A New Concept for Powder Coatings to Reduce Manufacturing Costs and Increase Throughput
Although some dispersion and color development of the pigment may occur during the dry-blending and mixing stages, the majority of the two processes, dispersion and color development, generally occurs in the extrusion stage, as this is where the majority of aggregates and agglomerates are separated into primary particles. If, as so often is the case, not all of the tinctorial strength of the pigment is developed, a decision as to whether to re-extrude must be made. This decision is made based upon cost of the pigment, the ability of the resin system to withstand additional heat, the effect on film properties, the ability to demonstrate a sufficient strength increase, and the physical ease or difficulty of performing this operation in production relative to the potential gain.
When a single pigment is involved, the decision is usually easier to make and often carried out after a short time of running, by testing the production material in the laboratory. The screw speed may then either be increased or decreased, depending upon the intended outcome. It is obvious that decreasing screw speed will increase residence time and may increase color development; it also reduces throughput and may have some effect on film appearance and performance.