Cathode ray tube apparatus for projection TV system

A cathode ray tube apparatus for a projection TV system which improves the color purity of the luminescence in the cathode ray tube, reduces the chromatic aberration by the projection lens, enables the same type of projection lens to be mounted for all of the green, red and blue CRT apparatuses, and enables manufacturing costs to be slashed by such a common use of components. A light-absorbing agent is incorporated into the panel glass so that the transmittance having the light of wavelengths other than the main wavelength of the spectrum of luminescence of the phosphor of the CRT apparatus, is reduced below the transmittance of the light of the main wavelength. By incorporating this agent into the panel glass of a green CRT apparatus the average value of the transmittance of the light of the wavelength in the range of 500 nm to 560 nm becomes higher than the transmittance of the light of the wavelengths outside this range. Alternatively, by incorporating the agent into the panel glass of a red CRT apparatus the average value of the transmittance of the light of the wavelength in the range of 600 nm to 700 nm is increased as compared with the transmittance of the light of the wavelength in the range of 500 nm to 600 nm.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cathode ray tube (CRT) apparatus used 
for a projection TV system (projector), more particularly to a CRT 
apparatus for a projection TV system which improves the purity of color of 
the light emitted therefrom. 
2. Description of the Related Art 
Television systems which have larger display screens and which are able to 
display larger images as compared with ordinary TV systems, include front 
type and rear projection type TV systems. In such projection TV systems, 
separate images are emitted from red (R), green (G), and blue (B) 
projection CRTs and are focused on a display screen to produce a single 
color image. Projection lenses are disposed at the front of the projection 
cathode ray tubes. On the inside surface of a panel glass of each CRT, a 
phosphor coating corresponding to each color is formed, and light is 
emitted in a predetermined pattern by irradiation of electron beams from 
an electron gun. The respective panel glasses emit the different colors of 
image light. 
In such a projection TV system, since luminance is determined prior to the 
determination of the material of the phosphor, the distribution of the 
spectrum of the luminescence of the phosphor is generally broad and the 
color purity is insufficient. Further, since the spectrum of the 
luminescence is broad, chromatic aberration will occur due to the 
projection lens and thus image loss such as degradation of resolution, 
contrast, etc. will occur. In particular, there have been strong demands 
for improvement in the color purity in the CRT which produces green image 
light, which has a high luminosity factor. 
Japanese Unexamined (Kokai) Patent Publication No. 3-61903 discloses a 
projection TV system in which the projection lenses have a light-absorbing 
substance added which absorbs light of the side bands of the luminescent 
characteristics of the cathode ray tubes. In the projection type TV 
system, it is possible to prevent image degradation to a certain extent. 
However, projection lenses especially for each color of R, G, and B are 
necessary and these have to be separately attached to the front of the 
cathode ray tubes. This makes the manufacturing process complicated and 
results in an increase in the manufacturing costs. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a cathode ray tube 
apparatus for a projection TV system which exhibits improved color purity 
of the luminescence in the cathode ray tube apparatus. 
Another object of the present invention is to provide a cathode ray tube 
apparatus for a projection TV system which reduces chromatic aberration by 
a projection lens. 
Still another object of the present invention is to provide a cathode ray 
tube apparatus for a projection TV system which enables the same type of 
projection lens to be mounted on each of the cathodes and thus reduce 
manufacturing costs through the multiple use of the same component. 
According to the present invention there is provided a cathode ray tube 
apparatus for a projection TV system used for projecting light of one of 
three primary colors on a display screen to display a color image on the 
display screen, and including panel glass and funnel glass, characterized 
in that a light-absorbing agent is incorporated into the panel glass so 
that the transmittance of the light of wavelengths other than the main 
wavelength of the spectrum of luminescence of the phosphor of the cathode 
ray tube in which the panel glass is used becomes lower than the 
transmittance of the light of the main wavelength. 
The light of wavelengths other than the main wavelength is absorbed by the 
light-absorbing agent of the panel glass. That is, it becomes possible to 
have the light of the side bands in the spectrum of luminescence of the 
phosphor of the cathode ray tube absorbed at a greater rate and thus the 
color purity of the image light emitted from the cathode ray tube 
apparatus is improved. Further, while a projection lens is disposed in 
front of the cathode ray tube, the chromatic aberration caused by the 
color dispersion of the index of refraction of the lens material of the 
projection lens is improved. 
Further, in the present invention, there is no need for coloring the 
projection lens, so the same type of projection lens may be used in common 
for each of the R, G, and B cathode ray tube apparatuses used in the 
projection TV and therefore the assembly and manufacturing costs can be 
reduced through the multiple use of the common component. 
Specifically, the panel glass in the green CRT is formed so that the 
average value of the transmittance of the light of the wavelength in the 
range of 500 nm to 560 nm is set higher than the transmittance of the 
light of the wavelengths outside this range. 
Also, specifically, the panel glass in the red CRT is formed so that the 
average value of the transmittance of the light of the wavelength in the 
range of 600 nm to 700 nm is set higher than the transmittance of the 
light of the wavelength in the range of 500 nm to 600 nm and 
wherein said cathode ray tube is used for projecting the red color image 
light. 
Further, according to the present invention, there is provided a projection 
TV system, including: a first cathode ray tube apparatus for projecting 
the green color image light and including a first panel glass and a first 
funnel grass, the first panel glass being formed so that the average value 
of the transmittance of the light of the wavelength in the range of 500 nm 
to 560 nm is set higher than the transmittance of the light of the 
wavelengths outside this range; a second cathode ray tube apparatus for 
projecting the red color image light and including a second panel glass 
and a second funnel glass, the second panel glass being formed so that the 
average value of the transmittance of the light of the wavelength in the 
range of 600 nm to 700 nm is set higher than the transmittance of the 
light of the wavelength in the range of 500 nm to 600 nm; and a third 
cathode ray tube apparatus for projecting the blue color image light and 
including a third panel glass and a third funnel glass.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Below, preferred embodiments of a cathode ray tube apparatus for a 
projection TV system according to the present invention will be explained 
in detail with reference to the drawings. 
The projection TV system 2 shown in FIG. 1A and 1B is a rear type 
projection TV system. Three projection TV cathode ray tube apparatuses 4, 
6, and 8 for emitting red (R), green (G), and blue (B) image light are 
attached to a chassis 10. Projection lenses 3, 5, and 7 are attached in 
front of the CRT apparatuses 4, 6, and 8. The chassis 10 has a first 
chassis member 11 to which the CRT apparatuses 4, 6, and 8 are directly 
attached and a pair of second chassis members 13 for supporting the two 
ends of the first chassis 11. The second chassis members 13 are attached 
on a support base 16 of a casing 14. 
At the top front part of the casing 14 a large-sized display screen 12 is 
attached. Inside the casing 14, further, a reflection mirror 18 for 
reflecting back the images projected from the CRT apparatuses 4, 6, and 8 
and forming an image at the reverse side of the display screen is 
attached. 
The display screen 12 is comprised of a plurality of screen laminate plates 
each having at least a Fresnel screen and a lenticular screen. 
The CRT apparatuses 4, 6, and 8 each have, as shown in FIG. 2, a panel 
glass 20 and funnel glass 22. The panel glass 20 and funnel glass 22 are 
fused together by frit glass 26. The inside of the CRT apparatus 
constituted by these glass pieces is held at a high degree of vacuum. An 
electron gun 24 is disposed inside the same. At the inside surface of the 
panel glass 20 is formed a phosphor coating 28. 
The panel glass 20 is comprised of a glass with a high mass-absorption 
coefficient and with components of a nature which are not easily reduced 
electron beams, for example, R.sub.2 O--BaO--SrO--ZrO.sub.2 --SiO.sub.2. 
Further, the funnel glass 22 is comprised of lead glass containing PbO for 
example. 
The above phosphor constituting the phosphor coating 28 formed on the inner 
surface of the panel glass 20 may be Y.sub.2 O.sub.3 :Eu for R (red), 
Gd.sub.2 O.sub.2 S:Tb for G (green), and ZnS:Ag for B (blue). 
In this embodiment, a light-absorbing agent (material) is incorporated into 
the panel glass 20 of each of the CRT apparatuses 4, 6, and 8 
corresponding to R, G, and B so that the transmittance of the light of the 
wavelength other than the main wavelength of the spectrum of luminescence 
of the phosphor becomes lower than the transmittance of the light of the 
main wavelength. For example, the spectrum of luminescence of the phosphor 
used in the G (green) CRT apparatus has side band peaks proximate 580 nm 
on the yellow wavelength band and about 625 nm on the red wavelength band 
side in addition to the main peak of the green wavelength (main 
wavelength) band as shown by the solid line curve G in FIG. 3. 
Accordingly, in this embodiment, for example, as shown by the dotted curve 
A1 of FIG. 3, a light-absorbing agent is incorporated into the panel glass 
of the G color CRT apparatus so that the average value of the 
transmittance of the light of the wavelength in the range of 500 nm to 560 
nm is higher than the transmittance of the light of the wavelength outside 
this range. 
Further, the spectrum of luminescence of the phosphor used for the R (red) 
color CRT apparatus, as shown by the solid line curve R of FIG. 4, has 
numerous side band peaks near the red wavelength band sides in addition to 
the main peak of the wavelength (main wavelength) band of red. In this 
embodiment, for example, as shown by the dotted curve A2 of FIG. 4, the 
light-absorbing agent is incorporated into the panel glass of the R color 
CRT apparatus so that the average value of the transmittance of the light 
of the wavelength in the range of 600 nm to 700 nm is higher than the 
transmittance of the light of the wavelength in the range of 500 nm to 600 
nm. 
For example, if a light-absorbing agent is incorporated into the panel 
glass for the G color CRT apparatus so as to give a transmittance curve as 
shown in FIG. 3, then as shown in FIG. 5, the spectrum of luminescence 
from the CRT apparatus changes from the spectral distribution of the solid 
line curve G to the spectral distribution of the dotted line curve G', 
light is absorbed in a greater rate at the side bands areas with respect 
to the light having the main wavelength, and the color purity of green is 
improved. 
A similar effect can be expected for a CRT apparatus for obtaining red or 
blue image light in addition to green, but by incorporating the 
above-mentioned light-absorbing agent into the panel glass of at least the 
CRT apparatus for obtaining the green image light, the color purity of the 
green, which has a particularly high luminosity factor, is improved and 
the image of the projection TV system can be improved. 
Note that the light-absorbing agent which can be used in accordance with 
the present invention may be, for example, FeO+Fe.sub.2 O.sub.3, Cr.sub.2 
O.sub.3, or Pr.sub.2 O.sub.3 for G, CdS.multidot.CdSe, Sb.sub.2 S, Cu, or 
Au for R, and CoO, CuO, FeO, Ti.sub.2 O.sub.3 S for B. 
To incorporate this light-absorbing agent into the panel glass, it is 
possible to use generally used methods of manufacture for making colored 
glass etc. The panel glass of the G color CRT can be coated with a film 
containing a phosphor the light emission characteristics of which are 
centered about Tb and which include Y.sub.3 Al.sub.1 O.sub.12 :Tb, 
Gd.sub.2 O.sub.2 S:Tb, or InBo.sub.3 :Tb. 
The panel glass, as shown in FIG. 2, is bonded by frit glass 26 to the 
funnel glass 22 in a state with the electron gun 24 etc. attached inside. 
The inside is maintained at a high degree of vacuum. 
Note that the present invention is not limited to the above-mentioned 
embodiments and can be modified in many ways. 
For example, the present invention is not limited to a cathode ray tube 
apparatus for a rear type projection TV system and may be similarly 
adapted to a cathode ray apparatus for a front type projection TV system 
as well. 
As explained above, according to the present invention, the color purity of 
the image light emitted from the CRT apparatus is improved. Further, while 
a projection lens is disposed in front of the cathode ray tube apparatus, 
the chromatic aberration caused by the color dispersion of the index of 
refraction of the lens material of the projection lens can be reduced. 
Further, in the present invention, there is no need for coloring the 
projection lenses, so the same type of projection lens may be used for 
each of the R, G, and B cathode ray tube apparatuses and therefore the 
assembly and manufacturing costs can be reduced through the common use of 
the same parts.