Study On The Preparation Of Photochromic Material And Its Application In Anti-counterfeiting

The application of photochromic materials in various fields of life has attracted more and more attention.Photochromic materials include chemical and physical colors.Carboxymethyl cellulose(CMC)is non-toxic,soluble in water and has good film-forming properties.CMC has a broad prospect in the synthesis of functional materials.It can be used to obtain UV-excited fluorescence materials by combining with rare earth ions.Structural color is caused by optical interference phenomena such as Bragg diffraction caused by submicron periodic structure and color polarization of birefringent materials.It exists widely in nature and provides great possibilities for the application of new devices,sensors and optical encryption.In this paper,the carboxymethyl cellulose based rare earth composite fluorescent material was synthesized by co-precipitation method,and the structure color ink was synthesized by control variable and cross experiment method,and the performance of the two kinds of photochromic materials and the application in the field of anti-counterfeiting were studied in depth.Its main contents include the following three parts:Firstly,CMC/La F₃:Eu³⁺composites were prepared by co-precipitation method.CMC molecules contain a large number of hydroxyl groups around the surface,which can effectively adsorb La F₃:Eu³⁺nanocrystals.The functionalized CMC/La F₃:Eu³⁺composites were characterized by FT-IR,XPS,SEM,XRD,TGA and fluorescence spectra.Considering the characterization results of infrared spectroscopy(FTIR),photoluminescence spectroscopy(PL),field emission scanning electron microscopy(FESEM),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD)and thermogravimetric analysis(TGA),the optimal doping ratio of Eu³⁺and La³⁺can be 4:6?5:5.The doping concentration of rare earth ions can be in the range of 30%?40%,and the temperature of preparing CMC/La F₃:Eu³⁺composites is preferably 70?80?.Therefore,this experiment provides an effective method for preparing environment-friendly fluorescent materials,which is expected to be applied in the field of photoluminescence anti-counterfeiting.Then,using the control variable method to prepare the structure color ink formula with excellent anti-counterfeiting effect.Structure color ink has excellent heterochromatic effect,so it can be used in the field of anti-counterfeiting.The properties of the ink were characterized by NDJ-79 rotary viscometer,X-Rite spectrophotometer,Novo-Gloss glossometer,3M tape,etc.The effect of structural-color ink printing was characterized by camera and UV-NIR spectrophotometer.Acid and alkali reagents,digital air drying oven and refrigerator were used to characterize the resistance of structural ink.Considering the characterization results of viscosity,chroma,color density,glossiness,adhesion fastness,color difference,reflectance spectrum curve and resistance test,it was obtained that the proportion of pigment in the structural color ink was about 13%,the proportion of resin was about 27%?30%,and the proportion of pearling pigment to light change pigment was 2:8.At this time,the ink printing effect was the best and its light change effect and pearlescent scintillation effect are better.The light change pigment with small particle size can achieve soft discoloration effect,while the contrast of color change in the structure of the light change pigment with large particle size is obvious.The pearlescent pigments with smaller particle size can present soft pearl light,while the pearlescent pigments with larger particle size can present flash pearl light,and the scintillating effect is obvious.Finally,the photochromic material obtained by the above method is applied to the anti-counterfeiting field of printing and packaging.Firstly,CMC/La F₃:Eu³⁺composite film was prepared by casting method from CMC/La F₃:Eu³⁺composite material.CMC itself has a good film-forming property,and the CMC/La F₃:Eu³⁺composite film with good properties was prepared by adding an appropriate amount of additives.In addition,the structure color ink will be printed on the ticket through screen printing for the ticket product security.The properties of CMC/La F₃:Eu³⁺composite films were characterized by field emission scanning electron microscopy,fluorescence spectrometer,PTI universal testing machine,UV-Vis spectrophotometer and UV lamp.Considering the characterization results of field emission scanning electron microscope,fluorescence emission spectrum,stress-strain curve,light transmittance curve and UV excitation macroscopic optical image,the transparent anti-counterfeiting film prepared by us shows good fluorescence intensity,transparency and excellent mechanical properties.CMC/La F₃:Eu³⁺composites show stable luminescence intensity within 20 days.Therefore,this work provides an effective method for the preparation of environmentally friendly films,which is expected to be applied in the field of photoluminescence anti-counterfeiting.At the same time,the structural color prints were characterized by ultraviolet near infrared spectrophotometer,and the spectral reflectance curves of the prints at different angles were obtained.The obtained structural color anti-counterfeiting samples had better heterochromatic effect with different angles and obvious flicker effect,which had broad application prospects in the field of anti-counterfeiting printing and packaging.