Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
1999-06-24
2004-12-07
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C445S024000, C445S040000
Reexamination Certificate
active
06827623
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of manufacturing plasma display panels, referred to hereinafter as PDPs, in which a pair of substrates with a discharge space therebetween is vacuum sealed along the respective peripheries thereof, and particularly relates to a sealing method to form such a panel having such a sealed discharge space.
2. Description of the Related Art
Hereinafter is described a structure of an AC-driven three-electrode surface discharge type PDP, as representative of plasma display panels in which the present invention can be embodied. As shown in
FIG. 19
, a perspective and partially cross-sectional view of a PDP, there is arranged for each line L of a display matrix a pair of display electrodes X & Y upon an inner surface of a front glass substrate
50
in order to generate a surface discharge along a surface of the front substrate
50
. The display electrodes X & Y may also be called sustain electrodes. The display electrodes X & Y are respectively formed of a stack, or laminate, of a wide, straight transparent electrode
52
formed of a thin film of ITO, Indium Tin Oxide, and a narrow straight bus electrode
53
formed of a thin metal film. The display electrodes X & Y are formed by means of a photolithography technique.
A dielectric layer
54
for the AC (alternating current) drive is formed on the inner surface of the front substrate
50
, so as to cover the display electrodes X & Y and protect same from discharges in the discharge space, by means of a screen printing method. Upon dielectric layer
54
is deposited a protecting layer
55
formed of MgO, Magnesium Oxide.
On the other hand, upon an inner surface of a back glass substrate
51
there are arranged, in order to generate address discharges, address electrodes
56
, orthogonal to the display electrodes X & Y and spaced by a constant pitch. The address electrodes
56
as well preferably are formed of a stack, or laminate, of metal films by means of a photolithography technique.
Upon the entire inner surface of the back glass substrate
51
, including the portions above the address electrodes
56
, there is formed a dielectric layer
57
by means of a screen printing method and, further, thereupon is provided a plurality of approximately 150 &mgr;m high straight separator walls, or barriers,
58
each centered between a respective pair of adjacent address electrodes
56
. Fluorescent materials
60
, of three primary colors R (red), G (green) and B (blue) for a full color display, are coated so as to cover the surface of dielectric layer
57
including the respective, exposed portions above corresponding address electrodes
56
and the sides of the separator walls
58
, by means of a screen printing method.
Within discharge space
59
is filled a discharge gas, such as typically a mixture of Ne—Xe, i.e. neon gas and xenon gas, of several hundreds Torr, for exciting the fluorescent materials by irradiating thereon ultra-violet rays during the gaseous discharge. A sealant (seal-glass layer)
61
is provided for sealing the discharge space
59
at the respective peripheral portions of the substrates
50
and
51
.
Front glass substrate
50
and back glass substrate
51
are separately prepared, and finally sealed together with sealant
61
so as to form the sealed discharge space therebetween. The structure of the PDP is thus completed.
Referring to
FIGS. 20A
,
20
B and
21
, hereinafter is described a prior art method of manufacturing the PDP, including a step to form the discharge space shielded from the external space (i.e., the surrounding exterior space) with the above described sealant
61
.
FIGS. 20A and 20B
illustrate a cross-sectional view and a plan view, respectively, of a PDP in a step for peripheral edge sealing; and
FIG. 21
illustrates heating and exhausting processing cycles as a function of time.
Sealant
61
shown in
FIGS. 20A and 20B
has been formed by coating a glass paste on the back glass substrate
51
and, next, solidifying the paste during preparing of the back glass substrate. The thus prepared sealant is melted once during the sealing step and solidified again so as to join front glass substrate
51
.
As shown in
FIG. 20B
, during the prior art process of sealing a PDP
71
, a front glass substrate
73
and a back glass substrate
72
are stacked with a layer of sealant
74
between their respective peripheries and are clamped with several clips
77
at the peripheries thereof. Clips
77
both fix the glass substrates
72
and
73
relatively to each other as well as impose a predetermined pressure onto the peripheral portions to be sealed while the sealant
74
is melted.
That is, in order to form the discharge space
76
during the sealing process using sealant
74
, it is necessary to melt the sealant
74
placed between the paired glass substrates
72
and
73
by heating same and to deform, i.e. press, the paired glass substrates
72
and
73
together so as to have the gap therebetween defined by the height of the separator walls. Accordingly, a pressure has to be imposed in a direction such that the paired glass substrates
72
and
73
approach each other. Several clips
77
are needed to generate the required pressure.
At the periphery of the back glass substrate
73
, a conduction pipe (a glass pipe)
75
is provided so as to make a channel connecting the discharge space
76
and the outside (i.e., the exterior) of the PDP
71
. The space
76
is exhausted of ambient air and then filled with a discharge gas via the pipe
75
. During the prior art sealing process, a pair of the substrates
72
and
73
, each of about 3 mm thickness, may be damaged by a stress due to direct clamping with many clips
77
. Accordingly, it is necessary to seal the pair of substrates
72
and
73
while weakly clamped over a long time process.
The illustrative prior art method is explained in more detail with reference to
FIG. 21
, showing processing cycles in above described prior art. The pair of substrates
72
and
73
, clamped with many clips
77
as shown in
FIG. 20B
, is carried into a furnace (not shown) for heating and then the seal head
5
(not shown) is closely mounted to the pipe
75
. The seal head is connected to a pump for exhausting, and then to gas cylinders for gas filling (not shown in FIG.
20
A).
While keeping (i.e., maintaining) such a state, a heater for heating the furnace is operated first so that the temperature inside the furnace is gradually raised so as to reach a melting temperature T
m
of the sealant
74
. This heating period is illustrated as a temperature-raising period T1. Next, the temperature inside the furnace is kept at the melting temperature T
m
of sealant
74
for a predetermined period, which is illustrated as a first temperature-holding period T2. During the temperature holding period T2, sealant
74
is melted so as to allow both the front and back glass substrates to reach a predetermined gap therebetween defined by the height of the separator walls (e.g., as shown at
58
in
FIG. 19
) by the pressure of clips
77
as shown in
FIGS. 20A and 20B
.
The first temperature holding period T2 is a relatively long period because the process, during the temperature holding period T2, has to be carried out while the substrates
72
and
73
are clamped with clips having weak, or low, pressure as described above. When the gap between front glass substrate
72
and back glass substrate
73
reaches the predetermined gap size defined by the height of the separator walls, the temperature inside the furnace is decreased down to a solidifying temperature of sealant
74
. This period is illustrated as a temperature-lowering period T3. During these periods of to T3, neither exhausting nor gas-filling is carried out from/into a discharge space
76
sealed by the sealing process.
Next, the temperature as lowered during the temperature lowering period T3 is held for a predetermined period, namely, a second, temperature holding period T4. This lowered temperature nevertheless is at a relatively
Fujimoto Akihiro
Fukui Minoru
Iwasaki Kazuhide
Kanagu Shinji
Nakatake Fumiaki
Colón German
Fujitsu Limited
Patel Nimeshkumar D.
Staas & Halsey , LLP
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