Rheology of coating systems

[摘要] ENGLISH ABSTRACT: Desired behaviour of paint during processing, storage, application and after application is of greatimportance in the coatings industry. Rheology (the study of flow and deformation behaviour) isused as a method to investigate the behaviour of the flow and deformation properties of the paintduring these stages. Some of the more important phenomena that can occur during these stages,which were examined rheologically, are:1. The rheological behaviour of certain complex raw materials during processing - vesiculatedbeads suspensions11. The paint behaviour during storage - in-can stability, e.g. phase separation andsedimentation of particles;Ill. The paint during application - ease of application, spatter, etc.;IV. The paint behaviour after application - sag, layer thickness, levelling (ability to hide brushmarks), etc.A rheometer was used to obtain rheological curves from a paint sample (± 1 ml). Correctinterpretation of these curves, which display rheological properties of the sample such as theviscosity, shear stress, structural strength and many more, produced information about theproperties mentioned in i, ii, iii and iv above. It was found that the rheological data correlated wellwith empirical tests carried out in the laboratory for spatter, sag, levelling behaviour and in-canstability of the paint.A wide variety of paints were studied ranging from tough/durable outdoor paints to smooth/velvetyindoor paints. The rheological behaviour explained the specific end-use properties of the paints.Paints from two different companies were compared on a rheological basis. In some cases largedifferences in rheological behaviour were observed. Rheology modifiers were tested on a new paint.It was found that specific rheology modifiers could be incorporated into the formulation to give thespecific rheological behaviour required. Rheological modelling was performed and it was foundthat the flow behaviour of paint cou1d be modelled accurately with existing viscosity models(Ostwald/de Waal, Bingham, Casson, Herschel-Bulkley, Cross and Philips-Deutsch). Otherrheological properties of paint were also modelled successfully with a simple linear regressionmodel. Rheology was also used as a method to examine the flow and deformation properties of vesiculatedbeads, a component of paint with very complex rheology. The most important factors that influencethe rheological behaviour of the vesiculated beads were determined. It was found that the type ofmanufacturing process for the beads affected the rheological behaviour. The effect of the rawmaterials used to manufacture the vesiculated beads were rheologically determined.

[发布机构] Stellenbosch University