Metallization is the process of adding a thin layer of aluminum to a plastic film in order to add barrier or optics to a package, or both. At Multifilm, we have a vacuum metallizer in-house, and here’s how the process works. A roll of plastic film to be metallized is inserted into a large vacuum chamber. Virtually all the air is pumped out of the chamber, leaving just a few oxygen molecules floating around in a near-perfect vacuum. Aluminum wires are then fed into heated ceramic “boats” that melt the aluminum. Since all liquids boil in vacuum, the melted aluminum turns into aluminum vapor. Several “boats” are placed just a few inches apart, creating a cloud of aluminum vapor. The cloud rises and hits the film just as it is traveling over a cold chill roller, and the aluminum solidifies instantly on the film.
The deposited layer of aluminum is extremely thin, at about 0.03 micron, and even though you can see through the film if you hold it up to strong light, it provides a tremendous barrier. We carefully control the amount of aluminum deposited, and thus the integrity of the barrier, by measuring the optical density, or the amount of light that is transmitted through the film.
We metallize a wide variety of substrates, including polyester, polypropylene, and polyethylene, as well as some of our proprietary twist films and bag films.
Most metallizers are wide web, between 80” and 200” wide. Wide web metallizers always require the film to be slit after metallizing, adding one more production step and one more risk of scratching the film. Multifilm runs up to 41” wide, which requires no slitting, therefore resulting in less risk of scratching. Finally, our machine can do stripe metallizing and can therefore serve markets that other processors would need at least an additional three steps of production to accomplish.