A coating applicator is a very reliable process and can effectively coat a variety of products over a range of process conditions, i.e., line speed, viscosity, coverage. The applicators are durable, and with appropriate maintenance and optimization the hardware can have an extended lifetime—over 20 years. Older coating methods, such as Meyer rod and roll coaters, are still in widespread use even though they were introduced at the start of the 20th century. However, a coating method can be become obsolete when it is no longer useful for current applications. Experience and familiarity with the method can make it hard to determine when it should be replaced.

In determining whether a specific method is obsolete, the converter needs to depend on the specific technical and economic requirements of the product and process. It's possible for a coating method to be obsolete for one set of requirements and adequate for another. There are several performance indicators that can be used to determine if the method is obsolete.

• The first indicator is the narrowing of the process coatability window, that region of process conditions in which the optimum results are achieved. All coating methods have a region in which good quality product is produced. When process conditions start to move out of the optimum region, the coating does not fail catastrophically. Instead, the applicator will continue to coat, but there will be a gradual reduction in quality, reproducibility and yield. Normal process variability can also make this type of obsolescence hard to determine.
• Process experiments should be run to determine the coatability window for specific formulations. To do this, coatings should be made over a wide range of conditions, viscosity, thickness, gap, line speed, etc., so that both good and defective materials are made. The quality can be evaluated at the applicator or by drying the product and then evaluating. From this data, a graph that shows the window where good product is made is produced. If this region is too small for routine production, or actual operating conditions are outside of the window, then the method is approaching obsolescence and an alternative method should be found.

Another indicator of coating-method obsolescence is that new-product requirements may not be achievable with the methods in use. New products tend to be much thinner than previous products, need improved quality and may require a much more uniform coating. Since each method has a specific range in which it can achieve these properties, the method in use may be obsolete because it cannot achieve these properties.

Environmental protection requirements can also lead to obsolescence. The use of a volatile solvent in an open coating system, such as a roll coater, can lead to excessive vapors in the atmosphere which may exceed allowable levels—thus rendering the applicator obsolete. Changing to a closed system, such as slot-die, will often allow environmental requirements to be met.

New formulation and product requirements can be another indicator of obsolescence. If the formulation performance properties contain a rapid-acting ingredient or are sensitive to aging after mixing, then any method in which the coating solution is recirculated will have a long variable aging time before coating—thus making the coating method obsolete. Similarly, if the product requires multiple layers, and the converter must apply the coating in two passes, then the method is obsolete, and a new method such as slot-die or slide coating should be considered.

The economic considerations of the current process can also lead to obsolescence. Market conditions can create the need for a significant improvement in costs and productivity to be profitable. To accomplish this, a major increase in coating speed may be required, which may not be possible with the current method. High-speed methods such as curtain coating or reverse-roll should be considered.

Perhaps the most important indicator that a change is required is the quality and cost of your competitor's product. If they have better quality and lower prices, the reason may be that they have a better process, which makes your process obsolete.

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