Coating of pharmaceutical powders by fluidized bed process. IV. Softening temperature of acrylic copolymers and its relation to film-formation in aqueous coating.

Abstract

The softening temperature (Ts) of films of commercially available and newly developed acrylic copolymers for aqueous coating was measured by thermomechanical analysis. The results are discussed in relation to the film-formation of their latices in the Wurster process. Methacrylic acid (MA).sbd.ethyl acrylate (EA) (1:1) copolymer dispersion (Eudragit L30D-55) containing 10% triacetin exhibited excellent film-forming ability in coating at a temperature (31.degree.C) far lower than its Ts (91.degree.C). The product exhibited no stickiness during drying at 60.degree.C. The dissolution properties were little changed by heating at 60.degree.C. On the other hand, the copolymer dispersion consisting of hydrophobic acrylic esters and minor quaternary ammonium esters (Eudragit RS30D, Ts = 83.degree.C) did not form a film under the same coating conditions in spite of its Ts being lowered to 49.degree.C by the addition of 10% triacetin. The product was sticky during drying at 60.degree.C. The copolymer consisting of only hydrophobic esters (Eudragit E30D) had a good film-forming ability due to its low Ts (18.degree.C), but the product was too sticky to be discrete particles even at room temperature. With the aqueous dispersion of EA-methyl methacrylate (MMA).sbd.2-hydroxyethyl methacrylate (HEMA) copolymer, newly developed in the previous study, the hydrophilic HEMA enhanced the film-formation. In particular, the EA.sbd.MMA.sbd.HEMA (6:12:8) copolymer exhibited excellent film-formation in spite of its high Ts (78.degree.C), and the prolonged release characteristic of the product was not changed by heating it at 60.degree.C. These results suggested that hydrophilic residues such as carboxyl and hydroxyl contribute to film-formation of the latices.