Cathode ray tube having an internal neutral density filter

Details Cathode ray tube having an internal neutral density filter Cathode ray tube having an internal neutral density filter

2003-02-27

2004-11-16

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Envelope

C313S466000

Reexamination Certificate

active

06819040

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a color cathode ray tube (CRT) and, more particularly to a luminescent screen assembly including an internal neutral density filter.
2. Description of the Related Art
A color cathode ray tube (CRT) typically includes an electron gun, an aperture mask, and a screen. The aperture mask is interposed between the electron gun and the screen. The screen is located on an inner surface of a faceplate of the CRT tube. The aperture mask functions to direct electron beams generated ir the electron gun toward appropriate color-emitting phosphors on the screen of the CRT tube.
The screen may be a luminescent screen. Luminescent screens typically have an array of three different color-emitting phosphors (e.g., green, blue and red) formed thereon. Each of the color-emitting phosphors is separated from another by a matrix line. The matrix lines are typically formed of a light absorbing black, inert material.
The faceplate of the CRT tube typically comprises a glass panel having a low transmission coefficient. However, the use of a glass panel with a low transmission coefficient may cause the CRT tube to exhibit a “Halo” effect, which is manifested by a reflection gradient from the perimeter to the center of the panel. As a result of this reflection gradient, the perimeter of the faceplate of the CRT undesirably appears darker than the center, when the tube is off.
Thus, a need exists for a luminescent screen that overcomes the above drawbacks.
SUMMARY OF THE INVENTION
The present invention relates to a composition and method of forming an internal neutral density filter on a luminescent screen assembly of a cathode ray tube (CRT). The luminescent screen assembly is formed on an interior surface of a glass faceplate panel of the CRT tube. The luminescent screen assembly includes a patterned light-absorbing matrix that defines three sets of fields corresponding to one of a blue region, a green region and a red region. An internal neutral density filter is formed on the light-absorbing matrix. An array of blue, green and red color phosphors are then formed on the internal neutral density filter corresponding to one of the blue region, the green region and the red region defined in the light-absorbing matrix.
The internal neutral density filter has a composition including a red pigment, a blue pigment and at least one non-pigmented oxide particle. The internal neutral density filter functions to decrease the reflection of the screen throughout the panel while eliminating the “Halo” effect of the CRT tube.


REFERENCES:
patent: 4521524 (1985-06-01), Yamashita
patent: 5160375 (1992-11-01), Otaki
patent: 5627429 (1997-05-01), Iwasaki
patent: 6366012 (2002-04-01), Lee et al.

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