Preparation Of Organic Reversible Thermochromic Microcapsule Pigment

The thermochromic material is a kind of intelligent material which changes color in the range of visible light absorption spectrum when heated or cooled in a certain temperature range. Among them, the organic reversible thermochromic materials suitable for low temperature conditions are the hotspots of domestic and foreign research because of the low price, bright color, rapid color change and the ability of color memory function to be used repeatedly. Therefore, it is widely used in military, textile, printing, anti-fake and construction and so on.In this paper, a series of organic reversible thermochromic complexes were prepared by changing the mass ratio between crystalline violet lactone, bisphenol A, 1-tetradecanol,hexadecanol and octadecanol. Through the comprehensive investigation of its discoloration performance, the optimal proportions of CVL and bisphenol A with 1-tetradecanol /hexadecanol / octadecanol were selected respectively as follows: 1:3:50,1:3:50, 1:4:50, the temperature range was 31.6℃～35.6 ℃,41.5 ℃-49.8 ℃,52.3 ℃-58.2℃ respectively,discoloration time were 76s,86s, 87s; color-recovery time were 31s,30s,34s,and the color transform repeatedly and reversibly between blue and colorless. By the analysis of IR and DSC, the thermochromic mechanism was summarized for the obtaining or losing the electrons among the molecules which is built on the basis of phase change.The microcapsules were prepared by the method of in-situ polymerization. Which core was organic reversible thermochromic material made by hexadecanol. And urea-formaldehyde resin was used as its shell. The best preparation conditions of the microcapsule were investigated as follows: n(urea):n(formaldehyde)=1: 1.5, the prepolymerization reaction pH of 8.5, the reaction temperature of 75 ℃, the reaction time of 1h. The core emulsifier of 5% arabic gum emulsified twice at 65 ℃ and 25 ℃ water bath. The optimum ratio (core to wall) of 1:7, the polycondensation reaction pH of 2.5, curing agent NaCl and anti-adhesion agent SiO2 of 8% within the weight of the wall prepolymer.The result of researches proved that the microencapsulation treatment has greatly improves the thermal stability,acid and alkali resistance and solvent resistance of organic reversible thermochromic materials, and has overcome its reliant to the environment. As a result, the new organic reversible thermochromic microcapsule pigments has excellent performance and prospected application.