Effect of functionalities of binders on rheological behavior of alumina suspensions and properties of green sheets

Abstract

The effect of functionalities of acrylic binders on rheological behavior of aqueous alumina suspensions and properties of green sheets was investigated to find optimal conditions for the tape casting process. The functionalities of binders were 35, 20 and 10 mg KOH/g. These binders had almost the same glass transition points (Tg) and molecular weights (MW). Suspensions containing binders with low functionalities showed high shear-thinning flow behavior and high yield stresses. The resultant green sheets had low packing densities, low strengths and small elongations. In contrast, suspensions containing binders with high functionalities showed low shear-thinning flow behavior and low yield stresses. Suspensions gave green sheets with high strengths and large elongations in this case. As functionalities of binders increased, the amounts of adsorbed binders on alumina particles decreased and solubilities of binder sheets in aqueous solutions increased. It is found that the dispersibility of suspension is controlled by adsorption of binder on alumina particles and binder solubility in aqueous solution. It is also found that the strength of green sheet is determined by that of binder sheet. The results are interpreted as follow; increase in functionality enhances the cross-linking of chain molecules in the binder by forming hydrogen bonds between carboxylic acid sites.