Carrier webs are used in roll-to-roll (R2R) processing for a number of reasons. They can provide a support for a substrate that will have the coating deposited upon it. It may be that the substrate is too fragile or stretchy or non-continuous to survive being wound and coated directly, but by providing a suitable supporting web, it becomes possible for the substrate to withstand the process.
Webs such as non-wovens, if coated in a typical R2R coater, would be wound around a cooled deposition drum that would become coated as the non-woven material has gaps between the fibers and some deposition will pass through the material. In this application the carrier web protects the deposition drum from being coated.
Using a carrier web can affect the process. As it adds more material into the vacuum system, it may increase the surface area, and so the outgassing rate of the web, and depending on how the carrier and substrate are attached it may change the heating/cooling characteristics of the substrate. So, often the use of a carrier web may result in a reduced production rate, but this is tolerated as it provides other valuable benefits.
Multiple-use carrier webs?
Some carrier webs can be reused many times whereas others are unsuitable for reuse. In the manufacture of flake pigments, some manufacturers apply a release coating onto the carrier web, deposit the coating and then separate the vacuum-deposited coating from the carrier using the release-layer properties. In some cases, the carrier web may have a new release layer applied, thus enabling its reuse. With some processes it is difficult to return the surface quality to the original state and, so to maintain the quality of the pigment, it requires the carrier web to be used only once.
In many applications, a key part of using carrier webs is the release layer which enables the carrier web to be separated from the substrate. A frequently employed example of this would be transfer foils where the aim is to control the adhesion of the vacuum-deposited coating to the substrate such that using any or all of heat, pressure and a higher-strength adhesive allows the metallized coating to be transferred to a different surface. In this example, the vacuum-deposited coating is the final product and the substrate is the carrier web.
Other applications use the release coating to enable a thin film to be temporarily laminated to a more substantial flexible substrate, which may provide dimensional and thermal stability to the thin substrate film during the deposition process. Following deposition, the thin web is released from the thicker, less-flexible substrate permitting the final product to be on a thinner, much more flexible web. This application is used in the flexible-electronic industry.