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Blown film process impact on seal strength
June 11, 2008
I was recently asked the question as to what impact does blown film blow up and draw down have on seal strength. However, the answer is a little complex because of what seal strength measurements really measure. What do I mean? Well for instance in heat seal strength measurements the measurement is generally made by pulling on the ends of the film attached to the seal. Because of this the measurement more likely measures the strength of the film rather than the strength of the seal. An exception to this which demonstrates the truth of the statement is a peelable seal.
With a peelable seal the failure occurs in the peeling apart of the heat seal surfaces. In most heat seals the seal is pulled and either the film tears through as in oriented films or the tail elongates as in cast films.
Therefore the answer to the question as to the effect of blow up and draw down ratio impact on seal strength will be that the seal strength will appear to increase if the tensile properties of the film, sealed together, is increased. Indeed you might see that the seal strength is a function of the measurement direction (MD vs. TD) and if this is apparent then you are not really measuring the strength of the seal so much as the strength of the film. In oriented films the ultimate seal strength is related more to the tear strength through the film than the strength of the sealant.
To eliminate the film from the measurement you should back the sample with a strong, non extensible tape so that the peel strength is more from the seal than the elongation and tearing of the film itself.
Posted by Eldridge M. Mount on June 11, 2008 | Comments (0)