Process vs. substrate
The quality of the coatings deposited are still open to improvement, but it is not clear if the responsibility for achieving this would be through a process change or simply starting with better quality substrates. Most metallized coatings suffer from pinholes, and a major source of these are from film surfaces that have particulate contamination where the particles may be metallized and then moved later leaving behind pinholes in the coating where the film is without any coating. Practically, it is hard and costly to produce high volumes of film that are free from contamination, and so metallizers look to modifications of the deposition process to limit this problem.
It has been shown that by using tacky rolls it is possible to improve the film-surface quality, but the current limitation in film length that can be reliably treated by this method inside the vacuum system. The tacky-roll process transfers the particles from the film to a high-tack accumulation roll but, as the particles are accumulated, the available area of high-tack surface reduces, and so the efficiency of the cleaning declines. On winding systems at atmospheric pressure, it is possible to refresh the high-tack roller by peeling off the saturated top layer periodically so that the next layer becomes exposed to the particles on the transfer roll. If there are sufficient layers available on the high-tack roll, it is possible to maintain a high efficiency of cleaning of the film even for very long film rolls.
To make use of this technology requires an automated system to be developed that can reliably and sequentially peel away the high-tack layers in vacuum at defined distances throughout the length of the substrate roll. The solution would need to be capable of working at widths compatible with the current metallizer widths available, and the solution would need to be cost-effective.
A truly significant development
This is only one development I would regard as significant. The tacky-roll cleaning system is already available and is used on relatively narrow, R2R vacuum systems at low speed and short lengths, and so there will be a number of engineering problems to overcome to make this robust and acceptable before it could be implemented. This option has been known about for years but still has not been developed, which I believe is typical of the slow rate of change of the aluminum-metallizing industry.
This lack of progress is the reason why there are few papers on aluminum metallization that are submitted to R2R vacuum-deposition conferences. Once upon a time, it was possible to attend a conference where half of the papers presented were on aluminum metallizing, whereas currently it is rare to get a whole session of three or four papers on the topic.
If you think I am wrong, I look forward to hearing from you or, better still, I look forward to sitting through your papers on your latest developments at the next AIMCAL R2 Conference USA.