Effects of Particle Size on Mixtures During Nonelectrostatic and Electrostatic Powder Coating

Abstract

Two mixtures, 44 and 256 mm NaCl and 64 and 191 mm starch, were nonelectrostatically or electrostatically coated onto an aluminum target. The coating processes cause the proportion of each powder in the mixture to be different on the target than in the initial mixture. First, some loss of powder occurs during the targeting step; thus, not all of the powder land on the target. This targeting loss is caused by the individual powder characteristics and interactions that occur between powders in the mixture. Also, an uneven distribution is produced on the target due to the way the powder is dispersed. Finally, adhesion loss occurs on the target, also due to individual and mixture characteristics. During nonelectrostatic coating, the largest cause of the change in proportion was targeting losses. During electrostatic coating, the largest cause was adhesion loss. Interactions in the mixture decreased the change in proportion, except for nonelectrostatically coated NaCl. PRACTICAL APPLICATIONSFood coatings consist of mixtures of powders of different sizes. It is desirable to maintain the same proportions of the powder components on each food sample as in the applied coating. Mixtures change proportions due to differences in particle size, so all of the powders in the mixture should have a similar size range to reduce changes during coating. During nonelectrostatic coating, the differences in targeting losses are the biggest cause of this change, so coating systems need to be designed to minimize the differences in targeting losses. Electrostatic coating reduced targeting loss by a large amount; therefore, it is one method to reduce the change in proportions caused by targeting 1 Corresponding

The influence of particle size on separation and dustiness in powder mixtures during nonelectrostatic and electrostatic coating

“…4). A decrease in transfer efficiency of fine powders and an increase in transfer efficiency of coarse powders in starch mixture were also observed by others [15]. For some powders, such as NaCl, KCl and soy protein, the changes in transfer efficiency was significant, while for other powders the trend was the same but was not statistically significant.…”

“…Greater transfer efficiency for coarse powders than fine powders due to gravity force was also found by others [8,13,19]. Not only differences in targeting loss cause separation, but also the differences in adhesion loss cause separation, particularly when the mixture is coated electrostatically [15]. Finally, differences in dust production also contribute to loss and separation of the powders.…”

“…A higher transfer efficiency of coarse powder than fine powders has been reported by others [3,13,21]. In a previous study, the difference in individual transfer efficiency was the biggest cause of separation in mixtures of NaCl and starch [15].…”

“…Separation can negatively affect flavor and appearance of the final product. While the composition of the powders contributes to the separation of mixtures [6], particle size has been reported to cause separation in a mixture as well [15,20]. Differences in particle trajectory cause the separation in the mixture containing powders with different size.…”

“…In a mixture of coarse and fine powders, differences in adhesion loss increase the separation. Fine powders with a higher charge adhere well on the target and increase the adhesion loss of coarse powders by creating a charged layer and repelling the incoming coarse powders [15]. However, in a mixture with similar size powders, using electrostatic coating decreased separation by decreasing targeting loss and adhesion loss of powders in the mixture [6,16].…”