Lifetime of metallized film.

Hi sir, follow up question on the lifetime of metallized but this time on the adhesion of the metallized coating on the cpp or pet film. Some customer complains that after a year their un-used laminated opp/vmcpp film delaminate. We observed that the metallized coating completely transfers to the opp. Did the bond between the cpp and the metallized was overcome by the bond of adhesive between opp and metallized coating. Did surface contamination plays part on this after a long period of storage.

Answer

As with all adhesion failures the recommendation is to first confirm the plane of the failure. The reason for this is that you do not want to be trying to solve the wrong problem.  Assuming the failure really is at the interface it is possible that this relates to the initial adhesion and then is time and temperature dependent.  Ideally the metal is bonded to the polymer at all possible points uniformly across the whole surface.  If the surface is not suitably prepared the metal will only be intermittently bonded to the polymer. In the spaces between bonds it is possible for material to migrate into the space and it is this material that can degrade the adhesion.  This migrating material could be moisture or low molecular weight unpolymerised fragments or any additives that might have been added to the polymer.

The rule of thumb is generally that the higher the original adhesion the longer the lifetime of the metal adhesion. The lower the adhesion the easier it is for material to migrate into the space between the unbonded metal and polymer swelling the space and leading to premature delamination.  Heating the material can accelerate any degradation process as it increases the rate of migration or diffusion through the polymer of any potential contaminant.

If you have a known problem of failures after a year of storage it should be possible to plot the progressive decrease in adhesion over the year.  The force used for delamination should reduce progressively.

Thus examining the surfaces may give some indication about contamination. If you have some material that is known to fail then sending this to a surface analytical laboratory and allowing them to delaminate some material in their controlled environment and then examine each of the metal and polymer surfaces by a technique such as X-ray Photoelectron Spectroscopy should allow you to identify the chemical composition of both surfaces.  If there has been some contamination it is likely that you will have the same material present on both the metal and polymer surface and it will not be the same chemistry as the original polymer surface.

There is also another factor that may be coming occurring and that is the adhesive between the OPP and MCPP may be also aging but in this case may be slightly improving in adhesion. It depends on the adhesive type but some do not fully cure immediately but take some time and so with time can increase in adhesion.  Thus if the adhesion on one side of the metal is reducing and on the other side it is increasing the failure may switch from one side to the other over time.

I hope this gives you something to work on.