Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2001-04-20
2002-12-17
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C349S153000
Reexamination Certificate
active
06495262
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flat display panel constructed as a hermetically sealed case, such as a plasma display panel, to a flat display device having the flat display panel, and to a method for forming the flat display panel.
2. Description of the Background Art
FIG. 15
shows the structure of an AC-type plasma display device as an example of a flat display device.
In
FIG. 15
, the AC-type plasma display device
201
has a plasma display panel
111
, a plasma display panel driving circuit
202
, address electrodes
204
, X electrodes
205
, and Y electrodes
206
. The address electrodes
204
, X electrodes
205
and Y electrodes
206
are all plural in number. The electrodes are arranged so that the address electrodes
204
perpendicularly intersect the X and Y electrodes
205
and
206
in a plurality of discharge cells
203
arranged to form a grid in the image display portion
111
a
of the plasma display panel
111
.
The address electrodes
204
, X electrodes
205
and Y electrodes
206
are all connected to the plasma display panel driving circuit
202
and supplied with driving voltage from the plasma display panel driving circuit
202
.
To obtain a desired image in this AC-type plasma display device
201
, first, the plasma display panel driving circuit
202
performs addressing operation. More specifically, for the addressing operation, write voltage is applied between the address electrodes
204
and the Y electrodes
206
, for example. This causes write discharge between these electrodes to set discharge cells
203
involved in the display operation. As is well known, this operation is write operation in which wall charge is stored in the dielectric in the plasma display panel of the AC-type plasma display device.
Subsequently, the plasma display panel driving circuit
202
performs discharge sustain operation (display operation). More specifically, for the discharge sustain operation, the discharge cells
203
set by the addressing operation are caused to discharge to present a display. For this purpose, sustain voltage is alternately applied between the X electrodes
205
and the Y electrodes
206
. This discharge sustain operation causes discharge between the X electrodes
205
and the Y electrodes
206
in the discharge cells
203
, displaying an image in the image display portion
111
a.
When given discharge sustain operation ends, the plasma display panel driving circuit
202
performs erasing operation to change the image displayed in the image display portion
111
a
(operation for eliminating the wall charge). More specifically, erase voltage is applied between the X electrodes
205
and the Y electrodes
206
to eliminate the wall charge.
FIG. 16
shows the structure of a conventional flat display panel
11
, e.g. the plasma display panel
111
.
FIG. 16
is a top view of the flat display panel
11
.
FIG. 17
is the sectional view taken along the line B—B of FIG.
16
.
FIG. 18
is a sectional view of the flat display panel
11
in a stage where it has not yet been heated and processed into the condition shown in FIG.
17
.
The flat display panel
11
has two substrates
1
A and
1
B made of glass etc. and a sealing layer
12
for bonding the substrates
1
A and
1
B together. In the case of a plasma display panel, for example, the substrates
1
A and
1
B are a display surface glass substrate and a back glass substrate opposing each other. The sealing layer
12
is arranged near and along the peripheries of the substrates
1
A and
1
B to keep the image display portion
11
a
in a hermetic state.
FIG. 16
shows the substrate
1
B with a broken line so that the sealing layer
12
can be seen.
FIG. 17
shows barrier ribs
13
sectioning individual discharge cells in the plasma display panel as an example of components in the image display portion
11
a.
A glass paste is generally used as the material of the sealing layer
12
; for example, a thermally soluble material, in which powder of a low-melting-point glass (frit glass) such as PbO—B
2
O
3
—SiO
2
type glass or PbO—B
2
O
3
—ZnO type glass, is mixed into a solvent together with a binder of nitrocellulose or acrylic resin, a filler of ceramics powder for adjusting the thermal expansion coefficient to those of the substrates
1
A and
1
B, and so forth. In this specification, “frit glass” stands for glass materials having lower melting points than ordinary glass; e.g. a glass material having a melting point around 400° C. In a broader sense, it stands for glass materials which melt at lower temperatures than the substrates
1
A and
1
B.
A common sealing procedure is now described referring to the plasma display panel as an example. (1) First, the sealing layer
12
is formed on the display surface glass substrate or on the back glass substrate (on the substrate
1
B in the example of
FIG. 18
) where internal components like the barrier ribs
13
have been previously formed. (2) Pre-firing is applied to cause desorption of the binder component in the sealing layer
12
. (3) Next, positioning is achieved with the display surface glass substrate and the back glass substrate facing each other. (4) The two glass substrates are fixed with a jig like a clip and appropriate pressure is applied to the sealing layer
12
. (5) The entire panel is heated. (6) The panel is cooled and the jig or clip is removed. (7) When the sealing is completed, the entire panel is evacuated, while being heated, through an exhaust tube previously attached to the panel, so as to remove impurity gas adsorbed in the panel. (8) A gas for discharge is entrapped (a mixture gas containing Ne, Xe, etc.) when the panel has reached a given temperature. (9) The exhaust tube is sealed.
Generally, the sealing layer
12
is required to satisfy the following conditions: (a) to have such fluidity that it will easily deform and fuse upon application of external pressure at the sealing temperature, (b) to have such rigidity that it will not deform by atmospheric pressure at the evacuating temperature, (c) to have thermal expansion coefficient at the same level as those of the display surface glass substrate and the back glass substrate so that the substrates will not crack during the sealing process and after the cooling process.
To satisfy the conditions above, the sealing layer
12
has generally been formed by using an amorphous glass paste which contains amorphous frit glass or using a crystallized glass paste which contains crystallized frit glass. The amorphous glass paste has superior fluidity and is not very susceptible to temperature condition. The crystallized glass paste, on the other hand, is poor in fluidity, but provides excellent thermal resisting stability after it is sealed.
Whichever glass paste is used, however, the sealing layer cannot sufficiently alleviate and absorb strain stress between the two substrates which is caused by the internal stress of the two substrates while they are being sealed and after they have been cooled. It is therefore difficult to obtain a large quantity of flat display panels with sufficiently ensured hermetic seal; for example, the hermetic seal of the flat display panel may be broken if the flat display device undergoes external force, such as vibrations and impacts, during its assembly or transportation after cooling, which results in lower yield.
Furthermore, the amorphous glass paste has lower softening point than the crystallized glass paste. Therefore, during the exhausting process following the sealing process, it requires that the temperature be set lower than when the crystallized glass paste is used, which may result in insufficient removal of the impurity gas. The temperature must be set lower because the bonded sealing part will otherwise be re-softened with heat during the exhaust and then the dynamic bonding strength will be reduced or the hermetic seal will be broken to cause leakage of the discharge gas.
On the other hand, the crystallized glass paste, having higher softening point than the amorphous glass paste, has
Birch & Stewart Kolasch & Birch, LLP
Blackwell-Rudasill G. A.
Jones Deborah
Mitsubishi Denki & Kabushiki Kaisha
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