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#1459
Author: Eldridge M. Mount III, EMMOUNT Technologies
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Subject: Metallized film shelf life
Shelf life is a difficult thing to describe without knowing the product composition. In general it should be six to 12 months. What usually limits the apparent life of metallized films for printing and laminations is surface contamination of the metal surface while in roll form. This may be more pronounced with oriented polypropylene than polyethylene terephthalate, but the apparent wetting tension of the metal will drop as the metal surface is contaminated. Often the metal can be cleaned by corona treatment on the converting equipment.
A second effect sometimes seen is oxidation of the metal by moisture at the ends of the roll. Consequently, storage should be such to minimize diffusion of additives or contaminants to the film surface. The film should be stored in a cool place and should be wrapped in a polyethylene cover, which is tucked into the core especially if storing for a long time. Storage temperature will be based on the shrinkage properties of the film to prevent the formation of baggy lanes or gauge bands.
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#1527
Author: Charles A. Bishop, C.A.Bishop Consulting Ltd.
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Subject: Metallized film shelf life
Shelf life is dependent on a number of factors. The surface treatment chemically modifies the material to a specific depth. Different treatments will reach different depths. The shallower the depth, the easier it is for the treatment to be reduced in effectiveness. Hence it is common for people to want to coat or laminate only after a very recent surface treatment.
There are several ways the surface treatment can be reduced. If there is low molecular weight material on the polymer surface before the treatment, it will not only be on the surface treated but also on the other side of the web. Some of the low molecular weight material transfers across while the roll is stored in the wound-up state. Any residual low molecular weight material on the reverse side will have time to transfer onto the treated surface while in storage. The longer the storage time, the greater the chance of transfer.
Similarly, the temperature the roll experiences during storage is important. Any residuals within the polymer that may migrate to the surface will do so more easily if the temperature rises. Also, any low molecular weight material will be more mobile at elevated temperatures. If the temperature cycles between daytime highs and overnight lows, the rolls will expand & contract. The relative movement of the layers of polymer will put additional contact pressures on the surfaces and also help any material transfer. This can, in extreme cases, put microscratches into the surface, particularly if one surface has filler particles protruding.
A final consideration is humidity. Moisture is another source of surface energy degradation. The moisture can start a chemical change by producing hydroxides that can reduce the surface activity.
Thus, to store rolls of film for a long time, it is preferable to maintain a constant, probably low, temperature and a controlled low humidity. Even then, a slow progressive decline in performance would be expected over time.
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