Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-11-21
2004-01-06
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C430S025000, C430S028000, C420S535000, C313S506000
Reexamination Certificate
active
06673473
ABSTRACT:
The invention relates to a display screen, in particular a colour display screen, based on a display-screen support with a single-layer or multi-layer coating which contains a red luminous substance and a colouring pigment. The invention is further directed towards a single-layer or multi-layer display-screen coating, means for producing the display-screen coating, including the production of a coated red luminous substance. Further subjects are directed towards the production of the display screen and its coating and also to the production of the coated luminous substance.
Display screens, such as colour display screens, colour monitors and plasma display panels, are frequently utilised in relatively bright ambient light. In order to make the screen image more visible in such illumination and in order to tire the eyes less, the display screen should be free from glare, low in reflection and rich in contrast. The contrast can be maximised by increasing [sic] the influence of external light in comparison with the intrinsic luminous density of the luminous substances in the display-screen coating. This can be obtained, for example, by virtue of colour filters in the form of inorganic pigments which are selected in such a way that they are as transparent as possible in respect of the colour emitted by the respective luminous substance and absorb the remaining portions of the spectrum, so that the diffuse reflection of the external light on the luminous-substance powder is suppressed.
A colouring pigment that, with a view to achieving the filtering effect, is suitable for use in an image layer or filter layer or for the pigmentation of a luminous substance has to have absorption properties that do not have a negative influence on the emission characteristic of the luminous substance. Moreover, a requirement of a pigmentation in an image layer or filter layer or for luminous-substance coatings is that it is stable in a vacuum, is not degraded by electron bombardment or gas discharges, is inert in relation to reducing, oxidizing or hydrolysing reagents and does not decompose at elevated temperature.
From published German patent application DE-OS 199 01 539 a colour display screen is known with a red luminous substance and a red to yellow oxide-nitride pigment corresponding to the formulae stated in said document. Suitable are, for example, oxide nitrides of the general formula A
1−x
A′
x
BO
2−x
N
1+x
with A=Mg, Ca, Ba, Sr, Zn, A′=La or another lanthanide element, Bi, Al, Fe; B=V, Nb, Ta, Mo, W and 0<x<1. The pigment is contained in a coating containing binding agent on the red luminous substance. Such an oxide nitride and a red luminous substance in the coating of a colour display screen provide a high-contrast and low-reflection image. Although the colour can be varied within the range from yellow to red—and hence the absorption spectrum can also be varied—through the choice of the O/N ratio in the oxide nitride, it is a question of very complex compounds; in addition, there only exists a supply of red pigments for red luminous substances.
The object of the invention is accordingly [sic] a further display screen, in particular a colour display screen, with a display-screen coating containing a red luminous substance and a red pigment. The red pigment should have a simpler chemical structure than the oxide nitrides that are known for this purpose with three or more cations. In addition, the pigment should be distinguished by an absorption edge that is as sharp as possible. The display screen with the red pigment should provide a high-contrast image, should possess low reflectance in respect of external light and should exhibit high emission luminance and good emission-colour quality.
The stated objects [sic], as well as further objects such as result from the further specification, are achieved by the subjects as claimed.
A display screen, in particular a colour display screen, has been found comprising a display-screen support and a single-layer or multi-layer display-screen coating which contains a red luminous substance and a colouring pigment, said display screen being characterised in that tantalum(V) nitride (Ta
3
N
5
), which may be coated with an oxidic material, is present by way of colouring pigment.
The dependent claims are directed towards preferred embodiments. Further claims are directed towards the coating, means for the production thereof, coated luminous substances and the production thereof. An essential feature of the invention in all embodiments is the presence of red tantalum(V)-nitride pigment (Ta
3
N
5
), which may also be coated. Tantalum(V) nitride is accordingly a means for producing the display screen as well as the coated luminous substances.
Tantalum(V) nitride for use in a display screen according to the invention and for the production of coated luminous substances can be obtained by nitriding an oxidic tantalum(V) compound with dry ammonia. According to EP 0 592 867 B1, tantalum(V) oxide hydrate of the formula Ta
2
O
5
·aq is nitrided. A better pigment quality is achieved by nitriding tantalum(V) oxide in the presence of an oxide such as SiO
2
—EP 1 031 536 A1.
According to a first embodiment, tantalum(V) nitride is located in a colour-filter layer which is arranged between a display-screen layer containing the red luminous substance and the display-screen support or the display-screen support which is covered with a black matrix.
According to a second embodiment, the Ta
3
N
5
pigment and the red luminous substance are located jointly side by side in a display-screen layer.
According to a third, particularly preferred embodiment, tantalum(V) nitride is located in an inorganic or organic coating on the red luminous-substance particles. The display-screen coating contains the luminous-substance particles that have been coated in this way in the active display-screen layer, which in turn is arranged directly on the display-screen support or on a display-screen support which is coated with a black matrix and/or with one or more filter layers.
In the case of the material of the display-screen support it is a question of a material that is stable under the operating conditions of the display screen, such as vacuum, electron radiation, gas discharges. Examples are glass, ceramic, metal and glazed metals; in particularly preferred manner the display-screen support consists of glass. In expedient manner a display-screen support made of glass is covered on the reverse with a metal film such as an aluminium film.
Preferred colour display screens contain, in one or more layers, luminous substances in the primary colours blue, red and green and, in addition, at least one pigment in one of the primary colours, preferably a pigment in each of all three primary colours. According to the invention, in the case of the red pigment it is a question of tantalum(V) nitride. According to a preferred embodiment of a display screen according to the invention, the active image layer contains a coated red luminous substance with tantalum(V)-nitride pigment in the coating. As needed, the blue and/or green luminous substances are also coated with a blue or green pigment, respectively. As an alternative to this, the pigments that are matched to the respective luminous substance may be present side by side in a filter layer.
A colour display screen with a red luminous substance and with a tantalum(V)-nitride pigment provides a high-contrast and low-reflection image, because the absorption properties of tantalum(V) nitride suit the emission properties of common red-luminescent luminous substances very well. The known state of the art provides no inducement to use pure and more readily accessible tantalum(V) nitride, which may also be coated, instead of oxide nitrides.
Tantalum(V) nitride is distinguished, in comparison with traditional Fe
2
O
3
pigments, by a steeper absorption edge in the red-orange spectral range and by a high absorptivity and constitutes an alternative to the oxide nitrides.
Ferro GmbH
Garrett Dawn L.
Kelly Cynthia H.
Rankin, Hill Porter & Clark LLP
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