Production of photochromic nanocomposite film via spray‐coating of rare‐earth strontium aluminate for anti‐counterfeit applications

New photochromic film was developed toward the preparation of anti‐counterfeiting documents utilizing inorganic/organic nanocomposite enclosing a photoluminescent inorganic pigment and a polyacrylic binder polymer. To generate a translucent film from pigment/polyacrylic nanocomposite, the phosphorescent strontium aluminum oxide pigment should be well‐dispersed in the solution of the polyacrylic‐based binder without agglomeration. The photochromic nanocomposite was applied efficiently onto commercial cellulose paper documents utilizing the effective and economical spray‐coating technology followed with thermofixation. A homogeneous photochromic film was immobilized onto cellulose paper surface to introduce a transparent film changing to greenish‐yellow upon exposure to ultraviolet light as depicted by CIE coloration measurements. The photochromic effect was monitored at lowest pigment concentration (0.25 wt%). The spray‐coated paper documents exhibit two absorbance bands at 256 and 358 nm, and two fluorescence peaks at 433 and 511 nm. The morphologies of the spray‐coated documents were explored. The spray‐coated paper sheets showed a reversible photochromic effect without fatigue under ultraviolet irradiation. The rheology of the produced photochromic composites as well as the mechanical properties and photostability of the spray‐coated documents were studied. Photochromic activity of novel nanocomposite film switching color from off‐white under visible light to green‐yellow under ultraviolet light for anti‐counterfeiting purposes.