Problem: We have laminated BOPP / ink / solvent less adhesive / metallized BOPP for several years, but nowadays we are finding delamination problem.
Question: The delamination occurs between adhesive and metallized BOPP face. The adhesive comes from the metallized surface to ink after some weeks of the lamination process. (We apply the adhesive on the metallized BOPP surface. We treat the surface in line with corona treatment)
We could not understand what is happening . Why this is happen after several weeks? Is it possible something migrating from BOPP? Is it possible a reaction between ink and adhesive? Did you have any experience related to this problem?
Reply: I have seen this on occasion and I believe it could be due to diffusion of additives from the OPP or perhaps the ink to the metal adhesive interface where it is stopped by the metal layer and then concentrates there and poisons the bond between the metal and the adhesive. I have seen this on several occasions. Typically it would take some time depending on the storage conditions or a variable source of contamination or additive levels in the film or ink. If it is a laminating ink I would not expect it to have migratory additives but if is a surface ink it would. If the outer OPP film is a slip film then it will contain migratory additives and the concentrations will likely be varied with the seasons and it is possible you have some film with higher slip concentrations. Because the adhesive/metal bond was good and then becomes poor, I don’t think there is a problem with the adhesive cure.
To determine what the cause is you have to chemically analyze the delamination surfaces to discover what is at the surface of the failure. Typically I have this done using both FTIR and XPS spectra. What I would look for first is that there is no adhesive on both surfaces of the failure. If there is adhesive on both surfaces then the failure is cohesive in the adhesive and any diffusing additives are weakening the adhesive such that it fails. If there is no adhesive on the metal surface then the failure is adhesive between the metal and the adhesive. In this case I would expect to find a low molecular weight contaminant at the metal surface such as erucamide (or other slip molecule) or a wax etc. To determine the source of the diffusing molecules I would extract each of the various components (film, adhesive and the ink) for chromatography analysis to see which of the laminations component contains the problem molecule.
The only way to know for sure what the source of the problem is, is to do the chemical analysis of the failed surface and then the analysis of each component will help pinpoint the exact cause.