Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
2000-07-14
2001-10-09
Thomas, Alexander S. (Department: 1772)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C428S001620
Reexamination Certificate
active
06300714
ABSTRACT:
The invention relates to a display panel comprising:
a glass backplate having a thermal coefficient of expansion of between 2.8*10
−6
and 10*10
−6
K
−1
, a first surface of which is provided with ribs of sintered glass frit, which ribs have a substantially parallel direction and bound channels, said backplate having electrodes extending in the direction of the ribs;
a plate-shaped front member comprising glass having a thermal coefficient of expansion of between 2.8*10
−6
and 10*10
−6
K
−1
and provided with light-transmissive electrodes which extend transversely to the channels, said front member resting on the ribs and being connected to the backplate in a gastight manner;
an ionizable gas in the channels.
A display panel of this type is known from U.S. Pat. No. 5,772,486.
The known display panel is a plasma-addressed display panel. The plate-shaped front member has a cavity between its electrodes and the backplate, which cavity is filled with an electro-optical material such as, for example, liquid crystals. When a gas discharge is generated in one or more of the channels because the relevant electrodes of the backplate are energized, and when a voltage is applied to one or more electrodes of the plate-shaped front member, the electro-optical material assumes a different orientation at the area where these electrodes cross the gas discharge. An image or alphanumerical information thereby becomes visible on the display panel. The visibility may be improved by passing light through the display panel.
When manufacturing the display panel, the ribs must be given the same substantially equal height throughout so as to achieve that the channels are separated from each other. To this end, the backplate with the sintered ribs is subjected to a grinding operation. The ribs must have a sufficient mechanical strength to prevent parts of its from breaking off during grinding.
In addition to mechanical strength, the thermal coefficient of expansion of the ribs is important. This expansion coefficient should correspond to that of the glass on which the ribs have been provided so as to prevent that the ribs come loose or that the panel gets warped. It is also important that the glass frit of the ribs can be sintered at a relatively low temperature because the backplate will otherwise lose its shape during sintering. In the manufacture of the known display panel, the sintering operation is carried out at a relatively high temperature: 540-600° C. (7:32). As the glass frit has a lower coefficient of expansion, the sintering temperature will, however, be generally higher because materials having a small coefficient of expansion, such as for example SiO
2
, have a high sintering temperature. A small coefficient of expansion and a low sintering temperature thus do not generally go together. On the other hand, the ribs should not flow too much but maintain their shape at temperatures of approximately 450° C. at which the backplate is connected in a gastight manner to the front member by means of, for example bonding glass.
In the known display panel, a commercially available glass frit paste is used to form the ribs therefrom (9:17-19). The above-cited U.S. Pat. No. 5,772,486 only states about the composition that it comprises glass grains, a resin binder, a solvent and other additions (6:10-12) and that a glass paste which is mixed with a ceramic material such as aluminum oxide is used (2:55-58). A glass frit having a coefficient of expansion which is too large in itself may be used because constituents have been added which have a smaller coefficient of expansion and thus render the coefficient of expansion of the total mixture relatively small. A considerable drawback of additions is, however, that they decrease the mechanical strength of the ribs and increase the risk of parts of the ribs breaking off during the grinding operation.
It is also important for the ribs that they do not transmit much light so as to achieve that light travels through the display panel substantially transversely to the display panel. To this end, pigments are often used as extra additions, which, however, also has a detrimental influence on the mechanical strength of the ribs.
Upon analysis of a number of commercial glass frits with Inductively Coupled Plasma Emission Spectrometry (ICP-AES) as known from Bul. de la Sociedad Espagnola de Ceramica y Vidrio, 553-558 (1992), the compositions given in Table 1 were found.
TABLE 1
Error!
SB5
NP7977M
BR3SB
Bookmark
not
defined.
color
dark grey
black
light grey
additive
PbTiO
3
0.9 Al
2
O
3
; 1.5
Pb
0.75
Ca
0.25
TiO
3
SiO
2
: 1.0 Li
2
O
wt %
70
37
40
pigment
CuCr
2
O
4
CuCr
2
O
4
/Fe
3
O
4
Fe
3
O
4
wt %
9
8
2
glass
0.7 Al
2
O
3
; 19 B
2
O
3
;
43 ZnO; 32 PbO;
0.5 Al
2
O
3
; 24
65.1 PbO; 3.8 ZnO;
25 B
2
O
3
SiO
2
; 75.5 PbO;
11.4 SiO
2
12.6 ZnO; 9.1
B
2
O
3
&agr;
6.7 * 10
−6
K
−1
>>7.5 * 10
−6
K
−1
9.5 * 10
−6
K
−1
wt %
21
55
58
It appears from this Table that the glass constitutes a small to very small part of the entire composition, that it has a relatively large coefficient of expansion and that it comprises a large to very large quantity of lead oxide. Pigment gives color to the glass frit. The pigment and the additives give the glass frit its coefficient of expansion and, also due to their large quantities, cause a mechanical weakness of ribs made of the frit. The high lead contents of these glass frits are also a drawback.
It is an object of the invention to provide a display panel of the type described in the opening paragraph, which display panel has ribs of glass frit having a high mechanical strength, a small lead content and a relatively low sintering temperature.
According to the invention, this object is achieved in that the glass frit comprises
90 to 97.5% by weight of ZnO, B
2
O
3
and V
2
O
5
, in which the mutual weight ratios of these components are between the points A, B, C and D of their ternary phase diagram, which points have the following compositions: A:44;36;20, B:59.6;20.4;20, C:63.3;31.7;5 and D:50.7;44.3;5 (% by weight of ZnO; % by weight of B
2
O
3
; % by weight of V
2
O
5
),
1.6 to 7% by weight of oxides chosen from CuO, PbO, and CuO plus PbO,
0.2 to 1.2% by weight of SiO
2
and
0.5 to 2.5% by weight of BaO.
In the glass frit of the ribs, additives and pigments are avoided so that the ribs have a great mechanical strength and the risk of breaking of portions from the ribs is effectively counteracted. Yet, the ribs are colored so that they are little transmissive or non-transmissive, with the color being dependent on the circumstances during their realization, for example, a treatment after sintering in a reducing environment such as, for example, H
2
/N
2
. Furthermore, the ribs have an extremely low lead content. The frit of the ribs surprisingly has a relatively low sintering temperature of approximately 525-550° C. and nevertheless a small thermal coefficient of expansion of approximately 4.5*10
−10
K
−1
. Due to the surprisingly favorable combination of a relatively small expansion coefficient and a relatively low sintering temperature, the display panel can be made in an easy and reliable way because it is not necessary to heat it to a high temperature, which effectively counteracts the risk of deformation of the backplate.
The glass frit comprises 90 to 97.5% by weight of ZnO, B
2
O
3
and V
2
O
5
because the expansion coefficient is too large at a quantity which is smaller than 90% by weight and the other components have too little influence at a quantity which is higher than 97.5% by weight.
The quantity of V
2
O
5
is between 5 and 20% by weight, because the sintering temperature of the glass is too high at quantities of less than 5% by weight and the expansion coefficient is too large at large quantities.
The quantities of ZnO and B
2
O
3
are between the values given by the points A, B, C and D of the ternary phase diagram of said three components, because the components do not form a stable glass outside the range indicated by these p
Busio Johannes Maria Marcus
Dohmen Petrus Jacobus Maria
Koopman Egbert Albertus
Thomas Alexander S.
U.S. Philips Electronics
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