Study On The Preparation Of Carboxyl Spiropyran Based-Photochromic Microcapsules And Its Application In Hydrophobic Security Paper

Organic photochromic materials have broaded application prospects in the fields of intelligent paper packaging,spinning products and anti-counterfeiting materials due to their bright colors and sensitive color changes.However,the photochromic molecules of this type of materials are unstable and easily affected by the external environment,resulting in poor fatigue resistance,which restricts their market-oriented development.Microcapsule technology can improve the external environment of color-changing materials,reducing the chance of contact between photochromic molecules and the outside world and thus to prolong their service life.At the same time,certain control methods can be adopted to enable immediate release,timed release or long-term release of photochromic molecules.And other features to achieve diversified functions and expand its application prospects.In order to solve this problem,this paper first used Fisher Alkali and salicylaldehyde derivatives by aldol condensation to synthesize carboxyspiropyran(SPCOOH).Subsequently,the photochromic compound(PC)containing SPCOOH was used as the core material,the melamine-urea-formaldehyde(MUF)prepolymer was used as the wall material,and the styrene-maleic anhydride copolymer(Styrene-maleic-anhydride,SMA)as an emulsifier,successfully prepared photochromic PC microcapsules,and applied it to the field of hydrophobic anti-counterfeiting paper.This paper explores and improves the stability of organic photochromic molecules,broadens the application field of photochromic materials,and has certain reference value for the development and application of photochromic anti-counterfeiting paper.Its main research results are as follows:(1)SPCOOH was synthesized by the aldol condensation of Fisher base and salicylaldehyde derivatives.The effect of solution medium on the photochromic properties of SPCOOH was explored.The kinetics of the extinction process of SPCOOH in different solvents was analyzed.The results show that the extinction process of SPCOOH in solution conforms to the first-order kinetic equation,and the extinction rate of SPCOOH in different solvents: chloroform>ethyl acetate>acetone.(2)On this basis,using SPCOOH-containing PC as the core material and partially etherified MUF resin as the wall material,SPCOOH-containing photochromic PC microcapsules were prepared by in-situ polymerization.The effects of different process parameters on the surface micromorphology,particle size,discoloration characteristics and anti-fatigue performance of PC microcapsules were studied.Through careful analysis of the effects of emulsifier content,emulsification time,wall-core ratio,initial p H value and SPCOOH concentration in PC core material on the preparation process of PC microcapsules,the optimal process synthesis conditions were determined as follows: emulsifier is 3.0 wt %,the emulsification time is 12 min,the initial p H is 5.6,the wall-core ratio is 4:3,and the concentration of SPCOOH in the core material is 0.452 wt%.The results show that the initial p H value and wall-core ratio have a great influence on the surface micromorphology and discoloration performance of PC microcapsules.After UV irradiation,the color difference value ?E* of PC microcapsules reached 22.3.After 16 cycles of irradiation,the color difference value ?E* of PC microcapsules tended to be stable,and the color difference value only decreased after 30 light-resistant fatigue cycles 4.08,PC microcapsules synthesized under the best conditions have good light fatigue resistance,light responsiveness and light reversible cycling characteristics.(3)A mixture of PC microcapsules,cetyltrimethylsilane,methyltrimethoxysilane,ammonia and anhydrous ethanol is used as a coating,and it is attached to the filter paper by spraying to prepare a super hydrophobic anti-counterfeit paper.The effects of spraying amount and PC microcapsule concentration on the hydrophobicity,discoloration,air permeability,opacity,wet and dry tensile strength and micro-surface of hydrophobic anti-counterfeiting paper were investigated.Experiments show that when the spray volume is 12.5 m L and the PC microcapsule concentration is 12 g/L,the prepared hydrophobic anti-counterfeiting paper has excellent color-changing properties,hydrophobic properties and physical properties.This work provides a new way to broaden the functional application of photochromic materials.