(6f) Production of Powder Coatings by Intensive Granulation

This paper presents an alternative powder coatings (pigment filled polymeric particles) manufacturing process. We describe an intensive granulation process based on non-isothermal Flow Induced Phase Inversion (FIPI) phenomenon of Akay [1,2]. In this alternative powder coatings manufacturing process, a powder coatings composition in melt state is subject to a well-defined flow field while being cooled. As a result of flow induced phenomena and fractional solidification, granule nucleus are formed and consequently the effective dispersed phase volume is gradually increased. This leads the continuous phase (melt) to crumble and form granules. In a continuous process which include all stages of granulation (namely, melting, filler dispersion, cooling, mixing, spontaneous melt-to-powder transition (crumbling) and powder conveying), the location of crumbling is important for equipment design and process control. Here, we present a method of controlling the crumbling location and granule size and its distribution in powder coating formulations.

The experiments were carried out in a purpose-built granulator which operates in a parallel-disc rotor- stator configuration. Cavities are machined on the rotor and stator discs to achieve mixing and pumping/ conveying. The heat transfer is improved by injecting fluids into the melt being processed. The fluid injection appeared to have a profound effect on the granulation mechanism and controlling of crumbling location yet there is no evidence of any adverse product performance. A correlation between the fluid injection rate and the particle size and its distribution has been found. The process was compared with the conventional process, which is based comminution, with respect to the product characteristics. The particle size span, morphology, flowability and pigment dispersion characteristics appeared to be better in the intensive granulation compared to the product obtained by the conventional process although the conventional process produced finer particles.

References: 1. G. Akay, Flow induced phase inversion in the intensive processing of concentrated emulsions, Chem. Eng. Sci., 53, 203-224 (1998). 2. G. Akay, Method and apparatus for processing flowable materials and microporous polymers, WO 2004/004880 (2004).