Cathode-ray tube and method for manufacturing the same

Details Cathode-ray tube and method for manufacturing the same Cathode-ray tube and method for manufacturing the same

2000-12-19

2003-05-27

Wong, Don (Department: 2821)

Electric lamp and discharge devices

Cathode ray tube

Envelope

C313S478000, C313S112000

Reexamination Certificate

active

06570317

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a cathode ray tube that, on an external surface of a face-panel thereof, has an anti-reflection film of an excellent leakage electromagnetic wave shielding effect and of optimized contrast. Further, the present invention relates to an efficient manufacturing method of cathode ray tubes having an anti-reflection film that is highly effective in shielding the leakage electromagnetic wave.
BACKGROUND ART
A color cathode ray tube that is used for TV Braun tube, computer display terminal or the like has, on an inner surface of a front panel (face-panel) of a face-plate, phosphor layers consisting of blue-emitting phosphor (B), green-emitting phosphor (G) and red-emitting phosphor (R), respectively. All of the respective phosphor layers are disposed in a prescribed pattern of dot or stripe. By bombarding the respective phosphor layers by an electron beam, the phosphors emit respective colors to display image.
Such cathode ray tubes are used under an ambient light. Therefore, an anti-reflective surface treatment film (anti-reflection film) is disposed on an external surface of the face-panel by laminating a multiple number of layers of different refractive index thereon (in general, bottom layer that is close to a face-panel is designated as a layer of high refractive index, and upper layer that is distanced far from the face-panel is designated to a layer of low refractive index). Respective lights reflected at respective boundaries of the layers of anti-reflection film interfere each other to cancel out.
In the cathode ray tubes having such an anti-reflection film, in order to improve the following characteristics thereof, various ideas have been proposed.
First of all, improvement of display contrast is being demanded. For improving the contrast, there is one method in which light transmittance of the face-panel is lowered to obtain a flat transmitting characteristic. However, this method reduces the brightness of the phosphors as well as superposition of the ambient light. Accordingly, this is not a desirable method.
Further, there are proposed several applications that employ neodymium oxide (Nd
2
O
3
) included in a face-panel itself as filter material (cf. U.S. Pat. No. 4,728,856, Japanese Patent Laid-Open Publication (KOKAI) No. Sho 57-134848, Japanese Patent Laid-Open Publication (KOKAI) No. Sho 57-134849 and Japanese Patent Laid-Open Publication (KOKAI) No. Sho 57-134850). Neodymium oxide (Nd
2
O
3
) has a selective absorption characteristic of visible light (the maximum absorption is shown in the range of wavelength of from 560 to 615 nm and the second maximum absorption is shown in the range of wavelength of from 490 to 545 nm). Accordingly, it can selectively absorb the ambient light to realize improvement of the contrast.
However, the face-panel including neodymium oxide shows BCP value (Brightness Contrast Performance) of from 1 to 1.05 and did not show a sufficient improvement of the contrast.
Here, the BCP is one of the indices that express the display contrast and shows a degree of deviation of the contrast from a reference. When the rate of deviation of the brightness from a reference is &Dgr;B and reflectivity of the ambient light is &Dgr;R
f
, the BCP is expressed by
BCP=&Dgr;B/{square root over (&Dgr;R
f
)}
Secondly, an anti-static measure is implemented on the surface of the face-panel. When the static is built up on the surface of the face-panel, dust or dirt adheres thereon. Accordingly, to prevent the static from building up, a conductive film is formed on the external surface of the face-panel. For example, U.S. Pat. No. 4,563,612 discloses a method in which a film including silicate and conductive metal is formed on the external surface of the face-panel, and Japanese Patent Laid-Open Publication (KOKAI) No. Sho 61-118946 or the like discloses a method in which silicon alcoholate is coated by spray method to form an anti-static film.
Thirdly, an anti-leakage measure against the generated Alternating Electric Field (AEF) is implemented. Recently, in cathode ray tubes such as TV Braun tubes or display terminals of computers, there is a concern that AEF generated in the neighborhood of an electron gun and deflection yokes disposed inside the cathode ray tube leaks outside thereof to adversely affect electronic instruments or human bodies in the surroundings thereof. In particular, in Europe, there is a movement to standardize TCO guideline (a guideline due to The Swedish Central Organization of Salaried Employees) for preventing the AEF from occurring.
As an anti-leakage measure of AEF, there is an idea to lower the value of surface resistance of the anti-reflection film formed on the external surface of the face-panel. As such an anti-reflection film of low resistance (conductive), various kinds of surface treatment films have been developed.
With surface treatment films that have been conventionally employed in cathode ray tube, characteristics such as display contrast and anti-reflection effect (low reflectivity), and lowness of the value of surface resistance (low resistivity) and so on are shown in Table 1. Incidentally, whether the anti-reflection effect is acceptable or not is judged based on the values of specular reflectance (Rlum%) and specular reflection chromaticity (color x/y) that are indices of anti-reflectivity. Incidentally, the specular reflectance means a product of a spectral reflectance of a regularly reflected light (that is, light of angle of reflection of 15°) of an incident light with an angle of incidence of 15° that is shown in
FIG. 5 and a
luminosity curve. When this value is 1.5% or less, it is judged to have an excellent anti-reflection effect.
Further, specular reflection chromaticity is the chromaticity of the specular reflection light that is shown in FIG.
5
and is required to be color of reflection that does not give uncomfortableness. It is required for its x-coordinate in chromaticity diagram to locate in the range of 0.170≦x≦0.330 and for its y-coordinate to have value in the range of 0.170≦y≦0.330. When any one of x and y coordinates deviates from the above values, the reflected light gives an uncomfortable feeling.
TABLE 1
Surface Treatment Film
A
B
C
D
E
F
G
H
Dyestuff
yes
yes
none
none
none
yes
yes
yes
its kind
a
b
a
a
a
Number of layers
1
2
2
3
1
2
2
2
Type of film of
smooth film
smooth silica
smooth silica
smooth film +
coarse silica
smooth silica
smooth silica
smooth silica
upper layer
film
film
coarse film
film
film
film
film
Conductive matter
non-colored
non-colored
colored ITO
colored ITO
non-colored
non-colored
non-colored
colored Ag
Li nitrate
ATO
ITO
ITO
ATO
BCP
improved
no change
no change
no change
deteriorated
improved
improved
deteriorated
AR
Rlum %
insufficient
good
good
good
insufficient
good
good
good
Color
uncomfortable
comfortable
comfortable
comfortable
uncomfortable
comfortable
comfortable
comfortable
AEF-TCO
inconformity
inconformity
conformity
conformity with
inconformity
inconformity
inconformity
conformity
with circuit
circuit correction
correction
Resolution
good
good
good
good
bad
good
good
good
In the row showing the kinds of dyestuffs, sign a denotes a dyestuff having a selective absorption at the wavelength of 575 nm such as Rhodamine B, and sign b denotes a dyestuff having a flat and non-selective absorption in the visible light region such as carbon black.
However, as shown in Table 1, there has not been obtained yet a surface treatment film that combines three major characteristics of high contrast, low reflectivity and low surface resistance corresponding to the TCO guideline, and further combines smoothness and high reliability.
That is, in a smooth and low reflection film of two layered structure in which an upper layer mainly consisting of SiO
2
is laminated on a transparent conductive bottom layer containing non-colored conductive matter such as non-colored ITO (Indium doped Tin Oxide) or non-colored ATO (Antimony doped Tin Oxide), when surface treatment films (F and G in table 1) in which a dyestuff (col

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