Process Principles and Formulation of Redispersible Powder Coatings

Waterborne coatings have long replaced solventborne coatings in the architectural coatings industry. The key benefits of water are being non-flammable, non-toxic, and non-VOC. However, removing water from the paint container during transportation and storage may provide even more benefits, such as reduced transportation costs and emissions, removal of in-can biocides, improved storage capacity, and decreased packaging material. In order to do this, polymer dispersions –which are inherently produced in water– should be converted into a powder form known as Redispersible Polymer Powders (RPPs).

Two main methods for producing RPPs are spray drying, a fast and cost-effective process, and freeze drying, suitable for thermally sensitive substances but more expensive. Our experiments utilized the cost-effective spray drying method.
In this work, polymer dispersions were first mixed with protective colloids, and an anticaking agent was added to prevent the caking of produced powders. The mixture was then spray dried at elevated temperatures to evaporate the water and separate powders. Produced polymer powders should be able to reconstitute the original dispersions when mixed with water, ideally maintaining the original particle size. Therefore, redispersibility and particle size of the produced powders were analyzed and it was seen that the average particle size increased from about 0.3μm to about 5.0 μm under optimized process conditions. Film formation analysis of redispersed powders under SEM showed that the particle coalescence occurred. Paints prepared by using RPPs showed wet scrub resistance of class 2 according to ISO 11998, EN 13300 classification.

Moreover, a vast amount of parameters required the optimization of the process. It has been seen that by optimizing the process parameters, stickiness to the walls of the equipment was reduced, and free-flowing powders with increased yield and reduced particle size could be produced.

This study systematically examined the role of each component in the RPP formulation, emphasizing the significance of understanding the fundamental processes involved. The results demonstrate the importance of these factors in optimizing the production and performance of RPPs in coating applications.