CRT frit capable of sealing a CRT bulb at a relatively low...

Details CRT frit capable of sealing a CRT bulb at a relatively low... CRT frit capable of sealing a CRT bulb at a relatively low...

2000-02-11

2003-06-24

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S017000, C501S049000, C501S075000, C501S076000

Reexamination Certificate

active

06583079

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a CRT (Cathode Ray Tube) frit and, in particular, to a CRT frit for use in sealing a panel and a funnel of a color CRT bulb.
Traditionally, a panel and a funnel of a color CRT bulb are sealed by the use of a crystallizing CRT frit comprising crystallizing glass powder of PbO—B
2
O
3
—ZnO—SiO
2
—BaO and refractory filler powder such as zircon. In a sealing step, the crystallizing CRT frit is held at a temperature between 440 and 460° C. for 30 to 60 minutes.
During an exhaust step following the sealing step, the bulb is heated again to a temperature between 350 and 400° C. Since the crystallizing CRT frit is excellent in heat resistance, no displacement of the panel and the funnel is caused in the exhaust step as a result of softening of the crystallizing CRT frit.
Following the recent improvement in the exhaust technique, it is possible to carry out exhaust by low-temperature heating. Therefore, the CRT frit is not required to have such a high heat resistance. Instead, in view of the reduction in energy cost and the improvement in productivity, it becomes important to seal the bulb at a lower temperature and in a shorter time. However, the existing CRT frit can not meet such a demand because high-temperature and long-time sealing is required as described above in order to obtain desired characteristics.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a CRT frit capable of sealing a panel and a funnel of a CRT bulb at a low temperature and in a short time.
According to this invention, there is provided a CRT frit which is for use in sealing a panel and a funnel of a CRT bulb and which comprises non-crystallizing glass powder and refractory filler powder, the non-crystallizing glass powder consisting essentially of, by weight percent, 75-90% PbO, 7-20% B
2
O
3
, 0-8% ZnO, 0-5% SiO
2
, and 0.1-8% Al
2
O
3
+Fe
2
O
3
.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, description will be made about this invention.
A CRT frit according to this invention comprises powder of a non-crystallizing glass and powder of a refractory filler.
The non-crystallizing glass used in this invention is highly stable and is hardly devitrified. The non-crystallizing glass has a glass transition point on the order between 290 and 310° C. and a softening point on the order between 330 and 370° C. The non-crystallizing glass is excellent in flowability because it is not crystallizable. Therefore, with the CRT frit of this invention, it is possible to seal the bulb at a low temperature and in a short time. Preferably, the non-crystallizing glass consists essentially of, by weight percent, 76-88% PbO, 8-18% B
2
O
3
, 0.1-5% ZnO, 0.1-4% SiO
2
, and 0.1-7% Al
2
O
3
+Fe
2
O
3
.
The non-crystallizing glass is classified into a first glass composition which essentially contains Al
2
O
3
and a second glass composition which essentially contains Fe
2
O
3
.
Specifically, the first glass composition consists essentially of, by weight percent, 76-90% PbO, 8-18% B
2
O
3
, 0-5% ZnO, 0.1-3% SiO
2
, and 0.1-3% Al
2
O
3
. The first glass composition tends to provide the glass having a relatively high softening point, as compared with the second glass composition. Therefore, displacement of the panel and the funnel resulting from softening of the glass and generation of bubbles from the glass hardly occur. In case where the exhaust temperature of the CRT bulb in an exhaust step can not sufficiently be lowered, the first glass composition is advantageous because of high stability. Description will hereinafter be made about the reason why the first glass composition is determined as mentioned above.
PbO is a component forming a network structure of the glass The content of PbO is 76-90%, preferably, 79-87%. If the content of PbO exceeds 90%, the coefficient of thermal expansion becomes too great. If the content is less than 76%, the flowability of the glass is lowered and the sealing temperature becomes excessively high.
B
2
O
3
is a component forming the network structure of the glass. The content of B
2
O
3
is 8-18%, preferably, 10-15%. If the content of B
2
O
3
exceeds 18%, chemical durability is degraded to a practically unfavorable level. If the content is less then 8%, the flowability of the glass is decreased.
ZnO serves to suppress devitrification of the glass if it is added in a predetermined amount. The content is 0-5%, preferably, 1-4%. If the content of ZnO exceeds the above-mentioned range, devitrification will readily occur.
SiO
2
serves to stabilize the glass of the above-mentioned composition. The content is 0.1-3%, preferably, 0.2-2.5%. If the content of SiO
2
is more than 3%, the softening point is elevated and the sealing temperature becomes excessively high. If the content is less than 0.1%, the glass becomes unstable and will be devitrified.
Al
2
O
3
serves to stabilize the glass of the above-mentioned composition. The content is 0.1-3%, preferably, 0.2-2.5%. If the content of Al
2
O
3
is more than 3%, the softening point is elevated and the sealing temperature becomes excessively high. If the content is less than 0.1%, the glass becomes unstable and will be devitrified.
Furthermore, V
2
O
5
or Bi
2
O
3
may be contained although V
2
O
5
or Bi
2
O
3
is not essential. In case where the softening point is excessively elevated as a result of addition of SiO
2
and Al
2
O
3
as the glass stabilizing components, addition of V
2
O
5
or Bi
2
O
3
is desired to control the softening point.
V
2
O
5
serves to lower the softening point of the glass of the above-mentioned composition. The content is 0-1%, preferably, 0-0.8%. If the content of V
2
O
5
is more than 1 %, devitrification will readily occur.
Bi
2
O
3
is a component which serves to lower the softening point of the glass of the above-mentioned composition. The content is 0-5%, preferably, 0-4%. If the content of Bi
2
O
3
is more than 5%, devitrification will readily occur.
As far as the glass does not become unstable, other components can be added. For example, in order to prevent the release of PbO, TiO
2
may be added up to 5%. In case where the glass is unstable and tends to be devitrified, Fe
2
O
3
or CuO may be added to stabilize the glass. The content of Fe
2
O
3
is 5% or less, preferably, 2% or less. The content of CuO is 3% or less, preferably, 1% or less.
On the other hand, the second glass composition consists essentially of, by weight percent, 75-90% PbO, 7-20% B
2
O
3
, 0-8% ZnO, 0-5% SiO
2
, and 0.1-5% Fe
2
O
3
. Since the second glass composition contains Fe
2
O
3
, the glass is highly stable and devitrification (surface crystal precipitation) upon sealing will very hardly occur. As compared with the first glass composition, the second glass composition tends to provides the glass having a relatively low softening point. Therefore, in order to further lower the sealing temperature, the second glass composition is advantageous. Description will hereinafter be made about the reason why the second glass composition is determined as mentioned above.
PbO is a component forming a network structure of the glass. The content of PbO is 75-90%, preferably, 79-87%. If the content of PbO exceeds 90%, the coefficient of thermal expansion becomes too great. If the content is less than 75%, the flowability of the glass is lowered and the sealing temperature becomes excessively high.
B
2
O
3
is a component forming the network structure of the glass. The content of B
2
O
3
is 7-20%, preferably, 9-15%. If the content of B
2
0
3
exceeds 20%, chemical durability is degraded to a practically unfavorable level. If the content is less then 7%, the flowability of the glass is degraded.
ZnO serves to suppress devitrification of the glass if it is added in a predetermined amount. The content is 0-8%, preferably, 1-5%. If the content of ZnO exceeds the above-mentioned range, devitrification will readily occur.
SiO
2
serves to stabilize the glass of the above-mentioned composition. The content is 0-5%, preferably, 0.2-2.5%. If the content of SiO
2
is more

Affiliated with

Also associated with

Rating

CRT frit capable of sealing a CRT bulb at a relatively low... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with CRT frit capable of sealing a CRT bulb at a relatively low..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and CRT frit capable of sealing a CRT bulb at a relatively low... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3128767