COATING OF PHARMACEUTICAL POWDERS BY FLUIDIZED-BED PROCESS .6. MICROENCAPSULATION USING BLEND AND COMPOSITE LATICES OF COPOLY(ETHYL ACRYLATE-METHYL METHACRYLATE-2-HYDROXYETHYL METHACRYLATE)

An aqueous acrylic latex which could exhibit a low degree of agglomera tion, low membrane permeation and high coating efficiency was develope d using copoly(ethyl acrylate (EA)-methyl methacrylate (MMA)-2-hydroxy ethyl methacrylate (HEMA)) whose molar ratio was 6:12:8 or 12:6:4. Ble nd latices composed of the hydrophilic 6:12:8 latex and the hydrophobi c 12:6:4 latex exhibited a very low degree of agglomeration. However, the coating operation had problems with particle adhesion and cohesion due to the low softening temperature (26 degrees C) of the 12:6:4 cop olymer. In addition, the release of lactose from the microcapsules coa ted with the substances, even if cured by heating, could not be suffic iently suppressed, with a fraction of fast releasing microcapsules rem aining due to a variation of the membrane structure formed by the rand om packing of latex particles. Hence, composite latices composed of th e low permeable 12:6:4 copolymer core and the nonadhesive 6:12:8 polym er shell were synthesized. A 6:4 (core:shell) composite latex formed a low permeable membrane by curing, so that the microcapsules of 53-63 mu m lactose 40% coated with it released only 10% of its lactose at 3 h without an initial burst. Moreover, composite latices exhibited a ve ry low degree of agglomeration, with the polymer yield remaining very high, and they did not induce any adhesive behavior. These properties were still effective even in the coating of corn starch as fine as 12 mu m. At a 50% level of coating, the mass median diameter of the produ ct was 16 mu m and it contained only 3% agglomerates. These results sh owed that by using the composite latex, the particles of the order of 10 mu m could be discretely coated as single-core microcapsules in the Wurster process, a kind of spouted bed process assisted with a draft tube.