#1136
Author: Charles A. Bishop, C.A.Bishop Consulting Ltd.
Email: cabuk1@freenetname.co.uk
Subject: It is common to assume that it is a failure of the interface and due to poor adhesion. However...
Is the polymer coating on the paper and the metallization on the polymer coating? If so I would check to confirm that it is the metallization that is failing. It is common to assume that it is a failure of the interface and due to poor adhesion. It is worth looking at both sides of the failed interface to confirm where the failure is located. It could be a cohesive failure in the bulk of the material that the metal has been deposited on. Any residual material on the interface side of the metal layer will be very thin and may easily be overlooked. Ideally using one of the surface analytical techniques will be able to identify any residual material, if this is not available using a microscope may allow you to see if there is anything more than metal there.
If the metal coating is directly onto the paper with the polymer coating on the opposite side of the paper then I would still check for the true point of failure. Are there any coatings, such as clay type whiteners, on the
paper to give gloss or smoothness before the metallization? Again the
reason for looking carefully at the failure is because it is as likely that the failure is within the substrate as it is that it is at the interface. Clays are laminar materials and may contain moisture that could be driven off at elevated temperatures allowing the laminar clay to fragment.
If the failure is within the underlying layer then nothing you can do in the vacuum deposition process is going to help eliminate this problem. If it really is a problem at the interface then the standard way of increasing the metal adhesion is to give the surface a plasma pre-treatment immediately before the metal deposition. This will increase the surface energy of the substrate and help the metal to wet the surface and adhere.
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