Black matrix composition for use in color cathode ray tube:
In a conventional shadow-mask-type CRT, graphic images are reproduced by red, green, and blue electron beams emitted from means for producing them which pass through a hole of a shadow mask, converge into a point, and collide with red, green, and blue phosphors formed on a phosphor screen of an inner surface of a panel.
The phosphor screen comprises red, green, and blue phosphors which have a pattern and black matrix which is formed on the same surface and between the phosphors. Generally, the black matrix is a photo-absorptive layer produced by using photoresisting effect of a photoresist.
The black matrix for a color CRT is produced by packing illuminescent absorptive materials between phosphors. The black matrix prevents the contrast of the CRT from decreasing, which is caused by luminescence of aluminium layer occurring when the electrons scattered around the inner panel of the CRT and the hole of a shadow mask collide with the phosphor screen. The black matrix also prevents the chromaticity from decreasing, which is caused by luminescence of dots and stripes of the phosphors when the neighboring dots and stripes are radiated by the electron beams.
The present invention provides a black matrix composition that improves the contrast and the color purity at the same time. The black matrix composition comprising colloidal graphite as a major component, and ferric oxide (Fe2 O3), cobalt aluminate(CoOxAl2 O3), or mixture thereof, at a certain ratio as a pigment. The iron and surfactant are added as a cohesive. The above mixed pigment absorbs the red and blue light so as to improve the contrast and the color purity. The iron partial having magnetism can strengthen the cohesion so as to form the preferable deposited thickness of the black matrix composition.
1. A black matrix composition for use in a color cathode ray tube comprising a colloidal graphite as a major component, which comprises 0.8-5 weight percentage of graphite, 0.1-1 weight percentage of iron, 1.7-4.2 weight percentage of pigment, 0.1-0.5 weight percentage of surfactant and remaining water.
2. The black matrix composition as claimed in claim 1, wherein the pigment comprises at least one of ferric oxide, cobalt aluminate, and mixtures thereof.
3. The black matrix composition as claimed in claim 1, wherein the particle size of graphite is up to 1 μm.
4. The black matrix composition as claimed in claim 1, wherein the particle size of iron is up to 1 μm.
5. A black matrix composition for use in a color cathode ray tube comprising a colloidal graphite as a major component, which comprises 0.8-5 weight percentage of graphite, 0.1-1 weight percentage of iron, 1.7-4.2 weight percentage of ferric oxide (Fe2 O3) and 1.7-4.2 weight percentage of cobalt aluminate (CoOX Al2 O3) as mixed pigment, 0.1-0.5 weight percentage of surfactant and remaining water.
6. The black matrix composition as claimed in claim 5, wherein the particle size of graphite is up to 1 μm.
7. The black matrix composition as claimed in claim 5, wherein the particle size of Fe is up to 1 μm.
Description:
The present invention relates to a black matrix composition which can be used as a black matrix deposited among phosphors, and specially to a black matrix composition comprising graphite and pigment(s that improves the contrast and the color purity of a screen of a color picture tube.
BACKGROUND OF THE INVENTION
A color picture is formed such that electron beams emitted from an electron gun strike phosphors deposited as stripes or dots on the fluorescent layer of a color picture tube. In this process, the conventional method provides that a black matrix is deposited among a color pattern in order to minimize reduction in color purity caused by electron beams' mislanding on corresponding phosphors.
Conventionally, a composition has been used as a composition for use in the black matrix, comprising graphite, surfactant, water and the other additives.
However, the black matrix maded of the above composition does not have the advantage of improving the contrast of the picture, since it cannot filter the internal light, especially a blue light with wave length of 450 nm and a red light with wave length of 620 nm occurring inside when the electron beams strike the phosphors and lowers the contrast.
In order to solve this problem, Japanese specification No. 84-215635 proposes that a blue refractive layer be deposited on blue phosphors and that this layer plays a part in a filter absorbing the internal light of the phosphors. However, this method lowers the color purity, and the complex fabricating process required results in bad productivity.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a black matrix with a material absorbing a major peak wave length of a phosphor added to the graphite composition, whereby the contrast and the color purity are improved at the same time.
To achieve this feature, the present invention proposes a black matrix composition comprising colloidal graphite, ferric oxide (Fe2 O3), cobalt aluminate (CoOxAl2 O3), or mixture thereof as a pigment which can absorb an internal and external light of a major peak wave length of the phosphor, wherein iron particles and a surfactant may be added as a cohesive.
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