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A method of encapsulation of inorganic additives with organic materials was developed to improve the fine power flowability and film quality for powder coating. The flowability tests angle of repose (AOR) and avalanche angle (AVA) were conducted for the coating samples to characterize the effectiveness of the encapsulated additives on group C fine powder flowability. The results show that both AOR and AVA are significantly affected by the encapsulating materials, the encapsulating material weight percentage, as well as the total loading ratios of additives added in fine powders. Polyester shows the best performance on the modification of the additive due to the high similarity to host powder coating. AOR/AVA first decreases and then decreases with the encapsulating material weight. An optimum percentage exists at approximately 10%. A similar trend is observed with the additive loading ratio, and the minimal AOR/AVA is obtained at additive loading ratios between 0.5% and 0.8%. The effective surface area coefficient (η) was introduced to improve the adhesion force model to determine the optimum additive loading ratio for various host particle and additive particle sizes, which agrees well with the experimental results. [ABSTRACT FROM AUTHOR]

Ultrafine powder coatings have superior film performance but poor flowability due to the high interaction between particles, which can be improved by the addition of inorganic flow additives. However, the improvement is limited and more importantly, the film performance deteriorates because of their incompatibility with the organic coating resin. In this study, a resin encapsulation approach was proposed to modify the commercial inorganic flow additives for the improvement of powder flowability and maintaining film quality. The effects of resin content and additive dosage on the flowability characterized by angle of repose (AOR) and avalanche angle (AVA), and film performance characterized by gloss, seed density and surface roughness were systematically investigated in two powder coating systems. It was found that the encapsulation of additives with the same resin of the host powder coating can enhance both flowability and film properties, compared to commercial nano-silica. With the increase of resin content, both the AOR and AVA first decrease to a minimal value at resin content of 5 % to 10 % and then increase when applying excessive resin encapsulation. Similar to the effect of resin content, there is also an optimal additive dosage at 0.3 to 0.5 wt% for the best flowability, while excessive additives lead to "bridge effect". The negative effect raised by the additives on film quality can be mitigated by resin encapsulation. Higher gloss and lower roughness are obtained at larger resin content, while the smallest seed density is at resin content of 10 %. The study provides an effective and facile way to ameliorate the function of the flow additive and enhance the properties of powder coating films. • A new strategy of encapsulation of flow additive with coating resin is proposed. • The encapsulation improves the compatibility between coating and flow additive. • The modified additives perform better in improving powder flowability. • The modified additives maintain better coating film properties. [ABSTRACT FROM AUTHOR]

Abstract: The characterization of powder flow properties is often required for reliable design and proper operation of industrial processes. The effect of the state of compaction and bed voidage on bulk solids flowability is probably the most critical area of understanding. The goal of the present study is to compare traditional characterization techniques with methodologies provided by the FT4 Powder Rheometer (Freeman Technology). The data from six different methods, covering low to high stress levels, were compared to examine the hypothetical relationships between them. These techniques were also evaluated with regard to their ability to discriminate between different powders. To make a comparison of the testing methods, a range of seven materials was selected to cover the entire range of fine powders, i.e., from nanoparticles to group B powders. The results showed that the characterization techniques clearly have different working ranges depending on the level of cohesiveness of the powder. The powder rheometer was found to allow quick and reproducible measurements of the powder response to various environments. The different blade testing methods provided data that were in good agreement with traditional characterization techniques. However, the powder rheometer measurements were difficult to interpret because they depend on many physical properties and environmental parameters. They were particularly useful to compare similar materials but did not allow good discrimination between very different materials. A more detailed understanding of the physical phenomena involved in blade testing techniques is still needed. Finally, this study showed that powders and bulk materials cannot be viewed as invariant entities. Their flow properties cannot be predicted by only one indicator. The connection of several characterization methods is required to ensure a complete understanding of the powder flow properties over a wide range of conditions. This approach allows better insight into the powder/process relationship. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]