VERRE POUR TUBES A RAYONS CATHODIQUES POUR L'AFFICHAGE D'IMAGES TELEVISUELLES

GLASS FOR CATHODE-RAY TUBES FOR DISPLAYING TELEVISION PICTURES

Abrégé anglais

ABSTRACT:
Glass for cathode-ray tubes for television
display having a considerably cheaper mixture. The mix-
ture is free of lithium compounds and contains less
potassium. The glass is characterized by having a com-
position between the limits in weight %:
<IMG>.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
1. A glass for cathode-ray tubes for displaying
television pictures, black-and-white pictures in par-
ticular, characterized in that it is free of Li2O and
that it has a composition between the following limits
in weight %.
<IMG>
2. An electron-beam tube of which at least a part
consists of glass as claimed in Claim 1.
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Description

-p~
; LO~P~ 3
29 . J . 19 ~ o
1~)5
"Glass for cathode-ray tubes for displaying tele~ision
pictures".
:: -: - .
The ~n~ention relates to glass for cathode-r~y
tubes for displaying television pictures, particularly
: :
black-and-white p.ictures~ and for the faceplate of che ~-
tube as well as for its coneO
Tbis glass must s~atisfy certain requirements
as rega~ds the number of physical prop,rtles which are
- associated with the shaping and sealing technique o~ the
tube parts- The tube parts, i. 2 the faceplate and the cone .
are p~oduced by pressing and~or spinning, whilst the par~s
10 . are sealed to~ether under the application of heat by
means of a flame with electrical~auxiliary heating th~ou&h
: the glass which has been rendèred properly~canducli~e b~
means of heating. When gas~es are removed by firing ~he ~ ~`
~:i tube on the exhaust line at elevated temperature, the
15 ~ tube must not be deformed.
: ~
: The~above results in the fact that the ~isco-
sity cur~e of the glass is rather accurately establi~h- :. .;
~d. The softening point, i.~.:the tempeIature a~t ~-hich .:~`
~ tha ~iscosity Or the glass amounts to 107' poi~ses must
be approximately 670 ~ 15C and~`the so-called "~-arm len~th~
i.e. the difference Oetween~the workin tempera~ure at
: wh~ch the ~iscosity of the glass is 10 poises and lihe ~ :

PHN 7987
29 .3 . 7G
~05~
softening point mui~t be approximately 350 + 15C.
Another important magnitude is the electrical
resistivity at an el~ated temperature. As a measure for
this a temperature has been chosen at which the resis~
tivity is equal to 100~0hm.cm = 10 Ohm. cm:TK 10
Usually this temperature ha3 a value of 290 + 10C.
A glass ,which has been customary so~ar for
bulbs for black-and-white television display is the fol-
lowing (in weight%)~
SiO2 6~.7 BaO13.6 ;
Na20 8-5 . Al232.5
K 0 6.6 Sb230.6.
Li20 ' O . 5 ' . .; `
In the last few years the prices of a number
of raw materials have risen drastically. Among the moSt
expensiYe raw materials for composing the mtxture for ~.
: the abo~e glass are lepidolite,~petalite or spodumene :~
which furnish the Li2Q and the~ potassium which is tlle
. raw material for the K20. It was an object of this in~
vention to provide a glass which requires a cheaper mix-
ture~ but which would not impair~the properties of the
bulb for a black-and-white television display tube~and
the display:~tube itself and which would not impede pro- : `
du c t i on of the glass.
: ~ : , , ~ - ~ , :
It has now appeared that no disadvantages are
experienced if for the T~ = 100 a ~alue was chosen:which
i~ 400C lower than the value which`has been usual sofar, ;~:
.
;, ~ ,
.

, PH~ 7987
-' ~ 29.3.76
.
:
~(15~
:
i.e. at least 2400C instead of at least 280C.
. If the Li20 is omitted from the ~bo~e glass ~nd ;
by ~hifting the ratio Na20/K20 in favour of the Na20, ~:
a glass was obtained ~lich has a TX = 100 which is up
to 4QoC lower but whose above viscous properti.es ha~e
remained substantially unchanged; `~
The glass composition according to the inven~lon ~: .
is ~Eee of Li20 and is characterized in that it is situat~
ed between the following limits in weight %:
SiO2 ` .62-69 `~ `
.
Na20 ~ K20 1~-17
1.4< Na20/K20 ~ 2.2
: ....... BaO ~-14 ~:
SrO . 0-2 - :
PbO 0
A123 ;~
` - Sb23 ~ As23 0-0.8
: F 0-~-5
~ Zr2 ~ 2
20 By way of example some compositions in weigh~
~ are given below which are within the scope of the in-
`~ ~ention and which are obtain~ed by melting a correspond~
; ing mixture, together with thé Tx 100~ the softening
point Tso~ (~ = 107-6 poises)~, the working tempera~ure
TW~r (~ = 104 poises) and the ratio YazO/KzO. :~
.
.
.: , ~
- . - ` ~ ~

' PH~ 7g~7
3 29.3.76
:J 05~
5~2 67.6 67.9 7.3 6~ 6 .8
I Na20 9.0 9,4 9.8 9-3 9.2
:l K20 6.ll 5-9 5:6 500 5-9
., , Li20 ~ _ _ _ _
l BaO 13.7 13.2 13.7 l3.3 13.7
i, ~ Zr2 O 0.2 ~ ~ _ _
SrO Q.2 0.2 0.2 0.2 0.2
pbO _ _ _ 3-7 _~
23 2.5 2.6 2.7 3.4 3.~
i ~ o.6 o.6 0.7 0.7 0.7
~ t% of total) _ _ ~ _ 0.35
, ~ ~ ~ '` ~' ~ .:-- -
1 ~ K - lQO(~ C) ~Z65 255 255 260 260
T90f (C) 6681 677 677 671 681
wor ( C) 1020 1027 1027 1Q28 1028
~-zO/~O 1.l~0 1.6 1.7S 1.86 1.S9
~ ." ' . ' .
:
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.:
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S1~34~
Till now screen glasses for colour TY-display were subject to requirements
different from those for screen glasses for black-and-white display. The
colour glass had to be "harder" than the black-and-white glasses, i.e. the
temperatures at which the glass possesses a definite value of ~he viscosity,
as the strain point (~ = 1014 6 poises), the annealing temperature ~ = 10
poises) and the softening point (~=107-65 poises) should be about 20-30 C
higher for the former glasses than for the latter ones. The reason for selec-
ting harder glasses for colour display is related to the fact, that upon
manufacture of a cathode ray tube for ~elevision display such high temperatures
are needed for sealing of the screen to the cone and for evacuating the tube,
that there is a risk of deformation,upon use of softer glasses.
In the last few years, ho~ever, the sealing temperatures and the
evacuation temperatures could be lowered considerably.
Thus it is possible to use the Li20-free glass of the invention for
colour TV-display.
An important advantage of this kind of glasses as compared with
glasses for colour TV, which were till now in use, is that upon polishing less
glass has to be removed; e.g. 0.08 mm of glass instead of 0;35 mm. The reason
for it is, that the glass is softer and that the shear-mark is much less deep.
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