Funnel glass for a cathode ray tube

Details Funnel glass for a cathode ray tube Funnel glass for a cathode ray tube

1999-06-30

2001-06-26

Sample, David R (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S069000, C501S070000, C501S072000, C313S480000

Reexamination Certificate

active

06251811

ABSTRACT:

The present invention relates to a funnel glass for cathode ray tube which is useful for a television receiver, a computer terminal display or the like.
A cathode ray tube is composed of a panel for displaying images, a neck for holding an electron gun and a funnel connecting them. These three sections are prepared separately in desired shapes, respectively, and then bonded to form a cathode ray tube. With a cathode ray tube, in order to illuminate the phosphors coated on the inner surface of the panel, a high voltage is applied to an anode to discharge electrons and irradiate them to the phosphors. At that time, X-rays will be generated, and the glass to be used for a cathode ray tube, is required to have an X-ray absorbing function. However, the glasses of these three sections are required to have different properties in addition to the X-ray absorbing function, and they are accordingly made of glasses having different compositions. Namely, for the panel, in order to shield X-rays generated and to prevent browning by such X-rays, as a component to shield X-rays, SrO or BaO is employed, and PbO is not employed. The funnel is required to have a higher X-ray absorbing function than the panel, and accordingly, as a component to shield X-ray, PbO having a larger X-ray absorbing coefficient than SrO or BaO, is employed in a large amount.
A part of cathode ray tubes after the end of useful life may be recovered and reused, and the rest will be stored as an industrial waste at a controlled site. The cathode ray tubes after the end of useful life stored outdoors, will be exposed to rain water for a long period of time, whereby glass components are likely to elute. Particularly, from a conventional funnel or neck glass containing lead, the lead is likely to elute.
In recent years, in order to cope with the above mentioned lead elution problem, a funnel glass whereby the lead elution into water is small, is desired. In order to reduce the lead elution from the funnel glass for a cathode ray tube into water, JP-A-7-206468 proposes a glass having PbO as one of the main components replaced by Bi
2
O
3
, and JP-A-8-290937 proposes a glass having TiO
2
incorporated. However, if the content of Bi
2
O
3
or TiO
2
in the funnel glass is increased, a problem such as depletion of the bismuth or titanium resource or an increase of the production cost, is likely to be brought about, since the production quantity of cathode ray tubes is very large.
Accordingly, it is an object of the present invention to provide a funnel glass which can be used for a funnel glass for a conventional cathode ray tube and which is composed of components which can be quantitatively secured as industrial resources and whereby the lead elution into water is little.
In a first aspect, the present invention provides a funnel glass containing PbO for a cathode ray tube, wherein when the composition is represented by wt % based on oxides, the content of SrO is at least 1.0 wt %, the content of BaO is at least 1.0 wt %, and the ratio of the content of PbO to the total amount of PbO, SrO, BaO, CaO and MgO, is at most 0.69, and whereby the lead elution A of the glass as measured by the following method A is at most 1.0 &mgr;g/cm
2
, and the X-ray absorption coefficient at a wavelength of 0.6 Å is at least 40 cm
−1
:
Method A: The glass is immersed in distilled and deionized water at 90° C. for 20 hours, whereupon the glass is taken out, and the amount of lead in the distilled and deionized water is measured by inductively coupled plasma spectrometry, and the measured value of the amount of lead is divided by the surface area of the glass, and the product is taken as the lead elution A.
Further, in a second aspect, the present invention provides a funnel glass containing PbO for a cathode ray tube, wherein when the composition is represented by wt % based on oxides, the content of SrO is at least 1.0 wt %, the content of BaO is at least 1.0 wt %, and the content of ZrO
2
is at least 0.3 wt %, and whereby the lead elution B of the glass as measured by the following method B is at most 4.0 &mgr;g/cm
2
, and the X-ray absorption coefficient at a wavelength of 0.6 Å is at least 40 cm
−1
:
Method B: The glass is immersed in distilled and deionized water at 90° C. for 20 hours, whereupon the glass is taken out, concentrated nitric acid is added to this distilled and deionized water and then the amount of lead is measured by inductively coupled plasma spectrometry, and the measured value of the amount of lead is divided by the surface area of the glass, and the product is taken as the lead elution B.
Now, the present invention will be described in detail with reference to the preferred embodiments.
Referring to the first aspect of the present invention, the lead elution A represents the amount of lead which elutes from the glass into distilled and deionized water when the glass is immersed in the distilled and deionized water at 90° C. for 20 hours and which is represented by a unit of &mgr;g/cm
2
as the weight of lead eluting per a unit surface area of the glass. Here, the distilled and deionized water is prepared by once distilling city water and further passing it through an ion exchange membrane. The above amount of lead is measured by inductively coupled plasma spectrometry (IPC) upon expiration of 7 days after completion of the immersion of the glass.
The lead elution A of the funnel glass for a cathode ray tube according to the first aspect of the present invention (hereinafter referred to simply as the glass according to the first aspect) is at most 1.0 &mgr;g/cm
2
, which is small as compared with the lead elution Å (1.2 &mgr;g/cm
2
) of the conventional funnel glass for a cathode ray tube (hereinafter referred to simply as the conventional glass) and thus is superior from the viewpoint of the environmental protection. The lead elution A is preferably at most 0.9 &mgr;g/cm
2
, more preferably at most 0.7 &mgr;g/cm
2
.
In the glass according to the first aspect of the present invention, PbO, SrO and BaO are essential, but CaO and MgO are not essential components.
When the composition of the glass according to the first aspect is represented by wt % based on oxides, if the ratio of the content of PbO to the total amount of PbO, SrO, BaO, CaO and MgO, exceeds 0.69, the lead elution is likely to be too much. The ratio is preferably at most 0.67.
In the second aspect of the present invention, the lead elution B is measured as follows.
(1) The glass (size: about 5 cm×5 cm, thickness: about 3 mm) is immersed in 100 cc of distilled and deionized water at 90° C. for 20 hours.
(2) From this distilled deionized water, the glass is taken out, and within 24 hours, 0.3 cc of concentrated nitric acid is added to the water.
(3) The amount of lead in the distilled and deionized water is measured by IPC upon expiration of 7 days from the completion of the immersion of the glass, and the measured amount is taken as the weight of the eluted lead.
(4) The weight of the eluted lead per a unit surface area of the glass is taken as the lead elution B (unit: &mgr;g/cm
2
).
The lead elution B of the funnel glass for a cathode ray tube according to the second aspect of the present invention (hereinafter referred to simply as the glass according to the second aspect) is at most 4.0 &mgr;g/cm
2
, which is small as compared with the lead elution B (4.6 &mgr;g/cm
2
) of the conventional glass and thus is superior from the viewpoint of the environmental protection. The lead elution B is preferably at most 3.6 &mgr;g/cm
2
, more preferably at most 3.0 &mgr;g/cm
2
, most preferably at most 2.3 &mgr;g/cm
2
.
When the lead elution A and the lead elution B from the same glass are compared, the lead elution B is usually larger than the lead elution A. The reason may be explained as follows.
In the measurement of the lead elution A, lead eluted from the glass into the distilled deionized water, will gradually precipitate in the form of a hydroxide as the time passes from the completion of immersion of the glass to the measur

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