Note: Descriptions are shown in the official language in which they were submitted.
108~810
BACKGROUND OF THE INVENTION
This invention relat~s to an improved color cathode
ray tube~ and more particularly to a color cathode ray tube in
which the improved shadow mask having apertures in the form of
slits and the improved screen having smooth edged continuous
elemental phosphor stripes are used to give a sufficient
electron beam landinq tolerance, especially near the edges of
the screen.
B~IEF DESC~IrTION OF THE D~A~INGS
10In the accompanying drawings, in which like numerals
denote like parts throughout the several views,
Fig. 1 is a fragmentary perspective view of a
prior art color cathode ray tube;
Fig. 2 is an enlarged rear elevational view of the
screen of the tube of Fig. l;
Fig. 3 is a perspective view, partly cut awa~, of a
color cathode ray tube according to this invention;
' Fig. 4 is a perspective diagram useful in explaining ~ '
the relation between the arrangemRnt of the ma,sk apertures
20 and the long light source according to this invention; ,
Fig~ 5 is a fragmentary elevational showing the
intersection lines on a spherical shadow mask according to
Fig. 4;
Fig. 6 is a fragmentary elevational showing t~e
arrangement of the mask apertures according to Fig~ 5;
Fig. 7 is a fragmentary enlarged view of the mask
apertures according to another embodiment of this inventionO
Descri~tion of Prior Art:
Conventional color cathode ray tubes employ an,
' 30 electroluminescent screen consisting of circular phosphor dots
surrounded by light absorbing material, and a shadow mask
having a circular aperture corresponding to each triad o
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phosphor dots as explained in United States Patent No. 3,146,368,
issued August 25, 1964 to Rauland Corporation, invented by
J.D. Fiore and S.H~ Kaplan. This screen construction is
advantageous to produce an imaye of enhanced brightness and
greater contrast. However, the conventional color cathode ray
tubes have some difficulties such as necessity of particular
consideration being given to electron beam landing tolerance
and necessity of many complex adjusting attachments, especially
beam convergence is complex.
A color ca~hode ray tube of a new type, called "in-line"
gun type has been developed to eliminate such difficulties.
It has an image screen including a plurality of phosphor stripes
spaced from each other by intermediate stripes made of light
absorbing material, a slotted shadow mask adjacent to the
screen and an electron gun means for projecting a central beam
and a pair of side beams which are disposed in the same plane.
With reference to Fig. 1 of the accompanying drawings
which shows a new type color cathode ray tube including a
phosphor screen (11) coated on the inner surface of a face
20 plate, a plurality of elemental phosphor stripes are arranged
cyclically, green, blue and red color phosphor stripes (12G),
(12B) and (12R), respectively, and light absorbing stripes (13)
a~e placed between and adjoining the color phosphor stripes
(12G), (l~B) and (12R).
The shadow mask (14) of this new tube have a plurality
of small rectangular apertures (15) being vertically spaced
apart by thin traverse bridge portions (16). These thin bridge
portions are significant in pressing the mask into a spherical
contour. The three electron guns of this tube are placed
horizontally adjacent in a so-called in-line configuration.
It has been recognized that such a color cathode ray
tube provided with a striped color phosphor screen, and a
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slotted aperture mask has higher color picture qualities than
a conventional color cathode ray tube provided with a circular
dot type phosphor screen. Namely, it is capable of reproducing
a much brighter image and easy adjustment of its color purity.
This newly developed color cathode ray tube, however,
has problems in the manufacturing process of the phosphor
screen as are mentioned hereinbelowO
The phosphor screen of this new tube is made b~ a
photographic method, using photosensitive resin on the surface
of the panel, the above mentioned shadow mask having a plurality
of 6mall rectangular beam passable apertures, and using a long
light source for projecting bright images of the apertures onto
the surface of the panel.
Though there are bridge portions at which the light
beam is i~tercepted in the row of apertures, the phosphor
stripe which is to be formed on the panel sur~ace by the bright
image of the apertures must be continuous throughout the vertical
length of ~he screen. By using an elongated light source
being parallel to the horizontal axis of the tube~ a continuous
, 20 stripelike bright image corresponding to the whole length of
the row of the mask apertures is acquiredi the dark image of
the bridge portion which is projected on the panel by the light
beam from an end of the light source is overlapped by a bright
image of the light coming through the aperture made from
- another end of the light source.
In rectangular color cathode ray tubes, the stripes
... .
of bright images of the mask apertures produced on the panel
,
-~ as above are sufficiently straight and uniform in width on and
near the vertical and horizontal axis of the panel. But, in
~- 30 the corner regions of the panel, the stripes of bright images
. .
- become considerably zigzagged and non-uniform in width. Con-
~- sequently, phosphor stripes in the corner regions are zigzagged
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and non-uniform in width as shown in Fig. 2, resulting in
decrease in quality of color picture reproduced by the screen.
Especially, the sufficient beam landing tolerance is
required near the corner of the screen. Consequently it is
very important to eliminate the non-uniformity in width of the
color phosphor stripes or the light absorbing stripes near
the corner of the screen. It was found that the zigzagged
form of the stripe images produced on the corner regions of
the panel is due to the angular difference between the tangent
face of each m~sk apertures in the lengthwise direction of the
aperture rows and the long axis of the light source. As a
result, we have improved the color tube by using the improved
shadow mask.
SUMMARY OF THE INVENTION
Accordingly, this invention provides a color cathode
ray tube comprising: a curved spherical panel having a
screen with different elemental color phosphor stripes running
cyclically on its inner surface, a shadow mask adjacent the
screen and having substantially the same curvature as said
screen, said mask having a number of beam-passable apertures
-- arranged in rows, said apertures along the length of each of
said rows being separated from ~ach other by narrow beam-
intercepting bridge portions, first means for generating three
electron beams which are arranged in-line horizontally and
are directed toward said screen for impinging on corresponding
phosphor stripes respectively, second means adjacent said
first means for deflecting said beams, said phosphor stripes
and the arranging row of apertures being substantially straight
and vertical on and near the vertical axis of the mask as
viewed in the direction of the central axis of the tube, and
the remainder of said phosphor stripes and the arranging rows
being outwardly curved in the horizontal axis direction, the
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curvature being concave toward the mask center and gradually
: increasing from the center to the periphery of the shadow mask.
In accordance with another aspect of this invention
there is provided a cathode-ray tube for displaying coloured
pictures comprising in an evacuated envelope means to generate
at least two electron beams having undeflected portions with
axes which are located in a first horizontal flat plane, a
display screen comprising a large number of linear regions
luminescing in at least two different colours, and a colour
selection electrode which is curved in two directions and
comprises a large number of elongate apertures which are
arranged in rows corresponding to the said linear luminescent
regions, said electron beams being each associated with lumi-
nescent regions of one colour by means of the said colour
selection electrode, characterized in that each of the said
rows of apertures has a center line which is located sub-
stantially in a second vertical flat plane with a line which,
in an apparent deflection point of one of the said electron
beams, intersects the said first horizontal flat plane through
the axes of the undeflected portions of the electron beams at
right angles.
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` 108~;810
DETAILED DESCRIPTION OF THE INV~NTION
For a better understanding of this invention, a
description will be given of a color cathode ray tube in which
the screen has light absorbing stripes
Fig. 3 shows a color cathode ray tube of in-line gun
type according to this invention. A rectangular-shaped glass
panel (31) has, on its inner surface, an electroluminescent
` screen (32) comprising alternating light absorbing stripes (33)
and elemental color phosphor stripes (34), (35) and (36), as
; 10 will be described in particular hereinafter, arranged in an
outwardly curved pattern in a vertical direction or Y-axis of
the tube.
ji A shadow mask (37) of a shape substantially corres-
;~ ponding to the panel is located inside the panel (31). The
, panel is fixed to a funnel (38) to construct an evacuated
envelope of the tube.
'.! The funnel (38) has, in its neck portion, an electron
~;j gun means (39) for emitting three electron beams (40), (41)
^ ~ and ~42) arranged in line in a common horizontal plane con-
taining X-axis of the tube. These electron beams are deflected
horizontaIly and vertically by deflection means (43), and are
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thereby caused to scan a curved spherical screen (32) through
~,, a shadow mask (37).
The shadow mask (37) has a number of small rectangular
apertures (44) which are arranged in rows to vertical direction
or Y-axis of the tube. The apertures (44) in each of the rows
... . .
~ ~ are aligned lengthwise, as if a very long continuous opening
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of the same width as that of it is divided into many apertures
`~ by very narrow bridge portions (45) of about 0.1 mm in width,
for example.
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las6sl0
In a conventional shadow mask having slit apertures,
each row of the mask aperturesare arranged in parallel to the
vertical or Y-axis of the tube over the whole effective area
of the shadow mask. But, in this invention, the rows of the
mask apertures arranged on the center region of the mask are
substantially parallel to the vertical axis of the tube and
the remainder of said rows of the mask apertures are transversely
curved with a curvature which is gradually increasing outwardly
from the center of the mask in the horizontal direction or X-
axis of the tube.
The light absorbing stripes (33) and the elementalcolor phosphor stripes (34), (35) and (36) are formed by the
usual light printing method employing a light beam passing
through the said shadow mask (37).
The detail arrangement of the mask apertures will be
hereinbelow discussed with reference to Fig. 4 which shows a
relationship between the arranging row of the mask apertures
and the long light source for forming the screen. The long
light source (46) is positioned at the deflection center of the
electron beams as viewed from the panel in the direction of
the central axis or Z~axis of the tvbe.
To make a striped screen, the panel (not shown)
with the shadow mask (37) attached thereon is placed with its
inner surface downward on the top of an exposing box (not
.
shown). A light source having a long slit window (46) is
provided on the bottom of the box for projecting light onto
the inner surface of the panel through the shadow mask (37)~ -~
In this invention, the rectangular apertures of
the shadow mask are arranged along the intersection lines (48)
3D which are produced with a flat plana (47) containing a long
axis L of the light source (46) intersects with the shadow
mask (37).
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Fig. 5 shows the intersection lines (48) as viewed
in the direction of the central axis z of the tube accordlng
to Fig. 4.
The intersection lines (48a) produced on and near
the Y-axis of the mask are almost straight or parallel to
the Y-axis. Ana the intersection lines (48b) produced near
the corner or far from the Y-axis are curved outwardly in the
X-axis direction with gradually increasing its curvature because
the mask has an outwardly curved spherical face.
The intersection line (48~ is an arc of ellipse when
viewed from the Z-axis direction and is expressed as follows:
{R + lR-M)2 _ 2(R-M) ~ ~ x2 + Xo2y2
+ 2Xo(R-U) ~-(R-M)~ /R2-Xo2 ~ X + Xo2 ~ (R-M)2-R2~ - 0 ...(1)
Eliminating X by converting (xo-d),
Xo2y~ - 2R2Xo~ + ~(R-M- ~R2 _ Xo ) + Xo } c~ = O .,. (2)
where R is the radius of curvature of the spherical mask (37),
and M is the distance from the deflection center of the electron
beams to the center of the mask as shown in Fig~ 4,
Fig. 6 shows an arrangement of the aperture (44) of
the shadow mask (37) being aligned along the intersection lines
as explained in Figs. 4 and 5.
According to this arrangement of the mask apertures,
the light emitted from the light source is projected on the
inner surface of the panel along a flat plane which is containing
said intersection line (48) and said long axis L of the light
source as explained in Fig. 4.
Therefore, it is impossible to eliminate the non~
uniformity in width of the bright stripe images due to the
angular difference between the tangent face of each mas~
apertures and the long axis L of the light source.
A striped screen on the panel is made by the light
printing method using the above described shadow mask. There
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1086810
fore, the light absorbing stripes and the elemental color
stripes are formed with a pattern corresponding to the inter-
section lines (48) of the shadow mask in Fig. 6. That is,
the stripes are substantially straight on and near the Y-axis
of the screen, and are curved gradually increasing in curvature
outwardly in the X-axis direction from the screen center.
Fig. 7 shows the another embodiment of the arrangement
of the mask apertures according to this invention.
The mask (37) has the very narrow bridge portions
~50) which are substantially parallel to the X-axis of the
tube to prevent moire phenomena.
Therefore, the mask apertures (52) arranged near
the corner of ~he mask become a parallelogram configuration.
As above mentioned, according to this invention, the
electroluminescent screen has smooth edged continuous color
phosphor stripes over the effective area of the screen. And
a color cathode tube according to this invention has sufficient
beam landing tolerance near the corners of the screen and
has higher color picture qualities. While in the above des-
cribed embodiment the color cathode ray tube has an ou~wardlycurved spherical screen and a spherical shadow mask, the
configuration of the screen and the mask may vary from spherical
`~ to cylindrical.
In addition to a color cathode ray tube having a
light absorbing stripe type screen, this invention is also
applicable to other color cathode ray tube in which the screen
ha~i ollly color phosphor :~tripe~.
