Monochrome Micron Capsule Electronic Ink Display Performance

Electronic ink display, also called microencapsulated electrophoretic image displays, is a non-emissive device based on microencapsulating the electrophoretic materials into individual microcapsules. This not only solves the particle agglomeration and lateral drift on a scale larger than the capsule size, but also realizes bistable display into the microcapsules. Today, microencapsulated EPDs are becoming one of the most appealing applications in electronic paper because electronic ink can be printed onto a suitable substrate to realize flexible display. By now, the research of electronic ink display is focused on monochrome displays, while full-color electronic ink display has been rarely reported. This paper focused on study of microencapsulated organic pigment electrophoretic liquids system.In this paper, the TiO₂ particles and pigment benzidine yellow (PY-12) have been used to prepare the microencapsulated electrophoreic ink by complex coacervation method using Gelatin and gum Arabic as wall materials. The responsive behavior of the microcapsules is also investigated under a DC electric field. In addition, electrophoretic display prototype was prepared by coating electrophoretic ink microcapsules slurry on ITO glass with nearly single layer and sealed by adhesives. The characters "Xigongda" was firstly displayed under a DC electric field. The experimental results are given as following:1. TiO₂ particles coated with PMMA were prepared via in situ polymerization. Before and after modified with PMMA and the contact angles between the particles and the tetrachloroethylene are measured. It is found that the modified particles have superior affinity for tetrachloroethylene. A kind of white electrophoretic ink microcapsules is prepared by complex coacervation using the modified TiO₂ particles as white pigments, tetrachloroethylene as dispersion and Gelatin and gum Arabic as wall materials. The morphology and size of microcapsules were checked through optical microscope. It was shown that the microcapsules were of good smoothness and transparence.2. A microcapsules containing organic pigement for electrophoretic display is prepared by complex coacervation of Gelatin and gum Arabic, in which organic pigment of benzidine yellow modified with octadecyl amine is taken as displaying particles, tetrachloroethylene and toluene as suspending fluid, oil soluble black dye as light absorber and Span 80 as stability agent. From the optical microscope images of shell surface, the microcapsules have relativelysmooth surfaces and the average thickness is well-proportioned. The response to the electric field (0.25/um) and display performance of microcapsules were also investigated. Fast and reversible display by the microcapsules was achieved in an electric field.3. In order to investigate the influence of octadecyl amine on the surface modification of the benzidine yellow particles, the dispersibility of the particles and the contact angles between the particles and the tetrachloroethylene are measured. It is found that the dispersing extent and lipophilicity of the benzidine yellow particles are improved due to their surface modification with octadecyl amine, and the electrophoresis velocity of the modified particles in tetrachloroethylene (TCE) is increased by five times compared to that of unmodified ones.4. Electrophoretic display prototype is prepared by coating electronic ink microcapsules dispersing in hydrosol solusion slurry on ITO glass (nearly single layer) and sealed by adhesive. The image is displayed under a DC electric field. It is found that elctrophoretic ink microcapsules containing TiC>2 particles has higher contrast, driven electric field (2.5V/um) and poor stability, but those ones containing benzidine yellow particles display has lower contrast x driven electric field (lV/um) and excellent stability.5. Electronic ink microcapsules in narrow dispersity are prepared by complex coacervation using Gelatin and gum Arabic as wall materials. The effect of various parameters, such as the content of sodium dodecyl sulphate (SDS) and agitation rate are investigated. From experiment, the average diameter and dispersity of core droplets decrease as the concentration of SDS and agitation rate increase. On the whole, narrow-dispersed microcapsules of various diameters can be obtained in controllable ways.6. From the research of microencapsulating technologies, the optimum process of the microencapsulation using gelatin and gum Arabic (GA) as wall materials is: the temperature is 40-50 "C, the concentration of SDS is 0.001 -0.015wt%, and the stirring rate is 700-900 rpm. The microcapsules prepared by the optimized process have the merit of even size, smooth surface and regular morphology. The average diameter and thickness is about 40um and 2u.m, respectively.