Composition of sealing glass

Details Composition of sealing glass Composition of sealing glass

1999-05-21

2001-09-11

Sample, David R (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S017000, C501S018000, C501S021000, C501S022000, C501S024000, C501S026000, C501S045000, C501S048000, C501S076000, C501S079000

Reexamination Certificate

active

06287995

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a composition for a display device, and more particularly to a composition of sealing glass for bonding the upper and lower substrates of a flat panel display device.
2. Description of the Prior Art
Recently, there have been actively developed flat panel display devices such as a liquid crystal display(LCD), a field emission display(FED), a plasma display panel(PDP) and so on. In the flat panel display device, the PDP has advantages in that it provides ease of manufacture of a large-scale screen due to its simple structure, and that it has a light view angle more than 160° and characteristics of being thin and light weight. The PDP exploits a gas discharge phenomenon to display a picture by radiating a fluorescent material with a vacuum ultraviolet ray generated during a gas discharge. A typical structure of the PDP will be described with reference to
FIG. 1
below.
FIG. 1
shows a structure of a discharge cell arranged in a matrix pattern in the conventional PDP. The PDP discharge cell includes an upper plate
28
having a sustaining electrode pair
12
A and
12
B, an upper dielectric layer
14
and a protective film
16
that are sequentially formed on an upper substrate
10
, and a lower plate
30
having an address electrode
20
, a lower dielectric layer
22
, a barrier rib
24
and a fluorescent material layer
26
that are sequentially formed on a lower substrate
30
. The upper substrate
10
is spaced in parallel from the lower substrate
18
by the barrier rib
24
. The sustaining electrode pair included in the upper plate
28
consists of a scanning/sustaining electrode
12
A and a sustaining electrode
12
B. The scanning/sustaining electrode
12
A is responsible for applying a scanning signal for an address discharge and a sustaining signal for a sustained discharge, etc. On the other hand, the sustaining electrode
12
B is responsible for applying a sustaining signal for a sustained discharge, etc. The upper dielectric layer
14
is formed on the upper substrate
10
on which the sustaining electrode pair
12
A and
12
B is provided. The protective film
16
is coated on the surface of the upper dielectric layer
14
. A MgO film is usually used as the protective film
16
. The protective film
16
protects the upper dielectric layer
14
from the sputtering phenomenon of plasma articles to prolong the life of the PDP and improve an emission efficiency of secondary electrons. Also, the protective film
16
reduces a variation in the discharge characteristic of a refractory metal due to a contamination of oxide. The address electrode
20
included in the lower plate
30
is formed on the lower substrate
18
in such a manner to be crossed with the sustaining electrode pair
12
A and
12
B. The address electrode
20
serves to apply a data signal for the address discharge. The lower dielectric layer
22
is formed on the lower substrate
18
on which the address electrode
20
is provided. The barrier rib
24
is arranged in parallel to the address electrode
20
on the lower dielectric layer
22
. The barrier rib
24
serves to provide a discharge space at the inner side of the discharge cell so as to shield electrical and optical interference between the adjacent discharge cells. Also, the barrier rib
24
serves to support the upper substrate
10
and the lower substrate
18
. The fluorescent material layer
26
is coated on the surfaces of the lower dielectric layer
22
and the barrier rib
24
to generate a red, green, or blue visible ray. Further, an inactive gas for the gas discharge is sealed into the discharge space. The PDP discharge cell having a structure as described above maintains a discharge by a surface discharge between the sustaining electrode pair
12
A and
12
B after being selected by an opposite discharge between the address electrode
20
and the scanning/sustaining electrode
12
A. In the PDP discharge cell, the fluorescent material
26
is radiated by an ultraviolet ray generated during the sustained discharge, thereby emitting a visible light to the outer side of the discharge cell. As a result, the PDP having discharge cells display a picture.
FIG. 2
explains a process of sealing the upper plate
28
and the lower plate
30
of the PDP shown in FIG.
1
. Referring to
FIG. 2
, there are separately provided the upper plate
28
in which the sustaining electrode pair
12
A and
12
B, the upper dielectric layer
14
and the protective film
18
are sequentially disposed on the upper substrate
10
, and the lower plate
30
in which the address electrode
20
, the lower dielectric layer
22
, the barrier rib
24
and the fluorescent material layer
26
are sequentially disposed on the lower substrate
13
. Next, a PDP device is completed by sealing the upper plate
28
and the lower plate
30
after coating a sealing glass made in a paste state at the edge portion of the upper substrate
10
, in which the sustaining electrode pair
12
A and
12
B, the upper dielectric layer
14
and the protective film
18
are not formed, in such a manner to have a width of about 1 Cm and a height of about 200 &mgr;m. In this case, a glass of PbO—B
2
O
3
—ZnO group having a compositions as indicated in the following Table 1 is used as the sealing glass.
TABLE 1
COMPO-
NENT
PbO
B
2
O
3
ZnO
SiO
2
Al
2
O
3
Na
2
O
Li
2
O
WEIGHT %
75-82
6-12
7-14
1-3
0-3
0.3-0.5
0.1-0.2
FIG. 3
is a flow chart for explaining a formation method of a sealing glass making use of a glass of PbO—B
2
O
3
—ZnO group step by step. Referring to
FIG. 3
, in step S
1
, a glass of PbO—B
2
O
3
—ZnO group having compositions as indicated in Table 1 are prepared into a powder having a particle size of about 3 to 5 &mgr;p. Next, in step S
2
, the PbO—B
2
O
3
—ZnO group glass powder is mixed with an organic vehicle, thereby making a paste state. In this case, a viscosity of the paste of about 100,000 cps is a proper value. In step S
3
, a sealing paste is coated on the edge portion of the upper substrate
10
by exploiting the screen printing technique. Subsequently, in step S
4
, a sealing of the upper and lower plates
28
and
30
is completed by matching the upper plate
28
and the lower plate
30
coated with the sealing paste and then calcining the same. In this case, a sealing of the upper and lower plates
28
and
30
is terminated by sintering and crystallizing the upper and lower plates
28
and
30
matched by the sealing paste during about 20 to 30 minutes at a temperature of about 450° C. under the atmosphere condition using a resistance heating furnace and cooling the same so as to form a sealing glass
32
. At this time, a thermal expansion coefficient of the PbO—B
2
O
3
—ZnO group glass is more than 100×10
−7
° C. However, if the PbO—B
2
O
3
—ZnO group glass is calcined, then a crystal structure of ZnB
2
O
4
and ZnO—2SiO
2
is produced. Accordingly, a coefficient of the PbO—B
2
O
3
—ZnO group glass is reduced to 85 to 90×10
−7
° C., and a color of the sealing glass is changed into black.
However, after the final sealing, a slight crack is produced at the sealing glass due to a stress generated from the electrodes
12
A,
12
B and
20
defined on the upper and lower substrates
10
and
18
, the upper and lower dielectric layer
22
and the fluorescent material layer
26
, etc. in the course of performing a thermal treatment for sintering the PbO—B
2
O
3
—ZnO group glass. Also, since a sintering temperature of the PbO—B
2
O
3
—ZnO group glass has a relatively low value of less then 450° C., many air holes remain in the interior of the paste to deteriorate an airtightness of the PDP device. Accordingly, external air enters the internal discharge space of the PDP device to thereby deteriorate a discharge characteristic. Moreover, the PbO—B
2
O
3
—ZnO group glass contains above 70 weight % of toxic PbO oxide causing serious environment and work performance problems.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a composition of seal

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