorescent material paste is supplied into the nozzle, the front of the fluorescent material paste moves along the plurality of fine attachments arranged in convergent relation. Therefore, the fluorescent material paste is convergently retained between the fine attachments and ejected from the nozzle without formation of a clot. Hence, the fluorescent layer can accurately be formed in the intended recess defined between the barrier ribs without adhesion thereof onto the top edges of the barrier ribs.
In accordance with the present invention, the fine attachments are adapted to control the eject line of the fluorescent material paste for guiding the fluorescent material paste to a predetermined position in the recess.
Specific example of the material for the fine attachments includes stainless.
The inventive fluorescent layer forming apparatus may be adapted to eject the fluorescent material paste with the distal ends of the fine attachments kept in contact with the bottom of the recess defined between the barrier ribs. In this case, the nozzle is scanned for the application of the fluorescent material paste, while the distal ends of the fine attachments fixed to the nozzle are kept in contact with the bottom of the recess. Therefore, the fluorescent material paste is guided along the fine attachments into the recess between the barrier ribs. Thus, the fluorescent layer can more accurately be formed in the intended recess between the barrier ribs.
In the inventive fluorescent layer forming apparatus, the fine attachments may each be composed of a material having a wetting contact angle of not greater than 60 degrees with respect to the fluorescent material paste. In this case, the fluorescent material paste supplied to the nozzle smoothly moves along the fine attachments composed of the material having a wetting contact angle of not greater than 60 degrees with respect to the fluorescent material paste without stagnation, and is ejected at a predetermined ejection rate from the nozzle without formation of a clot. As a result, the fluorescent layer thus formed has a uniform thickness.
In the inventive fluorescent layer forming apparatus, the fluorescent material paste may have a viscosity of 5 Pa·s to 50 Pa·s at a sheer rate of 4 s
−1
. In accordance with the present invention, the term “sheer rate” refers to a velocity gradient of a flux of the fluorescent material paste. More specifically, it refers to a velocity gradient determined by a flux of the fluorescent material past being ejected from the nozzle and a flux of the fluorescent material paste retained in a retaining portion of the nozzle at a position from the center line of the nozzle a predetermined distance.
An appropriate value of the viscosity of the fluorescent material paste can be determined in accordance with Hagen-Poiseuille's formula using the inner diameter of the nozzle, the amount of the fluorescent material paste to be ejected, the pressure under which the fluorescent material paste is to be ejected and the like as parameters. In this case, the fluorescent material paste having a viscosity of 5 Pa·s to 50 Pa·s at a sheer rate of 4 s
−1
is supplied to the nozzle and, therefore, smoothly moves along the fine attachments without stagnation and is ejected at a predetermined ejection rate from the nozzle without formation of a clot. As a result, the fluorescent layer thus formed has a uniform thickness.
In accordance with another aspect of the present invention, there is provided a fluorescent layer forming apparatus for applying a fluorescent material paste into a recess defined between barrier ribs formed on a substrate for formation of a fluorescent layer in a plasma display panel production process, the apparatus comprising: a nozzle for ejecting the fluorescent material past

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