Web Coating Process Characterization and Measurement Technology
Introduction
Edward D Cohen
Success in all endeavors starts with an understanding of the basic skills that are needed for the endeavor and the ability to successfully implement these basics.1 One of the better examples of this was the Green Bay Packers Power Sweep, which was developed by Vine Lombardi I the 60’s. This play would gain on average 4 yards per carry and worked almost 100 % of the time. It was the key to Green Bay’s winning record in the 60s. The success for this play was the lineman’s basic ability to rapidly pull from the line, effectively block and create the path for the runner. There was no deception of elaborate schemes, it just required implementing the basics. Interestingly no other team was able to duplicate the power sweep, because the lineman could not implement the basics.
The same is true in Science and Manufacturing. The Scientist needs an understanding of the laws of Thermodynamics, Kinetics, Chemical reactions and Mathematics to successfully develop new products and processes. Without these basics the projects will take longer, be more expensive and possibly not function as effectively as needed.
In manufacturing, one of the basics for an effective process is the ability to accurately and reproducibly measure and control process parameters. The web coating process is complex and has several elements with many process variables in each element. The appropriate process variables must be measured and controlled to insure process quality, uniformity, reproducibility and reduce defect losses.
A detailed list of the basic process measurements needed for a web coating machine is outlined in Table 1.
There are three classes of variables in web coater. The first type are those which are part of the control loops that are used to maintain needed process conditions, i.e., line speed, dryer air conditions, web tension, coating solution temperatures. These variables are dynamic and can vary over short time periods. They must be closely monitored and controlled for an effective process. Examples are web temperatures and lines speeds. The second class is those variables that are relatively stable and can change over a longer time. A control loop is not needed but they should b monitored. They variables are typically set at the start of a coating run. Examples of this class are dryer nozzle velocity and coating applicator gaps and roll speeds. The third class is those variables that are important to coater operation and can provide defects. Examples of this class are the return drying air conditions, filter pressures ambient air conditions in coater room, vault etc. If these defects are not routinely measured there are portable instruments that can be used. All of these variables should be recorded for analysis and troubleshooting if defects are subsequently found.
As a result of modern technology the cost of the needed technology is falling and reasonable cost accurate, sensors are available to measure a wide range of process properties. Once acquired, the data can be stored in digital format in a computer system for easy retrieval and analysis by anyone with a need.
The next article in this series will discuss available instruments and the use of obtained data.
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