Laminar body having phosphorescent properties, process for...

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Reexamination Certificate

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C428S917000, C428S471000, C313S506000, C523S172000, C252S301360, C252S30140R, C427S066000

Reexamination Certificate

active

06699598

ABSTRACT:

The present invention relates to a laminar body comprising a substrate and, applied thereto on one or both sides, at least one layer containing an enamel, wherein the layer contains at least one phosphor. Such a laminar body has phosphorescent properties. The present invention also relates to a process for producing the above-defined laminar body, to its use for giving phosphorescent properties to an article provided therewith and to these articles themselves.
The laminar body of the invention can be used wherever a situation dangerous to people can arise as a result of sudden failure of general lighting. This can be achieved in the form of markings and safety signs in the context of a safety guidance system possessing persistent phosphorescence in order to lead persons safely along a prescribed escape route to an exit or to a safe area.
Processes for producing steel enamel having persistent phosphorescence are known. Steel enamels having persistent phosphorescence have hitherto been produced using phosphors based on zinc sulphides.
In order to be able to achieve certain minimum phosphorescence values, a relatively thick phosphor-containing enamel coating had to be chosen. These processes allow no technical possibility of enamelling thin, flexible and thus more or less universally usable substrates, e.g. foils based on aluminium or aluminium alloys.
An attempt to lower the thicknesses of the enamel layer by use of laminated films led only to laminar bodies which are partly combustible or thermally decomposable. Such laminar bodies having persistent phosphorescence display good phosphorescence values but have the decisive disadvantage of thermal decomposability. This thermal decomposition of plastics is always associated with the liberation of irritating and toxic gases and therefore makes such laminar bodies unusable for a series of applications.
It was therefore an object of the present invention to produce laminar bodies which have good phosphorescence properties, are preferably not combustible and do not liberate any irritating or toxic gases under the action of heat. Furthermore, these laminar bodies should be able to be produced in any configuration by screen printing or else by other printing processes.
In addition, the laminar bodies should be inexpensive to produce, be usable and be replaceable without problems.
These and further objects are achieved by the laminar body of the invention.
The present invention accordingly provides a laminar body comprising a substrate which preferably contains aluminium or an aluminium alloy and, applied thereto on one or both sides, at least one layer containing an enamel, characterized in that the enamel layer or layers contains/contain a phosphor.
If complete noncombustibility in use is necessary, the laminar body of the invention can be constructed so as to be free of plastics.
As substrate in the laminar body of the invention, it is possible to use any substrates which can be enamelled, in particular those based on metals, e.g. ferrous materials, materials containing aluminium or an aluminium alloy, copper-, silver-, gold- and titanium-containing materials. Preference is given to using a substrate which contains aluminium or an aluminium alloy.
Although the thickness and structure of the substrate are subject to no particular restrictions, preference is given to using perforated metal sheets having a thickness of from about 0.2 to about 2.5 mm, more preferably from about 0.5 to about 2.0 mm and in particular from about 0.5 to about 1.5 mm, or foils having a thickness of from about 50 to about 500 &mgr;m, more preferably from about 100 to about 400 &mgr;m and in particular from about 200 to about 300 &mgr;m. There is virtually no restriction in respect of the free perforation area of the perforated metal sheets, but preference is given to using perforated metal sheets having a free perforation area of from about 20 to about 45%.
For the purposes of the present invention, it is in principle possible to use as substrate all known aluminium alloys in which the most important alloying constituents are, for example, copper, magnesium, silicon, manganese and zinc and also mixtures of two or more thereof and, in smaller amounts, nickel, cobalt, chromium, vanadium, titanium, lead, tin, cadmium, bismuth, zirconium and silver and also mixtures of two or more thereof.
In addition, the laminar body of the invention comprises a layer which contains an enamel and is applied to either one or both sides of the above-defined substrate.
For the purposes of the present application, the term “enamel” corresponds to the definition given in “Email und Emailliertechnik”, Petzold/Pöschmann, Deutscher Verlag für Grundstoffindustrie, Leipzig/Stuttgart, 2nd revised edition 1992, page 15. Accordingly, enamel is a preferably vitreous, solid material formed by melting or fritting and having an inorganic, mainly oxidic-siliceous composition which is to be melted or has been melted in one or more layers, sometimes together with additives, onto metal workpieces.
The enamel used according to the invention can be produced from an enamel frit which contains heavy metals or is free of heavy metals.
Here, the term “free of heavy metals” means that the enamel frit used is completely or essentially free of metals which have an atomic number greater than the atomic number of calcium.
In a preferred embodiment of the present invention, in which the substrate contains aluminium or an aluminium alloy, enamelling is carried out using an aluminium enamel. With regard to this, the following needs to be noted. The low melting point of aluminium and its alloys demands enamels which can be fired at from about 520° C. to 560° C. This corresponds to a softening temperature of about 450° C. Accordingly, the starting materials employed in this embodiment are enamel frits which have the abovementioned properties.
This can be achieved using, for example, glasses having a high content of Li
2
O, BaO and V
2
O
5
. Eutectics containing fluoride or enamels based on phosphate also meet the temperature requirement. Although the abovementioned conditions in respect of the softening point can be achieved by addition of these constituents, preference is given to adding further constituents to increase the chemical resistance of the resulting enamel. Thus, for example, good values for the resistance of the resulting enamel to aggressive media can be achieved by changing the ratios of Li
2
O and TiO
2
and the contents of alkaline earth metal and ZnO. Details on this subject may be found in Migonadziev, A. S., Steklo i keramika (1966), 12, p. 15.
Aluminium enamels can be produced in all colours and also in black and white. In the case of the white enamels, opacifiers such as TiO
2
are added and an appropriately high ratio of Li
2
O to TiO
2
, i.e. about 1:1.5-2, then has to be selected. Coloured aluminium enamels can be produced in many shades.
By way of example, the composition of an enamel which is very useful for the purposes of the invention will once more be described here:
100 parts of frit
15 parts of phosphorescent pigment
4 parts of boric acid
2 parts of KOH
1 part of water glass
45 parts of water
This mixture is milled in a porcelain mill to give a slip having a defined particle fineness of, for example, from 0.1 to 0.5 by the Bayer method and a specific gravity of, for example, from 1.5 to 2.0 g/cm
3
, preferably from 1.7 to 1.8 g/cm
3
.
This slip is usually applied to the part to be enamelled by a spraying method.
Further details of such aluminium enamels or the enamelling of substrates containing aluminium or aluminium alloys may be found, for example, in a review article “Mitteilungen des Vereins Deutscher Emailfachleute e.V.”, volume 43, 1995 (No. 5), p. 56 ff.
The thickness of the enamel layer or layers is preferably 400 &mgr;m or less, more preferably about 300 &mgr;m or less and in particular about 200 &mgr;m or less, with the lower limit of the thickness of the enamel being about 30 &mgr;m.
In a further, preferred embodiment, a reflective layer of a white or light-coloured enam

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