Preparation Of High-strength Gelatin-acacia Microcapsules And Their Performance For Electrophoretic Display

The electrophoretic microcapsules containing carbon black and TiO2particlesdispersed in tetrachloroethylene (TCE) were prepared by complex coacervationbetween gelatin and acacia, and the carbon black and TiO2particles in them wereprepared by ball milling. Various factors affecting the properties of the preparedmicrocapsules, such as the ratio of gelatin to acacia, temperature of the reactionsystem, concentration of surfactant, pH value and curing process, were experimentallyinvestigated. Meanwhile, the mechanical strength of the prepared microcapsules wascharacterized by the drop-ball test. The results show that the optimum preparationconditions are as follows: gelatin-acacia mass ratio1:1, reaction temperature50℃,SDS concentration0.001g mL-1, acetic acid concentration5.0wt%and glutaraldehydeconcentration10wt%. Besides, the microcapsule wall should be cured for60min atpH4.5to4.8(T=5℃) and then70min at pH8to11(T=50℃). Microcapsules withhigh mechanical strength and smooth surface can be obtained with more than90%yield by above technique, and their particle size distribution is in the range of30to80μm.When polyvinyl alcohol (PVA), polyurethane (PU), gelatin and cellulose were usedas adhesive for preparation of electronic ink, the display coating show a smoothsurface and good flexibility. The electro ink, which was prepared with the preparedcapsules and PVAin the mass ratio1:15, was coated with a blade (gap was0.45mm)on top of the anisotropic conductive layer on the ITO/PET film. At a pulse voltage of±15V, contrast ratio of the device prepared by the display coat was3.65. When theelectro ink was changed into the mixture of one part PU and40parts capsules andblade gap was set to0.35mm, contrast ratio of the device was6.58.At a pulse voltageof±10V, contrast ratio of the device composed of capsule layer including gelatinand capsules at mass ratio of1:65and formed at blade gap of0.40mm was3.25.When the capsule layer was prepared with the mixture of cellulose and capsules atmass ratio of1:75coated at blade gap of0.45mm, contrast ratio of the device was4.45. It is found that the contrast ratio of the display device reaches the maximumvalue6.58with PU as adhesive and response speed of the device with gelatin asadhesive is most rapid and the response time is200~400ms. The drive conditions of microcapsule display were optimized. The white particlereflectivity of display device driven by the sine wave with amplitude of1V andfrequency of20Hz is up to the maximum value33.2%. The black particle reflectivityof display device driven by the triangular wave with amplitude of1V and frequencyof10Hz reach the minimum value4.7%and the device shows the best contrast ratio6.78.