Preparation And Characterization Of Microencapsulated Colored Electronic Ink

Electronic ink display, as one of the electronic paper technologies has been the subject of intense research and development for applications in creating a flexible low-cost paper-like display. Electronic ink displays are fully reflective type display devices, which utilize electrophoretic phenomena of charged pigment particles dispersed in a colored solvent. Microencapsulated electronic ink concerns numerous microcapsules which is applied to encapsulate electrophoretic medium containing electrophoretic particles, suspension medium, charge control agent dispersion stabilizing agent. This paper mainly covers the preparation and characterization of colored electronic ink, especially the micro-encapsulation process, and the relationship between the characteristics of capsules and the performance of electronic inks.In the article, titanium dioxide was coated by polymethyl methacrylate to make white particles. Meanwhile, organic pigment Hansa Yellow 10G was selected as yellow electrophoretic particles, didecyl dimethyl ammonium chloride (BTC 1010) as charge control agent, and tetrachloroethylene-cyclohexane mixture as suspension medium. Hansa Yellow 10G was processed by three different methods including pulverization, ultrasonic bath and hyper-dispersion.Polyurea (PU) microcapsules were fabricated from tolyene 2,4- diisocyanate (TDI) and triethylene tetraamine (TETA) by interfacial polymerization method. Emulsifier influencing the dispersing process were experimentally investigated, including OP-10,Span 80,Tween 80 and SDS. PU microcapsules were characterized on structure, mean particle size, size distribution and morphology. The resulted microcapsules were clear, round, transparent, flexible and uniformly distributed, with a mean diameter of 80μm, a wall thickness of 1.5μm and a good sealing property. We have also found that the wall thickness of the microcapsules depends on the capsule diameter. Furthermore, by modifying triethylene tetraamine with glutaraldehyde, a kind of much stronger capsules were prepared. On the other hand, urea-melamine-formaldehyde (UF/MF) resin microcapsules were prepared by in-situ polymerization method, which gave better morphology and optical properties than pure UF resin. In addition, we have synthesized a kind of novel double layered microcapsules with PU as inner layer and UF as outer layer, which has a ultra-thick wall of 7μm.PU and UF/MF microcapsules were applied for making encapsulated electronic ink respectively. The electric response behavior of the electronic ink was studied under electrostatic field. The negatively charged yellow particles moved reversibly and quickly inside the PU microcapsules while the electric field alternated, with a response time of 150 ms approximately at E = 30V/mm. While in UF/MF capsules, the response time was 120 ms and no decline was detected after 5000 times of repeat.