Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2000-01-31
2002-03-12
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S015000, C501S046000, C501S047000, C501S048000
Reexamination Certificate
active
06355586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a low melting point glass containing no lead. Further, it relates to a glass ceramic composition containing a powder of this low melting point glass, which is useful for sealing a cathode ray tube or a flat display panel such as a plasma display panel (PDP) or a vacuum fluorescent display (VFD), for covering a substrate, or for forming partition walls in PDP or VFD.
2. Discussion of Background
Heretofore, a PbO-B
2
O
3
-ZnO-SiO
2
type crystallizable low melting point glass as disclosed, for example, in JP-B-36-17821, has been used for sealing a panel and a funnel of a cathode ray tube. Such a crystallizable low melting glass is coated on a sealing portion and then maintained at a temperature of from 440 to 450° C. for from 30 to 40 minutes, whereby the panel and the funnel will be sealed. The panel and the funnel thus sealed are evacuated while being heated at a temperature of from 300 to 380° C. to attain a high degree of vacuum with a pressure of at most 10
−6
Torr, and then sealed.
Further, heretofore, a low melting point glass has been used also for sealing a glass substrate in PDP or VFD, and it has been sealed at a temperature of from 440 to 500° C. In the case of VFD, the panel thus sealed is evacuated while being heated at a temperature of from 250 to 380° C. to attain a high degree of vacuum and then sealed. In the case of PDP, the panel is likewise evacuated while being heated at a temperature of from 250 to 380° C., and a discharge gas such as Ne, Ne—Xe or He—Xe is sealed in to a level of from 100 to 500 Torr, and then the panel is sealed.
Heretofore, a glass containing lead has been used as a low melting point glass for sealing. Recently, however, a glass containing no lead has been desired.
Further, the low melting point glass which has heretofore been used for sealing, does not match in the expansion coefficient with e.g. a panel or a funnel of a cathode ray tube, or with a glass substrate to be used for PDP or VFD, whereby it has been likely that the sealed glass tends to break. Further, it has happened that due to the heating at the time of evacuation, the low melting point glass at the sealing portion has tended to flow or foam, or the sealing portion has tended to break.
Further, a low melting point glass to be used for sealing, covering or forming partitions walls in PDP or VFD, is required not to contain an alkali metal oxide which is likely to lower the electrical insulating property, or even if it contains such an alkali metal oxide, the content is required to be small. As such a glass, an attention has been drawn to a tin zinc phosphate type glass.
However, a tin zinc phosphate type glass heretofore known, has had the following problems.
(1) Due to the heating at the time of evacuation, the low melting point glass at the sealing portion tends to flow or foam, or the sealing portion tends to break.
(2) The glass is likely to undergo crystallization during firing, and when firing and flowing are carried out twice or more, the glass tends to hardly flow in the second or subsequent firing. Further, the dimensional fluctuation increases with the progress of crystallization by repetition of firing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a low melting point glass and a glass ceramic composition which solve the above problems.
The present invention provides a low melting point glass (a glass of first embodiment) consisting essentially of, as represented by mol % based on the following oxides:
Mol %
SnO
2 to 37.5,
ZnO
5 to 73,
P
2
O
5
16 to 50,
Li
2
O
0 to 9,
Na
2
O
0 to 9,
K
2
O
0 to 9,
Al
2
O
3
0 to 20,
B
2
O
3
0 to 30,
SiO
2
0 to 20,
MgO
0 to 35,
CaO
0 to 35,
SrO
0 to 35,
BaO
0 to 35,
In
2
O
3
0 to 10,
WO
3
0 to 10,
wherein SnO+ZnO+P
2
O
5
+B
2
O
3
is at least 76 mol %, Li
2
O+Na
2
O+K
2
O is from 0 to 9 mol %, MgO+CaO+SrO+BaO is from 0 to 35 mol %, and the molar ratio of SnO to ZnO is less than 1.
Further, the present invention provides a low melting point glass (a glass of second embodiment) consisting essentially of, as represented by mol % based on the following oxides.
Mol %
SnO
2 to 37.5,
ZnO
32 to 73,
P
2
O
5
25 to 50,
Li
2
O
0 to 9,
Na
2
O
0 to 9,
K
2
O
0 to 9,
Al
2
O
3
0 to 20,
B
2
O
3
0 to 30,
SiO
2
0 to 20,
MgO
0 to 30,
CaO
0 to 30,
SrO
0 to 30,
BaO
0 to 30,
wherein Li
2
O+Na
2
O+K
2
O is from 0 to 9 mol %, MgO+CaO+SrO+BaO is from 0 to 30 mol %, and the molar ratio of SnO to ZnO is less than 1.
Still further, the present invention provides a low melting point glass (a glass of third embodiment) consisting essentially of, as represented by mol % based on the following oxides:
Mol %
SnO
2 to 35,
ZnO
5 to 45,
P
2
O
5
16 to 50,
Li
2
O
0 to 3,
Na
2
O
0 to 3,
K
2
O
0 to 3,
Al
2
O
3
0 to 10,
B
2
O
3
0.1 to 30,
MgO
0 to 35,
CaO
0 to 35,
SrO
0 to 35,
BaO
0 to 35,
In
2
O
3
0 to 10,
WO
3
0 to 10,
wherein Li
2
O+Na
2
O+K
2
O is from 0 to 3 mol %, MgO+CaO+SrO+BaO is from 0 to 35 mol %, Al
2
O
3
+In
2
O
3
+WO
3
is from 0 to 3 mol % and the molar ratio of SnO to ZnO is less than 1. The glass of third embodiment is effective particularly for solving the above-mentioned problem (2).
Further, the present invention provides a glass ceramic composition containing a powder of the low melting point glass of first, second or third embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The low melting point glass of the present invention (hereinafter referred to simply as the glass of the present invention) has a softening point T
s
of at most 600° C. If the softening point exceeds 600° C., it tends to be difficult to employ such a glass for sealing, covering or formation of partition walls for e.g. PDP or VFD. The softening point is preferably at most 580° C., more preferably at most 560° C., most preferably at most 550° C.
Further, when the glass is used for covering or formation of partition walls for e.g. PDP or VFD, T
s
is preferably at least 500° C. If it is less than 500° C., the covering or the formation of partition walls tends to be difficult. It is more preferably at least 510° C., particularly preferably at least 520° C., most preferably at least 530° C.
When the glass of the present invention is used for sealing, covering or formation of partition walls, it is usually pulverized for use. Such pulverized glass is mixed with a low expansion ceramic filler, a heat resistant pigment, etc., as the case requires, and then kneaded with a vehicle to obtain a paste. This glass paste is coated at a predetermined portion of a substrate glass and fired. Here, the substrate glass includes one having a transparent conductive film or the like coated on glass.
The crystallization temperature (T
c
) of the glass of the present invention is preferably higher by at least 40° C. than T
s
. if the difference between T
c
and T
s
, i.e. (T
c
−T
s
), is less than 50° C., the glass tends to be crystallizable during firing. Here, T
c
is the crystallization peak temperature obtainable by a differential thermal analysis, and when the crystallization peak is not observed, T
c
=∞. (T
c
−T
s
) is more preferably at least 60° C., particularly preferably at least 70° C. most preferably at least 80° C.
When the glass of the present invention is used for sealing for e.g. a cathode ray tube, PDP or VFD, the average linear expansion coefficient in a range of from 50 to 300° C. is preferably at most 120×10
−7
/° C. Hereinafter, the average linear expansion coefficient in a range of from 50 to 300° C. is represented by &agr;
300
.
When the glass of the present invention is used for covering or formation of partition walls for PDP or VFD, the average linear expansion coefficient in a range of from 50 to 250° C. is preferably at most 120×10
−7
/° C. If it exceeds 120×10
−7
/° C.,
Dotani Yasuko
Manabe Tsuneo
Tanabe Ryuichi
Usui Hiroshi
Asahi Glass Company Limited
Group Karl
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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