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Welcome to the New Year
January 3, 2008
First. welcome to the New Year. Hopefully this will find you well and without problems.
Late in 2007 we began with discussing film optical properties and introducing film surface-quality concepts. First. we will talk a little about surface cleanliness. Film surfaces are seldom clean on a molecular level. Generally what we hope for is a surface which is not covered with weakly adhering surface contaminates which will then come lose after converting and give a general adhesion failure. The sources of the surface contaminates are many, from material transfer from the opposing surface of the film, from all the surfaces it comes in contact with, degradation of the surface by treatment as well as diffusion of low molecular-weight material from the body of the film itself. If the surface contaminate is thin or incompletely covers the surface, then it may not interfere with the converting of the film which is generally the case. All substrates are prone to these surface contaminates, some more than others due to their manufacture and formulation. How do we insure a surface is fit for converting?
First we need to consider the converting process which is to be used as the process itself may clean the surface sufficiently to give good adhesion. For instance, if the process makes use of an organic solvent and the surface is contaminated with low molecular-weight molecules soluble in the solvent, then it will be removed and the surface cleaned. Alternatively, the surface can be cleaned of low molecular-weight molecules by oxidation as in a corona. The great danger of the corona is that it is overdone and damages the surface further. To guard against an unexpected failure due to surface contamination, you must develop an effective means of testing the surface. While treatment is oftentimes a measure, it is not a sure test.
Posted by Eldridge M. Mount on January 3, 2008 | Comments (0)