The use of fluorescent adhesives differs throughout the world.
The United States, the world's largest user of disposable diapers and thus the largest adhesive user, has no restrictions on fluorescent raw materials.
In Europe, however, some companies actually enhance the fluorescence of the adhesive formulation as a quality control measure so that the adhesive bondline can be seen under UV (fluorescent) light during the application process.
In Asia the use of fluorescent adhesives in nonwoven assembly applications is prohibited due to a Japanese law that equates fluorescence with carcinogenicity. This was precipitated by a discovery that fluorescent aromatic stamping oils used in the metal industry were carcinogens. From this observation, Japanese legislators drew the unsupportable conclusion that any material that fluoresces must be carcinogenic. While it is generally recognized that this legislation is based on badly flawed science, the Japanese government has proven reluctant to reverse it, and it has become the standard of the industry throughout Asia.
The nonwovens industry, including the assembly of diaper and feminine hygiene products, is obliged to use raw materials that will not fluoresce. Therefore, low- or non-fluorescing raw materials used in hot melt adhesives must be used in combination with ultra violet (UV) absorbers to eliminate residual fluorescence.
Hydrogenated hydrocarbon resins are the preferred resin choice for many formulators in major adhesive industries due to their light color and excellent thermal stability. Their fluorescence under exposure to UV radiation is an inherent property due to their chemical nature.
This property can be used to an advantage and therefore many European manufacturers of assembled products install UV light sources on their adhesive bonding lines in order to be able to see where the adhesive has been applied. Under the UV light any adhesive containing such resins will fluoresce brightly.
Figure 1 shows a spray pattern of a colorless hot melt adhesive fluorescing under UV at 365nm. Ordinarily the colorless adhesive would be very difficult to see under normal daylight and high coating speeds.
Figure 1: Spray-Coated Hot Melt Adhesive Viewed Under UV Irradiation @ 365nm