CLEAR LIQUID SEPARATION IN LATEX PAINTS CONTAINING CELLULOSIC ASSOCIATIVE THICKENER SYSTEMS

Clear liquid separation (CLS), often referred to as syneresis, is the spontaneous appearance of a transparent liquid over an opaque paint du ring storage. Often this occurs after months or years of aging, but ca n happen in as little as several hours. Although this problem has been observed in latex paints containing cellulosic or urethane type assoc iative thickeners (HEUR), it is particularly prevalent when both thick ener types are combined. The Cleveland Society for Coatings Technology Technical Committee undertook a project to investigate variables affe cting clear liquid separation: cellulosic molecular weight, cellulosic /HEUR ratio, ethylene or propylene glycol level, surfactant level and hydrophilic-lipophilic balance (HLB), pigment volume concentration (PV C), and nonvolatile by volume (NVV) content of the system. The results suggest that clear liquid separation can be predominately attributed to the use of two mutually exclusive thickening systems. Factors which improve the thickening efficiency of one may be detrimental to the th ickening efficiency of the other. Understanding these interactions and striving for balance in the thickening mechanism through careful sele ction of blend ratios, surfactant types, and the appropriate physical properties for the coating can greatly reduce or eliminate a substanti al amount of this phenomenon.