The Preparation of Electrophoretic Display Microcapsules and the Building of Y-Shape Micro Channel Reactor
|Keywords||Electrophoretic particles Surface modification In-situ Polymerization Electrophoretic display microcapsule Preparation condition Y-shape micro channel reactor|
The electronic paper which is based on electrophoretic display has already been a research hotspot. The key technology of the electronic paper is in the preparation of microcapsule electronic ink. Microcapsule electronic display, however, exhibits some defections such as monochrome display, slow renew frequency, only applying color filter tabula rasa and mainly using inorganic particles as electrophoretic particles etc.Y-shape micro channel reactor manufactured by the technology both of surface micromachining and of precision machining, is mainly used for the study of organic synthesis. When using Y-shape micro channel reactor, two reaction-liquid can be emulsified evenly and highly dispersed emulsion can be obtained. As the result, the uniform and size-controlled microcapsules can be prepared. So far, the applications of preparing microcapsules by Y-shape micro channel reactor were rarely reported in China.In this paper, electrophoretic particles containing phthalocyanine blue and TiO2 were surface modified to improve their dispersibility in tetrachloroethylene (TCE). Infrared Spectrum, Scanning Electron Microscope (SEM) and thermogravimetry analysis (TG) were used to characterize the result of modificated samples. The microcapsules used for electrophoretic display were prepared by in-situ polymerization. The core material contained electrophoretic particles (phthalocyanine blue and TiO2) and TCE, and the wall material were made of melamine-formaldehyde resin. The Optical Microscope, SEM, Surface Tensiometer and Static Light Scattering were used to characterize the particle size distributions, surface morphology and coating rate of microcapsules. The type and concentration of surfactant, the ratio of core material to wall material and the pH values were all experimentally investigated. Meanwhile, Y-shape micro channel reactor was built. The effect of different flowing phase and speed ratio on microcapsules preparation was studied respectively using Optical Microscope.The main results are summarized as follow:Octadecylamine can used to modify phthalocyanine blue, which had poor dispersibility in TCE. Hydrogen bond can be observed between Octadecylamine and phthalocyanine blue by FTIR, so that the dispersibility of phthalocyanine blue in TCE was enhanced greatly. The results of dispersing extent test suggested that the dispersing extent of phthalocyanine blue in TCE was up to 90%. Hence the modified phthalocyanine blue is suitable for being electrophoretic particles. 3-(trimethoxysilyl) propyl methacrylate (K570) was used to modify the TiO2, whose density is 4.0g/cm3 and surface is hydrophilic. Si-OH can be generated by the hydrolysis of K570. Then the Si-OH and the-OH which was on the surface of TiO2 formed the hydrogen bond. As a result, K570 was fixed to the surface of TiO2. Thus the surface of TiO2 was turned from hydrophilic to lipophilic. If the lipophilic TiO2 was coated with polystyrene (PS), styrene and C=C double bond of TiO2 can copolymerized. Therefore, TiO2/PS Core-Shell particles were obtained. Due to the similar density,1.78g/cm3 of TiO2/PS Core-Shell particles and 1.62g/cm3 of TCE, the modified TiO2 is suitable for using in electrophoretic display.After selecting different types of surfactants, macromolecule surfactant of Styrene-maleic anhydride copolymer (PDA) was found to be the appropriate surfactant for the preparation of melamine-formaldehyde resin microcapsules. The optimum preparation condition was as follow: concentration of surfactant is 1.0wt%, mass ratio of core material to wall material is 2.5, and pH value is 5.0.Microcapsules could not be formed with the built Y-shape micro channel reactor. It might be related to the capsulation reaction. However, the emulsion was of regular morphology. If the mechanism of capsulation reaction can be studied further, the microcapsules with regular morphology are expected to be prepared.