Note: Descriptions are shown in the official language in which they were submitted.
PHN 8121
1060079 ~ -
The invention relates to a method of manufactur;ng
a cathode ray tube for displaying coloured pictures and
comprising a display screen having a large number of triplets
each consisting of three linear regions luminescing in
different colours, means to generate three electron beams,
and a colour selection electrode wh;ch has a large number -~ .
of substantially parallel slots for assigning each electron
beam to luminescent regions of one colour in such manner ~ -
that each triplet corresponds to one slot, in which method
for providing the luminescent regions of each colour a ;~ -
photosensitive layer is exposed through the colour selection :
electrode from at least two positions in such manner that ; .
the light beams which pass through two juxtaposed slots
overlap each other on the photosensitive layer and an ~
unexposed region where the luminescent regions of the said - -
colour are to be provided is formed on the photosensitive
: layer between the light beams which pass through the same
slot. The invention also relates to a cathode ray tube ;
manufactured according to such a method.
German Offenlegungsschrift 2,248,878, which was
~ ~ ~ laid open to public inspection on April 19, 1973, discloses
: a method of manufacturing such a cathode ray tube in which
the photosensitive layer is exposed through the colour
selection electrode from at least two positions in such ~-
manner that the light beams which pass through two juxta~
posed slots overlap each other on the photosensit~ve layer
.
''"'.' "
~ 2 ~
. . . .
B ` : -
}~lr~. 8121
1 9 _ 1 _ 1 9 7 G
~060C~79
and an uncxposed region is formed on the photosensitjve
layer between the light beams which pass through the same
slot. In the method described in said Offenlegungsschrift
light-absorbing strips are provided on the said unexposed
regions which separate the linear regions from each other
which luminesce in different colours. The application of
the method described in said Offenlegungsschrift for
providing the luminescent regions themselves proves to meet
unexpected difficulties which will be described in detail
hereinaf-ter with reference to a drawing. As a matter of
fact, the result of the use of the exposure method
described in the Offenlegungsschrift for providing the
luminescent regions would be that the two outermost triplets
which during normal operation of the tube are present on
the extreme left and on the extreme right at the edge of the
display screen do not correctly display the colour. As a
result of this the displayed picture has edges which show
annoying colour defects.
It is to be noted that a slot in the colour
selection electrode may consist of one uninterrupted slot-
like aperture or of a row of elongate apertures having
narrow bridges between them.
It is the obJect of the invention to avoid the
above-mentioned colour defects.
~25 ~or that purpose, according to the:;nvention,
prior to providing the luminescent regions the photosensitlve
layer is exposed entirely through the colour selection
electrode in the region of the triplets which correspond to
the outermost slot but one on the two ~ides of the colour
: ,
--
,
.
- ~ PHN 8121
~60079
selection electrode as well as in the region between the
last-mentioned triplets after which a non-luminescent layer
is prov;ded on the unexposed parts of the photosensitive
layer.
The said non-lum;nescent layer preferably is a
light-absorbing layer which may form part of a dark
coloured picture frame.
The non-luminescent layer may also be a conductive
layer on which, when the luminescent regions are subsequently
provided electrophotographically, no charge can be maintained
and consequently no luminescent material is deposited.
In a cathode ray tube for d;splaying coloured
pictures according to the invention the electron beams ~
after passing through the outermost slot on either side ~ `-
of the colour selection electrode do not impinge upon
luminescent regions so that picture edges showing the said
colour defects are absent.
A suitable method of providing luminescent or
non-luminescent material on the unexposed regions of a
photosensitive layer is the electrophotographic method
disclosed in United States Patent Specification 3,475,169,
which issued to Zenith Radio Corp. on October 28, 1969,
in which the photosensitive layer is a photoconductive
layer which is provided with an electric charge pattern
which is developed by means of a suspension whlch contains
electrically charged grains of the material to be provided.
In another method the powder to be provided is provided in
a photosensitive layer which in the unexposed condition is
insoluble in the solvent and after the exposure is
soluble in the solvent. After exposure through the
-- 4 --
B
P~. &121
19-1-197G
1060079
colo~r selection electrode the photosensitive layer
containing the material to be provided is developed with
the solvent. These and similar methods are known from the
prior art.
The invention will be described in greater
detail with reference to the accompanying drawing, of
which:
~ig. 1 shows a colour television display tube
according to the invention,
Fig. 2 shows the pattern of slots in the colour
- ~selection electrode of the tube shown in Fig. 1,
~igs. 3a, b and c explain diagrammatically an
exposure method of manufac-turing a tube according to the
invention, and
Fig. 4 explains an extra step according to the
invention in this method.
The tube shown in ~ig. 1 comprises a glass en~elope
1 in which means 2 are- present to generate three electron
beams 3, 4 and 5, a display screen 6 and a colour selection
Z0 electrode 7. The electron beams are generated in one flat
plate through the axis 8 of the tube; during normal
operation of the tube said plane i9 horizontal and is the
plane of drawing of ~ig. 1. The displa~;screen 6 comprises
a large number of phosphor lines 9 wh~ch extend vertically
.
normal to the plane of drawing. The phosphor lines 9 are
, arranged in triplets containing a red, a green and a blue
luminescent phosphor line. ~ slot 10 in the colour selection
electrode 7 is associated with each triplet. The slots 10
-~ are norma1 to thei~plane of drawing and are formed by either
- , '
, ':
- 5 -
~ ~ PIIN. 8121,
_- ~ 12-2-1976,
1060(:~79
an uninterrupted slot or a row of eloIIgate apertures having
narrow bridges between them, as is shown in Fig. Z.
The slots in the colour selection electrode
ensure that the electron beam 3 impinges only on red
luminescent phosphor lines and the electron beams 4 and 5
- impinge only on green and blue luminescent phosphor lines,
respectively, The eloctron beams 3, 4 and 5 scan the display
screen 6 under the influence of the deflection coils 11.
For further explanation, Fig. 2 shows a front
elevation of the colour selection electrode with which the
arrangement of the elongate apertures 12 in vertical slots
10 is again explained. The two outermost slots 13 and 14
which are also shown in Fig, 1 do not correspond to a
triplet. According to the invention, in the places denoted
in Fig. 1 by 15 and 16 there is no triplet but a non-
luminescent~ preferably light-absorbing layer for reasons
to be given hereinafter.
An exposure method with which the tube shown in
Fig. 1 can be manufactured will now be described with
,; ~ .
~ ` 20 reference to Figs. 3a, b and c assuming thatj the extra step
;; in the method explained in Fig. 4 is also used.
~ Figs. 3A, B, C and 4 show diagrammatically
.: .. .
the display screen 6 and the colour selection electrode 7,
The longitudinal direction of the slots 10 of the
25 ~ colour selection electrode 7 is normal to the plane of
the drawing. The outermost slot on one side of the coIour
selection electrode is referenced 14, The places where the
blue, green and red luminescent phosphor lines should be
:~ .
~ provided are denoted by B, G and R,
~.,- .
- 6 -
., , ' , . .
PIIN. 8121.
12-2-1976,
~060079
In Fig. 3a the display screen is exposed from
two positions in such rnanner that the light beams 17 and
18 which pass through the same slot 10 ~orm an unexposed
region where a green luminescent phosphor line should be
provided. Between two slots 10 the light beamSoverlap each
other so that no unexposed region is formed at that area.
In a quite analogous manner exposure is carried
out in the manner shown in Fig. 3b for providing the blue
luminescent phosphor line and Fig. 3c for providing the
red luminescent phosphor line.
It also appears from Figs. 3a, b and c that the
region o~ the display screen opposite to which there are
no slots of the colour selection electrode also remains
unexposed and will hence also be provided with phosphor.
This does not matter when said phosphor is not provided in ~-
the region where a triplet corresponding to the outermost
- slot 14 would have to be present. However, it is obvious
from Fig. 3c that, because the light beam 19 denoted by
broken lines is not present because actually the slot 14 is
the outermost slot, red luminescent phosphor is provided
not only outside the region of the effective display screen
but also at the area where a blue luminescent phosphor line
is already present. The triplet corresponding to the -
outermost slot 14 thus does not display the correct colour,
which is expressed in a wrongly coloured edge of the
displayed picture the cause of which, as explained above,
proved to be difficult to find.
According to the invention by means
of an extra step in the method used the electron
, .. :
.~ , ^'. .
7 -
~'lr~. 8121
-~ ` 19~ J76
lQ60079
beams which pass through the outerlnost slot 14 do not
impinge upon a triplet. ~or that purpose, prior to
providing the phosphor lines, thephotosensitive layer is
exposed entirely in the manner as shown in Fig. 4 ~ith
the exception of the area behind the-outermost slot 14 and
the parts of the display screen which are present ~ven
farther to the outside. Said exposure ~hould be carried
out in two phases, namely for the left-hand edge of` the
display screen while the right-hand edge is covered and
for the right-hand edge of the display screen while the
left-hand edge is covered.
A non-luminescent layer of preferably a light
absorbin~ or electrically conductive material is provided
on the unexposed edges, after which according to the
1~ method of ~igs. 3a, b and c the phosphor lines are provided.
The extra exposure is carried out by moving a light source
in such a manner that the light beams 19 which pass thro~gh
the apertures 10 perform the movement as~denoted by the
arrows 20.
~ 20 As already noted, an electrophotographic method
- is a sui*able method of providing a phosphor pattern or a
pattern of light absorbing material nn the unexposed
regions of a photosensitive layer. Such a method is
disclosed in United States Patent Specification 3,475,169
~25 and therefore requires only & brief explanation. A firable
conductive la~er is provided on the window of the display
tube and then a firable photoconductive layer is provided.
The photoconductive layer is then provided with a negative
surface charge by means- of a corona discharge of electrodes
.- .
~ - 8 - ~
.
I'lTN. ~121
19-1-1976
~060079
which have n potential of, for example, -30 kV relative to
the conductive layer. ~he photoconductive layer is then
eXposed~ ccordi.ng to the desired pattern so that the
negative charge is maintained on].y on the unexposed places.
The photoconductive layer is t~:en developed by means of a
suspension of positively charged phosphor particles and
particles of a light absorbing material, respectively,
which deposit~on the pattern of unexposed regions of the
photoconductive layer. According to the invention, the
. regions 15 and 16 (Fig. 1) along the edge of the display
screen are first provided with conductive light absorbing
material by means of the exposure explained with reference .
to Fig. 4. In the subse~uent charging step no surface
.charge can be maintained in said regions so that during the
15 . development with phosphor suspension no phosphor deposits
on the regions 15 and 16.
_ 9 _
