Preparation And Application Of Dual-color Microencapsulated Electrophoretic Dispaly Materials

E-book is one of the most popular electronics in modern life due to the combined advantages of traditional paper and electronic display. As the core material of E-book, E-paper is using electrophoretic display (EPD) technology, where the charged particles in E-paper move in electric field to achieve the color display. At present, microencapsulated EPD is the mainstream of the commercial E-paper, while there is a certain shortage for the performance of microencapsulated EPD in people's vision, including the stability of the electrophoretic particles suspension in the electrophoretic liquid and the barrier property of microcapsules to minimize the release of the electrophoretic liquid.In this paper, to solve the above mentioned problems, first, we prepared a series of low density electrophoretic particles by inorganic/organic composite method. The particles can suspend stably in the medium and move rapidly under the electric field. Then, introducing the specific small molecular surfactants into the capsule wall materials, we prepared excellent performance microcapsules with low-cost and easy-to-obtain raw materials, gelatin (GE) and sodium carboxymethyl cellulose (NaCMC). Based on the obtained electrophoretic particles and microcapsules, we fabricated the EPD prototype devices driven at low voltage.N-(p-vinyl benzyl) phthalimide (VBP) was synthesized by N-alkylation reaction, which showed good solubility in non-aqueous solvents and high thermal stability. TiO2-g-PVBP composite particles were prepared via free radical polymerization. The effects of weight ratio of particle/monomer and reaction temperature on suspension stability and morphology of composite particles and the effects of type and the concentration of charge control agent on the electrophoretic characteristics were investigated. It is found that the composite particles with the apparent density of 1.9 g/cm3 can suspend stably in the medium with the particle/monomer weight ratio of 1/1 at 85℃. With 1.6 wt.% span85 as charge control agent, the zeta potential and the mobility of the composite electrophoretic liquid were 30.3 mV and 4.69×10-6 cm2/V·s, respectively. The poly (lauryl methacrylate) (PLMA) was grafted onto TiO2 surface via free radical polymerization. The prepared TiO2-g-PLMA composite particles with span85 can suspend well in the medium. The zeta potential and the mobility of the composite electrophoretic liquid were -37.1 mV and -5.74×10-6 cm2/V·s, respectively.Cu2Cr2O3-g-PLMA composite particles were prepared by grafting PLMA onto the surface of Cu2Cr2O3/SiO2 via free radical polymerization, with vinyl benzyl aminoethylaminopropyl trimethoxysilane as a coupling agent. The composite particles with span85 can suspend well in the electrophoretic liquid. The zeta potential and the mobility of the composite electrophoretic liquid were improved greatly to 62.5 mV and 9.81×10-6 cm2/V·s, respectively. Polyisobutylene succinimide (T151) were adsorbed onto carbon black surface. The prepared CB/T151 composite particles can stably suspend in the elctrophoretic liquid. The contrast of electrophoretic liquid with TiO2-g-PVBP/span85 as white particles and CB/T151 as black particles, can be up to 38.4:1 under 0.06 V/μm electric field.The GE-NaCMC-dioctyl sulfosuccinate sodium (DSS) microcapsules were prepared by complex coacervation method. The hydrophobic interaction between the double hydrocarbon chain of DSS and the non-polar chain of NaCMC is beneficial to improve the adsoption of NaCMC at oil/water interface. By optimizing the experimental conditions, the optical transparent, smooth surface, uniform microcapsules were obtained with 0.6mM DSS. The thermogravimetric analysis (TGA) and thermal release behavior results showed high thermal stability for the microcapsules. Morphology of microcapsules was characterized by scanning electron microscopy (SEM), and the results showed the elastic microcapsules with 300-400 nm thick capsule wall and the compact capsule wall structure.The fluorine was introduced into the capsule wall for the first time to improve the chemical resistance and the barrier property of the microcapsules using hydrocarbon/fluorocarbon composite surfactant. Surface tension and zeta potential of NaCMC with the mixture of sodium dodecyl sulfate (SDS)/perfluoro-nonene oxy benzene sulfonate (OBS) were analyzed, demonstrating that the hydrophobic interaction and the hydrogen bonding between NaCMC and SDS/OBS enhanced the adsorption of NaCMC at the oil/water interface and facilitated the formation of compact capsule wall. The obtained microcapsules were characterized in respect of morphology, particle size and thermal stability. Experimental results indicated that optical transparent microcapsules with uniform size, smooth surface and compact wall can be obtained by adjusting both the pH value of the reaction system and the concentration ratio of SDS/OBS. The elastic microcapsules with best thermal stability and barrier property were obtained with 0.5 mM SDS/0.2 mM OBS-gelatin-NaCMC at pH4.5.The clock display and matrix characters display (16×16 and 16×64) prototype devices were fabricated by coating the slurry containing microcapsules and adhesive on ITO/PET film, in static driven mode. The response time and the contrast ratio of prototype device with white particles and blue dye is about 800 ms and 2.7-3.2:1, respectively, driven at 9 V direct voltage (DC). The response time and the contrast ratio of prototype device with white particles and black dye is about 800 ms and 4.8～7.5:1, respectively, driven at 9 V DC. With 9 V DC, the response time and the contrast ratio of the prototype device with white and black electrophoretic particles is 1.4～2.0 s and 8.0-10.4:1, respectively.