Dynamic colour change of multifunctional thermochromic-fluorescent pigments

Abstract

The aim of presented paper was to prepare and characterise multifunctional thermochromic-fluorescent pigments with potential application in anti-counterfeiting patterns in security printing. Pigments were prepared by microencapsulation of chosen thermochromic system into melamine formaldehyde resin and the resin was modified with Uranine and Acid Red 52 fluorescent dyes, respectively. The fluorescence at low and high temperature was measured by spectrofluorometer. The concentration of 2.3 × 10–5 grams of fluorescent dye per one gram of polymer is sufficient for detection of fluorescence of modified polymeric shell. The dynamic colour change of prepared pigments was analysed in terms of cumulative colour difference obtained from reflectance measurements. Resulting multifunctional pigments exhibit much lower colour contrast and wider temperature sensitive interval in comparison with the bulk thermochromic system. However, the concept of two levels of verification based on two types of colour change embodied in one pigment has been approved.