Display device

A display device such as a color phosphor display panel has a panel assembly comprising a faceplate, a pair of spaced side plates, and a backplate 1c which are joined together to provide an evacuated interior space. The display device includes a color filter layer having red, green, and blue filters disposed on the inner surface of the faceplate, the filter layer containing fine particles of inorganic metal compounds. A plurality of phosphor layers of ZnO:Zn are disposed on the color filter layer. A grid is disposed in spaced relation between the phosphor layers and a cathode for controlling a flow of thermions emitted from the cathode toward the phosphor layers. The fine particles of inorganic metal compounds have a particle size ranging from 0.01 .mu.m to 0.02 .mu.m. Preferably, the red filter contains fine particles of Fe.sub.2 O.sub.3, the green filter contains fine particles of TiO.sub.2.ZnO.CoO.NiO, and the blue filter contains fine particles of CoO.Al.sub.2 O.sub.3. The phosphor layers are made of ZnO:Zn.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a display device for use as a color 
phosphor display panel, for example, in a speedometer on an automobile, 
for example. 
2. Description of the Prior Art 
There have heretofore been known color phosphor display tubes comprising a 
combination of a bluish green phosphor ZnO:Zn and color filters. The 
materials of the color filters that are used have to be thermally stable 
because a heat treatment process is usually carried out at about 
500.degree. C. when such a color phosphor display tube is manufactured. 
The color filters for use in those color phosphor display tubes are thus 
made of inorganic materials, rather than organic materials that are used 
in liquid crystal display panels, for example. 
It is preferable that the color filters have a high transmittance so as not 
to reduce the intensity of light emitted from the phosphor, and also have 
a low reflectance. 
The materials that have found wide use in the art are metal colloids (see, 
for example, "Two-color Graphic FLVFD with Internal Color Filters" by 
Yoshihisa Tsuruoka & Yoshinari Okamoto, proceeding Japan Display, P1-2 
(1992)). 
However, as shown in FIG. 1 of the accompanying drawings, red and blue 
filters of the conventional materials transmit light having wavelengths 
other than those of red and blue light. Therefore, the chromaticity points 
on a CIE chromaticity diagram shown in FIG. 2 of the accompanying drawings 
are represented by red: x/y=0.347/0.281, bluish green: x/y=0.235/0.405, 
and blue: x/y=0.260/0.297, resulting in a narrow color reproducing range. 
Consequently, no satisfactory colors can be produced by the conventional 
color phosphor display tubes. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a display 
device capable of reproducing colors in a wide color reproducing range. 
According to the present invention, there is provided a display device 
comprising a faceplate, a color filter layer comprising red, green, and 
blue filters disposed on said faceplate, said filter layer containing fine 
particles of inorganic metal compounds, a plurality of phosphor layers 
disposed on said color filter layer, a cathode for emitting thermions 
toward said phosphor layers, and a grid disposed in spaced relation 
between said phosphor layers and said cathode for controlling a flow of 
thermions emitted from said cathode toward said phosphor layers. 
The fine particles of inorganic metal compounds may have a particle size 
ranging from 0.01 .mu.m to 0.02 .mu.m. 
The red filter may contain fine particles of Fe.sub.2 O.sub.3. The green 
filter may contain fine particles of TiO.sub.2.ZnO.CoO.NiO. The blue 
filter may contain fine particles of CoO.Al.sub.2 O.sub.3. 
The display device may further comprise an indium tin oxide layer disposed 
between said color filter layer and said phosphor layers. 
The phosphor layers may be made of ZnO:Zn. 
The red, green, and blue filters are capable of separating red, green, and 
blue light more effectively from light emitted by the phosphor layers 7 
than the conventional color filters. As a result, the display device can 
emit light of purer three primaries. Since the color filters contain fine 
particles of inorganic metal compounds, these fine particles do not reduce 
the transmittance of light passing therethrough. 
The above and other objects, features, and advantages of the present 
invention will become apparent from the following description of 
illustrative embodiments thereof to be read in conjunction with the 
accompanying drawings, in which like reference numerals represent the same 
or similar objects.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 3A, a front-emission phosphor display panel as a display 
device according to the present invention includes a panel assembly 1 
comprising a faceplate 1a of glass, a pair of spaced side plates 1b of 
glass joined at one edges thereof to the faceplate 1a, and a backplate 1c 
joined to opposite edges of the side plates 1b. The panel assembly 1 has 
an evacuated interior space which is defined by the faceplate 1a, the side 
plates 1b, and the back plate 1c. An electrostatic and light shield film 2 
is disposed on the inner surface of the backplate 1c that faces the 
evacuated interior space in the panel assembly 1. The panel assembly 1 
houses therein filaments 3 and a grid 4 that are successively arranged in 
the order named in a direction from the backplate 1c toward the faceplate 
1a. The filaments 3 serve as a cathode for emitting thermions, and the 
grid 4, which is spaced from and disposed between the filaments 3 and the 
faceplate 1a, serves to control the flow of emitted thermions. 
A color filter layer composed of red, green, and blue filters 5R, 5G, 5B is 
deposited on the inner surface of the faceplate 1a according to a process 
described later on. On each of the filters 5R, 5G, 5B, there are disposed 
a transparent indium tin oxide (ITO) layer 6 that serves as an anode on 
the filter and a phosphor layer 7 on the ITO layer 6. The phosphor layer 7 
is made of a phosphor ZnO:Zn which emits bluish green light. 
A pigment of Fe.sub.2 O.sub.3 is dispersed in the red filters 5R. A pigment 
of TiO.sub.2.NiO.CoO.ZnO (1:1:1:1) is dispersed in the green filters 5G. A 
pigment of CoO.Al.sub.2 O.sub.3 (1:1) is dispersed in the blue filters 5B. 
These pigments should preferably have a particle size ranging from 0.01 
.mu.m to 0.01 .mu.m for increased filter transmittance. It is well known 
in the art that the transmittance of a filter is increased if the size of 
particles dispersed in the filter is sufficiently smaller than 1/2 of the 
wavelength of light incident on the filter. 
As shown in FIG. 3B, black stripes 8 made of carbon, Fe.sub.3 O.sub.4, an 
insulating material, or the like are interposed at predetermined spaced 
intervals between the faceplate 1a and the filters 5R, 5G, 5B for 
increasing the contrast of displayed images. Each of the filters 5R, 5G, 
5B is arranged so as to lie over adjacent two of the black stripes 8. 
FIG. 4 shows in fragmentary perspective a front-emission graphic phosphor 
display panel according to the present invention which incorporates the 
principles of the display device shown in FIGS. 3A and 3B. As shown in 
FIG. 4, the front-emission graphic phosphor display panel includes a 
faceplate 11a, a pair of spaced side plates 11b, and a backplate 11c which 
are joined together providing a hermetically sealed housing 11, which is 
evacuated through an exhaust pipe 20 mounted on the backplate 11c. A color 
filter layer composed of color filters as shown in FIG. 3B is disposed on 
the inner surface of the faceplate 11a. A striped phosphor layer 17 which 
is composed of phosphor layers 17R, 17G, 17B is disposed on ITO layers 
(not shown) which serve as an anode that are disposed on the color filter 
layer. 
The front-emission graphic phosphor display panel also has a grid 14 in the 
form of closely spaced parallel wires extending perpendicularly to the 
striped phosphor layer 17 and spaced therefrom by a spacer 19 of glass. A 
plurality of filaments 13 serving as a cathode are disposed between the 
grid 14 and the backplate 11c and extend in the same direction as the 
striped phosphor layer 17. The grid 14, the ITO layers, and the filaments 
13 are electrically connected to external circuits by grid leads 14a, 
anode leads 16a, and filament leads 13a that extend respectively 
therefrom. 
A process of manufacturing the display device shown in FIGS. 3A and 3B will 
be described below with reference to FIGS. 5A through 5I. 
First, as shown in FIG. 5A, a number of parallel black stripes 8 are formed 
on a faceplate 1c according to a known procedure. 
Then, as shown in FIG. 5B, the faceplate 1a and the black stripes 8 are 
coated on their entire surfaces with a PVA-ADC photosensitive liquid or an 
azido photosensitizer (such as of polyvinyl pyrrolidone) 21, which is 
thereafter dried. 
Areas 21G, 21B of the coated layer 21 which correspond to green and red 
color filters are exposed to ultraviolet radiation using a color selecting 
mask (not shown). 
Thereafter, the surface of the coated layer 21 is developed using pure 
water, thus removing areas 21R corresponding to red filters as shown in 
FIG. 5C. 
A suspension is prepared which is composed of 90% of water and 10% of a red 
pigment (e.g., DEFIC-R1007 (trade name) manufactured by The Dowa Mining 
Co. Ltd.) comprising fine particles of iron oxide (Al.sub.2 O.sub.3). The 
suspension is coated on the surface formed so far, and dried into a 
suspension layer 25 as shown in FIG. 5D. 
After an aqueous solution of hydrogen peroxide is sprayed over the 
suspension layer 25, it is developed in reverse with 10 weight % of pure 
water, thereby removing the photosensitizer and the pigment from those 
areas except the areas 25R. In this manner, red filters 5R are completed 
as shown in FIG. 5E. 
Then, the surface formed so far is coated with a PVA-ADC photosensitive 
liquid in which there is dispersed a blue pigment (e.g., Dyepyroxide TM 
blue #3410 (trade name) manufactured by Dainichiseika Color and Chemicals 
Corp.) composed of fine particles of CoO.Al.sub.2 O.sub.3, and the coated 
PVA-ADC photosensitive liquid is dried into a layer 22 as shown in FIG. 
5F. 
Areas 22B of the layer 22 which correspond to the blue filters are exposed 
to ultraviolet radiation using a color selecting mask (not shown). 
Thereafter, the surface of the coated layer 22 is developed using pure 
water, thus removing the unwanted photosensitizer and the pigment. In this 
manner, blue filters 5B are completed in addition to the red filter 5R as 
shown in FIG. 5G. 
Subsequently, the surface formed so far is coated with a PVA-ADC 
photosensitive liquid in which there is dispersed a green pigment (e.g., 
Dyepyroxide TM blue #3320 (trade name) manufactured by Dainichiseika Color 
and Chemicals Corp.) composed of fine particles of TiO.sub.2.ZnO.CoO.NiO, 
and the coated PVA-ADC photosensitive liquid is dried into a layer 23 as 
shown in FIG. 5H. 
Areas 23G of the layer 23 which correspond to the green filters are exposed 
to ultraviolet radiation using a color selecting mask (not shown). 
Thereafter, the surface of the coated layer 23 is developed using pure 
water, thus removing the unwanted photosensitizer and the pigment. In this 
manner, green filters 5G are completed in addition to the red and blue 
filters 5R, 5B as shown in FIG. 5I. 
Then, as shown in FIG. 3B, the ITO layers 6 and the phosphor layers 7 are 
formed on the filters 5R, 5G, 5B. 
The chromaticity points of the red, green, and blue filters 5R, 5G, 5B 
which have different transmittances were measured, and the results are 
shown in FIGS. 6A through 6C, and 7 and Table 1 below. The transmittance 
and relative luminance without color filters was set to 100%, and four 
types of color filters 5R-1.about.4, 5G-1.about.4, 5B-1.about.4 were 
formed for the respective colors as shown in FIGS. 6A through 6C and Table 
1. 
TABLE 1 
______________________________________ 
Phosphor ZnO:Zn 
Chromaticity point 
Relative 
Filter x y luminance 
______________________________________ 
5R - 1 0.459 0.500 21% 
5R - 2 0.512 0.470 15% 
5R - 3 0.567 0.419 7% 
5R - 4 0.595 0.389 4% 
5G - 1 0.230 0.460 66% 
5G - 2 0.229 0.503 52% 
5G - 3 0.226 0.541 39% 
5G - 4 0.225 0.585 24% 
5B - 1 0.179 0.349 56% 
5B - 2 0.171 0.340 50% 
5B - 3 0.134 0.284 33% 
5B - 4 0.116 0.260 16% 
No filters 
0.228 0.394 100% 
______________________________________ 
(Note) The relative luminance was 100% with no color filters. 
As can be understood from Table 1 and FIG. 7, a highly luminous phosphor 
display panel having a much wider color reproducing range than 
conventional phosphor display panels could be achieved according to the 
above embodiment of the present invention. Furthermore, the contrast of 
displayed images can be increased according to the above embodiment of the 
present invention. 
The phosphor layers may be made of any of various other materials than 
ZnO:Zn. For example, phosphor layers of SnO.sub.2 :Eu may be disposed on 
the red filters. The phosphor layers of SnO.sub.2 :Eu have luminance and 
chromaticity that are much higher with respect to the red filters than 
phosphor layers of ZnO:Zn, as shown in Table 2 below. 
TABLE 2 
______________________________________ 
Phosphor SnO.sub.2 :Eu 
Chromaticity point 
Relative 
Filter x y luminance 
______________________________________ 
5R - 1 0.598 0.401 60% 
5R - 2 0.600 0.399 56% 
5R - 3 0.607 0.393 37% 
5R - 4 0.614 0.385 23% 
______________________________________ 
(Note) The relative luminance was 100% with no color filters. 
The principles of the present invention are not limited to the illustrated 
embodiment, but may be applied to cathode-ray tubes, plasma display 
panels, or the like. 
According to the present invention, as described above, the display device 
employs color filters containing dispersed fine particles of inorganic 
metal compounds of Fe.sub.2 O.sub.3, TiO.sub.2.NiO.CoO.ZnO, or 
CoO.Al.sub.2 O.sub.3. Therefore, the display device, particularly a color 
phosphor display panel, has a wide color reproducing range and a high 
luminance. 
Having described preferred embodiments of the invention with reference to 
the accompanying drawings, it is to be understood that the invention is 
not limited to those precise embodiments and that various changes and 
modifications could be effected by one skilled in the art without 
departing from the spirit or scope of the invention as defined in the 
appended claims.