The metallization by evaporation under vacuum is a technique that allows to obtain thin layers of deposit metal on flexible media, media most often encountered are:
- movies of type polyester (PET), polypropylene (BOPP), nylon (BOPA), and polyethylene (PE), of polyimides (Kapton)…
We will strive to remove aluminum because widely used for large consumer (food packaging, insulation…):
Used aluminum can have several levels of purity, but generally used of the A5 (purity 99.5%) or even the A9 (purity to 99.9%) in some cases.
Machine to metallize by evaporation under vacuum
The machine to metallize is a vacuum (about 10-4 mbar) equipped with:
- 1 support to metalize unwinding station
- 1 or 2 Bank (s) evaporation (s) consisting of crucibles
- 1 or 2 drum (s) cooling (about – 20 ° C)
- 1 metallic support wrapping station
The principle consists in:
– place the support that you want metallized,
-get the support above the crucibles of evaporation (against the cooling drum)
-wrap the metallic support
The machine is also equipped with a system that measures continuous, the amount of aluminum that is deposited on the support. We measure this amount of aluminum either by the optical density (DO) a calculation of resistivity.
The crucibles of evaporation (usually in Boron Nitride) are heated at 1500 ° C to allow wire (1.5 mm) aluminium melted in the crucible. There is a passage of ‘ aluminum from the solid state to the liquid state (fusion), then a passage of State liquid to gas (evaporation). Aluminum molecules will come to condense on the media because it is cooled through the drum of cooling to-20 ° C. (You can make the analogy with steam that condenses on the single-glazed window, when you cook).
The desired amount of aluminum, will be obtained by the adequacy of the “aluminum wire speed” and the “speed of scrolling support. So when looking for a low deposit of aluminum, “speed of aluminum wire” will be weak and “support scroll speed” will be high and when looking for a high deposit, the “aluminum wire speed” will be high and the ‘ speed of. scroll support”will be low.
Benefits and applications
A machine with 2 banks of evaporation allows a greater range in the amount of aluminum that is filed. Thus one can produce films with low charge (10nm) for applications like one-way mirrors or movies with strong charge (80nm) for applications in the cryogenic insulation.
After metallization, aspect of the film is ‘mirror’, aluminium vacuum metallization may have several purposes:
-Make (oxygen, water vapour) barrier films for applications in the food industry (see article from the blog of 14/06/17)
-Make little emissivity movies for insulation
-Beautify the packaging in the case of luxury or textiles (see article of the blog from 05/05/17)