Coating of Pharmaceutical Powders by Fluidized Bed Process. VI.1) Microencapsulation Using Blend and Composite Latices of Copoly(Ethyl Acrylate-Methyl Methacrylate-2-Hydroxyethyl Methacrylate)

Abstract

An aqueous acrylic latex which could exhibit a low degree of agglomeration, low membrane permeation and high coating efficiency was developed using copoly(ethyl acrylate (EA)-methyl methacrylate (MMA)-2-hydroxyethyl methacrylate (HEM A)) whose molar ratio was 6 : 12 : 8 or 12 : 6 : 4. Blend latices composed of the hydrophilic 6: 12 :8 latex and the hydrophobic 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°C) of the 12 : 6 : 4 copolymer. In addition, the release of lactose from the microcapsules coated with the substances, even if cured by heating, could not be sufficiently suppressed, with a fraction of fast releasing microcapsules remaining due to a variation of the membrane structure formed by the random packing of latex particles. Hence, composite latices composed of the low permeable 12 : 6 : 4 copolymer core and the nonadhesive 6 : 12 : 8 polymer shell were synthesized. A 6 : 4 (core : shell) composite latex formed a low permeable membrane by curing, so that the microcapsules of 53—63 pm lactose 40% coated with it released only 10% of its lactose at 3 h without an initial burst. Moreover, composite latices exhibited a very 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 pm. At a 50% level of coating, the mass median diameter of the product was 16 pm and it contained only 3% agglomerates. These results showed that by using the composite latex, the particles of the order of 10 pm could be discretely coated as single-core microcapsules in the Wurster process, a kind of spouted bed process assisted with a draft tube. © 1994, The Pharmaceutical Society of Japan. All rights reserved.