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Embossing during orientation
August 25, 2008
I recently received a question about the possibility of embossing a film between the MD and TD orientation steps and how it might be done. This is an interesting question which I have not considered before. It should be possible, and the embossed pattern will survive the stretching step. Real question is why would you do it, and the second question is how would you do it.
First, you would want to establish a pattern on the film for a purpose. One purpose for a patterned film surface is to act as an antiblocking surface using the polymer of the film itself. I have seen two patents for this, one for PP and one for a capacitor film. In both instances, the pattern was put into the film on quenching. Figure 1 is a profile scan of a surface produced by casting onto a hot roll with a pattern etched in the chrome surface of the cast roll. Changes in the quenching from the differential surface of the roll (chrome / no-chrome) produce variations in alpha and beta crystals which give rise to the raised patterns after stretching (pattern is 1 micrometer across.
From this result, it is apparent that embossing a pattern physically into the film will result in surface variations in the finished film. We also know this from the formation of defects in films due to marks on stretch and cast rolls. Embossing a pattern would be easily accomplished on a film surface using a patterned roll surface pressed against the film surface. Having a low melting surface coextruded onto the film surface would make this easier.
Posted by Eldridge M. Mount on August 25, 2008 | Comments (0)