| With the development of nanotechnology,the fluorescent properties of quantum dots have attracted attention from the researchers.Zinc oxide quantum dots(ZnO QDs)are a wide band gap semiconductor material that can be excited by a light source of a specific wavelength to fluoresce at room temperature.Compared with other semiconductor quantum dots and organic fluorescent dyes,ZnO QDs have high abundance in nature,relatively simple preparation,low cost and no biological toxicity.Using ZnO QDs instead of traditional organic fluorescent materials to synthesize water-based fluorescent inks has broad application prospects in the field of anticounterfeiting printing.In this paper,3-aminopropyltriethoxysilane(APTES)was used as the surface modifier to obtain hydrophilic ZnO QDs.We used the quantum dots as the fluorescent dye,water as the solvent,and polyvinylpyrrolidone(PVP)as the viscosity modifier to prepare fluorescent ink that was suitable for screen printing.At the same time,we proposed different kinds of fluorescent ink dot combination anti-counterfeiting method to realize more secure multiple anti-counterfeiting.The ZnO QDs prepared by the sol-gel method were unstable in water,easy to agglomerate,and had poor fluorescence characteristics.We modified the surface of ZnO QDs with APTES.According to the analysis of the structural properties,crystallinity,radicals and optical properties of the ZnO QDs,the results showed that the modified ZnO QDs in a regular spherical shape were uniformly dispersed in water,and the average particle size was 7.4 nm.There were the silicon coating and hydrophilic groups on the surface.Under the excitation of 365 nm light,the modified ZnO QDs aqueous solution emitted bright yellow fluorescence,and the fluorescence intensity was more than three times that of the unmodified ZnO QDs.We explored the influence of the pH value and ZnO QDs concentration on the fluorescence performance of the ZnO QDs aqueous solution.The PVP was chose as the viscosity modifier.The fluorescence and printability were used as the evaluation indicators to prepare water-based fluorescent anti-counterfeiting ink.We tested the rheology and resistance of the ink to make it meet the application requirements of screen-printing inks.The results showed that when the pH was 7.5,the concentration of ZnO QDs was 4%,and the content of PVP was 0.15～0.17 g/m L,the stable ZnO QDs water-based fluorescent ink was formed,and it had great printability.It emitted obvious yellow fluorescence under ultraviolet light and had good resistance.Therefore,the fluorescent ink could meet the anti-counterfeiting requirements of fluorescent ink and had broad application prospects in the field of anti-counterfeiting green packaging.According to the halftone technology,color light additive method,fluorescence quenching of the ZnO QDs by acid,and acid resistance of the organic fluorescent ink,the different kinds of fluorescent ink dot combination anti-counterfeiting method was proposed.The homemade ZnO QDs fluorescent ink and organic fluorescent ink were printed with a combination of 50% dots.The color patch showed colorless under natural light and orange red under UV light,which had anti-replication.After the acid treatment,the fluorescence color changed.The difference between the two fluorescent colors before and after the acid treatment was obvious,which could be used for anti-counterfeiting identification.The effectiveness of this method was achieved from several aspects,such as the anti-replication of micro-dots,the variability of dot percentage,and the significant discoloration before and after acid treatment.The ZnO QDs water-based fluorescent ink prepared in this paper has the dual characteristics of functionality and environmental protection,which can be used for anti-counterfeiting packaging of food,medicines and clean daily necessities.Combining applicable printing methods and anti-counterfeiting methods,the beautiful,safe and effective product packaging can be achieved.The ZnO QDs ink will has wide application prospects and achieve better economic and social value. |
