There are exceptions where some vacuum systems have been developed to deposit either planarizing or over coatings or both, either side of the evaporated aluminum or alumina.
There are an ever-increasing number of applications that currently require a combination of both types of coating. In many cases, because the vacuum coating part of the structure is regarded as the expensive coating because it needs to be done in vacuum, there is a trend to develop atmospheric-coated alternatives to replace these vacuum-deposited coatings.
There are alternatives; one is that we become more expert at using other coating techniques inside the vacuum system so that the vacuum coating chamber becomes more of a one-stop coating system. A second alternative is that we improve the design of air-to-air systems that make the vacuum system simpler and cheaper such that they are not regarded as the most expensive of the coatings.
The problem with the first option is that the view and access of the process may be limited because everything is enclosed by the vacuum chamber. This can make setting up the process or troubleshooting the process more difficult as to make changes may require venting the system first and then waiting for the system to pump down before checking the change was of benefit. Where wet coatings are applied the chemistry may need to be changed. Typically UV curable coatings are used so that large quantities of solvent do not need to be pumped away. As the process will be in vacuum there is no need for any nitrogen blanket or oxygen inhibitor to be included as the amount of oxygen present in the vacuum will be limited.
The second option has the attraction that all the atmospheric-coating processes stay the same. The difficulty in this case is how to integrate the vacuum coating system into the production line. Vacuum systems tend not to be compact and so there needs to be space enough to fit the system into any existing coating line.
On either of these options the ideal is not to have to try to fit existing equipment together but is to design an optimized integrated production line. This would maximize the benefits and minimize the down time. To be able to do this requires that all the separate processes have already been optimized separately and that the line speeds have been matched so that as far as possible the whole process has been tested before investing in new equipment.
This is possibly an optimistic view of what is possible, which is why the vacuum-deposition process remains a batch process, and there is no great effort to develop air-to-air systems.