Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
2003-05-05
2004-11-30
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S463000, C313S466000
Reexamination Certificate
active
06825604
ABSTRACT:
This nonprovisional application claims priority under 35 U.S.C. 517 119(a) on Patent Application No(s). 2002-173264 filed in JAPAN on Jun. 13, 2002, which is(are) herein incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a phosphor screen, which displays video images and characters, and a cathodoluminescence having said phosphor screen, more precisely relates to a phosphor screen capable of preventing lights from scattering among neighbor phosphor sections.
Cathodoluminescences are widely used as television receivers, display devices of computers, etc. A cathode ray tube (CRT) is an example of the cathodoluminescences. The CRT basically comprises, an anode, an electron gun, a phosphor screen and an aluminum film on the phosphor screen. A theory of the CRT will be explained. Electrons extracted form the cathode are sharply focused by electrodes of the electron gun, and a focused electron beam irradiates the phosphor screen formed on the faceplate. The irradiated phosphor screen converts energy of the invisible electron beam into visible lights. In a color CRT, a shadow mask is provided with a proper distance away from a surface of a color phosphor screen, electron beams from three electron guns pass through holes of the shadow mask and irradiate phosphor sections, which correspond to the electron beams, so that the phosphor sections emit three color lights respectively.
The lights emitted by the phosphor screen go toward an inner part of the CRT, too. By forming an aluminum reflection film on the phosphor screen, all lights emitted by the phosphor screen go toward a viewer, so that brightness of the phosphor screen observed by the viewer can be double. By coating inner faces of a funnel and a neck tube with an electrically conductive material having proper thickness and by inputting anode voltage to the electric conductive film and the aluminum film on the phosphor screen, an inside space of the CRT, which has large capacity, has a uniform electric field. The electron beam from the electron gun travels in the uniform electric field of the CRT with constant sped, which is determined by anode potential. The electron beam moving in the inside space of the CRT at constant speed is deflected by a magnetic coil, which is installed outside of the CRT, and the deflected electron beam scans on entire phosphor screen from left to right and up to down. By scanning the electron beam, tiny spots in the phosphor screen sequentially emits cathodoluminescence lights; the viewer perceives uniformly emitting screen with after image effect of the eyes. Since the scanning electron beam is deflected to sequentially irradiate the tiny spots in the phosphor screen, the CRT must have a large vacuum space and a thick glass envelope, which can withstand the vacuum therein.
When the electron beam scanning the phosphor screen of the CRT is modulated with video signals, brightness of lighting spots on the phosphor screen synchronously vary with the video signals, so that video images are shown on the phosphor screen. Since the electron beam irradiating the phosphor screen has a highly concentrated energy, e.g., 4 KW/cm
2
, the number of 10
20
photons/(cm
2
, second) are emitted from the phosphor screen, so that the phosphor screen emits lights with the brightness of 15,000 cd/m
2
. Images on the phosphor screen in the CRT are shown with high brightness, without rise of temperature of the phosphor screen, that is a great advantage of the CRT. The CRT capable of showing highly bright images is superior to other display devices. Since the CRTs are suitable for showing digital video images, they will be used for screen units of digital television receivers.
FIG. 1
is a partial sectional view of a conventional phosphor screen of a monochrome CRT.
A display section
10
of the CRT comprises: a glass plate
11
which acts as a faceplate; a phosphor screen
12
which is formed on the faceplate
11
and made of phosphor particles
12
z
; and an aluminum film
13
. An electron beam
14
is irradiated from an electron gun (not shown). Lights
15
emitted from the phosphor particles
12
z
, which are irradiated by the electron beam
14
, are scattered. Resolution of images shown on the display section
10
depends on diameter of the electron beam
14
. In the CRT, the electron beams
14
from the electron gun (not shown) makes the phosphor particles
12
z
emit lights so as to show images on the phosphor screen. The phosphor particles
12
z
, to which the electron beam
14
irradiates, emit the scattered lights
15
, so that a viewer feels as if the neighbor phosphor particles
12
z
too emit lights in spite of emitting no lights. Namely, the scattered lights
15
irradiate the phosphor particles
12
z
, which is irradiated by no electron beam. Therefore, contrast and sharpness of images on the phosphor screen are badly influenced.
FIG. 2
is a partial sectional view of a conventional phosphor screen of a color CRT. A display section
10
a
of the color CRT comprises: the faceplate
11
; the phosphor screen
12
which is formed on the faceplate
11
and made of phosphor particles
12
z
; and the aluminum film
13
, as well as the monochrome CRT. Unlike the monochrome CRT, the phosphor screen
12
includes a lot of minute phosphor sections
12
d
, which irradiate different colors respectively and which are arranged on the faceplate
11
with prescribed separations. A black matrix film
16
is provided between the adjacent phosphor sections
12
d
. Ordinary thickness of the black matrices
16
is 1 &mgr;m or less and thinner than that of the phosphor screen
12
; the scattered lights
15
from one phosphor section
12
d
go into the neighbor phosphor sections
12
d
. Since the black matrices
16
are coated with no phosphor particles
12
z
or partially coated therewith, a large space exists between the aluminum film
13
and the phosphor screen
12
. The large space makes a range of scatter lights
15
long, so that the scattered lights
15
irradiate the neighbor phosphor sections
12
d
. Influence of the scattered lights
15
is greater in the color phosphor screen than in the monochrome phosphor screen. Therefore, the images shown on the phosphor screen
12
is whitened by increasing brightness, so that the images cannot be shown with pure colors.
In the color CRT, a plurality of layers of crystallized phosphor particles, whose diameter is about 3 &mgr;m, are piled so as to increase the brightness. Since the diameter of the electron beam is about 500 &mgr;m, which is much greater than that of the phosphor particles, the resolution of images on the phosphor screen is basically determined with the diameter of the electron beam irradiating the phosphor screen. Electron guns, which focus the electron beam to desired resolution on the phosphor screen, have well established, and they can show images on the phosphor screen with high resolution.
Since images on display devices are watched by human eyes, they should not irritate the eyes. Irritation of the eyes relates with quality of images and brightness thereof. To comfortably watch images on display devices for a long time, the screen brightness should be properly adjusted so as not to damage the eyes. The eyes have two kinds of light sensors, depending on light intensities: one responds on ordinary light intensities (photopic vision); and the other responds on dark light intensities (scotopic vision). Images on display devices are made with the high intensities of lights, so that the viewer observes the images with the photopic vision. The human eyes have a very wide field of vision; the viewer usually observes the images on the display device against a background of a room including furniture. If the room is made light to watch the background of the room with the photopic vision, the eyes will be comfortable to watch the images and the background, with the photopic vision, for a long time. If there is a difference in brightness between the images and the background, the two sensors in the eyes simultaneously are used for watching
Kabushiki Kaisha Kakuma
Patel Ashok
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