A case of pointing fingers
I can remember early in my career being told by a film supplier that all pinholes were the fault of the metallizer. Whereas the metallizers believed that their process was, not perfect, but was reproducible enough that particularly bad coated rolls must also have some inherent problems that were attributable to the film supplier.
Now we know that it is impossible to keep the film surfaces clean, and there will always be particulate contaminants on the film surface, any of which could result in a pinhole in the coating. We also know that if the evaporation process is kept stable, the number of pinholes is minimized and, conversely, that if the process is not kept stable, the number of pinholes rises. There also are papers that tell us that the more a film is handled the more defects will be present, that the number of surface particulates increases every time the film is slit, and that there are more particles present at the film edges than in the center of the web.
We have lots of information about what causes the problem of loss of barrier but not necessarily which of these factors is the most critical source of the problem.
It looks as if there is an opportunity for someone to grade the rolls of film before they are sold to whoever is going to coat them. I would assume the last operation that is done to the film, where it has to be unwound and rewound, would be where it is slit to width. If, on this machine, the film is also scanned to map out the number and size of the surface contamination, it also would enable the film to be graded with respect to what barrier performance might be expected of it once metallized. However, if the slitter is going to go to the expense and bother of measuring the defects, then surely it ought to be in their own interests to improve the surface quality by cleaning the film surfaces too, thus bringing down the number of particulates and increasing the potential barrier performance.
Predicting the performance by using data obtained during the process is fine and can be regarded as a manufacturing improvement. However, to me, it is still unsatisfactory because I know that the film could be produced with a cleaner surface which would produce an improvement in barrier performance. Simply by using a tacky roll to clean the web surfaces immediately before the rewind on the winder prior to the film going for metallizing would be an improvement.