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#25
Subject: Is it still AIMCAL's position that the optical densitometer is the preferred instrument?

I have been testing metallized PET samples w/ an optical densitometer and a contactless conductivity tester. I am trying to find a correlation among both or one of the test methods to metal detector peak sensitivity. I am finding a stronger correlation by measuring resistance. Is it still AIMCAL's position that the optical densitometer is the preferred instrument? If so, how can I explain that there is a better correlation between resistance and metal detection peak readings? I have also read that there is a correlation between optical density and the resistance, but my correlation is only 0.5. How can I explain this or what could I possibly be doing wrong in my testing?


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#26

The optical density test method is preferred in the industry.

#26
Author: Werner Geitner, HUECK FOLIEN Ges.m.b.H
Email:
Subject: The optical density test method is preferred in the industry.

The optical density test method is preferred in the industry, because in the past (and still today, I believe) the method for O.D. is faster and cheaper than the surface resistivity (SR) test. In addition, the packaging industry normally uses a metal thickness, which is better suitable for O.D. measurement. And for most of the applications, the precision of the O.D. value is good enough.

As I understand, your problem is the relationship between O.D. or S.R. versus metal detection. In this case, it might be possible, that the S.R. method is more precise. Every aluminum layer is building up an oxide layer, which can have big variations in thickness. With both methods (O.D. and S.R.) this oxide layer is not detected, but it could be the case that S.R. is more sensitive and precise in measuring the real metal thickness. This assumption makes sense keeping in mind, that O.D. is measuring an optical feature of the metal layer and S.R. is measuring an electrical value. As the metal detection also relates on electrical behavior of the metal layer, this could give you the more reliable values.

I hope, this could answer your question or at least help you to find an answer. Should you have additional questions, please do not hesitate to contact us again.

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