There are many parts of vacuum coating that are time-dependent. There are the obvious ones such as the aging of the film surface with time and temperature and, similarly, the aging of the aluminum as the oxide thickness grows with time.
Increasingly there is interest in the effects that can be produced by the use of nanoparticles. This includes carbon nanotubes. The speed of development of coatings and filled films is relatively quick in comparison with the speed of health and safety testing of the particles and the coatings or films into which they are incorporated.
We have seen plenty of work being done to increasing the rate and efficiency of manufacturing carbon nanotubes and are already seeing products that incorporate carbon nanotubes. As with all new materials we do not truly know the risks that these new materials pose. It has long been a concern that the carbon nanotubes have a similar aspect ratio to asbestos which in some forms is known to be a cause of cancer. It is possibly no surprise that the following information was reported in Current Biology in the Nov. 6, 2017, issue and is now being referenced in other journals and magazines such as AZO Nano as follows: "Currently, researchers have demonstrated for the first time in mice that long and thin nanomaterials known as carbon nanotubes could possibly have the same carcinogenic effect as asbestos: they can trigger the development of mesothelioma."
This has been seen only for certain high aspect ratio carbon nanotubes. Where the tube length is shorter or the tubes are tangled, the body is able to isolate and coat the material and then the body can dispose of the foreign body.
What it does flag up is that whenever using a new material it is better to be overprotective in the way the material is handled. It is far better for the workers to be inconvenienced in the short term to protect them from harm in the longer term.
I am old enough to remember the scare stories about cooking using aluminim saucepans and the link to Alzheimer’s that was publicized by the press but never proven.
What was apparent from the reporting is that there was little or no recognition that the surface of the aluminum is aluminum oxide and not the metal. Ceramic-coated saucepans were deemed safe whereas aluminum metal was demonized as potentially harmful. It did raise the question of what happens to operators of aluminum metallizers in the long term, and is there a higher than average proportion of them who go on to develop dementia? I imagine that this a very difficult question to answer as the exposure to aluminum dust when cleaning is an huge variable, operators may not stay in the job for very long, and each operator will respond differently. Also the numbers of people involved in metallizing in any one country is low, and so it would take a long time or collaboration across the world to obtain meaningful numbers.
This leads me to the conclusion that although aluminum metallizing has been done for 75+ years, in many ways it should still be classed as a new process as the long-term effects are still unknown. This means that the protective clothing and working practice should err on the side of caution as we still do not know what possible long-term effects could be slowly occurring.