Pigments fluorescent

The resins used to make fluorescent pigments are usually toluenesulphonamide-melamine-formaldehyde matrices. The dyes used for this purpose include Cl Disperse Yellow 11, Rhodamine 6G (Cl Basic Red 1) and Rhodamine B (Cl Basic Violet 10). More details of the fluorescent dyes used have been given in a review by Christie [31]. 

Unfortunately, the fluorescent effect is not directly proportional to the concentration of colorant present, since there is considerable quenching if quite low concentrations are exceeded. The light fastness of the fluorescent pigments is also less than that of many other organic pigments now available, but improvement can be achieved using overlayers containing ultra-violet absorbers. This is an area in which further research will clearly be needed. 

A recent survey of the technical and environmental aspects of inorganic pigments by Schwarz and Endriss [33] has put the importance of these products into numerical perspective. Of a total worldwide production of some 5M tonnes of pigments, 96% are inorganic. Of this 4.8M tonnes, carbon black and various whites account for 84%, that is just over 4M tonnes. This means that world production of coloured inorganic pigments is approximately 0.8M tonnes. 

The primary requirement for a compound to be of a white appearance is that it should not absorb any of the radiation in the visible part of the electromagnetic spectrum, that is, of wavelengths between 400 and 650 nm in practice this is seldom attainable and slightly less 

White pigments, some of rather variable composition, that have been used in the past include white lead (Cl Pigment White 1), refractive index 1.9 zinc oxide (Cl Pigment White 4), r.i. 1.9 lithopone (Cl Pigment White 5), r.i. 1.84 zinc sulphide (Cl Pigment White 7), r.i. 2.3 antimony oxide (Cl Pigment White 11), r.i. 2.2. All have been eclipsed by titanium dioxide (Cl Pigment White 6). 

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Fluorescent dyes Fluorescent lamps Fluorescent lights Fluorescent pigments... 

Table 1. Important Dyestuffs for Daylight-Fluorescent Pigments...

Fluorescent Pigments. The first patents for daylight fluorescent products were issued in 1947 (9,10), describing fluorescent dyed cellulose acetate fabrics with several barrier coats to improve long-term stability. These fabrics were brilliantly fluorescent and were widely used during World War II as signal panels. 

Early fluorescent pigments were promoted and adopted for use in screen inks for poster boards and paints for safety applications. These thermoset pigments were not well-suited because of their poor fightfastness. Also, because of their relatively coarse particle size, their use in thinner film applications, such as gravure or flexo, was limited. 

Recent pigment technology has yielded a wide range of products which ate much mote specialized for individual end use applications. New polymers have been combined with improved dyestuffs to yield fluorescent pigments with better performance properties and economics, and more desirable environmental characteristics. 

The primary manufacturers of daylight-fluorescent pigment at the present time are Dane and Co. (London) Day-Glo Color Corp. (Cleveland, Ohio) Nippon Keiko Kagaku Co. Ltd. (Tokyo) Nippon Shokubai (Osaka) Lawter Chemical Corp. (Skokie, Illinois) Radiant Color, Division of Magmder (Elizabeth, New Jersey) Sinloihi Co., Ltd. (Kamakura, Japan) and U.K. Seung (Busan, Korea). Smaller regional manufacturers are located in China, India, Russia, and Brazil. 

Sometimes a darker material forms that bleaches on further exposure to the incident light. In any case, reasonable stabiUty to light is one of the most important requisites of a useful fluorescent pigment, but the most difficult to achieve. An interesting discussion of the products of photolysis of 4-methyl-7-diethylaminocoumarin [91-44-1] is given in Reference 19. 

A polyester-type fluorescent resin matrix (22) is made by heating trimellitic anhydride, propylene glycol, and phthaUc anhydride with catalytic amounts of sulfuric acid. Addition of Rhodamine BDC gives a bright bluish red fluorescent pigment soluble in DME and methanol. It has a softening point of 118°C. Exceptional heat resistance and color brilliance are claimed for products of this type, which are useful for coloring plastics. 

Another fluorescent pigment class (23) is based on a urethane-type resin the primary raw materials are isocyanates, amines, and hydroxy compounds. 

Table 4 shows daylight fluorescent pigments with approximately equivalent colors manufactured by U.S. manufacturers. In addition to the colorants listed, other colors are available such as purples and shades which are stronger and between the shades Hsted. 

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