Luminescent. Afterglow. Glow-in-the-dark. No matter how you define it, self-emitting light technology continues to make a positive impact on the coatings industry worldwide. Recent advances in this technology enable some luminescent pigments to emit light for a significantly longer duration after charging by exposure to daylight, white lamplight or UV radiation. Fluorescent pigments, normally used for security applications, emit light when excited by an energy source. Phosphorescent products, typically referred to as "afterglow" products, continue to emit light after the energy source has been removed.
Select luminescent pigments can be used in photo-luminescent materials such as surface coatings, plastics, ceramic tiles, coated glass and enamels. Coating applications such as safety signs and safety-way guidance systems in warehouses, underground stations, tunnels and office buildings, as well as in high-stress marine, aircraft and manufacturing environments, increasingly demand products that offer improved luminosity and long afterglow properties.
Luminescence Based on Unique ChemistriesLumilux
The Lumilux FamilyLumilux luminescent pigments are synthetically produced organic and inorganic compounds that absorb and emit energy as visible light or, in special instances, as infrared or long-wave UV radiation. These emissions occur immediately after exposure and can be brief or continue for hours.
The pigments are compatible with existing processing methods for coatings and are developed and manufactured in a variety of types, colors and particle sizes for a wide range of applications, including safety. Lumilux N and SN phosphorescent pigments with long afterglow properties, for example, are integrated with specially designed components of standardized silk-screen-printed safety signs, dispersion paints and resins. They continue to emit yellow-green light for many hours and are suitable for photo-luminescent materials.
Lumilux zinc sulfide-based Green N grades and the newer, much brighter alkaline earth aluminates SN pigments are used for phosphorescent safety applications, including afterglowing guidance lines for surfaces, direction signs, markings on staircases and handrails. These pigments do not gray when exposed to strong sunlight or UV radiation, making them suitable for outdoor applications. They are stable against organic solvents and heat resistant up to 500 °C. They also can survive in oxygen-free atmospheres up to 800°C without significant loss of brightness.
Lumilux long-afterglow pigments that have a finer grain size cannot be produced by grinding larger particles because this will damage the crystal structure. They are synthesized independently under unique crystallizing conditions. This process reduces the negative differential in luminance compared with larger-grain-size grades. Coating manufacturers also can determine the intensity of brightness by manipulating particle size. Generally, the larger the particle the more luminous the coating.
Meeting Safety StandardsThe International Standards Organization (ISO) Committee continues to draft new international testing standards for photoluminescent safety markings and signs based on an increased demand worldwide. Pigments must meet minimum afterglow performance. In North America, safety sign standards are developed and approved by Underwriter Laboratories (UL). Standardized DIN regulations from the American National Standards Institute (ANSI) are internationally accepted.
Other requirements and regulations for safety signage are continually proposed and monitored by a wide range of national and international organizations, including the National Fire Protection Agency and American Standard Testing Materials in the United States.
In 1997, the International Maritime Organization (IMO) enacted a resolution that required low location lighting systems (LLLS) on marine vessels and ships with more than 35 passengers. These systems, often based on luminescent pigments, are necessary to guarantee orientation of passengers during emergencies such as power failure or fire.
Turning Challenges into OpportunitiesThe ability to coat substrates such as plastic and metal with luminescent pigments continues to improve. With powder coatings you can use larger particles, which increases efficiency and offers reduced overall costs. This is opposed to extrusion, where smaller particles are used. These pigments are not limited to use in powder coatings. Coatings with luminescent pigments offer greater brightness derived from concentrating luminescent particles on the surface of the substrate.
Adhering to the various standards and regulations for the growing safety signage market worldwide challenges manufacturers to develop and refine more viable materials, especially for high-stress environments. Many facilities today demand materials with improved flame retardancy. Coatings for metal signage and other applications that are comprised of luminescent pigments, for example, provide the essential properties needed in today's competitive, safety-driven market.
Processing Techniques (Silk Screen Printing Inks, Resins and Paint)Lumilux afterglowing pigments suitable for inks, synthetic resins and paints should be applied with a white substrate to gain higher afterglow brightness. For use in inks, the viscosity should be approximately 4000 poise. UV absorbers are recommended for use in coatings in order to extend the life of the luminescence. Higher afterglow brightness demands significantly higher pigment loading. Many safety sign manufacturers apply pigment loadings up to 600g/m2 and achieve extremely long afterglow.
For enamels, better brightness is achieved when the substrate is coated with a white primer to improve light reflection. Low processing temperatures and short processing time aid brightness. Fabrics such as cotton, polyester and polyamide are suitable for coating with afterglowing Lumilux pigments. Coatings can be applied using PVC-, PU- and PE-proven binders. Typical concentration of Lumilux pigments for coatings varies between 20 percent and 24 percent by weight.
Other ApplicationsManufacturers achieve desired luminescent effects with Lumilux for a wide range of other applications, including brand security and authentication, unique artistic and visual effects for toys, and afterglowing logos for the textile industry.
Other applications include televisions and displays, x-ray fluoroscope screens, low-pressure mercury discharge lamps, cathode ray tubes, electro luminescent backlights, dials and dashboards. Lumilux pigments also are used in dental applications.
Sidebar:The UN Headquarters complex in New York provides office space for 4,500 diplomats and staff members from almost 200 countries. To enhance building safety, the UN recently installed an emergency egress pathway marking system. The system, based on acrylic products from Dura Architectural Signage, a Honeywell Specialty Materials customer, guides occupants toward stairwells and out of the building in the event of a fire or other emergency.
United Nations Headquarters
Shines During 2003 Blackout
The system was put to the test on August 14, 2003, when a blackout hit much of eastern North America, knocking out electric power to Manhattan. On that day, the UN was able to quickly and safely evacuate diplomats, staff and visitors because exit routes were clearly and brightly illuminated with DuraGlow® signs and markers.
The UN Headquarters building consists of 41 stories above ground, with offices along the perimeter of a long corridor and large work areas at each end. Shorter corridors branch off in four locations. Stairwells are located at opposite ends of the main corridor. Below ground are three basement levels, each more than four city blocks long. These levels contain numerous office clusters, satellite corridors, cul-de-sacs and a host of workshops, mechanical, electric, storage and security rooms. Twenty-eight stairwells connect the basement levels to either the main building lobby or the outside.
The UN considered installing electric, mechanical and chemical systems to illuminate pathways during a fire, blackout or other emergency. However, it ultimately selected a photoluminescent egress pathway marking system from Dura Architectural Signage. Called DuraGlow, the system does not rely on any external energy source for activation. DuraGlow acrylic safety products, such as escape route signs and egress guidance systems, can be quickly applied to mark exit routes.
DuraGlow uses Lumilux®, a photoluminescent pigment designed and manufactured by Honeywell Specialty Materials. Lumilux absorbs and stores energy after being exposed to ambient light - daylight, white lamp light or UV-radiation. When the lights go out, Lumilux releases energy and instantly begins to emit a glow that continues for eight hours or longer. Lumilux recharges automatically and rapidly as soon as light is restored.
At UN Headquarters, all aboveground corridors are marked with photoluminescent acrylic arrows pointing to the nearest exit and signal choices of stairwells, when available, to improve traffic flow. All stairwell doors are clearly marked, as are handles. In the stairwells, the steps, landings and handrails are marked. Stairwell door locations are identified, and Americans With Disabilities Act-compliant Braille/Tactile stair and floor information is applied near each side of each stairwell door.
In the basement levels, extremely long, uninterrupted corridors intersected by branching corridors could lead to serious confusion during an emergency. Accordingly, photoluminescent enhancements were added to facilitate movement of occupants toward numerous exit doors.
The UN Headquarters now has in place a cost-effective, environmentally friendly egress marking system, the DuraGlow system using Lumilux. It was put to the test during the August 2003 blackout, and was so effective that some employees who left the building and were unable to get home returned to the United Nations and spent the night there. They reported that the next morning, the safety signs in the interior of the complex were still glowing sufficiently to guide them out of the building again.