DE9415950U1 - Plastic plate with a white fluorescent phosphor that can be excited by long-wave UV light - Google Patents

Description

DESCRIPTION
Field of the invention

The invention relates to the field of illuminated signs. Advertising signs and traffic signs that can be illuminated so that they can be seen over long distances at dusk and at night or in fog are well known.

State of the art

Technically speaking, these signs are housings or boxes made of metal or plastic that have an illuminated surface and inside which a lighting device is installed. Usually one or more fluorescent lamps are used, whereby the surface or side of the housing to be illuminated is made of glass or translucent plastic, usually with a milky light.

The side to be illuminated contains images or characters that can serve as advertising or traffic information. These signs are usually very high-contrast (e.g. a white arrow on a blue background on a traffic sign). As a rule, the signs have a relatively small depth for reasons of handiness and space. In order to achieve uniform illumination that ensures good perception even over long distances, a disproportionate number of lamps often have to be installed.

Another conceivable construction, such as illuminating signs that are not illuminated from the inside from a distance, is generally ruled out due to the possible glare of oncoming or cross traffic by the light source.

There are a number of disadvantages associated with conventional illuminated signs. For example, the energy supply costs are high, especially outside built-up areas. Energy consumption is also high. In addition, conventional illuminated signs have the disadvantage of a not insignificant glare effect on the human eye. This effect is particularly evident in the absence of other light sources such as street lighting, especially at dusk and at night outside built-up areas.

The aforementioned glare effect means that darker objects are harder to see. After passing a dazzling sign, it takes some time for the eye to adapt to the darker environment again. You initially drive into a "black hole". This increases the overall risk of participating in traffic.

Another way to make traffic or advertising signs visible is fluorescent luminous colors. Well-known applications include warning signs on clothing or emergency vehicles of rescue services such as fire departments, etc. The most well-known colors are mainly bright red, green, yellow and orange. The luminous effect is created by the excitation of the dye molecules by certain wavelengths of visible light, which in turn emit this energy in the form of light from a different, longer wavelength spectrum. The luminous effect is perceived by the human eye as glaring, which explains why its use is largely limited to warning signs.

There are also known phosphors that are excited by non-visible spectra, such as UV radiation, and emit visible light spectra. The majority of known phosphors require high-energy, short-wave UV radiation to enter the excited state. The use of these phosphors in signs would be opposed primarily by the health-endangering effect of the required radiation source and its long-term destructive effect on plastic.

An example of a phosphor that can be excited by harmless, long-wave UV radiation is NP 657-09-01 (Nichia Chemicals Europa GmbH), which can be excited in the wavelength range of 300-380 mn and in this state emits white fluorescent light. In contrast to the luminous colors mentioned at the beginning, the luminous effect is not glaring but rather pleasant for the human eye. The phosphor is NP 657-09-01 is a water-insoluble, white powder consisting of several components that fluorescent in the primary colors of the spectrum and have the following composition. The elements used for doping are listed after the colon.

Y ₂ O ₂ SiEu,

(Ba, Mg)O- 6Al ₂ O3iEu, Mn,

(Sr, Ca, Ba)5(PO4)3CI:Eu

The proportions of the components are chosen so that their fluorescence radiation adds up to white light.

The average grain size is approximately 6 μηι, the specific weight is 4.58 g/cm^ An application for the illumination of signs is not known. To stimulate this dye, commercially available mercury black light lamps can be used as a light source, for example, in which only the long-wave UV radiation is transmitted by means of a cobalt glass cover.

Task and solution

The aim of the present invention was to create a simple lighting device for illuminated signs that allows the human eye to have good, high-contrast perception, but at the same time is characterized by lower energy requirements and significantly lower glare. The light source used should

in any case be harmless to humans (and animals), i.e. not emit short-wave UV radiation. Surprisingly, the task could be solved by a plate made of thermoformable plastic (plastic plate), characterized in that it contains a white fluorescent phosphor that can be excited by long-wave UV radiation in the range of 300 mn.

The invention is explained by Figure 1, but should not be limited to the embodiment shown.

Figure 1: Example of the arrangement of a plastic plate (1) according to the invention designed as a traffic sign and a UV lamp (2) designed as a headlight over a lane of a two-lane motorway-like road (4) interrupted by a green strip (3). The beam direction of the headlight towards the plastic plate is indicated by dashed lines.

By using the invention, a relatively weak, energy-saving, but uniform and easily perceptible lighting is achieved compared to conventionally illuminated signs. The invention also has the advantages that a box structure for the sign is not required, since the lighting can be done from a distance, the lighting source emits a spectrum that is harmless to humans and is almost invisible to oncoming traffic and thus does not dazzle. An additional advantage is the ease of maintenance made possible by the separate construction of the sign (1) and light source (2), since no light box needs to be opened to change the lamp and the lamp itself can be placed in an easily accessible location. Particular advantages arise with signs that are difficult to access, e.g. mounted at a great height. The invention can be used to create practically any advertising or traffic sign that requires lighting.

Implementation of the invention

A white fluorescent phosphor that can be excited by long-wave UV radiation in the range of approx. 300 - 380 mn, preferably the phosphor NP 657-09-01 described at the beginning (Nichia Chemicals Europe GmbH, D-90429, Nuremberg) is incorporated into the manufacture of plates or panels made of commercially available thermoformable plastics or plastic mixtures suitable for signs. Weather-resistant, UV-permeable plastics or plastic mixtures, e.g. made of polymethyl methacrylate, are preferably used. The plastics can have additional modifications in a manner known per se, e.g. to improve their impact strength. Impact modifiers for polymethyl methacrylate are known, for example, from EP 0 368 094 Bl. The finished plastic sheets can also be provided with scratch-resistant coatings in a conventional manner.

Conventional methods for introducing pigments into polymer plastics can be used for incorporation. It is important to achieve an even distribution of the phosphor in the plastic. In the case of cast plastic, the phosphor can be added directly to the monomer or to a partially polymerized syrup. In the case of extruded plastic, it can be added to the extruder with the polymer granulate directly or, if necessary, in the form of a plastic-containing concentrate. When using NP 657-09-01, the phosphor is preferably used in amounts of approx. 0.5 - 2% by weight, particularly preferably 0.8 - 1.2% by weight. In addition, UV-reflecting pigments or other auxiliary substances, such as barium sulfate, can be incorporated to improve the light scattering properties. Barium sulfate can be used in amounts of approx. 0.1 to 2% by weight, preferably 0.5% by weight.

The resulting plastic panels are provided with the appropriate traffic or advertising information by applying foil, by printing or by covering them with colored plastic or by other suitable processes.

The plastic panels themselves can be square, round, ellipsoidal, square with rounded corners or any other desired shape. Typical dimensions are in the range of the well-known, conventionally illuminated signs and, depending on the shape, can range from approx. 50 cm in width and/or height to several meters in width and height, e.g. for signs installed above motorways. The thickness of the plastic panels can be from approx. 2 mm to approx. 50 mm. Very large signs can also be made up of several parts in order to limit the weight and dimensions in the interests of easier handling and transport.

The finished sign is irradiated at its installation location using a commercially available mercury black light lamp with a tube or outer bulb made of cobalt glass with an output of 10 to 100 W/m.2 with wavelengths of approx. 300 - 380 nm. For a traffic sign installed on a bridge, the lamp can be installed in a spotlight at a distance of approx. 10 m in an easily accessible location.

EXAMPLE

A plastic plate with dimensions lmxlmxlO mm (length x width x height) made of cast polymethyl methacrylate (®PLEXIGLAS 218), containing 1 % by weight of the phosphor NP 657-09-01 and 0.5% by weight of barium sulfate, is provided with a thin (0.2 mm) film with a colored advertising print on one side. The plate is illuminated from the back at a distance of 1 m with a commercially available mercury black light lamp with a tube made of cobalt glass (radiated wavelength approx. 300-380 mn) and an output of 20 watts. The plate now appears white fluorescent, which means that advertising information is evenly backlit. The effect is clearly visible even in daylight and improves even further when the surroundings or the room in which the panel is placed are darkened. The light emitted is perceived as pleasant to the eye and significantly less dazzling compared to conventional illuminated signs.

Claims (4)

PROTECTION CLAIMS 1. Plate made of thermoplastically deformable plastic (plastic plate) suitable as a carrier of optical information, characterized in that it contains a white fluorescent phosphor that can be excited by long-wave UV radiation in the range of 300 - 380 mn. 2. Plastic plate according to claim 1, characterized in that it contains 0.5 - 2 wt.% of the phosphor. 3. Plastic plate according to claim 1 or 2, characterized in that it consists essentially of polymethyl methacrylate. 4. Plastic plate according to one or more of claims 1 to 3, characterized in that it contains barium sulfate in a concentration of 0.2 to 2% by weight.