Quality of Coated Particles: Physical - Mechanical Characterization of Polymeric Film Coatings

All coated particle producers, when applying the coating layer(s) would like to know precisely what is the best coating system to use in order to answer customer’s requests. It is, therefore, of very high relevance for many industries, to have a clear understanding of what are the parameters I need to trigger in order to generate the requested quality. Such understanding was the target of this work. The specific equipments designed at Delft University of Technology enabled us to measure the resistance to attrition and the resistance to abrasion of both reference coating agents and commercially pre-mixed coating systems. The resistance to attrition was directly related to the intrinsic properties of the coating material, to the process parameters used to apply the coating layer (fluid bed coating in this case) and to the conditions in which the particles are stored. The viscoelastic properties of the coating layers were measured by using nano indentation. Very good correlation between the viscoelasticity term, tan ?, and the resistance to attrition was found. Cast and sprayed films were produced as representation of the coating film. The morphology and the structure of coating layers were mimicked much better by sprayed films which could be obtained by novel equipment designed during this work. To assess the quality of the coating layer and determine how efficient the coating process was, X-Ray micro tomography in combination with image analysis was used. This gave us a very robust set of data which could be used to correlate the quality of the coating layer to the parameters chosen during coating process and those two with the final performance of the coated particles in respect of resistance to attrition/abrasion. Finally commercially available pre-mixed coating systems were used as case study. By comparing them with the reference coating agents we could proof and quantify how important are the additives, plasticisers in primis, in increasing the coating quality and, therefore, the resistance to mechanical stresses.