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Film shrinkage as a function of temperature
March 20, 2008
In my earlier answer to Juan, I discussed the shrinkage characteristics of various films relative to a specification. During this, I said that the best dimensional stability, aka shrinkage, data was data as a function of temperature. That is primarily because a single temperature does not fully describe the behavior of the film itself. As an example of this is figure 1 which shows the thermal shrinkage for a polyethylene blown film which has been solid state stretch oriented approximately 200% in the MD. In this case the orientation erases the shrinkage behavior of the blown film itself and has created an MD shrink film.
What is interesting to note is that as the film shrinks in the MD (positive shrinkage value) the film gets wider in the TD (negative shrinkage value). Going back to the posting on “tin canning” this is the same behavior I was highlighting when a film is over tensioned on winding. I.e the recovery of MD elongation causes growth in the TD leading to tin canning. In this case the film gets wider as the film shrinks. If the film was used as a shrink label then the TD growth might cause wrinkles in the shrink label. The film formulation and the amount of TD growth will determine if the TD growth is a problem.
One thing this shows is that all of the film behaviors are related, heat shrinkage, tensile recovery, tin canning and shrink labels
MD oriented polyethylene film shrinkage as a function of temperature
Posted by Eldridge M. Mount on March 20, 2008 | Comments (0)