Patent Application
20100285284
Buildings and subway stations display emergency and exit signs in order to direct people to a safe location in the event of a fire, natural disaster, or other event. In many cases electrical power is lost during such an event. If the building goes dark, another means is required to illuminate the emergency signage.
One solution for such a problem is the use of photoluminescent materials. Photo luminescent materials can absorb light from the sun or from man made light sources. The light energy is then released, at a different wavelength. Some photo luminescent materials release the absorbed light energy at a slow rate, such as over several hours. The slow release of absorbed light energy is referred to as phosphorescence. Therefore, photoluminescent materials displaying phosphorescence can be charged with light from the sun or an artificial light source and then release the absorbed light energy in the dark over several hours providing illumination of emergency signage.
Some examples of inorganic photoluminescent compositions include alkaline earth aluminates doped with rare earths, such as strontium aluminate, and zinc sulfide doped with copper. These inorganic photoluminescent materials are commercially available in a powder form under the brand name Lumilux® (Honeywell US, Morristown, N.J.).
Conventional use of these inorganic photoluminescent material powders involves the dispersion of the powder into an organic or plastic matrix. This plastic matrix may then be formed using conventional plastics processing techniques such as compression molding, casting, extrusion and injection molding to create useful glow in the dark articles such as emergency signs, safety tape and toys. While numerous uses for this type of organic matrix photoluminescent article can be found there are important potential uses for photoluminescent articles for which this organic plastic matrix is poorly suited. The general use limitations associated with plastics in that they typically degrade when used in prolonged or sustained ultra violet (UV) radiation environments, degrade upon high temperature exposure and have poor wear resistance when subjected to an abrasive environment makes the use of organic plastic matrix photoluminescent articles unsuitable for applications such as emergency signage where fire is involved, outdoor tile subject to intense UV and floor tiling subject to high foot traffic.
The highly desirous potential benefits of using photoluminescent materials in floor tile are described in U.S. Pat. No. 6,841,785 to Nolt, entitled, “Photoluminescent Floor Tile”. This patent discloses a photoluminescent floor tile system in which conventional inorganic photoluminescent phosphors are incorporated within a tile body containing limestone or clay. This construction requires that a substantial amount of photoluminescent material be added to the tile body to produce the desired phosphorescent properties. As an alternate embodiment, Nolt discloses a tile body having a wear layer of non-transparent inorganic material incorporating a resinous thermoplastic binder and photoluminescent material adjacent to the top surface of the wear layer. While the proposed floor tiles disclosed in the patent to Nolt are an improvement over previous photoluminescent tiles, these tiles are still subject to high cost (due to the amount of photoluminescent material incorporated in the tile body), high wear rates (related to the unfired or conventionally processed tile body) resulting in additional frequent replacement costs and UV degradation due to the thermoplastic resinous binder which incorporates the photoluminescent material.
Another example of photoluminescent tile is described in U.S. Pat. No. 7,297,416 to Lee, entitled, “Photoluminescent Tile and Method for Fabricating the Same”. This patent discloses a photoluminescent tile construction in which a tile body has been machined or grooved to create a recess in the tile surface or body and a photoluminescent glaze powder (photoluminescent phosphor expressed by MAl2O4 (M: metal) in 50-90 wt % mixed with glass frit in 10-50 wt %) is used to fill the recessed areas, covered with a protective frit layer and then conventionally fired at a temperature between 500 C and 1200 C. The photoluminescent glaze powder when fired at temperatures up to about 1050 C as provided in the examples produces a glassy mixture which is contained within the recessed areas. This method of producing a tile with machined or formed recessed areas and subsequently filling with a photoluminescent glaze is an improvement over previous photoluminescent tiles employing thermoplastic resins however this type of processing is very expensive. As an alternate embodiment, Lee discloses a photoluminescent tile in which a tile body having no machined recesses or grooves has a photoluminescent glaze powder placed on the surface of the tile in a pattern, a wear glaze covering the patterned photoluminescent glaze and firing a temperature between 500 C and 1200 C. While this method of producing a tile is lower cost than the machined groove method, the flowing nature of the photoluminescent glaze powder while firing can result in a distorted photoluminescent pattern. Additionally, conventional firing of these articles above 1050 C for an extended period of time, typically result in a degradation of photoluminescent properties.
The present invention is directed towards a phosphorescent article and a method of producing said phosphorescent article having a formed layer made up of essentially inorganic photoluminescent phosphor comprising a rare earth doped alkaline earth aluminate, rare earth doped alkaline silicate or zinc sulfide doped with copper
There are numerous inorganic rare earth doped alkaline earth aluminate photoluminescent phosphors suitable for use in a phosphorescent article according to embodiments of the present invention. Some of these rare earth doped alkaline earth aluminates include formulations of strontium aluminate (SrAl2O4), calcium aluminate (CaAl2O4) and barium aluminate (BaAl2O4) or mixed combination. Photoluminescent phosphors of aluminates such as these may be doped with rare earth elements such as europium (Eu), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), dysprosium (Dy), holomiun (Ho), erbium (Er), thulium, (Tm), ytterbium (Yb), lutetium (Lu) or combinations thereof. Suitable inorganic photoluminescent phosphor materials are commercially available in a powder form under the brand names Lumilux®, produced by Honeywell US, or LumiNova® produced by Stone Nemoto Co., Ltd.
In accordance with an aspect of the present invention there is provided a method for producing a phosphorescent article comprising the steps of providing a photoluminescent phosphor comprising a rare earth doped alkaline earth aluminates, forming said photoluminescent phosphor into a shape using conventional ceramic processing techniques, firing said formed shape at a temperature between 1000 C and 1600 C in a controlled atmosphere.
Conventional ceramic processing techniques are used form the photoluminescent phosphor powders into a layer or shape. These techniques include pressing, slip casting, tape casting, injection molding, screen printing, etc. Organic processing aids, such as binders, dispersants, defoamers, etc may be used during the forming step to assist in the process. During the firing step these organic processing aids are volatilized and completely removed from the finished phosphorescent article. Firing takes place in a furnace or kiln capable of maintaining sustained temperatures of 1600 C and providing a controlled atmosphere. The firing can be carried out in air, an inert atmosphere such as Argon, or in a reducing atmosphere such as an atmosphere containing some portion of hydrogen. The type of atmosphere suitable for a phosphorescent article of the present invention is determined by the particular photoluminescent phosphor and preservation of the valence state of dopants within the phosphor.
In accordance with another aspect of the present invention there is provided a phosphorescent article having a composite structure. The composite structure includes a substrate layer bonded to a phosphorescent layer where the phosphorescent layer comprises greater than 90% by volume of photoluminescent phosphors. A phosphorescent article according to this aspect of the present invention may be formed providing a substrate and using ceramic processing techniques to apply the phosphorescent layer then firing the composite structure at a temperature between 1000 C. and 1600 C.
In accordance with yet another aspect of the present invention there is provided a phosphorescent article having a composite structure with at least three layers. These layers include a substrate layer, a wear layer and a phosphorescent layer positioned between and bonded to the substrate and wear layers. The composition of the phosphorescent layer is such that the photoluminescent phosphor makes up a substantial majority of the layer and is not mixed with a frit. Each layer can be formed separately and then stacked to form the composite structure, or the each layer can be formed by coating a previously formed layer. Each layer can be formed from a powder using conventional ceramic powder processing techniques. Layers may be coated onto previously formed layers by spraying, brushing, dipping, or other coating method. Once the layers have been formed, the composite structure can be fired to temperatures between 500 C and 1600 C for up to several hours. All of the layers can be fired together at one time, or the forming and firing can be divided into several steps were some layers are fired before forming subsequent layers.
In accordance with still another aspect of the present invention there is provided a phosphorescent article having a composite structure including a substrate layer, a reflective layer bonded to the substrate layer and a phosphorescent layer bonded to the reflective layer. The phosphorescent layer comprises photoluminescent phosphor. An optional wear layer may be bonded to the phosphorescent layer. The reflective layer is designed to reflect light emitted from the phosphorescent layer back through the phosphorescent layer providing a more pronounced and sustained phosphorescent effect. Suitable compositions for the reflective layer are those that reflect the wavelength of emitted light from a particular photoluminescent phosphor and include materials such as alumina (Al2O3), titania (TiO2) and mixtures thereof. Each layer can be formed separately and then stacked to form the composite structure, or the each layer can be formed by coating a previously formed layer. Each layer can be formed from a powder using conventional ceramic powder processing techniques. Layers may be coated onto previously formed layers by spraying, brushing, dipping, or other coating method. Once the layers have been formed, the composite structure can be fired to temperatures between 500 C and 1600 C for up to several hours. All of the layers can be fired together at one time, or the forming and firing can be divided into several steps were some layers are fired before forming subsequent layers.
Suitable wear layers for any of the aforementioned embodiments may include low or high fire glazes. The wear layer may include decorative patterns or colorants. Alternatively decorative layers may be added to the composite structure to provide improved aesthetic properties.
In accordance with still yet another aspect of the present invention there is provided a phosphorescent article where the phosphorescent layer takes the form of various indicia, graphics, designs or lettering to convey concepts to those who may view them. For example, the shaped phosphorescent phosphor may be formed into an arrow to convey a directional path for someone to follow in the case of emergency signage. A schematic design of a person taking a step may indicate a nearby flight of stairs. Wording may be formed such as “EXIT” denoting an exit location in the case of fire.
The phosphorescent articles of the present invention are well suited for creating dense, highly wear resistant, UV stable, high temperature use tiles for flooring, walls, pools, spas, outdoor pathway lighting, general low level lighting, backlighting of indoor or outdoor signage and other decorative uses. Additionally, photoluminescent articles of the present invention may be combined with other technologies for use in displays, electroluminescent devices and scintillation technology.
These aspects of the invention and the advantages thereof will be more clearly understated from the following description and drawings of preferred embodiments of the present invention:
Generally, an inorganic phosphorescent article of the present invention may be used in any location where it is desirous to have low level lighting such as a part of an emergency lighting system.
As is apparent, there are numerous modifications of the preferred embodiments described above which will become readily apparent to one skilled in the art, such as many variations and modifications of the inorganic phosphorescent article including many different variations of the photoluminescent phosphors, many variations of methods of phosphorescent article construction and controlled atmospheres. These modifications would be apparent to those having ordinary skill in the art to which this invention relates and are intended to be within the scope of the claims which follow.
This application claims the benefit of U.S. provisional patent application Ser. No. 61/177,097 filed on May 11, 2009.
| Number | Date | Country | |
|---|---|---|---|
| 61177097 | May 2009 | US |
