Abstract
Fumed silica is one of the most commonly used flow additives in the powder coating industry. To investigate the influence of the properties of fumed silica on powder coatings, three different types of fumed silica, Aerosil R812, R972, and R8200, were selected and introduced to an ultra-high-gloss powder paint by the dry-blending method with preset mixing conditions and times. Their effect on the powder flowability, coating application related properties and film properties were carefully studied. The angle of repose (AOR) and bed expansion height data, which represent the semi-dynamic and dynamic flowability of powders respectively, show a strong flowability enhancement for the powders with additives, and R812 exhibits the best performance compared to 8200 and R972, mainly due to its high hydrophobicity and specific surface area. For the ultra-high-gloss powder paint, all the flow additives cause slight gloss reductions, surface roughness increase and a significant effect on the distinctness of image (DOI). The addition of R972 is beneficial to the transfer efficiency of powders compared with the other two, while the additives impose only a minor influence in the Faraday cage effect. The melting and curing dynamics, i.e., gel time, and inclined plate flow, are not affected by the flow additives.
Highlights
Powder coatings are occupying an increasing proportion of the coating industry around the world
Flow additive is usually used to improve the flowability of powder coatings [7,8], which is a vital property of powder coatings, representing the ability of the powders to be handled and having a great influence on powder storage and transportation, fluidization, spraying process, and even the Coatings 2020, 10, 977; doi:10.3390/coatings10100977
It is known that powder flowability can be characterized by different techniques that matches the known that powder flowability can be characterized different that (AOR)
Summary
Powder coatings are occupying an increasing proportion of the coating industry around the world. A systematical study was conducted with three grades of widely used fumed silica flow additives, which were blended into one of the most commonly used powder coating: polyester powders. This powder coating system serves as the work horse in outdoor applications, because of their good weather resistance, such as on outdoor aluminum profiles and steel structures, courtyard metal appliances, highway guardrail boards, car wheel hubs, etc., while it is finding more and more applications on non-metal substrates like plastics and wood etc.
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