Plastic additives often contain metal ions. Sometimes the plastic formulation itself contains metal ions to achieve a better gliding effect. Some metal ions can cause changes in brightness and color force in fluorescent pigments and dyes. This is due to ion complexity with the fluorescent pigment components. Zinc and calcium salts of fatty acids are the most common metallic lubricants. Tests with additives containing zinc and calcium at the same time gave that the hue of the fluorescent pigment changed as follows:
- The intensity of the color change is directly proportional to the amount of metal components added.
- In pink-and magenta formulations, zinc and calcium have different effects on color nuance.
- In general, zinc causes a blue shift with reduced UV fluorescence, while calcium causes a yellow shift without affecting UV fluorescence.
- Yellow nuances are generally less sensitive to changes.
- These effects are stronger at higher processing temperatures.
- In equivalent formulations, which are applied with other types of plastic, the effects can be very different.
- Different types of pigment have different effects.
Metal-free lubricants, such as polyethylene homo polymers and modified waxes, hardly change the brightness and hue of the fluorescence pigment. They’re more inert. Fluorescent plastic pigments based on resins containing a remainder of unresponsive acid groups may react with fillers such as calcite and dolomite (especially at high temperatures) releasing Ca + + or Mg + + ions that Completing the fluorescent components and thus leading to fluorescence erasure. Iron ions also react under fluorescence erasure with fluorescence pigments. It is recommended to intensively examine whether it affects the brightness and hue of each additive to a fluorescence plastic system, especially if it is a metal ion containing additive.