- January 10, 2013, Mark Miller
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When coating a fluid onto a substrate, many factors come into play – chemistry of the fluid, surface tension of the substrate, curing conditions, slitting requirements, tension control of the web, etc… All these factors are interactive and require understanding of the limits and boundary conditions within each. These inherent limitations of the overall coating process provide the framework for the process engineer to understand the tweaks and turns that will develop the coating window of a given product. If you remember from past discussions, the coating window is the key to profitability in a coating facility. To maximize product yield, you need to know where the coated product is good and where it fails. By pushing the process to its limits and mapping the extent of these variables on a graph provides you with an understanding of a process that the coating can survive in.
However, the process engineer shouldn’t spend all available time hovering over the coating station. Ultimately the largest bottleneck of a coating operation tends to be the curing station; or more specifically, the energy available to manipulate the coating capability of a given product. Energy plays a significant role in the process of coating a fluid onto a substrate. The fluid and substrate both have an inherent amount of energy exhibited at the surface where they come in contact. If the energy within the fluid is high, relative to the substrate, the fluid will attract itself more and form droplets (i.e. coating defects). If the energy of the substrate is high, relative to the fluid, the fluid will be unable to resist the attractive force of the substrate and be willing to wet out the surface (i.e. good coated product). The key is to encourage the fluid to like this new dissimilar material it is coming in contact with and spread evenly over a large surface area.
In addition to the surface energy interactions of the fluid and substrate, the energy for curing can be the project focus if a new product has energy or economic requirements that surpass the current equipment capabilities. Many technologies exist for curing fluids in place on a given substrate-
1. Oven: Heat as a curing source is the most common form of energy that a coating manufacturing site utilizes. Awareness of oven profiles, energy sources, and line speed limitations are important to developing the framework of the coating window for a site.
2. UV: Light as a curing source allows for energy with less heat to chemically bond fluids into position on a substrate and can reduce the need for extensive ovens. Fluids that are opaque are not allowed in this technology platform and chemical end-group reaction knowledge is required.
3. E-beam: Electrons as a curing source allows for penetration of the fluid (even in opaque circumstances) for an extent of cure that has less concern with dwell time.
4. Reactive chemistry/cooling: Some fluids are self-reactive and just require time before hitting a face side idler. Cooling drums provide a quenching system for exothermic or hot melt coated products.
Whether these energy sources will match your current, growing, or changing needs is a critical question for both the product development team and the facility manager. Keep energy as a variable in the coating window mathematical function, and your business will succeed.
If you are interested in discussing this concept further, contact Mark D. Miller, Founder and CEO of Coating Tech Service, LLC (www.coatingtechservce.com) at email@example.com or (612) 605-6019.