By Dr. Edward D. Cohen
The web-coating process manufactures a wide variety of new and novel as well as upgraded current products. Each will have very different requirements such as coating weight, drying capacity, quality, coatweight uniformity, Td & Md uniformity, substrate thickness and type, and solvent needed.
To ensure that all products being coated can be made with excellent quality, at the required sales volume, and at low cost, it is essential to know the performance capability of the web-coating line being used. The needed product-process parameters must be attainable with the original design limits and current capabilities. The product may be able to be coated and still operate outside of these limits, but the quality, cost, uniformity and reproducibility will be compromised.
In addition, new concept products being developed may not be coatable because they require coater parameters that cannot be achieved. For example, the range drive for a coater designed to coat a thick substrate (over 7 mils) may not be capable of uniformly transporting a thin film (under 1 mil) without distorting the substrate.
High-tech but low volume
The number of new and upgraded products produced by the web-coating process is continuing to expand and has wider product requirements. One of the characteristics of these new products is typically that they will be specialty materials with relatively low volumes. And as previously stated, each will have very different requirements. As a result, the coating machine has to be versatile and capable of meeting these needs.
Usually, all new products will start the manufacturing cycle on an existing coating line, which may have been designed, fabricated and installed many years ago and thus may not have the capability to meet the new product’s needs. Often new materials are not a commercial success because the required properties could not be economically achieved due to a fundamental limitation of the existing coater that could not be overcome. Also, if a product is being made close to a specific hardware limitation, it can result in deficiencies, when normal variability results in occasionally operating the coater outside of its design limits.
Know your limitations
Another factor to consider is that often when product deficiencies occur, the cause is traced to operating outside of the web-coater design and current capability. Often this situation is not thought through and limits problem-solving efforts.
Also, when development personnel are designing new products, they need to understand the coater’s operating parameters to ensure it meets requirements. If the current system is insufficient, the product must be modified or another manufacturing source found. (see Converting Quarterly, Coating Concepts, 2019 Q4, page 16, for information on the role of contract coaters and converters). Fundamental coater limitations can be a major obstacle in developing new products and must be considered.
The web-coating process
The web-coating process typically includes 15 components). This encompasses 10 basic hardware modules and 10 ancillary modules.
These modules are designed to provide a specific treatment to the product, such as formulate solution, apply coating to substrate, dry the wet coating, transport the substrate through the coating line, so that the final product meets all of its requirements to be a commercial success. Each module also has many hardware components that must be specifically designed and fabricated to produce the intended product requirements. These designs typically have a range of parameters so that the coating line is versatile enough to handle more than just one unchanging product.
References
E.D. Cohen, “Web Coating Defects: Role of the Coater Module,” Converting Quarterly, 2012 Q4, page 22.
R. Wagner, Jr., and E.B. Water, Solvent-Based Coating Technology, Multilayer Flexible Packaging, Elsevier, 2nd ed., 2016.
J. Greener, G. Pearson, and M. Cakmak., Coating & Solidification in Roll-to-Roll Manufacturing: Process Elements and Recent Advances, John Wiley & Sons, 2018.