Study On The Preparation Of Low-temperature Reversible Thermochromic Microcapsule And Its Application In Coating

Thermochromic coating has been widely used in safety marking,chemical anti-counterfeiting and other aspects.However,most of them were changed at high temperature range.Low-temperature thermochoromic materials are mostly organic materials,which are greatly influenced by the pH of surrounding environment.Microcapsulation can be used to overcome the defects.Preparing stable low-temperature thermochoromic coating by adding thermochromic microcapsule into emulsion,is becoming a new direction.In this study,the preparation technology of thermochromic materials,thermochromic microcapsules and thermochromic coatings was studied.Simultaneously,the properties of microcapsules and coatings were investigated.In this paper,myristyl alcohol,bisphenol A and crystal violet lactone with the mass ratio of 1:3:60 were used as the core-material to prepare thermochromic microcapsules.The color-change temperature was studied by using DSC.The transformations of thermochromatic materials' structure were analyzed by using FTIR,and the mechanism was discussed.The microcapsule was prepared by in-situ polymerization with PVA and n-butyl aldehyde as the exterior membrane.The optimum conditions were determined as follows: the mass ratio of PVA and n-butyl aldehyde was 0.65:1,the pH range of prepolymer was 4~5,core-shell ratio of microcapsule was 2.5:1,the concentration of emulsifier dosage was 4%,the temperature of polymerization was 65?,and the stiring speed was 1500 r/min.The color-change temperature,exterior appearance and diameter distributing range were determined by DSC,SEM,TEM and laser diameter analyzer.The results revealed that the surface of microcapsules which is made in this condition is smooth.The thermochromic properties of microcapsule show very well.The microcapsules have clear core-shell structure,and the particle size distribution is 0.9~1.3 ?m.Based on elastic acrylic emulsion as base stock,the thermochoromic coating was preparated by adding dispersant,thickener,defoaming agent and flatting agent as accessory ingredient.Meanwhile,thermochoromic microcapsules,talcum powder and light calcium carbonate as the filler was added into the above mentioned coating.In the color paste,the contents of microcapsule and light calcium carbonate were 18.75% and 8.33%,respectively.The dosages of dispersant and thickener were 1.67% and 0.88%,respectively.The ratio of fillers and binders is 1.5:1.And the formula of the coating is given in the experiment.The test shows that the color-change temperature range of thermochoromic coating was 37.9~40.1 ?,and the basic properties can meet the technical indicator.